COS 55-4 - Different adaptive strategies of alien woody species are linked to reduced native richness and abundance in Caribbean forests

Background/Question/Methods

Understanding the role of alien species in forest communities and how native and alien species interact to shape the composition and structure of contemporary forests is of critical importance to invasion ecology and land management. In this study, we used vegetation data collected over a period of 20 years in 341 permanent plots located across Puerto Rico to: (1) evaluate interactions between native and alien woody species across a variety of forest types, (2) compare changes in the composition and abundance of native and alien woody species in plots with and without aliens, and (3) assess whether aliens and natives show divergence or convergence regarding functional roles and ecological strategies. We also tested the applicability of Grime’s CSR (competitive, stress-tolerant, and ruderal strategies) theory to explain naturalization success.

Results/Conclusions

Both species richness and abundance of natives are consistently lower in plots in which aliens are present compared to those without them. This negative relationship between aliens and natives has been consistent over 20 years and across all forest types. In contrast, aliens benefit from the presence and abundance of other aliens. Both native and total richness slightly increased over the 20-years, but the increase of native richness was three times lower in plots with aliens. The CSR classification provided insight into the naturalization success of aliens. Corroborating the “join the locals” hypothesis, aliens use the same functional spaces as do natives. The exception is the dry forest, where aliens and natives diverge in the use of functional spaces, a result that corroborates the “try harder” hypothesis. Generally, alien species were better competitors than natives, and natives were more stress-tolerant than aliens. Our combined results suggest that aliens are driving significant changes in native plant communities by transforming the assembly and dynamics of local forests. Ultimately, these modifications may have significant long-term implications for local forests, affecting their regeneration and productivity, as well as their capacity to cope with climate change and large-scale disturbances such as tropical storms and hurricanes.