Shifts in competitive structures can drive variation in species’ phenology

Characterizing patterns and drivers of species’ responses to various environmental contexts is useful in determining their adaptive capacity to the consequences of ongoing global environmental change. For many species, a well-documented response to anthropogenic climate change is a shift in the timing of their key life-history events or phenology. Often, these phenological shifts are associated with changes in abiotic factors used as proxies for resource availability or other suitable conditions. However, less is known about how species’ interactions that can lead to resource limitation influence phenological responses. Using long-term experimental data on small mammals monitored in the southwestern United States, we show that altered competitive landscapes can drive shifts in breeding timing and duration, and that, relative to a dominant competitor, other species exhibit less specific responses to environmental factors. These results suggest that plasticity of phenological responses, that is often described in the context of annual variation in abiotic factors, can occur in response to biotic context as well. Additionally, in response to competitive pressures, species may employ adaptive strategies, such as low phenological synchrony, to compensate for the adverse demographic impacts of mismatched resource and species’ phenology. Variation in phenological responses under different biotic conditions shown here further demonstrate that shifting biotic interactions are rampantly occurring in many natural systems and a more nuanced understanding of its impacts on population dynamics is useful to better understand and predict biodiversity patterns in a changing world.