As part of the first ever comprehensive survey of the mammal community of the Apostle Islands archipelago, we documented changes in distribution of small mammals since the establishment of the Apostle Islands National Lakeshore in 1970.
Using recent data, we also described trends in abundance and multiple aspects of small mammal species ecology. We trapped small mammals from 20 of the 22 islands of the archipelago (2017-2020) and compared those results to historical (1961- 2004) records. Small mammal community diversity was driven by island size and less so by island isolation, regardless of variation over time.
Since the establishment of the Lakeshore, Microtus pennsylvanicus distribution declined significantly, while Sorex cinereus distribution increased significantly, and Peromsyscus spp. colonized at least three islands, potentially through human-facilitated dispersal (i.e., boating, kayaking). Myodes gapperi remained widespread and abundant, making them an ecologically important aspect of the archipelago’s mammal community.
Habitat, parasitism, predation, and Myodes gapperi abundance and body condition interact to shape the ecology of Myodes gapperi within the archipelago.
Canada yew, Taxus canadensis, appears to play an important role in shaping these ecological interactions. Long-term changes in small mammal populations across the archipelago likely reflect reduction of human extractive activities following the establishment of the national lakeshore and the corresponding succession of vegetative communities.
Our work suggests that the small mammal communities of the archipelago have changed since the establishment of the national lakeshore 50 years ago. Moreover, island size appears to be an important factor mitigating small mammal community dynamics over time, and Canada yew may be an important habitat feature for small mammal species of the Apostle Islands National Lakeshore.
Dr. Erik Olson, Northland College
Erik Olson is Associate Professor of Natural Resources at Northland College.
Erik received his MS and PhD from the University of Wisconsin – Madison and his BS from the University of Wisconsin – Stevens Point.
Currently, his research focuses on three projects: 1) Canopy Ecology of Temperate Forests – a project examining the habitat-use of the upper canopy, 2) JaguarOsa – a long-term wildlife monitoring project in two Costa Rican National Parks, and 3) Great Lakes Island Ecology – focusing on the ecology of the Apostle Islands National Lakeshore archipelago.