Alien plants have greater impact than habitat fragmentation on native insect flower visitation networks
van Veen, FF
Diversity and Distributions
© 2017 John Wiley & Sons Ltd
Reason for embargo
Under embargo until 21 September 2018 in compliance with publisher policy
Aim Habitat fragmentation and alien species are among the leading causes of biodiversity loss. In an attempt to reduce the impact of forestry on natural systems, networks of natural corridors and patches of natural habitat are often maintained within the afforested matrix, yet these can be subject to degradation by invasion of non-native species. Both habitat fragmentation and alien invasive species disrupt the complex interaction networks typical of native communities. This study examines whether an invasive plant and/or the fragmented nature of the forestry landscape influences natural flower visitation networks (FVNs), flower–visitor abundance and richness or flower/visitor species composition. Location The species rich and diverse grasslands in the KwaZulu-Natal Midlands, South Africa is under threat from transformation, particularly by commercial forestry plantations, restricting much of the remaining untransformed grasslands into remnant grassland patches (RGPs). Remaining patches are under additional threat from the invasive Rubus cuneifolius Pursh (bramble). Sites were established in RGPs and in a nearby protected area (PA), with and without brambles present for both areas. Results Flower abundance and flower area of native plant species were greater within RGP than in PA, but only in the absence of R. cuneifolius. Flower–visitor assemblages differed between invaded and uninvaded sites and also differed between PA and RGP sites. Both areas lost specialist flower–visitor species in the presence of brambles. Network modularity was greatly reduced by the presence of bramble, indicating a reduction in complexity and organization. The structure of FVNs was otherwise unaffected by presence of bramble or being located in RGPs or the PA. Main conclusions The RPGs contribute to regional biodiversity conservation through additional compositional diversity and intact FVNs. Rubus cuneifolius reduces ecological complexity of both RGPs and PAs, however, and its removal must be prioritized to conserve FVNs.
Financial support was from the Green Landscapes Programme (DST/NRF grant) (Grant number 90139; Contract number 0054/2013) and the Mondi Ecological Networks Programme (MENP). This work was also supported by the European Union Marie Curie International Research staff Exchange Scheme (Contract number 318929).
This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record
Vol. 24 (1), pp.58-68