Effects of vegetation structure and floristic diversity on detritivore, herbivore and predatory invertebrates within calcareous grasslands

Abstract

Calcareous grasslands in Europe have shown wide scale declines in their extent and quality as a result of modern agricultural practices, increased atmospheric eutrophication and lack of management. In addition to being a key habitat for specialist plants, calcareous grasslands are also important for many threatened invertebrates. In this UK based study, we investigated the impact of military vehicle activity, floral species richness and vegetation structure on assemblages of detritivore, herbivore and predatory invertebrates. We also consider the impact that disturbance by military vehicle activity on the proportion of invertebrate species capable of flight, a surrogate for dispersal ability. Sward height was negatively correlated with detritivore, herbivore and predator species richness. Herbivores species richness was positively correlated with both forb and grass species richness. Spatial variation in the number of plant species was negatively correlated with herbivore species richness. Those sites most heavily disturbed by military vehicle activity supported the lowest proportions of flightless invertebrates. Successful management for calcareous grassland invertebrates should aim to maintain short swards with high floristic diversity, in terms of both the forbs and grasses. It should be noted, however, that these findings refer to principally surface rather than sward active invertebrates. While disturbance associated with military vehicle activity was not found to affect invertebrate species richness, it has negative consequences for the structure of invertebrate assemblages by selecting against invertebrates with low dispersal ability. To support invertebrate diversity in calcareous grasslands we emphasise the need for variety in the timing and type of management applied to promote heterogeneity in sward structure.

Enhancing beetle and spider communities in agricultural grasslands: The roles of seed addition and habitat management

“…The positive relationship between plant and phytophagous invertebrate diversity has been demonstrated in several other grassland studies (e.g. Siemann et al, 1998;Haddad et al, 2001;Woodcock and Pywell, 2010). For predatory invertebrates, including beetles and spiders, increased plant species richness would diversify sward structural complexity as the availability of novel physical structures linked with individual plant species would be increased (Morris, 2000;Haddad et al, 2001).…”

“…By enhancing floristic diversity in areas of agriculturally improved grasslands abundant and complex invertebrate communities may be supported (Siemann et al, 1998;Morris, 2000;Woodcock and Pywell, 2010;Littlewood et al, 2012). This may be achieved by the use simple and cost effective seed mixtures which contain species that have agronomic value, are able to establish effectively in fertile soils and are known to support a wide spectrum of associated invertebrates (Pywell et al, 2002;Mortimer et al, 2006).…”

“…For example, phytophagous beetles with endophagous seed-feeding larvae would be lost from grasslands where the frequency of management operations prevents the development of seed heads (Morris, 2000;Woodcock et al, 2006). Importantly, this means that the occurrence of a host plant alone may be insufficient for phytophagous species where management intensity results in the loss of a plant structures on which they feed (Morris, 2000;Woodcock and Pywell, 2010).…”

“…We also identify how different management types (cattle grazing vs. cutting), management intensities (intensive vs. extensive) and cultivation techniques (shallow vs. deep cultivation) impact on these same characteristics. We predict that: 1) the species richness and biomass of beetles and spiders will increase in response to a gradient of increasing plant diversity (Siemann et al, 1998;Woodcock and Pywell, 2010); 2) catastrophic management events that are implemented over a single day, such as cutting, will have a greater negative impact on beetle and spider species richness than more gradual grazing management (Morris, 2000;Humbert et al, 2009); 3) Extensive management that allows plants to flower and set seed will promote phytophagous beetle species richness (Morris, 2000;Woodcock et al, 2009). …”

Omnipresence of leaf herbivory by invertebrates and leaf infection by fungal pathogens in agriculturally used grasslands of the Swiss Alps, but low plant damage

“…Several studies with herbivores and pathogens in colline and montane grassland suggest that degree and diversity of herbivory and pathogen infection are affected by land use (Wettstein and Schmid 1999;Kruess and Tscharntke 2002), site productivity (Siemann 1998;Haddad et al 2000;Mulder et al 2002), and plant species diversity (Knops et al 1999;Mitchell et al 2002;Scherber et al 2006;Haddad et al 2009;Woodcock and Pywell 2010). Moreover, altitudinal effects on the extent of herbivory have been reported (Scheidel and Bruelheide 2001).…”