Testing the paradox of enrichment along a land use gradient in a multitrophic aboveground and belowground community

In the light of ongoing land use changes, it is important to understand how multitrophic communities perform at different land use intensities. The paradox of enrichment predicts that fertilization leads to destabilization and extinction of predator-prey systems. We tested this prediction for a land use intensity gradient from natural to highly fertilized agricultural ecosystems. We included multiple aboveground and belowground trophic levels and land use-dependent searching efficiencies of insects. To overcome logistic constraints of field experiments, we used a successfully validated simulation model to investigate plant responses to removal of herbivores and their enemies. Consistent with our predictions, instability measured by herbivore-induced plant mortality increased with increasing land use intensity. Simultaneously, the balance between herbivores and natural enemies turned increasingly towards herbivore dominance and natural enemy failure. Under natural conditions, there were more frequently significant effects of belowground herbivores and their natural enemies on plant performance, whereas there were more aboveground effects in agroecosystems. This result was partly due to the “boom-bust” behavior of the shoot herbivore population. Plant responses to herbivore or natural enemy removal were much more abrupt than the imposed smooth land use intensity gradient. This may be due to the presence of multiple trophic levels aboveground and belowground. Our model suggests that destabilization and extinction are more likely to occur in agroecosystems than in natural communities, but the shape of the relationship is nonlinear under the influence of multiple trophic interactions.

On the risk of extinction of a wild plant species through spillover of a biological control agent: analysis of an ecosystem compartment model

Invasive plant species can be controlled by introducing one or more of their natural enemies (herbivores) from their native range; however such introduction entails the risk that the introduced natural enemy will attack indigenous plant species in the area of introduction. The effect of spillover of a natural enemy from a managed ecosystem compartment (agriculture) in the area of introduction to a natural compartment (non-managed) in which an indigenous plant species is attacked by the introduced natural enemy, whereas another indigenous plant species, which competes with the first, is not attacked, has been studied. The combination of competition and herbivory may result in extinction of the attacked wild plant species. Using a modelling approach, the authors have determined model parameters that characterize the risk of extinction. The findings point to the importance of spillover and the relative attack rates (specificity) of introduced natural enemies with respect to target and non-target plant specie

Moving forward in circles: challenges and opportunities in modelling population cycles

Population cycling is a widespread phenomenon, observed across a multitude of taxa in both laboratory and natural conditions. Historically, the theory associated with population cycles was tightly linked to pairwise consumer–resource interactions and studied via deterministic models, but current empirical and theoretical research reveals a much richer basis for ecological cycles. Stochasticity and seasonality can modulate or create cyclic behaviour in non-intuitive ways, the high-dimensionality in ecological systems can profoundly influence cycling, and so can demographic structure and eco-evolutionary dynamics. An inclusive theory for population cycles, ranging from ecosystem-level to demographic modelling, grounded in observational or experimental data, is therefore necessary to better understand observed cyclical patterns. In turn, by gaining better insight into the drivers of population cycles, we can begin to understand the causes of cycle gain and loss, how biodiversity interacts with population cycling, and how to effectively manage wildly fluctuating populations, all of which are growing domains of ecological research

Reconciling Techno-simplicity and Eco-complexity for future food security

Ecological intensification has been proposed as a paradigm for ensuring global food security while preserving biodiversity and ecosystem integrity. Ecologicalintensification was originally coined to promote precise site-specific farming practices aimed at reducing yield gaps, while avoiding negative environmental impacts (techno-simplicity). Recently, it has been extended to stress the importance of landscape complexity to preserve biodiversity and ecosystem services (eco-complexity). While these perspectives on ecological intensification may seem distinct, they are not incompatible and should be interwoven to create more comprehensive and practical solutions. Here, we argue that designing cropping systems to be more diverse, across space and time would be an effective route to accomplish environmentally-friendly intensification of crop production. Such a novel approach will require better integration of knowledge at the landscape level for increasing agro-biodiversity(focused on interventions outside fields) with strategies diversifying croppingsystems to manage weeds and pests (focused on interventions inside fields).Fil: Poggio, Santiago Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Producción Vegetal; ArgentinaFil: Macfadyen, Sarina. CSIRO; AustraliaFil: Bohan, David A.. Institut National de la Recherche Agronomique; Franci

Predators reduce extinction risk in noisy metapopulations

Background Spatial structure across fragmented landscapes can enhance regional population persistence by promoting local “rescue effects.” In small, vulnerable populations, where chance or random events between individuals may have disproportionately large effects on species interactions, such local processes are particularly important. However, existing theory often only describes the dynamics of metapopulations at regional scales, neglecting the role of multispecies population dynamics within habitat patches. Findings By coupling analysis across spatial scales we quantified the interaction between local scale population regulation, regional dispersal and noise processes in the dynamics of experimental host-parasitoid metapopulations. We find that increasing community complexity increases negative correlation between local population dynamics. A potential mechanism underpinning this finding was explored using a simple population dynamic model. Conclusions Our results suggest a paradox: parasitism, whilst clearly damaging to hosts at the individual level, reduces extinction risk at the population level

Optimal phenotypic plasticity in a stochastic environment minimizes the cost/benefit ratio

This paper addresses the question of optimal phenotypic plasticity as a response to environmental fluctuations while optimizing the cost/benefit ratio, where the cost is energetic expense of plasticity, and benefit is fitness. The dispersion matrix \Sigma of the genes' response (H = ln|\Sigma|) is used: (i) in a numerical model as a metric of the phenotypic variance reduction in the course of fitness optimization, then (ii) in an analytical model, in order to optimize parameters under the constraint of limited energy availability. Results lead to speculate that such optimized organisms should maximize their exergy and thus the direct/indirect work they exert on the habitat. It is shown that the optimal cost/benefit ratio belongs to an interval in which differences between individuals should not substantially modify their fitness. Consequently, even in the case of an ideal population, close to the optimal plasticity, a certain level of genetic diversity should be long conserved, and a part, still to be determined, of intra-populations genetic diversity probably stem from environment fluctuations. Species confronted to monotonous factors should be less plastic than vicariant species experiencing heterogeneous environments. Analogies with the MaxEnt algorithm of E.T. Jaynes (1957) are discussed, leading to the conjecture that this method may be applied even in case of multivariate but non multinormal distributions of the responses

THE ECOLOGY OF MUTUALISM

Elementary ecology texts tell us that organisms interact in three fundamen­ tal ways, generally given the names competition, predation, and mutualism. The third member has gotten short shrift (264), and even its name is not generally agreed on. Terms that may be considered synonyms, in whole or part, are symbiosis, commensalism, cooperation, protocooperation, mutual aid, facilitation, reciprocal altruism, and entraide. We use the term mutual­ism, defined as an interaction between species that is beneficial to both, since it has both historical priority (311) and general currency. Symbiosis is the living together of two organisms in close association, and modifiers are used to specify dependence on the interaction (facultative or obligate) and the range of species that can take part (oligophilic or polyphilic). We make the normal apologies concerning forcing continuous variation and diverse interactions into simple dichotomous classifications, for these and all subsequent definitions

Investigations into stability in the fig/ fig-wasp mutualism

Fig trees (Ficus, Moraceae) and their pollinating wasps (Chalcidoidea, Agaonidae) are involved in an obligate mutualism where each partner relies on the other in order to reproduce: the pollinating fig wasps are a fig tree’s only pollen disperser whilst the fig trees provide the wasps with places in which to lay their eggs. Mutualistic interactions are, however, ultimately genetically selfish and as such, are often rife with conflict. Fig trees are either monoecious, where wasps and seeds develop together within fig fruit (syconia), or dioecious, where wasps and seeds develop separately. In interactions between monoecious fig trees and their pollinating wasps, there are conflicts of interest over the relative allocation of fig flowers to wasp and seed development. Although fig trees reap the rewards associated with wasp and seed production (through pollen and seed dispersal respectively), pollinators only benefit directly from flowers that nurture the development of wasp larvae, and increase their fitness by attempting to oviposit in as many ovules as possible. If successful, this oviposition strategy would eventually destroy the mutualism; however, the interaction has lasted for over 60 million years suggesting that mechanisms must be in place to limit wasp oviposition. This thesis addresses a number of factors to elucidate how stability may be achieved in monoecious fig systems. Possible mechanisms include: 1) a parasitoidcentred short ovipositor hypothesis in Ficus rubiginosa, which suggests that a subset of flowers are out of reach to parasitoid ovipositors making these ovules the preferred choice for ovipositing pollinators and allowing seeds to develop in less preferred ovules; 2) the presence of third-party mutualists such as non-pollinating fig wasps (F. burkei) and patrolling green tree ants on the fig surface (F. racemosa) that limit pollinator and parasitoid oviposition respectively; and 3) selection on fig morphology which constrains the size (and therefore fecundity) of the associated pollinators. I discuss the lack of evidence for a single unifying theory for mutualism stability and suggest that a more likely scenario is the presence of separate, and perhaps multiple, stabilising strategies in different fig/ fig-wasp partnerships

Metabolomics-based biomarker discovery for bee health monitoring : a proof of concept study concerning nutritional stress in Bombus terrestris

Bee pollinators are exposed to multiple natural and anthropogenic stressors. Understanding the effects of a single stressor in the complex environmental context of antagonistic/synergistic interactions is critical to pollinator monitoring and may serve as early warning system before a pollination crisis. This study aimed to methodically improve the diagnosis of bee stressors using a simultaneous untargeted and targeted metabolomics-based approach. Analysis of 84 Bombus terrestris hemolymph samples found 8 metabolites retained as potential biomarkers that showed excellent discrimination for nutritional stress. In parallel, 8 significantly altered metabolites, as revealed by targeted profiling, were also assigned as candidate biomarkers. Furthermore, machine learning algorithms were applied to the above-described two biomarker sets, whereby the untargeted eight components showed the best classification performance with sensitivity and specificity up to 99% and 100%, respectively. Based on pathway and biochemistry analysis, we propose that gluconeogenesis contributed significantly to blood sugar stability in bumblebees maintained on a low carbohydrate diet. Taken together, this study demonstrates that metabolomics-based biomarker discovery holds promising potential for improving bee health monitoring and to identify stressor related to energy intake and other environmental stressors