Population Growth & Regulation - WOU

Population Growth & Regulation• What is Ecology• Populations• Estimating population size• Changes in population Density• Exponential growth• Logistic growth• Density independent regulation• Density dependent regulation• Population Cycles• R and K life history strategies

What is Ecology?

• Ecology is the study of interrelationships of organisms and their environment.

• Levels of Ecology--• Biomes• Ecosystem• Community• Population• Physiological• Individuals

PopulationsEstimating population size

• Population Density• (#s/ area or volume)• Two methods• Quadrat method• Set up transect• Rectangular quadrats• Count #’s for each species

Desert

Mark-Recapture

• Capture and mark individuals

• Recapture• Count number of

marked individuals that were recaptured

N = number marked X total captured# marked recaptures

Changes in population Density

• Birth• Immigration• Death• Emigration

• Use rates• b= (# births/1000)• d= (# deaths/1000• r= (b-d)

• ∆N/∆t = r No

• N = No ert

• Doubling Time = ln 2/r

• ln 2 = .693

Exponential growth

Logistic growth• ∆N/∆t = r No• Add (K-N/K)

• ∆N/∆t = r No (K-N/K)

• K= carrying capacity• Maximum sustainable

population• Can vary year to year

due to environmental conditions

Logistic growth

Regulation of Populations

• Density independent regulation

• Physical factors• Freezes• Volcanos• Tsunami

Before and After

Density dependent regulation

• Decreased fecundity• Decreased survivorship

Regulation

• Due to:• Resource limitation• Space, food, competition, predation,

disease

Population Cycles

Population Cycles

Boom and bust cycles: overexploitation

R and K life history strategies

• Trade off between survival and reproduction• Cannot maximize both• Leads to r or k selection

Life History Trade Off

Life History

• K Strategy

• Larger offspring• Fewer offspring• Live longer• Reproduce many

times (iteroparity), Late

• Some parental care

• R strategy

• Smaller offspring• Larger #’s• Shorter lifespan• Reproduce once

(semelparity), early• No parental care