Comparison of pollinators and natural enemies: a meta‐analysis of landscape and local effects on abundance and richness in crops

Abstract

To manage agroecosystems for multiple ecosystem services, we need to know whether the management of one service has positive, negative, or no effects on other services. We do not yet have data on the interactions between pollination and pest-control services. However, we do have data on the distributions of pollinators and natural enemies in agroecosystems.Therefore, we compared these two groups of ecosystem service providers, to see if the management of farms and agricultural landscapes might have similar effects on the 2 abundance and richness of both. In a meta-analysis, we compared 46 studies that sampled bees, predatory beetles, parasitic wasps, and spiders in fields, orchards, or vineyards of food crops. These studies used the proximity or proportion of non-crop or natural habitats in the landscapes surrounding these crops (a measure of landscape complexity), or the proximity or diversity of non-crop plants in the margins of these crops (a measure of local complexity), to explain the abundance or richness of these beneficial arthropods. Compositional complexity at both landscape and local scales had positive effects on both pollinators and natural enemies, but different effects on different taxa. Effects on bees and spiders were significantly positive, but effects on parasitoids and predatory beetles (mostly Carabidae and Staphylinidae) were inconclusive. Landscape complexity had significantly stronger effects on bees than it did on predatory beetles and significantly stronger effects in non-woody rather than in woody crops. Effects on richness were significantly stronger than effects on abundance, but possibly only for spiders. This abundance-richness difference might be caused by differences between generalists and specialists, or between arthropods that depend on non-crop habitats (ecotone species and dispersers) and those that do not (cultural species).We call this the 'specialist-generalist' or 'cultural difference' mechanism. If complexity has stronger effects on richness than abundance, it might have stronger effects on the stability than the magnitude of these arthropod-mediated ecosystem services. We conclude that some pollinators and natural enemies seem to have compatible responses to complexity, and it might be possible to manage agroecosystems for the benefit of both. However, too few studies have compared the two, and so we cannot yet conclude that there are no negative interactions between pollinators and natural enemies, and no trade-offs between pollination and pest-control services. Therefore, we suggest a framework for future research to bridge these gaps in our knowledge.

Pollination and biological control research: are we neglecting two billion smallholders

“…It is well-established that insufficient pollination and biological control services can limit crop production when other factors such as soil nutrients and water are sufficient [21]. Evidence is now emerging to support the theory that pollination and biological control respond to similar drivers, such as floral resources and landscape structure [22][23][24], and it is therefore logical to consider them together.…”

“…The number of biological control studies was a quarter of that expected (11%, n = 11) and, whilst higher, the number of pollination studies was also less than expected (27%, n = 22). Mediterranean Shackelford et al [22] Local and landscape complexity 28 28 Unique studies (n) 138 102…”

“…The interaction of local and landscape factors can be important for ES delivery as was the case for flower visitation and production in commercial South African sunflower fields where the enhancement of floral diversity within fields ameliorated the negative effects of isolation from natural habitat [52]. Cultural species (dependent on crop habitats) of pollinators and natural enemies might be negatively affected by landscape complexity, whilst ecotone species and dispersers (dependent on non-crop habitats) might be positively affected [22].…”

Scientific Opinion addressing the state of the science on risk assessment of plant protection products for non‐target arthropods

“…Landscape structure modulates biodiversity: implication for the definition of tolerable magnitude of effects Landscape structure and heterogeneity plays a pivotal role in modulating local and regional biodiversity (e.g. Tscharnke et al, 2012;Ekroos et al, 2013Ekroos et al, , 2014Shackelford et al, 2013).…”

Protecting an Ecosystem Service

“…The value of 1038 flower-rich habitats is typically measured through assessment of pollinator abundance and 1039 species richness relative to other habitats , and is likely influenced by the 1040 composition and complexity of the landscape Shackelford et al, 2013). 1041 Surprisingly, it is still poorly understood whether the attraction of pollinators to flowering 1042 crops is enhanced with nearby engineered habitats, although the positive influence of semi-1043 natural habitats has to some extent been demonstrated (Chacoff and Aizen, 2006;1044 Sutherland, 2003;Klein et al, 2003;Kremen et al, 2004;Morandin and Winston, 2006).…”