Plant diversity and functional identity alter ant occurrence and activity in experimental grasslands

Abstract

Increasing plant species richness has been shown to positively affect the diversity of a range of other organisms, both above-and belowground. Although ants have a multitude of interactions with other organisms through their role as predators and mutualists, ants are a taxon that has rarely been investigated in studies of biodiversity effects. Ants are known to respond to changes in microclimatic conditions such as temperature and humidity, and these microclimatic conditions are known to be affected by vegetation characteristics such as standing biomass, which in turn can be affected by plant diversity. We investigated the effects of plant species richness (1-60), the number of plant functional groups (FGs; 1-4), and the presence of particular FGs on the occurrence and activity of ants, in the context of a grassland biodiversity experiment. Ant abundance, estimated as the mean number of workers in pitfall traps, and the number of colonies within plots, but not ant species richness, were negatively affected by plant species richness, and also by the identity of plant FGs, particularly legumes (negative effects) and grasses (positive effects). Statistical approaches showed that these effects were largely mediated by biotic (aboveground plant biomass: negative effect) and abiotic variables (soil temperature: positive effect). Notably, ant activity, measured as the mean number of workers foraging on baits and with a disproportionate dominance of a single species (Lasius niger), showed a more complex pattern, where plant species richness and number of FGs interacted to explain differential attractiveness to different resources (represented by sugar and tuna baits), likely representing current nutritional requirements for ants. Similarly, increasing soil temperature increased the level of ant activity, indicating that abiotic factors might impose thermal constraints on ectotherms inhabiting temperate grasslands. Our results indicate that a higher number of plant species and higher plant biomass had a negative effect on ants in experimental grasslands. Understanding the responses of an ecologically important group such as ants will allow us to infer the effects that biodiversity loss could have on animal-mediated ecosystem processes.

Plant diversity stabilizes soil temperature

“…While our findings focus mainly on temperature at 5 cm soil depth, we also analysed data collected at 15 cm (all plots) and 60 cm depth (available only in one of the four experimental blocks; Extended Data Figs. 1,7,8,9). Overall, we observed that the effects of plant diversity at deeper soil depths were consistent with the results at 5 cm soil depth, although the effects at 60 cm depth were attenuated (Extended Data Figs.…”

“…Global climate change has led to changes in soil temperatures and has caused greater variance through climate extremes 6 . Soil temperature affects many physical, chemical, and biological processes and reactions, including water and nutrient uptake 3 , microbial activities, root growth 7 , carbon dioxide flux 8 , ant activity 9 and plant pests development 10 , thereby affecting seed germination, plant growth and productivity 4 . Fluctuations in soil temperature, including sudden chilling, freezing, or warming, can have dramatic impacts on plants, microorganisms, and soil animals 11 .…”

Forest gaps increase true bug diversity by recruiting open land species

“…However, even after controlling for abundance, the higher number of species was maintained and the true bug communities in open canopy treatments were consistently more diverse. Such a pattern may be common for insects in habitats with more light and higher temperatures (Achury et al 2022 ; Lettenmaier et al 2022 ) and might be related to the metabolic ecology of ectotherms (Prather et al 2018 ), where greater quatities of direct radiation in gaps increase the abundance and population growth of insects due to higher temperatures. Concurently, an increased amount and diversity of food resources, available for herbivores (Richards and Windsor 2007 ), might enhance the higher diversity in gaps.…”

Agricultural landscape composition alters ant communities in maize fields more than plant diversity enrichment

“…The higher composition of ants in the treatment plots suggests an intrinsic demand for the resources and biotope condition patterns required by the ant species. Plant species diversity influences ants establishment and foraging parameters (Achury et al 2022).…”