Alien plants have greater impact than habitat fragmentation on native insect flower visitation networks

• Published in: Diversity & distributions Vol. 24; no. 1/2; pp. 58 - 68
• Main Authors: Hansen, Simone, Roets, Francois, Seymour, Colleen L., van Veen, F.J. Frank, Pryke, James S., Thébault, Elisa S.
• Format: Journal Article
• Language: English
• Published: Oxford John Wiley & Sons Ltd 01.01.2018; John Wiley & Sons, Inc; Wiley
• Subjects: Abundance; Afforestation; Biodiversity; Biodiversity and Ecology; biodiversity conservation; Biodiversity loss; BIODIVERSITY RESEARCH; brambles; Complexity; conservation areas; Corridors; ecological networks; Ecology, environment; Environmental Sciences; flower network analyses; Flowers; food web; Forestry; Fragmentation; Grasslands; Habitat fragmentation; Habitats; Herbivores; Indigenous plants; Indigenous species; insect conservation; introduced plants; Introduced species; Invasive plants; Invasive species; landscape ecology; landscapes; Life Sciences; Modularity; Networks; Plant species; Plantations; Plants (botany); pollination; Protected areas; Rubus cuneifolius; South Africa; Species composition; species diversity; Wildlife conservation; South Africa
• ISSN: 1366-9516; 1472-4642
• DOI: 10.1111/ddi.12656

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 nonnative 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.