Island area, not isolation, drives taxonomic, phylogenetic and functional diversity of ants on land-bridge islands

Aim: To explore the impact of island area and isolation on multiple
dimensions of ant biodiversity (taxonomic, phylogenetic, and functional
diversity) and the underlying processes of community assembly on islands.
Location: Thousand Island Lake, Zhejiang, China, created by dam
construction in 1959. Taxon: Ants. Methods: We sampled ants on 33 islands,
built a species-level phylogenetic tree and measured five morphological
traits of all species collected to estimate taxonomic, phylogenetic, and
functional diversity. We used multiple linear regression models and null
models to examine the relationships between diversity metrics and island
variables (area and isolation). Results: We recorded 97 ant species on the
study islands. We verified positive diversity–area relationships for
species richness, phylogenetic diversity, and functional diversity.
However, although functional and phylogenetic community structure were
indistinguishable from random communities, phylogenetic structure tended
to be clustered, whereas functional structure tended to be over dispersed.
Additionally, we found the structure of ant communities shifted from
phylogenetic and functional clustering on smaller islands to phylogenetic
and functional overdispersion on larger islands. Main conclusions: Our
results support the hypothesis that environmental filtering is the
dominant process structuring ant communities on smaller islands, and that
competitive exclusion becomes more important on larger islands. Thus,
island area acts as an important filter even though ant community
structure on the study islands was indistinguishable from random
communities. Moreover, our results show that environmental filtering
influences phylogenetic community structure of ants, whereas competitive
exclusion influences functional community structure of ants. These
findings highlight the need to examine both phylogenetic and functional
diversity in order to understand the mechanisms that govern the assembly
of natural communities on islands.