|Date||27 Jan 2020|
Across taxa worldwide, ecological communities are dominated by one or a few species that tend to be common, with many more species that are rare. The Resource Breadth Hypothesis (Brown 1984, Brown et al 1995) proposes a mechanism for this general pattern. Widespread, abundant species are resource generalists, attaining a broad distribution and high abundances within because they are capable of thriving off a diversity of resources. On the other hand, rare, restricted species are resource specialists: they are rare within their narrow ranges because they require a small number of specific resources. For all of its intuitive appeal, the Resource Breadth Hypothesis has proven surprisingly difficult to test. This may be because the positive correlation between species abundance and species distribution—known as an “abundance-occupancy relationship”—is often constructed with data across entire geographic ranges of species. However, the mechanism posited by the Resource Breadth Hypothesis (namely, resource specialization) requires tracking individual animals through time as they are confronted with shifting resource availability.
Specifically, I am testing two hypotheses: (1) abundant, widespread species are diet generalists (using a variety of available foods) while rare, restricted species are diet specialists (using a narrow subset of available foods) [Brown, 1984]; and (2) abundant, widespread species exhibit greater fitness (i.e. increased survival, increased reproduction or both) compared to rare, restricted species [Buckley & Freckleton, 2010]. I am identifying dietary generalists as individuals (within species) whose diet (i.e., food use) closely mirrors food availability, and I am identifying dietary specialists as individuals whose diet does not change markedly with food availability.
Therefore, testing these hypotheses requires determining the diets of abundant, widespread species and rare, restricted species in the face of shifting food availability. I will quantify food availability at my study sites through a combination of sampling understory vegetation, quantifying composition diet of the small mammals using DNA metabarcoding of fecal samples, and to comparing patterns of diet versus food availability for species that differ in their abundance and extent of their distributions.
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|Date||27 Jan 2020|
Leo Malingati tags a small rodent (a fringe tailed gerbil) with small Monel ear tags.
A tagged and sampled fringe tailed gerbil (Gerbiliscus robustus) ready for release. Gerbils have strong hind feet for jumping to escape predators and large eyes for quickly spotting predators. © Sarah Weiner