ABSTRACT

Aim Studying the interaction between macroevolutionary and ecological factors is critical for understanding the principles of diversity regulation, as well as for predicting the effects of human activities. Here, we use the Hawaiian archipelago as a testbed to examine the interaction between island age and strong climatic factors (i.e., precipitation) on patterns of native and non-native tree taxonomic, functional and phylogenetic diversity.
Location The islands of Hawai’i, Maui Nui, and O’ahu in the Hawaiian archipelago
Major Taxa studied Trees
Time period 2003-2021
Methods We estimated patterns of tree species diversity from 375 forest plots spread across three islands that ranged from ~0.5-3 million years old, each encompassing a large precipitation gradient. We included data on species traits and phylogenies, as well as their abundances, so that we could calculate multiple facets of diversity (taxonomic, functional and phylogenetic) and with different weightings for common versus rare species (i.e., the Hill number continuum). We used general linear models to investigate the interaction between island age and precipitation, and examined species compositional turnover along the precipitation gradient. We compared results between plots that were less and more heavily invaded by non-native species to discern how the patterns were altered.
Results We found a strong positive relationship between precipitation and each facet of diversity on the oldest island (O’ahu), but no such relationship on the two younger islands (islands in the Maui Nui complex and Hawai’i). We also found high species turnover between drier and wetter environments, and thus higher ecological specialization, only on the oldest island. When we included highly invaded plots, precipitation had a larger effect on diversity and turnover on the younger islands.
Main Conclusions Our results demonstrate that macroevolutionary and ecological processes interactively shape tree species diversity, but that biological invasions are degrading these signatures.
KEYWORDS : Alien species, alpha diversity, beta diversity, oceanic islands, Hawaiian forest, precipitation.