Grasshopper assemblage response to conservation ecological networks in a timber plantation matrix

Abstract

Grasshopper assemblages are well known to be sensitive and responsive to changes occurring in habitats, enabling their application as bioindicators. Large-scale ecological networks (ENs) have been proposed as a conservation mitigation measure, and are used extensively in southern Africa to offset the impacts on biodiversity of commercial afforestation. Here, grasshopper response to an EN of 15 semi-natural grassland sites embedded in an exotic timber plantation matrix was investigated over two time periods, one year apart. The aim was to determine which environmental variables had a significant effect on grasshoppers, whether this response was robust among seasons, and the extent of phylogenetic variability in the response. The results showed that grasshopper species responded strongly and consistently to area of the site, time lapse since the last fire, and inconsistently to proportion of short grasses. Generalized least squares models with phylogenetic adjustment showed that there was a strong phylogenetic signal in species response to habitat quality, illustrating that site occupancy patterns were distinct for species from different subfamilies. Since grasshopper assemblages are more sensitive to internal patch-level environmental factors of ENs than to patch isolation, ENs may indeed be a suitable mitigation measure, although effectiveness is expected to vary among taxa.