12116370
Spatial patterns of an endemic Mediterranean palm recolonizing old fields
Abstract Throughout Europe, increased levels of land abandonment lead to (re)colonization of old lands by forests and shrublands. Very little is known about the spatial pattern of plants recolonizing such old fields. We mapped in two 21–22‐ha plots, located in the Doñana National Park (Spain), all adult individuals of the endozoochorous dwarf palm Chamaerops humilis L. and determined their sex and sizes. We used techniques of spatial point pattern analysis (SPPA) to precisely quantify the spatial structure of these C. humilis populations. The objective was to identify potential processes generating the patterns and their likely consequences on palm reproductive success. We used (1) Thomas point process models to describe the clustering of the populations, (2) random labeling to test the sexual spatial segregation, and (3) mark correlation functions to assess spatial structure in plant sizes. Plants in both plots showed two critical scales of clustering, with small clusters of a radius of 2.8–4 m nested within large clusters with 38–44 m radius. Additional to the clustered individuals, 11% and 27% of all C. humilis individuals belonged to a random pattern that was independently superimposed to the clustered pattern. The complex spatial pattern of C. humilis could be explained by the effect of different seed‐dispersers and predators' behavior and their relative abundances. Plant sexes had no spatial segregation. Plant sizes showed a spatial aggregation inside the clusters, with a decreasing correlation with distance. Clustering of C. humilis is strongly reliant on its seed dispersers and stressful environmental conditions. However, it seems that the spatial patterns and dispersal strategies of the dwarf palm make it a successful plant for new habitat colonization. Our results provide new information on the colonization ability of C. humilis and can help to develop management strategies to recover plant populations.
53693
Unravelling conflicting density- and distance-dependent effects on plant reproduction using a spatially explicit approach
Summary 
 
Density- and distance-dependent (DDD) mechanisms are important determinants of plant reproductive success (PRS). Different components of sequential PRS can operate either in the same or in different directions and thus reinforce or neutralize each other, and they may also operate at different spatial scales. Thus, spatially explicit approaches are needed to detect such complex DDD effects across multiple PRS components and spatial scales. 
To reveal DDD effects of different components of early PRS of the Iberian pear (Pyrus bourgaeana) sampled over three consecutive years, we used marked point pattern analysis. Our special interest is to identify conflicting processes that regulate populations at different spatial scales, for example whether DDD on fruit initiation and on fruit development acted in opposite directions. To evaluate the significance of observed mark correlation functions based on empirical data (e.g. fruiting success), we compared them to expectations given by spatially explicit null models. 
Diverse DDD processes affected several aspects of PRS in a variable extent over the three seasons. First, fruit initiation was higher for individuals with more neighbours at small distances (i.e. up to 40 m). However, P. bourgaeana fruit development decreased with increasing number of nearby neighbours, but these effects cancelled for overall fruit set that did not show DDD effects. Secondly, the absolute number of fruits produced (crop sizes) by trees showed positive density dependence in 2011 and 2012 but not in 2013. Finally, the total number of seeds produced did not show DDD effects, indicating that conflicting demographic processes can disrupt the initial spatial pattern of tree investment in reproduction. 
Synthesis. Understanding complex spatial effects of DDD processes requires dissection of component processes to attain the complete picture since contrasting DDD processes may be hidden behind a single cumulative measure of reproductive success. The combination of novel and classic mark correlation functions used here constitutes a powerful spatially explicit tool that can be broadly applied to unravel conflicting mechanisms of DDD regulating the persistence of sessile organisms at a range of spatial scales. Our findings help to explain why some authors failed to find expected DDD of PRS and highlight the importance of detailed multiyear field studies on plant reproductive success.
3576350
Analyzing the spatial structure of a Sri Lankan tree species with multiple scales of clustering.
Clustering at multiple critical scales may be common for plants since many different factors and processes may cause clustering. This is especially true for tropical rain forests for which theories explaining species coexistence and community structure rest heavily on spatial patterns. We used point pattern analysis to analyze the spatial structure of Shorea congestiflora, a dominant species in a 25-ha forest dynamics plot in a rain forest at Sinharaja World Heritage Site (Sri Lanka), which apparently shows clustering at several scales. We developed cluster processes incorporating two critical scales of clustering for exploring the spatial structure of S. congestiflora and interpret it in relation to factors such as competition, dispersal limitation, recruitment limitation, and Janzen-Connell effects. All size classes showed consistent large-scale clustering with a cluster radius of approximately 25 m. Inside the larger clusters, small-scale clusters with a radius of 8 m were evident for recruits and saplings, weak for intermediates, and disappeared for adults. The pattern of all trees could be divided into two independent patterns: a random pattern (nearest neighbor distance > 8 m) comprising approximately 12% of the trees and a nested double-cluster pattern. This finding suggests two independent recruitment and/or seed dispersal mechanisms. Saplings were several times as abundant as recruits and may accumulate several recruit generations. Recruits were only weakly associated with adults and occupied about half of the large-scale clusters, but saplings almost all. This is consistent with recruitment limitation. For approximately 70% (95%) of all juveniles the nearest adult was less than 26 m away (53 m), suggesting a dispersal limitation that may also be related to the critical large-scale clustering. Our example illustrates the manner in which the use of a specific and complex null hypothesis of spatial structure in point pattern analysis can help us better understand the biology of a species and generate specific hypotheses to be further investigated in the field.
23832449
Hierarchical mechanisms of spatially contagious seed dispersal in complex seed-disperser networks.
Intra- and interspecific spatially contagious seed dispersal has far-reaching implications for plant recruitment, distribution, and community assemblage. However, logistical and analytical limitations have curtailed our understanding concerning the mechanisms and resulting spatial patterns of contagious seed dispersal in most systems and, especially, in complex seed-disperser networks. We investigated mechanisms of seed aggregation using techniques of spatial point pattern analysis and extensive data sets on mutispecific endozoochorous seed rain generated by five frugivorous mammals in three Mediterranean shrublands over two seasons. Our novel analytical approach revealed three hierarchical and complementary mechanisms of seed aggregation acting at different levels (fecal samples, seeds, pairs of seed species) and spatial scales. First, the three local guilds of frugivores tended to deliver their feces highly aggregated at small and intermediate spatial scales, and the overall pattern of fecal delivery could be described well by a nested double-cluster Thomas process. Second, once the strong observed fecal aggregation was accounted for, the distribution of mammal feces containing seeds was clustered within the pattern of all feces (i.e., with and without seeds), and the density of fecal samples containing seeds was higher than expected around other feces containing seeds in two out of the three studied seed-disperser networks. Finally, at a finer level, mark correlation analyses revealed that for some plant species pairs, the number of dispersed seeds was positively associated either at small or large spatial scales. Despite the relatively invariant patterning of nested double-clustering, some attributes of endozoochorous seed rain (e.g., intensity, scales of aggregation) were variable among study sites due to changes in the ecological context in which seeds and their dispersers interact. Our investigation disentangles for the first time the hierarchy of synergic mechanisms of spatially contagious seed dispersal at a range of spatial scales in complex seed-disperser networks, thus providing a robust and widely applicable framework for future studies.
56039162
POPULATION STRUCTURE, SPATIAL PATTERN AND REPRODUCTIVE CAPACITY OF TWO SEMI-DESERT UNDERSHRUBS SENNA HOLOSERICEA AND FAGONIA INDICA IN SOUTHERN SINDH, PAKISTAN
Size class distribution is important in understanding population structure, demography and stability of populations. In this study, the size structures of two semi-desert under-shrub populations, soil characteristics of habitats, spatial pattern of plant populations and reproductive capacity of the populations of two plant species i.e., Senna holoceracea and Fagonia indica were examined in two different sites. Size class distribution of both species were positively skewed, having greater frequencies in the smaller classes that represents adequate recruitment. This shows adequate recruitment in the populations of both the species. The examination of spatial pattern, using sample plot and plotless methods, disclosed aggregated pattern of both the species populations. Soil characteristics were also found spatially variable, showing higher fertility (organic matter, nitrogen, Ca, Mg and K) underneath the selected plants and lower in the gaps, which is one of the principal cause of aggregation in species populations. Fecundity of the two plants were also found to be different, particularly differences were found in the fecundity of same plant at the two sites which was presumably due to difference in plant size.
205991889
Recruitment in Tropical Tree Species: Revealing Complex Spatial Patterns
Seed dispersal should leave a signature on the spatial distribution of recruits that can be quantified using sophisticated techniques of spatial pattern analysis. Here we study spatial patterns of five frugivore‐dispersed tropical tree species at the Barro Colorado Island forest, Panama, to describe detailed properties of the spatial patterns of recruits and to investigate whether these patterns were produced by temporally consistent mechanisms. Our spatial point pattern analyses detected the existence of surprising spatial structures, such as double‐cluster and superposition patterns, and they allowed for a detailed quantification of their properties. The spatial recruitment patterns were composed of two independent components comprising a random component and a component showing a complex spatial pattern with two critical scales of clustering. The analysis allowed an estimation of the relative contribution of scatter dispersal versus clump dispersal in effective seed dispersal for our study species. Additionally, the cluster characteristics were temporally consistent over 25 years and correlated with several species traits. We are just beginning to discover the richness of spatial patterns found at tropical forests, and we are confident that a combination of advanced point pattern analysis with field data will allow for significant advances in establishing the link between spatial patterns and processes.
21286056
What's new about old fields? Land abandonment and ecosystem assembly.
Environmental and socio-economic changes are leading to increased levels of land abandonment worldwide. The assembly of plant communities on old fields has informed much ecological theory, which in turn has facilitated efforts at ecological restoration. The interaction of the cultivation legacy with inherent soil and vegetation characteristics will determine the dynamics of plant community assembly on old fields and indicate the level of effort required to restore historical vegetation states. The abandonment of traditional agricultural lands in some areas will create old fields that require limited or no restoration. Yet intensification of agriculture and rapid environmental change will lead to increasing numbers of old fields that show little recovery towards an historic vegetation state. The restoration of these old fields will pose significant scientific and policy challenges.
82034148
Plant Evolution in the Mediterranean
Preface Introduction: Themes, objectives, and structure 1. The historical context of differentiation and diversity 2. The biogeography and ecology of endemism 3. The evolution of endemism : from population differentiation to species divergence 4. Trait variation, adaptation, and dispersal in the Mediterranean mosaic 5. Variation and evolution of reproductive traits in the Mediterranean mosaic 6. Ecology and evolution of domesticated and invasive species Conclusions: Endemism, adaptation, and conservation References Species list and nomenclature Index
84215415
Spatial and temporal pattern of white spruce regeneration within mixed-grass prairie in the Spruce Woods Provincial Park of Manitoba
Aim 
 
Thirty white spruce [Picea glauca (Moench) Voss] islands were sampled to study the temporal and spatial pattern of white spruce regeneration at its southern limit of distribution. 
 
 
 
Location 
 
The study was conducted within three mixed-grass prairies in the Spruce Woods Provincial Park (SWPP) of south-western Manitoba. 
 
 
 
Methods 
 
White spruce seedlings, saplings and trees were mapped and measured in relation to eight sectors and five zones delimited by four transect lines extending through the centre of each island oriented north to south, west to east, north-west to south-east and north-east to south-west. 
 
 
 
Results 
 
Temporal patterns of regeneration were negatively correlated with July temperature at the time of establishment and up to 30 years after establishment. Height growth of seedlings and saplings were also negatively correlated with July temperature. Seedlings, saplings and trees were concentrated on the north vs. south aspect and within 4–12 m from the island centre. Seedlings grew almost exclusively in association with creeping juniper (Juniperus horizontalis Moench). 
 
 
 
Main conclusions 
 
Results of the study suggest that white spruce recruitment and growth reflect past climatic variation, and microclimatic and microsite conditions promoting soil moisture retention and/or fire risk reduction facilitate white spruce germination and establishment.
84693999
Modeling Mating Patterns Given Mutual Mate Choice: The Importance of Individual Mating Preferences and Mating System
When we consider structured populations with sexual reproduction, the distribution of characters among mating pairs may influence the population biology, namely its dynamics and genetics. In the present paper, we propose a general framework to estimate the population mating patterns taking into account individual mating preferences and mating system, thus taking into account the inter- and intra-sexual interactions such as mate competition and mate choice. According to our results, mating patterns are not a direct reflection of mating preferences, but also depend upon the average sex ratio between individuals that are ready to mate at any given time (i.e., the Operational Sex Ratio, OSR). Therefore, mating patterns should be assessed not only in function of preferences, but also of OSR. It is then possible to distinguish three OSR regions: (1) the equilibrium OSR, where there is a predominance of assortative mating patterns due to differential access to mates (inter-sexual interactions); (2) the slightly biased OSR, where there is a high diversity of mating patterns and no clear predominance of inter- or intra-sexual interactions; and (3) the highly biased OSR where there is a predominance of mating patterns corresponding to single-sex uniform preferences and an increased influence of intra-sexual interactions. We hope that this approach may allow to further explore the interaction between OSR and mate choice, namely how such interaction may affect sexual selection and mate choice tactics.
23739465
Spatially structured metapopulation models: global and local assessment of metapopulation capacity.
We model metapopulation dynamics in finite networks of discrete habitat patches with given areas and spatial locations. We define and analyze two simple and ecologically intuitive measures of the capacity of the habitat patch network to support a viable metapopulation. Metapopulation persistence capacity lambda(M) defines the threshold condition for long-term metapopulation persistence as lambda(M)>delta, where delta is defined by the extinction and colonization rate parameters of the focal species. Metapopulation invasion capacity lambda(I) sets the condition for successful invasion of an empty network from one small local population as lambda(I)>delta. The metapopulation capacities lambda(M) and lambda(I) are defined as the leading eigenvalue or a comparable quantity of an appropriate "landscape" matrix. Based on these definitions, we present a classification of a very general class of deterministic, continuous-time and discrete-time metapopulation models. Two specific models are analyzed in greater detail: a spatially realistic version of the continuous-time Levins model and the discrete-time incidence function model with propagule size-dependent colonization rate and a rescue effect. In both models we assume that the extinction rate increases with decreasing patch area and that the colonization rate increases with patch connectivity. In the spatially realistic Levins model, the two types of metapopulation capacities coincide, whereas the incidence function model possesses a strong Allee effect characterized by lambda(I)=0. For these two models, we show that the metapopulation capacities can be considered as simple sums of contributions from individual habitat patches, given by the elements of the leading eigenvector or comparable quantities. We may therefore assess the significance of particular habitat patches, including new patches that might be added to the network, for the metapopulation capacities of the network as a whole. We derive useful approximations for both the threshold conditions and the equilibrium states in the two models. The metapopulation capacities and the measures of the dynamic significance of particular patches can be calculated for real patch networks for applications in metapopulation ecology, landscape ecology, and conservation biology.
86216267
An evaluation of the state of spatial point pattern analysis in ecology
Over the last two decades spatial point pattern analysis (SPPA) has become increasingly popular in ecological research. To direct future work in this area we review studies using SPPA techniques in ecology and related disciplines. We first summarize the key elements of SPPA in ecology (i.e. data types, summary statistics and their estimation, null models, comparison of data and models, and consideration of heterogeneity); second, we review how ecologists have used these key elements; and finally, we identify practical difficulties that are still commonly encountered and point to new methods that allow current key questions in ecology to be effectively addressed. 
 
Our review of 308 articles published over the period 1992–2012 reveals that a standard canon of SPPA techniques in ecology has been largely identified and that most of the earlier technical issues that occupied ecologists, such as edge correction, have been solved. However, the majority of studies underused the methodological potential offered by modern SPPA. More advanced techniques of SPPA offer the potential to address a variety of highly relevant ecological questions. For example, inhomogeneous summary statistics can quantify the impact of heterogeneous environments, mark correlation functions can include trait and phylogenetic information in the analysis of multivariate spatial patterns, and more refined point process models can be used to realistically characterize the structure of a wide range of patterns. Additionally, recent advances in fitting spatially-explicit simulation models of community dynamics to point pattern summary statistics hold the promise for solving the longstanding problem of linking pattern to process. All these newer developments allow ecologists to keep up with the increasing availability of spatial data sets provided by newer technologies, which allow point patterns and environmental variables to be mapped over large spatial extents at increasingly higher image resolutions.
84626402
Spatial pattern of adult trees and the mammal-generated seed rain in the Iberian pear
The degree to which plant individuals are aggregated or dispersed co-determines how a species uses resources, how it is used as a resource, and how it reproduces. Quantifying such spatial patterns, however, presents several methodological issues that can be overcome by using spatial point pattern analyses (SPPA). We used SPPA to assess the distribution of P. bourgaeana adult trees and their seeds (within fecal samples) dispersed by three mammals (badger, fox, and wild boar) within a 72-ha plot across a range of spatial scales. Pyrus bourgaeana trees in our study plot (n =75) were clearly aggregated with a critical spatial scale of ca 25 m, and approximately nine randomly distributed tree clusters were identified. As expected from their marking behaviors, the spatial patterns of fecal deposition varied widely among mammal species. Whereas badger feces and dispersed seeds were clearly clustered at small spatial scales ( < 10 m), boar and fox feces were relatively scattered across the plot. A toroidal shift null model testing for independence indicated that boars tended to deliver seeds to the vicinity of adult trees and thus could contribute to the maintenance and enlargement of existing tree clusters. Badgers delivered feces and seeds in a highly clumped pattern but unlike boars, away from P. bourgaeana neighborhoods; thus, they are more likely to create new tree clusters than boars. The strong tree aggregation is likely to be the result of one or several non-exclusive processes, such as the spatial patterning of seed delivery by disposers and seedling establishment beneath mother trees. In turn, the distinctive distribution of P. bourgaeana in Donana appeared to interact with the foraging behavior of its mammalian seed dispersers, leading to neighbourhood-specific dispersal patterns and fruit-removal rates. Our study exemplifies how a detailed description of patterns generates testable hypotheses concerning the ecology of zoochorous. Pyrus bourgaeana dispersers were unique and complementary in their spatial patterning of seed delivery, which likely confers resilience to their overall service and suggests lack of redundancy and expendability of any one species.
19115723
Spatial Segregation of the Sexes and Nutrients affect Reproductive Success in a Dioecious Wind-pollinated Grass
In many dioecious plant species in which spatial distributions of males and females have been examined, the sexes are spatially segregated – usually along an environmental gradient. Unless pollen is uniformly distributed in a population, spatial segregation of the sexes should reduce the average mating success of individuals. In three Californian populations of Distichlis spicata – a wind-pollinated grass species that exhibits spatial segregation of the sexes – I examined patterns of pollen movement and the effects of pollen load and nutrient availability on seed set to determine whether spatial segregation of the sexes actually reduces mating success for both males and females. In two of the populations, pollen dispersal was restricted, and pollen augmentation consistently, significantly increased seed set. However, in the third population – which had the lowest seed set – I found that although there were some indications of pollen limitation, pollen dispersal was not restricted, and seed production was limited primarily by nutrient availability. These results imply that in some populations of D. spicata nutrient limitation on the production of seeds by females may be sufficiently strong that spatial segregation of the sexes causes a fairly low cost to reproductive success compared with a more random distribution of the sexes. However, in other populations, pollen does limit mating success, and the spatial segregation of males and females in these populations is reducing the fecundity of both males and females.
41910559
Effects of Sex and Mycorrhizal Fungi on Gas Exchange in the Dioecious Salt Marsh Grass Distichlis spicata
Premise of research. In dioecious plant species, males and females often differ in physiology, and mycorrhizal fungal relationships are likely to influence these differences. However, few data are available on the potential role of mycorrhizal fungi in altering sex-specific physiology and population sex ratios of dioecious plant species. Methodology. In this study, we measured leaf gas exchange in a multifactorial greenhouse experiment with and without mycorrhizal fungal additions and under field conditions in Distichlis spicata, a dioecious C4 salt marsh grass, displaying extreme spatial sex ratio variation. Pivotal results. We found a significant interaction between gas exchange, plant sex, and mycorrhizal fungal infection. Specifically, females but not males had significantly lower transpiration rates and higher water use efficiency (WUE) in treatments with increased mycorrhizal fungi. Additionally, field data showed similar WUE between plants at female-majority sites and male-majority sites, despite significantly lower rates of net assimilation and stomatal conductance in plants at female-majority sites. Conclusions. Our results suggest that the higher WUE associated with increased mycorrhizal fungi in female D. spicata plants may be an important physiological attribute enabling female success in the higher-stress saltwater environment contributing to the spatial segregation of the sexes observed in this dioecious species.
86137657
GENDER‐SPECIFIC SELECTION DURING EARLY LIFE HISTORY STAGES IN THE DIOECIOUS GRASS DISTICHLIS SPICATA
Bias in the adult sex ratio of a population, if not due to a biased primary sex ratio, may be due to differential mortality of males and females, which can occur during any life history stage. Yet, although adult sex-ratio bias is common in dioecious plant species, little is known about the demography of prereproductive individuals. Using a RAPD-PCR (randomly amplified polymorphic DNA) marker that co-segregates with female phenotype, I studied juvenile demography in the saltmarsh grass Distichlis spicata, which exhibits within-population sex-ratio variation (spatial segregation of the sexes) and has genetic sex determination. First, I surveyed populations of D. spicata to ascertain whether any environmental factor co-varies with local sex ratio, and I found that habitats with female majorities are located at significantly lower elevations in the marsh than are habitats with male majorities. In randomly collected seeds, the sex ratio was significantly biased toward females, but male and female seeds did not differ in mass. Using a subsample of these seeds, I conducted greenhouse and field experiments to examine whether differences in seed germination or seedling survival between the sexes explain sex-ratio variation along the micro-elevation gradient in the marsh. In greenhouse treatments designed to mimic field habitats with female majorities, more male seeds germinated than did female seeds. In habitats with female majorities in the field, significantly more female seedlings survived an extreme high tide than did male seedlings (25.17% of females vs. 13.49% of males). These results suggest that, in habitats with female majorities, gender-specific bias in seedling survivorship, rather than seed germination, is a causal factor in the underlying sex-ratio bias. In habitats with male majorities, seed germination and seedling survival did not differ between the sexes. This study is the first to document environment-dependent differential seed germination and seedling mortality between males and females in a dioecious plant species.
31541136
Population structure and spatial pattern in the dioecious shrub Ceratiola ericoides
The dioecious shrub Ceratiola ericoides (Florida rosemary) dominates xeric, infrequently burned Florida scrub vegetation, often to the near-exclusion of other woody species. We studied the spatial pattern, age, sex and size structure of four populations in Florida, USA: two coastal scrub populations subject to recurrent local disturbances due to sand movement, and two inland scrub populations in sites periodically burned by stand-replacing fires. The age structure of individual genets was estimated from node counts and used to describe the age structure of the populations. The sex ratio of males to females was not significantly different from 1:1, except within a fe- male-biased coastal population subject to frequent sand move- ment. Node counts indicated that the mean age for reproduc- tive individuals was 15 - 16 yr for the inland populations and 13 - 16 yr for the coastal populations. In all sites, there was no difference in mean age between males and females. Vegeta- tive reproduction was uncommon except for the least-dis- turbed coastal population where 72 % of the reproductive individuals originated through layering. Individuals were gen- erally randomly dispersed at the coastal sites, whereas signifi- cant aggregation of males and females occurred in the inland sites where the populations were initiated following fire. Seed- ling recruitment was continuous in the disturbed coastal scrub site, where 35 % of the individuals were juveniles. Most juve- niles were dispersed from 0.5 to 0.75 m around females. At one of the inland sites, where juveniles comprised 11 % of the population, juveniles were clustered at 0.25 to 5.75 m around females. Coastal populations were all-aged, while inland populations were uneven-aged. Recruitment appears to follow periods of disturbance; infrequent fire in the inland populations and continuous sand movement on the coast are factors initiat- ing recruitment.
84317210
Competition among plants can lead to an increase in aggregation of smaller plants around larger ones
We re-examined traditional explanations regarding relationships between competition among plants and spatial patterns. We focused particularly on the prevailing view, which is that competition between smaller plants and larger plants serves only as a repulsive force between neighbors, and always decreases the degree of aggregation between smaller plants and larger plants over time. We propose an alternative underlying mechanism explaining the observed spatial patterns using a spatially explicit, individual-based model with general assumptions regarding the nature of competition among plants. We statistically estimated parameters for the model from observed census data collected over 30 years in an even-aged experimental fir forest (Abies sachalinensis). The results of our simulations, based on field data, indicated that asymmetric competition among plants led to the aggregation of smaller plants around a larger plant (i.e., not toward a uniform spatial pattern). This spatial pattern was generated by the growth suppression of plants near larger plants during the early growth stages, and more importantly, by the existence of a zone with lower competition intensity (referred to as competition-induced shelter, CiS) around a larger plant after the early growth stages. Larger plants compete for resources with large and medium-sized neighbors to the extent that the neighbors die and are removed, resulting in CiS. The results also indicate that competition between smaller plants and larger plants in an even-aged population exerts not only the traditionally recognized repulsive force but also a pseudo-attractive force, such as CiS, which promotes aggregation of smaller plants around a larger plant.
84260818
The allometry of reproduction within plant populations
Summary 1. The quantitative relationship between size and reproductive output is a central aspect of a plant’s strategy: the conversion of growth into fitness. As plant allocation is allometric in the broad sense, i.e. it changes with size, we take an allometric perspective and review existing data on the relationship between individual vegetative (V, x-axis) and reproductive (R, y-axis) biomass within plant populations, rather than analysing biomass ratios such as reproductive effort (R ⁄ (R+V)). 2. The allometric relationship between R and V among individuals within a population is most informative when cumulative at senescence (total R–V relationship), as this represents the potential reproductive output of individuals given their biomass. Earlier measurements may be misleading if plants are at different developmental stages and therefore have not achieved the full reproductive output their size permits. Much of the data that have been considered evidence for plasticity in reproductive allometry are actually evidence for plasticity in the rate of growth and development. 3. Although a positive x-intercept implies a minimum size for reproducing, a plant can have a threshold size for reproducing without having a positive x-intercept. 4. Most of the available data are for annual and monocarpic species whereas allometric data on long-lived iteroparous plants are scarce. We find three common total R–V patterns: short-lived, herbaceous plants and clonal plants usually show a simple, linear relationship, either (i) passing through the origin or (ii) with a positive x-intercept, whereas larger and longer-lived plants often exhibit (iii) classical log–log allometric relationships with slope <1. While the determinants of plant size are numerous and interact with one another, the potential reproductive output of an individual is primarily determined by its size and allometric programme, although this potential is not always achieved. 5. Synthesis. The total R–V relationship for a genotype appears to be a relatively fixed-boundary condition. Below this boundary, a plant can increase its reproductive output by: (i) moving towards the boundary: allocating more of its resources to reproduction, or (ii) growing more to increase its potential reproductive output. At the boundary, the plant cannot increase its reproductive output without growing more first. Analysing size-dependent reproduction is the first step in understanding plant reproductive allocation, but more integrative models must include time and environmental cues, i.e. development.
17660903
Hierarchical Levels of Seed Predation Variation by Introduced Beetles on an Endemic Mediterranean Palm
Seed predators can limit plant recruitment and thus profoundly impinge the dynamics of plant populations, especially when diverse seed predators (e.g., native and introduced) attack particular plant populations. Surprisingly, however, we know little concerning the potential hierarchy of spatial scales (e.g., region, population, patch) and coupled ecological correlates governing variation in the overall impact that native and introduced seed predators have on plant populations. We investigated several spatial scales and ecological correlates of pre-dispersal seed predation by invasive borer beetles in Chamaerops humilis (Arecaceae), a charismatic endemic palm of the Mediteranean basin. To this end, we considered 13 palm populations (115 palms) within four geographical regions of the Iberian Peninsula. The observed interregional differences in percentages of seed predation by invasive beetles were not significant likely because of considerable variation among populations within regions. Among population variation in seed predation was largely related to level of human impact. In general, levels of seed predation were several folds higher in human-altered populations than in natural populations. Within populations, seed predation declined significantly with the increase in amount of persisting fruit pulp, which acted as a barrier against seed predators. Our results revealed that a native species (a palm) is affected by the introduction of related species because of the concurrent introduction of seed predators that feed on both the introduced and native palms. We also show how the impact of invasive seed predators on plants can vary across a hierarchy of levels ranging from variation among individuals within local populations to large scale regional divergences.
42790882
Dangerous liaisons disperse the Mediterranean dwarf palm: fleshy-pulp defensive role against seed predators.
We chose the interaction between the Mediterranean dwarf palm (Chamaerops humilis) and its major seed disperser, the Eurasian badger (Meles meles), to evaluate the hypothesis that endozoochory is characterized by a mixture of conflicting and overlapping interests, with the capacity of being positive or negative for plant fitness. For instance, because of the potential protective role against invertebrate seed predators of C. humilis pulp, we expected that badger-ingested diaspores (i.e., seeds without pulp) would show lower survival than control seeds with the pulp attached. Conversely, due to the possible germination inhibitory function of C. humilis fruit pulp, it was also likely that badger-ingested seeds germinate in higher proportion than control seeds. We evaluated our predictions by carrying out a field sowing and monitoring it over two years. We estimated several stage-specific transition probabilities as well as the cumulative probability of seedling recruitment under different treatments. Our experimental results revealed the multifunctionality of C. humilis fruit pulp and that fruit ingestion by badgers had conflicting outcomes for the palm. As predicted, seed survival was much lower and seed predation by invertebrates much higher for badger-ingested than for control seeds, suggesting a defensive role of C. humilis ripe fruit pulp. All early-emerged seedlings came from badger-ingested seeds, suggesting an inhibitory function of fruit pulp. Though we did not find an effect of removal from the maternal environment on most components of fitness, seedling survival for badger-ingested seeds was higher away from than beneath conspecifics. Badgers imposed a sizeable short-term fitness cost to C. humilis and therefore could be categorized as a "dangerous liaison." Nonetheless, because of the high mobility of the badger, its dispersal service appears paramount given the severe fragmentation and isolation of most C. humilis populations across the highly humanized Mediterranean basin. Our study thus illustrates the necessity of assessing concurrently direct and indirect effects of plant-disperser interactions at different stages of the plant life cycle and recruitment process.
84511242
An experimental study of the interaction between the dwarf palm (Chamaerops humilis) and its floral visitor Derelomus chamaeropsis throughout the life cycle of the weevil.
Palm pollination can be quite diverse but has been poorly studied. This paper describes the life cycle of Derelomus chamaeropsis, a Coleoptera that inhabits the inflorescences of the Mediterranean dwarf palm Chamaerops humilis. D. chamaeropsis is specific to Chamaerops inflorescences, where it eats pollen and the rachis of inflorescences on pistillate plants. They usually lay eggs only on staminate inflorescences where larvae develop and bore into the inflorescence rachis. Larvae do not develop on pistillate inflorescences, except for cases with almost no fruit development. Pistillate plants can thus protect themselves from weevil predation. When visiting pistillate inflorescences, weevils can feed on rachis but usually do not find the brood place reward. Pollination is thus by deceit and weevils should be selected to avoid pistillate inflorescences. D. chamaeropsis pupate within the rachis of staminate inflorescences, but disperse before collecting pollen, thus staminate plants do not have an individual advantage in breeding weevils. However, because larvae develop on dead tissues, the costs of larval development are likely to be low for the plant. This study provides a new example of pollination symbiosis where the pollinator develops on the plant it pollinates, and illustrates how the evolutionary functioning of such relationships can be diverse.
84402770
A systematic comparison of summary characteristics for quantifying point patterns in ecology
Many functional summary characteristics such as Ripley's K function have been used in ecology to describe the spatial structure of point patterns to aid understanding of the underlying processes. However, their use is poorly guided in ecology because little is understood how well single summary characteristics, or a combination of them, capture the spatial structure of real world patterns. Here, we systematically tested the performance of combinations of eight summary characteristics [i.e. pair correlation function g(r), K-function K(r), the proportion E(r) of points with no neighbor at distance r, the nearest neighbor distribution function D(r), the spherical contact distribution Hs(r), the kth nearest-neighbor distribution functions Dk(r), the mean distance nn(k) to the kth neighbor, and the intensity function λ(x)]. To this end we used point pattern data covering a wide range of spatial structures including simulated (stationary) as well as real, possibly non-stationary, patterns on tree species in a tropical forest in Panama. To measure the information contained in a given combination of summary characteristics we used simulated annealing to reconstruct the observed patterns based only on the limited information provided by this combination and assessed how well other characteristics of the observed pattern were recovered. 
 
We found that the number of summary characteristics required to capture the spatial structure of stationary patterns varied between one (for patterns with near random structures) and three (for patterns with complex cluster and superposition structures), but with a robust ranking g(r), Dk(r), and Hs(r) that was largely independent on pattern idiosyncrasies. Stationary summary characteristics [with ranking g(r), Dk(r), Hs(r), E(r)] captured small- to intermediate scale properties of non-stationary patterns, but for describing large-scale spatial structures the intensity function was required. Our finding revealed that the current practice in ecology of using only one or two summary characteristics bears danger that essential characteristics of more complex patterns would not be detected. The technique of pattern reconstruction presented here has wide applications in ecology.
10816877
How individual species structure diversity in tropical forests
A persistent challenge in ecology is to explain the high diversity of tree species in tropical forests. Although the role of species characteristics in maintaining tree diversity in tropical forests has been the subject of theory and debate for decades, spatial patterns in local diversity have not been analyzed from the viewpoint of individual species. To measure scale-dependent local diversity structures around individual species, we propose individual species–area relationships (ISAR), a spatial statistic that marries common species–area relationships with Ripley's K to measure the expected α diversity in circular neighborhoods with variable radius around an arbitrary individual of a target species. We use ISAR to investigate if and at which spatial scales individual species increase in tropical forests' local diversity (accumulators), decrease local diversity (repellers), or behave neutrally. Our analyses of data from Barro Colorado Island (Panama) and Sinharaja (Sri Lanka) reveal that individual species leave identifiable signatures on spatial diversity, but only on small spatial scales. Most species showed neutral behavior outside neighborhoods of 20 m. At short scales (<20 m), we observed, depending on the forest type, two strongly different roles of species: diversity repellers dominated at Barro Colorado Island and accumulators at Sinharaja. Nevertheless, we find that the two tropical forests lacked any key species structuring species diversity at larger scales, suggesting that “balanced” species–species interactions may be a characteristic of these species-rich forests. We anticipate our analysis method will be a starting point for more powerful investigations of spatial structures in diversity to promote a better understanding of biodiversity in tropical forests.
16317185
Stochastically driven adult–recruit associations of tree species on Barro Colorado Island
The spatial placement of recruits around adult conspecifics represents the accumulated outcome of several pattern-forming processes and mechanisms such as primary and secondary seed dispersal, habitat associations or Janzen–Connell effects. Studying the adult–recruit relationship should therefore allow the derivation of specific hypotheses on the processes shaping population and community dynamics. We analysed adult–recruit associations for 65 tree species taken from six censuses of the 50 ha neotropical forest plot on Barro Colorado Island (BCI), Panama. We used point pattern analysis to test, at a range of neighbourhood scales, for spatial independence between recruits and adults, to assess the strength and type of departure from independence, and its relationship with species properties. Positive associations expected to prevail due to dispersal limitation occurred only in 16% of all cases; instead a majority of species showed spatial independence (≈73%). Independence described the placement of recruits around conspecific adults in good approximation, although we found weak and noisy signals of species properties related to seed dispersal. We hypothesize that spatial mechanisms with strong stochastic components such as animal seed dispersal overpower the pattern-forming effects of dispersal limitation, density dependence and habitat association, or that some of the pattern-forming processes cancel out each other.
45272289
Neighborhood diversity of large trees shows independent species patterns in a mixed dipterocarp forest in Sri Lanka.
Interactions among neighboring individuals influence plant performance and should create spatial patterns in local community structure. In order to assess the role of large trees in generating spatial patterns in local species richness, we used the individual species-area relationship (ISAR) to evaluate the species richness of trees of different size classes (and dead trees) in circular neighborhoods with varying radius around large trees of different focal species. To reveal signals of species interactions, we compared the ISAR function of the individuals of focal species with that of randomly selected nearby locations. We expected that large trees should strongly affect the community structure of smaller trees in their neighborhood, but that these effects should fade away with increasing size class. Unexpectedly, we found that only few focal species showed signals of species interactions with trees of the different size classes and that this was less likely for less abundant focal species. However, the few and relatively weak departures from independence were consistent with expectations of the effect of competition for space and the dispersal syndrome on spatial patterns. A noisy signal of competition for space found for large trees built up gradually with increasing life stage; it was not yet present for large saplings but detectable for intermediates. Additionally, focal species with animal-dispersed seeds showed higher species richness in their neighborhood than those with gravity- and gyration-dispersed seeds. Our analysis across the entire ontogeny from recruits to large trees supports the hypothesis that stochastic effects dilute deterministic species interactions in highly diverse communities. Stochastic dilution is a consequence of the stochastic geometry of biodiversity in species-rich communities where the identities of the nearest neighbors of a given plant are largely unpredictable. While the outcome of local species interactions is governed for each plant by deterministic fitness and niche differences, the large variability of competitors causes also a large variability in the outcomes of interactions and does not allow for strong directed responses at the species level. Collectively, our results highlight the critical effect of the stochastic geometry of biodiversity in structuring local spatial patterns of tropical forest diversity.
85836873
Reproductive phenology, seed-set and pollination in Chamaedorea alternans, an understorey dioecious palm in a rain forest in Mexico
The pollination ecology and reproductive phenology of a dioecious palm, Chamaedorea alternans were studied at Los Tuxtlas Biological Station in Veracruz state, Mexico during the 1995-96 flowering season. The sexes flower synchronously from October to January. Field observations investigated reproductive phenology, flower visitors and inflorescence and fruit production. Males produce more flowers and inflorescences than females. Seed-set was 13%, indicating low reproductive efficiency. Individual plants showed a great variation in number of inflorescences produced. Five female and eight male plants (out of 25 and 37 plants, respectively) produced 45% of all inflorescences in the population studied. These five females also produced c. 75% of all fruits. Seed production did not show significant differences between insect-excluded and open-pollinated inflorescences, in experiments to test the efficiency of wind pollination. Flowers of this species are wind-pollinated but a great activity of undetermined species of thrips (Thysanoptera) was observed in male inflorescences.
39202154
Niche relations among three sympatric Mediterranean carnivores
Abstract Previous studies carried out in the Doñana National Park reported that red foxes (Vulpes vulpes) were killed by Iberian lynxes (Lynx pardinus), whereas similar-sized Eurasian badgers (Meles meles) were not. Therefore, we predicted that fox would avoid lynx predation risk by niche segregation whereas we did not expect such a segregation between badger and lynx. As an approach for evaluating our predictions, we compared their diet, activity patterns, and habitat use in an area of Doñana where the three carnivores are sympatric. Lynxes preyed almost uniquely on European rabbits (Oryctolagus cuniculus), and though badgers and foxes were omnivorous, rabbits also were a major prey, resulting in high overlaps throughout the year. However, badgers preyed largely on small rabbits, whereas lynxes and foxes preyed mainly on medium-sized rabbits. There were also interspecific differences in activity patterns. Maximum levels of activity among lynxes were during sunrise and dusk (49–67%). Foxes were most active during dusk and night (34–67%), and badgers were mainly nocturnal (53–87%). Though there were seasonal differences in the amount of activity of each species, specific activity patterns changed little throughout the year. There was a strong difference in annual habitat use by the three species (P < 0.0001). Lynxes used mainly the Mediterranean scrubland during both the active (PMAX) and the resting (PMIN) periods. During PMIN, foxes used the Mediterranean scrubland intensively (40% of locations on average), but during PMAX, they used the pastureland much more intensively despite this habitat being poorer in their main prey (rabbits). As a consequence, foxes and lynxes exhibited segregation in their habitat use during the active period. Badgers also used the Mediterranean scrubland intensively, especially during PMIN. There were no seasonal differences in habitat use for lynx and fox, but there was for badgers (P < 0.015). Within the study area, the three species selected habitat suggesting they were sensitive to factors such as vegetation and prey abundance. However, in general, carnivore habitat use did not correlate with rabbit abundance. We propose that foxes avoided lynxes by using, during activity, habitats not frequented by lynxes, and that a low predation risk associated with the distinctive foraging mode of badgers may facilitate its coexistence with other carnivores.
86777146
Spatial organization, group living and ecological correlates in low‐density populations of Eurasian badgers, Meles meles
Summary 
 
 
1 
 Territoriality and group living are described in a low-density population of Eurasian badgers, Meles meles L., by studying the patterns of spatial grouping and territory marking, as well as the differences between individuals in some of their characteristics (body condition and dispersal) and in their space use (seasonally, periods of activity and interaction between pairs of individuals) under strong seasonal fluctuations in the availability of the key resource (young rabbits, Oryctolagus cuniculus L.). Finally, the role of the spatial distribution of the main prey (young rabbits) in the development of sociality was also studied in order to test some of the assumptions and predictions of the resource dispersion hypothesis (RDH). 
 
2 
 Badgers were territorial, showing a flexible system of territory marking, which includes the marking of the most used areas (sett-latrines at the centres of activity) and additionally, at the smaller territories, a system of border-latrines in the areas of contact between territories. The maximum use of border-latrines was associated with the reproductive season, and that of sett-latrines with the season of food scarcity. 
 
3 
 In the study area where badgers had rabbits as main prey, territories were occupied by small groups of animals, formed by one adult female who reproduced, one adult male who also showed signs of reproductive activity, the cubs of the year (if there was reproduction) and some animals born during previous years, which remained in their natal territory until their dispersal (normally during the mating season of their third or fourth year of life). This system was not strictly fixed as males, given the opportunity, expanded their territories to encompass additional females. Territories in another study site were occupied by one adult female (marked), plus the cubs of the year and another adult individual (unmarked). 
 
4 
 In winter and spring dominant females and subordinates used only a small fraction of their territories, moved short distances, at a low speed and covering small areas per night. These seasons corresponded with the reproduction of rabbits (highest food availability). Dominant females were the only individuals using all the territory available in the summer (lowest food availability), when badgers had the worst body condition. Food availability increased again in autumn, as did body condition, while range sizes were again reduced. Dominant males used the same proportion of their territories over all seasons. However, in winter (reproductive season) they moved faster, over longer distances, and covered larger areas per period of activity. These results indicate that use of space by dominant males was affected by different factors from that of dominant females and subordinates. 
 
5 
 RDH does not seem to explain group living in our populations because: (a) territoriality in each pair of primary animals was driven by different factors (trophic resources for females and females for males); (b) dominant males acted as expansionists; and (c) territory size was related to its richness and not to patch dispersion. 
 
6 
 We propose an integrative hypothesis to explain not only group formation but also interpopulation variability in the social organization of badgers within ecological, demographic and behavioural constraints and in the light of current theory on delayed dispersal.
67833217
Natural regeneration and gender-specific spatial pattern of Taxus baccata in an old-growth population in Foresta Umbra (Italy)
English yew is rare and endangered dioecious species. Research on regeneration processes of endangered taxa is important to understand the mechanisms allowing a species to survive under several ecological scenarios, to predict future distribution shifts, to achieve best management practices and conser- vation policies. Our investigation was focusing on one of the oldest yew population in Europe, in Foresta Umbra in Italy. The main aim of this study was to understand spatial regeneration processes and dynamics related with parent trees' sex distribution. Geostatistical analysis showed that seedlings occur in patches avoiding direct competition with adult yews. Negative relationship between regeneration and yew density and basal area was found. A general model for the reproductive ecology is proposed: females are less competitive and more envi- ronmentally demanding than males, because of their reproductive effort. Indeed, male and female fitness responds differently across environmental gradients, thus favouring spatial segregation of seedlings. Un- derstanding the yew's adaptive effectiveness is essential to ensure the conservation of existing populations, and encourage the species' resilience into areas where yew is endangered.
5653044
Sex ratio and gender-dependent neighboring effects in Podocarpus nagi, a dioecious tree
We analyzed sex ratio, growth rates, and spacing among individuals of Podocarpus nagi, a dioecious tree, on Mt. Mikasa, Nara City, Japan. The sex ratio of reproductive trees ≥ 5 cm in stem diameter at breast height (dbh, 130 cm above ground level) was significantly male-biased. The sex ratio was male-biased in the < 20 cm and ≥ 50 cm size classes, while it did not depart from 1:1 in the 20 ≤ dbh < 50 cm class. Growth rate varied with tree size in males but not in females. The precocity and vigor of males suggests that differences in reproductive costs between sexes induce the biased sex ratio. Random labeling tests on the positions of reproductive trees showed that in the < 30 cm class, males and females were distributed randomly and independently from each other. In the ≥ 30 cm class, males were significantly clumped, whereas females were randomly distributed. Males and females showed significant repulsion, i.e., a spatial segregation of sexes. Both intra- and intersexual effects on the growth rate of crowding by neighbors were significant for females, but not for males. Maximum competitive interference was observed at a distance of 5 m, which corresponded approximately to the radius of clumps of large males and to the significant repulsive distance between large males and females. These results suggest that sexual differences in sensitivity to local crowding are related to the formation of gender-dependent spatial patterns. Formation of female-repulsive male clumps and a male-biased sex ratio may intensify the decreased probability of regeneration near males, as suggested by the limited seed-dispersal range of this species, thereby promoting coexistence with other species.
36996539
A survey and overview of habitat fragmentation experiments.
Habitat destruction and fragmentation are the root causes of many conservation problems. We conducted a literature survey and canvassed the ecological community to identify experimental studies of terrestrial habitat fragmentation and to determine whether consistent themes were emerging from these studies. Our survey revealed 20 fragmentation experiments worldwide. Most studies focused on effects of fragmentation on species richness or on the abundance(s) ofparticular species. Other important themes were the effect offragmentation in interspecific interactions, the role of corridors and landscape connectivity in in- dividual movements and species richness, and the influences of edge effects on ecosystem services. Our com- parisons showed a remarkable lack of consistency in results across studies, especially with regard to species richness and abundance relative to fragment size. Experiments with arthropods showed the best fit with the- oretical expectations of greater species richness on larger fragments. Highly mobile taxa such as birds and mammals, early-successional plant species, long-lived species, and generalist predators did not respond in the "expected" manner. Reasons for these discrepancies included edge effects, competitive release in the habitat fragments, and the spati.al scale of the experiments. One of the more consistently supported hypotheses was that movement and species richness are positively affected by corridors and connectivity, respectively. Tran- sient effects dominated many systems;,for example, crowding of individuals on fragments commonly was ob- served afterfragmentation, followed by a relaxation toward lower abundance in subsequentyears. The three long-term studies (?14 years) revealed strong patterns that would have been missed in short-term investiga- tions. Our results emphasize the wide range of species-specific responses to fragmentation, the need for eluci- dation of behavioral mechanisms affecting these responses, and the potentialfor changing responses to frag- mentation over time.
84173515
Consequences of subpopulation isolation for pollination, herbivory, and population growth in Clarkia concinna concinna (Onagraceae)
The importance of the spatial arrangement of populations for long-term persistence has been debated. Plant species will be influenced mostly by the responses of their pollinators and herbivores to changes in population isolation, making it hard to predict how habitat fragmentation may affect a plant species. I have used a common annual to examine how population isolation may affect reproductive success and ultimately population growth and persistence. Clarkia concinna concinna exhibits considerable pollen limitation when small populations are isolated, although it also endures less herbivory. For this plant, isolation appears mostly to depress population growth and therefore to enhance risks of extinction. Experimental investigations on common species such as C. concinna concinna can be used to better diagnose threats to endangered taxa, and to design appropriate restoration activities.
2982917
Propagule pressure: a null model for biological invasions
Invasion ecology has been criticised for its lack of general principles. To explore this criticism, we conducted a meta-analysis that examined characteristics of invasiveness (i.e. the ability of species to establish in, spread to, or become abundant in novel communities) and invasibility (i.e. the susceptibility of habitats to the establishment or proliferation of invaders). There were few consistencies among invasiveness characteristics (3 of 13): established and abundant invaders generally occupy similar habitats as native species, while abundant species tend to be less affected by enemies; germination success and reproductive output were significantly positively associated with invasiveness when results from both stages (establishment/spread and abundance/impact) were combined. Two of six invasibility characteristics were also significant: communities experiencing more disturbance and with higher resource availability sustained greater establishment and proliferation of invaders. We also found that even though ‘propagule pressure’ was considered in only ~29% of studies, it was a significant predictor of both invasiveness and invasibility (55 of 64 total cases). Given that nonindigenous species are likely introduced non-randomly, we contend that ‘propagule biases’ may confound current paradigms in invasion ecology. Examples of patterns that could be confounded by propagule biases include characteristics of good invaders and susceptible habitats, release from enemies, evolution of ‘invasiveness’, and invasional meltdown. We conclude that propagule pressure should serve as the basis of a null model for studies of biological invasions when inferring process from patterns of invasion.
18807470
The keystone saguaro (Carnegiea gigantea, Cactaceae): a review of its ecology, associations, reproduction, limits, and demographics
This paper reviews the basics of a Sonoran Desert keystone cactus species, including the ecology of its establishment and high mortality, its association with nurse plants to provide ameliorated conditions for survival, and variability in longevity and reproduction over its range such as delayed reproduction in hotter and more arid populations where this delay is met with longer lifespans. The production of flowers, branches, and spines from areoles is reviewed, as well as current methods for estimating individual age despite great variability in growth rates, most notably linked to summer rainfall. Possible implications of anthropogenic influences that impact populations as well as global climate change are discussed as are implications for potential range shifts in the future. This paper also provides a table listing of over 100 birds, mammals, insects, reptiles, and other animal species that use Carnegiea and highlighting its keystone status.
25670383
Fluctuating patch boundaries in a native annual forb: the roles of niche and dispersal limitation.
Abiotic, biotic, and dispersal constraints jointly control the spatial distributions of species, but few studies have directly evaluated how these forces interact and vary over time to create dynamic spatial distributions. Through three years of observation and two years of field manipulation, I investigated simultaneous constraints on the spatial distribution of Lupinus nanus, a native annual legume that grows in dense patches in California grasslands. I transplanted L. nanus across its own patch boundaries, yet within apparently suitable habitat, and assessed the demographic success of naturally occurring and seeded plants in plots with and without competitor removal in years that varied in temperature and rainfall. Core sites were defined as those consistently densely occupied, whereas peripheral sites were densely occupied only during some years, and exterior sites were consistently unoccupied or very sparsely occupied. Site types (core, periphery, and exterior) differed in soil moisture, P, and NO3. Competition limited emergence in all site types in the dry/warm year and in patch peripheries in the wet/cool year. Population fitness (seeds produced per seed added) was > 1.0 in cores during all years. Peripheral sites had fitness near replacement in the wet/cool year, which was greatly increased by competition removal. Exterior fitness was < 1.0 in both experimental years, regardless of seed addition and competitor removal. Seed addition did not increase site-specific fitness, and a seed bank was found to be present in all site types. Herbivory was greater in patch cores and peripheries than in exteriors. Soil variation exerted the most consistent control over patch limits, while competition played an intermittent role in excluding Lupinus from patch peripheries. The dynamic distribution of L. nanus is the product of temporal variation in specific abiotic and biotic niche axes, primarily soil characteristics and competition, rather than dispersal limitation.
86165324
Spatio-temporal variation in fruit production and seed predation in a perennial herb influenced by habitat quality and population size
1. In patchily distributed plant species, seed production is likely to be influenced both by local abiotic factors affecting plant size and conditions for fruit maturation, and by population characteristics affecting the intensity of interactions with mutualists and antagonists. However, the relative importance of these effects is poorly known. 2. We used multiple regression and path models to examine the importance of abiotic factors (sun exposure, soil depth) and population characteristics (size, density and connectivity) for variation in flower and fruit production and intensity of seed predation among 39 populations of the long-lived herb Vincetoxicum hirundinaria in three consecutive years. In addition, we manipulated water availability in a field experiment and recorded short-term and long-term effects on fruit output, and conducted a supplemental hand-pollination experiment. 3. Flower production varied little, while fruit initiation, fruit abortion and fruit predation varied considerably among years. Sun exposure and soil depth affected fruit production per plant indirectly and positively through their effects on flower number. Population density affected fruit production negatively through its effect on flower number. Both fruit initiation and the proportion of fruits attacked by the tephritid fly Euphranta connexa were related positively to population size. 4. The number of full-size fruits per plant was related positively to sun exposure and population size in two years each, and related negatively to population density in one year. However, because of seed predation, the number of intact mature fruits was related significantly to population characteristics in only one of three years. 5. The field experiments showed that both shortage of water and insufficient pollination may limit fruit set in V. hirundinaria. 6. Synthesis. These results demonstrate that the relative importance of local abiotic conditions and population characteristics may vary considerably along the chain of events from flower formation to intact fruit, and also among years. They further show that, at least in species with a naturally patchy distribution, connectivity may be relatively unimportant for variation in reproductive output compared to effects of habitat quality, population size and density.
18486654
Phenologically explicit models for studying plant–pollinator interactions under climate change
Climate change is significantly influencing phenology. One potential effect is that historically interacting partners will respond to climate change at different rates, creating the potential for a phenological mismatch among previously synchronized interacting species, or even sexes of the same species. Focusing on plant demographics in a plant–pollinator interaction, we develop a hybrid dynamical model that uses a “non-autonomous” differential equation system (Zonneveld model) for within-season dynamics and discrete equations for season-to-season dynamics. Our model outlines how and when changes in the relative phenologies of an interacting species pair will alter the demographic outcome of the interaction. For our plant–pollinator system, we find that plant population growth rates are particularly sensitive to phenology mismatch when flowers are short-lived, when pollinators are short-lived, or when flowers and pollinators exhibit high levels of within-population synchrony in emergence or arrival dates. More generally, our aim is to introduce the use of hybrid dynamical models as a framework through which researchers can directly explore the demographic consequences of climatically driven phenological change.
83836712
Central and peripheral Hornungia petraea populations: patterns and dynamics
Summary 
 
 
1 
More or less continuous distributions tend to become fragmented towards species’ distribution limits. Peripheral or isolated populations of a species are predicted to have lower population sizes and densities than central populations, as a result of environmental and/or genetic stress. Population densities at the periphery may be reduced by decreased reproduction or higher interannual variation in reproduction. In particular, fecundity and survival are likely to be reduced by less favourable growing conditions. 
 
2 
We compared populations of the annual species Hornungia petraea (Brassicaceae) in two contrasting regions of the species’ range and at the population scale within regions. Ten populations in Italy (central to the species range) and 10 German populations (peripheral) were monitored for three growing periods from spring 1999 to spring 2001. 
 
3 
All life-cycle stages, adult plant density, seed production and pre- and post-dispersal seed bank density were studied in a nested sampling design and variation in various demographic factors was attributed to the effects of the two countries, of populations nested within country and to temporal effects. 
 
4 
Peripheral populations had higher densities than populations in the centre of the species distribution, both as adult plants and in the seed bank. 
 
5 
Fecundity was strongly influenced by temporal effects, but only affected to a minor degree by the study region. High interannual variation in fecundity was not reflected in high interannual variation of either adult plant density in spring or of the seed bank. Significant regional differences were, however, found in seasonal seed bank dynamics, which were more pronounced in peripheral German populations than in central Italian populations. 
 
6 
We conclude that seasonal seed bank dynamics are a key factor in explaining differences in H. petraea density patterns, particularly in central populations, where fewer seeds are incorporated into the seed bank.
9377401
Testing the abundant center model using range-wide demographic surveys of two coastal dune plants.
It is widely accepted that species are most abundant at the center of their geographic ranges and become progressively rarer toward range limits. Although the abundant center model (ACM) has rarely been tested with range-wide surveys, it influences much thinking about the ecology and evolution of species' distributions. We tested ACM predictions using two unrelated but ecologically similar plants, Camissonia cheiranthifolia and Abronia umbellata. We intensively sampled both throughout their one-dimensional distributions within the Pacific coastal dunes of North America, from northern Baja California, Mexico, to southern Oregon, USA. Data from > 1100 herbarium specimens indicated that these limits have been stable for at least the last 100 years. Range-wide field surveys detected C. cheiranthifolia at 87% of 124 sites and A. umbellata at 54% of 113 sites, but site occupancy did not decline significantly toward range limits for either species. Permutation analysis did not detect a significant fit of geographical variation in local density to the ACM. Mean density did not correlate negatively with mean individual performance (plant size or number of seeds/plant), probably because both species occur at low densities. Although size and seeds per plant varied widely, central populations tended to have the highest values for size only. For C. cheiranthifolia, we observed asymmetry in the pattern of variation between the northern and southern halves of the range consistent with the long-standing prediction that range limits are imposed by different ecological factors in different parts of the geographical distribution. However, these asymmetries were difficult to interpret and likely reflect evolutionary differentiation as well as plastic responses to ecological variation. Both density and seeds per plant contributed to variation in seed production per unit area. In C. cheiranthifolia only, sites with highest seed production tended to occur at the range center, as predicted by the ACM and assumed by theory proposing that range limits evolve via antagonism between natural selection and gene flow.
14554119
Between-population variation in size-dependent reproduction and reproductive allocation in Pinguicula vulgaris (Lentibulariaceae) and its environmental correlates
Several important fitness components in herbaceous perennial plants are commonly related to plant size: flowering probability, reproductive allocation and fecundity. However, evidence for such size-dependence of fitness components is mostly anecdotal and unconnected to other life history traits. Here we report size-dependence for flowering probability and reproductive allocation in 11 populations of Pinguicula vulgaris and relate it to environmental factors. Flowering probability was size-dependent in all populations of P. vulgaris, and indicated the existence of a threshold size for reproduction. Populations at low altitudes and in wet soils showed a significantly higher threshold size for reproduction. Reproductive mass was also size-dependent in all populations. We found considerable between-population differences in the slope and the intercept of the regression between plant size and reproductive mass. This variation was weakly related to the environmental factors measured. In general, relationships between different size-dependent fitness components were low. Instead of showing a covariation of traits, in line with interpretations in terms of life history “tactics”, P. vulgaris seemed to independently vary each size-dependent fitness component in each locality. In particular, no significant relationship was found between threshold size for reproduction and the slope of size-dependent reproductive allocation, as predicted by previous authors. Neither we found a significant influence of somatic cost of reproduction on size-dependent fitness components.
26395117
Seed Dispersal in the Iberian Pear, Pyrus bourgaeana: A Role for Infrequent Mutualists
Abstract: Seed dispersal by animals is a key interaction, with effects on the population ecology and evolution of many plant lineages. Despite the fact that infrequent seed dispersers can potentially provide important services to plant populations, little attention has been paid so far to scarce mutualists. We assessed different aspects of quantity and quality of seed dispersal from fruit removal to seed germination in the Iberian pear, Pyrus bourgaeana, finding that fruit consumers markedly differed in the nature of their interaction with the tree. Whereas the abundant rodents, rabbits, and deer damaged all seeds eaten, the uncommon carnivores badger and fox and the abundant boars dispersed a large fraction of ingested seeds as viable propagules, acting as legitimate seed dispersers. Despite low rates of visitation by badgers to fruiting trees, they transported more viable seeds than the abundant boars, due to better seed treatment and a higher feeding rate on pears. Seed dispersal by all 3 legitimate dispersers, especially the badger, enhanced post-dispersal P. bourgaeana seed survival, supporting the “escape” predation hypothesis. Pyrus bourgaeana showed relatively high frequencies of visits by a myriad of frugivores; however, it relied on the dispersal service provided by an infrequent carnivore, the badger, rather than on those provided by the abundant mammalian herbivores. Therefore, under some circumstances, uncommon animal counterparts play major roles in their mutualistic interactions with flowering plants. Nomenclature: Váldes et al., 2007.
29366561
Dangerously few liaisons: a review of mate-finding Allee effects
In this paper, we review mate-finding Allee effects from ecological and evolutionary points of view. We define ‘mate-finding’ as mate searching in mobile animals, and also as the meeting of gametes for sessile animals and plants (pollination). We consider related issues such as mate quality and choice, sperm limitation and physiological stimulation of reproduction by conspecifics, as well as discussing the role of demographic stochasticity in generating mate-finding Allee effects. We consider the role of component Allee effects due to mate-finding in generating demographic Allee effects (at the population level). Compelling evidence for demographic Allee effects due to mate-finding (as well as via other mechanisms) is still limited, due to difficulties in censusing rare populations or a failure to identify underlying mechanisms, but also because of fitness trade-offs, population spatial structure and metapopulation dynamics, and because the strength of component Allee effects may vary in time and space. Mate-finding Allee effects act on individual fitness and are thus susceptible to change via natural selection. We believe it is useful to distinguish two routes by which evolution can act to mitigate mate-finding Allee effects. The first is evolution of characteristics such as calls, pheromones, hermaphroditism, etc. which make mate-finding more efficient at low density, thus eliminating the Allee effect. Such adaptations are very abundant in the natural world, and may have arisen to avoid Allee effects, although other hypotheses are also possible. The second route is to avoid low density via adaptations such as permanent or periodic aggregation. In this case, the Allee effect is still present, but its effects are avoided. These two strategies may have different consequences in a world where many populations are being artificially reduced to low density: in the first case, population growth rate can be maintained, while in the second case, the mechanism to avoid Allee effects has been destroyed. It is therefore in these latter populations that we predict the greatest evidence for mate-finding Allee effects and associated demographic consequences. This idea is supported by the existing empirical evidence for demographic Allee effects. Given a strong effect that mate-finding appears to have on individual fitness, we support the continuing quest to find connections between component mate-finding Allee effects (individual reproductive fitness) and the demographic consequences. There are many reasons why such studies are difficult, but it is important, particularly given the increasing number of populations and species of conservation concern, that the ecological community understands more about how widespread demographic Allee effects really are, and why.
85865301
Inequalities in fruit-removal and seed dispersal: consequences of bird behaviour, neighbourhood density and landscape aggregation
Summary 1. Frugivores disperse the seeds of the majority of woody plant species world-wide. Thus, insights on how frugivores influence the dispersal of plants and the variability of this process are crucial for understanding plant population dynamics in a rapidly changing world. 2. We used a spatially explicit, stochastic, individual-based model that simulates fruit-removal and seed dispersal by birds to assess bird density, landscape and neighbourhood effects on the inequalities of within-population fruit-removal rates and seed dispersal. We also compared model predictions with spatially-explicit field data. 3. In our simulations, bird density had a strong effect on the distribution of fruit-removal rates creating large inequalities among plants. Also, for equal bird densities, inequalities increased with the landscape level aggregation of plants. 4. Fruit removal increased with increasing plant neighbourhood density although there was a tendency to decline at the highest densities. Neighbourhood density also changed average dispersal distances, but with shorter distances at higher densities. Plants with few neighbours not only had longer distance dispersal but also a larger variance in seed rain across distances than plants with ten or more neighbours. These relationships between neighbourhood density and fruit removal and dispersal distance were scale-dependent with a peak in correlations at 150-m radius. 5. Similar to model predictions, field data shows an inverse relationship between dispersal distances (inferred from bird movements) and fruiting neighbourhood density. Also, fruit-removal rates observed in the field show large numbers of plants receiving little or zero fruit-removal. Fruitremoval rate distributions were statistically indistinguishable between the simulation and field data. But, distributions were strikingly different from two alternative models that lacked spatial effects. 6. Synthesis . Our model and field data show that as fruiting plants become aggregated, inequalities in fruit-removal rates increase and seed dispersal distance decreases. Both of these processes could help create and maintain plant aggregation and affect genetic structuring. The model also predicts that small-scale neighbourhood effects can be controlled by large-scale processes such as overall frugivore abundance and landscape-level plant aggregation. Most importantly, both simulations and field data shows an interaction between plant spatial pattern and bird foraging, which results in neighbourhood-specific dispersal and rates of fruit removal.
35797679
Crop Size and Fruit Neighborhood Effects on Bird Visitation to Fruiting Schefflera morototoni Trees in Puerto Rico
Studies of zoochorous seed dispersal systems often consider crop size, yet seldom consider the kinds and amounts of fruits surrounding parent plants (the fruit neighborhood) when attempting to explain among-plant variation in fruit removal. We studied avian frugivory at 24 Schefflera morototoni trees from February to May 1998 in central Puerto Rico. The number of fruits removed by avian seed dispersers per visit was similar among focal trees (typically 2–4). In contrast, visitation rate was highly variable (range: 0–71 visits per 4 h). We used multiple regression analyses to evaluate the relative roles of crop size (focal tree ripe fruit abundance) and fruit neighborhood variables (measured within 30 m of focal trees) in affecting visitation to focal trees by avian frugivores. Visitation rate was positively related to crop size (although this variable was only significant in one of four regression models considered) and negatively related to the presence or abundance of conspecific fruits, suggesting that trees competed intraspecifically for dispersers. Relationships between visitation and heterospecific fruits were mixed—some kinds of fruits appeared to enhance visitation to focal trees, while others seemed to reduce visitation. In most regression models, neighborhood variables had larger effects on visitation than focal tree fruit crop size. Our results highlight the important effects of local fruiting environments on the ability of individual plants to attract seed dispersers.
84490190
Herbivores and the Number of Tree Species in Tropical Forests
A high number of tree species, low density of adults of each species, and long distances between conspecific adults are characteristic of many low-land tropical forest habitats. I propose that these three traits, in large part, are the result of the action of predators on seeds and seedlings. A model is presented that allows detailed examination of the effect of different predators, dispersal agents, seed-crop sizes, etc. on these three traits. In short, any event that increases the efficiency of the predators at eating seeds and seedlings of a given tree species may lead to a reduction in population density of the adults of that species and/or to increased distance between new adults and their parents. Either event will lead to more space in the habitat for other species of trees, and therefore higher total number of tree species, provided seed sources are available over evolutionary time. As one moves from the wet lowland tropics to the dry tropics or temperate zones, the seed and seedling predators in a habitat are hypothesized to be progressively less efficient at keeping one or a few tree species from monopolizing the habitat through competitive superiority. This lowered efficiency of the predators is brought about by the increased severity and unpredictability of the physical environment, which in turn leads to regular or erratic escape of large seed or seedling cohorts from the predators.
4428057
Pervasive density-dependent recruitment enhances seedling diversity in a tropical forest
Negative density-dependent recruitment of seedlings, that is, seeds of a given species are less likely to become established seedlings if the density of that species is high, has been proposed to be an important mechanism contributing to the extraordinary diversity of tropical tree communities because it can potentially prevent any particular species from usurping all available space, either in close proximity to seed sources or at relatively larger spatial scales. However, density-dependent recruitment does not necessarily enhance community diversity. Furthermore, although density-dependent effects have been found at some life stages in some species, no study has shown that density-dependent recruitment affects community diversity. Here we report the results of observations in a lowland, moist forest in the Republic of Panamá in which the species identities of 386,027 seeds that arrived at 200 seed traps were compared with the species identities of 13,068 seedlings that recruited into adjacent plots over a 4-year period. Across the 200 sites, recruit seedling diversity was significantly higher than seed diversity. Part of this difference was explained by interspecies differences in average recruitment success. Even after accounting for these differences, however, negative density-dependent recruitment contributes significantly to the increase in diversity from seeds to seedling recruits.
24634027
Widespread density-dependent seedling mortality promotes species coexistence in a highly diverse Amazonian rain forest.
Negative density-dependent mortality can promote species coexistence through a spacing mechanism that prevents species from becoming too locally abundant. Negative density-dependent seedling mortality can be caused by interactions among seedlings or between seedlings and neighboring adults if the density of neighbors affects the strength of competition or facilitates the attack of natural enemies. We investigated the effects of seedling and adult neighborhoods on the survival of newly recruited seedlings for multiple cohorts of known age from 163 species in Yasuni National Park, Ecuador, an ever-wet, hyper-diverse lowland Amazonian rain forest. At local scales, we found a strong negative impact on first-year survival of conspecific seedling densities and adult abundance in multiple neighborhood sizes and a beneficial effect of a local tree neighborhood that is distantly related to the focal seedling. Once seedlings have survived their first year, they also benefit from a more phylogenetically dispersed seedling neighborhood. Across species, we did not find evidence that rare species have an advantage relative to more common species, or a community compensatory trend. These results suggest that the local biotic neighborhood is a strong influence on early seedling survival for species that range widely in their abundance and life history. These patterns in seedling survival demonstrate the role of density-dependent seedling dynamics in promoting and maintaining diversity in understory seedling assemblages. The assemblage-wide impacts of species abundance distributions may multiply with repeated cycles of recruitment and density-dependent seedling mortality and impact forest diversity or the abundance of individual species over longer time scales.
24532465
When, how and how much: Gender-specific resource-use strategies in the dioecious tree Juniperus thurifera.
BACKGROUND AND AIMS
In dioecious species male and female plants experience different selective pressures and often incur different reproductive costs. An increase in reproductive investment habitually results in a reduction of the resources available to other demands, such as vegetative growth. Tree-ring growth is an integrative measure that tracks vegetative investment through the plant's entire life span. This allows the study of gender-specific vegetative allocation strategies in dioecious tree species thoughout their life stages.


METHODS
Standard dendrochronological procedures were used to measure tree-ring width. Analyses of time-series were made by means of General Mixed Models with correction of autocorrelated values by the use of an autoregressive covariance structure of order one. Bootstrapped correlation functions were used to study the relationship between climate and tree-ring width.


KEY RESULTS
Male and female trees invest a similar amount of resources to ring growth during the early life stages of Juniperus thurifera. However, after reaching sexual maturity, tree-ring growth is reduced for both sexes. Furthermore, females experience a significantly stronger reduction in growth than males, which indicates a lower vegetative allocation in females. In addition, growth was positively correlated with precipitation from the current winter and spring in male trees but only to current spring precipitation in females.


CONCLUSIONS
Once sexual maturity is achieved, tree rings grow proportionally more in males than in females. Differences in tree-ring growth between the genders could be a strategy to respond to different reproductive demands. Therefore, and responding to the questions of when, how and how much asked in the title, it is shown that male trees invest more resources to growth than female trees only after reaching sexual maturity, and they use these resources in a different temporal way.