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Diversity within species can have community‐level effects similar in magnitude to those of species diversity. Intraspecific diversity in producers and consumers has separately been shown to affect trophic interactions, yet we have little understanding of how variation at these two levels could simultaneously affect trophic interactions. Salt marshes dominated by Spartina alterniflora are an ideal system in which to ask this question as this plant exhibits substantial genetically based trait variation. Further, herbivores can have sizable impacts on Spartina, but the impact of herbivore trait variation is not well understood. We conducted an experiment in a Massachusetts salt marsh to determine how herbivorous crab (Sesarma reticulatum) size diversity and Spartina genotypic diversity affect the plant community. Herbivore effects on plant traits varied by herbivore size, with large crabs generally having stronger impacts on plants. At times, the effect of small crabs on plant traits depended on plant genotypic diversity. The effects of crab size diversity (i.e., small and large crabs combined) were most often predicted by the independent effects of each size class, though there were synergistic effects on stem density, flowering stems, and mean stem height. Finally, we tested whether herbivore size or size diversity could have reciprocal effects on plant genotypic diversity. Small‐ and mixed‐crab treatments promoted plant genotypic richness, whereas large crabs did not. Our results demonstrate that intraspecific diversity at multiple trophic levels can have simultaneous and sometimes interactive effects on species interactions, highlighting the importance of variation within species for understanding species interactions and community processes.
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Consumers Modulate Effects of Plant Diversity on Community Stability
ABSTRACT Biotic complexity, encompassing both competitive interactions within trophic levels and consumptive interactions among trophic levels, plays a fundamental role in maintaining ecosystem stability. While theory and experiments have established that plant diversity enhances ecosystem stability, the role of consumers in the diversity–stability relationships remains elusive. In a decade‐long grassland biodiversity experiment, we investigated how heterotrophic consumers (e.g., insects and fungi) interact with plant diversity to affect the temporal stability of plant community biomass. Plant diversity loss reduces community stability due to increased synchronisation among species but enhances the population‐level stability of the remaining plant species. Reducing trophic complexity via pesticide treatments does not directly affect either community‐ or population‐level stability but further amplifies plant species synchronisation. Our findings demonstrate that the loss of arthropod or fungal consumers can destabilise plant communities by exacerbating synchronisation, underscoring the crucial role of trophic complexity in maintaining ecological stability.
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- Award ID(s):
- 1831944
- PAR ID:
- 10582005
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Ecology Letters
- Volume:
- 28
- Issue:
- 3
- ISSN:
- 1461-023X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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