Integrating dynamic multispecies occupancy and structural equation models to understand coastal amphibian community responses to extreme weather event
One of the primary ways in which climate change will impact coastal freshwater wetlands is through changes in the frequency, intensity, timing, and distribution of extreme weather events. Disentangling the direct and indirect mechanisms of population- and community-level responses to extreme events is vital to predicting how species composition of coastal wetlands will change under future conditions.
Disturbance regimes influence the structure and diversity of natural communities. Extreme weather events such as cyclonic storms and heavy rainfall events are perhaps one of the most ecologically important disturbance forces in coastal ecosystems. Multiple axes of disturbance will therefore be changing simultaneously, making resultant patterns in coastal species diversity difficult to predict.
Here, we extended static structural equation modeling approaches to incorporate system dynamics in a multi-year multi-species occupancy model to quantify the effects of extreme weather events on a coastal freshwater wetland system. We use data from an 8-year study (2009 to 2016) conducted at St. Marks National Wildlife Refuge (hereafter referred to as St. Marks) in Florida, USA, to quantify species-specific and community-level changes in amphibian and fish occupancy associated with two flooding events, one in 2012 and a second in 2013. Tropical Storm Debby impacted the Florida panhandle in June 2012, completely flooding wetlands throughout St. Marks. This led to noticeable changes in wetland hydroperiod and the colonization frequency of fishes to previously fishless wetlands. An additional flood associated with heavy rainfall in 2013 maintained high colonization and persistence of fishes across the refuge. These changes provide a unique opportunity to examine the effects of climate and species interactions on wetland community dynamics. Specifically, we examine how physical changes to the landscape, including potential changes in wetland conductivity (a proxy for wetland salinity) and increased connectivity, may have contributed to or exacerbated the effects of these extreme weather events on the biota of coastal wetlands. In doing so, we develop a novel, flexible framework for predicting species-specific and community-level responses to variable environments and a changing climate. |
We provide evidence that the primary effects of flooding on the amphibian community were through indirect mechanisms via changes in the composition of the sympatric fish community that may have had lethal (i.e., through direct predation) or non-lethal (i.e., through direct or indirect competitive interactions) effects. In addition, we shown that amphibian species differed in their sensitivity to direct flooding effects and indirect changes in the fish community and wetland specific conductance, which led to variable responses across the community. These effects led to the overall decline in amphibian species richness from 2009 to 2016, suggesting that wetland-breeding amphibian communities on St. Marks National Wildlife Refuge may not be resilient to predicted changes in coastal disturbance regimes because of climate change.
Understanding both direct and indirect effects, as well as species interactions, is important for predicting the effects of a changing climate on individual species, communities, and ecosystems
Understanding both direct and indirect effects, as well as species interactions, is important for predicting the effects of a changing climate on individual species, communities, and ecosystems
Check out our 2023 paper in the Journal of Animal Ecology for more information!