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1 Demographic and environmental stochasticity in population processes 1) Population dynamics 2) Community dynamics 3) Selection in fluctuating environments Steinar Engen, Centre for Biodiversity Dynamics, Dept. of Mathematical Science, NTNU, Trondheim, Norway 2 For more detailed lectures on diffusion, extinction, dynamics ,agestructure and abundance models see www.math.ntnu.no/~steinaen/lovund_2012 and more on age-structure www.math.ntnu.no/~steinaen/ISEC_2012 and/or Lande, Engen and Sæther 2003, Stochastic Population Dynamics in Ecology and Conservation, Oxford University Press. These lectures are based on co-authored papers with Russell Lande and Bernt-Erik Sæther during the last 20 years. For a list see my home page www.math.ntnu.no/~steinaen 3 Single species population dynamics Environmental and demographic stochasticity Diffusion theory Extinction Some harvesting statistics Age structure Steinar Engen, Centre for Biodiversity Dynamics, Department of Mathematical Sciences 4 Population fluctuations for some species 5 6 7 8 9 10 Distribution of individual fitness w for two bird species 11 12 13 14 15 16 17 18 The Green function 19 Expected time to extinction 20 21 22 23 24 25 The expected time to extinction is often very large 26 27 28 29 30 31 32 The rate of increase in fitness of any organism at any time is equal to its genetic variance in fitness at that time 33 The rate of increase in fitness of any organism at any time is equal to its genetic variance in fitness at that time The rigour of its demonstration requires that the terms employed should be used stricktly as defined; the ease of its interpretation may be increased by appropriate conventions of measurement. For example, the ratio p:q should stricktly be evaluated at any instant by enumeration, not necessarily of the census population, but of all individuals having reproductive value, weighted according to the reproductive value of each. 34 35 36 37 The total reproductive value V of the population growth exactly exponential, and lnV has exactly linear growth. R. A. Fisher The age distribution approaches the stable age distribution 38 Age-structured population, no density regulation. (The total reproductive value serves as a filter) Population size Total reproductive value 39 40 41 42 Community dynamics History The infinite allele model – neutral models Independent species dynamics Comparison of two dynamic models giving Fisher’s log series model 43 The discovery of abundance patterns by Corbet and Williams in 1942: 44 45 Poisson Gamma negative binomial 46 47 48 49 50 51 10 minutes’ break 52 53 54 55 56 57 58 Homogeneous models with speciations and extinctions 59 60 Homogeneous models with speciations and extinctions Inhomogeneous Poisson process Homogeneous Poisson process 61 62 63 64 65 66 67 So what is the difference between the two types of model? Answer: Temporal fluctuations of abundant (observable) species are very different. Neutral model with demographic noise only: extremely small fluctuations and species turnover rates Gamma model with environmental noise: More realistic fluctuations and turnover rates 68 69 Neutral model, demographic noise only Typical lifetime of species Model with environmental noise 70 Stochastic components of selection Decomposition of the Robertson-Price equation, covariance formula for selection in an agestructured population Density-dependent selection, r- and K-selection in a stochastic environment Evolutionary effects of different non-selective harvesting strategies in a fluctuating population 71 72 73 74 75 76 77 78 For more details see Engen and Sæther (2013 Evolution, in press) 79 80 Figure 1. Observed decline in mean carapace length of rock lobsters captured in the fishery at two locations off the coast of Western Australia from 1972 to 2005 [10]. Only animals with a carapace length of greater than 76 mm (dotted line) can be legally harvested. This decline apparently is partially an evolutionary response to extremely high annual exploitation rates of adults (∼75%), combined with a required minimum carapace length of 76 mm in harvested individuals. (Allendorf et al. 2008) 81 What about non-selective harvesting? What are the effects? With a given mean annual yield, are there differences between harvesting strategies? 82 This result can be generalized to a sexual population with multinormally distributed z and constant G-matrix (Engen et al. 2012) 83 84 85 86 87 88 89 90 91 92 93 94 95 96 We can now investigate the evolutionary component due to harvesting for different harvesting strategies: Constant harvesting Proportional harvesting Threshold harvesting 97 98 99 10 0 10 1 10 2 Demographic and environmental stochasticity in population processes 1) Population dynamics 2) Community dynamics 3) Selection in fluctuating environments Steinar Engen, Centre for Biodiversity Dynamics, Dept. of Mathematical Science, NTNU, Trondheim, Norway