Midterm 1b Results Mean = 26.4 Minimal score : 9 Maximal score: 37 62 students improved their score.
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Transcript of Midterm 1b Results Mean = 26.4 Minimal score : 9 Maximal score: 37 62 students improved their score.
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Midterm 1b Results
Mean = 26.4Minimal score : 9Maximal score: 3762 students improved their score.
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Habitat Mosaic:
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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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Golden-mantled ground squirrel
Highest elevation: near the timberline, late snowmelt
Lowest elevation: lush forests, early snowmelt
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At the highest elevation (2730 m):
emergence from hibernation: late May newborn females take two seasons to maturefemales are larger at first reproductionaverage litter size: 4.518% of pregnancies survived to 1 year-old
At the lowest elevation (1460 m):
emergence from hibernation: early Aprilnewborns take one season to maturefemales are smaller at first reproductionaverage litter size: 5.318% of pregnancies survived to 1 year-old
Metapopulations in the Sierra Nevada:
Bronson 1979
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Highest elevation: R0 = 0.998
Lowest Elevation: R0 = 1.01
Net reproductive rates:
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A sink-population:
A deme within a metapopulation where mortality exceeds birth rates. Habitats remain occupied onlydue 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.
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Source and Sink Populations:
High value habitat:R0 > 1 source
Lower value habitatR0 < 1 sink
Net m
igration
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Source and Sink Populations:
Source population: b>d and i > e
Sink population: b<d and i< e
N(t+1) = (1+b-d+e-i) N(t)
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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?
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Eastern kingbird(Tyrannus tyrannus)
Rivers, floodplains, uplands and farmer’s fields
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Survivorship:
Murphy 2001
The floodplain is the safest habitat for adult birds.
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Reproductive success:
Murphy 2001
Reproduction was slightly lower in the floodplain (Clutch sizes were the same but the floodplain had more egg predators.
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Population growth rates:
Murphy 2001
In the year of the study, populations growth was positive only on the floodplain.
Floodplain >> Creek > Upland
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Dispersal probabilities:
Murphy 2001
Most net dispersal happens from the floodplain to the creek.
Creek and Upland are local sinks.The floodplain is the local source.
From habitat:
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50-year simulation based on actual population growth and dispersal parameters:
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!
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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.
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The Charlotte Valley kingbird study shows that:
Most members of the metapopulation may live in sinkpopulations, i.e. habitats that, if isolated, would not
support the species.
Relatively small improvements in a fraction of the totalhabitat, 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.
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Excel Worksheets:
• Source-Sink populations
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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.