From landscape to host-plant scales: Bottom-up heterogeneity affects invertebrate diversity and interactions

Vanbergen, Adam John. 2006. From landscape to host-plant scales: Bottom-up heterogeneity affects invertebrate diversity and interactions. PhD Thesis, Cardiff University.

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Abstract

The influence of ecological heterogeneity on invertebrate diversity, trophic guild structure, and host-parasitoid interactions was assessed at landscape, habitat and host-plant scales. Variation in the cover of forest and spatial heterogeneity of six landscapes affected the diversity of epigeal beetles and soil fauna, indicating human land-use can structure communities that operate at fine spatial scales. Invertebrate taxon identity determined if species richness, abundance or both were affected by landscape structure and whether the relationship was linear or hump-shaped. Above-ground diversity positively correlated with soil fauna diversity, but worm and collembola diversity correlated with different plant functional groups. Using the presence of cattle grazing in birch woodlands the impact of disturbance to semi-natural habitat on invertebrate diversity and trophic interactions was studied. Grazing led to a reduction in the height of understorey vegetation, and concomitant increase in plant diversity. This grazing-dependent habitat heterogeneity was correlated with a decline in the diversity of generalist secondary consumers but left herbivores unaffected. A host-parasitoid interaction was affected by the presence of cattle in birch woods. Increased floral diversity in the grazed sward indirectly (via increases in host density) and directly increased parasitism rates, a rare example of a tertiary trophic level being positively affected by anthropogenic disturbance. Using this host-parasitoid system we examined the influence of habitat patch size and isolation on this antagonistic interaction. The largest patches supported the greatest herbivore densities, but the parasitoid was unaffected. This differential impact of habitat structure meant that parasitism was inversely density-dependent and the potential stability of the interaction (CV > 1) was reduced, providing a refuge from parasitism for the host. Bottom-up sources of heterogeneity at different scales affect diversity at higher trophic levels. Anthropogenic disturbance to plant communities can alter trophic guild structure and interactions between insect species.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Biosciences
Subjects:	Q Science > Q Science (General)
ISBN:	9781303205514
Funders:	CEH Science budget
Date of First Compliant Deposit:	30 March 2016
Last Modified:	12 Feb 2016 23:15
URI:	https://orca.cardiff.ac.uk/id/eprint/56104

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