Local and landscape effects in a host–parasitoid interaction network along a forest–cropland gradient

Abstract

Land-use driven habitat modification is a major driver of biodiversity loss and impoverishment of interaction diversity. This may affect ecosystem services such as pollination and biological control. Our objective is to analyze the effects of local (nesting environment: farms vs. tree stands) and landscape (forest-cropland gradient) factors on the structure and composition of a cavity-nesting bee-wasp (CNBW) community, their nests associates (henceforth parasitoids), and their interactions. We set up 24 nest-trapping stations in a fragmented, extensively farmed area of ~100 km². We obtained 2035 nests containing 7572 brood cells representing 17 bee and 18 wasp species, attacked by 20 parasitoid species. Community structure and composition, as well as network structure, were much more dependent on local than on landscape factors. Host abundance and richness were higher in farms. In addition, host abundance was positively correlated to cropland cover. We also found highly significant differences between nesting environments in host community composition. Structure and composition of the parasitoid community were conditioned by the structure and composition of the host community. Network structure was affected by nesting environment but not by landscape factors. Interactions tended to be more diverse in farms. This result was mostly explained by differences in network size (greater in farms). However, generality was significantly higher in farms even after controlling for network size, indicating that differences in species' interaction patterns associated to differences in community composition between the two nesting environments are also affecting network structure. In conclusion, open habitats associated with extensively farmed exploitations favor local CNBW diversity (especially bees) and result in more complex host-parasitoid interaction networks in comparison to forested areas. The conservation value of this kind of open habitat is important in view of the progressive abandonment of extensively cultivated farmland taking place in Europe at the expense of agricultural intensification and reforestation.

Spatial variability of hosts, parasitoids and their interactions across a homogeneous landscape

“…Since parasitoids tend to have high levels of trophic specialization (Hawkins, 1994; Jeffs & Lewis, 2013; Poulin et al, 2011), we might expect a high correspondence between host and parasitoids communities. Thus, former studies conducted in contrasted habitat types also showed a high dependency of the community structure of the higher trophic level on the lower trophic level (Albrecht et al, 2007; Ebeling, Klein, Weisser, & Tscharntke, 2012; Osorio et al, 2015; Weiner, Werner, Linsenmair, & Blüthgen, 2014). However, and again refuting our second hypothesis, we did not find a strong matching in species composition between hosts and parasitoids across space, indicating that host‐parasitoid systems can be less specialized than previously thought (Blüthgen et al, 2007; Fontaine et al, 2009; Price, 1997; Schowalter, 1996).…”

“…Previous studies working with cavity‐nesting bees and wasps analyze composition differences between seasons, habitats, or environmental gradients (Albrecht, Duelli, Schmid, & Müller, 2007, Tylianakis, Tscharntke, & Lewis, 2007, Osorio, Arnan, Bassols, Vicens, & Bosch, 2015, Osorio‐Canadas et al, 2018, Morris et al, 2014, Staab et al, 2016; review in Staab et al, 2018). Conversely, our study was conducted across a habitat that can be considered uniform (at a landscape scale), with no physical barriers or strong environmental gradients and dominated by a single vegetation type, and addresses spatial variability at a local scale (distance between plots is ca.…”

Trap nests for bees and wasps to analyse trophic interactions in changing environments—A systematic overview and user guide

“…These findings also support general biodiversity‐ecosystem functioning theory (Cardinale et al., ) and the emerging hypothesis that bottom‐up effects of plant diversity on higher trophic levels already occur at small spatial scales (Albrecht et al., ; Ebeling et al., ; Fabian et al., ). Differing flower availability also explains why bees usually numerically dominate trap‐nesting communities in open landscapes (e.g., Osorio et al., ; Steckel et al., ), while in closed forests, wasps are more abundant (e.g., Staab et al., ; Stangler, Hanson, & Steffan‐Dewenter, ).…”

“…Nevertheless, representing organisms in a high trophic level and thus being especially sensitive to environmental change, direct influences of landscape variables such as habitat isolation and fragmentation (e.g., Schüepp, Herrmann, Herzog, & Schmidt-Entling, 2011), forest cover (e.g., Klein et al, 2006) or plant diversity (e.g., Staab et al, 2016; following the enemies hypothesis: Root, 1973) on parasitoids have been shown. Landscape variables not only influence parasitoid diversity but also host-parasitoid interaction networks, which are usually simpler and less stable in more intensively used landscapes (Osorio et al, 2015;Tylianakis et al, 2007). Conversely, habitat restoration can increase the stability of host-parasitoid interactions in trap nests (Albrecht et al, 2007) (Matos et al, 2013;Stangler et al, 2015).…”

“…Even though parasitoids in trap nests attack potentially beneficial insects, parasitoid diversity and parasitism rates can be used as proxies for overall parasitism pressure (e.g., Albrecht et al., ; Klein, Steffan‐Dewenter, & Tscharntke, ; Steckel et al., ), e.g., representing pest control services in agricultural ecosystems. Thus, trap nests simultaneously reveal multiple interaction types spanning multiple trophic levels, making them an ideal tool to investigate species interaction networks and to test how interactions are influenced by natural (Morris, Sinclair, & Burwell, ; Staab et al., ) and anthropogenic (Osorio, Arnan, Bassols, Vicens, & Bosch, ; Tylianakis et al., ) changes in the environment.…”