Chapter 52: Population Ecology
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Transcript Chapter 52: Population Ecology
Chapter 52: Population Ecology
Population ecology
Study of populations in relationship to the
environment
Includes environmental influences on population
density, distribution, age structure, & size
Population
Individuals of one species simultaneously
occupying the same general area, utilizing the
same resources, & influences by similar
environmental factors
Characteristics of populations
Population density
Number of individuals per unit area
Measuring density
Count all individuals in a representative sample area
Estimates based on indirect indicators such as nest, burrows, droppings, or
tracks
Mark-recapture method
Population dispersion
The pattern of spacing among individuals within the designated
geographic boundaries
Types
Clumped
Uniform
Individuals are aggregated in patches
Most common
Spacing of individuals is even
Rare but territoriality is often the reason
Random
Varies in an unpredictable way
Occurs in absence of strong attractions/repulsions of individuals
Rare
Ex. Windblown dandelions
Demography
Study of factors that affect the growth & decline of
populations
Age structure & sex ratio
Age structure
Birth rate/fecundity
Death rate
Generation time
The average span of time between birth of individual & the birth of their
offspring
Sex ratio
Relative number of individuals of each age in the population
Proportion of individuals of each sex found in a population
Life Tables & survivorship curves
Type I
Type II
Death rate increases in elderly but is flat for other ages
Death rate constant throughout all age spans
Type III
Death rate high in young & elderly
Life History
Traits affecting organism’s schedule of reproduction & survival
Life histories are highly diverse but exhibit patterns
Includes:
When reproduction begins
How often an individual reproduces
How many offspring an individual produces
Limited resources mandate tradeoffs between investment in
reproduction vs. own survival
Semelparity
Organism invests most of their energy into growth & development then
expends all energy into a single reproductive effort before dying
Ex. Annual plants, salmon, bamboo
Favored in highly variable, unpredictable environments with low offspring
survival rates
Iteroparity
Organism produces fewer offspring at a time but over several reproductive
seasons
Favored in dependable environments with high competition for resources
Population Growth Models
Exponential model
Idealized population in an unlimited environment
Logistic model
Incorporates the concept of carrying capacity (K)
Carrying capacity= maximum population size an
environment can support
Regulation of Population Growth
Intra-specific competition
2 or more individuals of the same species rely on a
limited resource.
Density-dependant factors
intensify as the population increases
Competition for resources
Territoriality
Health (i.e. disease)
Predation
Toxic waste
Intrinsic factors (i.e. stress syndrome in white footed
mice)
Population Dynamics
Study of the interactions between biotic &
abiotic factors that cause variations in
population size
Some populations have regular boom & bust
cycles
Small herbivores lemmings show a 3-5 year cycle
Large herbivores snowshoe hare shows a 9-11
year cycle
Insect Cicada show a 13-17 year cycle
In some species crowding effects the endocrine
system=reduced fertility
Human Population Growth
For centuries humans have appeared to grow
exponentially…
Agricultural revolution increased birth rate & decreased
death rate
Industrial revolution improved sanitation, nutrition, &
health care
Can not grow indefinitely….
Population ecologists do not agree on the human carrying
capacity
Age structure within each country causes variations in population
growth
Humans can consciously control reproduction through contraception
or government sponsored family planning
Agricultural & industrial technology has increased carrying capacity
Social changes, individual choice, government intervention and/or
increased mortality due to environmental limitations will cause the
human population to stop growing