Populations & Ecology

•Distribution: geographic and ecological range (i.e. North America) (i.e. desert)Often determined by presence or absence of suitable habitat

•Does it include migration areas?Yes!

•Dispersion: spacing of individuals

Populations: individuals of same species at the same place and timeDemography: Study of populations

Clumped: in groupsCan be social, due to resources, safety

Uniform (spaced): minimum distance from one anothernot common in animalsseen in plants such as oaks, creosote and sages

Random: no pattern, spaced without regard to one another

Survivorship Curves

r vs. k selection life history strategies

r-selected

Many small offspringRapid developmentShort livedPoor competitorsFast dispersersLittle parental care

Examples??Weedsants

k-selected

Fewer offspringSlow developmentLong livedGood competitorsSlow dispersersMuch parental care

Examples??Treesbears

r-selected = opportunistic k-selected = equilibrium

Exponential Growth: increases by multiples

N = numberin population

t = time

r = rate of increase

Population Growth Rates

• Exponential growth -increases by multiplesstarts off slowly than rapid increase

J-shaped curve

• Logistic growth –population slows than stops growing at carrying capacity (K)

S-shaped curve

• Carrying capacity (K): the number of individuals the environment can support

Density: number of individuals per area

• Density dependent factors:Crowding causes these factors to have more

of an influence on population regulationi.e. food, water, shelter, predators, disease

• Density-independent factors:Crowding has no influencei.e. earthquakes, temperature

Natural Populations all normally reach K

Natural Regulations

• Territory sizemammals/birdsresources defendable

• Physiological impairmentWhite-tailed deer: reabsorption of embryos with poor nutrition

Oscillations: predator/prey cycles

Kaibab Deer Story

• Kaibab plateau in the grand canyon• 200 deer/200 acres• In early 1900’s – predator elimination program• Between 1900-1911: 781 mountain lions, 556 bobcats,

31 wolves, 5000 coyotes killed• By 1911: 500 deer/200 acres• Massive starvation due to severe overgrazing• By 1950 only 50 deer/200 acres due to environmental

degradation

Human Population Growth: r or K selected?

Age-structure diagrams: show proportion of populationat each age groupWhich is stable? Unstable?

Types of overpopulation

• People Overpopulation: too many people for the areaLDCs=lesser developed countries

• Consumption Overpopulation: a few people use most of the resourcesMDCs=more developed countries