Trait-mediated competition drives an ant invasion and alters functional diversity

Abstract

The assumption that differences in species' traits reflect their different niches has long influenced how ecologists infer processes from assemblage patterns. For instance, many assess the importance of environmental filtering versus classical limiting-similarity competition in driving biological invasions by examining whether invaders’ traits are similar or dissimilar to those of residents, respectively. However, mounting evidence suggests that hierarchical differences between species' trait values can distinguish their competitive abilities (e.g. for the same resource) instead of their niches. Whether such trait-mediated hierarchical competition explains invasions and structures assemblages is less explored. We integrate morphological, dietary, physiological and behavioural trait analyses to test whether environmental filtering, limiting-similarity competition or hierarchical competition explain invasions by fire ants on ant assemblages. We detect both competition mechanisms; invasion success is not only explained by limiting similarity in body size and thermal tolerance (presumably allowing the invader to exploit different niches from residents), but also by the invader's superior position in trait hierarchies reflecting competition for common trophic resources. We find that the two mechanisms generate complex assemblage-level functional diversity patterns—overdispersion in some traits, clustering in others—suggesting their effects are likely missed by analyses restricted to a few traits and composite trait diversity measures.

Forest disturbance increases functional diversity but decreases phylogenetic diversity of an arboreal tropical ant community

“…However, these changes are expected, if a large proportion of the community is excluded. The robustness of the PD and FD to non-native ant exclusion suggests a surprising resistance of the local ecosystem to the non-native species, contrasting other findings with invasive fire ants which reduced FD (Wong et al, 2020(Wong et al, , 2022. In Madagascar, swidden agriculture is also associated with influxes of invasive species, but these have limited negative impact on native species (Finch et al, 2022).…”

“…Comparing both FD and PD after disturbance can further provide insights into underlying community assembly processes (Cavender‐Bares et al., 2009), but is not without caveats (Gerhold et al., 2015). For instance, if a community is clustered in its traits and phylogeny following disturbance, it potentially indicates niche‐based habitat filtering, since only species with traits suitable to the environment are selected and thus more uniform than expected at random (Kraft et al., 2015; but see Gerhold et al., 2015; Wong et al., 2022). Overdispersion, on the other hand, can be an indicator for competitive exclusion, where communities are more dissimilar resulting from inter‐specific competition (limiting similarity principle; MacArthur & Levins, 1967).…”