Summer Precipitation Predicts Spatial Distributions of Semiaquatic Mammals

Adam A. Ahlers,Mark A. Mitchell,Lisa A. Cotner,Edward J. Heske,Robert L. Schooley,Patrick J. Wolff,Gil Bohrer

doi:10.1371/journal.pone.0135036

Abstract

Climate change is predicted to increase the frequency of droughts and intensity of seasonal precipitation in many regions. Semiaquatic mammals should be vulnerable to this increased variability in precipitation, especially in human-modified landscapes where dispersal to suitable habitat or temporary refugia may be limited. Using six years of presence-absence data (2007–2012) spanning years of record-breaking drought and flood conditions, we evaluated regional occupancy dynamics of American mink (Neovison vison) and muskrats (Ondatra zibethicus) in a highly altered agroecosystem in Illinois, USA. We used noninvasive sign surveys and a multiseason occupancy modeling approach to estimate annual occupancy rates for both species and related these rates to summer precipitation. We also tracked radiomarked individuals to assess mortality risk for both species when moving in terrestrial areas. Annual model-averaged estimates of occupancy for mink and muskrat were correlated positively to summer precipitation. Mink and muskrats were widespread during a year (2008) with above-average precipitation. However, estimates of site occupancy declined substantially for mink (0.56) and especially muskrats (0.09) during the severe drought of 2012. Mink are generalist predators that probably use terrestrial habitat during droughts. However, mink had substantially greater risk of mortality away from streams. In comparison, muskrats are more restricted to aquatic habitats and likely suffered high mortality during the drought. Our patterns are striking, but a more mechanistic understanding is needed of how semiaquatic species in human-modified ecosystems will respond ecologically in situ to extreme weather events predicted by climate-change models.

Highlights

Many studies attempt to predict species’ responses to climate change [1] and most focus on changes in geographic distributions [1,2,3] and potential in situ evolutionary adaptation [4,5]
Annual occupancy of stream segments by mink and muskrats was strongly related to summer precipitation
Occupancy rates for both species were higher during years with above-average precipitation than years with below-average precipitation (Fig 2)

Summary

Introduction

Many studies attempt to predict species’ responses to climate change [1] and most focus on changes in geographic distributions [1,2,3] and potential in situ evolutionary adaptation [4,5]. Many animal species will need to make ecological adjustments within geographic range interiors, such as altering habitat selection, to deal with increased environmental stochasticity. These responses should have consequences for species persistence and may be affected by human alterations of the landscape. Species obligately associated with wetland and stream habitats are at risk due to extreme fluctuations in water levels As these climate-sensitive habitats become less stable, species dispersal [8], recruitment [9], and survival [9,10,11,12] could be compromised. Semiaquatic species might need to move to other suitable habitat patches to persist during times of environmental stress, but moving across terrestrial areas can be costly [13,14], especially in regions where agriculture and urbanization have destroyed linkages and reduced connectivity

Methods

Results

Conclusion