Wurst, S. | bioRxiv Science

bioRxiv2019

Live and inanimate predator-associated cues suppress the population of sap-feeding prey and induce polyphenism

Non-consumptive effect of predation is a well-researched subject of which certain non-consumptive and predator-mimetic facets are yet to be investigated in plant-parasite systems One clone of the green peach aphid Myzus persicae (Sulzer), raised on a model crop Brassica oleracea (L.), was exposed to different regimes of risks associated with ladybird Coccinella septempunctata (L.). This encompassed consumption, consumption alternated by non-consumptive effects, isolated predators, dead predator, predator dummy, as well as dummy, plants or soil cued with predator-borne suspension, and predator removal (exposure to plants previously visited and marked by a predator). Over time, the respective risk regimes variably negatively impacted the prey population; the corpses, cued plants and dummies had considerable persistent negative effects on aphid reproductive success, contrary to the observation under predator removal. By the end of the experiment, polyphenism (winged morph production) also differed and was animated under the presence of a starved isolated predator; but faded when a predator corpse was present; and vanished under the dummy. Our findings, in this model aphid-crop system, contribute to the rapidly developing area of the ecology of fear, as we provide insights and novel means for aphid management that merit further examination across different eco-agricultural contexts.

ecology↗

bioRxiv2019

While shoot herbivory mitigates, root herbivory exacerbates eutrophication’s impact on diversity in a grassland model

1Eutrophication is widespread throughout grassland systems and expected to increase during the Anthropocene. Trophic interactions, like aboveground herbivory, have been shown to mitigate its effect on plant diversity. Belowground herbivory may also impact these habitats response to eutrophication, but the direction of its influence is much less understood, and likely to depend on factors such as the herbivores preference for dominant species and the symmetry of belowground competition. If preferential towards the dominant, fastest growing species, root herbivores may reduce these species relative fitness and support diversity during eutrophication. However, as plant competition belowground is commonly considered to be symmetric, root herbivores may be less impactful than shoot herbivores because they do not reduce any competitive asymmetry between the dominant and subordinate plants.\n\nTo better understand this system, we used an established, two-layer, grassland community model to run a full-factorially designed simulation experiment, crossing the complete removal of aboveground herbivores and belowground herbivores with eutrophication. After 100 years of simulation, we analyzed communities diversity, competition on the individual-level, as well as their resistance and recovery. The model reproduced both observed general effects of eutrophication in grasslands and the short-term trends of specific experiments. We found that belowground herbivores exacerbate the negative influence of eutrophication on Shannon diversity within our model grasslands, while aboveground herbivores mitigate its effect. Indeed, data on individuals above- and belowground resource uptake reveals that root herbivory reduces resource limitation belowground. As with eutrophication, this shifts competition aboveground. Since shoot competition is asymmetric--with larger, taller individuals gathering disproportionate resources compared to their smaller, shorter counterparts--this shift promotes the exclusion of the smallest species. While increasing the root herbivores preferences towards dominant species lessens their negative impact, at best they are only mildly advantageous, and they do very little reduce the negative consequences of eutrophication. Because our models belowground competition is symmetric, we hypothesize that root herbivores may be beneficial when root competition is asymmetric. Future research into belowground herbivory should account for the nature of competition belowground to better understand the herbivores true influence.

ecology↗