Quantifying spatially explicit differences in the underlying vital rates that govern population dynamics is a crucial step in understanding the factors that contribute to invasion success. Schinus terebinthifolia Raddi, a woody shrub native to Brazil, Paraguay and Argentina and globally invasive around the subtropics, has been introduced in two separate introductions in Florida that have subsequently hybridized in a hybrid zone in the middle of the state. As is common with many shrubs, it exhibits plasticity in growth form, a trait hypothesized to increase invasion success, which means that several metrics of plant size are necessary to fully predict plant performance.
We constructed integral projection models for six sites across the Florida range, where the probabilities of survival, growth and reproduction were modeled as functions of two continuous metrics of size, diameter and height. We performed a LTRE (life-table-response-experiment) analysis to determine how spatial variation in the underlying vital rates contributed to spatial variation in the population growth rate.
Results/Conclusions
Only one of the sites (Chekika, λ = 1.01) had a population growth rate that was significantly different from the other sites (Wild Turkey, λ = 1.17; Fort Pierce, λ = 1.13; Big Cypress, λ = 1.12; Cape Canaveral, λ = 1.10, and Punta Gorda, λ = 1.09). We found extensive spatial variation in the influence of the underlying vital rates on the population growth rate. Both the probability of seedling survival and the probability of maturation from the seedling domain to the adult domain were lowest at Chekika. According to the LTRE analysis, the probability of seedling maturation had the largest effect on among-site differences in the population growth rate. Survival and growth of the adults had the highest total elasticity, indicating that management actions that impact reproductive adults would have the greatest effect in reducing the population growth rate.