Population Dynamics and Conservation

Bringing Back the Sea OtterKeystone species:

Sea otter

Sea urchin

Kelp beds

Ode to the Sea OttersBefore

1 million sea otters lived in the pacific

Hunters believed to have killed all the sea otters in the early 1900sAfter

1938: 300 sea otters were counted

After the U.S. Endangered species act and the marine mammal protection act, now about 2,300 sea otters swim the pacific

Population Dynamics Depend On:Size: number of individuals in a population at a given timeDensity: number of individuals of a population in a certain location at a given timePopulation dispersionAge distribution

Population Dispersion:ClumpingMembers in clusters or groupsFood resources found in clumpsSource of protectionHelpful during mating season

Uniform DispersionIndividuals of the same species compete for resources that are scarce and spread evenly.Cresote bush release toxins that prevent seeds from growing near it.

Random DispersionUnpredictable patternResources and conditions are uniform in the habitatRare in nature

Age StructurePrereproductive: younger than sexual maturityReproductivePostreproductive: older than the maximum age of reproduction

Biotic Potential: Capacity for GrowthIntrinsic rate of increase (r)Produce many offspringExponential Growth

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Exponential Growth in Bacteria

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Reaching the Carrying Capacity (K)Lack of food/ space in the petri dish?S-shaped curve (logistic growth)Amount of light, water, space, nutrients

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Reaching Carrying Capacity on a Logistic Growth Chart

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Which strategy would you use?Many offspring at young ageMost offspring die before reproducingGeneralist specieR-selected Species

And what about these organisms?Few offspringTake care of youthOffspring usually lives to reproduceSpecialistK-selected Species

What limits growth?4 VariablesBirths DeathsImmigrationEmigration

This occurs when (Births + Immigration) - (Deaths + Emigration) = 0ZERO POPULATION GROWTH

MVPQ: When do you stop using the same resource (ie. fish) for food?

A: You stop before reaching the resources minimum viable population (MVP) It is the min. pop. size needed for breeding

Environmental ResistanceAll factors working together to limit the growth of a population

Biotic Potential + Envir. Resistance determine a populations Carrying Capacity

Density Independent vs. Density Dependent Population ControlDensity IndependentFloodsHurricanesEarthquakesLandslidesDensity DependentCompetition ParasitismPredationDisease

1. Fragmentation and degradation2. Simplifying ecosystem3. Strengthening some populations of pest species and bacteria (speeding up nat. selection)4. Eliminating some predators5. Deliberately or accidentally introducing new speciesHow have humans modified ecosystems?

6. Overharvesting potential renewable resources

7. Interfering with normal chemical cycling and energy flow (CFCs, Ozone, etc.)

What do we do about it???

GLOBAL CPR

C = ConservationP = PreservationR = Restoration(We are the worldwe are the children)

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