Download Chapter 35

Chapter 35
Population and Community
Ecology
Populations
• Groups of organisms of the same species
that live within a given area
• Key characteristics:
– Dispersion patterns
– Population density
– Growth rate
Examples of Populations
• All the e coli bacteria in a petri dish
• All the rainbow trout in a stream
• All the sunflowers in a prairie.
Dispersion Patterns Within
Populations
Three common patterns of population
distribution are:
Sampling Techniques
• Quadrats-mark off and survey a defined
area
• Indirect counting- counting nests or
burrows, used to determine populations of
difficult to find species. Ex. Mountain lion
• Mark recapture
Online biology activity
• Distribution patterns
go to online activity 35.1
Population Growth rate
Exponential vs. Logistical Growth
Survivorship in Populations
Reproductive Strategies
– Long life span
• r- Selected (maximum
growth rate, below
carrying capacity)
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–
–
–
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Early reproduction
Short life span
High mortality rate
Little or no parental care
Large investment in
producing large numbers of
offspring
– Below carrying capacity
– Examples:
• Bony fish
• Grasshoppers
• K-Selected (maximizes
population size near
carrying capacity)
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–
–
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Late reproduction
Low mortality rate
Extensive parental care
Greater investment in
maintenance and survival
of adults
– At or near carrying capacity
– Examples:
• Sharks
• Elephants
Limits on Population Growth
• Density Dependent Limits
– Food
– Water
– Shelter
– Disease
• Density Independent Limits
– Weather
– Climate
Boom and Bust Population growth
Populations with boom and bust patterns have rapid growth and decline rates.
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.
Human Population Growth
• Human population growth does not currently
show density effects that typically characterize
natural populations.
• In natural populations, per capita population
growth rate decreases with population size,
whereas global human population growth rate
has a positive relationship.
• 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 DensityIndependent 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.
Interspecific relationships
• Interspecific competition
Interspecific relationships
• Predation
• Symbiotic relationships
• Parasitism
Mutualism
• Commensalism
go to online activity 35.4
Determining population size
• Do this prelab activity before beginning the
lab exercise