BioGt Ch36: Population structure and Dynamics

36.1

• Population ecology

  • The study of how and why populations change

  • Relates to populations as described in chapter 34

  • Population ecologists study increase and decrease in populations, as well as the influence of biotic and abiotic factors on them

36.2

• Important population variables

  • Population density

    • Number of individuals in a species per unit area

    • Estimation is often required

  • Dispersion patter

    • The way individuals are spaced within their area

    • Clumped

      • Most common

    • Random

      • Often results from interactions between individuals

36.3

Life tables are used to track survivorship, or the chance of an individual in a given population to survive to various ages

• Survivorship curves

  • Plot survivorship as the proportion of individuals from an initial population alive at each age.

  • Used to identify the most vulnerable stages for an organism.

36.4

Idealized models predict patterns of population growth

• Population size fluctuates, although some are more constant and some are rapid

• Exponential growth model

  • G=rN

    • (Growth rate= per capita rate of increase x population size)

    • Per capita rate of increase = births-deaths

  • Idealized picture of reproduction

  • No limiting factors

• Logistical growth model

  • Limiting factors restrict population growth

  • G=rN x (k-n)

  • k= carrying capacity, or maximum population size that a particular environment can sustain

36.5

Multiple factors may limit population growth

• Density dependent factors

  • Factors related to population density that control population

  • Intraspecific competition

    • Competition among members of a species for limited resources.

  • Competition for food, shelter, and other resources are density dependent

  • Competition limits the ability to survive

• Density independent factors

  • Factors not related to population density that control population

  • Weather

  • Season changes

  • Fire

  • Human activity

36.6

“Boom and bust” cycles are characterized by rapid exponential growth followed by a “bust” back to minimal level

• Graph moves up and down

36.7

Evolution and natural selection shape life histories

• Life history

  • Made up by traits that shape an organism’s schedule of reproduction and death

  • Age of reproduction, frequency of reproduction, number of offspring, and parental care.

  • Not all traits can be optimized by natural selection at once

• R-selection

  • Smaller organisms

  • Many offspring

  • Little parental care

  • Lots of resources

• K-selection

  • Larger organisms

  • Few offspring

  • More parental care

  • Less resources

36.8

Population ecology principles have practical applications

• Sustainable resource management: harvesting without damaging the resource.

• Helps to optimize growth rate for resources used by humans

• Pest control also relies on population ecology