Coping with Invasive Alien Species and Environmental Stressors: Linking Behavioral Studies with Management for Anuran Amphibians

Science Center Objects

Climate change and invasive species are two key drivers of biodiversity loss. Knowing how amphibians respond to climate change and invasive species can greatly improve predictions of species' persistence in the face of these factors and can help guide resource managers and conservation biologists in developing strategies to manage for these encroaching disturbances. 

PROJECT COMPLETED

Coping with Invasive Alien Species and Environmental Stressors: Linking Behavioral Studies with Management for Anuran Amphibians
Climate change and invasive species are currently two key drivers for biodiversity loss. 

The Science Issue and Relevance: Climate change and invasive species are two key drivers of current biodiversity loss. Knowledge of how amphibians respond to climate change and invasive species can greatly improve predictions of species’ persistence in the face of these factors and can help guide resource managers and conservation biologists in developing strategies to manage for these encroaching perturbations. Along the Gulf of Mexico and the south Atlantic regions of the United States, factors associated with climate change (i.e., sea level rise and altered patterns of hurricane activity) are already affecting coastal freshwater wetlands that are important habitats for many species of amphibians. Additionally, isolated coastal wetlands are periodically exposed to saline waters as a result of storm surges during hurricane events, such as those associated with four hurricanes that hit the Gulf Coast in 2004 and 2005.

Climate change may also facilitate the persistence and spread of non-indigenous species which, in turn, could have profound consequences for the structure and stability of natural ecosystems. As alien predators, various introduced species are known to be contributing to amphibian population declines around the world. The range of the non-native Cuban treefrog (Osteopilus septentrionalis) is rapidly expanding throughout Florida where it occurs syntopically with several native anuran amphibians. Under natural conditions, the presence of Cuban treefrogs negatively affects site occupancy of coexisting green and squirrel treefrogs (Hyla cinerea and H. squirella, respectively). Cuban treefrogs are known to prey upon adults of native species; because of their smaller maximum adult size, squirrel treefrogs are assumed to be more vulnerable to predation than are green treefrogs.

Coping with Invasive Alien Species and Environmental Stressors: Linking Behavioral Studies with Management for Anuran Amphibians
Research looks at salinity tolerances of various species of tadpoles, and potential predatory and competitive interactions among adult species. 

Methodology for Addressing the Issue: We are conducting a series of laboratory experiments to determine the salinity tolerances of various species of native and non-native anuran tadpoles, and to observe potential predatory and competitive interactions among adult O. septentrionalis, H. cinerea and H. squirella. Thus far, we have conducted replicated acute salinity trials using 6 different salinity concentrations with the larvae of 7 species of anuran amphibians. We also are beginning a series of behavioral trials to observe whether Cuban Treefrogs preferentially prey (non-lethally) on either species of native amphibian and, if so, whether selection for smaller-sized species (squirrel treefrog) versus differential behavior of the two native species, is the mechanism by which Cuban Treefrogs are disproportionately impacting one species over the other. Other behavioral trials will be conducted to determine whether Cuban Treefrogs are competitively superior (as foragers) to native species and, if so whether the impact of this invasive species on native ones that is observed in nature could be a consequence of competitive exclusion. Understanding the mechanisms by which amphibians cope with environmental stressors associated with climate change, along with invading, alien species, is germane to ARMI’s goal of elucidating the factors contributing to amphibian declines.

Future Steps: Our next steps in this research will be to conduct chronic (long-term) salinity trials with the same species tested in acute trials. We will also test animals in a “common garden” experiment (both acute and chronic trials) from coastal populations, where populations may have “adapted” to pulses of  increased salinity during hurricane overwash events, versus inland populations that presumably have had no exposure to saline conditions. Similarly, we will test for possible adaptive responses to the risk of competition and predation by conducting behavioral experiments with animals originating from south Florida, where these species have coexisted since at least 1951, as well as from north central Florida, where Osteopilus was first recorded as recently as 2002.