No abstract

No abstract

Shrub encroachment is altering the structure and species composition of natural communities across the globe. However, little research has focused on how shrub encroachment influences wetland vertebrates, including small mammals. We sought to determine how vegetative structure and shrub cover influenced the occurrence of a threatened semiaquatic mammalian subspecies, the Sanibel Island rice rat (Oryzomys palustris sanibeli). We evaluated the influence of vegetation and metrics of inundation on probability of occurrence and localized seasonal colonization and extinction rates of the Sanibel Island rice rat over a 3-year period. We found Sanibel Island rice rats on 18 (33.3%) of our 54 sites. Their occurrence was positively associated with greater sand cordgrass (Spartina bakeri) cover and increased elevation, but negatively associated with greater shrub cover. Their probability of localized colonization was negatively associated with greater shrub cover. Localized extinction probabilities for Sanibel Island rice rats were positively associated with increased rainfall totals in the preceding 3 months and greater shrub cover. Using aerial photography from across the Sanibel Island rice rat’s range, we found 5.5-fold greater shrub cover in 2015 than in 1944. We suggest that increases in shrub cover and reduced cordgrass cover may be driving the decline of this once ubiquitous endemic species and that the encroachment of freshwater wetlands requires greater attention due to its potential to imperil wetland-dependent wildlife.

Shrub encroachment is altering the structure and species composition of freshwater wetlands across the globe. These changes are likely to be particularly detrimental for threatened wetland vertebrates. However, little research has focused on how shrub encroachment influences threatened wetland vertebrates. We sought to determine how vegetative structure and shrub cover influenced the occurrence of a threatened semi-aquatic mammal species, the Sanibel Island rice rat (Oryzomys palustris sanibeli). Using aerial photography from across the Sanibel Island rice rat’s range, we found a 5.5-fold increase in shrub cover over a 71-year period. To link these changes to the current distribution of the species, we evaluated the influence of vegetation and metrics of inundation on probability of occurrence and localized colonization and extinction rates over a three-year period. We found Sanibel Island rice rats on 18 (33.3%) of our 54 sites. Their occurrence was positively associated with elevated sand cordgrass (Spartina bakeri) cover and increased elevation, but negatively associated with elevated shrub cover. Their probability of colonization was negatively associated with increased shrub cover. Extinction probabilities for Sanibel Island rice rats were positively associated with increased rainfall totals in the preceding three months and increased shrub cover. Increases in shrub cover reduce sand cordgrass cover, which additively may be driving the decline of this once ubiquitous species. We conclude that shrub encroachment of freshwater wetlands requires greater attention due to its potential to imperil wetland endemic wildlife species.