Merilä, J. & Kotze, J. D. 2003: Preface: Extinction Thresholds: Insights from ecology, genetics, epidemiology and behaviour — Ann. Zool. Fennici 40: 69.
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Benton, T. G. 2003: Understanding the ecology of extinction: are we close to the critical threshold? — Ann. Zool. Fennici 40: 71–80.
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Ovaskainen, O. & Hanski, I. 2003: Extinction threshold in metapopulation models. — Ann. Zool. Fennici 40: 81–97.
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Bascompte, J. 2003: Extinction thresholds: insights from simple models. — Ann. Zool. Fennici 40: 99–114.
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Deredec, A. & Courchamp, F. 2003: Extinction thresholds in host–parasite dynamics. — Ann. Zool. Fennici 40: 115–130.
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Gårdmark, A., Enberg, K., Ripa, J., Laakso, J. & Kaitala, V. 2003: The ecology of recovery. — Ann. Zool. Fennici 40: 131–144.
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Doherty, P. F. Jr., Boulinier, T. & Nichols, J. D. 2003: Local extinction and turnover rates at the edge and interior of species' ranges. — Ann. Zool. Fennici 40: 145–153.
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Gaggiotti, O. E. 2003: Genetic threats to population persistence. — Ann. Zool. Fennici 40: 155–168.
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Whitlock, M. C., Griswold, C. K. & Peters, A. D. 2003: Compensating for the meltdown: The critical effective size of a population with deleterious and compensatory mutations. — Ann. Zool. Fennici 40: 169–183.
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Nunney, L. 2003: The cost of natural selection revisited. — Ann. Zool. Fennici 40: 185–194.
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Taylor, J. E. & Jaenike, J. 2003: Sperm competition and the dynamics of X chromosome drive in finite and structured populations. — Ann. Zool. Fennici 40: 195–206.
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Kokko, H. & Brooks, R. 2003: Sexy to die for? Sexual selection and the risk of extinction. — Ann. Zool. Fennici 40: 207–219.
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Møller, A. P. 2003: Sexual selection and extinction: why sex matters and why asexual models are insufficient. — Ann. Zool. Fennici 40: 221–230.
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Bessa-Gomes, C., Danek-Gontard, M., Cassey, P., Møller, A. P., Legendre, S. & Clobert, J. 2003: Mating behaviour influences extinction risk: insights from demographic modelling and comparative analysis of avian extinction risk. — Ann. Zool. Fennici 40: 231–245.>
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The Spatial Ecology Programme. — Ann. Zool. Fennici 40: 247.
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Benton, T. G. 2003: Understanding the ecology of extinction: are we close to the critical threshold? — Ann. Zool. Fennici 40: 71–80.
How much do we understand about the ecology of extinction? A review of recent literature, and a recent conference in Helsinki gives a snapshot of the "state of the art". This "snapshot" is important as it highlights what we currently know, the tools available for studying the process of extinction, its ecological correlates, and the theory concerning extinction thresholds. It also highlights that insight into the ecology of extinction can come from areas as diverse as the study of culture, the fossil record and epidemiology. Furthermore, it indicates where the gaps in knowledge and understanding exist. Of particular note is the need either to generate experimental data, or to make use of existing empirical data — perhaps through meta-analyses, to test general theory and guide its future development.
Back to the top
Ovaskainen, O. & Hanski, I. 2003: Extinction threshold in metapopulation models. — Ann. Zool. Fennici 40: 81–97. Back to the top
Bascompte, J. 2003: Extinction thresholds: insights from simple models. — Ann. Zool. Fennici 40: 99–114. Back to the top
Deredec, A. & Courchamp, F. 2003: Extinction thresholds in host–parasite dynamics. — Ann. Zool. Fennici 40: 115–130. Back to the top
Gårdmark, A., Enberg, K., Ripa, J., Laakso, J. & Kaitala, V. 2003: The ecology of recovery. — Ann. Zool. Fennici 40: 131–144. Back to the top
Doherty, P. F. Jr., Boulinier, T. & Nichols, J. D. 2003: Local extinction and turnover rates at the edge and interior of species' ranges. — Ann. Zool. Fennici 40: 145–153. Back to the top
Gaggiotti, O. E. 2003: Genetic threats to population persistence. — Ann. Zool. Fennici 40: 155–168. Back to the top
Whitlock, M. C., Griswold, C. K. & Peters, A. D. 2003: Compensating for the meltdown: The critical effective size of a population with deleterious and compensatory mutations. — Ann. Zool. Fennici 40: 169–183. Back to the top
Nunney, L. 2003: The cost of natural selection revisited. — Ann. Zool. Fennici 40: 185–194. Back to the top
Taylor, J. E. & Jaenike, J. 2003: Sperm competition and the dynamics of X chromosome drive in finite and structured populations. — Ann. Zool. Fennici 40: 195–206. Back to the top
Kokko, H. & Brooks, R. 2003: Sexy to die for? Sexual selection and the risk of extinction. — Ann. Zool. Fennici 40: 207–219. Back to the top
Møller, A. P. 2003: Sexual selection and extinction: why sex matters and why asexual models are insufficient. — Ann. Zool. Fennici 40: 221–230. Back to the top
Bessa-Gomes, C., Danek-Gontard, M., Cassey, P., Møller, A. P., Legendre, S. & Clobert, J. 2003: Mating behaviour influences extinction risk: insights from demographic modelling and comparative analysis of avian extinction risk. — Ann. Zool. Fennici 40: 231–245.
The term extinction threshold refers to a critical value of some attribute, such as the amount of habitat in the landscape, below which a population, a metapopulation, or a species does not persist. In this paper we discuss the existence and behavior of extinction thresholds in the context of metapopulation models. We review and extend recent developments in the theory and application of patch occupancy models, which have been developed for assessing the dynamics of species inhabiting highly fragmented landscapes. We discuss the relationship between deterministic and stochastic models, the possibility of alternative equilibria, transient dynamics following perturbations from the equilibrium state, and the effect of spatially correlated and temporally varying environmental conditions. We illustrate the theory with an empirical example based on the Glanville fritillary butterfly (Melitaea cinxia) metapopulation in the Åland Islands in southwest Finland.
There are two types of deterministic extinction thresholds: demographic thresholds such as the Allee effect, and parametric thresholds such as a critical effective colonization rate or a minimum amount of available habitat for metapopulation persistence. I introduce briefly both types of thresholds. First, I discuss the Allee effect in the context of eradication strategies of alien species. Then, I consider an example of parametric threshold: the critical amount of suitable habitat below which a metapopulation goes deterministically extinct. I review how this spatial threshold changes in relation to the level of spatial detail and the complexity of the food web. Since classical metapopulation models assume an infinite number of patches, I proceed by considering how the extinction threshold is affected by environmental variability acting on a small number of patches. Finally, I consider recent work suggesting that if the network of connectivity among patches is not random but highly heterogeneous, the extinction threshold may disappear.
In this paper, we review the main thresholds that can influence the population dynamics of host–parasite relationships. We start by considering the thresholds that have influenced the conceptualisation of theoretical epidemiology. The most common threshold involving parasites is the host population invasion threshold, but persistence and infection thresholds are also important. We recap how the existence of the invasion threshold is linked to the nature of the transmission term in theoretical studies. We examine some of the main thresholds that can affect host population dynamics including the Allee effect and then relate these to parasite thresholds, as a way to assess the dynamic consequences of the interplay between host and parasite thresholds on the final outcome of the system. We propose that overlooking the existence of parasite and host thresholds can have important detrimental consequences in major domains of applied ecology, including in epidemiology, conservation biology and biological control.
The current high rate of population declines and attempts to `manage' their recovery, call for a better understanding of recovery dynamics of populations. In many cases, recovery of a population may primarily be determined by a single life history property or ecological interaction, allowing for straightforward management actions. For example, a generalist predator may prevent the recovery of its prey, and populations with sex-biased dispersal are particularly vulnerable to demographic stochasticity. However, linking life history with intra- and interspecific population dynamics is needed to assess the relative importance of these factors. A clear example is depensatory dynamics that can be caused either by e.g., mutual predation or cooperative breeding. Moreover, dynamics of a recovering population can alter both its physiological and behavioural traits, affecting its interspecific interactions. Here we review life histories (reproduction, resource use and dispersal) and species interactions affecting recovery processes, and discuss their implications for management.
One hypothesis for the maintenance of the edge of a species' range suggests that more central (and abundant) populations are relatively stable and edge populations are less stable with increased local extinction and turnover rates. To date, estimates of such metrics are equivocal due to design and analysis flaws. Apparent increased estimates of extinction and turnover rates at the edge of range, versus the interior, could be a function of decreased detection probabilities alone, and not of a biological process. We estimated extinction and turnover rates for species at the interiors and edges of their ranges using an approach which incorporates potential heterogeneity in species detection probabilities. Extinction rates were higher at the edges (0.17 ± 0.03 [SE]) than in the interiors (0.04 ± 0.01), as was turnover. Without taking the probability of detection into account these differences would be artificially magnified. Knowledge of extinction and turnover rates is essential in furthering our understanding of range dynamics, and in directing conservation efforts. This study further illustrates the practical application of methods proposed recently for estimating extinction rates and other community dynamic parameters.
Human activities are having a devastating effect on the survival of natural populations. The reduction in population size and changes in the connectivity of populations due to human disturbances enhance the effect of demographic and genetic factors that can lead to population extinction. This article provides an overview of our current understanding of the role of genetic factors in the extinction of populations. The three primary genetic factors are loss of genetic variability, inbreeding depression, and accumulation of mildly deleterious mutations. The effects of these factors are discussed in the context of three different scenarios: isolated populations, local populations with immigration, and metapopulations.
In the short term, the persistence of species depends on the continued existence of suitable habitat and protection from extraordinary causes of mortality, essentially ecological and socioeconomic problems. On a longer time-scale, however, genetic problems could become paramount. Populations that have only deleterious mutations eventually decline in fitness to extinction, because of the fixation by genetic drift of a small fraction of these mutations. This proceeds fastest in small populations, because genetic drift is a more powerful factor in these circumstances. If, as is biologically reasonable, some mutations are beneficial to the population, there will exist a critical effective size above which the population can persist indefinitely, because fixation of beneficial alleles can balance the effects of deleterious mutations. This critical effective size is likely to be in the hundreds, meaning a census population size in the thousands. If some mutations act to compensate for the detrimental effects of others, then the rate of beneficial mutations will increase as fitness declines; this causes the critical effective size to be even lower. In this paper, we review the theoretical impact of beneficial and compensatory mutations on the probability of extinction, as well as the substantial theoretical and empirical literature on compensation. There are many possible mechanisms for compensatory mutations. There are insufficient data to make quantitative predictions, but it is clear that there is more hope for preserving the genetic integrity of threatened species than previously thought.
In a constantly changing environment, organisms must continuously adapt or face extinction. J. B. S. Haldane argued that the "cost of natural selection" (also called the cost of substitution) puts an upper limit on the rate of adaptation, and showed that the cost (C) was a decreasing function of the initial frequency of the beneficial alleles. Based on mutation-selection balance and 10% selective mortality, he suggested that the limit to adaptive evolution was about one allelic substitution per 300 generations. I have tested Haldane's results using simulations of a population limited by density-dependent regulation and subject to a constantly changing environment that affects n (= 1–7) independent survival traits, each controlled by a single locus. I investigated the influence of carrying capacity (K), mutation rate (u), number of beneficial mutations per generation (approximated by M = 2Ku) and net reproductive rate (R). Of these, M has the predominant influence. The effect of large changes in R was relatively small. The cost of selection (C) was measured as the shortest number of generations between an allelic substitution at all loci under selection that was consistent with population persistence. The results differed from Haldane's solution. Across a range of conditions, the cost of simultaneous selection at n loci was determined by the linear relationship C = C0(M) + nC1(M), where C0(M) is the intercept and C1(M) is the slope of the linear regression of C on n, for a given M. The intercept defined a positive fixed cost of substitution, that appears to reflect genetic deaths occurring during the stochastic phase when the beneficial alleles are rare. For M > 1/2, the cost of natural selection is substantially less than Haldane's estimate; however, when M < 1/2, the cost (and particularly the fixed cost) increases in an accelerating fashion as M is lowered. This result has important implications for conserved populations, since for u ~ 5 x 10–6 the carrying capacity of the population must be 50000 for M = 1/2. To avoid low M, smaller populations should be linked together into a large metapopulation whenever possible. This large unit would be capable of adapting when the isolated parts could not. It also suggests that if M << 1, small gains in K through increases in habitat can have a very large positive influence on the future survival of the population in a changing environment.
Of the several deleterious consequences that sex chromosome meiotic drive can have for a population, extinction is the most severe. Several studies of this phenomenon have suggested that males carrying a driving X chromosome may be disadvantaged during sperm competition. Deterministic modeling indicates that sperm competition can maintain a balanced polymorphism of driving and non-driving X chromosomes, but that if the frequency of the driving chromosomes exceeds some threshold value, then these chromosomes will spread to fixation and the population will go extinct. In this article we present the results of individual-based simulations of a stochastic model of X chromosome drive in finite and structured populations. We show that in large populations the balanced polymorphism can be maintained for hundreds of thousands of generations, but that reductions in population size and certain forms of population structure promote fixation of the driving chromosome.
Sexual selection is a field with a strong focus on the `costs' of traits. However, whether such costs have an influence on the demography of the population is very rarely discussed. Here we present various processes through which sexual selection might have an impact on population viability and thus increase or decrease the risk of extinction. We argue that evolutionary `suicide' — as sometimes suggested e.g. to have caused the extinction of the Irish elk — is unlikely in deterministic environments, except if costs are not paid by the same individual that bears the trait. Thus, intra- or inter-locus sexual conflict could in principle drive a population extinct, and we do not know why this does not frequently happen. Whether sexual selection increases or decreases extinction risks when populations face variable or unforeseen environmental conditions is likewise unknown, and we outline mechanisms that could account for either pattern. Inbreeding is another factor that could either increase or decrease population viability in sexually selected species. Inbreeding may be caused by a high mating skew, but it could also be reduced if females adaptively choose mates to avoid inbred offspring. Finally, when intraspecific competition for resources is taken into account, it is unclear how individual viabilities translate to extinction risks faced by the population. We show an example where greater mortality of males due to sexual dimorphism improves the carrying capacity of the environment, and thus presumably population viability.
Most studies of extinction risk and modelling of population viability do not take into account that higher organisms generally have two sexes, and that sex-specific demographic and other variables may play an important role in determining risks of extinction. I briefly review recent analyses of the importance of sex in demographic stochasticity and assessment of minimum populations required for maintenance of viable populations. Secondly, I review sex-specific factors that may influence such sex-specific demographic parameters. Thirdly, I review sex-specific extrinsic and intrinsic mortality factors that may contribute to increased risks of extinction. Finally, I review sex-specific genetic factors that may influence risks of extinction. Future empirical and theoretical approaches to assess extinction thresholds should consider the importance of sex.
Mating behaviour has long been proposed as a potential cause of inverse density dependence that can affect the viability of small populations through the reduction of female mating rates. However, under the general designation of mating behaviour we may find a diversity of traits that are likely to influence the mating rate. In the present study, we have analysed the influence of the social mating system, mate choice and mating opportunities on population dynamics given a demographic model that explicitly takes mating behaviour into account. The effect of mate choice on extinction risk depends on aspects such as the social mating system, the probability of accepting unattractive males, mating opportunities and variation in reproductive success. Thus, mate choice per se only leads to a significant increase in extinction risk if the social mating system is monogamous. If mating opportunities are limited, however (e.g. reduced encounter rate), the extinction probability associated with mate choice increases considerably. The risk of extinction associated with mate choice further increases when differences in reproductive success due to male attractiveness are taken into account. A comparative analysis of the establishment success of introduced bird species supports our predictions concerning mate choice. Sexually dichromatic species have a significantly lower establishment success than monochromatic species. However, the establishment success of non-native species was not significantly correlated with the social mating system, so that monogamous species are not less likely to be successful than polygamous species.