Abstract
Ecological theory predicts that if animals with very similar dietary requirements inhabit the same landscape, then they should avoid niche overlap by either exploiting food resources at different times or foraging at different spatial scales. Similarly, it is often assumed that animals that fall in different body mass modes and share the same body plan will use landscapes at different spatial scales. We developed a new methodological framework for understanding the scaling of foraging (i.e. the range and distribution of scales at which animals use their landscapes) by applying a combination of three well‐established methods to satellite telemetry data to quantify foraging patch size distributions: (1) first‐passage time analysis; (2) a movement‐based kernel density estimator; and (3) statistical comparison of resulting histograms and tests for multimodality. We demonstrate our approach using two sympatric, ecologically similar species of African ducks with quite different body masses: Egyptian Geese (actually a shelduck), and Red‐billed Teal. Contrary to theoretical predictions, the two species, which are sympatric throughout the year, foraged at almost identical spatial scales. Our results show how ecologists can use GPS tracking data to explicitly quantify and compare the scales of foraging by different organisms within an animal community. Our analysis demonstrates both a novel approach to foraging data analysis and the need for caution when making assumptions about the relationships among niche separation, diet, and foraging scale.
Highlights
One of the fundamental questions of community ecology is that of what drives variation in the numbers and kinds of species that occur in different ecosystems
While we have the beginnings of a “first-principles theory” with roots in body mass, body plan, and metabolic rate (Brown, 1984, 1995), these mechanisms have proved difficult to translate into predictions about broader-scale patterns in community composition (Ritchie & Olff, 1999)
We demonstrate our approach using a combination of dietary information and GPS satellite telemetry data from two African ducks: Red-billed Teal (Anas erythrorhyncha) and Egyptian Geese (Alopochen aegyptiaca)
Summary
One of the fundamental questions of community ecology is that of what drives variation in the numbers and kinds of species that occur in different ecosystems. Given the similarities in their diets and the differences in their body masses, was that we would find evidence for niche separation in the form of clear- cut differences in the scales at which these species forage across the landscape Note that in this analysis, we do not attempt to directly test the TDH or related explanations; we seek to develop and demonstrate the virtues of a method by which more exhaustive studies of animal communities, using a much larger range of species, could approach the problem
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