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TRANSCRIPT
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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.