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Lecture 9 Fragmented landscapes

Lecture 9 Fragmented landscapes. Landscape ecology Agroecology. Fragmented landscapes. Macropterous Carabidae. Dimorphic Carabidae. Brachypterous Carabidae. Colonization. Persistence. Nebria brevicollis. Notiophilus biguttatus. Carabus nemoralis. Predictable species occurrences.

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Lecture 9 Fragmented landscapes

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  1. Lecture 9 Fragmented landscapes Landscapeecology Agroecology

  2. Fragmented landscapes Macropterous Carabidae Dimorphic Carabidae Brachypterous Carabidae Colonization Persistence Nebria brevicollis Notiophilus biguttatus Carabus nemoralis Predictablespeciesoccurrences Idiosyncratic species Idiosyncratic species Highly nested Lowspeciesturnover Not nested High speciesturnover Slightly nested Moderatespeciesturnover Colonization driven system Random system Extinction driven system

  3. Glanvillefritillary Melitaeacinxia

  4. Themetapopulation of Melitaeacinxia

  5. Mainland – island pattern Patchy regional distribution A combination of these patterns Patchy regional distribution without dispersal Different types of metapopulations

  6. The Lotka – Volterra model of population growth Levins (1969) assumed that the change in the occupancy of single spatially separated habitats (islands) follows the same model. Assume P being the number of islands (total K) occupied. Q= K-P is then the proportion of not occupied islands. m is the immigration and e the local extinction probability. Immigration At equilibrium dP/dt = 0 Emigration

  7. The basic function of the theory of island colonization of McArthur and Wilson The basic Levins model The models describe changes in species numbers and occupancies in time The last model describes the changes occurrence probability on patch i at colonization rate m and extinction rate e The basic model of metapopulation ecology Additional „canonical’ assumptions describes the probability of occurrence in terms of mean patch distances dij, the average migration distance a, and the source island area Aj

  8. What does metapopulation ecology predict? Blue: occurrences Red absences Line: 50% chance to occur Occurrences of Hesperia comma in fragmented landscapes in southern England (from Hanski 1994) In fragmentedlandscapesoccupancydeclinesnonlinearwithdecreasingpatcharea and withdecreasingconncetivity Thereis a lowerthreshold of regional (metapopulation) extinction. Thisthresholdcan be predictedfromtheLevin’s model ifspeciesdispersalratesareknown.

  9. 1 0.8 0.6 networks Fraction of occupied 0.4 0.2 0 0 10 20 30 40 Number of patches per network Data from the Glanville Fritillary redrawn from Thomas and Hanski (1997). Theoretical threshold The fraction of occupied networks depends on the number of patches in a network. Bełow a certainthresholdthespeciesgoesextinct.

  10. 1200 1000 800 Median time to extinction 600 400 200 0 0 1 2 3 4 5 6 7 0.5 P K Regionalextinctiontimes TR: regional extinction time TL: local extinction time K : regional number of patches p : Mean number of occupied patches Long term survival is only possible when the average proportion P/K of occupied patches is larger than 3 K-1 /2: P > 3K1/2 The model of Gurney and Nisbet(1978)(based on a stochastic form of the metapopulation model of Levins) predicts long term regional survival of a species if the average proportion of occupied patches is larger than 3 times K-0.5.

  11. Extinctiontimes of Mazurangroundbeetles Localextinctiontimesareroughlyproportional to localabundances

  12. SPOMSIM

  13. Today’s reading Metapopulation: http://en.wikipedia.org/wiki/Metapopulation Metapopulation research group: http://www.helsinki.fi/science/metapop/ Metapopulation and extinction: http://faculty.plattsburgh.edu/thomas.wolosz/metapop.htm Landscapeecology: The state of art http://www.edc.uri.edu/nrs/classes/nrs534/NRS_534_readings/Turner_AnnRevEcoSys_2005.pdf

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