Population Dynamics and Conservation

Bringing Back the Sea Otter Keystone 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 dispersion Age 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 Reproductive Postreproductive: older than the maximum age of reproduction

Biotic Potential: Capacity for Growth Intrinsic rate of increase (r) Produce many offspring Exponential Growth

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

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 offspring Take care of youth Offspring usually lives to reproduce Specialist K-selected Species

What limits growth? 4 Variables Births Deaths Immigration Emigration

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 Resistance All 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 Floods Hurricanes Earthquakes Landslides Density Dependent Competition Parasitism Predation Disease

1. Fragmentation and degradation 2. Simplifying ecosystem 3. Strengthening some populations of pest species and bacteria (speeding up nat. selection) 4. Eliminating some predators 5. 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 = Conservation P = Preservation R = Restoration (We are the world…we are the children…)