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Population Ecology

Outline for today

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Population dynamics

The study of the change in populationnumbers and the factors influencing thosechanges

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Population a collection of organisms ofthe same species occupying a definedgeographic area

Population

sizeBirthImmigration

DeathEmmigration

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Factors affecting populationdynamics

Natality the number of individuals bornor hatched in a specified period

Recruitment the number that are bornand survive to adulthood

Why make a distinction?

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Factors affecting populationdynamics

Total mortality death of an individual,also percentage of a population that diesin one year

Natural mortality - death caused bypredation, starvation, disease, accidents,etc.

Harvest mortality

death caused byhunting or fishing. Artificial term, actually atype of predation

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Mortality

Total mortality depends on the carryingcapacityof the habitat.

Source of mortality does not change totalmortality.

Harvestable surplus

the number ofanimals that can be removed withoutadversely affecting population.

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Compensatory mortality

A certain number of animals die due to foodshortage, disease, predation each season

Harvest a portion of those that would havedied

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Compensatory mortality - If huntingmortality increases, then there is acompensatory decrease in nonhunting

mortality such that hunting mortality hasno effect on annual survival

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Compensatory mortality

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Mortality

What happens if we harvest more animalsthan would normally die?

Additive mortality when harvest mortalityresults in a total mortality that exceedswhat would have occurred naturally.

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Additive mortality

When might you want additive mortality?

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Population

sizeNatality

Recruitment

Natural

mortality

Harvestmortality

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How many do we harvest?

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Model population growth

A population model is a mathematicalestimation of how a population behaves

Given a set of parameters, can makepredictions about populations

Used for setting harvest limits.

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Models of Population Growth

Exponential Growth

Birth exceeds death

Birth and death rate independent ofpopulation size

Ignore migration

Nt = RtN0

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Time, in generations

Populati

on

size

Exponential growth density independent

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Can this happen in nature?

Yes

Invasive species

Uniform habitat No predators

No disease

Unlimited area

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Density independence birth and deathrate independent of population size

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Constraints on population growth

Density dependence death rate increases andbirth rate decreases as population sizeincreases

Inversity When adult density is high, natalityand recruitment are low, when adult density islow, natality and recruitment are high.

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Time, in generations

Population

size

N = rN(K-N)

K

Logistic equation density dependent

K

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K = Carrying capacity

The maximum biomass of a species that ahabitat can support for a prolonged periodof time

Not constant, it fluctuates.

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Factors that affect K

Density-independent factors

Weather (storms, cold, drought)

Density-independent diseases (DDT

poisoning)

Density-dependent factors

Food

Space (territories, denning sites, nest cavities)

Density-dependent epizootics (rabies, SARS)

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Harvest strategies

Maximum sustained yield the maximumnumber of animals you can removewithout affecting future harvest

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Time, in generations

Population

siz

e

Maximum sustained yield

Maximum sustainable yield

K

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Optimum sustained yield Goal issomething other than harvesting themaximum number of animals

Harvest the best, or the largest animals

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Population structure

A population that is 75% adults, 25%juveniles is very different from a populationof 25% adults and 75% juveniles.

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Population structure

Age structure distribution of ages in apopulation. For animals with determinantgrowth.

Size structure distribution of sizes in apopulation. For animals with indeterminantgrowth.

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Population structure

In a harvested population, age and sizestructure is influenced by huntingregulations.