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Midterm 1b Results

Midterm 1b Results. Mean = 26.4 Minimal score : 9 Maximal score: 37 62 students improved their score. Habitat Mosaic:. Source and Sink Populations:. High value habitat. Lower value habitat. Note: populations are too far apart, dispersal too infrequent, to establish IDF.

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Midterm 1b Results

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  1. Midterm 1b Results Mean = 26.4 Minimal score : 9 Maximal score: 37 62 students improved their score.

  2. Habitat Mosaic:

  3. Source and Sink Populations: High value habitat Lower value habitat Note: populations are too far apart, dispersal too infrequent, to establish IDF.

  4. Lowest elevation: lush forests, early snowmelt Highest elevation: near the timberline, late snowmelt Golden-mantled ground squirrel

  5. Metapopulations in the Sierra Nevada: At the highest elevation (2730 m): emergence from hibernation: late May newborn females take two seasons to mature females are larger at first reproduction average litter size: 4.5 18% of pregnancies survived to 1 year-old At the lowest elevation (1460 m): emergence from hibernation: early April newborns take one season to mature females are smaller at first reproduction average litter size: 5.3 18% of pregnancies survived to 1 year-old Bronson 1979

  6. Net reproductive rates: Highest elevation: R0 = 0.998 Lowest Elevation: R0 = 1.01

  7. 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. Rescue Effect: The persistence of a deme with negative population growth through the influx of immigrants.

  8. Source and Sink Populations: High value habitat: R0 > 1 source Lower value habitat R0 < 1  sink Net migration

  9. Source and Sink Populations: N(t+1) = (1+b-d+e-i) N(t) Source population: b>d and i > e Sink population: b<d and i< e

  10. What are the implications for source-sink structure in a metapopulation for stability and persistence? • Do sink populations constitute a “drain” on a metapopulation? • Do sink populations still provide the safety in numbers? • Do sinks always remain sinks, and sources always sources? • Where do most individuals reside, in source or sink populations?

  11. Eastern kingbird (Tyrannus tyrannus) Rivers, floodplains, uplands and farmer’s fields

  12. Survivorship: The floodplain is the safest habitat for adult birds. Murphy 2001

  13. Reproductive success: Reproduction was slightly lower in the floodplain (Clutch sizes were the same but the floodplain had more egg predators. Murphy 2001

  14. Population growth rates: In the year of the study, populations growth was positive only on the floodplain. Floodplain >> Creek > Upland Murphy 2001

  15. Dispersal probabilities: From habitat: Most net dispersal happens from the floodplain to the creek. Creek and Upland are local sinks. The floodplain is the local source. Murphy 2001

  16. 50-year simulation based on actual population growth and dispersal parameters: Number of pairs Best model fit was achieved assuming a 5% immigration rate from the outside into the upland population. Still, the Charlotte Valley Kingbird population was predicted to decline: It is a regional sink!

  17. Number of pairs What does it take to stabililize the Charlotte Valley kingbird population? - 5% increase in survivorship in creek populations ? - The creek population became a local source, and stabilized the floodplain population.

  18. The Charlotte Valley kingbird study shows that: Most members of the metapopulation may live in sink populations, i.e. habitats that, if isolated, would not support the species. Relatively small improvements in a fraction of the total habitat, including a sink habitat, can help maintain larger portions of the metapopulation. Local source populations may be part of a metapopulation that is itself a sink on a larger spatial scale.

  19. Excel Worksheets: • Source-Sink populations

  20. Summary: • Not all demes would support viable populations on their own. • sink population = not viable by itself • source population = viable, generates dispersers • Even so, because sink populations also remain occupied most of the time, they • increase total population size (genetic diversity etc.) • reduce the risk of regional extinction • can help restart source populations after a local extinction. • Thus, sink populations can stabilize meta-populations.

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