Midterm 1b Results Mean = 26.4 Minimal score : 9 Maximal score: 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 mature females are larger at first reproduction average litter size: % 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: % of pregnancies survived to 1 year-old Metapopulations in the Sierra Nevada: Bronson 1979

Highest elevation: R 0 = Lowest Elevation: R 0 = 1.01 Net reproductive rates:

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.

Source and Sink Populations: High value habitat: R 0 > 1  source Lower value habitat R 0 < 1  sink Net migration

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:

Number of pairs 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!

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.

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 themetapopulation. 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.