Population Ecology - Zamora's Science Zone
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Transcript Population Ecology - Zamora's Science Zone
Populations are described by density, spatial distribution, and growth rate.
Populations are groups of the same species in
the same area.
Characteristics of population include:
Density
Spatial Distribution
Growth rate
Population density
The number of organisms per unit area is
population density.
Spatial distribution
Dispersion is the pattern of spacing of individuals
of a population within an area.
Three kinds: clumped, uniform, and random
Limiting factors are biotic or abiotic forces
that keep population from increasing
indefinitely.
Limiting factors are either densityindependent or density-dependent.
Density-independent factors
Any factor in the environment that does not
depend on the number of members in a
population per unit area is a density-independent
factor.
Usually abiotic, and include:
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Weather events
Fire
Human alteration of the landscape
Air, land, and water pollution
Density-dependent factors
Any factor in the environment that depends on
the number of members in a population per unit
area is a density-dependent factor.
Often biotic, and include:
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Predation
Competition
Disease
Parasites
Population growth rate
The population growth rate (PGR) describes how
fast a given population grows.
▪ Natality: birthrate of a population in a given year.
▪ Mortality: death rate of a population in a given year
▪ Emigration: number of individuals moving away from
the population
▪ Immigration: number of individuals moving into a
population
Births
Births and immigration
add individuals to
a population.
Immigration
Deaths
Deaths and emigration
remove individuals
from a population.
Emigration
Exponential growth model
▪ Occurs when growth rate is proportional to population
size.
▪ All populations grow exponentially until they encounter
a limiting factor.
Logistic growth model:
▪ Occurs when a population’s growth slows or stops
following exponential growth.
▪ A population stops increasing when the number of
births < number of deaths, or when emigration >
immigration.
Carrying capacity
▪ Carrying capacity is the maximum number of individuals
of a species (pop size) that an environment can support.
Reproductive patterns
Species vary in the number of births per
reproduction cycle, age that reproduction begins,
and in the life span.
Plants and animals are placed into groups based
on these patterns.