Post on 05-Jan-2016
Midterm 1b Results
Mean = 26.4Minimal score : 9Maximal score: 3762 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.
Golden-mantled ground squirrel
Highest elevation: near the timberline, late snowmelt
Lowest elevation: lush forests, early snowmelt
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
Highest elevation: R0 = 0.998
Lowest Elevation: R0 = 1.01
Net reproductive rates:
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.
Source and Sink Populations:
High value habitat:R0 > 1 source
Lower value habitatR0 < 1 sink
Net m
igration
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)
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?
Eastern kingbird(Tyrannus tyrannus)
Rivers, floodplains, uplands and farmer’s fields
Survivorship:
Murphy 2001
The floodplain is the safest habitat for adult birds.
Reproductive success:
Murphy 2001
Reproduction was slightly lower in the floodplain (Clutch sizes were the same but the floodplain had more egg predators.
Population growth rates:
Murphy 2001
In the year of the study, populations growth was positive only on the floodplain.
Floodplain >> Creek > Upland
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.
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.
Excel Worksheets:
• Source-Sink populations
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.