Biology subjects

Loeuille, N.

Publications and source records attributed to Loeuille, N..

5 recordsLinked to original sources

bioRxiv2018

Ecosystem tipping points in an evolving world

There is growing concern over tipping points arising in ecosystems due to the crossing of environmental thresholds. Tipping points lead to strong and possibly irreversible shifts between alternative ecosystem states incurring high societal costs. Traits are central to the feedbacks that maintain alternative ecosystem states, as they govern the responses of populations to environmental change that could stabilize or destabilize ecosystem states. However, we know little about how evolutionary changes in trait distributions over time affect the occurrence of tipping points, and even less about how big scale ecological shifts reciprocally interact with trait dynamics. We argue that interactions between ecological and evolutionary processes should be taken into account for understanding the balance of feedbacks governing tipping points in nature.

ecology↗

bioRxiv2018

From apparent competition to facilitation, impacts of consumer niche construction on the coexistence and stability of consumer-resource communities.

O_LIIn addition to their direct trophic effects, some consumers have a positive indirect effect on their resource, due to niche construction. A predator can facilitate its prey resource acquisition, through prey transport, or through modifications of nutrient cycling. Other predators defend their prey against other predators, or actively manage it, as in agriculture, which is found in numerous taxa such as humans, but also ants, beetles, fishes and microbes.\nC_LIO_LIHere we investigate the ecological consequences of considering such positive effects in a simple two resource-one predator module, in which the consumer has a positive effect on one of the resources.\nC_LIO_LIWe consider several scenarios, in which the positive effect of the resource is either non costly, ie resulting from a by-product of the consumer phenotype such as nutrient cycling, or costly. The cost either decreases the exploitation of the helped resource or the opportunity to forage the alternative resource.\nC_LIO_LIWe show that by modifying the trophic interactions in the module, niche construction alters the apparent competition between the resources, thereby impacting their coexistence.\nC_LIO_LIWe investigate how the intensity of niche construction impacts species coexistence, the distribution of biomass among the three species, and the stability of the community. When niche construction has little or no cost, it leads to higher consumer and helped resource densities, while decreasing the alternative resource density. Alternatively, when niche construction has a strong cost, the alternative resource can increase in density, niche construction thereby leading to the emergence of facilitative interactions among resource species.\nC_LI

ecology↗

bioRxiv2018

Parasitism effects on coexistence and stability within simple trophic modules

Parasites are important components of food webs. Although their direct effects on hosts are well-studied, indirect impacts on trophic networks, thus on non-host species, remain unclear.\n\nIn this study, we investigate the consequences of parasitism on coexistence and stability within a simple trophic module: one predator consuming two prey species in competition. We test how such effects depend on the infected species (prey or predator). We account for two effects of parasitism: the virulence effect (parasites affect the infected species intrinsic growth rate through direct effects on fecundity or mortality) and the interaction effect (increased vulnerability of infected prey or increased food intake of infected predators).\n\nResults show that coexistence is favored when effects have intermediate intensity. We link this result to modifications of direct and apparent competitions among prey species. Given a prey infection, accounting for susceptible-infected population structure highlights that coexistence may also be reduced due to predator-parasite competition.\n\nParasites affect stability by modulating energy transfer from prey to predator. Predator infection therefore has a stabilizing effect due to increased energy fluxes and/or predator mortality.\n\nOur results suggest that parasites potentially increase species coexistence. Precise predictions however require an assessment of various parasite effects. We discuss the implications of our results for the functioning of trophic networks and the evolution of foraging strategies within food webs.

ecology↗

bioRxiv2018

Adaptive harvesting drives fishing down processes, regime shifts, and resilience changes in predator-prey systems

Many world fisheries display a declining mean trophic level of catches. This "fishing down the food web" is often attributed to reduced densities of high-trophic-level species. We show here that the fishing down pattern can actually emerge from the adaptive harvesting of two- and three-species food webs, where changes in fishing patterns are driven by the relative profitabilities of the harvested species. Shifting fishing patterns from a focus on higher trophic levels to a focus on lower trophic levels can yield abrupt changes in the system, strongly impacting species densities. In predator-prey systems, such regime shifts occur when the predator species is highly valuable relative to the prey, and when the top-down control on the prey is strong. Moreover, we find that when the two species are jointly harvested, high adaptation speeds can reduce the resilience of fisheries. Our results therefore suggest that flexibility in harvesting strategies will not necessarily benefit fisheries but may actually harm their sustainability.

ecology↗

bioRxiv2017

Selective effects of temperature on body mass depend on trophic interactions and network position

Body mass is a key trait constraining interspecific interactions in food webs through changes in metabolic requirements. Because climate warming affects metabolic rates, it creates direct selective effects on body mass. Many empirical studies suggest that body mass decreases under warming, although important exceptions have been noted. We first analyze the evolution of body mass in a simple consumer-resource model to provide conditions under which a body mass increase or decrease may be expected. We then extend our model to a multi-trophic food web context that allows for the coevolution of body mass and of feeding preferences. We focus here on how the trophic position of a consumer influences its evolutionary response to warming under different scenarios for the temperature dependence of attack rates. We observe that body masses can remain constant or increase with temperature when attack rates are constant or increasing with temperature, while body mass reductions in response to warming are only expected when attack rates have a thermal optimum and populations are initially locally adapted. We also found that body masses at lower trophic levels vary less under warming than body masses at higher trophic levels, which may be explained by decreasing levels of stabilizing selection along food chains.

ecology↗