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A landscapes mosaic:. Only some pieces of the mosaic are suitable for a given species:

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Presentation on theme: "A landscapes mosaic:. Only some pieces of the mosaic are suitable for a given species:"— Presentation transcript:

1 A landscapes mosaic:

2 Only some pieces of the mosaic are suitable for a given species:

3 The populations in the landscape mosaic are not totally isolated, But only weakly connected by migrating individuals:

4 A population: a group of individuals of the same species that live and breed in the same space. A metapopulation:a group of several local populations connected by the occasional movement of individuals between populations (immigration and emigration). A deme:a population that is part of a metapopulation. Metapopulation Dynamics:The dynamics of patch occupancy. Local extinction:a deme goes extinct. Colonization:an empty but suitable habitat is repopulated by emigrants. Definitions

5 How do we characterize the dynamics of metapopulations? 1) We only ask whether patches are occupied or not: 16 patches 4 occupied 12 empty 2) The state variable we follow is the fraction of occupied patches f. f = 4/16 = 0.25

6 The relevant rates in metapopulation dynamics: Probability of local extinction p e the probability that in a given amount of time a local population will go extinct. Probability of local colonization p i : the probability that in a given amount of time, a site will be colonized. pepe pipi

7 The rate of occupancy loss: The rate of re-colonization: The rate of change in f:

8 The Island-Mainland model: The probability of immigration is constant. mainland islands Island-mainland model: a constant “propagule rain” originating on the mainland.

9 Fraction of occupied sites f Extinction or Immigration rate pepe Island-Mainland Model: If p i > 0 there is always a positive equilibrium: metapopulations always persist.

10 The Internal Colonization model: The probability of immigration depends on the patches occupied: islands The immigration probability is proportional to the occupied patches:

11 Internal colonization model: Metapopulations may not persist. Positive equilibrium only if p e < i.

12 Rescue Effect: The probability of extinction depends on the patches occupied: extinctions are less likely the more islands are occupied. islands The extinction probability is proportional to the occupied patches:

13 Four possible models: External colonization Internal colonization IndependentRescue effect extinction

14 A sink-population: A deme within a metapopulation where mortality exceeds birth rates. Habitats remain occupied only due to immigration. A source-population: A deme within a metapopulation where birth rates exceed mortality. Surplus individuals leave this habitat to settle (breed) elsewhere. Other variations The demes may not be equal in quality. Some may have higher extinction probabilities than others, perhaps because the habitat maintains smaller populations.


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