Testing Darwin’s naturalization conundrum based on taxonomic, phylogenetic, and functional dimensions of vascular plants

Abstract

Charles Darwin posited two alternative hypotheses to explain the success of nonnative species based on their relatedness to natives: nonnative species that are closely related to native species could experience (1) higher invasion success because of an increased probability of habitat suitability (conferred by trait similarity) or (2) lower invasion success due to biotic interference, such as competition and limiting similarity. The paradox raised by the opposing predictions of these two hypotheses has been termed "Darwin's naturalization conundrum" (DNC). Using plant communities measured repeatedly across an experimental fire gradient in an oak savanna (Minnesota, USA) over 31 yr, we evaluated the DNC by incorporating taxonomic, functional, and phylogenetic information. We used a "focal-species" approach, in which the taxonomic, functional, and phylogenetic structure of species co-occurring with a given nonnative (focal) species in local communities was quantified. We found three main results: first, nonnative species tended to co-occur most with closely related natives, except at the extreme ends of the fire gradient (i.e., in communities with no fire and those subjected to high fire frequencies); second, with increasing fire frequency, nonnative species were functionally more similar to native species in recipient communities; third, functional similarity between co-occurring nonnatives and natives was stable over time, but their phylogenetic similarity was not, suggesting that dynamic external forces (e.g., climate variability) influenced the phylogenetic relatedness of nonnatives to natives. Our results provide insights for understanding invasion dynamics across environmental gradients and highlight the importance of evaluating different dimensions of biodiversity in order to draw stronger inferences regarding species co-occurrence at different spatial and temporal scales.

Addressing context dependence in ecology

“…Ecological studies examining the same question or process often reach different conclusions. In invasion ecology, for example, studies have found that the phylogenetic relatedness of alien to native species can inhibit or facilitate invasion [1,2], the relationship between native and alien species richness can vary from positive to negative [3,4], and the effect of disturbance on invasion is equivocal and inconsistent [5,6]. When studies addressing the same question reach different conclusions, the different outcomes are often attributed to context dependence (see Glossary).…”

Exotic fishes that are phylogenetically close but functionally distant to native fishes are more likely to establish

“…Many studies have investigated this conundrum across different taxonomic groups and ecosystems using observational approaches (Bezeng et al, 2015;Duncan & Williams, 2002;Park et al, 2020;Pinto-Ledezma et al, 2020;Qian et al, 2021;Strauss et al, 2006). However, the vast majority of these studies were based primarily on observations of successfully invaded exotic species, but did not consider those that were introduced but failed to establish.…”

The invasion paradox dissolves when using phylogenetic and temporal perspectives

“…While recent advances have helped disentangle this invasion paradox, relatively few studies have moved beyond species richness as the key measure of native diversity (but see work related to Darwin's naturalization conundrum; e.g. Ma et al, 2016;Marx et al, 2016;Pinto-Ledezma et al, 2020). Over-reliance on richness is a potential limitation of diversity-invasibility studies evaluating biotic resistance, as the number of native species present in a community may be a poor proxy for available niche space.…”