Plant architecture and vegetation structure: Two ways for insect herbivores to escape parasitism

Abstract

Abstract.Interactions between herbivorous insects and their parasitoids occur in highly structured and complex environments. Habitat structure can be an important factor affecting ecological interactions between different trophic levels. In this study the influence of plant architecture and surrounding vegetation structure on the interaction between the tansy leaf beetle, Galeruca tanaceti L. (Coleoptera: Chrysomelidae) and its egg parasitoid, Oomyzus galerucivorus Hedqvist (Hymenoptera: Eulophidae), was investigated at two small spatial scales in the field. It was expected that high and structurally complex plants or vegetation represent an enemy free space for the herbivore by making host search more difficult for the parasitoid. At the scale of individual plants, plant height had a positive influence on herbivore oviposition and egg clutch height a negative impact on parasitism. In addition, the beetle was more likely to oviposit on simple plants than on plants with branches, while the parasitoid remained unaffected by the degree of branching. At the microhabitat scale (r = 0.1 m around an oviposition site), both height and density of the vegetation affected beetle oviposition positively and egg parasitism negatively. The herbivore and its parasitoid, therefore, were influenced in opposite ways by habitat structure at both spatial scales investigated, suggesting the existence of an enemy free space for the herbivores' eggs on tall plants and in tall and complex vegetation. This study indicates that structural components of the environment are important for interactions among organisms of different trophic levels.

Construction of energy landscapes can clarify the movement and distribution of foraging animals

“…For example, although it is widely accepted that many birds enhance their flight capacities by making use of predictable sources of rising air [5] and that terrestrial animals expend more energy moving over soft substrate than hard [6], general consideration of the energetic costs of animals moving through their variable landscapes is minimal (but see [7]). Landscapes vary in character in both space and time with, for example, heterogeneous vegetation landscapes changing during succession [8,9] and over the growing season [10], becoming correspondingly more problematic for animals to move through [11]. Indeed, the degree of variation in the landscape (e.g.…”

Opportunistic predator prefers habitat complexity that exposes prey while reducing cannibalism and intraguild encounters

“…Interestingly, interactions between arthropod predators seem to be more strongly affected by structure than the consumption of prey from a different trophic level (Roda et al 2000;Finke and Denno 2002;Obermaier et al 2008). A recent metaanalysis concluded that habitat structure should promote persistence of predators by reducing intraguild predation (Janssen et al 2007), which can have important impacts on herbivore control (Finke and Denno 2006).…”

Are macrophyte-dwelling Chironomidae (Diptera) largely opportunistic in selecting plant species?

“…Langelotto & Denno, 2004;Crist et al, 2006;Obermaier et al, 2008;Randlkofer et al, 2009). In terrestrial systems density, height and fragmentation of the vegetation seem to be the most important at the habitat level and at the individual plant level it is mainly plant height that has a strong positive influence on herbivore distribution and oviposition (Crist et al, 2006;Obermaier et al, 2008;Randlkofer et Fig. 6.…”