Intraguild Interactions and Island Biogeography Drivers of Carnivore Spatiotemporal Distributions in a Temperate Archipelago

Spatiotemporal distributions of carnivores can be affected by ecological contexts and life histories, and teasing apart the drivers of carnivore distributions is essential to effective and efficient carnivore management and conservation. Our objectives were to determine how intraguild interactions and island biogeography structure mammalian carnivore communities within the Apostle Islands National Lakeshore, an archipelago of islands in Lake Superior, Wisconsin. Over five years, we monitored 19 of 21 islands in the archipelago using 160 camera traps placed on the islands using a systematic random design based on a 1 km2 grid. Camera traps captured over 300,000 photographs and detected all but two of the terrestrial mammalian carnivores extant in Wisconsin. To determine how intraguild interactions are driving species spatiotemporal distributions, we used the Optimized Hotspot Analysis tool in ArcMap to identify statistically significant spatial “hotspots” of activity of species within the Mustelid (American marten (Martes americana) and fisher (Martes pennant)) and Canid (coyote (Canis latrans), red fox (Vulpes vulpes), and grey fox (Urocyon cinereoargeneus)) guilds. We then compared the resulting Z-values within the Mustelid guild and the Canid guild, which resulted in a spatial overlap value for each pair of species. To determine how island biogeography is driving species distributions, we tested a set of a-priori hypotheses using generalized linear models with species relative abundance on a given island as the dependent variable, and the possible independent variables included: island size, island distance from mainland, minimum interisland distance, maximum elevation, and island isolation. Overall, both the Mustelids and the Canids showed high temporal overlap suggesting potential for intra-guild agonistic interactions or interference competition. Our results suggest that mammal diversity on the islands is a dynamic interplay of biogeographic and life-history effects. Hence, managers should monitor island communities to determine their usefulness as local reservoirs of animal diversity.