Temporal Biotic Homogenisation Patterns due to Urbanisation Are Taxon-Dependent

Aim

Accelerated urbanisation poses a major threat to global biodiversity. However, few studies have explored patterns of temporal biotic homogenisation due to urbanisation across multiple taxa.

Location

Tokyo, Japan.

Methods

We examined the temporal changes in species richness and composition in 15 remnant green spaces across the Tokyo metropolitan area, Japan, focusing on native species of three taxa (plants: 15 sites, birds: 7 sites and butterflies: 7 sites). First, we compared gamma diversity and species composition (dispersion and composition) between two surveys at a regional scale that included all study sites. Furthermore, we assessed temporal change in alpha diversity (species richness over time) and temporal beta diversity (changes in species composition over time) at each green space. We also clarified the relationships between those indices and environmental variables. To determine the species more impacted by urbanisation, we examined the relationship between the rate of species loss and their traits related to dispersal and adaptation.

Results

Gamma diversity decreased from the first to the second survey regardless of taxa. However, the pattern of temporal diversity changes due to urbanisation varied among taxa. For plants, temporal changes in alpha diversity decreased with the number of years between surveys. For birds, temporal beta diversity increased with the number of years between surveys. For butterflies, the dispersion of species composition at the regional scale decreased slightly from the first to the second survey. Annual herb and water-dispersal plant species, as well as bird species with higher diet specialisation, were more prone to loss due to urbanisation.

Main Conclusions

Our findings demonstrate that patterns of temporal biotic homogenisation due to urbanisation vary among taxa. Therefore, enhancing species diversity within each green space and promoting species composition differences among green spaces are necessary to maximise multi-taxa diversity in urban areas.