No evidence for trade‐offs in plant responses to consumer food web manipulations

Abstract

Plants face a range of trade-offs as they attempt to maximize their fitness within a complex web composed of competitors, mutualists, and herbivores. In addition to growth-defense and competition-defense trade-offs, plants must balance their response to a wide range of potential enemies including pathogens and vertebrate and invertebrate herbivores. We tested for trade-offs in plant species' responses to different types of consumers using a foodweb manipulation experiment in which we selectively excluded large vertebrate herbivores and removed foliar fungi, soil fungi, and insects from natural and experimentally planted grassland communities. We found no evidence for trade-offs in the ability of plants to defend themselves against different sets of consumers, although plants varied widely in their responses to removal of different consumer groups. In addition, the species-level responses to consumer removal in monoculture were uncorrelated with each species' response in more diverse communities, highlighting the important role of local context (e.g., competition and apparent competition) in determining the effects of consumers. Plants must balance their allocation of energy among a wide variety of tasks including growing, competing for limited resources, and defending themselves against an array of potential enemies. We found that while plant species differed greatly in their response to the removal of consumers, species that were susceptible to the effects of one consumer group (e.g., insect herbivores) also were susceptible to other consumer groups (e.g., fungal pathogens). This suggests that plants differ in their overall allocation to defense, but defense investment can proffer protection against a wide array of natural enemies. We also found that plant responses to consumers depended on the diversity of the surrounding plant community, suggesting that among-plant interactions can alter their susceptibility to the impacts of consumers.

Stability of grassland production is robust to changes in the consumer food web

“…However, like stability, asynchrony was robust to trophic manipulations despite changes in species relative abundances (Seabloom et al . ) and diversity. While our study was not designed to parse apart the specific mechanisms that can alter asynchrony, our results are concordant with suggestions that interspecific interactions may play a smaller role in community synchrony and variability than factors such as species responses to environmental fluctuations (Houlahan et al .…”

“…Our work also highlights the importance of including microbial pathogens and symbionts alongside invertebrate and vertebrate herbivores in models and experiments of trophic cascades, food web dynamics, plant community dynamics and functioning and stability of ecosystems (Mitchell 2003). Trophic impacts of foliar and soil pathogens (and symbionts) can be as large or even exceed the effects of vertebrate and invertebrate herbivores in these prairies, and removal of pathogens can cause large changes in above and belowground primary production and its temporal variability, influence foliar chemistry, plant community composition and impact grassland diversity (Borer et al 2015;Seabloom et al 2017Seabloom et al , 2018.…”

“…; Seabloom et al . , ). Consequently, when plant–heterotroph interactions are manipulated, such as by removing one or more of these heterotrophic guilds, plant communities may come to be dominated by more or less variable species, have more or less interspecific competition, and fluctuate more or less synchronously in response to abiotic factors, ultimately affecting overall ecosystem stability and the plant diversity–stability relationship (Yachi & Loreau ; Thébault & Loreau ; Loreau & de Mazancourt ).…”

“…Herbivores, for example, influence plant community composition, diversity, production, biomass, tissue allocation and chemistry via direct consumption of some species and avoidance of others, and indirect effects on interspecific interactions among plants (Augustine & McNaughton 1998;Olff & Ritchie 1998;Lind et al 2013;Borer et al 2014). Similarly, foliar and soil microbes have been shown to drive changes in plant community diversity, composition and biomass as well as strongly influence diversity-ecosystem function relationships (Holah & Alexander 1999;Mitchell 2003;Schnitzer et al 2011;Bagchi et al 2014;Seabloom et al 2017Seabloom et al , 2018. Consequently, when plant-heterotroph interactions are manipulated, such as by removing one or more of these heterotrophic guilds, plant communities may come to be dominated by more or less variable species, have more or less interspecific competition, and fluctuate more or less synchronously in response to abiotic factors, ultimately affecting overall ecosystem stability and the plant diversity-stability relationship (Yachi & Loreau 1999;Th ebault & Loreau 2005;Loreau & de Mazancourt 2013).…”

Effects of nutrient supply, herbivory, and host community on fungal endophyte diversity

“…). For example, concurrent changes in predation and nutrient supply have been observed to induce changes in the microbiome of corals (Shaver et al. 2017), and nutrients and herbivory can induce turnover in the microbial composition within plants (Faeth and Fagan , Pineda et al.…”