Amphibians are important components of aquatic and terrestrial habitats and can represent an important energetic link between the two, particularly in the tropics where diversity and abundance are greatest. However, amphibian populations are declining dramatically around the world, with catastrophic losses occurring even in remote, undisturbed regions of the tropics. Declines often result in the disappearance of over 75% of amphibians at a site, particularly species that breed in streams, and massive losses are reported from 13 Latin American countries in the last 20 years. This research will assess the ecological consequences of amphibian declines by investigating how these losses affect stream structure and function, including biodiversity, productivity, nutrient cycling, and energy and nutrient exchanges between streams and forests. This will be accomplished through intensive examinations of streams located along a moving disease front in Panama before and after disease-driven declines occur.
This research addresses an urgent, global problem and will provide information critical for understanding the ecological consequences of extinction and the loss of biodiversity, one of the eight ?grand challenges? and four focal areas of research in the environmental sciences recommended by the National Research Council. Understanding the potential large-scale and far-reaching consequences of catastrophic reductions in biodiversity and extinction events such as these will allow for more accurate predicting of ecological function in light of declining global biodiversity.
This collaborative research project focused on the ecological consequences of the loss of an entire species assemblage, showing that extinction is a much larger issue than species loss, with cascading ecosystem-level consequences. Quantifying and predicting the ecological consequences of declining biodiversity is an urgent challenge, particularly in freshwater ecosystems where species declines and losses are among the highest. We quantified ecological effects of the loss of a stream-dwelling frog assemblage from a fungal (Batrachochytrium dendrobatidis) disease in highland streams of Panama. Prior to their decline, larval frogs (tadpoles) were the most abundant and diverse group of stream vertebrates in many highland streams of Central America: our study streams in Panama contained 20 stream-dwelling species and densities often greater than 50 individuals m-2. Our research findings establish the key role that larval frogs played in stream ecosystem function before they were extirpated. Larval tadpoles controlled the amount of basal resources in the stream food web, significantly decreasing algal standing crop and accrual rates and enhancing rates of leaf decomposition. Following their extirpation, the biomass of algal primary producers increased by over two fold, with greater than 50% reduction in rates of nitrogen uptake. Post-extirpation studies (over 3 years) showed that changes in rates of ecosystem processes (resulting from loss of the frog assemblage) were not compensated for by other functionally redundant consumer organisms (e.g., aquatic insects). Our findings do not support the assumption that tropical ecosystems with high biodiversity are more resilient to extinction events because of the greater potential for ecological redundancy. Instead, we found that ecosystem-level consequences of declining biodiversity were not offset by ecological redundancy, at least in the short-term (over 3 years). By quantifying ecosystem-level consequences of the loss of biodiversity at relevant spatial and temporal scales, we have addressed one of the "grand challenges" and focal areas of ecological research designated by the National Academy of Sciences’ National Research Council. Moreover, our project has resulted in a unique long-term data set (2000-present) on ecosystem structure and function before and after an extinction event. Virtually no long-term data sets of this kind exist, given the paucity of pre-extinction data on ecosystem structure and function. Consequently, our data set provides an invaluable foundation for future quantification of long-term effects of species loss on ecosystems.
