Colonization resistance and establishment success along gradients of functional and phylogenetic diversity in experimental plant communities

Abstract

Functional and phylogenetic diversity (FD and PD respectively) of the resident community are expected to exert a key role in community resistance to colonization by surrounding species, and their establishment success. However, few studies have explored this topic experimentally or evaluated the interactive effects of these diversity measures. We implemented a diversity experiment to disentangle the role of FD and PD by sowing mixtures of 6 species, drawn from a pool of 19 species naturally coexisting in central European mesic meadows. The mixtures were designed to cover four independent combinations of high and low FD and PD. Species covers were estimated in spring and late summer over two growing seasons. We then assessed the establishment success of colonizers as a function of their mean traits and phylogenetic distance to the resident (i.e. sown) communities, as well as the resistance of the resident communities to natural colonizers as a function of their functional and phylogenetic structure. Results generally indicated a temporal shift regarding which trait values made a colonizer successful, from an acquisitive strategy in early stages to a more conservative trait syndrome in later stages. FD decreased community resistance to natural colonization. However, PD tempered this effect: with high PD, FD was not significant, suggesting complementary information between these two components of biodiversity. On average, colonizing species were more functionally distant from the resident species in sown communities with high functional diversity, i.e. those that were more colonized. Synthesis. Our results confirm an interplay between FD and PD during community assembly processes, namely resistance to colonizers, suggesting that these two descriptors of biodiversity only partially overlap in their contribution to the overall ecological structure of a community. The hypothesis that higher FD increases resistance through a more complete use of resources was challenged. Results rather suggested that greater FD could provide an unsaturated functional trait space allowing functionally unique species to occupy it.

Is phylogenetic and functional trait diversity a driver or a consequence of grassland community assembly?

“…Both FD and PD give us unique, complementary information; Cadotte et al () suggest that PD may be a good measure for studies interested in highlighting multivariate conserved ecologically similar traits while FD or single traits may be best for highlighting more recent changes or impacts. The experimental manipulation of both PD and FD done by Galland et al () and others (e.g. Hipp et al, ) supports the idea that FD and PD give different information.…”

“…Khalil et al () took traditional intraspecific trait variation measures but compared them across spatial scales (e.g., population vs. community intraspecific trait variation) to measure the extent and strength of external and internal filtering for driving competitive interactions. Galland et al () measured FD and PD using Rao's index, but used it to understand how trait/evolutionary uniqueness or redundancy impacted colonization. Miller et al () used unique statistical approaches in their 19‐year dataset to address whether FD is a passenger or driver of community assembly following drought.…”

“…Many researchers took unique approaches to manipulating diversity or to investigating what impacts it. Galland et al () manipulated both FD and PD in a fully factorial experiment that sought to look at the impacts of both on colonization. They included an N‐addition treatment to explore the impacts of resource availability.…”

Genomic Analyses of Phenotypic Differences Between Native and Invasive Populations of Diffuse Knapweed (Centaurea diffusa)

“…Which functional traits are important for invasion success may be context dependent and vary among invasive species. Important functional traits may change over the progression of the invasion (Dietz and Edwards, 2006;Catford et al, 2019;Galland et al, 2019) and may depend on the habitats invaded (Lachmuth et al, 2011), the traits of species in the invaded community (Roscher et al, 2018), or the trait diversity of other conspecific invaders (Turner et al, 2020a). Most traits relevant for predictive ecological or evolutionary modeling of invasions require data on continuous intraspecific variation and trait-environmental relationships; these traits have to be measured on individual plants in their respective environments (Kattge et al, 2020), and thus are likely to be correlated with individual variation at the genetic level.…”

“…Most traits relevant for predictive ecological or evolutionary modeling of invasions require data on continuous intraspecific variation and trait-environmental relationships; these traits have to be measured on individual plants in their respective environments (Kattge et al, 2020), and thus are likely to be correlated with individual variation at the genetic level. The complexity of the context dependency in invasion success thus highlights the need to incorporate molecular data into our ecological understanding of invasions (Galland et al, 2019).…”