Relative importance of management vs. design for implementation of large-scale ecological networks

Abstract

Ecological networks (ENs) are used to mitigate landscape-scale habitat loss, and are managed and designed to conserve regional biodiversity. In our study region in southern Africa, ENs of isolated grassland remnants are specifically set aside and managed for conservation, and are complemented by corridor-like power line servitudes which are maintained by regular mowing. Using grasshoppers, a sensitive and reliable bioindicator taxon, we determine whether ENs effectively conserve biodiversity. We used cluster analysis and variation partitioning to select the best subset of environmental variables which explained the patterns of species composition. We then compared the relative importance of environmental variables grouped by the scale of their influence: local-scale variables affected by management practices vs. landscape-scale variables affected by design of ENs. Management was consistently and significantly 2–5 times more influential than design in determining grasshopper assemblages within ENs and servitudes. Servitudes had a higher proportion of bare ground, lower proportion of tall grasses and higher abundance of grasshoppers relative to ENs. Three grasshopper species were strongly associated with servitudes and exhibited traits consistent with early colonizers. As management actions are primarily responsible for vegetation succession, the use of ENs for conservation efforts should first focus on appropriate management strategies, such as fire regime and grass height management before altering the landscape structure (e.g. increasing connectivity or enlarging patches). The conservation implications of these results are that, if ENs are managed and designed for heterogeneity and to simulate multiple successional stages, they may be beneficial for biodiversity conservation.