Increase in spatial overlap of ecologically similar rain forest mammals is associated with higher human density

Daniel Gorczynski and Lydia Beaudrot, Department of BioSciences, Rice University, Houston, TX, Chia Hsieh, Program in Ecology and Evolutionary Biology, Rice University, Houston, TX, Jorge Ahumada, TEAM Network, Moore Center for Science, Conservation International, Emmanuel Akampurira, Institute of Tropical Forest Conservation, Mbarara University of Science and Technology, Kabale, Uganda, Emmanuel Akampurira, Department of Conflict and Development Studies, Ghent University, Belgium, Patricia Alvarez-Loayza, Center for Tropical Conservation, Duke University, Durham, NC, Mahandry Hugues Andrianarisoa, Centre ValBio, Ranomafana National Park, Ranomafana, Madagascar, Kelly Boekee, Center for Tropical Forest Science, Smithsonian Tropical Research Institute, Balboa, Panama, Ahimsa Campos-Arceiz, School of Geography, University of Nottingham Malaysia Campus, Mengla, Malaysia, Santiago Espinosa, Escuela de Ciencias Biológicas, Pontificia Universidad Católica del Ecuador, Quito, Ecuador, Krisna Gajapersad, Conservation International Suriname, Paramaribo, Suriname, Johanna Hurtado Astaiza, La Selva Biological Station, Organization for Tropical Studies, Puerto Viejo de Sarapiqui, Costa Rica, Patrick A. Jansen, Smithsonian Tropical Research Institute, Balboa, Panama, Steig E. Johnson, Department of Anthropology and Archaelogy, University of Calgary, Calgary, Canada, Charles Kayijamahe, International Gorilla Conservation Programme, Kigali, Rwanda, Marcela Lima, Universidade Federal do Pará, Badru Mugerwa, Leibniz Institute for Zoo and Wildlife Research, Tim O'Brien, Global Conservation Programs, Wildlife Conservation Society, New York, NY, Francesco Rovero, Tropical Biodiversity Section, MUSE-Museo delle Scienze, Trento, Italy, Julia Salvador, Wildlife Conservation Society, Fernanda Santos, Department of Mastozoology, Museu Paraense Emílio Goeldi, Belém, Brazil, Douglas Sheil, Forest Ecology and Forest Management Group, Wageningen University & Research, Wageningen, Netherlands, Wilson R. Spironello, Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil

Background/Question/Methods
Species distributions are shaped in part by biotic interactions with other species, which can affect the extent to which pairs of species occupy the same areas and therefore co-occur. Novel anthropogenic influences may also affect species co-occurrence patterns and thereby alter ecological dynamics. Species with similar functional traits often require similar resources, which can lead to aggregation in locations where resources are available. However, competition for similar resources can lead to the exclusion of one species by another and may result in spatial segregation. The distribution and quantity of resource availability is often associated with environmental characteristics of the system, like primary productivity and habitat heterogeneity, but can also be altered by anthropogenic disturbance. Therefore, differences in anthropogenic disturbance, primary productivity and habitat heterogeneity may influence patterns of segregation and aggregation among mammals through their functional traits. Using a Bayesian framework, we investigated the co-occurrence strength of 1,242 mammal species pairs from 14 tropical forest protected areas as a function of species functional traits (e.g. body size, diet, activity period etc.) and park-level measurements of primary productivity, habitat heterogeneity and human density, while controlling for functional diversity.
Results/Conclusions
We found that functionally similar species were more likely to co-occur in parks with high human densities than in parks with low human density. This effect was stronger than the effects of primary productivity and habitat heterogeneity, which were associated with lower species co-occurrence overall and for functionally similar species. Our results indicate that anthropogenic presence may increase the strength of co-occurrence for functionally similar mammal species in protected tropical forests. We suggest further investigation of resource distributions and competition among mammals in tropical forests under anthropogenic disturbance to clarify the ecological processes underlying these patterns.