Dalea foliosa (A. Gray) Barneby (Fabaceae, leafy prairie clover) is a federally endangered, short-lived herbaceous perennial endemic to cedar glades of central Tennessee and northern Alabama and has five disjunct populations at the northern edge of its range in Illinois. The objectives of this research were to use annual census data to project population viability and to determine what weather variables explain variation in population size. In addition, comparisons of projected population size under different emission scenarios were investigated. Annual census data from 1997-2008 for the population at the Midewin National Tallgrass Prairie in Will County Illinois, USA, consisted of counts of seedlings, nonflowering adults and flowering adults. Count-based population viability analysis (PVA) was used to determine the probability of extinction (Pe) at 50 and 80 years. Weather data from the nearest station to the population were used in a linear regression analysis to determine which weather variables best explained variation in count data and population growth (l). Projected temperature and precipitation from 16 climate change models under three emission scenarios were used to project what population size would be at the weather conditions projected for the Midewin population at 50 and 80 year time points.
Results/Conclusions
Count-based PVA indicated a Pe of 0.2% at both 50 and 80 years. Most variation in population size was explained by snowfall (R2 = 0.786, p <0.001, b = 13.15). Other important variables included precipitation in September and high temperature in February. Population growth rate (λ) was best explained by number of days below 32 F in Fall (R2 = 0.511, p = 0.013) and mean temperature in November (R2 = 0.376, p = 0.045). Because weather conditions projected by climate models included only temperature and precipitation, the regression model used to project population size at 50 and 80 year time points consisted of mean temperature in February and precipitation in September (R2 = 0.715, p = 0.007). Population size projections varied greatly among the 16 climate models due to widely varied weather projections by the models. There was little difference in projected population size among emission scenarios for most models. Close to half of the models projected population extinction. In conclusion, despite the low Pe projected by count-based PVA, population size projections based on climate models suggest that the Midewin population may not be protected against extinction even under low emissions scenarios.