The ecological niche provides a broad theoretical framework for addressing questions in both basic (e.g. species coexistence) and applied (e.g. biological invasions) ecology. However, the challenge of empirically quantifying a species’ ecological niche in situ has limited our ability to test theory and improve ecological forecasting. As niche space is ultimately determined by the persistence of populations, demography provides particularly relevant methods for empirically quantifying the niche. In this study, we integrate demographic and environmental sampling to examine the ecological niche of Alliaria petiolata (“garlic mustard”), an aggressive invasive plant in forest understories of the Eastern U.S. We established a total of 160 plots at 16 sites across Massachusetts, Connecticut, and New York invaded by A. petiolata. We measured the size, survival, and fecundity of 2,345 A. petiolata individuals during four censuses between June 2018 and April 2019 (with sampling anticipated to continue through 2021). In addition, we quantified light availability, soil nitrogen, soil pH, and soil moisture. By elucidating environmental and biological drivers, this work ultimately aims to improve forecasting and risk assessment of ecosystem invasibility and impact by A. petiolata.
Results/Conclusions
In the first year of sampling, we observed substantial variation in both environmental variables and demographic outcomes across the 16 sites. The survival, growth, and fecundity of A. petiolata individuals were strongly size-dependent, with an overall 25% survival rate for 1st year plants between June and September, followed by 22% survival between September and April. Size-dependent demographic vital rate models were moderately to substantially improved by incorporating plot-level environmental variables. Environmental drivers were often best incorporated with a second-order term, highlighting the potential for quantifying the demographic niche and also indicating that our range of environmental conditions was biologically relevant. Later in the growing season (July - September), only growth was well-modeled by including environmental drivers, and survival was best modeled by plant size and the random effect of sampling location. These initial results highlight the potential to quantitatively describe the ecological niche of A. petiolata given continued sampling over multiple generations.