The Impact of Tree Diversity on Different Aspects of Insect Herbivory along a Global Temperature Gradient - A Meta-Analysis.
Forests with higher tree diversity are often assumed to be more resistant to insect herbivores but whether this effect depends on climatic conditions is so far poorly understood. In particular, a forest's resistance to herbivory may depend on mean annual temperature (MAT) as a key driver of plant and insect phenology. We carried out a global meta-analysis on regression coefficients between tree diversity and four aspects of insect herbivory, namely herbivore damage, abundance, incidence rate and species richness. To test for a potential shift of tree diversity effects along a global gradient of MAT we applied mixed-effects models and estimated grand mean effect sizes and the influence of MAT, experimental vs. observational studies and herbivores diet breadth. There was no overall effect of tree diversity on the pooled effect sizes of insect herbivore damage, abundance and incidence rate. However, when analysed separately, we found positive grand mean effect sizes for herbivore abundance and species richness. For herbivore damage and incidence rate we found a significant but opposing shift along a gradient of MAT indicating that with increasing MAT diversity effects on herbivore damage tend towards associational resistance whereas diversity effects on incidence rates tend towards associational susceptibility. Our results contradict previous meta-analyses reporting overall associational resistance to insect herbivores in mixed forests. Instead, we report that tree diversity effects on insect herbivores can follow a biogeographic pattern calling for further in-depth studies in this field.
Department of Community Ecology, Helmholtz-Centre for Environmental Research, Halle (Saale), Germany.|Institute of Biology/Geobotany and Botanical Garden, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
Stephan
http://orcid.org/0000-0003-3585-5837
S
Kambach
Department of Community Ecology, Helmholtz-Centre for Environmental Research, Halle (Saale), Germany.|Institute of Biology/Geobotany and Botanical Garden, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.|German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Leipzig, Germany.
Ingolf
I
Kühn
BIOGECO, INRA, Univ. Bordeaux, 33610 Cestas, France.
Bastien
B
Castagneyrol
Institute of Biology/Geobotany and Botanical Garden, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.|German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Leipzig, Germany.
Helge
H
Bruelheide
D063147:Animal Distribution / Q000502:physiology*; D000818:Animals; D044822:Biodiversity; D065928:Forests; D060434:Herbivory / Q000502:physiology*; D006790:Host-Parasite Interactions; D007313:Insecta / Q000502:physiology*; D015233:Models, Statistical; D011157:Population Dynamics; D018401:Sample Size; D013696:Temperature; D014197:Trees / Q000469:parasitology*