Consequences for host–parasitoid interactions of grazing-dependent habitat heterogeneity
Article first published online: 19 APR 2006
Journal of Animal Ecology
Volume 75, Issue 3, pages 789–801, May 2006
How to Cite
VANBERGEN, A. J., HAILS, R. S., WATT, A. D. and JONES, T. H. (2006), Consequences for host–parasitoid interactions of grazing-dependent habitat heterogeneity. Journal of Animal Ecology, 75: 789–801. doi: 10.1111/j.1365-2656.2006.01099.x
- Issue published online: 19 APR 2006
- Article first published online: 19 APR 2006
- Received 1 November 2005; accepted 22 February 2006
- ecosystem engineer;
- Pteromalus elevatus;
- Tephritis conura
- 1Environmental heterogeneity can produce effects that cascade up to higher trophic levels and affect species interactions. We hypothesized that grazing-dependent habitat heterogeneity and grazing-independent host plant heterogeneity would influence directly and indirectly a host–parasitoid interaction in a woodland habitat.
- 2Thistles were planted randomly in 20 birch woodlands, half of which are grazed by cattle. The abundances of two species of seed herbivore and their shared parasitoid were measured, and related to habitat and host-plant heterogeneity.
- 3The presence of cattle grazing created a structurally and compositionally distinct plant assemblage from the ungrazed seminatural situation. Grazing did not affect the number or dispersion of the host plant underpinning the host–parasitoid interaction.
- 4The density of one insect herbivore, Tephritis conura, and its parasitoid Pteromalus elevatus was significantly increased by the presence of cattle; but another herbivore, Xyphosia miliaria, was unaffected. The percentage of parasitism of T. conura was increased in grazed habitat occurring at twice the rate found in ungrazed habitat.
- 5The increase in T. conura abundance was correlated with increased species richness and cover of forbs in grazed sites. This effect of grazing-dependent habitat variation on host insect density cascaded up to parasitoid density and percentage of parasitism. Habitat heterogeneity had a further direct, positive effect on parasitoid density and percentage of parasitism after controlling for host-insect density.
- 6Independent of grazing, heterogeneity in host-plant flowering, architecture and stature further affected T. conura and its parasitoid's densities. Parasitoid density was also affected by the dispersion of the host plant.
- 7A combination of habitat and host-plant scale environmental heterogeneity influenced a host–parasitoid interaction indirectly and directly, providing a rare example of an anthropogenic disturbance positively affecting a tertiary trophic level. This finding highlights the need to consider not only the importance of bottom-up effects for top-down processes, but also the role of environmental heterogeneity arising from anthropogenic disturbance for trophic interactions such as parasitism.