Abstract

Small mammals use multiple foraging strategies to compensate for fluctuating resource quality in stochastic environments. These strategies may lead to increased dietary overlap when competition for resources is strong. To quantify temporal contributions of high (C-3) versus low quality (C-4) resources in diets of silky pocket mice (Perognathus flavus), we used stable carbon isotope (delta C-13) analysis of 1391 plasma samples collected over 2years. Of these, 695 samples were from 170 individuals sampled >= 3 times across seasons or years, allowing us to assess changes in dietary breadth at the population and individual levels across a boom-bust population cycle. In 2014, the P. flavus population increased to 412 captures compared to 8 captures in prior and subsequent years, while populations of co-occurring small mammals remained stable. As intraspecific competition increased, the population-wide dietary niche of P. flavus did not change, but individual specialization increased significantly. During this period, similar to 27% (41/151) of individuals sampled specialized on C-3 resources, which were abundant during the spring and previous fall seasons. Most of the remaining individuals were C-3-C-4 generalists (64%) (96/151), and only 9% (14/151) specialized on C-4 resources. In 2015, P. flavus population density and resource availability declined, individual dietary breadth expanded (84% generalists), no C-3 specialists were found, and specialization on C-4 resources increased (16%). Our results demonstrate a high degree of inter-individual plasticity in P. flavus foraging strategies, which has implications for how this species will respond to environmental change that is predicted to decrease C-3 resources in the future.