Utility of Measuring Abundance versus Consistent Occupancy in Predicting Biodiversity Persistence
Christopher P. Grouios and Lisa L. Manne
Point-count survey data can be used to design protected area networks that contain more persistent populations than presence-absence survey data for a large group of east coast North American birds, as reported in an article by Toronto Chapter President Christopher Grouios and his MSc supervisor Dr. Lisa Manne in the October 2009 edition of Conservation Biology.
The primary goals of reserve selection are to represent all chosen units of biodiversity and to ensure their long-term persistence while minimizing costs. We considered two simple proxies of species persistence: a time series of point-count data to calculate abundance and a time series of presence–absence data to calculate permanence (a measure of consistent occupancy over time). Using two 10-year intervals of data from the North American Breeding Bird Survey, we compared the performance of each measure at predicting persistence 18 years later. For non-rare species, abundance and permanence predicted persistence similarly well. We performed complementarity-based reserve selections with data on species abundance and permanence (from 1970 to 1979) and then evaluated the effectiveness of the reserve networks at maintaining species populations and efficiency in land use (data from 1997 to 2006). Abundance proved a better predictor of future local persistence than permanence, which justifies the relatively larger financial and temporal costs of collecting a time series of point-count data to estimate abundance. If future extinction events were used as a measure of reserve-network effectiveness, the performance of abundance and permanence did not differ markedly. Nevertheless, when future abundance, which is a more sensitive measure of network effectiveness, was used, abundance was significantly better than permanence at selecting longer-term, high-quality, species-specific habitat but required larger reserves to do so.
Multispecies crayfish declines in lakes: implications for species distributions and richness
Brie A. Edwards*, Donald A. Jackson, and Keith M. Somers
A recent study led by Toronto Chapter Vice-President Brie Edwards found that freshwater crayfish, an important member of freshwater ecosystems, have experienced significant declines across the province of Ontario. These declines were observed for all species in the region, both native and non-native. The authors hypothesized that these declines are indicative of environmental and anthropogenic changes having a negative effect on freshwater lakes. Some of these drivers might include increases in human development, the introduction of non-native fish predators, and chemical changes due to industrial pollution and historical acidification. Work is continuing to further elucidate the causes of crayfish decline, and the effects that this decline and other changes in lakes might have on these valued ecosystems.
Aquatic communities are highly threatened by anthropogenic and climate change. However, despite their importance in these communities, information regarding temporal changes in populations and assemblages of North American crayfish is scarce. Long-term monitoring of crayfish populations in south-central Ontario, Canada, indicates that the populations are in a significant state of decline. We sought to determine whether these population declines are spatially and taxonomically broad, and if so, what factors might be associated with the declines. We sampled crayfish abundance (catch per unit effort) in 100 lakes, and compared current abundances to survey results from the early 1990s. Abundances of all species (natives and nonnatives) declined significantly during this interval. Declines were both severe (63–96% loss of abundance) and geographically widespread for all species. Previous studies have documented native species declines caused by the invasive crayfish Orconectes rusticus, but this species was absent from almost all lakes and was not a factor in the declines. We hypothesize that the introduction of predatory smallmouth bass (Micropterus dolomieui), increases in Al concentrations, and reduced Ca concentrations in these lakes are negatively affecting crayfish populations.
Edwards, B.A., Jackson, D.A., and K.M. Somers. 2009. Multispecies crayfish declines in lakes: implications for species distributions and richness. Journal of the North American Benthological Society 28(3): 709-718