Predator-mediated interactions through changes in predator home range size can lead to local prey exclusion

The effects of indirect biotic interactions on species occurrence are difficult to quantify in the wild. In theory, the exclusion of a prey species can occur through the numerical and functional responses of a predator to another prey. Few studies assessed the relative effects of these responses on the net interaction strength between multiple prey sharing common predators, in part because empirically based multi-species functional response models are very rare. To investigate whether the presence of a prey species affects predation rates and population growth rate of another prey species, we used a multi-prey mechanistic model of predation along with a population matrix model. The predation model was parameterized using a combination of behavioral, demographic, and experimental data acquired in an arctic vertebrate community. It includes the arctic fox (Vulpes lagopus), a predator feeding primarily on small mammals as well as eggs of various bird species such as sandpipers and colonial nesting geese. Our results showed that the positive effects of the presence of a goose colony on sandpiper nesting success (due to the handling time of goose eggs by the predator) were outweighed by the negative effect of an increase in fox density. The numerical response of the arctic fox was driven by a reduction in home range size in the goose colony. As a result, the net interaction from the presence of geese was negative. Our results also showed that this interaction could lead to local exclusion of sandpipers over a range of adult sandpiper annual survival observed in the wild, which is coherent with previous observations of their co-distribution. Our approach takes into account diverse proximate mechanisms underpinning interaction strengths in a multi-prey system and generates novel insights on some of the predator behavioral responses that may influence prey coexistence (and the lack of) in vertebrate communities.