Foraging strategies of individual silky pocket mice over a boom–bust cycle in a stochastic dryland ecosystem
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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 (C3) versus low quality (C4) resources in diets of silky pocket mice (Perognathus flavus), we used stable carbon isotope (δ13C) analysis of 1391 plasma samples collected over 2 years. 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, ~ 27% (41/151) of individuals sampled specialized on C3 resources, which were abundant during the spring and previous fall seasons. Most of the remaining individuals were C3–C4 generalists (64%) (96/151), and only 9% (14/151) specialized on C4 resources. In 2015, P. flavus population density and resource availability declined, individual dietary breadth expanded (84% generalists), no C3 specialists were found, and specialization on C4 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 C3 resources in the future.
KeywordsGeneralists Intraspecific competition Niche variation hypothesis Perognathus flavus Specialists
We thank N. Wilson, A. Richins, and M. Rodriquez Curras for assistance with fieldwork, and L. Burkemper and V. Atudorei for stable isotopes for analytical support. The research was completed with start-up funding to SDN, grants from NSF to the University of New Mexico for Long-term Ecological Research, and graduate research scholarships to JDN.
Author contribution statement
SDN and BOW conceived and designed the study, SDN and JDN collected field data, JDN processed samples, analyzed data and drafted the manuscript, AJH and KM helped with data analysis and graphics, and all authors provided text and edited the manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no competing interests.
Fieldwork was conducted with permission from the Fish and Wildlife Service and Institutional Animal Care and Use Committee (IACUC #13-100970-MC). All applicable institutional and/or national guidelines for the care and use of animals were followed.
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