Phylogenetic diversity of plants alters the effect of species richness on invertebrate herbivory

Abstract

Long-standing ecological theory proposes that diverse communities of plants should experience a decrease in herbivory. Yet previous empirical examinations of this hypothesis have revealed that plant species richness increases herbivory in just as many systems as it decreases it. In this study, I ask whether more insight into the role of plant diversity in promoting or suppressing herbivory can be gained by incorporating information about the evolutionary history of species in a community. In an old field system in southern Ontario, I surveyed communities of plants and measured levels of leaf damage on 27 species in 38 plots. I calculated a measure of phylogenetic diversity (PSE) that encapsulates information about the amount of evolutionary history represented in each of the plots and looked for a relationship between levels of herbivory and both species richness and phylogenetic diversity using a generalized linear mixed model (GLMM) that could account for variation in herbivory levels between species. I found that species richness was positively associated with herbivore damage at the plot-level, in keeping with the results from several other recent studies on this question. On the other hand, phylogenetic diversity was associated with decreased herbivory. Importantly, there was also an interaction between species richness and phylogenetic diversity, such that plots with the highest levels of herbivory were plots which had many species but only if those species tended to be closely related to one another. I propose that these results are the consequence of interactions with herbivores whose diets are phylogenetically specialized (for which I introduce the term cladophage), and how phylogenetic diversity may alter their realized host ranges. These results suggest that incorporating a phylogenetic perspective can add valuable additional insight into the role of plant diversity in explaining or predicting levels of herbivory at a whole-community scale.

Tree seedling richness, but not neighborhood composition, influences insect herbivory in a temperate deciduous forest community

“…We were also unable to assess the effects of more complex metrics of plant neighborhood similarity, such as phylogenetic distance among individuals, which may mask the role of neighbor relatedness in our study. Dinnage (), testing the resource concentration hypothesis in an old field community, found mean phylogenetic distance of neighboring plants to be negatively correlated with herbivore damage. Interestingly, he found the exact opposite relationship when using species richness, suggesting that insect herbivores may respond to plant neighborhood composition in complex ways.…”

“…While the resource concentration hypothesis has been important in both ecological research and agricultural management, a recent review of the literature revealed only moderate overall support for the expected negative relationship between plant species richness and insect herbivore load/damage (Dinnage ). Specifically, Dinnage () reported an equal number of studies showing a nonsignificant, or even positive, relationship between diversity and insect damage as did studies showing the expected negative relationship. Such positive relationships between diversity and damage are often thought to be a result of dietary mixing, where generalist herbivores benefit from feeding on a wide variety of host plant resources (Bernays et al.…”

“…), the composition of the insect community (especially the relative abundance of specialist versus generalist herbivores; Schuldt et al. ), and through variation in environmental resource gradients such as light and soil nutrients (Dinnage ).…”

Early positive effects of tree species richness on herbivory in a large‐scale forest biodiversity experiment influence tree growth

“…Plant species richness can have significant effects on the levels of herbivore damage (Jactel & Brockerhoff ; Cardinale et al . ), but the strength and direction of these effects vary among ecosystems (see Dinnage and Scherer‐Lorenzen for an overview). Differences in the degree of host specialization of the dominant herbivores may be one of the reasons for this observed variability (Jactel & Brockerhoff ).…”

Plant diversity in a nutshell: testing for small‐scale effects on trap nesting wild bees and wasps

“…Thus declining plant species richness can have cascading effects, releasing herbivores from this control and leading to reduced ecosystem functioning (Knops et al 1999, Balvanera et al 2006. The relationships between abundance and diversity of different trophic levels is therefore difficult to predict, and it is not surprising that recent studies showed varying effects of plant diversity on the abundance or diversity of higher trophic levels, yielding positive (Albrecht et al 2007, Dinnage 2013, neutral (Ebeling et al 2012) or negative (Schuldt et al 2011) relationships. However, positive effects dominate, with a reported decrease in the strength of the relationship for higher trophic levels (Scherber et al 2010a).…”