Seedling maturation drives spatial variability in demographic dynamics of an invader with multiple introductions: insights from an LTRE analysis

Authors: ERICKSON, KELLEY - Missouri Botanical Garden; Pratt, Paul; Rayamajhi, Min; HORVITZ, CAROL - University Of Miami

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2020
Publication Date: 4/18/2020
Citation: Erickson, K., Pratt, P.D., Rayamajhi, M.B., Horvitz, C. 2020. Seedling maturation drives spatial variability in demographic dynamics of an invader with multiple introductions: insights from an LTRE analysis. Biological Invasions. 22:2185-2203. https://doi.org/10.1007/s10530-020-02249-x.
DOI: https://doi.org/10.1007/s10530-020-02249-x

Interpretive Summary: Brazilian peppertree is an invasive shrub that was introduced into Florida multiple times and has subsequently hybridized, resulting in three different plant types: eastern, western and hybrids. Do these plant types have different population growth rates? We monitored 1480 different plants across six populations from the three types. We found higher population growth rates for the western populations compared to the eastern or hybrids. We learned that the higher population growth rate of the western population was driven by seedlings that quickly developed into reproductive adults. The survival and growth of the largest individuals had the highest elasticity, suggesting that management (control) actions that are able to decrease growth and survival of these larger plants would have the greatest effect on the population growth rate. These population growth rates serve as a benchmark with which future management efforts can be compare. Researchers in the future, for instance, can compare Brazilian peppertree growth rates after the release of a biological control agent(s) to learn if the herbivore has reduced the plant's invasive characteristics.

Technical Abstract: Multiple introductions are hypothesized to facilitate the success of invasive plant species, as these introductions can result in novel genotypes through intraspecific hybridization and potentially increase the ability to adapt to the novel environment. Through this combination of genes and the environment, how an invader performs may vary across its invaded range. The ability to evaluate the success of any management action, such as the introduction of a biocontro l agent, could therefore be spatially dependent and requires an understanding of the population dynamics of the invasive species prior to management action. Brazilian Ppepper (Schinus terebinthifolia Raddi), a shrub that has invaded the global subtropics, was introduced in Florida in two separate introductions (an Eastern biotype and a Western biotype) and intraspecific hybridization has resulted in a hybrid biotype. We constructed integral projection models where the probabilities of survival, growth and reproduction were functions of two size variables (diameter and height). We performed a Life Table Response Experiment analysis Tto decompose the effects of the different biotypes on the population dynamics of Brazilian Ppepper in the absence of any biocontrol we performed a Life Table Response Experiment analysis. We found that the higher population growth rate of the Western population was driven by the comparatively rapid maturation of the Western seedlings into reproductive adults. The survival and growth of the largest individuals had the highest elasticity, suggesting that management actions that are able to decrease these vital rates would have the greatest effect on the population growth rate. Due to spatial variation in the magnitude and quality of dispersal services, the differences amongst the population growth rates may be even greater than those reported in this study.