Effects of vineyard management and landscape context on taxonomic diversity and interaction networks of flower-visiting insects in the Cape Floristic Region biodiversity hotspot

[摘要] ENGLISH ABSTRACT: Both taxonomic diversity and diversity of species interaction networks are experiencingdeclines as a result of agricultural intensification at habitat and landscape scales. Reversingthis trend is a key conservation issue, particularly for important functional groups such asflower-visiting insects and the networks within which they interact. This is of great concernin regions of high conservation priority such as the Cape Floristic Region (CFR), known forits high level of floral and faunal endemism and exceptional species turnover. Holisticapproach to conservation in agricultural landscapes involves both preservation of natural landand wildlife friendly management of the farm land to achieve conservation targets. The valueof these extensive management approaches is yet to be fully assessed, especially in perennialsystems such as vineyards.I examined here the effects of vineyard management and landscape context on speciesrichness and abundance of flower-visiting insects and their species interaction networks.Possible taxon specific effects were verified. I also investigated whether vineyards underorganic and conventional management homogenized insect-flower interaction networks andwhether vineyards with different management practices vary in patterns of species turnover. Isampled flower-visiting insects and their interactions in organic and conventional vineyards,and in natural reference sites. Inclusion of natural reference sites enabled me to makemanagement recommendations for patches of natural vegetation in CFR agriculturallandscape.Statistical models showed taxon-specific benefit of organic farm management, and oflandscape (distance to natural habitat). There was benefit to monkey beetles (Scarabaeidae)but not to bees (Apidae). Organic vineyards had a higher number of insect-flower interactionsthan conventional ones, but vineyards under the two types of management were similar interms of other important network indices. However, networks of the vineyards were more nested than the natural sites, indicating that they may be potentially more stable toperturbation and random extinctions. Multivariate dispersion tests revealed insect-flowerinteraction networks were not homogenized by both organic and conventional vineyardsacross the landscapes. I also found, through additive partitioning, that organic andconventional vineyards were similar in terms of species turnover of bees and floweringplants.The findings of this study provide heuristic value to current debates on the value ofvineyard habitats for insect conservation. Both organic and conventional vineyards thatpromote sustainable management of the non-crop floral vegetation between vineyard rowsare potential solutions for conservation of flower-visiting insects and their interactions. Also,attention has to be paid to the quality and connectivity of the natural habitat patches that arewithin CFR agricultural landscape. Site specific management and assessment of the value ofthese landscape elements is important. Management approaches such as carefully controlledburning may be beneficial, as the CFR natural vegetation is a fire-driven community.

[发布机构] Stellenbosch University