One Century Later: Species Richness and Temporal Turnover in Mammals and Amphibians on a Small, Temperate Island

Islands can be proxies for understanding species-occupancy dynamics—like rates of immigration, extirpation, and persistence—in a world of increasingly isolated habitat patches. These dynamics have been investigated extensively at short and long timescales (e.g., a few versus tens of thousands of years), but intermediate periods are less frequently considered. Here, we report a resurvey of the amphibians and mammals of Charity Island, in Saginaw Bay of Lake Huron, ∼100 years after the island was first surveyed in 1910. We conducted surveys via visual and auditory monitoring, as well as targeted trapping. We found 7 species not previously documented on the island, although it is likely that only Tamias striatus (Eastern Chipmunk), Lithobates catesbeianus (= Rana catesbeiana) (American Bullfrog), and Hyla versicolor (Gray Treefrog) are genuinely new arrivals. In contrast, the previously detected Lepus americanus (Snowshoe Hare), Sylvilagus floridanus (Eastern Cottontail), Anaxyrus americanus (Eastern American Toad), and Lithobates (= Rana) palustris (Pickerel Frog) were not detected in our surveys. These findings indicate that modest but detectable species turnover occurs on isolated, high-latitude islands, even among otherwise common species.