Natural environments throughout the world are experiencing increasing levels of unnatural noise. Many animals rely on sound to communicate. Unnatural noise can interfere with communication and therefore lead to reduced survival and reproduction. Studies of ecological impacts of increased noise on animals typically focus on noise from human activities, such as from transportation. Non-native animals may also be a source of noise as some invasive species produce loud sounds to attract mates and defend territories. These sounds may occur at certain sound frequencies or times, making it difficult for native animals to communicate. As a result, native and non-native animals may compete for the ability to send and receive signals, just as they compete for food and shelter, but this is poorly understood. The proposed research will use the invasion of Cuban treefrogs in Florida to understand how noisy invaders can impact native frog communication. By characterizing the calls of native frogs from invaded and uninvaded locations, and their responses to broadcasted Cuban treefrog sounds, this research will test whether noise produced by invasive species impacts the calling behavior of native frogs in the short- and long-term. This project will enhance our understanding of the ecological impact of unnatural noise, and identify the importance of acoustic competition for structuring animal communities.
Invasive species are one of the leading causes of global biodiversity loss and cost billions of dollars each year in the United States alone. Cuban treefrogs destroy electrical equipment, invade homes, and cause skin irritations in humans. They are also likely to affect native frogs by competing with them for available resources. Native frogs play an important role in the ecosystem, eat pest insects that damage crops, and are used by humans for food, bait, and pets. Identifying the impact of Cuban treefrogs on native frogs will help prioritize management efforts to protect these important animals. The findings of this research will be shared with Florida residents, and school-aged children in central Pennsylvania, through presentations and interactive displays. Additionally, Penn State University undergraduate students from groups poorly represented in science will be involved in the research and outreach components of the proposed work.
Summary Ecosystems throughout the world are experiencing increasing levels of sound from novel sources, but the population- and community-level consequences of this are poorly understood. These sounds may interfere with critical organismal interactions, as the ability to send and receive acoustic signals is necessary for survival, and species may compete acoustically for their signals to be heard. This research examined the effects of two novel forms of sounds on the ecology of native species: noise from road traffic, and breeding calls from an acoustically communicating invasive species. Using acoustic monitoring and playback experiments, we explored the impacts of these novel sounds on native frog behavior and physiology. Specifically, we asked (1) how does loss of acoustic space due to novel noise affect calling behavior of native frogs, and (2) can populations adapt to the impacts of novel sounds over relatively short time-scales? We played sounds of invasive Cuban treefrogs (Osteopilus septentrionalis) to native green (Hyla cinerea) and pine woods treefrogs (Hyla femoralis) to determine the impact of acoustic interference by Cuban treefrog calls on native frog calling behavior. We found that native species with similar acoustic behavior to that of the invasive Cuban treefrogs modified their calls: green treefrogs called at a faster rate during Cuban treefrog playback, presumably to avoid acoustic competition. In contrast, native species (pine woods treefrogs) with very different calls to Cuban treefrogs did not alter their calling behavior when exposed to this novel noise. Additionally, we examined whether native populations can adapt to the pressures imposed by novel sounds. We played traffic noise to lab-reared native wood frogs (Lithobates sylvaticus) from quiet and highway-adjacent (noisy) ponds, and found that frogs from noisy ponds were less physiologically stressed by traffic noise. We also found evidence that prolonged noise exposure altered the presence of antimicrobial peptides produced in the granular glands of frogs from quiet sites, the first line of defense against infection. These results provide important insight into potential ecological consequences of increasing environmental noise for native populations and communities. Scientific Merit The role of competition in shaping ecological community structure remains a fundamental question in ecology. Despite increasing ambient sound throughout the world, we have a poor understanding of the how competition for acoustic space affects populations and communities – particularly of species that rely on sound to survive. Invasive species that produce acoustic breeding calls provide an excellent opportunity to explore how acoustic competition structures species assemblages. Additionally, the fitness consequences of prolonged exposure to novel noise, and whether populations can adapt to these novel sounds, is poorly understood. This project advances theoretical discussions of the role of competition in structuring communities, and provides insight into the impacts and adaptive responses of native taxa to changes in their acoustic environment. Broader Impacts The results of this research identify additional pathways through which invasive species may alter native populations and communities, and enhance our understanding of the long-term ecological impact of rapidly increasing ambient sound. Our results suggest potential effects of noisy invasive species on native communities, and that native populations can adapt over ecological time scales to reduce fitness consequences of living in high noise environments. This sheds important light on the long-term impacts of this pervasive anthropogenic impact. This project provided training of minority undergraduate researchers who were involved in the collection of these data, mentored by the graduate student on this project. The graduate student, undergraduate researchers, and PI involved high school minority students from inner-city communities in this research, through the Upward Bound Math and Science program. The high school students were engaged in all aspects of the scientific process, including experimental design, data collection, data analysis and presentation/dissemination of results to the public. The graduate student on this project used themes from this research to lead Science Nights for elementary through high school students from a low-income transitional housing community, and the PI ran workshops introducing pre-K children to amphibians and their responses to global environmental change.
