Parasitoid diversity reduces the variability in pest control services across time on farms

Abstract

Recent declines in biodiversity have increased interest in the link between biodiversity and the provision and sustainability of ecosystem services across space and time. We mapped the complex network of interactions between herbivores and parasitoids to examine the relationship between parasitoid species richness, functional group diversity and the provision of natural pest control services. Quantitative food webs were constructed for 10 organic and 10 conventional farms. Parasitoid species richness varied from 26 to 58 species and we found a significant positive relationship between parasitoid species richness and temporal stability in parasitism rates. Higher species richness was associated with lower variation in parasitism rate. A functional group analysis showed significantly greater parasitoid species complementarity on organic farms, with on average more species in each functional group. We simulated parasitoid removal to predict whether organic farms experienced greater robustness of parasitism in the face of local extinctions. This analysis showed no consistent differences between the organic and conventional farm pairs in terms of loss of pest control service. Finally, it was found that the different habitats that make up each farm do not contribute equally to parasitoid species diversity, and that hedgerows produced more parasitoid species, significantly more so on organic farms.

Agricultural landscape simplification reduces natural pest control: A quantitative synthesis

“…Stability of ecosystem functions is thought to increase with species richness due to niche complementarity, facilitation, or sampling effects (Hooper et al, 2005); a positive relationship that has been found for a variety of ecosystem functions including biomass production, crop pollination, and pest control (Garibaldi et al, 2011;Isbell et al, 2009;MacFadyen et al, 2011). Studies linking natural enemy diversity to pest control services have focused on temporal stability, while spatial stability remains largely unexplored although considerable spatial heterogeneity in terms of abundance of natural enemies and their prey have been observed within fields (Holland et al, 2004;Winder et al, 2005;MacFadyen et al, 2011). Because landscape complexity is known to enhance natural enemy diversity and abundance, we expected to find a lower within-field stability (higher variability) in pest control in simple compared with more complex landscapes.…”

Complementarity and redundancy of interactions enhance attack rates and spatial stability in host–parasitoid food webs

“…The effects of predator or parasitoid species richness on prey attack rates and stability have been tested previously (e.g., Cardinale et al 2003, Ives et al 2005, Snyder et al 2006, Tylianakis et al 2006, Macfadyen et al 2011, and we were interested here in whether trophic complementarity and redundancy provide more information than does simple, and more easily measured, species richness. Therefore, we also incorporated, in all the models, host species richness, parasitoid species richness, and the weighted number of different interactions (quantitative connectance; Bersier et al 2002) as covariates, so that we could test for effects of interaction structure on parasitism rates after accounting for the effects of the number of species in webs and the number of links between species.…”

Modest enhancements to conventional grassland diversity improve the provision of pollination services

“…; Macfadyen et al . ; Brittain, Kremen & Klein ). This is true for the stability of pollination services; if complementary pollinator functional groups visit different plant species, or the same plant species at different times, this can enhance the overall visitation and pollination of plant communities (Hoehn et al .…”