Land-use and spatial scale effects on the arthropod communities of Azores

Background/Question/Methods Land-use change in the oceanic islands of Azores is a relatively recent phenomenon, which can be traced to the beginning of human settlement. Most of the habitats are no longer natural and often support arthropod assemblages with low conservation value. However, the composition of the surrounding landscape may have an effect which can vary according to the spatial scale. The aim of this study was to understand the effect of spatial scale on the composition of epigean arthropod assemblages from different habitat types in the Azores. Eighty-one sites of four different habitat types (Native and exotic forests, semi-natural and intensive pastures) were sampled in the island of Terceira, Azores, North-Atlantic. Arthropods were captured with pitfall traps during summer months at each site and identified. A MDS analysis was used to perceive differences between sites and habitat types. The landscape composition around each site was characterized at the radius of 100 to 5000 meters. Spearman correlation tests were made between land-use distribution and heterogeneity at different scales and species richness, percentages of endemic, native and introduced species, dispersal characteristics of species and abundance of endemic species.

Results/Conclusions

Differences between habitat types were very marked. The species richness of a site was influenced by the presence of different land-use types at different spatial scales. In almost all parameters of species richness and composition, the presence of the most undisturbed and disturbed habitats (native forests and intensive pastures respectively) were most strongly influencing the assemblages at a local scale, although this influence was also felt at large scales. On the contrary, the “intermediate disturbance” habitat types, exotic forests and semi-natural pastures, were not influencing the composition of arthropod assemblages at the local scale, but only at a large-scale. The heterogeneity of the landscape, as determined by the Shannon index, was also found to influence species richness and composition of sites, especially at intermediate scales. Most of the endemic species are positively influenced by the presence of native forest. The results indicate that the species richness and composition of sites is mostly determined by the presence of native forests or intensive pastures in the surrounding landscape. These two habitats seem to be the main drivers of species composition of a site, with all other habitat types presenting a mixture of the species coming from those habitats. Most endemic species benefit from the presence of native forests, especially at a small scale.