Multi-species Systems Research Articles

Climate change impacts in multispecies systems: drought alters food web size structure in a field experiment

Experimental data from intergenerational field manipulations of entire food webs are scarce, yet such approaches are essential for gauging impacts of environmental change in natural systems. We imposed 2 years of intermittent drought on stream channels in a replicated field trial, to measure food web responses to simulated climate change. Drought triggered widespread losses of species and links, with larger taxa and those that were rare for their size, many of which were predatory, being especially vulnerable. Many network properties, including size-scaling relationships within food chains, changed in response to drought. Other properties, such as connectance, were unaffected. These findings highlight the need for detailed experimental data from different organizational levels, from pairwise links to the entire food web. The loss of not only large species, but also those that were rare for their size, provides a newly refined way to gauge likely impacts that may be applied more generally to other systems and/or impacts.

Escape from parasitoids leave larvae vulnerable to predators and has unexpected outcomes for pest suppression

It is well recognised that interactions among multiple species of natural enemies can have important consequences for the population dynamics of the species involved, particularly when intra-guild predation (IGP) occurs. However, these interactions are highly dependent on the type and behaviour of the prey, an aspect of IGP that is frequently overlooked. Here we demonstrate how a parasitoid (Dolichogenidea tasmanica) facilitates attack on a lepidopteran larva (Epiphyas postvittana) by a predatory mite (Anystis baccarum). We show that anti-predator behaviour of the lepidopteran larva is the mechanism that facilitates this. E. postvittana is protected by its silken leaf roll which limits predation by the mite except when the larva is attacked by the parasitoid causing the larva to leave its shelter. We explored the implications of the interactions among these three species for pest suppression by modelling changes in mite density and mite predation intensity. The presence of mites (the IG predator) always leads to a decrease in ability of the parasitoid to control E. postvittana and, as mite predation intensity increases, the ability of the parasitoid to suppress E. postvittana decreases. The results from the experiment show a synergistic interaction, but results from the population model show an interaction resulting in pest release. These findings support the general idea that if uni-directional IGP occurs, and competition is strong between the top and intermediate predator, then a single best control agent will likely be more effective at suppressing the prey population than multiple control agents combined. These findings have important implications for the management of E. postvittana in vineyards across Southern Australia and for other multi-species systems.

Population synchrony decreases with richness and increases with environmental fluctuations in an experimental metacommunity

Fluctuations of local but connected populations may show correlation or synchrony whenever they experience significant dispersal or correlated environmental biotic and abiotic variability. Synchrony may be an important variable in multispecies systems, but its nature and implications have not been explicitly examined. Because the number of locally coexisting species (richness) affects the population variability of community members, we manipulated richness under different regimes of environmental fluctuation (EF). We predicted that the temporal synchrony of populations in a species should decline with increasing richness of the metacommunity they live in. Additionally, we predicted that specialist species that are sensitive to a specific environmental factor would show higher synchronization when EF increases. We thus created experimental communities with varied richness, EF, and species specialization to examine the synchronizing effects of these factors on three aquatic invertebrate species. We created four levels of richness and three levels of EF by manipulating the salinity of the culture media. Monocultures exhibited higher population synchrony than metacommunities of 2-4 species. Furthermore, we found that species responded differently to EF treatments: high EF enhanced population synchrony for the specialist and intermediate species, but not for the generalist species. Our findings emphasize that the magnitude of EF and species richness both contribute to determine population synchrony, and importantly, our results suggest that biotic diversity may actually stabilize metacommunities by disrupting synchrony.

Urgent need for a common metric to make precipitation manipulation experiments comparable

Urgent need for a common metric to make precipitation manipulation experiments comparable

Insights into the virulence of oral biofilms: discoveries from proteomics

This review covers developments in the study of polymicrobial communities, biofilms and selected areas of host response relevant to dental plaque and related areas of oral biology. The emphasis is on recent studies in which proteomic methods, particularly those using mass spectrometry as a readout, have played a major role in the investigation. The last 5–10 years have seen a transition of such methods from the periphery of oral biology to the mainstream, as in other areas of biomedical science. For reasons of focus and space, the authors do not discuss biomarker studies relevant to improved diagnostics for oral health, as this literature is rather substantial in its own right and deserves a separate treatment. Here, global gene regulation studies of plaque-component organisms, biofilm formation, multispecies interactions and host–microbe interactions are discussed. Several aspects of proteomics methodology that are relevant to the studies of multispecies systems are commented upon.

OptCom: A Multi-Level Optimization Framework for the Metabolic Modeling and Analysis of Microbial Communities

Microorganisms rarely live isolated in their natural environments but rather function in consolidated and socializing communities. Despite the growing availability of high-throughput sequencing and metagenomic data, we still know very little about the metabolic contributions of individual microbial players within an ecological niche and the extent and directionality of interactions among them. This calls for development of efficient modeling frameworks to shed light on less understood aspects of metabolism in microbial communities. Here, we introduce OptCom, a comprehensive flux balance analysis framework for microbial communities, which relies on a multi-level and multi-objective optimization formulation to properly describe trade-offs between individual vs. community level fitness criteria. In contrast to earlier approaches that rely on a single objective function, here, we consider species-level fitness criteria for the inner problems while relying on community-level objective maximization for the outer problem. OptCom is general enough to capture any type of interactions (positive, negative or combinations thereof) and is capable of accommodating any number of microbial species (or guilds) involved. We applied OptCom to quantify the syntrophic association in a well-characterized two-species microbial system, assess the level of sub-optimal growth in phototrophic microbial mats, and elucidate the extent and direction of inter-species metabolite and electron transfer in a model microbial community. We also used OptCom to examine addition of a new member to an existing community. Our study demonstrates the importance of trade-offs between species- and community-level fitness driving forces and lays the foundation for metabolic-driven analysis of various types of interactions in multi-species microbial systems using genome-scale metabolic models.

The economics and institutional economics of wildlife on private land in Africa

In southern Africa, there are now 10,000 to 14,000 private ranchers that promote wildlife enterprises alone or in some in combination with domestic livestock. An important conservation success, this new bio-experience economy also creates social well-being through economic growth and job creation. It is an economic sector that needs to be taken seriously, not least because it pioneers policies that inform the valorization and sustainable management of ecosystem services. The article describes the historical emergence of a sustainable use approach to wildlife conservation since the Arusha Conference in 1963. It suggests that indigenous multi-species systems may have ecological advantages over modern livestock production systems, but these are difficult to quantify in complex dryland ecosystems and are trumped by economics and political processes. However, wildlife provides the foundation for a bio-experience economy that has a decided comparative economic advantage over agro-extractive commodity production (like beef) in drylands. We describe how new policy approaches, especially the valorization of wildlife and the devolution of proprietorship to landholders and communities, have allowed wildlife's economic advantages to be reflected in land use decisions through both ‘game ranching’ and ‘community-based natural resource management’. Institutional changes have modified the economics of wildlife in drylands, promoting both conservation and development by allocating environmental raw materials to higher-order goods and services. A further goal of the paper is to describe practical economic methods for assessing and explaining the wildlife sector to policy makers in terms of its profitability, both to individual landholders and to society through jobs and economic growth. The paper covers a 50-year period between the PhD studies of the four authors and takes a trans disciplinary approach which values the knowledge of practitioners as much as the academic literature.

Melting properties of two-dimensional multi-species colloidal systems in a parabolic trap

The angular and radial melting properties of two-dimensional classical systems consisting of different types of particles confined in a parabolic trap are studied through modified Monte Carlo simulations. A universal behavior of the angular melting process is found, which occurs in multiple steps due to shell depended melting temperatures. The melting sequence of the different shells is determined by two major factors: (1) the confinement strength which each shell is subjected to, and (2) the specific structure of each shell. Further, a continuous radial disordering of the particle types forming a single circular shell is found and analyzed. This phenomenon has never been observed before in two-dimensional mono-dispersive systems. This continuous radial disordering results from the high energy barrier between different particle types in multi-species systems.

A non-invasive fluorescent staining procedure allows Confocal Laser Scanning Microscopy based imaging of Mycobacterium in multispecies biofilms colonizing and degrading polycyclic aromatic hydrocarbons

To study the micro scale interactions of Mycobacterium with bacteria belonging to other genera by means of Confocal Laser Scanning Microscopy (CLSM), a procedure was developed to non-invasively and fluorescently stain Mycobacterium without compromising the signal produced by commonly used fluorescent reporter genes. The procedure makes use of the commercial non-specific nucleic acid stain Syto62 and was optimized to efficiently stain Mycobacterium cells in suspensions and biofilms. The staining procedure was found non-invasive towards overall cell viability, biofilm architecture and fluorescence signals emitted by other organisms expressing the fluorescent reporter genes gfp and dsRed. The procedure was successfully applied to visualize the comportment of the PAH-degrading Mycobacterium sp. VM552 in triple species biofilms containing, in addition to strain VM552, the GFP labeled PAH-degrading Sphingomonas sp. LH128-GFP and DsRed-labeled Pseudomonas putida OUS82(RF), and colonizing a glass substrate coated with phenanthrene crystals in flow chambers. CLSM imaging and subsequent appropriate image processing of the biofilms show that the comportment of strain Mycobacterium sp. VM552 was largely affected by the presence of the other organisms. The data support the value of the staining procedure to study ecological questions about micro scale behavior and niche occupation of Mycobacterium in multi-species systems.

A multispecies perspective on ecological impacts of climatic forcing

1. In the prevailing context of concerns over climate change and its potential impacts on ecosystems, evaluating ecological consequences of climatic forcing has become a critical issue. 2. Historical data on the abundance of organisms have been extensively used to characterize the ecological effects of climatic forcing through specific weather and/or climatic variables, with most of the studies confined to single population models. 3. However, population responses to environmental fluctuations typically depend upon positive and negative feedbacks induced by interactions with other species. It is therefore important to integrate the insights gained from single population approaches into a multispecies perspective. 4. Here we combine the hierarchical Bayesian modelling approach with the state-space formulation to extend the scope of previously proposed models of population dynamics under climatic forcing to multi-species systems. 5. We use our model to analyse long-term macro-moth (Lepidoptera) community data from the Rothamsted Insect Survey network in the UK, using winter rainfall and winter temperature as environmental covariates. 6. The effects of the two weather variables were consistent across species, being negative for winter rainfall and positive for winter temperature. The two weather variables jointly explained 15-40% of the total environmental variation affecting the dynamics of individual species, and could explain up to 90% of covariances in species dynamics. 7. The contribution of interspecific interactions to community-level variation was found to be weak compared to the contributions of environmental forcing and intraspecific interactions.

Functional GacS in Pseudomonas DSS73 prevents digestion by Caenorhabditis elegans and protects the nematode from killer flagellates

The success of biocontrol bacteria in soil depends in part on their ability to escape predation. We explored the interactions between Pseudomonas strain DSS73 and two predators, the nematode Caenorhabditis elegans and the flagellate Cercomonas sp. Growth of the nematode in liquid culture was arrested when it was feeding on DSS73 or a DSS73 mutant (DSS73-15C2) unable to produce the biosurfactant amphisin, whereas a regulatory gacS mutant (DSS73-12H8) that produces no exoproducts supported fast growth of the nematode. The flagellate Cercomonas sp. was able to grow on all three strains. The biosurfactant-deficient DSS73 mutant caused severe dilation of the nematode gut. In three-species systems (DSS73, Cercomonas and C. elegans), the nematodes fed on the flagellates, which in turn grazed the bacteria and the number of C. elegans increased. The flagellates Cercomonas sp. usually kill C. elegans. However, DSS73 protected the nematodes from flagellate killing. Soil microcosms inoculated with six rhizobacteria and grazed by nematodes were colonized more efficiently by DSS73 than similar systems grazed by flagellates or without grazers. In conclusion, our results suggest that C. elegans and DSS73 mutually increase the survival of one another in complex multispecies systems and that this interaction depends on the GacS regulator.

Minimal coexistence configurations for multispecies systems

We deal with strongly competing multispecies systems of Lotka–Volterra type with homogeneous Neumann boundary conditions in dumbbell-like domains. Under suitable non-degeneracy assumptions, we show that, as the competition rate grows indefinitely, the system reaches a state of coexistence of all the species in spatial segregation. Furthermore, the limit configuration is a local minimizer for the associated free energy.

Responses of three benthic organisms (Hyallela azteca, Limnodrillus hoffmeisteri and Stagnicola attenuata) to natural sediment spiked with zinc when exposed in single or multi-species test systems

In order to determine the influence of the presence of one or more species in a system on Zn toxic response, acute (LC50 at 72 h) and sublethal toxicity (Zn uptake kinetics, and quantification of total protein content and lipid peroxidation levels) were evaluated in three benthic organisms (Hyallela azteca, Limnodrillus hoffmeisteri and Stagnicola attenuata). They were exposed either singly or together (single or multi-species test systems) to Zn-spiked sediment from Ignacio Ramírez Reservoir. Both assays showed that Zn-spiked sediments from Ignacio Ramírez Reservoir were toxic to S. attenuata, L. hoffmeisteri and H. azteca, and that toxic response was modified according to the number of species in the system. These differences may be due to multiple factors: such as benthic bioturbation which modifies physical and chemical characteristics of sediments and affects the fate and partitioning of sediment-bond contaminants, such as spiked Zn or other pollutants in sediments from Ignacio Ramírez Reservoir. In addition, the presence of more than one species in the system may lead to microenvironmental changes (pH, temperature, and organic matter and metabolic waste content), which can also contribute to toxic response differences. Also, particular characteristics of each of the species involved in the study became evident. The snail and amphipod are facultative benthic organisms, while the worm is obligate. Such way of life differences may have modified the bioavailability of contaminants, determining their toxicity.

Water flux and canopy conductance of natural versus planted forests in Patagonia, South America

In NW Patagonia, South America, natural shrublands and mixed forests of short Nothofagus antarctica (G. Forst.) Oerst. trees are currently being replaced by plantations with Pseudotsuga menziesii (Mirb) Franco. This land use change is controversial because the region is prone to drought, and replacement of native vegetation by planted forests may increase vegetation water use. The goal of this study was to examine the physiological differences, especially the response of water flux and canopy conductance to microclimate, that lead to greater water use by exotic trees compared to native trees. Meteorological variables and sapflow density of P. menziesii and four native woody species were measured in the growing season 2005–2006. Canopy conductance (gc) was estimated for both the exotic (monoculture) and native (multi-species) systems, including the individual contributions of each species of the native forest. Sapflow density, stand-level transpiration and gc were related to leaf-to-air vapor pressure difference (VPD). All native species had different magnitudes and diurnal patterns of sapflow density compared to P. menziesii, which could be explained by the different gc responses to VPD. Stomatal sensitivity to VPD suggested that all native species have a stronger stomatal control of leaf water potential and transpiration due to hydraulic limitations compared to P. menziesii. In conclusion, differences in water use between a P. menziesii plantation and a contiguous native mixed forest of similar basal area could be explained by different gc responses to VPD between species (higher sensitivity in the native species), in addition to particular characteristics of the native forest structure.

Critical slowing down as an indicator of transitions in two-species models

Transitions in ecological systems often occur without apparent warning, and may represent shifts between alternative persistent states. Decreasing ecological resilience (the size of the basin of attraction around a stable state) can signal an impending transition, but this effect is difficult to measure in practice. Recent research has suggested that a decreasing rate of recovery from small perturbations (critical slowing down) is a good indicator of ecological resilience. Here we use analytical techniques to draw general conclusions about the conditions under which critical slowing down provides an early indicator of transitions in two-species predator–prey and competition models. The models exhibit three types of transition: the predator–prey model has a Hopf bifurcation and a transcritical bifurcation, and the competition model has two saddle-node bifurcations (in which case the system exhibits hysteresis) or two transcritical bifurcations, depending on the parameterisation. We find that critical slowing down is an earlier indicator of the Hopf bifurcation in predator–prey models in which prey are regulated by predation rather than by intrinsic density-dependent effects and an earlier indicator of transitions in competition models in which the dynamics of the rare species operate on slower timescales than the dynamics of the common species. These results lead directly to predictions for more complex multi-species systems, which can be tested using simulation models or real ecosystems.

Global solutions to a class of multi-species reaction-diffusion systems with cross-diffusions arising in population dynamics

In this paper, an n -species strongly coupled cooperating diffusive system is considered in a bounded smooth domain, subject to homogeneous Neumann boundary conditions. Employing the method of energy estimates, we obtain some conditions on the diffusion matrix and inter-specific cooperatives to ensure the global existence and uniform boundedness of a nonnegative solution. The globally asymptotical stability of the constant positive steady state is also discussed. As a consequence, all the results hold true for multi-species Lotka–Volterra type competition model and prey–predator model.

Nitrogen and Phosphorus Release from Mixed Litter Layers is Lower than Predicted from Single Species Decay

Ecosystem-level nutrient dynamics during decomposition are often estimated from litter monocultures. If species effects are additive, we can statistically predict nutrient dynamics in multi-species systems from monoculture work, and potential consequences of species loss. However, if species effects are dependent on interactions with other litter species (that is, non-additive), predictions based on monoculture data will likely be inaccurate. We conducted a 3-year, full-factorial, mixed-litter decomposition study of four dominant tree species in a temperate forest and measured nitrogen and phosphorus dynamics to explore whether nutrient dynamics in mixtures were additive or non-additive. Following common approaches, we used litterfall data to predict nutrient dynamics at the ecosystem-level. In mixtures, we observed non-additive effects of litter mixing on nutrient dynamics: the presence of nutrient-rich species in mixture facilitated nutrient release, whereas nutrient-poor species facilitated nutrient retention. Fewer nutrients were released from mixtures containing high-quality litter, and more immobilized from mixtures containing low-quality litter, than predicted from monocultures, creating a difference in overall nutrient release between predicted and actual dynamics in litter mixtures. Nutrient release at the ecosystem-level was greatly overestimated when based on monocultures because the effect of species interactions on nutrient immobilization was not accounted for. Our data illustrate that the identity of species in mixtures is key to their role in non-additive interactions, with repercussions for mineral nutrient availability and storage. These results suggest that predictions of ecosystem-level nutrient dynamics using litter monoculture data likely do not accurately represent actual dynamics because the effects of litter species interactions are not incorporated.

Stability for a Holling Type IV Food Chain System With Impulsive Perturbations

Abstract. We investigate a three species food chain system with a Holling type IVfunctional response and impulsive perturbations. We find conditions for local and globalstabilities of prey(or predator) free periodic solutions by applying the Floquet theory andthe comparison theorems. 1. IntroductionIt is currently very much in vogue to study population models with impulsiveperturbations containing biological and chemical controls. Especially, simple multi-species systems consisting of a three species food chain with impulsive perturbationshave been discussed by a number of researchers [13], [17], [18], [19], [20] and thereare also many literatures on impulsive prey-predator population models [10], [11],[12].A well-known model of such systems is a food chain system with Holling typeIV functional response [7], [14], [20], which can be described the following equation:(1.1)x 0 (t) = x(t)(a−bx(t))−c 1 x(t)y(t)1+e 1 x 2 (t),y 0 (t) = −d 1 y(t)+c 2 x(t)y(t)1+e 1 x 2 (t)−c 3 y(t)z(t)1+e

Comparing ecotoxicological effect concentrations of chemicals established in multi-species vs. single-species toxicity test systems

Most ecological effect assessment methodologies use effect concentrations derived from single-species testing (EC x ,single-species-test) as the basis to estimate ‘safe’ environmental concentrations (such as environmental quality criteria). Here, we examined to what extent such EC x ,single-species-test are representative for population-level effect concentrations in a community setting (EC x ,multi-species-test). Data from USEPA's ECOTOX database revealed the existence of considerable scatter around the relationship between EC x ,single-species-test (endpoint: mortality) and EC x ,multi-species-test (endpoint: population abundance). However, we demonstrate that this scatter is reduced when EC x ,single-species-test and EC x ,multi-species-test are determined simultaneously and by the same research group. Indeed, if these conditions are fulfilled, the quotient of both EC x values for invertebrates approaches 1 for chemicals that directly target invertebrates. Unfortunately, comparable data for other classes of chemicals and/or taxonomic groups were not found. However, theoretical ecosystem model simulations, which confirmed the results based on the above-mentioned analysis of the ECOTOX database, indicated that for phytoplankton, EC 10,single-species-test>EC 10,multi-species-test, for chemicals that directly target invertebrates. For chemicals that directly target phytoplankton, the ecosystem model simulations suggest that EC x ,single-species-test>EC x ,multi-species-test for both phytoplankton and invertebrates. Hence, our observation based on the analysis of existing experimental data that the EC x ,single-species-test is similar to the EC x ,multi-species-test may be biased by the fact that only data were available for invertebrates and for chemicals targeting invertebrates. Experimental research is required to test the predictions made by the model simulations for phytoplankton as well as for chemicals directly targeting phytoplankton.

Coexistence and segregation for strongly competing species in special domains

We deal with strongly competing multispecies systems of Lotka-Vol– terra type with homogeneous Dirichlet boundary conditions. For a class of nonconvex domains composed by balls connected with thin corridors, we show the occurrence of pattern formation (coexistence and spatial segregation of all the species), as the competition grows indefinitely. As a result we prove the existence and uniqueness of solutions for a remarkable system of differential inequalities involved in segregation phenomena and optimal partition problems.