Pollinator behavioural responses to grazing intensity

Abstract

It has been suggested that intensive grazing management, aimed at maintaining plant diversity, might not be the optimal choice to preserve diversity of insects in semi-natural pastures. In the present study the behaviour of flower visiting insects was studied in two semi-natural pastures in central Sweden. Two grazing treatments were established with one grazed from mid-May, ''continuous'', and one grazed from mid-July, ''late''. Flower visitors were followed for 9 weeks in summer 2003 in 7 pairs of 5 · 5 m plots on two sides of a fence dividing the two grazing treatments. Visitor behaviour was studied on three decision levels between: (1) habitats, (2) flowers and (3) activities on flowers. The pattern varied between decision levels: More species and individual visitors chose to forage in the late grazing treatment. Visitation rate and flower constancy did not differ between treatments and was related, to a large extent, to plant species richness. In relation to flowers, insects utilized a broader diversity of activities in the late grazing treatment. All patterns were consistent across sites and during the whole study period. The differences in pollinator abundance and activities on flowers were best explained by the higher abundance of flowers. It is suggested that studies of insect behaviour may be a useful tool when deciding on management recommendations. Late grazing is recommended as a useful management regime and might potentially function as a substitute for mowing in the future.

Investigating plant—pollinator relationships in the Aegean: the approaches of the project POL-AEGIS (The pollinators of the Aegean archipelago: diversity and threats)

“…We expect that this approach will produce results that will give a prospective description of the future under different climate change scenarios and allow us to forecast the impact of climate change on pollinator diversity and pollination networks, highlighting possible local extinction threats. In the case of temporal mismatches between plants and their pollinators we expect a disruption of the pollination network, which will be compared with already studied networks of the region and various null models (Petanidou et al, 2008;Schweiger et al, 2008;Kallimanis et al, 2009 Topic 5: Impacts of livestock grazing on pollinator diversity, pollination services, and plant-pollinator network structure Plant-pollinator interactions represent ecosystem functions that are influenced considerably by the extent, intensity and type of grazing (Carvell, 2002;Kruess and Tscharntke, 2002;Sjödin, 2007). Consequently, grazing constitutes a regulating factor in the structure and dynamics of pollinator communities (Potts et al, 2003b;Navarro et al, 2006), further influencing pollination services.…”

“…With respect to insect pollinators, grazing can: (i) influence the foraging behaviour of pollinators because of a change in floral rewards (Chittka et al, 1999;Vohland et al, 2005), or influence their movement when, for example, grazing alters the height of the vegetation (Goulson, 2000); (ii) influence the number of nesting sites available to ground-dwelling wild pollinators by causing an expansion of areas of bare soil, which are favoured nesting sites (Petanidou and Ellis, 1996;Potts et al, 2003a), or alter the availability of water, that is essential for nest construction (Gess and Gess, 1993;Vinson et al, 1993); (iii) directly influence the survival rate of pollinators by trampling of the grazing animals (Sjödin, 2007) or indirectly, by decreasing the extent of shelters in the vegetation (Potts et al, 2009); and (iv) increase the abundance of bees whereas the influence on their diversity remains unknown (Vulliamy et al, 2006). This topic aims at investigating how the pollinator diversity and effectiveness, as well as the structure of plant-pollinator networks are influenced by various grazing intensities.…”

How do sheep affect plant communities and arthropod populations in temperate grasslands?

“…Exploiting plots during short grazing periods decreases the time grassland arthropods are exposed to disturbance compared with continuous grazing, with late grazing favoring phytophagous species that can benefit from higher food resources throughout most of the grazing season. Late grazing and fertilizer cessation can also favor pollinator abundance and species richness via positive trophic interactions with flowering plants (Carvell, 2002;Sjö din, 2007).…”

“…Exploiting plots during short grazing periods decreases the time grassland arthropods are exposed to disturbance compared with continuous grazing, with late grazing favoring phytophagous species that can benefit from higher food resources throughout most of the grazing season. Late grazing and fertilizer cessation can also favor pollinator abundance and species richness via positive trophic interactions with flowering plants (Carvell, 2002;Sjö din, 2007).Sheep differ from large ruminants in terms of their nutrient requirements relative to gut capacity, their ability to feed selectively and their slightly lower ability to digest low-quality forages (Demment and Greenwood, 1988). Their behavioral adjustments in response to reduced food availability are therefore chiefly geared to maintaining the nutrient value of the diet (Hodgson et al, 1991;Dumont et al, 1995;Garcia et al, 2003).…”

Towards an agroecological assessment of dairy systems: proposal for a set of criteria suited to mountain farming

“…Milchunas et al (1988 predicted a bell-shaped relationship between grazing intensity and plant diversity: high stocking rates favour competitive grasses with high leaf-growth rate and white clover, whereas at the other end of the gradient very low grazing intensities enhance dominance of tall grasses that exert competition for light on small-sized species. Besides the reduction of stocking rate, practices that favour flowering intensity, for example, excluding animals from pastures at flowering peak (Farruggia et al, 2012), late grazing (Sjödin, 2007), preserving legume-rich grasslands (Goulson et al, 2005) and introducing wildflower margin strips at the edge of arable fields (Aviron et al, 2011), benefit biodiversity, as plants that are allowed to flower provide important resources for nectar-and pollen-feeding guilds of invertebrates.…”