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How do individual foraging decisions impact populations and communities?
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Foraging and resource use directly regulate populations and communities through fitness consequences and competitive interactions. Further, foraging drives animal movements and habitat use, and is the primary mechanism by which animals influence ecosystems (e.g., herbivory, predation, pollination, seed dispersal). Foraging dynamics also respond strongly to human disturbances, with direct consequences for all levels of biological organization. Understanding foraging ecology is therefore critical to contemporary science, policy, and management needs, particularly in human-modified landscapes.
In collaboration with the Newsome Lab and the Sevilleta LTER, I am using long-term biological sampling and mark-recapture data to quantify the impact of individual foraging decisions on population and community dynamics in a desert rodent community. The Sevilleta is a rapidly changing arid ecosystem, and our research uses stable isotope analyses, quantitative magnetic resonance imaging (qMRI), and mark-recapture models to assess the relationship between foraging, physiology, and demography.
Fig 1. Left: Annual variation in foraging strategies by Heteromyid rodents (lines connect individuals). Right: Relationship between foraging strategy and apparent survival from mark-recapture models (CJS). RINI represents a gradient of foraging strategies ranging from complete specialization (0) to complete generalization (1).
We used long term stable isotope measurements to calculate a relative specialization index (RINI; 0 = specialist, 1 = generalist; Fig. 1) and found widespread variation in foraging strategies across individuals, populations, and within the community (Manlick et al. 2021). This variation was ultimately driven by a combination of competition (i.e., conspecific and heterospecific density) and resource availability (plant abundance), such that individuals specialize in the face of increased competition. However, this dietary flexibility did not provide increased fitness, as survival decreased significantly with dietary specialization.
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Ongoing Research: This research has expanded to develop a framework for consumer-resource dynamics that combines isotopes, DNA metabarcoding of feces, and plant chemistry with mechanistic foraging models to quantify the observed and theoretical resource niches of consumers in this rapidly changing arid ecosystem. Ultimately, this research seeks to uncover the causes and consequences of foraging plasticity by quantifying interactions between resource quality (e.g., % N, metabolite concentrations), resource quantity (e.g., NPP, phenology), and resource selection (e.g., value vs. predation risk) in this highly stochastic ecosystem.
Support for this work is provided by:
