Population Dynamics and Conservation

Bringing Back the Sea OtterKeystone species:

Sea otter

Sea urchin

Kelp beds

Ode to the Sea Otters…Before

1 million sea otters lived in the pacific

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

After

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 time

Density: number of individuals of a population in a certain location at a given time

Population dispersionAge distribution

Population Dispersion:Clumping

Members in clusters or groups

Food resources found in clumps

Source of protection

Helpful during mating season

Uniform Dispersion

Individuals 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 Dispersion

Unpredictable pattern

Resources and conditions are uniform in the habitat

Rare in nature

Age Structure

Prereproductive: younger than sexual maturity

ReproductivePostreproductive:

older than the maximum age of reproduction

Biotic Potential: Capacity for Growth

Intrinsic rate of increase (r)

Produce many offspring

Exponential Growth

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

Reaching Carrying Capacity on a Logistic Growth Chart

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Which strategy would you use?

Many offspring at young age

Most offspring die before reproducing

Generalist specie

R-selected Species

And what about these organisms?

Few offspringTake care of

youthOffspring

usually lives to reproduce

SpecialistK-selected

Species

What limits growth?4 Variables

Births DeathsImmigrationEmigration

This occurs when (Births + Immigration) - (Deaths +

Emigration) = 0

ZERO POPULATION GROWTH

MVP…

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

A: You stop before reaching the resource’s 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 population’s Carrying Capacity

Density Independent vs. Density Dependent Population Control

Density Independent

FloodsHurricanesEarthquakesLandslides

Density 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 species

How 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 world…we are the children…)