| 1. |
- Gyllenberg, Mats, et al.
(författare)
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Single-species metapopulation dynamics : A structured model
- 1992
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Ingår i: Theoretical Population Biology. - 0040-5809 .- 1096-0325. ; 42:1, s. 35-61
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Tidskriftsartikel (refereegranskat)abstract
- We describe and analyse a general metapopulation model, which consists of a model of local dynamics within a habitat patch, and balance equations for dispersing individuals and the metapopulation. The model includes the effects of emigration and immigration on local dynamics. We derive the equilibrium population size distribution, which is skewed towards either small or large populations, depending on the relative magnitudes of local and metapopulation time scales. The model predicts a generally positive relationship between the fraction of occupied patches and the average local population size. Such a relationship has been commonly observed in nature. The model allows alternative stable equilibria, not found in models which ignore the effect of dispersal on local dynamics. We discuss the implications of our results for biological invasions and conservation biology
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| 2. |
- Nåsell, Ingemar
(författare)
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An extension of the moment closure method
- 2003
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Ingår i: Theoretical Population Biology. - : Elsevier BV. - 0040-5809 .- 1096-0325. ; 64:2, s. 233-239
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Tidskriftsartikel (refereegranskat)abstract
- The moment closure method was recently shown in Nasell (Theor. Popul. Biol. 63 (2) (2003a) 159) to give asymptotic approximations of the first few cumulants for the stochastic logistic model. A slight extension of the method is introduced. It is shown to be robust with regard to the specific distributional assumption that is used to achieve moment closure. The phenomenon of spurious solutions is shown to be related to the domain of attraction of the non-spurious critical point.
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| 3. |
- Nåsell, Ingemar
(författare)
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Moment closure and the stochastic logistic model
- 2003
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Ingår i: Theoretical Population Biology. - : Elsevier BV. - 0040-5809 .- 1096-0325. ; 63:2, s. 159-168
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Tidskriftsartikel (refereegranskat)abstract
- The quasi-stationary distribution of the stochastic logistic model is studied in the parameter region where its body is approximately normal. Improved asymptotic approximations of its first three cumulants are derived. It is shown that the same results can be derived with the aid of the moment closure method. This indicates that the moment closure method leads to expressions for the cumulants that are asymptotic approximations of the cumulants of the quasi-stationary distribution.
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| 4. |
- Aguilar, Elliot, et al.
(författare)
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Modeling the genealogy of a cultural trait
- 2015
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Ingår i: Theoretical Population Biology. - : Elsevier BV. - 0040-5809 .- 1096-0325. ; 101, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The mathematical study of genealogies has yielded important insights in population biology, such as the ability to estimate the time to the most recent common ancestor (MRCA) of a sample of genetic sequences or of a group of individuals. Here we introduce a model of cultural genealogies that is a step toward answering similar questions for cultural traits. In our model individuals can inherit from a variable, potentially large number of ancestors, rather than from a fixed, small number of ancestors (one or two) as is typical of genetic evolution. We first show that, given a sample of individuals, a cultural common ancestor does not necessarily exist. We then introduce a related concept: the most recent unique ancestor (MRUA), i.e., the most recent single individual who is the earliest cultural ancestor of the sample. We show that, under neutral evolution, the time to the MRUA can be staggeringly larger than the time to MRCA in a single ancestor model, except when the average number of learning opportunities per individuals is small. Our results point out that the properties of cultural genealogies may be very different from those of genetic genealogies, with potential implications for reconstructing the histories of cultural traits.
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| 5. |
- Alvarez-Castro, Jose
(författare)
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Effects of epistasis and the evolution of genetic architecture: Exact results for a 2-locus model
- 2009
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Ingår i: Theoretical Population Biology. - : Elsevier BV. - 0040-5809 .- 1096-0325. ; 75, s. 109-122
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Tidskriftsartikel (refereegranskat)abstract
- We study a two-locus model of a quantitative trait with a continuum-of alleles and multilinear epistasis that evolves under mutation, selection, and genetic drift. We derive analytical results based on the so-called House of Gauss approximation for the genetic variance, the mean phenotype, and the mutational variance in the balance of the evolutionary forces. The analytical work is complemented by extensive individual-based Computer simulations. We find that (1) analytical results are accurate in a large parameter space; (2) epistasis always reduces the equilibrium genetic variance, as predicted in earlier studies that exclude drift; (3) large-scale stochastic fluctuations and non-equilibrium phenomena like adaptive inertia can strongly influence the evolution of the genetic architecture of the trait. (C) 2009 Elsevier Inc. All rights reserved.
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| 6. |
- Ammunét, Tea
(författare)
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Consequences of asymmetric competition between resident and invasive defoliators: A novel empirically based modelling approach
- 2014
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Ingår i: Theoretical Population Biology. - : Elsevier BV. - 0040-5809 .- 1096-0325. ; 92, s. 107-117
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Tidskriftsartikel (refereegranskat)abstract
- Invasive species can have profound effects on a resident community via indirect interactions among community members. While long periodic cycles in population dynamics can make the experimental observation of the indirect effects difficult, modelling the possible effects on an evolutionary tithe scale may provide the much needed information on the potential threats of the invasive species on the ecosystem. Using empirical data from a recent invasion in northernmost Fennoscandia, we applied adaptive dynamics theory and modelled the long term consequences of the invasion by the winter moth into the resident community. Specifically, we investigated the outcome of the observed short-term asymmetric preferences of generalist predators and specialist parasitoids on the long term population dynamics of the invasive winter moth and resident autumnal moth sharing these natural enemies. Our results indicate that coexistence after the invasion is possible. However, the outcome of the indirect interaction on the population dynamics of the moth species was variable and the dynamics might not be persistent on an evolutionary time scale. In addition, the indirect interactions between the two moth species via shared natural enemies were able to cause asynchrony in the population cycles corresponding to field observations from previous sympatric outbreak areas. Therefore, the invasion may cause drastic changes in the resident community, for example by prolonging outbreak periods of birch-feeding moths, increasing the average population densities of the moths or, alternatively, leading to extinction of the resident moth species or to equilibrium densities of the two, formerly cyclic, herbivores. (c) 2014 Elsevier Inc. All rights reserved.
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| 7. |
- Andersen, K H, et al.
(författare)
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Life-history constraints on the success of the many small eggs reproductive strategy
- 2008
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Ingår i: Theoretical Population Biology. - : Elsevier BV. - 1096-0325 .- 0040-5809. ; 73:4, s. 490-497
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Tidskriftsartikel (refereegranskat)abstract
- The reproductive strategy of most fishes is to produce a large number of tiny eggs, leading to a huge difference between egg size and asymptotic body size. The viability of this strategy is examined by calculating the life-time reproductive success R-0 as a function of the asymptotic body size. A simple criterion for the optimality of producing small eggs is found, depending on the rate of predation relative to the specific rate of consumption. Secondly it is shown that the success of the reproductive strategy is increasing with asymptotic body size. Finally the existence of both upper and lower limits on the allowed asymptotic sizes is demonstrated. A metabolic upper limit to asymptotic body size for all higher animals is derived.
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| 8. |
- Bengtsson, Göran, et al.
(författare)
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Statistical analysis of the influence of conspecifics on the dispersal of a soil collembola.
- 2002
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Ingår i: Theoretical Population Biology. - : Elsevier BV. - 1096-0325 .- 0040-5809. ; 61:2, s. 97-113
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Tidskriftsartikel (refereegranskat)abstract
- The evidence for dispersal activity among soil-living invertebrates comes mainly from observations of their movement on artificial substrates or of colonisation of defaunated soils in the field. In an attempt to elucidate the dispersal pattern of soil collembolans in the presence of conspecifics, statistical analyses were undertaken to describe and simulate the movement of groups of Onychiurus armatus released in trays of homogeneous soil. A chi(2) test was used to reject the null hypothesis that individuals moved independently of each other and uniformly in all directions. The mean radial distance moved (1-2 cm day(-1)) and the radial standard deviation varied temporally and with the density of conspecifics. To capture the interaction between the moving individuals, four dispersal models (pure diffusion, diffusion with drift interaction, drift interaction and synchronised diffusion, and drift interaction and behavioural mood), were formulated as stochastic differential equations. The parameters of the models were estimated by minimising the deviance between the observed replicates and replicates that were simulated using the models. The dynamics of movement were best described by modelling the drift interaction as dependent on whether individuals were in a social or an asocial mood.
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| 9. |
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| 10. |
- Brännström, Åke, et al.
(författare)
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Stochastic analogues of deterministic single-species population models
- 2006
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Ingår i: Theoretical Population Biology. - : Elsevier BV. - 0040-5809 .- 1096-0325. ; 69:4, s. 442-451
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Tidskriftsartikel (refereegranskat)abstract
- Although single-species deterministic difference equations have long been used in modeling the dynamics of animal populations, little attention has been paid to how stochasticity should be incorporated into these models. By deriving stochastic analogues to difference equations from first principles, we show that the form of these models depends on whether noise in the population process is demographic or environmental. When noise is demographic, we argue that variance around the expectation is proportional to the expectation. When noise is environmental the variance depends in a non-trivial way on how variation enters into model parameters, but we argue that if the environment affects the population multiplicatively then variance is proportional to the square of the expectation. We compare various stochastic analogues of the Ricker map model by fitting them, using maximum likelihood estimation, to data generated from an individual-based model and the weevil data of Utida. Our demographic models are significantly better than our environmental models at fitting noise generated by population processes where noise is mainly demographic. However, the traditionally chosen stochastic analogues to deterministic models—additive normally distributed noise and multiplicative lognormally distributed noise—generally fit all data sets well. Thus, the form of the variance does play a role in the fitting of models to ecological time series, but may not be important in practice as first supposed.
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