Conservation Biocontrol in Fragmented Landscapes: Persistence and Parasitation in a Host-Parasitoid Model

Abstract

Abstract:In the context of agricultural landscapes, conservation biocontrol practitioners attempt to secure and enhance the presence and effectiveness of natural enemies of insect pest species, for example parasitoids. Conservation biocontrol aims at maximizing both parasitoid persistence and parasitation rate. It is, however, still poorly understood how the amount, fragmentation and isolation of non-crop habitat of the host and its parasitoid affect persistence and parasitation rate. We developed a spatially explicit simulation model of a host and its specialized parasitoid and simulated their spatiotemporal population dynamics in virtual landscapes. We found that the total habitat amount in the landscape modulates the impact of fragmentation on parasitoid persistence. If habitat is abundant, parasitoid persistence decreases with fragmentation, whereas if habitat is scarce, persistence is highest at intermediate levels of fragmentation. In any case, persistence is best for intermediate levels of isolation. Parasitation rate, on the other hand, is negatively influenced by fragmentation and isolation regardless of the habitat amount. Our results suggest that in landscapes with abundant habitat, both parasitation rates and parasitoid persistence can be increased by arranging habitat to be as clumped as possible. However, if habitat is scarce, landscape management can optimize either parasitation rates or parasitoid persistence but not both simultaneously.

Habitat amount modulates the effect of patch isolation on host-parasitoid interactions

“…Our results support theoretical predictions that parasitism decreases with patch isolation (Visser et al, 2009). However, we found pronounced and temporally consistent interactive effects of habitat amount and isolation on parasitoid abundance and parasitism rates.…”

“…In particular, potential interactive effects among habitat loss and isolation on trophic interactions remain largely unexplored (Herrera and Doblas-Miranda, 2013). Visser et al (2009) modeled such interactive effects for a simple host-parasitoid system, predicting interactions on parasitoid persistence, whereas parasitism should be primarily negatively affected by isolation, regardless of habitat amount. In contrast to these predictions, Fahrig (2013) posits that ecological responses at the patch level should be essentially driven by the amount of habitat within the landscape, irrespective of patch isolation and size (habitat amount hypothesis).…”

“…Because species at higher positions in the food chain may be particularly vulnerable to habitat loss (Holt et al, 1999;Kruess and Tscharntke, 2000;Cagnolo et al, 2009;Valladares et al, 2012), species richness of parasitoids should increase strongly with the amount of habitat in a landscape, even if the size of the sampled habitat patch is constant (Fahrig, 2013). If higher parasitoid diversity leads to higher parasitism rate (e.g., Tylianakis et al, 2006;Fenoglio et al, 2012), negative effects of isolation on parasitism rate, as predicted by Visser et al (2009), may be mitigated by higher habitat amount within the landscape. As a result, decline in parasitism rate with isolation should be more pronounced in simple, habitat-poor landscapes compared to more complex landscapes with high habitat amount.…”

The role of ecological models in linking ecological risk assessment to ecosystem services in agroecosystems

“…A more biologically detailed system was modeled by Visser et al (2009) who developed a spatially explicit simulation model for a pest, the rape pollen beetle, and its parasitoid to investigate the role of offcrop habitat, including the amount, fragmentation and isolation, for parasitoid persistence. Both species can reside in a single habitat cell where the processes of reproduction, mortality and parasitation occur.…”

Local and Landscape Drivers of Ant Parasitism in a Coffee Landscape

“…Thus, we must focus on understanding how to promote less intensive agricultural production in order to prevent the increase of insect pests, reduced pollination, and loss of other ecological services (Kruess and Tscharntke 1994, Steffan-Dewenter 2002, Jha and Vandermeer 2010. Agricultural intensification and habitat complexity may strongly affect host-parasitoid interactions Feener 2007, 2012;Visser et al 2009;Jonsson et al 2012). Natural enemies, especially the parasitic Hymenoptera, play an important role in pest regulation (Rodríguez andHawkins 2000, Varone andBriano 2009), and parasitoids and parasitism are affected by local habitat changes and changes at the landscape level (Klein et al 2002, Fischer andLindenmayer 2007).…”