Collaborative Research: Experimental manipulation of a macroecological pattern: dispersal, resource generalism, and vital rates as drivers of abundance-occupancy relationships

Have you ever wondered why some species of animals like raccoons, American robins, and largemouth bass seem to be common just about everywhere, while others, such as black-footed ferrets, California condors, and bull trout are rare and don’t occur in many places? For many decades, ecologists have been trying to understand why these “abundance-occupancy relationships” seems to occur with just about every group of organisms we study, every place we study them. Two particularly important ideas deal with species differences in movement and food consumption. Regarding movement, the Core-Satellite hypothesis predicts that common animals within big geographic ranges move more frequently, and over longer distances, than their rare, more restricted counterparts. Regarding food consumption, the Resource Breadth hypothesis predicts that common, widespread species can thrive on a wide variety of foods, whereas rare, restricted species are picky eaters that require a narrow range of foods to survive and reproduce. Although previous investigations have been valuable, they often test one of these hypotheses (but not both), they typically are conducted across vast areas that make experiments impossible, and they frequently use many approaches that aren’t comparable among studies. In a group of small mammal species within a broader large-mammal exclusion experiment, this project will entail two manipulations—fencing to restrict movements, and removal of preferred foods (tree seeds)—to assess the conditions under which movement, food choice, or both drive abundance-occupancy relationships. This “apples-to-apples” approach will result in major progress in our understanding of why species tend to be either common and widespread, or rare and restricted. Workshops centered on big data (large volumes of camera trap images, diets reconstructed through DNA metabarcoding) processing, classification of camera trap images (for large mammals in the aforementioned broader experiment) using AI versus traditional methods, and computer programming will be conducted for professional development of early- and mid-career scientists. Along with student and postdoctoral training, this project will therefore contribute to STEM and biotechnology workforce development. This project will provide a standardized comparison of three particularly influential ideas in macroecology—the Core-Satellite hypothesis, the Resource Breadth hypothesis, and the Vital Rates hypothesis—in driving interspecific abundance-occupancy relationships. The Core-Satellite hypothesis states that dispersal is necessary to maintain rare, restricted in locales, and it predicts that the erection of dispersal barriers (i.e., hardware cloth fences) should result in population declines of rare, restricted species while common, widespread species persist (because they enjoy relatively high survival and fitness). The Resource Breadth hypothesis states that, following the removal of preferred resources (i.e., Acacia spp seeds), populations of rare, restricted species should decline while individuals of common, widespread species simply switch diets. Finally, the Vital Rates hypothesis states that common, widespread species should exhibit higher survival and reproduction irrespective of interspecific differences in dispersal and resource breadth. By focusing on how each manipulation (dispersal barriers, resource removal) by itself or interactively shapes population growth within abundance-occupancy relationships, this project has strong potential to shed light on one of the most puzzling patterns in ecology, first identified over 150 years ago. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.