Density-dependent Selection Research Articles

Phoresy Involving Insects as Riders or Rides: Life History, Embarkation, and Disembarkation

AbstractThe ability to disperse is vital for all organisms, but especially for those whose habitats deteriorate, necessitating relocation to better feeding or breeding sites. Phoresy is assisted dispersal in which one organism uses another as its vehicle. In this review, phoresy will be largely restricted to cases wherein the rider is not parasitic on the vehicular stage used for dispersal, and in which insects are riders or rides. Phoresy occurs in organisms with limited mobility, and in secondarily brachypterous or completely wingless insects. Intraspecific phoresy also occurs. Generally, immature stages resistant to environmental assaults, such as dauers in nematodes, triungulins in beetles, or deutonymphs in mites, undertake phoresy. A size differential between rider and rider enables several conspecifics to board the same vehicle, likely ensuring mating opportunities at the destination. Riders may have special attachment devices or adhesive secretions to ensure safety during travel. Life cycles of riders and vehicles are often synchronized, and when phoresy is mutualistic, vehicles may also employ chemical tactics to achieve this synchrony. Chemical cues help to identify the appropriate vehicle, for disembarkation, or to lure the vehicle towards riders. Most riders prefer female vehicles, possibly to ensure access to rich nesting sites. Density-dependent selection may operate to limit the number of riders on a vehicle and phoresy may also facilitate sexual selection among riders. Whether vehicles can avoid phoresy is barely understood. This review attempts to place phoresy within a broad evolutionary context and points out the paucity of knowledge in certain research areas.

The emergence of adaptive diversification from plant's light competition

Light competition, the main force in shaping plant height, is ubiquitous in the plant kingdom. Plant height was commonly treated as a competitive strategy and investigated under the game-theoretic framework. However, how plant heights are shaped by light environment under natural selection has not yet been fully understood. Aiming at revealing the potential mechanism causing the height diversification and complex evolutionary dynamics, we here propose an eco-evolutionary model of the plant competing for light, in which the benefit and cost due to light competition as well as density-dependent selection are considered. We provide the criteria for producing different evolutionary consequences. The results show that the moderate levels of competitive costs boost the diversity of plant height, and that the eco-evolutionary feedback results in complex nature of the height evolution. In the power-type cost, the evolutionary consequence of plant height highly depends on the shape of benefit and cost functions, and the height evolution under convex benefit or concave cost displays a trend of evident diversification, which is most pronounced when the two factors are added together, whereas a homogenization tendency of the height evolution occurs in the opposite cases. Meantime, the classification of evolutionary states under different benefit-cost combinations exhibits distinct structure patterns. Generally, more complex evolutionary dynamics are caused if we consider the Hill-type cost: the multiple evolutionary equilibria and phase transitions between these evolutionary equilibria could occur. These results help us in part understand why plant heights in the plant kingdom are highly diverse.

Why aren't warning signals everywhere? On the prevalence of aposematism and mimicry in communities.

Warning signals are a striking example of natural selection present in almost every ecological community - from Nordic meadows to tropical rainforests, defended prey species and their mimics ward off potential predators before they attack. Yet despite the wide distribution of warning signals, they are relatively scarce as a proportion of the total prey available, and more so in some biomes than others. Classically, warning signals are thought to be governed by positive density-dependent selection, i.e. they succeed better when they are more common. Therefore, after surmounting this initial barrier to their evolution, it is puzzling that they remain uncommon on the scale of the community. Here, we explore factors likely to determine the prevalence of warning signals in prey assemblages. These factors include the nature of prey defences and any constraints upon them, the behavioural interactions of predators with different prey defences, the numerical responses of predators governed by movement and reproduction, the diversity and abundance of undefended alternative prey and Batesian mimics in the community, and variability in other ecological circumstances. We also discuss the macroevolution of warning signals. Our review finds that we have a basic understanding of how many species in some taxonomic groups have warning signals, but very little information on the interrelationships among population abundances across prey communities, the diversity of signal phenotypes, and prey defences. We also have detailed knowledge of how a few generalist predator species forage in artificial laboratory environments, but we know much less about how predators forage in complex natural communities with variable prey defences. We describe how empirical work to address each of these knowledge gaps can test specific hypotheses for why warning signals exhibit their particular patterns of distribution. This will help us to understand how behavioural interactions shape ecological communities.

Age-specific habitat preference, carrying capacity, and landscape structure determine the response of population spatial variability to fishing-driven age truncation.

Understanding the mechanisms underlying spatial variability of exploited fish is critical for the sustainable management of fish stocks. Empirical studies suggest that size‐selective fishing can elevate fish population spatial variability (i.e., more heterogeneous distribution) through age truncation, making the population less resilient to changing environment. However, species differ in how their spatial variability responds to age truncation and the underlying mechanisms remain unclear.We hypothesize that age‐specific habitat preference, together with environmental carrying capacity and landscape structure, determines the response of population spatial variability to fishing‐induced age truncation. To test these hypotheses, we design an individual‐based model of an age‐structured fish population on a two‐dimensional landscape under size‐selective fishing. Individual fish reproduces and survives, and moves between habitats according to age‐specific habitat preference and density‐dependent habitat selection.Population spatial variability elevates with increasing age truncation, and the response is stronger for populations with stronger age‐specific habitat preference. On a gradient landscape, reducing carrying capacity elevates the relative importance of density dependence in habitat selection, which weakens the response of spatial variability to age truncation for populations with strong age‐specific habitat preference. On a fragmented landscape, both populations with strong and weak age‐specific habitat preferences are restricted at local optimal habitats, and reducing carrying capacity weakens the responses of spatial variability to age truncation for both populations. Synthesis and applications. We demonstrate that to track and predict the changes in population spatial variability under exploitation, it is essential to consider the interactive effects of age‐specific habitat preference, carrying capacity, and landscape structure. To improve spatial management in fisheries, it is crucial to enhance empirical and theoretical developments in the methodology to quantify age‐specific habitat preference of marine fish, and to understand how climatic change influences carrying capacity and landscape continuity.

The ecology of the genome and the dynamics of the biological dark matter

Transposable elements (TEs) are essential components of the eukaryotic genomes. While mostly deleterious, evidence is mounting that TEs provide the host with beneficial adaptations. How ‘selfish’ or ‘parasitic’ DNA persists until it helps species evolution is emerging as a major evolutionary puzzle, especially in asexual taxa where the lack of sex strongly impede the spread of TEs. Since occasional but unchecked TE proliferations would ultimately drive host lineages toward extinction, asexual genomes are typically predicted to be free of TEs, which contrasts with their persistence in asexual taxa. We designed innovative ‘Eco-genomic’ models that account for both host demography and within-host molecular mechanisms of transposition and silencing to analyze their impact on TE dynamics in asexual genome populations. We unraveled that the spread of TEs can be limited to a stable level by density-dependent purifying selection when TE copies are over-dispersed among lineages and the host demographic turn-over is fast. We also showed that TE silencing can protect host populations in two ways; by preventing TEs with weak effects to accumulate or by favoring the elimination of TEs with large effects. Our predictions may explain TE persistence in known asexual taxa that typically show fast demography and where TE copy number variation between lineages is expected. Such TE persistence in asexual taxa potentially has important implications for their evolvability and the preservation of sexual reproduction.

Long-term patterns in winter habitat selection, breeding and predation in a density-fluctuating, high Arctic lemming population.

Habitat selection is expected to balance benefits and costs that maximizes fitness. Using a rare data set on collared lemming (Dicrostonyx groenlandicus) winter nest location spanning more than two decades, we show that lemmings actively select for Salix snow beds, likely due to its favorable micro-climate, and that lemming habitat selection was density-dependent. Lemmings nevertheless exhibited some flexibility in their habitat selection, which appeared to be influenced by the year-to-year variation in snow conditions. The likelihood of both lemming breeding and nest predation by stoats (Mustela erminea) was not directly linked to habitat despite a delicate interplay between habitat, nest size, breeding, and predation. Hence, the larger lemming nests were found in Salix snow beds, and these were more often used for breeding, but both larger nests and nests used for breeding were also predated more often than other nests. Our study provides a clear example of how density-dependent habitat selection acts to balance fitness in the various habitats utilized by collared lemmings.

Whole plastomes are not enough: phylogenomic and morphometric exploration at multiple demographic levels of the bee orchid clade Ophrys sect. Sphegodes.

Plastid sequences have long dominated phylogeny reconstruction at all time depths, predicated on a usually untested assumption that they accurately represent the evolutionary histories of phenotypically circumscribed species. We combined detailed in situ morphometrics (124 plants) and whole-plastome sequencing through genome skimming (71 plants) in order to better understand species-level diversity and speciation in arguably the most challenging monophyletic group within the taxonomically controversial, pseudo-copulatory bee orchid genus Ophrys. Using trees and ordinations, we interpreted the data at four nested demographic levels-macrospecies, mesospecies, microspecies, and local population-seeking the optimal level for bona fide species. Neither morphological nor molecular discontinuities are evident at any level below macrospecies, the observed overlap among taxa suggesting that both mesospecies and microspecies reflect arbitrary division of a continuum of variation. Plastomes represent geographic location more strongly than taxonomic assignment and correlate poorly with morphology, suggesting widespread plastid capture and possibly post-glacial expansion from multiple southern refugia. As they are rarely directly involved in the speciation process, plastomes depend on extinction of intermediate lineages to provide phylogenetic signal and so cannot adequately document evolutionary radiations. The popular 'ethological' evolutionary model recognizes as numerous 'ecological species' (microspecies) lineages perceived as actively diverging as a result of density-dependent selection on very few features that immediately dictate extreme pollinator specificity. However, it is assumed rather than demonstrated that the many microspecies are genuinely diverging. We conversely envisage a complex four-dimensional reticulate network of lineages, generated locally and transiently through a wide spectrum of mechanisms, but each unlikely to maintain an independent evolutionary trajectory long enough to genuinely speciate by escaping ongoing gene flow. The frequent but localized microevolution that characterizes the Ophrys sphegodes complex is often convergent and rarely leads to macroevolution. Choosing between the contrasting 'discontinuity' and 'ethology' models will require next-generation sequencing of nuclear genomes plus ordination of corresponding morphometric matrices, seeking the crucial distinction between retained ancestral polymorphism-consistent with lineage divergence-and polymorphisms reflecting gene flow through 'hybridization'-more consistent with lineage convergence.

Habitat selection patterns are density dependent under the ideal free distribution.

Despite being widely used, habitat selection models are rarely reliable and informative when applied across different ecosystems or over time. One possible explanation is that habitat selection is context‐dependent due to variation in consumer density and/or resource availability. The goal of this paper is to provide a general theoretical perspective on the contributory mechanisms of consumer and resource density‐dependent habitat selection, as well as on our capacity to account for their effects.Towards this goal we revisit the ideal free distribution (IFD), where consumers are assumed to be omniscient, equally competitive and freely moving, and are hence expected to instantaneously distribute themselves across a heterogeneous landscape such that fitness is equalised across the population. Although these assumptions are clearly unrealistic to some degree, the simplicity of the structure in IFD provides a useful theoretical vantage point to help clarify our understanding of more complex spatial processes. Of equal importance, IFD assumptions are compatible with the assumptions underlying common habitat selection models.Here we show how a fitness‐maximising space use model, based on IFD, gives rise to resource and consumer density‐dependent shifts in consumer distribution, providing a mechanistic explanation for the context‐dependent outcomes often reported in habitat selection analysis. Our model suggests that adaptive shifts in consumer distribution patterns would be expected to lead to nonlinear and often non‐monotonic patterns of habitat selection.These results indicate that even under the simplest of assumptions about adaptive organismal behaviour, habitat selection strength should critically depend on system‐wide characteristics. Clarifying the impact of adaptive behavioural responses may be pivotal in making meaningful ecological inferences about observed patterns of habitat selection and allow reliable transferability of habitat selection predictions across time and space.

Spatial and density-dependent multilevel selection on weed-infested maize

Spatial and density-dependent multilevel selection on weed-infested maize

The eco-evolutionary dynamics of a predator-prey system across an r/K continuum

The effects of a single trait on more than one ecological function is called ecological pleiotropy. Traits that exhibit ecological pleiotropy are relevant to eco-evolutionary dynamics because the structure of interaction between the trait and its ecological functions alters how eco-evolutionary feedback loops emerge. Density-dependent selection (DDS) assumes that a single trait affects both density-independent and density-dependent population growth through ecological pleiotropy, and is one of the simplest routes for feedback loops. The r/K theory proposes a mechanism by which DDS occurs, but its predictions were poorly explored in an eco-evolutionary context. Some assumptions of the r/K theory seems to be relevant for the eco-evolution of predator-prey interactions. However, the relationship between these theories were poorly explored. Here, we investigate how does the r/K theory relates to the eco-evolution of predator-prey systems. We seek to answer two questions: (1) What are the system’s parameters that affect the predominance of r- and K-selection? (2) Does system’s qualitative behaviour depends on whether the predominant selection on prey population is an r- or a K-selection? To answer these questions, we built a model of differential equations describing the eco-evolutionary dynamics of a predator-prey system. We assume that prey vulnerability to predation is an adaptive trait that affects preys density-dependent growth rate through ecological pleiotropy. Then, we partitioned the selection gradient in its r- and K-selection components and evaluate how their magnitude relates to systems behaviour. We found that stable predator-prey cycles only occurs when K-selection is predominant. When r-selection is predominant, cycles lead to a runaway dynamics. Furthermore, the way predators parameters affect prey position in the r/K continuum depends on how they affect predation risk. While increasing predation risk increases K-selection, decreasing it increases r-selection. We discuss the relevance of the structure of ecological pleiotropy to our results and the perspectives that unifies the r/K theory and eco-evolutionary dynamics.

Phenotypic evolution in stochastic environments: The contribution of frequency- and density-dependent selection.

Understanding how environmental variation affects phenotypic evolution requires models based on ecologically realistic assumptions that include variation in population size and specific mechanisms by which environmental fluctuations affect selection. Here we generalize quantitative genetic theory for environmentally induced stochastic selection to include general forms of frequency- and density-dependent selection. We show how the relevant fitness measure under stochastic selection relates to Fisher's fundamental theorem of natural selection, and present a general class of models in which density regulation acts through total use of resources rather than just population size. In this model, there is a constant adaptive topography for expected evolution, and the function maximized in the long run is the expected factor restricting population growth. This allows us to generalize several previous results and to explain why apparently " -selected" species with slow life histories often have low carrying capacities. Our joint analysis of density- and frequency-dependent selection reveals more clearly the relationship between population dynamics and phenotypic evolution, enabling a broader range of eco-evolutionary analyses of some of the most interesting problems in evolution in the face of environmentalvariation.

Invasion implies substitution in ecological communities with class-structured populations

Long-term evolution of quantitative traits is classically and usefully described as the directional change in phenotype due to the recurrent fixation of new mutations. A formal justification for such continual evolution ultimately relies on the “invasion implies substitution”-principle. Here, whenever a mutant allele causing a small phenotypic change can successfully invade a population, the ancestral (or wild-type) allele will be replaced, whereby fostering gradual phenotypic change if the process is repeated. It has been argued that this principle holds in a broad range of situations, including spatially and demographically structured populations experiencing frequency- and density-dependent selection under demographic and environmental fluctuations. However, prior studies have not been able to account for all aspects of population structure, leaving unsettled the conditions under which the “invasion implies substitution”-principle really holds. In this paper, we start by laying out a program to explore and clarify the generality of the “invasion implies substitution”-principle. Particular focus is given on finding an explicit and functionally constant representation of the selection gradient on a quantitative trait. Using geometric singular perturbation methods, we then show that the “invasion implies substitution”-principle generalizes to well-mixed and scalar-valued polymorphic multispecies ecological communities that are structured into finitely many demographic (or physiological) classes. The selection gradient is shown to be constant over the evolutionary timescale and that it depends only on the resident phenotype, individual growth-rates, population steady states and reproductive values, all of which are calculated from the resident dynamics. Our work contributes to the theoretical foundations of evolutionary ecology.

Territoriality drives preemptive habitat selection in recovering wolves: Implications for carnivore conservation

According to the ideal-free distribution (IFD), individuals within a population are free to select habitats that maximize their chances of success. Assuming knowledge of habitat quality, the IFD predicts that average fitness will be approximately equal among individuals and between habitats, while density varies, implying that habitat selection will be density dependent. Populations are often assumed to follow an IFD, although this assumption is rarely tested with empirical data, and may be incorrect when territoriality indicates habitat selection tactics that deviate from the IFD (e.g. ideal-despotic distribution or ideal-preemptive distribution). When territoriality influences habitat selection, species' density will not directly reflect components of fitness such as reproductive success or survival. In such cases, assuming an IFD can lead to false conclusions about habitat quality. We tested theoretical models of density-dependent habitat selection on a species known to exhibit territorial behaviour in order to determine whether commonly applied habitat models are appropriate under these circumstances. We combined long-term radiotelemetry and census data from grey wolves Canis lupus in the Upper Peninsula of Michigan, USA to relate spatiotemporal variability in wolf density to underlying classifications of habitat within a hierarchical state-space modelling framework. We then iteratively applied isodar analysis to evaluate which distribution of habitat selection best described this recolonizing wolf population. The wolf population in our study expanded by >1,000% during our study (~50 to >600 individuals), and density-dependent habitat selection was most consistent with the ideal-preemptive distribution, as opposed to the ideal-free or ideal-despotic alternatives. Population density of terrestrial carnivores may not be positively correlated with the fitness value of their habitats, and density-dependent habitat selection patterns may help to explain complex predator-prey dynamics and cascading indirect effects. Source-sink population dynamics appear likely when species exhibit rapid growth and occupy interspersed habitats of contrasting quality. These conditions are likely and have implications for large carnivores in many systems, such as areas in North America and Europe where large predator species are currently recolonizing their former ranges.

Contrasting patterns of density-dependent selection at different life stages can create more than one fast-slow axis of life-history variation.

There has been much recent research interest in the existence of a major axis of life‐history variation along a fast–slow continuum within almost all major taxonomic groups. Eco‐evolutionary models of density‐dependent selection provide a general explanation for such observations of interspecific variation in the "pace of life." One issue, however, is that some large‐bodied long‐lived “slow” species (e.g., trees and large fish) often show an explosive “fast” type of reproduction with many small offspring, and species with “fast” adult life stages can have comparatively “slow” offspring life stages (e.g., mayflies). We attempt to explain such life‐history evolution using the same eco‐evolutionary modeling approach but with two life stages, separating adult reproductive strategies from offspring survival strategies. When the population dynamics in the two life stages are closely linked and affect each other, density‐dependent selection occurs in parallel on both reproduction and survival, producing the usual one‐dimensional fast–slow continuum (e.g., houseflies to blue whales). However, strong density dependence at either the adult reproduction or offspring survival life stage creates quasi‐independent population dynamics, allowing fast‐type reproduction alongside slow‐type survival (e.g., trees and large fish), or the perhaps rarer slow‐type reproduction alongside fast‐type survival (e.g., mayflies—short‐lived adults producing few long‐lived offspring). Therefore, most types of species life histories in nature can potentially be explained via the eco‐evolutionary consequences of density‐dependent selection given the possible separation of demographic effects at different life stages.

Life‐history strategy varies with the strength of competition in a food‐limited ungulate population

Fluctuating population density in stochastic environments can contribute to maintain life-history variation within populations via density-dependent selection. We used individual-based data from a population of Soay sheep to examine variation in life-history strategies at high and low population density. We incorporated life-history trade-offs among survival, reproduction and body mass growth into structured population models and found support for the prediction that different life-history strategies are optimal at low and high population densities. Shorter generation times and lower asymptotic body mass were selected for in high-density environments even though heavier individuals had higher probabilities to survive and reproduce. In contrast, greater asymptotic body mass and longer generation times were optimal at low population density. If populations fluctuate between high density when resources are scarce, and low densities when they are abundant, the variation in density will generate fluctuating selection for different life-history strategies, that could act to maintain life-history variation.

A matrix model for density-dependent selection in stage-classified populations, with application to pesticide resistance in Tribolium

The study of eco-evolutionary dynamics is based on the idea that ecological and evolutionary processes may operate on the same, or very similar, time scales, and that interactions of ecological and evolutionary processes may have important consequences. Here we develop a model that combines Mendelian population genetics with nonlinear demography to create a truly eco-evolutionary model. We use the vec-permutation matrix approach, classifying individuals by stage and genotype. The demographic component is female dominant and density-dependent. The genetic component includes random mating by stage and genotype, and arbitrary effects of genotype on the demographic phenotype. Mutation is neglected. The result is a nonlinear matrix population model that projects the stage × genotype distribution. We show that the results can include bifurcations of population dynamics driven by the response to selection. We present analytical criteria that determine whether one allele excludes the other or if they persist in a protected polymorphism. The results are based on local stability analysis of the homozygous boundary equilibria.As an example, we use a density-dependent stage-classified model of the flour beetle Tribolium castaneum. Our model permits arbitrary life-cycle complexity and nonlinearity. Tribolium has developed resistance to the pesticide malathion due to a dominant allele at a single autosomal locus. Using parameters reported from laboratory experiments, we show that the model successfully describes the dynamics of both resistant and susceptible homozygotes, and the outcome of a selection experiment containing both alleles. Stability analysis of the boundary equilibria confirms that the resistant allele excludes the susceptible allele, even in the absence of malathion, agreeing with previously reported results.

Territorial landscapes: incorporating density-dependence into wolf habitat selection studies.

Habitat selection is a process that spans space, time and individual life histories. Ecological analyses of animal distributions and preferences are most accurate when they account for inherent dynamics of the habitat selection process. Strong territoriality can constrain perception of habitat availability by individual animals or groups attempting to colonize or establish new territory. Because habitat selection is a function of habitat availability, broad-scale changes in habitat availability or occupancy can drive density-dependent habitat functional responses. We investigated density-dependent habitat selection over a 19-year period of grey wolf (Canis lupus) recovery in Michigan, USA, using a generalized linear mixed model framework to develop a resource selection probability function (RSPF) with habitat coefficients conditioned on random effects for wolf packs and random year intercepts. In addition, we allowed habitat coefficients to vary as interactions with increasing wolf density over space and time. Results indicated that pack presence was driven by factors representing topography, human development, winter prey availability, forest structure, roads, streams and snow. Importantly, responses to many of these predictors were density-dependent. Spatio-temporal dynamics and population changes can cause considerable variation in wildlife–habitat relationships, possibly confounding interpretation of conventional habitat selection models. By incorporating territoriality into an RSPF analysis, we determined that wolves' habitat use in Michigan shifted over time, for example, exhibiting declining responses to winter prey indices and switching from positive to negative responses with respect to stream densities. We consider this an important example of a habitat functional response in wolves, driven by colonization, density-dependence and changes in occupancy during a time period of range expansion and population increase.

Food quality influences density-dependent fitness, but not always density-dependent habitat selection, in red flour beetles (Coleoptera: Tenebrionidae)

AbstractDensity-dependent habitat selection models inherently rely on the negative relationship between population density and mean fitness in different habitats. Habitats differing in quality, such as different food sources or habitat structure, can have different strengths of density-dependent relationships, which can then affect patterns of density dependence in habitat selection. We tested the hypothesis that density dependence in fitness dictates the patterns in density-dependent habitat selection: individuals should prefer higher-quality habitat over lower-quality habitat. We used controlled experiments with red flour beetles (Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)) to measure density dependence of fitness and to examine density-dependent habitat selection by beetles in wheat (Triticum Linnaeus (Poaceae)), corn (Zea mays Linnaeus (Poaceae)), and soy (Glycine max (Linnaeus) Merrill (Fabaceae)) flour habitats. Despite large differences in fitness between habitats (fitness was the highest in wheat flour, lower in corn flour, and zero in soy flour), beetles showed only weak preference for wheat over corn flour and for corn over soy flour, but showed strong preference for wheat over soy flour. These preferences were the strongest at low density. This study gives insight into the relationship between habitat quality and density-dependent habitat selection in flour beetles.

Scaling up the effects of inbreeding depression from individuals to metapopulations.

Inbreeding is common in nature, and many laboratory studies have documented that inbreeding depression can reduce the fitness of individuals. Demonstrating the consequences of inbreeding depression on the growth and persistence of populations is more challenging because populations are often regulated by density- or frequency-dependent selection and influenced by demographic and environmental stochasticity. A few empirical studies have shown that inbreeding depression can increase extinction risk of local populations. The importance of inbreeding depression at the metapopulation level has been conjectured based on population-level studies but has not been evaluated. We quantified the impact of inbreeding depression affecting the fitness of individuals on metapopulation persistence in heterogeneous habitat networks of different sizes and habitat configuration in a context of natural butterfly metapopulations. We developed a spatial individual-based simulation model of metapopulations with explicit genetics. We used Approximate Bayesian Computation to fit the model to extensive demographic, genetic and life-history data available for the well-studied Glanville fritillary butterfly (Melitaea cinxia) metapopulations in the Åland islands in SW Finland. We compared 18 semi-independent habitat networks differing in size and fragmentation. The results show that inbreeding is more frequent in small habitat networks, and consequently, inbreeding depression elevates extinction risks in small metapopulations. Metapopulation persistence and neutral genetic diversity maintained in the metapopulations increase with the total habitat amount in and mean patch size of habitat networks. Dispersal and mating behaviour interact with landscape structure to determine how likely it is to encounter kin while looking for mates. Inbreeding depression can decrease the viability of small metapopulations even when they are strongly influenced by stochastic extinction-colonization dynamics and density-dependent selection. The findings from this study support that genetic factors, in addition to demographic factors, can contribute to extinctions of small local populations and also of metapopulations.

The generalized ideal free distribution model: Merging current ideal free distribution models into a central framework

Density-dependent habitat selection is a central theme in ecology. Empirical studies collect data with increasing resolution and provide greater opportunities for its testing. However, several different density-dependent habitat selection models exist in the literature incorporating many different scenarios. We attempt to unify some of these models in a single framework, to increase our predictive power, and assist researchers in making predictions from combinations of these models. To achieve this, we created the generalized ideal free distribution, an expansion of the ideal free distribution model. With this model, we synthesize many of the previous theoretical developments in habitat selection to better incorporate temporal dynamics. By using community matrices to represent the interaction between individuals, we demonstrated that thirteen scenarios represented in other studies can be combined into a single model. In addition, for four of these scenarios, our predictions are similar to the original studies that developed these scenarios. Additionally, we derived four novel predictions that take advantage of using community matrices to represent distribution. We discuss how this model creates a connection between community interactions and the distribution of individuals, and its uses in other subjects in ecology.