Responses of invertebrate trophic level, feeding guild and body size to the management of improved grassland field margins

Abstract

Summary1. Management of lowland mesotrophic grasslands in north-west Europe often makes use of inorganic fertilizers, high stocking densities and silage-based forage systems to maximize productivity. The impact of these practices has resulted in a simplification of the plant community combined with wide-scale declines in the species richness of grassland invertebrates. We aim to identify how field margin management can be used to promote invertebrate diversity across a suite of functionally diverse taxa (beetles, planthoppers, true bugs, butterflies, bumblebees and spiders). 2. Using an information theoretic approach we identify the impacts of management (cattle grazing, cutting and inorganic fertilizer) and plant community composition (forb species richness, grass species richness and sward architecture) on invertebrate species richness and body size. As many of these management practices are common to grassland systems throughout the world, understanding invertebrate responses to them is important for the maintenance of biodiversity. 3. Sward architecture was identified as the primary factor promoting increased species richness of both predatory and phytophagous trophic levels, as well as being positively correlated with mean body size. In all cases phytophagous invertebrate species richness was positively correlated with measures of plant species richness. 4. The direct effects of management practices appear to be comparatively weak, suggesting that their impacts are indirect and mediated though the continuous measures of plant community structure, such as sward architecture or plant species richness. 5. Synthesis and applications. By partitioning field margins from the remainder of the field, economically viable intensive grassland management can be combined with extensive management aimed at promoting native biodiversity. The absence of inorganic fertilizer, combined with a reduction in the intensity of both cutting and grazing regimes, promotes floral species richness and sward architectural complexity. By increasing sward architecture the total biomass of invertebrates also increased (by c. 60% across the range of sward architectural measures seen in this study), increasing food available for higher trophic levels, such as birds and mammals.

Does delaying the first mowing date benefit biodiversity in meadowland?

“…Invertebrates were expected to show an even stronger response to delayed mowing than plants, due to their heavy dependence on vegetation structure [33,64,65] and high susceptibility to mechanized harvesting processes [66]. However, only invertebrate species richness showed a clear overall significant positive response (Figure 4), while no effect was detected on invertebrate abundance.…”

Habitat associations of epigeal spiders in upland calcareous grassland landscapes: the importance for conservation

“…The single heath associated species without a particular preference for woodland or heathland, Walckenareia acuminata is a habitat generalist, but again occupies the ground zone (Harvey et al 2002). The greater proportion of ground hunters in grassland habitats reflects the crucial role of refuges within the sward, such as those of tussock forming grasses, in habitat suitability for ground dwelling predators (Woodcock et al 2009;Maelfait and De Keer 1990). For example, Trochosa terricola, associated with calcareous grassland in the present study, utilises tufts of Festuca ovina, the second most abundant plant species in these upland calcareous grasslands (Lyons et al 2017).…”

“…In the present study, though heath had greater overall vegetation height than the grassland habitats, the ground layer was denser in the latter resulting in greater structural complexity at the ground level in grasslands (personal observation). Indeed, increased structural complexity provides increased potential for niche differentiation (Woodcock et al 2009). In structurally complex swards containing a full range of phenological structures there is increased potential for resource utilisation for phytophagous prey taxa (Denno 1980;Woodcock et al 2009;Morris 2000), and greater abundance than in structurally less complex swards (Dennis et al 1998(Dennis et al , 2008.…”

“…Indeed, increased structural complexity provides increased potential for niche differentiation (Woodcock et al 2009). In structurally complex swards containing a full range of phenological structures there is increased potential for resource utilisation for phytophagous prey taxa (Denno 1980;Woodcock et al 2009;Morris 2000), and greater abundance than in structurally less complex swards (Dennis et al 1998(Dennis et al , 2008. Further, as structural complexity increases, the availability of niches suitable for the construction of different types of webs also increases (Bell et al 2001;Robinson 1981;Woodcock et al 2009).…”

Enhancing floral resources for pollinators in productive agricultural grasslands

“…The extensive management was intended to provide a summer window to allow the full phenological development of the sward and thus provide flowers for insect pollinators Woodcock, et al, 2009). The combination of early and late season grazing management strategies has also been shown to have beneficial effects on floral diversity in mesotrophic grasslands (Smith, et al, 2000).…”