Population Dynamics

Case Study of the Peninsular Big Horn Sheep.

Big Horn Sheep: population fluctuations?

Summary of endangered listing

Six years after they were originally proposed for endangered listing, on March 18, 1998, the United States Peninsular Ranges population of desert bighorn sheep was federally listed as an endangered species pursuant to the Endangered Species Act (ESA) of 1973, as amended. The U.S. Fish & Wildlife Service (overseers of the Federal ESA) determined that Peninsular bighorn sheep are in danger of extinction throughout a significant portion of their range due to: (1) disease; (2) insufficient lamb recruitment; (3) habitat loss, degradation, and fragmentation by urban and commercial development; and (4) predation coinciding with low population numbers.

Range and Abundance

Identifying factors for analysis

Loss of habitat and increased

interaction with humans

Causes of mortality for bighorn sheep

Anaylsis suggests that predation by mountain lions is most important

What type of survivorship is expected given this data?

What are the different effects of adding adults to populations with different survivorship strategies?

When is protection of offspring the most viable alternative?

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20 30 40 50 60population size

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The consumption of toxic plants by bighorn sheep in relation to population size. Values on the y-axis reflect percentage of plants consumed in comparison to control plots from

which sheep were excluded.

Density Dependent Factors: Toxic Plant Effects

Recovery

Center for Biological Diversity

Why do populations fluctuate?

Geometric and Exponential Growth

r and K Selection

Persistence and Population Dynamics

Florida panther

Population Dynamics and Vulnerability to ExtinctionIn the wild, the breeding season of the San Joaquin kangaroo rat typically runs from December to August, but this species is also known to breed throughout the year (2) (3). The gestation period lasts only 32 days, and the young are born in the underground burrow (1) (5) (8). There are usually up to 3 offspring per litter, and the young are relatively well developed at birth, weighing about 4 grams and opening their eyes at 10 to 11 days old (3) (8). The young San Joaquin kangaroo rats first leave the burrow at about 14 to 18 days old and are weaned at 21 to 24 days, attaining adult weight after about 2.5 to 3 months (3). The San Joaquin kangaroo rat reaches sexual maturity as early as 82 days old (5), and females may potentially give birth to up to three litters a year

Fresno kangaroo rat

Listing Status: Endangered

Boom and Bust Cycles – Recovery and Disaster

Fragmentation and loss of habitat are the primary causes for the decline and continued threat to the survival of Buena Vista Lake shrews. The historical Buena Vista Lake is now drained and cultivated and Kern Lake has been reduced to 33 acres with a small pond that is artificially maintained and contains a more xeric (drier) plant community. Kern Lake Preserve is privately owned and a Conservation Agreement to protect the only known population of this species has not been negotiated. Because of the smallness and isolation of the population, the Buena Vista Lake shrew also faces high risks of extinction from genetic and environmental factors

Area dependence and patch geometry

Quantifying the Metapopulation Model

• Pe and Pc• Levins Model• SPOM