Effects of agricultural diversification on the abundance, distribution, and pest control potential of spiders: a review

Abstract

A review of the literature showed that spider abundance was increased by diversification in 63% of studies. A comparison of diversification modes showed that spider abundance in the crop was increased in 33% of studies by 'aggregated diversification' (e.g. intercropping and non-crop strips) and in 80% of studies by 'interspersed diversification' (e.g., undersowing, partial weediness, mulching and reduced tillage). It is suggested that spiders tend to remain in diversified patches and that extending the diversification throughout the whole crop (as in interspersed diversification) offers the best prospects for improving pest control. There is little evidence that spiders walk in significant numbers into fields from uncultivated field edges, but diversification at the landscape level serves to foster large multi-species regional populations of spiders which are valuable as a source of aerial immigrants into newly planted crops. There are very few manipulative field studies where the impact of spiders on pests has been measured in diversified crops compared with undiversified controls. It is encouraging, however, that in those few studies an increased spider density resulted in improved pest control. Future work needs are identified.

Local and Landscape Correlates of Spider Activity Density and Species Richness in Urban Gardens

“…Increased abundance and diversity of flowering trees, shrubs, and ornamental or crop species that are often associated with agricultural habitats may attract many potential prey items (Rebek et al 2005). An increase in prey abundance or richness would also encourage an increase in activity density and diversity of spiders (Sunderland and Samu 2000). Alternatively, studies have shown that spiders are more abundant in habitats with higher structural complexity (Langellotto andDenno 2004, Shrewsbury andRaupp 2006).…”

“…This is likely due to prey density and polyphagous eating habits of spiders. Agricultural areas generally attract high numbers and a variety of arthropods, which in turn may attract spiders as predators (Sunderland and Samu 2000). Additionally, ballooning (aerial dispersal) is the most efficient dispersal technique at the landscape scale and allows spider individuals to survey separated, varying habitats in a short span of time to find mates or resources, reduce competition, or avoid cannibalism (Weyman 1993).…”

“…They are polyphagous, obligate carnivores, and feed primarily on insects and other spiders (Bristowe 1941, Nentwig 1987, Nyffeler 1999, Turnbull 1973. Differences in prey preference, hunting methods, and timing of predation are complementary and allow for effective pest control (Sunderland and Samu 2000). Different spider species utilize a variety of hunting techniques, including ambush or sitand-wait, nocturnal or diurnal wandering, and web spinning (Marc et al 1999, Riechert 1999.…”

Spider community responds to litter complexity: insights from a small-scale experiment in an exotic pine stand

“…Spiders tend to remain in habitats where conditions are optimal (Sunderland & Samu, 2000). Patches with complex substrate possibly received high immigrations associated with reduced emigration rates during the course of the experiment, as suggested by Langellotto & Denno (2004).…”

“…Spiders can aff ect ecosystem functions through top-down eff ects on herbivores or decomposers, and their foraging strategies are key functional traits to explain such eff ects (Liu et al, 2015a). In general, they are considered benefi cial to agroecosystems by controlling the abundance of various pest species (Sunderland & Samu, 2000). Nevertheless, studies and management actions employing habitat structural modifi cations to promote predators are still rare but are beginning to arise (e.g.…”