The resource availability hypothesis revisited: a meta‐analysis

Abstract

Summary1. Several theories have provided a framework for understanding variation in plant defence against herbivores. Among them, the plant apparency theory and the resource availability hypothesis (RAH) have aimed to explain the patterns of defence investment and the selective pressures that have led to the variety of defensive strategies across species. Here we provide a historical review of both theories, present evidence that shaped their development and contrast their predictions. 2. We present the results of a meta-analysis of the utility of the RAH 25 years after it was proposed and compare it to apparency theory. We performed a meta-analysis of 50 studies that have examined plant growth, defences and herbivory in relation to resource availability across latitude and ontogeny. Specifically, we tested four predictions that follow the RAH: (i) species adapted to resource-rich environments have intrinsically faster growth rates than species adapted to resourcepoor environments; (ii) fast-growing species have shorter leaf lifetimes than slow-growing species; (iii) fast-growing species have lower amounts of constitutive defences than slow-growing species; and (iv) fast-growing species support higher herbivory rates than slow-growing species. 3. Our results confirm the predictions that species adapted to resource-poor environments grow inherently more slowly, invest more in constitutive defences and support lower herbivory than species from more productive habitats. Our data also showed that variation in growth rate among species better explains the differences in herbivory than variation in apparency, suggesting that the evolution of different defensive strategies across species is resource, rather than herbivore driven. We also found that the application of this theory appears robust across latitude and ontogeny, as the magnitude of the effect sizes for most of the predictions did not vary significantly between ecosystems or across ontogenic stages. 4. We conclude that the RAH has served as a valid framework for investigating the patterns of plant defences and that its applicability is quite general.

Do soil fertilization and forest canopy foliage affect the growth and photosynthesis of Amazonian saplings?

“…A mass often declines as LMA increases (Osnas et al, 2013), and in several species leaf longevity is greater in thick (high-LMA) leaves than in thinner ones, as an adaptive strategy to compensate for the high investment in constitutive defenses to avoid leaf damage (i.e. herbivory; Endara and Coley, 2011). The slight trend of A max to respond to changes in LT but not to variation in LMA suggests that leaf density (the other component of LMA) negatively affects A max , as previously reported for the A mass /leaf density relationship (Niinemets, 1999).…”

Laccase detoxification mediates the nutritional alliance between leaf-cutting ants and fungus-garden symbionts

“…They are primarily present in the waxy leaf cuticle and cell vacuoles and, provided sufficient plant resources are available, particularly abundant in the fast-growing plant parts that many large grazers and browsers prefer (6).…”

Ungulate saliva inhibits a grass–endophyte mutualism

“…According to widely supported plant defence theories (i.e. resource availability hypothesis and protein competition model), the discrepancy between populations may arise because constitutive defences are evolutionarily favoured in marginal environments [17,18]. Plants near F. rubra's southern limit may have therefore evolved permanent upregulation as an adaptation for water-stressed conditions.…”