Both arthropods and large grazing herbivores are important components and drivers of biodiversity in grassland ecosystems, but a synthesis of how arthropod diversity is affected by large herbivores has been largely missing. To fill this gap, we conducted a literature search, which yielded 141 studies on this topic of which 24 simultaneously investigated plant and arthropod diversity. Using the data from these 24 studies, we compared the responses of plant and arthropod diversity to an increase in grazing intensity. This quantitative assessment showed no overall significant effect of increasing grazing intensity on plant diversity, while arthropod diversity was generally negatively affected. To understand these negative effects, we explored the mechanisms by which large herbivores affect arthropod communities: direct effects, changes in vegetation structure, changes in plant community composition, changes in soil conditions, and cascading effects within the arthropod interaction web. We identify three main factors determining the effects of large herbivores on arthropod diversity: (i) unintentional predation and increased disturbance, (ii) decreases in total resource abundance for arthropods (biomass) and (iii) changes in plant diversity, vegetation structure and abiotic conditions. In general, heterogeneity in vegetation structure and abiotic conditions increases at intermediate grazing intensity, but declines at both low and high grazing intensity. We conclude that large herbivores can only increase arthropod diversity if they cause an increase in (a)biotic heterogeneity, and then only if this increase is large enough to compensate for the loss of total resource abundance and the increased mortality rate. This is expected to occur only at low herbivore densities or with spatio-temporal variation in herbivore densities. As we demonstrate that arthropod diversity is often more negatively affected by grazing than plant diversity, we strongly recommend considering the specific requirements of arthropods when applying grazing management and to include arthropods in monitoring schemes. Conservation strategies aiming at maximizing heterogeneity, including regulation of herbivore densities (through human interventions or top-down control), maintenance of different types of management in close proximity and rotational grazing regimes, are the most promising options to conserve arthropod diversity.

/pdf/effects-of-large-herbivores-on-grassland-arthropod-diversity-4fnfljuaok.pdf

Effects of large herbivores on grassland arthropod diversity

Biotic interactions affecting habitat use of myrmecophilous butterflies in Northern Europe

Using ants for rangeland monitoring: Global patterns in the responses of ant communities to grazing

Species richness, equitability, and abundance of ants in disturbed landscapes

Results The analyses of generic composition and community structure were congruent, supporting a strong affinity between the Western Palaearctic ant fauna and modern Indomalayan and Australasian assemblages, and of a widespread Holarctic ant palaeofauna, and affinity between fossil Caribbean and modern Neotropical faunas. In addition, neither generic composition nor community structure of fossil assemblages showed evidence of taphonomic bias towards arboreal taxa.

Integration of global fossil and modern biodiversity data reveals dynamism and stasis in ant macroecological patterns

We examined the role of cattle grazing, plants, and soil attributes on species richness, abundance, and composition of ground-dwelling ants in northern California serpentine and nonserpentine grasslands. In addition, we analyzed the relationship between three numerically dominant ant species and overall ant species richness and abundance. We used pitfall traps to collect worker ants at 80 sites over a 2-wk period in May 2002. Twenty species of ants were identified from a total of 5,149 worker ants; 80% of all individuals belonged to three dominant species: Messor andrei (Mayr), Pheidole californica Mayr, and Solenopsis xyloni McCook. Ant species richness was negatively affected by grazing on nonserpentine soils only. In general, soil chemistry and texture formed the most consistent associations with the ant community. Plants were less important than soil attributes in explaining variation in overall ant species richness and abundance, but the abundance of the three dominant ant species was significantly correlated with plant biomass or plant richness. Based on logistic regression analysis, the presence or absence of each dominant ant species was negatively correlated with the abundance of the other two dominants. However, the three numerically dominant ant species did not correlate with overall ant species richness or abundance.

https://bioone.org/journals/environmental-entomology/volume-34/issue-1/0046-225X-34.1.96/Species-Richness-Abundance-and-Composition-of-Ground-Dwelling-Ants-in/10.1603/0046-225X-34.1.96.pdf

April M. Boulton

Papers

Species Richness, Abundance, and Composition of Ground-Dwelling Ants in Northern California Grasslands: Role of Plants, Soil, and Grazing