Biology subjects

Leibold, M. A.

Publications and source records attributed to Leibold, M. A..

15 recordsLinked to original sources

bioRxiv2025

Strengthening intraguild predation increases the temporal variability of biomass across all trophic levels in model food webs

Multiple global-change forces, from habitat alterations to warming, are altering food webs and trophic interaction strengths. Such changes in trophic interactions have important implications, as it is a tenet of ecology that trophic interactions are linked to the functioning and stability of ecosystems. For example, changes in the presence or strength of intraguild predation (IGP), the consumption of a predator by another predator that competes for shared prey, can have cascading effects on the biomasses of species and trophic levels. For this reason, IGP can affect key ecosystem functions at the base of the food web and is of special interest to practitioners of biological pest control. However, the relationship between IGP and ecosystem stability is not yet well understood, especially whether and how IGP might affect the stability of non-adjacent lower trophic levels including primary producers. In this study we simulate the dynamics of a six-species, four-trophic-level food web plus a limiting nutrient to explore the relationship between IGP strength and the temporal variability of species- and trophic group-biomass. By varying the IGP rate given the abundance of the eaten predator, we find that the model food web abruptly shifts between equilibria in which all species maintain either constant biomass or stable limit cycles where all trophic levels exhibit sustained and significant oscillations. While complex feedback in the model creates a divergence between the IGP functional response and the resulting realized IGP strength, both stronger IGP functional responses and stronger realized IGP are associated with a higher likelihood of oscillations. Furthermore, analyses indicate that the strongest consumptive interaction induces the oscillating behavior in an indirect effect initiated by the change in IGP. Overall, these results suggest that as food web structure changes in ecosystems worldwide, strengthening IGP runs the risk of inducing destabilizing effects that extend to the base of food webs, while weakening IGP could confer stability to ecosystem functions such as primary production. Finally, we discuss relevance to management, including the implication that IGP among biological control agents should be minimized to maintain stable crop production.

ecology↗

bioRxiv2025

Modeling and Inferring Metacommunity Dynamics with Maximum Caliber

A major challenge for community ecology is using spatio-temporal data to infer parameters of dynamical models without conducting laborious experiments. We present a novel framework from statistical physics - Maximum Caliber - to characterize the temporal dynamics of complex ecological systems in spatially extended landscapes and infer parameters from empirical data. As an extension of Maximum Entropy modeling, Maximum Caliber aims at modeling the probability of possible trajectories of a stochastic system, rather than focusing on system states. We demonstrate the ability of the Maximum Caliber framework to capture ecological processes ranging from near-to far from-equilibrium, using an array of species interaction motifs including random interactions, apparent competition, intraguild predation, and non-transitive competition, along with dispersal among multiple patches. For spatio-temporal data of species occupancy in a metacommunity, the parameters of a Maximum Caliber model can be estimated through a simple logistic regression to reveal migration rates between patches, interactions between species, and local environmental suitabilities. We test the accuracy of the method over a range of system sizes and time periods, and find that these parameters can be estimated without bias. We introduce "entropy production" as a measure of irreversibility in system dynamics, and use "pseudo-R2" to characterize predictability of future states. We show that our model can predict the dynamics of metacommunities that are far from equilibrium. The capacity to estimate basic parameters of dynamical metacommunity models from spatio-temporal data represents an important breakthrough for the study of metacommunities with application to practical problems in conservation and restoration ecology.

ecology↗

bioRxiv2023

Sunfish as zooplankton control agents to improve yields of wastewater-cultivated algae

Wastewater algal cultivation (WAC) in outdoor raceway ponds is a promising means of removing polluting nutrients from water while producing biomass feedstock for products like fertilizer or biofuel. However, algal cultivation in open ponds is often plagued by underproduction due to contamination by zooplankton. The use of biological controls, i.e., natural predators to control zooplankton, was evaluated as a potential low-cost solution in this study. Eighteen pilot-scale raceway ponds were inoculated with cultured algae and naturally-occurring zooplankton; bluegill sunfish (Lepomis macrochirus) were tested as biological control agents to suppress zooplankton. We installed cages in the ponds to protect the fish from the paddlewheels and control the area the fish could access. The cage either surrounded the paddlewheel - in which case the fish had access to the remaining area - or the cage was opposite the paddlewheel, in which case the fish had access to the smaller area inside the cage. We also implemented fishless controls. After 19 days, ponds with cages surrounding the paddlewheel had 93% more zooplankton, but the fish had reduced zooplankton by 89% on average across cage treatments. Cage placement did not affect algal biomass, but ponds with fish had 45% higher algal dry weight and 84% higher algal biovolume. However, no differences in nutrient levels were recorded among treatments after 19 days. We concluded hardy zooplanktivorous fish represent a promising means of boosting algal production in WAC, although further research is needed to determine whether the change in algal biomass could eventually translate to improved nutrient removal.

ecology↗

bioRxiv2023

Environmental DNA captures the internal structure of a pond metacommunity

Technological progress is enabling ecologists to create repeated, large-scale, structured, and standardised community surveys. However, it is unclear how best to extract information from these novel community data. We metabarcoded 48 vertebrate species from their eDNA in 320 ponds in England and applied the internal-structure approach, which uses joint species distribution models to explain community compositions as the outcome of four metacommunity assembly processes: environmental filtering, dispersal, species interactions, and stochasticity. We find that the environment plays an important role in community assembly and that the inferred environmental preferences of species are consistent with their ecologies. We also infer negative biotic covariances between fish and amphibians, which is consistent with predator-prey interactions, and high spatial autocorrelation for the palmate newt, which is consistent with its hypothesised relictual distribution. Comparing sites in the metacommunity, environmentally and spatially distinctive sites are better explained by their environmental covariates and geographic locations, respectively, revealing sites where environmental filtering and dispersal limitation act more strongly. Furthermore, species belonging to different trait groups differ in how well environmental covariates, biotic covariances, and geographical locations explain their distributions. Overall, our results highlight the value of a modern interpretation of metacommunity ecology that embraces the fact that assembly processes differ between individual species and sites. We discuss how novel community data make feasible several study-design improvements that will strengthen the inference of metacommunity assembly processes from observational data.

ecology↗

bioRxiv2023

Integrating ecosystem and contaminant models to predict the effects of ecosystem fluxes on contaminant dynamics

Pollution is one of the major drivers of ecosystem change in the Anthropocene. Toxic chemicals are not constrained to their source of origin as they cross ecosystem boundaries via biotic (e.g., animal migration) and abiotic (e.g., water flow) vectors. Meta-ecology has led to important insights on how spatial flows or subsidies of matter across ecosystem boundaries can have broad impacts on local and regional ecosystem dynamics but has not yet addressed the dynamics of pollutants. Understanding how these meta-ecosystem processes on contaminant dynamics may reverberate up a food chain is important even if they might be difficult to predict. Here we derive a modelling framework to predict how spatial ecosystem fluxes can influence contaminant dynamics and how the severity of this impact is dependent on the type of ecosystem flux leading to the spatial coupling (e.g., herbivore movement vs abiotic chemical flows). We mix an analytical and numerical approach to analyze our integrative model which couples two distinct sub-components - an ecosystem model and a contaminant model. We observe an array of dynamics for how chemical concentrations change with increasing nutrient input and loss rate across trophic levels. When we tailor our range of chemical parameter values to specific organic chemicals our results demonstrate that increasing nutrient input rates can lead to trophic dilution in pollutants such as polychlorinated biphenyls across trophic levels. Yet, increasing nutrient loss rate causes an increase in concentrations of chemicals across all trophic levels. A sensitivity analysis demonstrates that nutrient recycling is an important ecosystem process impacting contaminant concentrations, generating predictions to be addressed by future empirical studies. Importantly, our model demonstrates the utility of our framework for identifying drivers of contaminant dynamics in connected ecosystems including the importance that a) ecosystem processes, and b) movement, especially movement of lower trophic levels, have on contaminant concentrations. For example, how increasing nutrient loss rate leads to increasing contaminant concentrations, or how movement of lower trophic levels contributes to elevated herbivore contaminant concentrations. This dynamic is particularly relevant given that the flow of matter between ecosystems also serves as a vector for the transport of contaminants.

ecology↗

bioRxiv2023

Getting More by Asking for Less: Linking Species Interactions to Species Co-Distributions in Metacommunities

One of the more difficult challenges in community ecology is inferring species interactions on the basis of patterns in the spatial distribution of organisms. At its core, the problem is that distributional patterns reflect the realized niche, the net result of a complex interplay of processes involving dispersal, environmental, and interaction effects. Disentangling these effects can be difficult on at least two distinct levels. From a statistical point of view, splitting a populations variation into contributions from its interaction partners, abiotic environment and spatial proximity requires natural experiments where all three factors somehow vary independently from each other. On a more conceptual level, it is not even clear how to meaningfully separate these processes: for instance, species interactions could depend on the state of the abiotic and biotic environment, and these two processes may combine in highly non-additive ways. Here we show that the latter issue arises almost inescapably, even in a simple theoretical setting designed to minimize it. Using a model of competitive metacommunity dynamics where direct species interactions are assumed to be context-independent, we show that inferring these interactions accurately from cross-species correlations is a major challenge under all but the most restrictive assumptions. However, we also find that it is possible to estimate the statistical moments (mean value and variance) of the species interactions distribution much more robustly, even if the precise values cannot be inferred. Consequently, we argue that study of multi-species spatial patterns can still be informative for theoretical approaches that build on statistical distributions of species parameters to predict macroscopic outcomes of community assembly.

ecology↗

bioRxiv2021

Beyond the fish-Daphnia paradigm: testing the potential for Neoplea striola (Hemiptera: Pleidae) to cause a trophic cascade in subtropical ponds

Trophic cascades, or indirect effects of predators on non-adjacent lower trophic levels, have become paradigmatic in ecology, though they are thought to be stronger in aquatic ecosystems. Most research on freshwater trophic cascades focused on temperate lakes, where fish are present and where Daphnia tend to dominate the zooplankton community. These studies identified that Daphnia often play a key role in facilitating trophic cascades by linking fish to algae with strong food web interactions. However, Daphnia are rare or absent in most tropical and subtropical lowland freshwaters, and fish are absent from small and temporary water bodies, where invertebrates fill the role of top predator. While invertebrate predators are ubiquitous in freshwater systems, most have received little attention in food web research. Therefore, we aimed to test whether trophic cascades are possible in small warmwater ponds where small invertebrates are the top predators and Daphnia are absent. We collected naturally occurring plankton communities from small fishless water bodies in central Texas and propagated them in replicate pond mesocosms. We removed zooplankton from some mesocosms, left the plankton community intact in others, and added one of two densities of the predaceous insect Neoplea striola to others. Following an incubation period we then compared biomasses of plankton groups to assess food web effects between the trophic levels including whether Neoplea caused a trophic cascade by reducing zooplankton. The zooplankton community became dominated by copepods which prefer large phytoplankton and exhibit a fast escape response. Perhaps due to these qualities of the copepods and perhaps due to slow consumption rates by Neoplea on key grazers, no evidence for food web effects were found other than somewhat weak evidence for zooplankton reducing large phytoplankton. More research is needed to understand the behavior and ecology of Neoplea, but trophic cascades may generally be weak or absent in fishless low-latitude lowland water bodies where Daphnia are rare.

ecology↗

bioRxiv2020

Spatial community variability: Interactive effects of predators and isolation on stochastic community assembly

In the absence of environmental heterogeneity, spatial variation among local communities can be mostly attributed to demographic stochasticity (i.e., ecological drift) and historical contingency in colonization (i.e. random dispersal and priority effects). The consequences of demographic stochasticity are highly dependent on community size, gamma, and alpha diversity, which, along with historical contingency, can be strongly affected by dispersal limitation and the presence of predators. We used freshwater insect communities to experimentally test whether and how the presence of a generalist predatory fish and dispersal limitation (i.e., isolation by distance from a source habitat) can change the relative importance of stochastic and non-stochastic processes on community variability. We found that dispersal limitation can have both negative and positive effects on community variability, and their importance may depend on the presence of predatory fish. Negative effects happened because predatory insects cannot always successfully colonize highly isolated ponds, causing herbivores and detritivores to increase in abundance. As a consequence, community size increases, decreasing the importance of demographic stochasticity on community structure. However, when fish is absent, these effects are counterbalanced by an increase in the importance of priority effects generating more distinct communities in more isolated ponds. Such effects can be caused by either pre or post-colonization mechanisms and were absent in the presence of fish predators, likely because fish prevented both predatory and non-predatory insects from becoming more abundant, irrespective of their order of colonization.

ecology↗

bioRxiv2020

Multilevel community assembly of the tadpole gut microbiome

The assembly of local communities is likely to reflect the effects of local environmental factors associated with filters that act at larger spatial scales. Dissecting these multiscale effects remains a timely challenge that is particularly important for host-associated microbiomes. We investigated the relative roles of local selection (due to host species identity) and regional effects (due to water body identity) on the community structure of bacteria in the gut of tadpoles from three biogeographic areas and used graph theory and metanetwork approaches to explore and illustrate the distribution of bacteria across different ponds. The pond of origin, which represents a regional species pool of bacteria, was in general more important in shaping the gut microbiome of tadpoles than host species identity. The resulting metanetworks are modular and indicate relatively few species of bacteria occurring in more than one pond. Thus, each pond represents a relatively distinct species pool of bacteria available for community assembly of the tadpole microbiomes. Our findings indicate that microbiome community assembly in amphibian larvae, as in many other communities, is a multiscale process with important regional effects that constrain how local (i.e. host-dependent) filters act to influence microbiome community composition.Competing Interest StatementThe authors have declared no competing interest.View Full Text

ecology↗

bioRxiv2020

The Internal Structure of Metacommunities

Current analyses of metacommunity data largely focus on global attributes across the entire metacommunity, such as mean alpha, beta, and gamma diversity, as well as the partitioning of compositional variation into single estimates of contributions of space and environmental effects and, more recently, possible contributions of species interactions. However, this view neglects the fact that different species and sites in the landscape can vary widely in how they contribute to these metacommunity-wide attributes. We argue for a new conceptual framework with matched analytics with the goals of studying the complex and interactive relations between process and pattern in metacommunities that is focused on the variation among species and among sites which we call the internal structure of the metacommunity. To demonstrate how the internal structure could be studied, we create synthetic data using a process-based colonization-extinction metacommunity model. We then use Joint Species Distribution Models to estimate how the contributions of space, environment and biotic interactions driving metacommunity assembly differ among species and sites. We find that this approach to the internal structure of metacommunities provides useful information about the distinct ways that different species and different sites contribute to metacommunity structure. Although it has limitations, our work points at a more general approach to understand how other possible complexities might affect internal structure and might thus be incorporated into a more cohesive metacommunity theory.

ecology↗

bioRxiv2020

Modeling How Community Assembly Alters the Functioning of Ecosystems

Although the effects of species richness on ecosystem functioning have been extensively studied, there is increased interest in understanding how community assembly in general might alter the functioning of ecosystems. We focus on two complementary approaches for evaluating how community assembly influences ecosystem function (here, productivity). The first quantifies the relative importance of complementarity and selection by contrasting monocultures with polycultures. The second identifies the effects of species losses and/or gains relative to the baseline polyculture, as well as the indirect effects on other species productivity. We evaluate and contrast these two approaches, using simulated communities structured by different, known competition mechanisms, where species compete for different resources and experience varying levels of environmental heterogeneity. We find that the metrics provided by these approaches can jointly discriminate the mechanisms of competition driving productivity. We then apply our methods to data from a long-term biodiversity-ecosystem experiment (the Jena Experiment) and find that the data do not correspond to any of the competition scenarios we modeled. We address two additional possible complications: facilitation by nitrogen fixing plants, and non-equilibrium behavior during community assembly, and find that a combination of resource competition and facilitation by nitrogen fixing plants is the more likely explanation for the results obtained at Jena.

ecology↗

bioRxiv2019

Top predator introduction changes the effects of spatial isolation on freshwater community structure

The importance of local selective pressures on community structure is predicted to increase with spatial isolation when species favored by local conditions also have higher dispersal rates. In freshwater habitats, the introduction of predatory fish can produce trophic cascades because fish tend to prey upon intermediate predatory taxa, such as predatory insects, which indirectly benefits herbivores and detritivores. Similarly, spatial isolation is known to limit predatory insect's colonization rates more strongly than of herbivores and detritivores, thus generating similar effects. Here we tested the hypothesis that the effect of introduced predatory fish on macroinvertebrate community structure increases across a gradient of spatial isolation by conducting a field experiment where artificial ponds with and without fish (the Redbreast Tilapia) were constructed at three different distances from a source wetland. Overall results show that fish do reduce the abundance of predatory insects but have no effect on the abundance of herbivores and detritivores. Spatial isolation, however, does strengthen the trophic cascade caused by dispersal limitation of predatory insects, but only in the absence of fish. More importantly, macroinvertebrate communities with and without fish tend to diverge more strongly at higher spatial isolation, however, this pattern was not due to an increase in the magnitude of the effect of fish, as initially hypothesized, but to a change in the effect of isolation in the presence of fish. We argue that as spatial isolation increases, suitable prey, such as predatory insects become scarce and fish increases predation pressure upon herbivores and detritivores, dampening the positive effect of spatial isolation on them. Our results highlight the importance of considering interspecific variation in dispersal and multiple trophic levels to better understand the processes generating metacommunity structures.

ecology↗

bioRxiv2019

Predator complementarity dampens variability of phytoplankton biomass in a diversity-stability trophic cascade

Trophic cascades - indirect effects of predators that propagate down through food webs - have been extensively documented. It has also been shown that predator diversity can mediate these trophic cascades, and separately, that herbivore biomass can influence the stability of primary producers. However, whether predator diversity can cause cascading effects on the stability of lower trophic levels has not yet been studied. We conducted a laboratory microcosm experiment and a field mesocosm experiment manipulating the presence and coexistence of two heteropteran predators and measuring their effects on zooplankton herbivores and phytoplankton basal resources. We predicted that if the predators partitioned their zooplankton prey, for example by size, then co-presence of the predators would reduce zooplankton prey mass and lead to 1) increased average values and 2) decreased temporal variability of phytoplankton basal resources. We present evidence that the predators partitioned their zooplankton prey, leading to a synergistic suppression of zooplankton; and that in turn, this suppression of zooplankton reduced the variability of phytoplankton biomass. However, mean phytoplankton biomass was unaffected. Our results demonstrate that predator diversity may indirectly stabilize basal resource biomass via a "diversity-stability trophic cascade," seemingly dependent on predator complementarity, but independent of a classic trophic cascade in which average biomass is altered. Therefore predator diversity, especially if correlated with diversity of prey use, could play a role in regulating ecosystem stability. Furthermore, this link between predator diversity and producer stability has implications for potential biological control methods for improving the reliability of crop yields.

ecology↗

bioRxiv2018

Towards an applied metaecology

The complexity of ecological systems is a major challenge for practitioners and decision-makers who work to avoid, mitigate and manage environmental change. Here, we illustrate how metaecology - the study of spatial interdependencies among ecological systems through fluxes of organisms, energy, and matter - can enhance understanding and improve managing environmental change at multiple spatial scales. We present several case studies illustrating how the framework has leveraged decision-making in conservation, restoration and risk management. Nevertheless, an explicit incorporation of metaecology is still uncommon in the applied ecology literature, and in action guidelines addressing environmental change. This is unfortunate because the many facets of environmental change can be framed as modifying spatial context, connectedness and dominant regulating processes - the defining features of metaecological systems. Narrowing the gap between theory and practice will require incorporating system-specific realism in otherwise predominantly conceptual studies, as well as deliberately studying scenarios of environmental change.

ecology↗

bioRxiv2018

Regional neutrality evolves through local adaptive niche evolution

Joost Vanoverbeke, Department of Biology, Katholieke Universiteit Leuven, Leuven, Belgium. Abstract: Biodiversity in natural systems can be maintained either because niche differentiation among competitors facilitates stable coexistence or because equal fitness among neutral species allows for their long-term co-occurrence despite a slow drift toward extinction. Whereas the relative importance of these two ecological mechanisms has been well-studied in the absence of evolution, the role of local adaptive evolution in maintaining biological diversity through these processes is less clear. Here we study the contribution of local adaptive evolution to coexistence in a landscape of interconnected patches subject to disturbance. Under these conditions, early colonists to empty patches following disturbance can often adapt to novel local conditions sufficiently fast to prevent successful colonization by other pre-adapted species. Over the long term, the iteration of these local-scale priority effects results in niche convergence of species at the regional scale even though species tend to monopolize local patches. Thus, the dynamics evolve from stable coexistence through niche differentiation to neutral co-occurrence at the landscape level while still maintaining strong local niche differentiation. Our model results show that neutrality can emerge at the regional scale from local, niche-based adaptive evolution, potentially resolving why ecologists often observe neutral distribution patterns at the landscape level despite strong niche divergence among local communities. Our results also demonstrate how local adaptive evolution can shape cryptic eco-evolutionary dynamics and thus alter the regional mechanisms that determine biological diversity and resistance to disturbance.

ecology↗