Testing the link between species interactions and co-occurrence in a trophic network

30 June 2019

Thurman, Lindsey; Barner, Allison ; Garcia, Tiffany; Chestnut, Tara

Species interactions are dynamic processes that vary across environmental and ecological contexts, and operate across scale boundaries, making them difficult to quantify. Nevertheless, ecologists are increasingly interested in inferring species interactions from observational data using statistical analyses of their spatial co-occurrence patterns. Trophic interactions present a particular challenge, as predators and prey may frequently or rarely co-occur, depending on the spatial or temporal scale of observation. In this study, we investigate the accuracy of inferred interactions among species that both compete and trophically interact. We utilized a long-term dataset of pond-breeding amphibian co-occurrences from Mt. Rainier National Park (Washington, USA) and compiled a new dataset of their empirical interactions from the literature. We compared the accuracy of four statistical methods in inferring these known species interactions from spatial associations. We then used the best performing statistical method, the Markov network, to further investigate the sensitivity of interaction inference to spatial scale-dependence and the presence of predators. We show that co-occurrence methods are generally inaccurate when estimating trophic interactions. Further the strength and sign of inferred interactions were dependent upon the spatial scale of observation and predator presence influenced the detectability of competitive interactions among prey species. However, co-occurrence analysis revealed new patterns of spatial association among pairs of species with known interactions. Overall, our study highlights a limiting frontier in co-occurrence theory and the disconnect between widely implemented methodologies and their ability to accurately infer interactions in trophically-structured communities.