BayCEER Workshop 2015
October 8, 2015
NW III, University of Bayreuth
Contrasting patterns of insect herbivory and predation pressure across a tropical rainfall and tree species richness gradient
2 Department of Zoology, University of Oxford, Oxford, OX1 3 PS, UK; Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Panama
3 Department of Zoology, University of Oxford, Oxford, OX1 3PS, UK
4 Functional and Tropical Plant Ecology, University of Bayreuth, 95440 Bayreuth, Germany; Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Panama
P 1.5 in Special SPECIES and species' specialties
Introduction
The extraordinarily high tree α-diversity of tropical lowland forests has been suggested to be shaped and maintained by specialist insect herbivores that preferentially attack the most abundant tree species in a distance- and density-dependent manner and thereby create a rare species advantage in a community compensatory trend. Insect populations and herbivory might further be enhanced by more stable and favorable climates of everwet tropical forests, driving an increase of tree species richness with rainfall. Yet, intensified top-down control in wetter, aseasonal forests could reduce the strength of herbivore imposed control on tree species. However, empirical studies on abundance-specific insect herbivory and its regulation by predators across gradients of tree species richness are lacking.
Material and Methods
The presented study quantifies insect herbivory rates in six forest sites across a neotropical rainfall and tree species richness gradient, while considering local abundances of in total 56 tree species, and simultaneously measuring predation pressure.
Results
Insect herbivory showed a mixed pattern with tree species abundance: More abundant species experienced a higher risk, but lower amount of herbivory. Overall, insect herbivory strongly decreased with increasing rainfall. Contrarily, predation pressure was higher in a wetter forest.
Conclusions
Insect herbivores might thus contribute to local tree species coexistence, yet seem unlikely to drive the increase in tree species richness with rainfall. The results support the urgent need for long-term studies on the variation of multi-trophic interactions across environmental gradients to enlighten our understanding of the processes shaping and maintaining tree α-diversity and ecosystem functioning, and ultimately develop predictions of ecosystem responses to future climate change, as well as effective conservation strategies.
Keywords: Janzen-Connell, community compensatory trend, multi-trophic interactions,tree species richness, precipitation gradient, insect herbivory, top-down control, Panama