The arbuscular mycorrhizal (AM) fungi are a globally distributed group of soil organisms that play critical roles in ecosystem function. However, the ecological niches of individual AM fungal taxa are poorly understood.

Anthropogenic disturbance has generated a significant loss of biodiversity worldwide and grazing by domestic herbivores is a contributing disturbance. Although the effects of grazing on plants are commonly explored, here we address the potential multi‐trophic effects on animal biodiversity (e.g. herbivores, pollinators and predators). We conducted a meta‐analysis on 109 independent studies that tested the response of animals or plants to livestock grazing relative to livestock excluded. Across all animals, livestock exclusion increased abundance and diversity, but these effects were greatest for trophic levels directly dependent on plants, such as herbivores and pollinators. Detritivores were the only trophic level whose abundance decreased with livestock exclusion. We also found that the number of years since livestock was excluded influenced the community and that the effects of grazer exclusion on animal diversity were strongest in temperate climates. These findings synthesise the effects of livestock grazing beyond plants and demonstrate the indirect impacts of livestock grazing on multiple trophic levels in the animal community. We identified the potentially long‐term impacts that livestock grazing can have on lower trophic levels and consequences for biological conservation. We also highlight the potentially inevitable cost to global biodiversity from livestock grazing that must be balanced against socio‐economic benefits.

No abstract

Abstract1. When placing roots in the soil, plants integrate information about soil nutrients, plant neighbours and beneficial/detrimental soil organisms. While the fine-scale spatial heterogeneity in soil nutrients and plant neighbours have been described previously, virtually nothing is known about the spatial structure in soil biotic quality (measured here as a soil Biota-Induced plant Growth Response, or BIGR), or its correlation with nutrients or neighbours. Such correlations could imply trade-offs in root placement decisions.2. Theory would predict that soil BIGR is (1) negatively related to soil fertility and (2) associated with plant community structure, such that plants influence soil biota (and vice versa) through plant-soil feedbacks. We would also expect that since plants have species-specific impacts on soil organisms, spatially homogeneous plant communities should also homogenize soil BIGR.3. Here, we test these hypotheses in a semi-arid grassland by (1) characterizing the spatial structure of soil BIGR at a scale experienced by an individual plant and (2) correlating it to soil abiotic properties and plant community structure. We do so in two types of plant communities: (1) low-diversity patches dominated by an invasive grass (Bromus inermis Leyss.) and (2) patches covered mostly by native vegetation, with the expectation that dominance by Bromus would homogenize soil BIGR. 4. Soil BIGR was spatially heterogeneous, but not autocorrelated. This was true in both vegetation types (Bromus-invaded vs. native patches). Conversely, soil abiotic properties and plant community structure were frequently spatially autocorrelated at similar scales. Also, contrary to many studies, we found a positive correlation between soil BIGR and soil fertility. Soil BIGR was also associated with plant community structure. 5.Synthesis. The positive correlation between soil BIGR and some soil nutrient levels suggests that plants do not necessarily trade-off between foraging for nutrients vs.biotic interactions: nutritional cues could rather indicate the presence of beneficial soil biota. Moreover, the spatial structure in plant communities, coupled with their correlation with soil BIGR, jointly suggest that plant-soil feedbacks operate at local scales in the field: this has been identified in modelling studies as an important driver of plant coexistence. K E Y W O R D Sinformation integration, mutualisms, nutritional cues, phenotypic plasticity, plant coexistence, plant-soil feedbacks, root foraging behaviour, soil biota, soil micro-organisms, spatial scale

The size dependence of competitive interactions is starting to be highlighted as an important driver of species diversity within communities; however, it is still unknown whether all species are equally impacted by size‐asymmetric competition and what resources drive it. Here, we test species‐specific responses to size‐asymmetric competition under various soil environments by manipulating plant size as well as soil fertility, nutrient heterogeneity and the initial suppression of microbial communities within a three‐species community. Competition was primarily size‐asymmetric; however, the degree to which competition was size‐asymmetric was species‐specific, where three out of five soil treatments resulted in size‐asymmetric competition in some species but size‐symmetric competition in others. Overall, soil fertility and nutrient heterogeneity altered the degree of size‐asymmetric competition, while the initial suppression of microbial communities had no effect. Contrary to past predictions, when they had an effect, increased soil fertility and the presence of a high‐quality patch reduced the degree of size‐asymmetric competition, while the presence of a low‐quality patch increased it. This suggests that the role nutrient heterogeneity plays on the degree of size‐asymmetric competition is dependent on the quality and location of the patch relative to an individual's neighbours. These findings challenge the current understanding that competition for soil resources is always size‐symmetric and demonstrate that species within the same community may not experience the same degree of size‐dependent competition. These differential responses suggest we must consider variations in tolerance and suppression between species during size‐dependent plant–plant interactions, which may promote species coexistence as all small individuals may not be negatively impacted during size‐dependent competition. A plain language summary is available for this article.