Competitive exclusion drives termite community assembly process on islands

Context

Abiotic filtering, including environmental and dispersal filtering, is frequently observed resulting in reduced diversity and more similar species assemblages following habitat fragmentation. Nonetheless, the significance of competitive exclusion is often underestimated.

Objectives

We investigated the dominant assembly process among termite communities on land-bridge islands, focusing on species known for their high territoriality. We hypothesized that competitively superior species tend to dominate more favorable habitats, such as larger and less isolated islands. Consequently, we anticipated lower diversity and greater similarity in species assemblages than would be expected.

Methods

Termite communities were surveyed using standardized transects on 24 islands. We quantified the standardized effects of island area and isolation on taxonomic, phylogenetic and functional diversity by comparing observed patterns with randomly generated communities (i.e., stochastic process). A phylogenetic generalized linear mixed model (PGLMM) was conducted to examine species-specific responses to environmental factors and competition intensity (i.e., heterospecific abundance).

Results

We found that taxonomic, phylogenetic and functional diversity were lower than expected on larger and less isolated islands, suggesting that competitive exclusion was the dominant mechanism shaping termite communities in TIL. PGLMM showed that two fungus-growing species with larger body sizes increased with competition intensity, while other species exhibited negative responses. Notably, the abundance of fungus-growing species showed sharper increase with island area and decrease with isolation compared to other feeding groups. These findings demonstrate that competitively superior species prefer high-quality habitats and are more sensitive to habitat fragmentation.

Conclusions

Our study highlights the significance of competitive exclusion in shaping termite communities and emphasizes the need to consider both competitive and niche difference among species or functional groups when predict changes in community structure and biodiversity loss resulting from habitat fragmentation.