POPULATION ECOLOGY
By: CHRISTIAN HENRICH A GARIN
ENVIRONMENTAL SCIENCE
TERMINOLOGY
• Niche: role, function or boundaries of an organism
• Habitat: the place where a plant or animal normally lives
• Population: a group of individuals of one species
in an area
• Community: many populations of different kinds of organisms living in the same
place
• Ecosystem: assemblages of organisms together with
their physical and chemical environments
• Biome: an ecosystem of a large geographic area in
which plants are of one formation
BASIC CHARACTERISTICS OF A
POPULATION
• The suitability of habitats influences the geographic
distribution of a species.
• Insights can be gained by studying the spatial distributions
of populations within habitats.
POPULATION AGE STRUCTURE
• Differences in environmental conditions and past history may cause populations
to differ in their age distributions.
• The future growth of a population depends on its current age distribution.
DENSITY-INDEPENDENT POPULATION
GROWTH
• Simple models describe how idealized
populations would grow in an infinite
environment.
• In these models, populations increase to
infinity or decrease to zero.
• Continuous Model
• Reproduction occurs in the population at all
times.
• Discrete Model
• Populations reproduce only at certain times.
DENSITY-DEPENDENT POPULATION
GROWTH
• In density dependent population growth, the per capita growth rate decreases
as the population approaches a carrying capacity.
• When population growth rate depends on current population size, the
population smoothly approaches carrying capacity.
• When there is a delay such that population growth depends on past
population sizes, the population may cycle or have chaotic dynamics.
DYNAMICS OF LAGGED LOGISTIC
GROWTH MODELS
• As growth rate increases, populations
overshoot carrying capacity (K).
• Further increases cause the population to cycle.
HUMAN POPULATION GROWTH
• Human population growth does not currently show density effects that
typically characterize natural populations.
• In natural populations, the per capita population growth rate decreases with
population size, whereas the global human population growth rate has a
positive relationship.
• The human population growth rate has been growing more than
exponentially.
• Limited resources eventually will cause human population growth to slow,
but global human carrying capacity is not known.
DENSITY-DEPENDENT AND DENSITY-
INDEPENDENT EFFECTS ON POPULATIONS
• In many habitats, the forces that limit population sizes are independent of
population density. For example, extreme weather events may decrease
populations.
• For most species, density-dependent factors limit birth rates or increase death rates
at least some of the time. This type of population determination often is referred
to as “regulation.”
• Disease outbreaks and starvation are two factors that may increase with population
density.
EXPONENTIAL GROWTH
• a population's per capita (per individual) growth rate stays the same regardless
of population size, making the population grow faster and faster as it gets
larger.
• Exponential growth produces a J-shaped curve
LOGISTIC GROWTH RATE
• In logistic growth, a population's per capita growth rate gets smaller and smaller as
population size approaches a maximum imposed by limited resources in the environment,
known as the carrying capacity
• logistic growth produces an S-shaped curve.
POPULATION GROWTH RAT E FORMUL AS
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