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.