Partial clearing of a road corridor leads to homogenisation of the invertebrate fauna

Abstract

A recent plan to extend a highway in south-west Western Australia has been abandoned, but not before a 10–200m wide strip of vegetation along the alignment had been cleared. Attempts are now being made to rehabilitate the cleared area. The aim of this paper is 2-fold. First, it documents the changes in invertebrate abundance, richness and evenness in this abandoned landmark development. Second, it explores the changes in invertebrate species composition, concentrating on ants, in terms of known trends in biodiversity, with particular emphasis on biotic homogenisation. We report on the immediate changes in invertebrate assemblages from a spatial continuum of sites passing through six discrete woodland communities. A total of 69 species of ants were sampled by pitfall traps from the sites, with 50 being sampled in the 7 reference sites and 46 in the 13 cleared sites. As far as most of these simple indices are concerned, the previously cleared areas generally exhibited values that are not appreciably different from those of the reference sites, except that species richness was marginally higher in the reference sites and ant abundance was higher in the cleared area sites. There was considerable variation in numbers of ant species within Ant Niche Template categories in both the reference and cleared area sites. However, numbers of nest specialists and trophic specialists were significantly lower in cleared area sites; opportunistic species and one generalist were more abundant in cleared areas. The two-dimensional solution of the multi-dimensional scaling ordination grouped all cleared sites close together, with the reference sites and modified native vegetation site being widely scattered across the graph. The tight bunching of the cleared sites suggests that clearing for the proposed highway has resulted in homogenising the ant fauna, creating a characteristic assemblage that differed from all of the original reference sites. When considered at the ordinal level, significantly less Clitellata (worms), Malacostraca (slaters), Araneae (spiders), Blattodea (cockroaches), Dermaptera (earwigs) and Coleoptera (beetles) were sampled from the cleared sites, but significantly more Collembola (springtails), Homoptera and Heteroptera (both types of sucking bugs) were sampled in these sites. Collembola may be responding to the abundance of exotic grasses whereas the sucking bugs may have benefitted from the lush herb and shrub layer associated with the regrowth and rehabilitation efforts.