Abstract
Top-down control of prey by predators are magnified in productive ecosystems due to higher sustenance of prey communities. In soil micro-arthropod food webs, plant communities regulate the availability of basal resources like soil microbial biomass. Mixed plant communities are often associated with higher microbial biomass than monocultures. Therefore, top-down control is expected to be higher in soil food webs of mixed plant communities. Moreover, higher predator densities can increase the suppression of prey, which can induce interactive effects between predator densities and plant community composition on prey populations. Here, we tested the effects of predator density (predatory mites) on prey populations (Collembola) in monoculture and mixed plant communities. We hypothesized that top-down control would increase with predator density but only in the mixed plant community. Our results revealed two contrasting patterns of top-down control: stronger top-down control of prey communities in the mixed plant community, but weaker top-down control in plant monocultures in high predator density treatments. As expected, higher microbial community biomass in the mixed plant community sustained sufficiently high prey populations to support high predator density. Our results highlight the roles of plant community composition and predator densities in regulating top-down control of prey in soil food webs.
Highlights
Top-down control of prey by predators are magnified in productive ecosystems due to higher sustenance of prey communities
In treatments with high predator densities, total Collembola densities decreased in the mixed plant community, while they increased in monoculture plant communities (Figure 2a)
The interactive effect of predator density and plant community composition on total Collembola density was driven by the response of Proisotoma minuta - the smallest body-sized prey species in our experiment (GLMM, F 5 5.62, P 5 0.01; Figure 2b)
Summary
Top-down control of prey by predators are magnified in productive ecosystems due to higher sustenance of prey communities. Higher microbial community biomass in the mixed plant community sustained sufficiently high prey populations to support high predator density. Plant communities with a high number of species produce higher plant biomass providing sufficient energy to support greater communities of herbivores and detritivores, which cascade to higher densities of predators[6,7], with a subsequent increase in top-down effects[7] These findings of a productivity-driven proportional increase in the strength of trophic interactions at higher trophic levels agree with the classical Oksanen et al (1981)[8] hypothesis that predicts increased top-down control of prey by predators at high productivity (higher resource availability for prey). Different plant groups create heterogeneous environments in soil[27] that may favour predators in suppressing prey[5,28]
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