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Abstract Plant‐microbial‐herbivore interactions play a crucial role in the structuring and maintenance of plant communities and biodiversity, yet these relationships are complex. In grassland ecosystems, herbivores have the potential to greatly influence the survival, growth and reproduction of plants. However, few studies examine interactions of above‐ and below‐ground grazing and arbuscular mycorrhizal (AM) mycorrhizal symbiosis on plant community structure.We established experimental mesocosms containing an assemblage of eight tallgrass prairie grass and forb species in native prairie soil, maintained under mycorrhizal and nonmycorrhizal conditions, with and without native herbivorous soil nematodes, and with and without grasshopper herbivory. Using factorial analysis of variance and principal component analysis, we examined: (a) the independent and interacting effects of above‐ and below‐ground herbivores on AM symbiosis in tallgrass prairie mesocosms, (b) independent and interacting effects of above‐ and below‐ground herbivores and mycorrhizal fungi on plant community structure and (c) potential influences of mycorrhizal responsiveness of host plants on herbivory tolerance and concomitant shifts in plant community composition.Treatment effects were characterized by interactions between AM fungi and both above‐ground and below‐ground herbivores, while herbivore effects were additive. The dominance of mycorrhizal‐dependent C4grasses in the presence of AM symbiosis was increased (p < 0.0001) by grasshopper herbivory but reduced (p < 0.0001) by nematode herbivory. Cool‐season C3grasses exhibited a competitive release in the absence of AM symbiosis but this effect was largely reversed in the presence of grasshopper herbivory. Forbs showed species‐specific responses to both AM fungal inoculation and the addition of herbivores. Biomass of the grazing‐avoidant, facultatively mycotrophic forbBrickellia eupatorioidesincreased (p < 0.0001) in the absence of AM symbiosis and with grasshopper herbivory, while AM‐related increases in the above‐ground biomass of mycorrhizal‐dependent forbsRudbeckia hirtaandSalvia azureawere eradicated (p < 0.0001) by grasshopper herbivory. In contrast, nematode herbivory enhanced (p = 0.001) the contribution ofSalvia azureato total biomass.Synthesis. Our research indicates that arbuscular mycorrhizal symbiosis is the key driver of dominance of C4grasses in the tallgrass prairie, with foliar and root herbivory being two mechanisms for maintenance of plant diversity.
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High among‐species variability in the context dependence of herbivory across disturbance, weather and topoedaphic gradients
Abstract Species interaction effects on populations can vary in both magnitude (i.e. strong vs. weak) and sign (positive, negative, or no effect). Context‐dependent effects of species interactions occur when the sign or strength of the interaction's effect on population growth rate changes across abiotic gradients.We know that species can vary substantially in the degree of context dependence they exhibit, even across similar abiotic gradients. However, few studies have characterised context dependence of co‐occurring species, limiting our ability to understand the implications of context dependence for species interaction effects on community composition.Using over three decades of data collected for 13 tallgrass prairie forbs at the Konza Prairie Biological Station, we parameterise density structured population models that predict population dynamics as functions of abiotic conditions and bison herbivory. We use these models to estimate the degree of context dependence in responses to bison herbivory for 13 species across three abiotic gradients: weather, fire frequency and soil type.All species showed significant context dependence for fire frequency in the same direction, though with variable magnitude, such that herbivory increased cover with more frequent fires. Context dependence with weather and soil type varied dramatically across species in both direction and magnitude. For example, herbivory effects on 3/13 species were stronger in wet conditions, but herbivory effects on 5/13 species were stronger in dry conditions. Thus, context dependence exhibited by individual species, as opposed to effects of abiotic conditions on the relative abundances of species, could generate much of the weather‐dependent effects of herbivory on community composition.Synthesis: Our work suggests that species can vary dramatically in the presence, direction and magnitude of context dependence, even when occurring in the same community and when considering the same species interaction (i.e. response to a herbivore). In addition, we find that context dependence could drive substantial variation in the effect of species interactions on community characteristics (e.g. composition) across multiple abiotic gradients.
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- Award ID(s):
- 2025849
- PAR ID:
- 10633915
- Publisher / Repository:
- British Ecological Society
- Date Published:
- Journal Name:
- Journal of Ecology
- Volume:
- 112
- Issue:
- 10
- ISSN:
- 0022-0477
- Page Range / eLocation ID:
- 2237 to 2248
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1111/1365-2745.14390
