Article

A newly discovered role of evolution in previously published consumer–resource dynamics

May 2014
Ecology Letters 17(8)

May 2014
17(8)

DOI:10.1111/ele.12291

Authors:

Nelson Hairston

Cornell University

Laura E Jones

Bassett Research Institute

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Consumer–resource interactions are fundamental components of ecological communities. Classic features of consumer–resource models are that temporal dynamics are often cyclic, with a ¼-period lag between resource and consumer population peaks. However, there are few published empirical examples of this pattern. Here, we show that many published examples of consumer–resource cycling show instead patterns indicating eco-evolutionary dynamics. When prey evolve along a trade-off between defence and competitive ability, two-species consumer–resource cycles become longer and antiphase (half-period lag, so consumer maxima coincide with minima of the resource species). Using stringent criteria, we identified 21 two-species consumer–resource time series, published between 1934 and 1997, suitable to investigate for eco-evolutionary dynamics. We developed a statistical method to probe for a transition from classic to eco-evolutionary cycles, and find evidence for eco-evolutionary type cycles in about half of the studies. We show that rapid prey evolution is the most likely explanation for the observed patterns.

Biomonitoring for the 21st century: integrating next-generation sequencing into ecological network analysis

Book

Full-text available

Jan 2018

Ecological network analysis (ENA) provides a mechanistic framework for describing complex species interactions, quantifying ecosystem services, and examining the impacts of environmental change on ecosystems. In this chapter, we highlight the importance and potential of ENA in future biomonitoring programs, as current biomonitoring indicators (e.g. species richness, population abundances of targeted species) are mostly descriptive and unable to characterize the mechanisms that underpin ecosystem functioning. Measuring the robustness of multilayer networks in the long term is one way of integrating ecological metrics more generally into biomonitoring schemes to better measure biodiversity and ecosystem functioning. Ecological networks are nevertheless difficult and labour-intensive to construct using conventional approaches, especially when building multilayer networks in poorly studied ecosystems (i.e. many tropical regions). Next-generation sequencing (NGS) provides unprecedented opportunities to rapidly build highly resolved species interaction networks across multiple trophic levels, but are yet to be fully exploited. We highlight the impediments to ecologists wishing to build DNA-based ecological networks and discuss some possible solutions. Machine learning and better data sharing between ecologists represent very important areas for advances in NGS-based networks. The future of network ecology is very exciting as all the tools necessary to build highly resolved multilayer networks are now within ecologists reach.

Cascading Community Consequences of Fish Adaptation

Article

May 2019

Zachary T. Wood

Trophic interactions are an enduring framework for ecological thought. Broad and growing evidence for contemporary evolution has demonstrated that ecology and evolution dynamically interact on similar time scales. In this dissertation, I seek to understand how genetic and plastic trait change in human-influenced systems shape trophic dynamics, how such trait changes are constrained by inherent tradeoffs, and the broad implications of such trait change for ecological communities. I advance the premise that competition-defense tradeoffs are the essential mechanism behind many eco-evolutionary trophic dynamics that can reshape multi-trophic communities. In support of this view, I assess the presence of ecologically relevant genetic evolution along a competition-defense tradeoff in a model species. I also employ models and experiments to quantify how the particularly strong genetic and plastic trait changes in population phenotypes generated by humans can rearrange ecological communities by altering trophic interaction strengths.

Eco-evolutionary feedback as a driver of periodic state shifts in tri-trophic food chains

Article

Full-text available

Nov 2023
EVOL ECOL

Eco-evolutionary feedback can result in periodic shifts with long intervals between alternative community states. Simulations using a food chain model with three trophic levels, namely the resource-prey–predator system, with evolution of an anti-predator trait possessed by the prey (prey trait) have shown long-term oscillations that ecological dynamics alone cannot attain. The alternative community states are characterized by stable states slowly changing with prey trait evolution and fast cycles at the lower two trophic levels. This shift of community dynamical states with large intervals was governed by the evolution of the prey trait. The abrupt state shifts between long and intermittent stationary periods were caused by the interaction between community ecological dynamics and trait evolution. We further examined the effects of genetic variation on the stability of the community. A faster evolutionary rate with larger genetic variance tended to stabilize eco-evolutionary dynamics.

Eco‐evolution from deep time to contemporary dynamics: The role of timescales and rate modulators

Article

Full-text available

Oct 2023
ECOL LETT

Eco‐evolutionary dynamics, or eco‐evolution for short, are often thought to involve rapid demography (ecology) and equally rapid heritable phenotypic changes (evolution) leading to novel, emergent system behaviours. We argue that this focus on contemporary dynamics is too narrow: Eco‐evolution should be extended, first, beyond pure demography to include all environmental dimensions and, second, to include slow eco‐evolution which unfolds over thousands or millions of years. This extension allows us to conceptualise biological systems as occupying a two‐dimensional time space along axes that capture the speed of ecology and evolution. Using Hutchinson's analogy: Time is the ‘theatre’ in which ecology and evolution are two interacting ‘players’. Eco‐evolutionary systems are therefore dynamic: We identify modulators of ecological and evolutionary rates, like temperature or sensitivity to mutation, which can change the speed of ecology and evolution, and hence impact eco‐evolution. Environmental change may synchronise the speed of ecology and evolution via these rate modulators, increasing the occurrence of eco‐evolution and emergent system behaviours. This represents substantial challenges for prediction, especially in the context of global change. Our perspective attempts to integrate ecology and evolution across disciplines, from gene‐regulatory networks to geomorphology and across timescales, from today to deep time.

Mathematical Modeling of Development Scenarios of Plankton Community During Evolution

Conference Paper

Oct 2022

Eco-evolution from deep time to contemporary dynamics: the role of timescales and rate modulators

Preprint

Full-text available

Oct 2022

Eco-evolutionary dynamics, or eco-evolution for short, are thought to involve rapid demography (ecology) and equally rapid phenotypic changes (evolution) leading to novel, emergent system behaviours. This focus on contemporary dynamics is likely due to accumulating evidence for rapid evolution, from classical laboratory microcosms and natural populations, including the iconic Trinidadian guppies. We argue that this view is too narrow, preventing the successful integration of ecology and evolution. While maintaining that eco-evolution involves emergence, we highlight that this may also be true for slow ecology and evolution which unfold over thousands or millions of years, such as the feedbacks between riverine geomorphology and plant evolution. We thereby integrate geomorphology and biome-level feedbacks into eco-evolution, significantly extending its scope. Most importantly, we emphasize that eco-evolutionary systems need not be frozen in state-space: We identify modulators of ecological and evolutionary rates, like temperature or sensitivity to mutation, which can synchronize or desynchronize ecology and evolution. We speculate that global change may increase the occurrence of eco-evolution and emergent system behaviours which represents substantial challenges for prediction. Our perspective represents an attempt to integrate ecology and evolution across disciplines, from gene-regulatory networks to geomorphology and across timescales, from contemporary dynamics to deep time.

The effects of the toxic dinoflagellate Alexandrium on feeding, reproduction and mortality of the copepod Acartia: A systematic review employing weighted linear models

Article

May 2024
HARMFUL ALGAE

Community density patterns estimated by species distribution modeling: the case study of an insect virus interaction

Preprint

Full-text available

Feb 2024

Time delays complicates the analysis of trophic dependence, which requires large time series data to study local associations. Here we propose using species distribution modeling. This approach removes confounding time lag effects and allows using data obtained separately in the different species. Since the approach is correlative, it cannot be interpreted in terms of causality. We apply the method to the interaction between the invasive potato moth Tecia solanivora and its granulovirus PhoGV in the Northern Andes. Host density was analyzed based on 1206 pheromone trap data from 106 sampled sites in Ecuador, Colombia and Venezuela. Virus prevalence was evaluated in 15 localities from 3 regions in Ecuador and Colombia. glm models were optimized for both variables on bioclimatic variables. Predicted virus prevalence was not significantly correlated to host density in the sampled virus sites. Across the climatic range covered by the study, correlation was R=−0.053. Of the total population of insect in this range, 26% were expected to be infected. Infection status was also analyzed for spatial structure at different scales: storage bag, storage room, field, locality, country. Locality and storage bag explained respectively 8% and 26% of the total deviance in infection status in glm analysis. Field and storage structure differed within locality but not always in the same direction. This basic method may help studying statistical relationships between species density across a number of trophic models making use of existing non sympatric data, with none or limited additional sampling effort.

The shape of density dependence and the relationship between population growth, intraspecific competition and equilibrium population density

Article

Dec 2023

The logistic growth model is one of the most frequently used formalizations of density dependence affecting population growth, persistence and evolution. Ecological and evolutionary theory, and applications to understand population change over time often include this model. However, the assumptions and limitations of this popular model are often not well appreciated. Here, we briefly review past use of the logistic growth model and highlight limitations by deriving population growth models from underlying consumer–resource dynamics. We show that the logistic equation likely is not applicable to many biological systems. Rather, density‐regulation functions are usually non‐linear and may exhibit convex or concave curvatures depending on the biology of resources and consumers. In simple cases, the dynamics can be fully described by the Schoener model. More complex consumer dynamics show similarities to a Maynard Smith–Slatkin model. We show how population‐level parameters, such as intrinsic rates of increase and equilibrium population densities are not independent, as often assumed. Rather, they are functions of the same underlying parameters. The commonly assumed positive relationship between equilibrium population density and competitive ability is typically invalid. We propose simple relationships between intrinsic rates of increase and equilibrium population densities that capture the essence of different consumer–resource systems. Relating population level models to underlying mechanisms allows us to discuss applications to evolutionary outcomes and how these models depend on environmental conditions, like temperature via metabolic scaling. Finally, we use time‐series from microbial food chains to fit population growth models as a test case for our theoretical predictions. Our results show that density‐regulation functions need to be chosen carefully as their shapes will depend on the study system's biology. Importantly, we provide a mechanistic understanding of relationships between model parameters, which has implications for theory and for formulating biologically sound and empirically testable predictions.

Coevolution of species colonisation rates controls food‐chain length in spatially structured food webs

Article

Full-text available

Jun 2023
ECOL LETT

How the complexity of food webs depends on environmental variables is a long‐standing ecological question. It is unclear though how food‐chain length should vary with adaptive evolution of the constitutive species. Here we model the evolution of species colonisation rates and its consequences on occupancies and food‐chain length in metacommunities. When colonisation rates can evolve, longer food‐chains can persist. Extinction, perturbation and habitat loss all affect evolutionarily stable colonisation rates, but the strength of the competition‐colonisation trade‐off has a major role: weaker trade‐offs yield longer chains. Although such eco‐evo dynamics partly alleviates the spatial constraint on food‐chain length, it is no magic bullet: the highest, most vulnerable, trophic levels are also those that least benefit from evolution. We provide qualitative predictions regarding how trait evolution affects the response of communities to disturbance and habitat loss. This highlights the importance of eco‐evolutionary dynamics at metacommunity level in determining food‐chain length.

Spatial and ontogenetic variance in local densities modify selection on demographic traits

Article

Full-text available

Apr 2023
FUNCT ECOL

Local density can affect individual performance by altering the strength of species interactions. Within many populations, local densities vary spatially (individuals are patchily distributed) or change across life stages, which should influence the selection and eco‐evolutionary feedback because local density variance affects mean fitness and is affected by traits of individuals. However, most studies on the evolutionary consequences of density‐dependent interactions focus on populations where local densities are relatively constant through time and space. We investigated the influence of spatial and ontogenetic variance in local densities within an insect population by comparing a model integrating both types of local density variance with models including only spatial variance, only ontogenetic variance, or no variance. We parameterized the models with experimental data, then used elasticity and invasion analyses to characterize selection on traits that affect either the local density an individual experiences (mean clutch size) or individuals' sensitivity to density (effect of larval crowding on pupal mass). Spatial and ontogenetic variance reduced population elasticity to effects of local density by 76% and 34% on average, respectively. Spatial variance modified selection and adaptive dynamics by altering the tradeoff between density‐dependent and density‐independent vital rates. In models including spatial variance, strategies that maximized density‐dependent survival were favoured over fecundity‐maximizing strategies even at low population density, counter to predictions of density‐dependent selection theory. Furthermore, only models that included spatial variance, thus linking the scales of oviposition and density‐dependent larval survival, had an evolutionarily stable clutch size. Ontogenetic variance weakened selection on mean clutch size and sensitivity to larval crowding by disrupting the relationship between trait values and performance during critical life stages. We demonstrate that local density variance can strongly modify selection at empirically observed interaction strengths and identify mechanisms for the effects of spatial and ontogenetic variance. Our findings reveal the potential for local density variance to mediate eco‐evolutionary feedback by shaping selection on demographically important traits. Read the free Plain Language Summary for this article on the Journal blog.

Confronting population models with experimental microcosm data: from trajectory matching to state-space models

Article

Full-text available

Apr 2023

Population and community ecology traditionally has a very strong theoretical foundation with well-known dynamical models, such as the logistic and its variations, and many modifications of the classical Lotka–Volterra predator–prey and interspecific competition models. More and more, these classical models are being confronted with data via fitting to empirical time series for purposes of projections or for estimating model parameters of interest. However, using statistical models to fit theoretical models to data is far from trivial, especially for time series data where subsequent measurements are not independent. This raises the question of whether statistical inferences using pure observation error models, such as simple (non-)linear regressions, are biased, and whether more elaborate process error models or state-space models have to be used to address this complexity. In order to help empiricists, especially researchers working with experimental laboratory populations in micro- and mesocosms, make informed decisions about the statistical formalism to use, we here compare different error structures one could use when fitting classical deterministic ordinary differential equation (ODE) models to empirical data. We consider a large range of biological scenarios and theoretical models, from single species to community dynamics and trophic interactions. In order to compare the performance of different error structure models, we use both realistically simulated data and empirical data from microcosms in a Bayesian framework. We find that many model parameters can be estimated precisely with an appropriate choice of error structure using pure observation error or state-space models, if observation errors are not too high. However, Allee effect models are typically hard to identify and state-space models should be preferred when model complexity increases. Our work shows that, at least in the context of low environmental stochasticity and high quality observations, deterministic models can be used to describe stochastic population dynamics that include process variability and observation error. We discuss when more complex state-space model formulations may be required for obtaining accurate parameter estimates. Finally, we provide a comprehensive tutorial for fitting these models in R.

Trait adaptation enhances species coexistence and reduces bistability in an intraguild predation module

Article

Full-text available

Jan 2023

Disentangling how species coexist in an intraguild predation (IGP) module is a great step toward understanding biodiversity conservation in complex natural food webs. Trait variation enabling individual species to adjust to ambient conditions may facilitate coexistence. However, it is still unclear how coadaptation of all species within the IGP module, constrained by complex trophic interactions and trade‐offs among species‐specific traits, interactively affects species coexistence and population dynamics. We developed an adaptive IGP model allowing prey and predator species to mutually adjust their species‐specific defensive and offensive strategies to each other. We investigated species persistence, the temporal variation of population dynamics, and the occurrence of bistability in IGP models without and with trait adaptation along a gradient of enrichment represented by carrying capacity of the basal prey for different widths and speeds of trait adaptation within each species. Results showed that trait adaptation within multiple species greatly enhanced the coexistence of all three species in the module. A larger width of trait adaptation facilitated species coexistence independent of the speed of trait adaptation at lower enrichment levels, while a sufficiently large and fast trait adaptation promoted species coexistence at higher enrichment levels. Within the oscillating regime, increasing the speed of trait adaptation reduced the temporal variability of biomasses of all species. Finally, species coadaptation strongly reduced the presence of bistability and promoted the attractor with all three species coexisting. These findings resolve the contradiction between the widespread occurrence of IGP in nature and the theoretical predictions that IGP should only occur under restricted conditions and lead to unstable population dynamics, which broadens the mechanisms presumably underlying the maintenance of IGP modules in nature. Generally, this study demonstrates a decisive role of mutual adaptation among complex trophic interactions, for enhancing interspecific diversity and stabilizing food web dynamics, arising, for example, from intraspecific diversity. We found that trait adaptation within multiple species greatly enhanced the coexistence of all species in the module. Increasing the speed of trait adaptation buffered the detrimental effects of enrichment on the temporal variability of biomasses of all species. The bistability encountered in the non‐adaptive IGP model was strongly reduced when allowing trait adaptation.

The rate of environmental change as an important driver across scales in ecology

Article

Full-text available

Dec 2022
OIKOS

Global change has been predominantly studied from the prism of ‘how much' rather than ‘how fast' change occurs. Associated to this, there has been a focus on environmental drivers crossing a critical value and causing so‐called regime shifts. This presupposes that the rate at which environmental conditions change is slow enough to allow the ecological entity to remain close to a stable attractor (e.g. an equilibrium). However, environmental change is occurring at unprecedented rates. Equivalently to the classical regime shifts, theory shows that a critical threshold in rates of change can exist, which can cause rate‐induced tipping (R‐tipping). However, the potential implications of R‐tipping in ecology remain understudied. We aim to facilitate the application of R‐tipping theory in ecology with the objective of identifying which properties (e.g. level of organisation) increase susceptibility to rates of change. First, we clarify the fundamental difference between tipping caused by the magnitude as opposed to the rate of change crossing a threshold. Then we present examples of R‐tipping from the ecological literature and seek the ecological properties related to higher sensitivity to rates of change. Specifically, we consider the role of the level of ecological organisation, spatial processes, eco‐evolutionary dynamics and pair–wise interactions in mediating or buffering rate‐induced transitions. Finally, we discuss how targeted experiments can investigate the mechanisms associated to increasing rates of change. Ultimately, we seek to highlight the need to better understand how rates of environmental change may induce ecological responses and to facilitate the systematic study of rates of environmental change in the context of current global change.

Mesostats—A multiplexed, low-cost, do-it-yourself continuous culturing system for experimental evolution of mesocosms

Article

Full-text available

Jul 2022
PLOS ONE

Microbial experimental evolution allows studying evolutionary dynamics in action and testing theory predictions in the lab. Experimental evolution in chemostats (i.e. continuous flow through cultures) has recently gained increased interest as it allows tighter control of selective pressures compared to static batch cultures, with a growing number of efforts to develop systems that are easier and cheaper to construct. This protocol describes the design and construction of a multiplexed chemostat array (dubbed “mesostats”) designed for cultivation of algae in 16 concurrent populations, specifically intended for studying adaptation to herbicides. We also present control data from several experiments run on the system to show replicability, data illustrating the effects of common issues like leaks, contamination and clumps, and outline possible modifications and adaptations of the system for future research.

Prey naiveté alters the balance of consumptive and non‐consumptive predator effects and shapes trophic cascades in freshwater plankton

Article

Full-text available

Jul 2022

Predators drive trophic cascades by reducing prey biomass and altering prey traits, selecting for prey that exhibit constitutive and induced anti‐predator defenses that decrease susceptibility to consumption. These defense traits are often costly, generating a tradeoff between consumptive (CEs) and non‐consumptive predator effects (NCEs). The ecological and evolutionary experience that prey share with a given predator may determine their position along this tradeoff curve, affecting the nature and strength of top–down control of ecosystems. Conceptual models predict that predator‐experienced prey suffer greater NCEs than predator–naive prey, which suffer stronger CEs and total predator effects (CEs + NCEs), but this has not been tested in diverse prey communities. We tested these predictions by comparing the effects of predation (CEs + NCEs) and predation risk (NCEs only) of planktivorous fish on food web structure in pond mesocosms with diverse natural communities of either predator‐naive or predator‐experienced zooplankton. Contrary to expectations, top–down control of zooplankton and phytoplankton biomass was strengthened by prey community experience: in systems with experienced relative to naive zooplankton communities both predation risk (NCEs only) and predation (CEs + NCEs) had stronger effects on zooplankton prey biomass and trophic cascades were twice as strong. These results show that the ecological and evolutionary experience of diverse prey communities alters the balance of consumptive and non‐consumptive predator effects and influences trophic cascade strength.

How does genetic architecture affect eco-evolutionary dynamics? A theoretical perspective

Article

Full-text available

May 2022

Masato Yamamichi

Recent studies have revealed the importance of feedbacks between contemporary rapid evolution (i.e. evolution that occurs through changes in allele frequencies) and ecological dynamics. Despite its inherent interdisciplinary nature, however, studies on eco-evolutionary feedbacks have been mostly ecological and tended to focus on adaptation at the phenotypic level without considering the genetic architecture of evolutionary processes. In empirical studies, researchers have often compared ecological dynamics when the focal species under selection has a single genotype with dynamics when it has multiple genotypes. In theoretical studies, common approaches are models of quantitative traits where mean trait values change adaptively along the fitness gradient and Mendelian traits with two alleles at a single locus. On the other hand, it is well known that genetic architecture can affect short-term evolutionary dynamics in population genetics. Indeed, recent theoretical studies have demonstrated that genetic architecture (e.g. the number of loci, linkage disequilibrium and ploidy) matters in eco-evolutionary dynamics (e.g. evolutionary rescue where rapid evolution prevents extinction and population cycles driven by (co)evolution). I propose that theoretical approaches will promote the synthesis of functional genomics and eco-evolutionary dynamics through models that combine population genetics and ecology as well as nonlinear time-series analyses using emerging big data. This article is part of the theme issue ‘Genetic basis of adaptation and speciation: from loci to causative mutations’.

Mesostats – A multiplexed, low-cost, do-it-yourself continuous culturing system for experimental evolution of mesocosms

Preprint

Full-text available

Apr 2022

Microbial experimental evolution allows studying evolutionary dynamics in action and testing theory predictions in the lab. Experimental evolution in chemostats (i.e. continuous flow through cultures) has recently gained increased interest as it allows tighter control of selective pressures compared to static batch cultures, with a growing number of efforts to develop systems that are easier and cheaper to construct. This protocol describes the design and construction of a multiplexed chemostat array (dubbed “mesostats”) designed for cultivation of algae in 16 concurrent populations, specifically intended for studying adaptation to herbicides. We also present control data from several experiments run on the system to show replicability, data illustrating the effects of common issues like leaks and contamination, and outline possible modifications and adaptations of the system for future research.

Evolutionary dynamics of predator in a community of interacting species

Article

Full-text available

Apr 2022
NONLINEAR DYNAM

We propose a discrete-time model of predator-prey dynamics with Holling type II response function. Each population in the community is considered to be under density limitation of Verhulst low. Predator evolution is considered by taking into account Mendelian inheritance of a lifecycle trait of the diploid predator by a single diallelic locus. In accordance with r-K-selection, the predator genotypes’ fitnesses functionally depends on the prey abundance; thus, its genotypes differing in reproductive potentials adapt unequally to food resource limitation. The proposed model is analytically and numerically studied. The asymptotic genetic composition of the predator is generally determined by the mutual ratio of its genotypes’ fitnesses, expressions for which were obtained to depend only on the predator genotypic parameters. The set of parameters characterizing reproduction processes in prey and predator populations, as well as interspecies interaction, determines community dynamics. The stability loss of model fixed points was shown to occur according to the Neimark–Sacker scenario and a cascade of period-doubling bifurcations. Bistability and multistability are also revealed in the model; therefore, in such regions, the initial conditions determine which of the coexisting dynamics modes will attract. Various attractors are shown to emerge in the community depending on the prey abundance. Maintaining polymorphism for a predator is possible even without overdominance, provided prey abundance fluctuations with large amplitude changing the direction of selection in the predator population. Moreover, varying dynamics of predator genetic composition during evolution process changes the prey dynamics mode.

Quantifying the capacity for contemporary trait changes to drive intermittent predator–prey cycles

Article

Full-text available

Mar 2022
ECOL MONOGR

A large and growing body of theory has demonstrated how the presence of trait variation in prey or predator populations may affect the amplitude and phase of predator–prey cycles. Less attention has been given to so‐called intermittent cycles, in which predator–prey oscillations recurrently disappear and re‐appear, despite such dynamics being observed in empirical systems and modeling studies. A comprehensive understanding of the conditions under which trait changes may drive intermittent predator–prey dynamics, as well as their potential ecological implications, is therefore missing. Here we provide a first systematic analysis of the eco‐evolutionary conditions that may give rise to intermittent predator–prey cycles, investigating 16 models that incorporate different types of trait variation within prey, predators, or both. Our results show that intermittent dynamics often arise through predator–prey coevolution, but only very rarely when only one trophic level can adapt. Additionally, the frequency of intermittent cycles depends on the source of trait variation (genetic variation or phenotypic plasticity) and the genetic architecture (Mendelian or quantitative traits), with intermittency occurring most commonly through Mendelian evolution, and very rarely through phenotypic plasticity. Further analysis identified three necessary conditions for when trait variation can drive intermittent cycles. First, the intrinsic stability of the predator–prey system must depend on the traits of prey, predators, or both. Second, there must be a mechanism causing the recurrent alternation between stable and unstable states, leading to a “trait” cycle superimposed on the population dynamics. Finally, these trait dynamics must be significantly slower than the predator–prey cycles. We show how these conditions explain all the abovementioned patterns. We further show an important unexpected consequence of these necessary conditions: they are most easily met when intraspecific trait variation is at high risk of being lost. As trait diversity is positively associated with ecosystem functioning, this can have potentially severe negative consequences. This novel result highlights the importance of identifying and understanding intermittent cycles in theoretical studies and natural systems. The new approach for detecting and quantifying intermittency we develop here will be instrumental in enabling future study.

Environmental perturbations and transitions between ecological and evolutionary equilibria: an eco-evolutionary feedback framework

Article

Full-text available

Nov 2021

Tim Coulson

I provide a general framework for linking ecology and evolution. I start from the fact that individuals require energy, trace molecules, water, and mates to survive and reproduce, and that phenotypic resource accrual traits determine an individual’s ability to detect and acquire these resources. Optimum resource accrual traits, and their values, are determined by the dynamics of resources, aspects of the environment that hinder resource detection and acquisition by imposing risks of mortality and reproductive failure, and the energetic costs of developing and maintaining the traits – part of an individual’s energy budget. These budgets also describe how individuals utilize energy by partitioning it into maintenance, development and/or reproduction at each age and size, age and size at sexual maturity, and the size and number of offspring produced at each reproductive event. The optimum energy budget is consequently determined by the optimum life history strategy that describes how resources are utilized to maximize fitness by trading off investments in maintenance, development, and reproductive output at each age and size. The optimum life history in turn determines body size. An eco-evolutionary feedback loop occurs when resource accrual traits evolve to impact the quality and quantity of resources that individuals accrue, resulting in a new optimum life history strategy and energy budget required to deliver it, a change in body size, and altered population dynamics that, in turn, impact the resource base. These feedback loops can be complex, but can be studied by examining the eco-evolutionary journey of communities from one equilibrium state to another following a perturbation to the environment.

Drivers and Cascading Ecological Consequences of Gambusia affinis Trait Variation

Article

Full-text available

Oct 2021
AM NAT

Phenotypic trait differences among populations can shape ecological outcomes for communities and ecosystems. However, few studies have mechanistically linked heritable and plastic components of trait variation to generalizable processes of ecology, such as trophic cascades. Here we assess morphological and behavioral trait variation in nine populations of common-garden reared western mosquitofish (Gambusia affinis) from three distinct ancestral predator environments (three populations per environment), each reared in the presence and absence of predator cues. We then use a pond mesocosm experiment to examine the ecological consequences of trait variation and density variation. Our results show significant among-population trait variation, but this variation was generally unrelated to ancestral predator environment. When traits did vary congruently with respect to ancestral predator environment, this trait variation was driven by gene-by-environment interactions. Variation in several mosquitofish traits altered the cascading effects of mosquitofish on zooplankton and primary producers, but the effect of any given trait was typically weaker than that of density. We note that the relatively stronger ecological effects of density may mask the effects of traits in some systems. Our example here shows that trait variation can be highly noncongruent with respect to a perceived selective agent, phenotypic change is a product of complex interactions between genes and the environment, and numerous interacting phenotypes generate significant but potentially cryptic cascading ecological change.

Confronting population models with experimental microcosm data: from trajectory matching to state-space models

Preprint

Full-text available

Apr 2022

Population and community ecology traditionally has a very strong theoretical foundation with well-known models, such as the logistic and its many variations, and many modification of the classical Lotka-Volterra predator-prey and interspecific competition models. More and more, these classical models are confronted to data via fitting to empirical time-series for purposes of projections or for estimating model parameters of interest. However, the interface between mathematical population or community models and data, provided by a statistical model, is far from trivial. In order to help empiricists, especially researchers working with experimental laboratory populations in micro- and mesocosms, make informed decisions, we here ask which error structure one should use when fitting classical deterministic ODE models to empirical data, from single species to community dynamics and trophic interactions. We use both realistically simulated data and empirical data from microcosms to answer this question in a Bayesian framework. We find that many model parameters can be estimated precisely with an appropriate choice of error structure using pure observation error or state-space models, if observation errors are not too high. However, Allee effect models are typically hard to identify and state-space models should be preferred with when model complexity increases. Our work shows that, at least in the context of experimental laboratory populations, deterministic models can be used to describe stochastic population dynamics that include process variability and observation error. Also, many scenarios do not require a complex state-space model formulation and simpler trajectory matching is sufficient for accurate parameter estimates. Finally, we provide a comprehensive tutorial for fitting these models in R.

MODELING PREDATOR EVOLUTION IN INTERACTING SPECIES COMMUNITY

Article

Jan 2021

The paper proposes a model of a predator evolution in a community of two species which interact as a predator and a prey. We assume that the predator's fitness depends on food supplies. The model was examined analytically and numerically. It is shown that the fixed-point stability loss can go according to both, the Neimark-Sacker scenario and the period doubling bifurcation. The model reveals bistability and multistability; therefore, initial conditions determine which of the coexisting dynamic modes will be attracting. It is demonstrated that different dynamic modes can be implemented depending on the prey abundance.

The evolution of niche overlap and competitive differences

Article

Full-text available

Mar 2021
Nat. Ecol. Evol.

Competition can result in evolutionary changes to coexistence between competitors but there are no theoretical models that predict how the components of coexistence change during this eco-evolutionary process. Here we study the evolution of the coexistence components, niche overlap and competitive differences, in a two-species eco-evolutionary model based on consumer–resource interactions and quantitative genetic inheritance. Species evolve along a one-dimensional trait axis that allows for changes in both niche position and species intrinsic growth rates. There are three main results. First, the breadth of the environment has a strong effect on the dynamics, with broader environments leading to reduced niche overlap and enhanced coexistence. Second, coexistence often involves a reduction in niche overlap while competitive differences stay relatively constant or vice versa; in general changes in competitive differences maintain coexistence only when niche overlap remains constant. Large simultaneous changes in niche overlap and competitive difference often result in one of the species being excluded. Third, provided that the species evolve to a state where they coexist, the final niche overlap and competitive difference values are independent of the system’s initial state, although they do depend on the model’s parameters. The model suggests that evolution is often a destructive force for coexistence due to evolutionary changes in competitive differences, a finding that expands the paradox of diversity maintenance.

Humans as the world’s greatest eco-evolutionary force

Preprint

Full-text available

Jan 2021

Humans are dominant global drivers of ecological and evolutionary change, rearranging ecosystems and natural selection in many ways. Here, we show increasing evidence that human activity also plays a disproportionate role in shaping the eco-evolutionary potential of systems. We suggest the net outcome of human influences on trait change, ecology, and the feedbacks that link them, will often (but not always) be to increase the intensity of eco-evolutionary coupling, with important consequences for stability and resilience of populations, communities, and ecosystems. We also integrate existing ecological and evolutionary metrics to predict and manage the eco-evolutionary dynamics of human-impacted systems. To support this framework, we use a simple eco-evo feedbacks model to show that factors affecting coupling strength are major determinants of eco-evolutionary dynamics. Our framework suggests that proper management of anthropogenic effects requires a science of human-effects on eco-evolutionary potential.

Effects of life history and individual development on community dynamics: A review of counterintuitive consequences

Article

Full-text available

Nov 2020

André Marc de Roos

Even though individual life history is the focus of much ecological research, its importance for the dynamics and structure of ecological communities is unclear, or is it a topic of much ongoing research. In this paper I highlight the key life history traits that may lead to effects of life history or ontogeny on ecological communities. I show that asymmetries in the extent of food limitation between individuals in different life stage can give rise to an increase in efficiency with which resources are used for population growth when conditions change. This change in efficiency may result in a positive relationship between stage‐specific density and mortality. The positive relationship between density and mortality in turn leads to predictions about community structure that are not only diametrically opposite to the expectations based on theory that ignores population structure but are also intuitively hard to accept. I provide a few examples that illustrate how taking into account intraspecific differences due to ontogeny radically changes the theoretical expectations regarding the possible outcomes of community dynamics. As the most compelling example I show how a so‐called double‐handicapped looser, that is, a consumer species that is both competitively inferior in the absence of predators and experiences higher mortality when predators are present, can nonetheless oust its opponent that it competes with for the same resource and is exposed to the same predator. Individual life history is often ignored in dynamic models of interacting populations, which tend to be formulated in terms of total densities of identical individuals. However, the consequences of differences between conspecific individuals that arise from differences in their developmental state are substantial and often counterintuitive. This paper reviews these community consequences and discusses under what conditions life history differences will be important.

Allometric Trophic Networks From Individuals to Socio-Ecosystems: Consumer–Resource Theory of the Ecological Elephant in the Room

Article

Full-text available

May 2020

Neo Martinez

A well-known parable is that of the blind men studying an elephant each of which assert the elephant is the part they first hold in their hands, e.g., “rope!” says the tail holder while the leg holder asserts “tree!” The various subdisciplines of ecology appear similar in that we each engage in our enthusiastic but at least somewhat myopic study with remarkably limited agreement or even discussion about the overall system which we all study. Allometric trophic network (ATN) theory offers a path out of this dilemma by integrating across scales, taxa, habitats and organizational levels from physiology to ecosystems based on consumer-resource interactions among co-existing organisms. The network architecture and the metabolic and behavioral processes that determine the structure and dynamics of these interactions form the first principles of ATN theory, which in turn provides a synthetic overview and powerfully predictive framework for ecology from organisms to ecosystems. Beyond ecology, ATN theory also synthesizes eco-evolutionary and socio-ecological research still largely based on consumer-resource mechanisms but respectively integrated with different processes including natural selection and market mechanisms. This paper briefly describes foundations, advances, and future directions of ATN theory including predicting an ecosystem’s phenotype from its community’s genotype in order to accelerate more predictive and unified understanding of the complex systems studied by ecologists and other environmental scientists.

ENVIRONMENTAL PERTURBATIONS AND TRANSITIONS BETWEEN ECOLOGICAL AND EVOLUTIONARY EQUILIBRIA: AN ECO-EVOLUTIONARY FEEDBACK FRAMEWORK

Preprint

Full-text available

Feb 2020

Tim Coulson

In this paper I provide a general framework for linking ecology and evolution. I start from the fact that individuals require energy, trace molecules, water, and mates to survive and reproduce, and that phenotypic resource accrual traits determine an individual's ability to detect and acquire these resources. Optimum traits, and their values, are determined by the dynamics of resources, aspects of the environment that hinder resource detection and acquisition by imposing risks of mortality and reproductive failure, and the energetic costs of developing and maintaining the traits-part of an individual's energy budget. These budgets also describe how individuals utilize energy by partitioning it into maintenance, development and/or reproduction at each age and size, age and size at sexual maturity, and the size and number of offspring produced at each reproductive event. The optimum energy budget and body size is consequently determined by the optimum life history strategy that maximizes fitness by trading off size-and age-specific mortality and development rates with any reproductive gains due to extending development and delaying the onset of reproduction. An eco-evolutionary feedback loop occurs when resource accrual traits evolve impacting the quality and quantity of resources that individuals accrue, leading to a new optimum body size and life history strategy and altered population dynamics that, in turn, impact the resource base. These feedback loops can be complex, but can be studied by examining the eco-evolutionary journey of communities from one equilibrium state to another following a perturbation to the environment.

Prey adaptation along a competition-defense tradeoff cryptically shifts trophic cascades from density- to trait-mediated

Article

Full-text available

Mar 2020
OECOLOGIA

Trophic cascades have become a dominant paradigm in ecology, yet considerable debate remains about the relative strength of density- (consumptive) and trait-mediated (non-consumptive) effects in trophic cascades. This debate may, in part, be resolved by considering prey experience, which shapes prey traits (through genetic and plastic change) and influences prey survival (and therefore density). Here, we investigate the cascading role of prey experience through the addition of mosquitofish (Gambusia affinis) from predator-experienced or predator-naïve sources to mesocosms containing piscivorous largemouth bass (Micropterus salmoides), zooplankton, and phytoplankton. These two sources were positioned along a competition-defense tradeoff. Results show that predator-naïve mosquitofish suffered higher depredation rates, which drove a density-mediated cascade, whereas predator-experienced mosquitofish exhibited higher survival but fed less, which drove a trait-mediated cascade. Both cascades were similar in strength, leading to indistinguishable top-down effects on lower trophic levels. Therefore, the accumulation of prey experience with predators can cryptically shift cascade mechanisms from density- to trait-mediated.

Destabilizing evolutionary and eco-evolutionary feedbacks drive empirical eco-evolutionary cycles

Article

Full-text available

Jan 2020

We develop a method to identify how ecological, evolutionary, and eco-evolutionary feedbacks influence system stability. We apply our method to nine empirically parametrized eco-evolutionary models of exploiter–victim systems from the literature and identify which particular feedbacks cause some systems to converge to a steady state or to exhibit sustained oscillations. We find that ecological feedbacks involving the interactions between all species and evolutionary and eco-evolutionary feedbacks involving only the interactions between exploiter species (predators or pathogens) are typically stabilizing. In contrast, evolutionary and eco-evolutionary feedbacks involving the interactions between victim species (prey or hosts) are destabilizing more often than not. We also find that while eco-evolutionary feedbacks rarely altered system stability from what would be predicted from just ecological and evolutionary feedbacks, eco-evolutionary feedbacks have the potential to alter system stability at faster or slower speeds of evolution. As the number of empirical studies demonstrating eco-evolutionary feedbacks increases, we can continue to apply these methods to determine whether the patterns we observe are common in other empirical communities.

Evolvability Costs of Niche Expansion

Article

Nov 2019
TRENDS GENET

What prevents generalists from displacing specialists, despite obvious competitive advantages of utilizing a broad niche? The classic genetic explanation is antagonistic pleiotropy: genes underlying the generalism produce 'jacks-of-all-trades' that are masters of none. However, experiments challenge this assumption that mutations enabling niche expansion must reduce fitness in other environments. Theory suggests an alternative cost of generalism: decreased evolvability, or the reduced capacity to adapt. Generalists using multiple environments experience relaxed selection in any one environment, producing greater relative lag load. Additionally, mutations fixed by generalist lineages early during their evolution that avoid or compensate for antagonistic pleiotropy may limit access to certain future evolutionary trajectories. Hypothesized evolvability costs of generalism warrant further exploration, and we suggest outstanding questions meriting attention.

Maladapted Prey Subsidize Predators and Facilitate Range Expansion

Article

Full-text available

Oct 2019
AM NAT

Dispersal of prey from predator-free patches frequently supplies a trophic subsidy to predators by providing more prey than are produced locally. Prey arriving from predator-free patches might also have evolved weaker defenses against predators and thus enhance trophic subsidies by providing easily captured prey. Using local models assuming a linear or accelerating trade-off between defense and population growth rate, we demonstrate that immigration of undefended prey increased predator abundances and decreased defended prey through eco-evolutionary apparent competition. In individual-based models with spatial structure, explicit genetics, and gene flow along an environmental gradient, prey became maladapted to predators at the predator's range edge, and greater gene flow enhanced this maladaptation. The predator gained a subsidy from these easily captured prey, which enhanced its abundance, facilitated its persistence in marginal habitats, extended its range extent, and enhanced range shifts during environmental changes, such as climate change. Once the predator expanded, prey adapted to it and the advantage disappeared, resulting in an elastic predator range margin driven by eco-evolutionary dynamics. Overall, the results indicate a need to consider gene flow-induced maladaptation and species interactions as mutual forces that frequently determine ecological and evolutionary dynamics and patterns in nature.

Consumer-resource dynamics is an eco-evolutionary process in a natural plankton community

Article

Full-text available

Sep 2019
Nat. Ecol. Evol.

When traits affecting species interactions evolve rapidly, ecological dynamics can be altered while they occur. These eco-evolutionary dynamics have been documented repeatedly in laboratory and mesocosm experiments. We show here that they are also important for understanding community functioning in a natural ecosystem. Daphnia is a major planktonic consumer influencing seasonal plankton dynamics in many lakes. It is also sensitive to succession in its phytoplankton food, from edible algae in spring to relatively inedible cyanobacteria in summer. We show for Daphnia mendotae in Oneida Lake, New York, United States, that within-year ecological change in phytoplankton (from spring diatoms, cryptophytes and greens to summer cyanobacteria) resulted in consumers evolving increasing tolerance to cyanobacteria over time. This evolution fed back on ecological seasonal changes in population abundance of this major phytoplankton consumer. Oneida Lake is typical of mesotrophic lakes broadly, suggesting that eco-evolutionary consumer-resource dynamics is probably common.

The effects of functional diversity on biomass production, variability, and resilience of ecosystem functions in a tritrophic system

Article

Full-text available

May 2019

Diverse communities can adjust their trait composition to altered environmental conditions, which may strongly influence their dynamics. Previous studies of trait-based models mainly considered only one or two trophic levels, whereas most natural system are at least tritrophic. Therefore, we investigated how the addition of trait variation to each trophic level influences population and community dynamics in a tritrophic model. Examining the phase relationships between species of adjacent trophic levels informs about the strength of top-down or bottom-up control in non-steady-state situations. Phase relationships within a trophic level highlight compensatory dynamical patterns between functionally different species, which are responsible for dampening the community temporal variability. Furthermore, even without trait variation, our tritrophic model always exhibits regions with two alternative states with either weak or strong nutrient exploitation, and correspondingly low or high biomass production at the top level. However, adding trait variation increased the basin of attraction of the high-production state, and decreased the likelihood of a critical transition from the high- to the low-production state with no apparent early warning signals. Hence, our study shows that trait variation enhances resource use efficiency, production, stability, and resilience of entire food webs.

Strategies within predator-prey interactions – from individuals to ecosystems

Thesis

Jan 2019

Michael Raatz

Predator-prey interactions provide central links in food webs. These interaction are directly or indirectly impacted by a number of factors. These factors range from physiological characteristics of individual organisms, over specifics of their interaction to impacts of the environment. They may generate the potential for the application of different strategies by predators and prey. Within this thesis, I modelled predator-prey interactions and investigated a broad range of different factors driving the application of certain strategies, that affect the individuals or their populations. In doing so, I focused on phytoplankton-zooplankton systems as established model systems of predator-prey interactions. At the level of predator physiology I proposed, and partly confirmed, adaptations to fluctuating availability of co-limiting nutrients as beneficial strategies. These may allow to store ingested nutrients or to regulate the effort put into nutrient assimilation. We found that these two strategies are beneficial at different fluctuation frequencies of the nutrients, but may positively interact at intermediate frequencies. The corresponding experiments supported our model results. We found that the temporal structure of nutrient fluctuations indeed has strong effects on the juvenile somatic growth rate of {\itshape Daphnia}. Predator colimitation by energy and essential biochemical nutrients gave rise to another physiological strategy. High-quality prey species may render themselves indispensable in a scenario of predator-mediated coexistence by being the only source of essential biochemical nutrients, such as cholesterol. Thereby, the high-quality prey may even compensate for a lacking defense and ensure its persistence in competition with other more defended prey species. We found a similar effect in a model where algae and bacteria compete for nutrients. Now, being the only source of a compound that is required by the competitor (bacteria) prevented the competitive exclusion of the algae. In this case, the essential compounds were the organic carbon provided by the algae. Here again, being indispensable served as a prey strategy that ensured its coexistence. The latter scenario also gave rise to the application of the two metabolic strategies of autotrophy and heterotrophy by algae and bacteria, respectively. We found that their coexistence allowed the recycling of resources in a microbial loop that would otherwise be lost. Instead, these resources were made available to higher trophic levels, increasing the trophic transfer efficiency in food webs. The predation process comprises the next higher level of factors shaping the predator-prey interaction, besides these factors that originated from the functioning or composition of individuals. Here, I focused on defensive mechanisms and investigated multiple scenarios of static or adaptive combinations of prey defense and predator offense. I confirmed and extended earlier reports on the coexistence-promoting effects of partially lower palatability of the prey community. When bacteria and algae are coexisting, a higher palatability of bacteria may increase the average predator biomass, with the side effect of making the population dynamics more regular. This may facilitate experimental investigations and interpretations. If defense and offense are adaptive, this allows organisms to maximize their growth rate. Besides this fitness-enhancing effect, I found that co-adaptation may provide the predator-prey system with the flexibility to buffer external perturbations. On top of these rather internal factors, environmental drivers also affect predator-prey interactions. I showed that environmental nutrient fluctuations may create a spatio-temporal resource heterogeneity that selects for different predator strategies. I hypothesized that this might favour either storage or acclimation specialists, depending on the frequency of the environmental fluctuations. We found that many of these factors promote the coexistence of different strategies and may therefore support and sustain biodiversity. Thus, they might be relevant for the maintenance of crucial ecosystem functions that also affect us humans. Besides this, the richness of factors that impact predator-prey interactions might explain why so many species, especially in the planktonic regime, are able to coexist.

Effects of variations in adaptation potential on invasion speeds and species ranges

Preprint

Full-text available

Jan 2019

Confronted with global changes and their potential impacts on biodiversity, an important question is to understand the ecological and evolutionary determinants of species geographical distributions. In order to understand how adaptation in heterogeneous environments constrains such distributions, we analyze how the potential of adaptation along an environmental cline affects the geographical distribution and propagation dynamics (invasion or extinction) of a single species. We re-analyse a model initially proposed by Kirkpatrick and Barton using propagation speed to assess whether species distribution is spatially limited or not. We found that for big adaptation potentials, the species invades space following Fisher’s model, whereas for small adaptation potentials the propagation depends on the evolutionary challenge to overcome. We have explicit approximations for the propagation speeds in both cases. We discuss the utility of these propagation speeds as an eco-evolutionary index based on empirical studies.

Eco-evolutionary feedback as a driver of periodic state shifts in tri-trophic food chains

Preprint

Full-text available

Jun 2022

Eco-evolutionary feedback can result in periodic shifts with long intervals between alternative community states. Simulations using a linear food chain model, namely the resource-prey-predator system with prey evolution have shown such an ecologically unfeasible pattern of long-term dynamics. The alternative community states are characterized by stable internal equilibria and fast synchronized perturbations at the lower two trophic levels. This trait-mediated community shift was governed by the evolution of the anti-predator trait of prey and is referred to as “eco-evolutionary oscillation (EEO)”. The observed EEO was interpreted to be because of the interaction between community ecological dynamics and trait evolution. We further examined the effects of genetic variation on the trait-performance relationship on the global stability of the community. The rapid evolutionary rate with high genetic variance and the strong relationship between trait values and predator avoidance tended to stabilize eco-evolutionary dynamics and cause the EEO to vanish.

Aging is selected for, adaptive, and programmed. 8. The ecology and genetics of aging-related adaptation

Preprint

Full-text available

Dec 2022

Kurt Heininger

Individual-based eco-evolutionary framework: towards unifying ecology and evolution

Preprint

Sep 2022

Jan Hrcek

Coevolution of species colonization rates controls food-chain length in spatially structured food webs

Preprint

Full-text available

Oct 2022

The complexity of food webs and how it depends on environmental variables is a long-standing question in ecology. Food-chain length depends on many factors, such as productive space, disturbance and spatial processes. It is not clear though how food-chain length should vary with adaptive evolutionary changes of the constitutive species. Assuming that each trophic level is subject to a competition-colonization trade-off, we model the adaptive evolution of their colonization rates and its consequences on equilibrium occupancies and food-chain length. When colonization rates are allowed to evolve, longer food chains can persist. Extinction, perturbation and habitat loss all affect the evolutionary-stable colonization rates, but trade-off strength (costs of dispersal) has a major role: weaker trade-offs yield longer chains. Our results suggest a strong link between within-trophic level competition, spatial occupancies and food-chain length. Although these eco-evo dynamics partly alleviate the constraint on food-chain length in metacommunities, we show it is no magic bullet: the highest, most vulnerable, trophic levels are also those that least benefit from evolution. Our model generates qualitative predictions regarding how trait evolution affects the response of communities to disturbance and habitat loss. This highlights the importance of eco-evolutionary dynamics at metacommunity level in determining food-chain length.

Structure, stability and functioning of food webs

Thesis

Jan 2022

Christian Guill

In this thesis, a collection of studies is presented that advance research on complex food webs in several directions. Food webs, as the networks of predator-prey interactions in ecosystems, are responsible for distributing the resources every organism needs to stay alive. They are thus central to our understanding of the mechanisms that support biodiversity, which in the face of increasing severity of anthropogenic global change and accelerated species loss is of highest importance, not least for our own well-being. The studies in the first part of the thesis are concerned with general mechanisms that determine the structure and stability of food webs. It is shown how the allometric scaling of metabolic rates with the species' body masses supports their persistence in size-structured food webs (where predators are larger than their prey), and how this interacts with the adaptive adjustment of foraging efforts by consumer species to create stable food webs with a large number of coexisting species. The importance of the master trait body mass for structuring communities is further exemplified by demonstrating that the specific way the body masses of species engaging in empirically documented predator-prey interactions affect the predator's feeding rate dampens population oscillations, thereby helping both species to survive. In the first part of the thesis it is also shown that in order to understand certain phenomena of population dynamics, it may be necessary to not only take the interactions of a focal species with other species into account, but to also consider the internal structure of the population. This can refer for example to different abundances of age cohorts or developmental stages, or the way individuals of different age or stage interact with other species. Building on these general insights, the second part of the thesis is devoted to exploring the consequences of anthropogenic global change on the persistence of species. It is first shown that warming decreases diversity in size-structured food webs. This is due to starvation of large predators on higher trophic levels, which suffer from a mismatch between their respiration and ingestion rates when temperature increases. In host-parasitoid networks, which are not size-structured, warming does not have these negative effects, but eutrophication destabilises the systems by inducing detrimental population oscillations. In further studies, the effect of habitat change is addressed. On the level of individual patches, increasing isolation of habitat patches has a similar effect as warming, as it leads to decreasing diversity due to the extinction of predators on higher trophic levels. In this case it is caused by dispersal mortality of smaller and therefore less mobile species on lower trophic levels, meaning that an increasing fraction of their biomass production is lost to the inhospitable matrix surrounding the habitat patches as they become more isolated. It is further shown that increasing habitat isolation desynchronises population oscillations between the patches, which in itself helps species to persist by dampening fluctuations on the landscape level. However, this is counteracted by an increasing strength of local population oscillations fuelled by an indirect effect of dispersal mortality on the feeding interactions. Last, a study is presented that introduces a novel mechanism for supporting diversity in metacommunities. It builds on the self-organised formation of spatial biomass patterns in the landscape, which leads to the emergence of spatio-temporally varying selection pressures that keep local communities permanently out of equilibrium and force them to continuously adapt. Because this mechanism relies on the spatial extension of the metacommunity, it is also sensitive to habitat change. In the third part of the thesis, the consequences of biodiversity for the functioning of ecosystems are explored. The studies focus on standing stock biomass, biomass production, and trophic transfer efficiency as ecosystem functions. It is first shown that increasing the diversity of animal communities increases the total rate of intra-guild predation. However, the total biomass stock of the animal communities increases nevertheless, which also increases their exploitative pressure on the underlying plant communities. Despite this, the plant communities can maintain their standing stock biomass due to a shift of the body size spectra of both animal and plant communities towards larger species with a lower specific respiration rate. In another study it is further demonstrated that the generally positive relationship between diversity and the above mentioned ecosystem functions becomes steeper when not only the feeding interactions but also the numerous non-trophic interactions (like predator interference or competition for space) between the species of an ecosystem are taken into account. Finally, two studies are presented that demonstrate the power of functional diversity as explanatory variable. It is interpreted as the range spanned by functional traits of the species that determine their interactions. This approach allows to mechanistically understand how the ecosystem functioning of food webs with multiple trophic levels is affected by all parts of the food web and why a high functional diversity is required for efficient transportation of energy from primary producers to the top predators. The general discussion draws some synthesising conclusions, e.g. on the predictive power of ecosystem functioning to explain diversity, and provides an outlook on future research directions.

The Demographic Consequences of Adaptation: Evidence from Experimental Evolution

Article

Full-text available

Jan 2022

ABSTRACT The process of adaptation towards novel environments is directly connected to the acquisition of a higher fitness relative to others. Such an increased fitness is obtained by changes in life history traits that may directly impact population dynamics. From a functional perspective, increased fitness can be achieved through a higher resource use or more efficient resource use, each potentially having its own impact on population dynamics. In case of the first, adaptation is expected to directly translate into higher population growth. In the second case, adaptation requires less energy, and hence, may lead to higher carrying capacity. Adaptation may thus lead to changes in the ecological dynamics, and vice versa. Here, by using a combination of evolutionary experiments with spider mites and a population dynamic model, we investigate how an increase in fecundity (a validated proxy for adaptation) affects a population’s ecological dynamics. Our results show that adaptation can positively affect population growth rate and both positively or negatively affect the carrying capacity depending on the ecological condition leading to variation in adaptation. These findings show the importance of evolution for population dynamics in changing environments, which may ultimately affect the stability and resilience of populations.

Can Eco-Evo Theory Explain Population Cycles in the Field?

Article

Sep 2021

Efforts to explain animal population cycles often invoke consumer-resource theory, which has shown that consumer-resource interactions alone can drive population cycles. Eco-evo theory instead argues that population cycles are partly driven by fluctuating selection for resistance in the resource, but support for eco-evo theory has come almost entirely from laboratory microcosms. Here we ask, Can eco-evo theory explain population cycles in the field? We compared the ability of eco-evo models and classical "eco-only" models to explain data on cycles in the insect Lymantria dispar, in which outbreaks of the insect are terminated by a fatal baculovirus. We carried out a statistical comparison of the ability of eco-only and eco-evo models to explain combined data from L. dispar outbreak cycles and baculovirus epizootics (epidemics in animals). Both models require high host variation in resistance to explain the epizootic data, but high host variation in the eco-evo model leads to consistently accurate predictions of outbreak cycles, whereas in the presence of high host variation the eco-only model can explain outbreak cycles only by invoking high levels of stochasticity, which leads to highly variable and often inaccurate predictions of outbreak cycles. Our work provides statistically robust evidence that eco-evo models can explain population cycles in the field.

The Importance of Eco-evolutionary Potential in the Anthropocene

Article

Full-text available

Mar 2021
BIOSCIENCE

Humans are dominant global drivers of ecological and evolutionary change, rearranging ecosystems and natural selection. In the present article, we show increasing evidence that human activity also plays a disproportionate role in shaping the eco-evolutionary potential of systems—the likelihood of ecological change generating evolutionary change and vice versa. We suggest that the net outcome of human influences on trait change, ecology, and the feedback loops that link them will often (but not always) be to increase eco-evolutionary potential, with important consequences for stability and resilience of populations, communities, and ecosystems. We also integrate existing ecological and evolutionary metrics to predict and manage the eco-evolutionary dynamics of human-affected systems. To support this framework, we use a simple eco–evo feedback model to show that factors affecting eco-evolutionary potential are major determinants of eco-evolutionary dynamics. Our framework suggests that proper management of anthropogenic effects requires a science of human effects on eco-evolutionary potential.

Effects of Rapid Evolution on Population Cycles and Extinction in Predator–Prey Systems

Chapter

Oct 2020

Masato Yamamichi

Traditionally ecologists have tended to consider species as the smallest unit for understanding community dynamics. However, recent studies demonstrated that there is substantial amount of intraspecific genetic variation and the resultant microevolution can affect ecological dynamics. Here I introduce recent studies showing how adaptive phenotypic changes affect community dynamics, especially in predator–prey systems. First, I review the effects of rapid evolution on predator–prey cycles. Experimental and theoretical studies have demonstrated that the phase lag between predator and prey densities can be changed from the classic quarter to the half (“antiphase cycles”) or three-quarters (“clockwise cycles”) by prey defense evolution or coevolution, respectively. In addition, prey defense evolution can cause “cryptic cycles” where predator densities fluctuate whereas prey densities stay almost constant. Second, I explain how rapid adaptive evolution can prevent extinction (“evolutionary rescue”). Evolutionary rescue with interspecific interactions can create counterintuitive dynamics and will be important for understanding species coexistence in communities. Finally, I discuss future perspectives of empirical and theoretical studies on eco-evolutionary dynamics in complex communities.

Ecosystem size shapes antipredator trait evolution in estuarine threespine stickleback

Article

Aug 2020

Ecosystem size is known to influence both community structure and ecosystem processes. Less is known about the evolutionary consequences of ecosystem size. A few studies have shown that ecosystem size shapes the evolution of trophic diversity by shaping habitat heterogeneity, but the effects of ecosystem size on antipredator trait evolution have not been explored. Ecosystem size may impact antipredator trait evolution by shaping predator presence (larger ecosystems have longer food chains) and habitat complexity (larger ecosystems may have more diverse habitat structure). We tested these effects using threespine stickleback from bar‐built estuaries along the Central Coast of California. These stickleback populations are polymorphic for Ectodysplasin‐A (Eda ), a gene that controls bony lateral plates used as antipredator defense. We inferred Eda genotypes from lateral plate phenotypes and show that the frequency of the complete (C) allele, which is associated with greater number of lateral plates, increases as a function of ecosystem size. Predator presence and habitat complexity are both correlated to ecosystem size. The strongest proximate predictor of Eda allele frequencies was the presence of predatory fishes (steelhead trout and sculpin). Counter to expectations, habitat complexity did not have a strong modifying effect on Eda allele frequencies. Our results point to the importance of ecosystem size for determining predator presence as being the primary pathway to evolutionary effects. Ecosystem size has received much attention in ecology. Our work shows that it may be an important determinant of adaptive evolution in wild populations. This article is protected by copyright. All rights reserved.

Eco‐evolutionary dynamics driven by fishing: From single species models to dynamic evolution within complex food webs

Article

Full-text available

Aug 2020
EVOL APPL

Evidence of contemporary evolution across ecological time scales stimulated research on the eco‐evolutionary dynamics of natural populations. Aquatic systems provide a good setting to study eco‐evolutionary dynamics owing to a wealth of long‐term monitoring data and the detected trends in fish life‐history traits across intensively harvested marine and freshwater systems. In the present study, we focus on modelling approaches to simulate eco‐evolutionary dynamics of fishes and their ecosystems. Firstly, we review the development of modelling from single‐species to multispecies approaches. Secondly, we advance the current state‐of‐the‐art methodology by implementing evolution of life‐history traits of a top predator into the context of complex food web dynamics as described by the allometric trophic network (ATN) framework. The functioning of our newly developed eco‐evolutionary ATNE framework is illustrated using a well‐studied lake food web. Our simulations show how both natural selection arising from feeding interactions and size‐selective fishing cause evolutionary changes in the top predator and how those feed back to its prey species and further cascade down to lower trophic levels. Finally, we discuss future directions, particularly the need to integrate genomic discoveries into eco‐evolutionary projections.

Diversity and coexistence are influenced by time-dependent species interactions in a predator-prey system: Coexistence in a predator-prey system

Article

Full-text available

Apr 2020
ECOL LETT

Although numerous studies show that communities are jointly influenced by predation and competitive interactions, few have resolved how temporal variability in these interactions influences community assembly and stability. Here, we addressed this challenge in experimental microbial microcosms by employing empirical dynamic modelling tools to: (1) detect causal interactions between prey species in the absence and presence of a predator; (2) quantify the time‐varying strength of these interactions and (3) explore stability in the resulting communities. Our findings show that predators boost the number of causal interactions among community members, and lead to reduced dynamic stability, but higher coexistence among prey species. These results correspond to time‐varying changes in species interactions, including emergence of morphological characteristics that appeared to reduce predation, and indirectly facilitate growth of predator‐susceptible species. Jointly, our findings suggest that careful consideration of both context and time may be necessary to predict and explain outcomes in multi‐trophic systems.

Size-dependent eco-evolutionary feedback loops in exploited ecosystems

Preprint

Full-text available

Apr 2020

A bstract Harvesting may drive body downsizing along with population declines and decreased harvesting yields. These changes are commonly construed as consequences of direct harvest selection, where small-bodied, early-reproducing individuals are immediately favoured. However, together with directly selecting against a large body size, harvesting and body downsizing alter many ecological features, such as competitive and trophic interactions, and thus also indirectly reshape natural selection acting back on body sizes through eco-evolutionary feedback loops (EEFLs). We sketch plausible scenarios of simple EEFLs in which one-dimensional, density-dependent natural selection acts either antagonistically or synergistically with direct harvest selection on body size. Antagonistic feedbacks favour body-size stasis but erode genetic variability and associated body-size evolvability, and may ultimately impair population persistence and recovery. In contrast, synergistic feedbacks drive fast evolution towards smaller body sizes and favour population resilience, but may have far-reaching bottom-up or top-down effects. We illustrate the further complexities resulting from multiple environmental feedbacks using a co-evolving predator-prey pair, in which case outcomes from EEFLs depend not only on population densities, but also on whether prey sit above or below the optimal predator/prey body-size ratio, and whether prey are more or less evolvable than their predators. EEFLs improve our ability to understand and predict nature’s response to harvesting, but their integration into the research agenda will require a full consideration of the effects and dynamics of natural selection.

PERSPECTIVE: THE PACE OF MODERN LIFE: MEASURING RATES OF CONTEMPORARY MICROEVOLUTION

Article

Full-text available

Dec 1999
EVOLUTION

We evaluate methods for measuring and specifying rates of microevolution in the wild, with particular regard to studies of contemporary, often deemed "rapid," evolution. A considerable amount of ambiguity and inconsistency persists within the field, and we provide a number of suggestions that should improve study design, inference, and clarity of presentation. (1) Some studies measure change over time within a population (allochronic) and others measure the difference between two populations that had a common ancestor in the past (synchronic). Allochronic studies can be used to estimate rates of "evolution," whereas synchronic studies more appropriately estimate rates of "divergence." Rates of divergence may range from a small fraction to many times the actual evolutionary rates in the component populations. (2) Some studies measure change using individuals captured from the wild, whereas others measure differences after rearing in a common environment. The first type of study can be used to specify "phenotypic" rates and the later "genetic" rates. (3) The most commonly used evolutionary rate metric, the darwin, has a number of theoretical shortcomings. Studies of microevolution would benefit from specifying rates in standard deviations per generation, the haldane. (4) Evolutionary rates are typically specified without an indication of their precision. Readily available methods for specifying confidence intervals and statistical significance (regression, bootstrapping, randomization) should be implemented. (5) Microevolutionists should strive to accumulate time series, which can reveal temporal shifts in the rate of evolution and can be used to identify evolutionary patterns. (6) Evolutionary rates provide a convenient way to compare the tempo of evolution across studies, traits, taxa, and time scales, but such comparisons are subject to varying degrees of confidence. Comparisons across different time scales are particularly tenuous. (7) A number of multivariate rate measures exist, but considerable theoretical development is required before their utility can be determined. We encourage the continued investigation of evolutionary rates because the information they provide is relevant to a wide range of theoretical and practical issues.

FROM THE CELL CYCLE TO POPULATION CYCLES IN PHYTOPLANKTON–NUTRIENT INTERACTIONS

Article

Full-text available

Apr 1997

The internal demographic structure of a population influences its dynamics and its response to the environment. Most models for phytoplankton ignore internal structure and group all cells in a single variable such as total biomass or density. However, a cell does have a life history, the cell division cycle. We investigate the significance of the cell cycle to phytoplankton population dynamics in a variable nutrient environment, using chemostat models. Following the transition point hypothesis, nutrient uptake affects cell development only within a limited segment of the cell cycle. Simulation results demonstrate oscillations in cell numbers and population structure generated by this interaction. When nutrient input is varied periodically, the population displays an aperiodic response with frequencies different from that of the forcing. These results also hold for a model that includes nutrient storage by the cells. These dynamics differ from those of traditional chemostat models and from cell cycle models driven by light cycles. Resource control of cell cycle progression may explain the time delays previously postulated to explain oscillatory transients in chemostat experiments. The internal demographic structure of a population influences its dynamics and its response to the environment. Most models for phytoplankton ignore internal structure and group all cells in a single variable such as total biomass or density. However, a cell does have a life history, the cell division cycle. We investigate the significance of the cell cycle to phytoplankton population dynamics in a variable nutrient environment, using chemostat models. Following the transition point hypothesis, nutrient uptake affects cell development only within a limited segment of the cell cycle. Simulation results demonstrate oscillations in cell numbers and population structure generated by this interaction. When nutrient input is varied periodically, the population displays an aperiodic response with frequencies different from that of the forcing. These results also hold for a model that includes nutrient storage by the cells. These dynamics differ from those of traditional chemostat models and from cell cycle models driven by light cycles. Resource control of cell cycle progression may explain the time delays previously postulated to explain oscillatory transients in chemostat experiments.

Development rates, longevity and fecundity of six-spotted mite (Eotetranychus sexmaculatus) at constant temperatures

Article

Full-text available

Aug 2007

Six-spotted mite (Eotetranychus sexmaculatus) is a key pest of avocados in New Zealand. Six-spotted mite feeding on leaves can cause excessive leaf drop and a subsequent reduction in tree productivity and yield. Sixspotted mite development, longevity and fecundity were determined at six constant temperatures ( 10, 13, 18, 21, 25, 30°C) on avocado leaf discs. No larvae hatched from eggs at 10°C. The number of days to complete egg development ranged from 5.3 days at 30°C to 23.9 days at 13°C. Total developmental time (egg to adult) ranged from 29.6 days at 18°C to 11 days at 30°C. Mean adult longevity ranged from 18.8 days at 30°C to 41.4 days at 18°C. The number of eggs laid per female ranged from 6.9 to 20.9. Degree-day models were developed for eggs, larvae and nymphs. It was estimated that 202.8 degree-days, above a threshold temperature of 12.2°C, were required to complete development from egg to adult.

Epigenetic Transgenerational Actions of Endocrine Disruptors and Male Fertility

Article

Full-text available

Jun 2005

Transgenerational effects of environmental toxins require either a chromosomal or epigenetic alteration in the germ line. Transient exposure of a gestating female rat during the period of gonadal sex determination to the endocrine disruptors vinclozolin (an antiandrogenic compound) or methoxychlor (an estrogenic compound) induced an adult phenotype in the F1 generation of decreased spermatogenic capacity (cell number and viability) and increased incidence of male infertility. These effects were transferred through the male germ line to nearly all males of all subsequent generations examined (that is, F1 to F4). The effects on reproduction correlate with altered DNA methylation patterns in the germ line. The ability of an environmental factor (for example, endocrine disruptor) to reprogram the germ line and to promote a transgenerational disease state has significant implications for evolutionary biology and disease etiology.

Phenotypic Variation in a Zooplankton Egg Bank

Article

Full-text available

Dec 1996

Dormant propagule pools may store potentially significant genetic variation that can influence the rate and direction of microevolution via directional selection, temporally fluctuating selection, and evolution of trait covariance between timing of emergence from the propagule pool and fitness characters expressed in the active population. The third process can interact with either of the first two to produce distinct effects. Each process can lead to a different distribution of genotypes and phenotypes between active and dormant subpopulations. We compared the phenotypic distributions of an important fitness character for individuals collected from active and diapausing subpopulations of a freshwater copepod, Diaptomus sanguineus, with a long-lived egg bank. The character, seasonal timing of the switch from production of immediately hatching eggs to diapausing eggs, determines the relative representation of copepods with different switch dates in future generations and is subject to fluctuating selection due to year-to-year changes in the timing and intensity of the seasonal onset of fish predation. The mean timing of diapause is significantly later in the season for copepods reared eggs than it is for copepods reared from individuals collected from the water column. Phenotypic variance for diapause timing does not differ between the two subpopulations. Within the sediment subpopulation, the distribution gf diapause timing depends upon two features of the diapausing eggs: (1) individuals originating from eggs near the sediment surface exhibit a slightly earlier switch date with greater phenotypic variance than individuals from deep in the sediments, and (2) individuals from eggs that hatched shortly after they were collected from sediments have a later seasonal switch to diapause than those that hatched later in time. We hypothesize that our results are explained bg adaptive covariance between traits that influences how long an egg spends in the sediments before hatching and traits that influence the seasonal timing of diapause. The covariance may result from either phenotypic plasticity or from genetic covariance between diapause timing and hatching probability.

A Field Experiment Demonstrating Plant Life-History Evolution and Its Eco-Evolutionary Feedback to Seed Predator Populations

Article

Full-text available

May 2013

The extent to which evolutionary change occurs in a predictable manner under field conditions and how evolutionary changes feed back to influence ecological dynamics are fundamental, yet unresolved, questions. To address these issues, we established eight replicate populations of native common evening primrose (Oenothera biennis). Each population was planted with 18 genotypes in identical frequency. By tracking genotype frequencies with microsatellite DNA markers over the subsequent three years (up to three generations, approximate to 5,000 genotyped plants), we show rapid and consistent evolution of two heritable plant life-history traits (shorter life span and later flowering time). This rapid evolution was only partially the result of differential seed production; genotypic variation in seed germination also contributed to the observed evolutionary response. Since evening primrose genotypes exhibited heritable variation for resistance to insect herbivores, which was related to flowering time, we predicted that evolutionary changes in genotype frequencies would feed back to influence populations of a seed predator moth that specializes on O. biennis. By the conclusion of the experiment, variation in the genotypic composition among our eight replicate field populations was highly predictive of moth abundance. These results demonstrate how rapid evolution in field populations of a native plant can influence ecological interactions.

Phagotrophy by flagellate selects for colonial prey: A possible origin of multicellularity

Article

Full-text available

Feb 1998

Predation was a powerful selective force promoting increased morphological complexity in a unicellular prey held in constant environmental conditions. The green alga, Chlorella vulgaris, is a well-studied eukaryote, which has retained its normal unicellular form in cultures in our laboratories for thousands of generations. For the experiments reported here, steady-state unicellular C. vulgaris continuous cultures were inoculated with the predator Ochromonas vallescia, a phagotrophic flagellated protist (`flagellate'). Within less than 100 generations of the prey, a multicellular Chlorella growth form became dominant in the culture (subsequently repeated in other cultures). The prey Chlorella first formed globose clusters of tens to hundreds of cells. After about 10–20 generations in the presence of the phagotroph, eight-celled colonies predominated. These colonies retained the eight-celled form indefinitely in continuous culture and when plated onto agar. These self-replicating, stable colonies were virtually immune to predation by the flagellate, but small enough that each Chlorella cell was exposed directly to the nutrient medium.

Ecological and evolutionary responses in complex communities: Implications for invasions and eco-evolutionary feedbacks

Article

Full-text available

Mar 2014

Sharon Y Strauss

It is easier to predict the ecological and evolutionary outcomes of interactions in less diverse communities. As species are added to communities, their direct and indirect interactions multiply, their niches may shift, and there may be increased ecological redundancy. Accompanying this complexity in ecological interactions, is also complexity in selection and subsequent evolution, which may feed back to affect the ecology of the system, as species with different traits may play different ecological roles. Drawing from my own work and that of many others, I first discuss what we currently understand about ecology and evolution in light of simple and diverse communities, and suggest the importance of escape from community complexity per se in the success of invaders. Then, I examine how community complexity may influence the nature and magnitude of eco‐evolutionary feedbacks, classifying eco‐evolutionary dynamics into three general types: those generating alternative stable states, cyclic dynamics, and those maintaining ecological stasis and stability. The latter may be important and yet very hard to detect. I suggest future directions, as well as discuss methodological approaches and their potential pitfalls, in assessing the importance and longevity of eco‐evolutionary feedbacks in complex communities. Synthesis The ecology, evolution and eco‐evolutionary dynamics of simple and diverse communities are reviewed. In more diverse communities, direct and indirect interactions multiply, species’ niches often shift, ecological redundancy can increase, and selection may be less directional. Community complexity may influence the magnitude and nature of eco‐evolutionary dynamics, which are classified into three types: those generating alternative stable states, cyclic dynamics, and those maintaining ecological stasis and stability. Strengths and pitfalls of approaches to investigating eco‐evolutionary feedbacks in complex field communities are discussed.

Reintroducing domesticated wild mice to sociality induces adaptive transgenerational effects on MUP expression

Article

Full-text available

Nov 2013
P NATL ACAD SCI USA

Significance When wild-derived laboratory mice are reintroduced to socially competitive populations, they quickly adapt by producing attractive sons that otherwise have no fitness advantages, consistent with the sexy sons model of sexual selection. These attractive sons inherit up-regulated expression of several pheromones belonging to the major urinary protein (MUP) family. Up-regulation is controlled by maternal social experience, and is associated with epigenetic modifications of MUP promoters that could enhance transcription. Inheritance of up-regulated MUPs is likely adaptive because females have odor preferences for male scent marks with higher MUP concentration. These results represent one of only a few cases where parental social experience adaptively modifies progeny phenotype.

Existence and Bifurcation of Canards in R^3 in the Case of a Folded Node

Article

Full-text available

Jan 2005
SIAM J APPL DYN SYST

Martin Wechselberger

We give a geometric analysis of canards of folded node type in singularly perturbed systems with two-dimensional (2D) folded critical manifold rising the blow-up technique. The existence of two primary canards is known provided a nonresonance condition μ∉ℕ is satisfied, where μ=λ 1 /λ 2 denotes the ratio of the eigenvalues of the associated folded singularity of the reduced flow. We show that, due to resonances, bifurcation of secondary canards occurs. We give a detailed geometric explanation of this phenomenon using an extension of Melnikov theory to prove a transcritical bifurcation of canards for odd μ. Furthermore, we show numerically the existence of a pitchfork bifurcation for even μ and a novel turning point bifurcation close to μ∈ℕ. We conclude the existence of [(μ-1)/2] secondary canards away from the resonances. Finally, we apply our results to a network of Hodgkin-Huxley neurons with excitatory synaptic coupling and explain the observed slowing of the firing rate of the synchronized network due to the existence of canards of folded node type.

Variance and the Value of Information

Article

Full-text available

Jul 1989

David William Stephens

A simple way to approximate the value of information is proposed. Two kinds of quantities are important in determining the value of information: 1) the optimal behaviors that would be chosen if the decision maker knew which subtype (or state) of the resource it faced; and 2) the costs of small deviations from these subtype optima. The value of information is approximately equal to the product of the mean cost of small deviations from the subtype optima and the variance of a modified distribution of the optimal behaviors. This helps to resolve the conflict between a result from economics, which shows that the value of information does not increase with the variance of subtypes, and results from theoretical behavioral ecology, which show that the effect of adding incomplete information to "conventional' models is greatest when the variance of subtypes is greatest. There is no conflict as long as an increase in the variance of subtypes results in an increase in the variance of subtype optima, as is often the case. Changes in a problem's payoff structure change the value of information. -from Author

The Ontogenetic Niche and Species Interactions in Size-Structured Populations

Article

Full-text available

Nov 2003
Annu Rev Ecol Systemat

Documents the widespread existence of ontogenetic shifts in diet and habitat and explores the consequences of such shifts for species interactions and community structure. Most examples are from the lower vertebrates and invertebrates in freshwater communities. The second part offers a conceptual framework for predicting ontogenic shifts and suggests preliminary approaches for exploring their ecological and evolutionary consequences. It is shown how such life histories may be incorporated into a population dynamics framework.-from Authors

Palmelloids formation in Chlamydomonas reinhardtii: Defence against rotifer predators?

Article

Full-text available

Jun 2006
ANN LIMNOL-INT J LIM

The green alga Chlamydomonas reinhardtii usually occurs in cultures as single, biflagellated cells. However, C. reinhardtii is known for its ability to form gelatinous and palmelloid stages that arise as a result of an interaction with its environment. Exponentially growing unicellular C. reinhardtii formed palmelloid colonies rapidly within 25 h when cultured together with their enemy the rotifer Brachionus calyciflorus. Consequences of palmelloid formation for population dynamics of both C. reinhardtii and B. calyciflorus were examined in continuous flow systems. Palmelloids were only formed in a one-stage system where B. calyciflorus grazers and C. reinhardtii prey were cultured together, but not in a two-stage system in which mainly unicellular C. reinhardtii was pumped into a rotifer culture placed in darkness. The rotifer abundance was lower and the algal biomass higher in the one-stage system compared to the grazing unit of the two-stage system. Inasmuch as palmelloids seemed to give C. reinhardtii cells resistance to grazing, we suggest that at least one of the reasons why C. reinhardtii is capable of forming palmelloids is to cope with herbivory.

Spatial Segregation of the Sexes of Dioecious Plants

Article

Full-text available

Jul 1988

Several recent studies have shown that males and females in some populations of dioecious plants are spatially segregated with respect to an environmental gradient. The inference is often made that such spatial segregation of the sexes (SSS) is favoured by selection because it reduces competition between individuals of opposite sex (sexual "niche partitioning'). SSS can be favoured if male fitness and female fitness respond differently across environments (because of differences in reproductive biology). A reduction in competition between males and females is unlikely to be an evolutionary cause of SSS. Differential mortality is unlikely to evolve as a proximate mechanisms for achieving adaptive SSS. Such a pattern is reported in 21 of 32 species studied, but this may overestimate its true natural frequency. Few studies have sought evidence that an observed pattern of SSS evolved in response to selection, and few have ruled out nonadaptive differential mortality as the cause of the pattern observed. No study has demonstrated that competition between males and females is ultimately responsible for SSS. The evidence currently available indicates that most reported cases of SSS (whether due to adaptation or differential mortality) are caused by differences in the reproductive biology of male and female plants. -from Authors

The Population Dynamics of Microparasites and Their Invertebrate Hosts

Article

Full-text available

Apr 1981

The encyclopaedia of simple disease models.

EFFECT OF RESOURCE ENRICHMENT ON A CHEMOSTAT COMMUNITY OF BACTERIA AND BACTERIOPHAGE

Article

Dec 1997

Consumer-Resource Dynamics (MPB-36)

Book

Dec 2013

PREY ADAPTATION AS A CAUSE OF PREDATOR-PREY CYCLES

Article

Dec 1997
EVOLUTION

We analyze simple models of predator-prey systems in which there is adaptive change in a trait of the prey that determines the rate at which it is captured by searching predators. Two models of adaptive change are explored: (1) change within a single reproducing prey population that has genetic variation for vulnerability to capture by the predator; and (2) direct competition between two independently reproducing prey populations that differ in their vulnerability. When an individual predator's consumption increases at a decreasing rate with prey availability, prey adaptation via either of these mechanisms may produce sustained cycles in both species' population densities and in the prey's mean trait value. Sufficiently rapid adaptive change (e.g., behavioral adaptation or evolution of traits with a large additive genetic variance), or sufficiently low predator birth and death rates will produce sustained cycles or chaos, even when the predator-prey dynamics with fixed prey capture rates would have been stable. Adaptive dynamics can also stabilize a system that would exhibit limit cycles if traits were fixed at their equilibrium values. When evolution fails to stabilize inherently unstable population interactions, selection decreases the prey's escape ability, which further destabilizes population dynamics. When the predator has a linear functional response, evolution of prey vulnerability always promotes stability. The relevance of these results to observed predator-prey cycles is discussed.

THE ROLES OF FLUCTUATING SELECTION AND LONG-TERM DIAPAUSE IN MICROEVOLUTION OF DIAPAUSE TIMING IN A FRESHWATER COPEPOD

Article

Feb 1999
EVOLUTION

Direct observations of selection response in natural, unmanipulated populations in the wild are rare. Those that exist have resulted from major changes in environment during an ongoing study. Selection response should be more common and more readily observable in short-lived organisms where the direction of selection changes from year to year. We examined how the interaction of fluctuating selection, and emergence from long-term diapause, caused ongoing microevolutionary change over eight years in an important life-history trait (diapause timing) in the freshwater calanoid copepod Diaptomus sanguineus. Emergence from long-term diapause releases into the population lineages that did not experience the most recent bout of selection, thereby promoting the maintenance of the heritable trait variation that allows continual selection response. A mechanistic selection model was created on the basis of field and laboratory studies to predict how interannual variations in predation intensity generate year-to-year changes in mean diapause timing and in net reproductive success for alternate trait values. The predicted selection response and the estimated effect of emergence from diapause were both significantly correlated with observed changes in trait mean. A linear model combining selection response and emergence from diapause explained 59% of the variance in year-to-year changes in trait mean. According to this model, strong selection occurred in about half of the years studied, and the average annual contributions to changes in trait mean from selection and emergence were roughly equal. Thus, both fluctuating natural selection and emergence from prolonged diapause affect the expression of diapause timing by D. sanguineus. Fluctuating selection is ubiquitous in nature and may provide opportunities in other populations to witness ongoing natural selection without directional trends in mean phenotype.

Studies on marine planktonic diatoms. 1. Cyclotella nana Hustedt and Detonula confervacea (Cleve) Gran

Article

Jan 1962
CAN J MICROBIOL

Generalized Additive Models: An Introduction With R

Book

Jan 2006

Simon N. Wood

The first edition of this book has established itself as one of the leading references on generalized additive models (GAMs), and the only book on the topic to be introductory in nature with a wealth of practical examples and software implementation. It is self-contained, providing the necessary background in linear models, linear mixed models, and generalized linear models (GLMs), before presenting a balanced treatment of the theory and applications of GAMs and related models. The author bases his approach on a framework of penalized regression splines, and while firmly focused on the practical aspects of GAMs, discussions include fairly full explanations of the theory underlying the methods. Use of R software helps explain the theory and illustrates the practical application of the methodology. Each chapter contains an extensive set of exercises, with solutions in an appendix or in the book’s R data package gamair, to enable use as a course text or for self-study.

Consumer-Resource Dynamics

Article

Jan 2013

Despite often violent fluctuations in nature, species extinction is rare. California red scale, a potentially devastating pest of citrus, has been suppressed for fifty years in California to extremely low yet stable densities by its controlling parasitoid. Some larch budmoth populations undergo extreme cycles; others never cycle. In Consumer-Resource Dynamics, William Murdoch, Cherie Briggs, and Roger Nisbet use these and numerous other biological examples to lay the groundwork for a unifying theory applicable to predator-prey, parasitoid-host, and other consumer-resource interactions. Throughout, the focus is on how the properties of real organisms affect population dynamics. The core of the book synthesizes and extends the authors' own models involving insect parasitoids and their hosts, and explores in depth how consumer species compete for a dynamic resource. The emerging general consumer-resource theory accounts for how consumers respond to differences among individuals in the resource population. From here the authors move to other models of consumer-resource dynamics and population dynamics in general. Consideration of empirical examples, key concepts, and a necessary review of simple models is followed by examination of spatial processes affecting dynamics, and of implications for biological control of pest organisms. The book establishes the coherence and broad applicability of consumer-resource theory and connects it to single-species dynamics. It closes by stressing the theory's value as a hierarchy of models that allows both generality and testability in the field.

Introduction To Quantitative Genetics

Article

Jan 1960

D.S. Falconer

Physiological variation and electrophoretic banding patterns of genetically different seasonal populations of Skeletonema costatum (Bacillariophyceae)

Article

Jan 1982

J.C. Gallagher

Population Fluctuation, an Experimental and Theoretical Approach

Article

Jan 1957

S. Utida

Excerpt This is a brief summary of my work carried out for several recent years on the fluctuation of population density, approached from experimental and partly theoretical ways. The fluctuation of population is one of the main features of an animal population, which however has the opposite attribute that the population always tends to converge to a level of steady state. These two opposed attributes of population have been believed to be only upon a phenomenon from two different sides. It may be reasonable to think of these two different attributes as a unified phenomenon. From this point of view, this study attempts to show experimentally and theoretically how the fluctuation of population occurs under a constant condition of environment, in regard to the three population systems which are different in the combination of component species of population, namely: (1) A system of a single species population, (2) an interacting system...

An Introduction to Population Ecology

Article

Jun 1979

The General Theory of Natural Selection

Book

Jan 1930

R. A. S. Fisher

Prey Adaptation as a Cause of Predator-Prey Cycles

Article

Dec 1997

A Statistical Analysis of the 10-Year Cycle in Canada

Article

Oct 1974

M. G. Bulmer

(1) The main features of the ten-year cycle are the regularity of the period and the irregularity of the amplitude of the oscillations; these features are obvious in data on the lynx cycle, and in the correlogram and periodogram calculated from the data. (2) A statistical model is proposed for the analysis of the 10-year cycle which takes these features into account by including both a strictly periodic term and an autoregressive term depending on the size of the population in the previous year; it is shown that this model fits the data better than the second-order autoregressive model used by Moran (1953). (3) All data on the ten-year cycle in Canada have the same period of about 9.63 years. The other parameters in the model can be estimated by the method of least squares, and estimates of the phase and the average amplitude of the oscillations can then be obtained. (4) This method is used to analyse data on the fur-bearing mammals of Canada between 1751 and 1969. A 10-year cycle exists during at least part of this time in the following species: coyote, fisher, red fox, lynx, marten, mink, muskrat, skunk, wolf, wolverine and snowshoe rabbit. A cycle has also been confirmed in the Atlantic salmon. There is a tendency for the cycle to be most pronounced in the midwest of Canada and to become weaker and later as one moves away from this region. A similar cycle exists in the taiga zone of Russia. (5) The simplest theory is that the cycle in all other species is caused, directly or indirectly, by the cycle in the snowshoe rabbit. The food habits of all the cyclic species are reviewed with this theory in mind. There is considerable difficulty in linking some of the cyclic species convincingly with the snowshoe rabbit, but this is nevertheless still thought to be the most likely explanation since no cyclic meteorological factor has been discovered.

An Analysis of the Predatory Interaction Between Paramecium and Didinium

Article

Oct 1979

B. G. Veilleux

(1) The interaction between the predator Didinium nasutum and its prey Paramecium aurelia was studied in the laboratory. The Paramecium was fed the bacterium Aerobacter aerogenes. (2) The addition of Methyl Cellulose to the culture medium prolonged the coexistence of the species by reducing the rate of ciliate movement and, indirectly, by decreasing the net energy profit of the cells. (3) In the Methyl Cellulose regime, the outcome of the interaction depended upon the concentration of the bacterial nutrient Cerophyl in the medium. The Cerophyl concentration regulates the amount of bacterial food available to the Paramecium and, therefore, can be related to the degree of Paramecium starvation. (4) The efficiency of Didinium as a predator is directly related to the nutritional adequacy of the Paramecium. As the Cerophyl concentration in the medium is reduced and the prey become more starved, the predatory ability of Didinium declines. (5) The type of dynamic behaviour exhibited by the Didinium-Paramecium system at a given Cerophyl concentration is related to the predatory efficiency of Didinium. (6) At low Cerophyl concentrations, the predator and prey coexisted at a numerically stable equilibrium. At intermediate Cerophyl concentrations, although the species coexisted over time, the population densities oscillated with an amplitude related to the Cerophyl level. At high Cerophyl concentrations, the species were unable to coexist. (7) The data was interpreted in terms of the graphical predation theory. The predator and prey zero isoclines were constructed and their points of intersection noted. The comparison of the observed dynamics with those predicted by the graphical model indicated that the theory described the outcome of the Didinium-Paramecium interaction if it was modified to account for time-lags in the response of the predator population to changes in the density of the prey.

The Roles of Fluctuating Selection and Long-Term Diapause in Microevolution of Diapause Timing in a Freshwater Copepod

Article

Feb 1999

Phase Relations in the Ten-Year Cycle

Article

Jun 1975

M. G. Bulmer

It is suggested that the 10-year cycle in any cyclic species, except the snowshoe rabbit, is driven by another cyclic species which either eats it or is eaten by it. A model is set up to investigate the theoretical phase difference between predator and prey when one of them drives a cycle in the other, taking into account factors such as continuous or discrete generations, age at first breeding, density-dependence and delayed implantation. If there is no density-dependence in the driven species the predator should cycle about a quarter of a period behind the prey. Density-dependence decreases the phase difference for prey driving predator but increases it for predator driving prey. The observed phase relations between cyclic species in Canada are discussed in the light of the theoretical findings.

Smoothing spline ANOVA models

Book

Jan 2013

Chong Gu

Introduction.- Model Construction.- Regression with Gaussian-Type Responses.- More Splines.- Regression and Exponential Families.- Regression with Correlated Responses.- Probability Density Estimation.- Hazard Rate Estimation.- Asymptotic Convergence.- Penalized Pseudo Likelihood.

An Introduction to Population Biology

Article

Jan 1978

G.Evelyn Hutchinson

Perspective: The Pace of Modern Life: Measuring Rates of Contemporary Microevolution

Article

Dec 1999
EVOLUTION

Mixotrophy and the toxicity of Ochromonas in a pelagic food web

Article

Nov 2012

1. Toxic compounds produced by many phytoplankton taxa are known to have negative effects on competitors (allelopathy), anti-predatory effects on grazers (mortality or impaired reproduction) or both. Although mixotrophs of the genus Ochromonas are known to be toxic to zooplankton, it has often been assumed in studies of plankton community processes that all flagellates in the size range of this taxon are edible to typical zooplankton grazers (i.e. cells ≤30 μm for Daphnia, ≤6 μm for rotifers). 2. We explored the toxicity of a species of Ochromonas to other planktonic taxa, including its competitors (two species of phytoplankton and protists) and consumers (two species of zooplankton). To test if mode of nutrition by this mixotroph influences its toxicity to other taxa, we exposed each test species to Ochromonas cultured in chemostats under four different nutritional regimes: osmotrophy (labile dissolved organic carbon) and phagotrophy (bacterial prey) in both light and dark conditions (i.e. with or without photosynthesis). 3. Filtrate from osmotrophically fed Ochromonas had a significant negative effect on the population growth rate of two obligate phototrophic phytoplankton, Cryptomonasozolini and Chlamydomonas reinhardtii. The protists Tetrahymena tetrahymena and Paramecium aurelia were also negatively affected by Ochromonas filtrate. Ochromonas cells were toxic to both the rotifer Brachionus calicyflorus and the cladoceran Daphnia pulicaria, with the toxic effects significantly more severe when fed at high cell densities (75 000 cells mL−1) than at low densities (7500 cells mL−1). Ochromonas cultured osmotrophically in the light was more toxic to the Daphnia than cells cultured under other conditions. In contrast, Ochromonas from all nutritional conditions was equally highly toxic to Brachionus. 4. Our findings support the view that Ochromonas can be toxic to other components of the food web with which it interacts. It is especially toxic to zooplankton that directly consume it, although the effect depends upon Ochromonas cell density and whether or not a good food source is simultaneously present. Our results call into question the common practice of pooling flagellates into a single ‘functional group’ included in an ‘edible phytoplankton’ category of cells <30 μm in diameter.

Foraging Theory

Book

Jan 1986

Unpredictable Evolution in a 30Year Study of Darwin’s Finches

Article

The Effect of Space and Enrichment on a Predator-Prey System

Article

Aug 1974

Leo S. Luckinbill

The prolonged coexistence of the predator Didinium nasutum and its prey Paramecium aurelia was obtained in these experiments. In a large experimental volume, predators reduced the prey population to a low density but were unable to capture them all. In small experimental volumes, all the P. aurelia were captured. In large—volume experimental systems enriched with abundant bacterial food, Didinium also captured all the prey. Thus, a large arena and the limitation of the prey population by its food supply are necessary for stable interaction and assure the survival of both predator and prey. Damped population oscillations of predator and prey occurred in the absence of refuges for prey or of physical heterogeneity. See full-text article at JSTOR

Smoothing spline ANOVA models Springer-Verlag

Article

Jan 2013

C. Gu

Understanding the role of environmental variation in population and community dynamics - Introduction

Article

Nov 2003

Peter Chesson

The Elements of Physical Biology

Article

Jan 1925

A. J. Lotka

From the Cell Cycle to Population Cycles in Phytoplankton-Nutrient Interactions

Article

Apr 1997

Coexistence in Laboratory Populations of Paramecium Aurelia and Its Predator Didinium Nasutum

Article

Nov 1973

Leo S. Luckinbill

Previous attempts at the prolonged laboratory study of predator-prey systems lacking refuges or physical complexity have been unsuccessful. The addition of Methyl Cellulose to interacting laboratory populations of Paramecium aurelia and its predator, Didinium nasutum, prolongs coexistence by reducing the frequency of contact between predator and prey. The study of this system under controlled conditions revealed the perturbing influence of a time delay in the predator population that resulted in oscillations of increasing amplitude terminating with D. nasutum's extinction. Enrichment of the system by supplying excess bacteria resulted in the extinction of P. aurelia. The perturbing effect of D. nasutum's time delay was counteracted by reducing the amount of bacterial food for Paramecium. In this system, prey became food-limited at their peak density, resulting in limit cycle oscillations of predator and prey at approximately constant amplitude. The medium used for these experiments lack physical inconsistencies that might act as barriers to movement and did not provide the prey with a superior dispersal ability. Coexistence of the predator and prey in this experimental system did not result from the introduction of refuges or physical complexity.

Morphological changes in Scenedesmus induced by substances releasedfrom Daphnia Arch

Article

Jan 1993
HYDROBIOLOGIA

Effect of Resource Enrichment on a Chemostat Community of Bacteria and Bacteriophage

Article

Dec 1997

We determined the responses of a model laboratory community to resource enrichment and compared these responses to the predictions of prey-dependent and ratiodependent food chain models. Our model community consisted of Escherichia coli B and bacteriophage T4 in chemostats supplied with different concentrations of glucose. We observed the following responses to enrichment: (1) a large and highly significant increase in the equilibrium population density of the predator, bacteriophage T4, (2) a small but significant increase in the equilibrium population density of the prey, E. coli, and (3) a large and highly significant decrease in the stability of both the predator and prey populations. These responses were better predicted by a prey-dependent model (altered to include a time delay between consumption and reproduction by predators) than by a ratio-dependent model Enrichment had a large effect on evolutionary change in our system. Enrichment significantly decreased the amount of time required for mutants of E. coli that were resistant to predation by bacteriophage to appear in the chemostats. Enrichment also significantly increased the rate at which these bacteriophage-resistant mutants invaded the chemostats. These results were also better predicted by the prey-dependent model. Invasion by bacteriophage-resistant mutants had a large effect on the subsequent population dynamics of both predator and prey. Both the equilibrium density and stability of the E. coli population increased following invasion, and the population shifted from being primarily limited by predators to being primarily limited by resources. After invasion by the mutants, the T4 population decreased in equilibrium density, and the population cycled with an increased period. These results were compared to the predictions of a ratio-dependent model and a prey-dependent model altered to include T4-resistant mutants. The dynamics of this community were better predicted by the modified prey-dependent model; however, this model was more complex mathematically than the simpler ratio-dependent model.

Spline Models of Observational Data

Book

Jan 1990

G Wahba

This monograph is based on a series of 10 lectures at Ohio State University at Columbus, March 23–27, 1987, sponsored by the Conference Board of the Mathematical Sciences and the National Science Foundation. The selection of topics is quite personal and, together with the talks of the other speakers, the lectures represent a story, as I saw it in March 1987, of many of the interesting things that statisticians can do with splines. I told the audience that the priority order for topic selection was, first, obscure work of my own and collaborators, second, other work by myself and students, with important work by other speakers deliberately omitted in the hope that they would mention it themselves. This monograph will more or less follow that outline, so that it is very much slanted toward work I had some hand in, although I will try to mention at least by reference important work by the other speakers and some of the attendees. The other speakers were (in alphabetical order), Dennis Cox, Randy Eubank, Ker-Chau Li, Douglas Nychka, David Scott, Bernard Silverman, Paul Speckman, and James Wendelberger. The work of Finbarr O'Sullivan, who was unable to attend, in extending the developing theory to the non-Gaussian and nonlinear case will also play a central role, as will the work of Florencio Utreras.

Temporal dynamics of a simple community with intraguild predation: An experimental test

Article

Apr 2013

We explore how adding complexity to a typical predator–prey interaction affects temporal dynamics. Intraguild predation webs contain competition, predation, and omnivory in a system of three species where theory and empirical results can be compared. We studied a planktonic microcosm community in which an alga is consumed by a flagellate and by a rotifer that also consumes the flagellate. Previously published theory predicts that phase lags between the species are the outcome of a ''tug of war'' among the intraguild-predation links: rotifers$algae, flagellates$algae, and rotifers$flagellates. We observed sustained oscilltions with abundance peaks that corresponded exactly to theoretical predictions in all replicates: peaks of the rotifers and flagellates fell on either side of a quarter-period lag behind the prey (algae) peaks, with the peak of the intermediate predator (flagellates) preceding that of the top predator (rotifers). The phase lags in these experiments suggest that temporal variation in flagellate growth rate is primarily driven by variation in the intensity of its consumption by rotifers, rather than by variation in the density of its algal prey. This system illustrates how interaction strength affects the pattern of intraguild predation cycles and provides an opportunity to explore how evolution of interaction strength may affect those dynamics.

Demographic stochasticity reduces the synchronizing effect of dispersal in predator–prey metapopulations

Article

Jul 2012

Joseph Simonis

Dispersal may affect predator-prey metapopulations by rescuing local sink populations from extinction or by synchronizing population dynamics across the metapopulation, increasing the risk of regional extinction. Dispersal is likely influenced by demographic stochasticity, however, particularly because dispersal rates are often very low in metapopulations. Yet the effects of demographic stochasticity on predator-prey metapopulations are not well known. To that end, I constructed three models of a two-patch predator-prey system. The models constitute a hierarchy of complexity, allowing direct comparisons. Two models included demographic stochasticity (pure jump process [PJP] and stochastic differential equations [SDE]), and the third was deterministic (ordinary differential equations [ODE]). One stochastic model (PJP) treated population sizes as discrete, while the other (SDE) allowed population sizes to change continuously. Both stochastic models only produced synchronized predator-prey dynamics when dispersal was high for both trophic levels. Frequent dispersal by only predators or prey in the PJP and SDE spatially decoupled the trophic interaction, reducing synchrony of the non-dispersive species. Conversely, the ODE generated synchronized predator-prey dynamics across all dispersal rates, except when initial conditions produced anti-phase transients. These results indicate that demographic stochasticity strongly reduces the synchronizing effect of dispersal, which is ironic because demographic stochasticity is often invoked post hoc as a driver of extinctions in synchronized metapopulations.

Rosenzweig, M. L. & MacArthur, R. H. Graphical representation and stability conditions of predator-prey interactions. Am. Nat. 97, 209-223

Article

Jul 1963

Predator-prey interactions are examined in phase space to deduce stability criteria from the isoclines.

A newly discovered role of evolution in previously published consumer–resource dynamics

Abstract

No full-text available

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