Traits and land transformation change the fortunes of grasshopper generalists vs. specialists in a biodiversity hotspot

Abstract

Understanding the link between species traits and how they use various elements in a heterogeneous agro-natural landscape is essential for conservation planning. Land-use and season affect the availability of resources for herbivorous insects such as grasshoppers. Also, the level at which these herbivores utilise these resources on the landscape depend on their traits. We focus here on the Cape Floristic Region biodiversity hotspot, which is rich in both endemic plants and narrow-range grasshoppers. We assessed dispersion patterns and abundance of the grasshopper species across the agro-natural mosaic, while specifically focusing on species traits and how they change over two seasons (spring and summer). We found that land-use and species traits played major roles in grasshopper spatial dispersion across the landscape, with season a highly significant variable. Not surprisingly, highly mobile, generalist feeders were abundant and widely dispersed across the landscape. Importantly however, this was especially the case in late season, when they could take advantage of high plant productivity in the vineyards. In contrast, low mobility, specialist feeders were limited to occupying only natural fynbos vegetation in both seasons. Generally, the highly mobile generalists benefitted in two ways: occupation of transformed areas, and receiving a population boost late season. This was not the case for the low-mobility specialists, which were doubly disadvantaged: not able to move far, and lacking their specific host plants in the transformed areas. From a conservation perspective, our results indicate the importance of improving functional connectivity using natural fynbos for conservation of the endemic specialists, while the generalists can largely look after themselves across this agro-natural mosaic.