Download 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
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Number of individuals per unit area
Measuring density
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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
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The pattern of spacing among individuals within the designated
geographic boundaries
Types
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Clumped
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Uniform
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Individuals are aggregated in patches
Most common
Spacing of individuals is even
Rare but territoriality is often the reason
Random
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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
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Age structure & sex ratio
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Age structure
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Birth rate/fecundity
Death rate
Generation time
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The average span of time between birth of individual & the birth of their
offspring
Sex ratio
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Relative number of individuals of each age in the population
Proportion of individuals of each sex found in a population
Life Tables & survivorship curves
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Type I
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Type II
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Death rate increases in elderly but is flat for other ages
Death rate constant throughout all age spans
Type III
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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:
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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
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Semelparity
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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
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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
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Idealized population in an unlimited environment
Logistic model
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Incorporates the concept of carrying capacity (K)
Carrying capacity= maximum population size an
environment can support
Regulation of Population Growth
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Intra-specific competition
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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)
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Population Dynamics
 Study of the interactions between biotic &
abiotic factors that cause variations in
population size
 Some populations have regular boom & bust
cycles
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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…
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Agricultural revolution increased birth rate & decreased
death rate
Industrial revolution improved sanitation, nutrition, &
health care
Can not grow indefinitely….
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Population ecologists do not agree on the human carrying
capacity
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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