Impact of invasive Typha and wetland interspersion on muskrat declines in North America

Muskrat (Ondatra zibethicus) populations are declining in North America. The exact cause of these declines is largely unknown. Along a similar timeframe, wetlands have been experiencing an invasion of cattail (Typha) throughout the continent. Specifically, T. x glauca, a hybrid of native T. latifolia and non-native T. angustifolia, has been increasing in range and abundance. This hybrid is associated with many negative impacts on wetland ecosystems, including reductions in biodiversity, open water habitat, and interspersion of water and emergent vegetation, the latter of which is an important habitat feature for muskrats. We sought to determine the impact of invasive T. x glauca on muskrat populations. We sampled 39 Typha-dominated marshes in southern Ontario, Canada to test the hypotheses that muskrats are declining in North America due to: (1) the increased relative abundance of T. x glauca in marshes, and (2) reduced wetland interspersion, which is associated with T. x glauca invasions. We estimated muskrat population density using house counts, sampled Typha communities to determine the relative abundance of T. x glauca, and measured interspersion using remote sensing techniques. We found that muskrat population density was positively associated with interspersion, but not associated with the relative abundance of T. x glauca. However, most sites were highly dominated by T. x glauca, limiting our inference. Our findings suggest that changing wetland structure may be contributing to muskrat population declines in North America, but more research is needed to determine the full impact of T. x glauca invasions on muskrat population declines.