Interaction diversity within quantified insect food webs in restored and adjacent intensively managed meadows

Abstract

Summary 1.We studied the community and food-web structure of trap-nesting insects in restored meadows and at increasing distances within intensively managed grassland at 13 sites in Switzerland to test if declining species diversity correlates with declining interaction diversity and changes in food-web structure. 2. We analysed 49 quantitative food webs consisting of a total of 1382 trophic interactions involving 39 host/prey insect species and 14 parasitoid/predator insect species. Species richness and abundance of three functional groups, bees and wasps as the lower trophic level and natural enemies as the higher trophic level, were significantly higher in restored than in adjacent intensively managed meadows. Diversity and abundance of specific trophic interactions also declined from restored to intensively managed meadows. 3. The proportion of attacked brood cells and the mortality of bees and wasps due to natural enemies were significantly higher in restored than in intensively managed meadows. Bee abundance and the rate of attacked brood cells of bees declined with increasing distance from restored meadows. These findings indicate that interaction diversity declines more rapidly than species diversity in our study system. 4. Quantitative measures of food-web structure (linkage density, interaction diversity, interaction evenness and compartment diversity) were higher in restored than in intensively managed meadows. This was reflected in a higher mean number of host/prey species per consumer species (degree of generalism) in restored than in intensively managed meadows. 5. The higher insect species and interaction diversity was related to higher plant species richness in restored than in intensively managed meadows. In particular, bees and natural enemies reacted positively to increased plant diversity. 6. Our findings provide empirical evidence for the theoretical prediction that decreasing species richness at lower trophic levels should reduce species richness at higher trophic levels, and in addition lead to even stronger reductions in interaction diversity at these higher levels. Species at higher trophic levels may thus benefit relatively more than species at lower trophic levels from habitat restoration in the grassland ecosystems studied. We also demonstrate enhanced compartment diversity and lower interaction evenness in restored than in intensively managed meadows, both of which are theoretically positively associated with increased ecosystem stability in restored meadows.

Plant diversity has contrasting effects on herbivore and parasitoid abundance in Centaurea jacea flower heads

“…However, the variation in strength of the effect indicates that, although diversity may act in a similar way in different years, other drivers of herbivore abundance (such as climate or dispersal) may frequently mask the effects of plant diversity. In contrast, and in line with the Enemies Hypothesis (Root, 1973) and a range of more recent studies (Albrecht, Duelli, Schmid, & Muller, 2007; Bianchi et al., 2006; Haddad et al., 2009; Vanbergen, Hails, Watt, & Jones, 2006), parasitoid abundance increased with plant diversity. We found that both plant species richness and functional group richness were important components of diversity that affected the abundance of higher trophic levels.…”

Biodiversity, Species Interactions and Ecological Networks in a Fragmented World

“…Fragmentation should therefore have increasingly negative effects on more specialised parasitoids, and several empirical studies support this conclusion (moth parasitoids: Elzinga et al, 2007;aphid parasitoids: Rand and Tscharntke, 2007;leafminer parasitoids: Cagnolo et al, 2009; parasitoids of cavity-nesting bees and wasps: Holzschuh et al, 2010). These findings suggest that the effects of fragmentation on parasitoids will largely be mediated by altered host distributions, which are often coupled to plant densities (for herbivorous hosts) at the patch scale (Albrecht et al, 2007;Amarasekare, 2000;Cronin et al, 2004;Holzschuh et al, 2010;Kruess, 2003;Schnitzler et al, 2011;Vanbergen et al, 2007).…”

“…Coral reef photos are used by kind permission of José Eduardo Silva, Stephen Leahy, Nick Graham and James Acker (respective photo credits, from top to bottom). diversity of species (Albrecht et al, 2007). This suggests a strong impact of habitat fragmentation on trophic networks and that interaction diversity might decline more rapidly than species diversity in fragmented systems.…”

“…Biodiversity is organised at local scales into complex networks of interacting species, which provide the ecosystem processes that ultimately underpin the goods and services of value to human societies (Rossberg, 2012). These links (italicised terms, see Glossary) among interacting species are often ignored in the context of global change even though they will disappear from local communities as a precursor to local (and ultimately global) extinctions (Albrecht et al, 2007;Sabatino et al, 2010;Tylianakis et al, 2007;Woodward et al, 2010a). Understanding the causes and consequences of the loss of species interactions therefore promises to provide critical new insights into ecological responses to perturbations (Mulder et al, 2012;Tylianakis et al, 2010).…”

“…The planet's ecosystems are losing biodiversity at an accelerating rate (Dyer et al, 2010;Fahrig, 2003;Gonzalez et al, 2011;Millennium Ecosystem Assessment, 2005) due to land-use change, deforestation, agricultural intensification, pollution, urbanisation, climate change and habitat fragmentation (Albrecht et al, 2007;Hanski, 2005;Ledger et al, 2012;Meerhoff et al, 2012;Mintenbeck et al, 2012;Tilman et al, 2001). The latter in particular could severely disrupt ecological networks and the goods and services they provide (e.g.…”