| Summary: | Ecological theory posits that the strength of interspecific interactions is fundamentally underpinned by the population sizes of the involved species. Nonetheless, contemporary approaches for modelling species interactions predominantly centre around occupancy states. Here, we use simulations to illuminate the inadequacies of modelling species interactions solely as a function of occupancy, as is common practice in ecology. We demonstrate erroneous inference into species interactions due to bias in parameter estimates when considering species occupancy alone. To address this critical issue, we propose, develop, and demonstrate an occupancy-abundance model designed explicitly for modelling abundance-mediated species interactions involving two or more species. When modelling interactions as a function of abundance rather than occupancy, we uncover previously unidentified interactions. Through an empirical case study and comprehensive simulations, we demonstrate the importance of accounting for abundance when modelling species interactions, and we present a statistical framework equipped with MCMC samplers to achieve this paradigm shift in ecological research. Funding provided by: New York State Department of Environmental Conservation Award Number: W-173-G In the case study using empirical data, we examine the intraguild interactions between three carnivores, a top mesopredator in the system, the coyote, an intermediate mesopredator, the fisher , and a small carnivore, the American marten . There is a long history of examining intraguild interactions between fisher and marten through harvest (e.g., Hardy, 1907; Krohn, Zielinski, & Boone, 1997). Recent harvest-based evidence was used to infer negative interactions between all three species, with fishers being limited through intraguild killing by coyotes, and martens being limited by both fisher and coyotes (Jensen & Humphries, 2019). Nonetheless, the three species co-occur over much of the marten's limited range in New York State and recent analysis ...
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