COS 81-8 - Herbivore-mediated apparent competition predicts plant performance at the community level

Thursday, August 15, 2019: 10:30 AM
L016, Kentucky International Convention Center
Warwick Allen1,2, Lauren Waller1,2, Jason M. Tylianakis2,3, Barbara I.P. Barratt4 and Ian A. Dickie2, (1)The Bio-Protection Research Centre, Lincoln University, Lincoln, New Zealand, (2)School of Biological Sciences, University of Canterbury, Christchurch, New Zealand, (3)Department of Life Sciences, Imperial College London, (4)AgResearch Invermay, Mosgiel, New Zealand
Background/Question/Methods

Indirect species interactions mediated by shared natural enemies (e.g., apparent competition) play a fundamental role in ecological communities, but we lack a framework for predicting their strength and impact. We used a network approach to investigate whether plant provenance, phylogenetic relatedness, and trait similarity can predict the potential for apparent competition. We manipulated plant-herbivore interaction networks for 180 plant communities in a large mesocosm experiment, designed from a pool of 39 plant species and varying in provenance, phylogeny, and traits (e.g., woodiness, mycorrhizal status). Half of the mesocosms had 20 species of invertebrate herbivores added to herbivore exclusion cages, while the other half experienced reduced herbivory. We constructed plant-herbivore interaction networks and used them to calculate each species’ potential to exert or suffer from apparent competition based on shared herbivores. We tested whether 1) plants that shared many herbivores with others had lower biomass; 2) exotic and native plants differed in their potential for apparent competition; and 3) potential for apparent competition can be predicted by plant phylogenetic relatedness or trait similarity.

Results/Conclusions

Plant biomass was lower for plants that shared a greater proportion of their herbivores with other community members, but only in mesocosms with herbivores added. This finding suggests that apparent competition was a key contributor to final plant biomass, rather than other factors such as resource competition. Interestingly, exotic plant species had higher potential to exert apparent competition effects than native species, driven by their higher herbivore loads. Our results suggest that indirect effects can be predicted at the community level by estimating the potential for apparent competition from quantitative interaction networks. We further explore pairwise strength of apparent competition between species in the context of phylogenetic relatedness, trait similarity, and other types of species interactions. Our findings have important implications for understanding the causes and consequences of biological invasions and predicting indirect outcomes of proposed ecosystem management practices (e.g., biological control or species eradication).