Grasses and the resource availability hypothesis: the importance of silica-based defences
journal contributionposted on 2023-06-07, 14:21 authored by Fergus P. Massey, Roland A. Ennos, Susan Hartley
The resource availability hypothesis (RAH) predicts that allocation of resources to anti-herbivore defences differs between species according to their growth rate. We tested this hypothesis by assessing the growth and defence investment strategies of 18 grass species and comparing them against vole feeding preferences. In addition, we assessed the effectiveness of silica, the primary defence in many grasses, in influencing vole feeding behaviour. Across species, we found that there was a strong negative relationship between the overall investment in defence and growth rate, thus supporting predictions of the RAH. However, no such relationship was found when assessing the various individual anti-herbivore defences, suggesting that different grass species show significant variation in their relative investment in strategies such as phenolic concentration, silica concentration and leaf toughness. Silica was the most influential defensive factor in determining vole feeding preference. Experimentally induced increases in leaf silica concentration deterred vole feeding in three of the five species tested, and altered feeding preference ranks between species. The strong positive relationship between silica concentration and leaf abrasiveness, when assessed both within and between species, suggests that increased abrasiveness is the mechanism by which silica deters feeding. Although grasses are often considered to be tolerant of herbivore damage rather then defended against it, they do follow predictions of defence allocation strategy based on their growth rates, and this affects the feeding behaviour of generalist grass-feeding herbivores.
JournalJournal of Ecology
Department affiliated with
- Biology and Environmental Science Publications
NotesThe definitive version is available at www.blackwell-synergy.com. Hartley directed the study, designed the experiments and substantially contributed to the writing. This is the first test of the resource availability hypothesis in grasses, demonstrating that their growth rate is a good predictor of their defence strategy despite expectations that grasses invest in tolerance not defence.
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