Vegetation cover and not size of remnants determines composition and diversity of ground-dwelling arthropods in native vegetation remnants

Human urban populations continually grow and expand around the globe, and the urban footprint
can directly and indirectly have deleterious effects on biodiversity of native flora and fauna
through fragmentation. This study examined whether remnant area and habitat type between
urban remnants affected arthropod biodiversity. Eighteen remnants within urban areas of a
growing city in the South-western Australian Global Biodiversity Hotspot were surveyed using
pitfall traps for ground-dwelling arthropods. Contrary to our hypothesis that arthropod diversity
would increase in larger remnants, we found that size of remnant habitats had no effect on
arthropod diversity; rather habitat composition had a much greater influence on arthropod
diversity. Although remnant size had no significant effect on arthropod diversity, larger remnants
supported a greater diversity of species that utilise the same type of resources, known as functional
guilds. In our study we found that phytophagous (herbivores) and parasitoid functional guilds
were more abundant in larger fragments, while the habitat structure and cover in each remnant
affected scavengers, detritovores and pollinators. The abundance of angiosperms in remnants
increased arthropod pollinator diversity, while increased sedge (Cyperaceae) cover decreased
pollinator diversity. Interestingly, an increase in tree and leaf-litter cover decreased the number of
detritivores collected. As all sites were identified as “ecologically functional” with maintenance of
biogeochemical cycling, this is likely to closely reflect the arthropod diversity in Albany’s remnants
and would have outweighed the effects of remnant size on diversity. This concludes that healthy
habitat patches of all sizes are useful to maintain arthropod populations.