Environmental Science: Chapter 4 - Populations and Communities

Population Growth

Change in population size

Population Growth is Zero when:

Births + Immigration = Deaths + Emigration

Population growth rate

the amount the population changes over time

Constant Growth

Ending Population = A Constant x Time + Starting Population

Exponential Growth (J-Curve)

Time to double the population remains constant

• In 1 day, the population goes from 2 to 4

  • In another 1 day, the population goes from 4 to 8

  • In another 1 day, the population goes from 8 to 16

Logistic Growth (S-Curve)

• Some process slows growth so it levels off near carrying capicity

Reproductive Rate (r)

he number of offspring individuals can produce in a given time if resources are unlimited

Carrying capacity (K)

Maximum population of a species a habitat can support without being ruined

Biotic Potential

Number of offspring (births, eggs, seeds, spores) produced under ideal conditions

Abiotic

(non-living things)

r-strategists

Produce lots of young, but short survival – high biotic potential

• Low recruitment (survival to reproduction)

• Rapid reproduction, rapid movement, short life span

• Adapted to a rapidly changing environment

• “Weedy” or “opportunistic” species, usually small

• Examples: Housefly, dandelion, and cockroach

K-strategists

Lower biotic potential

• Care for and protect young

• Live in a stable environment already populated by the species

• Larger, longer lived, well-adapted

• Their populations fluctuate around carrying capacity

• Examples: Elephants, kangaroo, California condor

Population density

Number of individuals per area

Recruitment

Survival through early growth stages to become part of the

breeding population

– Young must survive and reproduce to have any effect on

population size

Environmental Resistance

The biotic and abiotic factors that limit a population’s increase

Biotic

living things

Critical Number

Minimum population base allowing the survival and recovery of a population

Threatened Species

Populations are declining rapidly

Endangered species

Populations are near the critical number

Carnivores

Primarily eat other animals

Herbivores

Primarily eat plants & producers

Omnivores

Eats both other animals and plants/producers

Parasites

Feed on their hosts and can weaken them over time so they are more susceptible to predation

Keystone species

Role is essential for the survival of many other species in an ecosystem by preventing other species from taking over an area and letting less competitive species to flourish

Mutualism

Relationship between two species that benefits both.

Commensalism

Rare interaction where one species benefits but the other is unaffected

Evolution

occurs through natural selection

Selective Pressure

Environmental factors acting on an individual; effect which individuals survive

Natural selection

Specific traits of an individual favoring survival against various pressures

Biologic evolution

Modification of the gene pool of a species over time

Fitness

Features (traits) that adapt an organism for survival and reproduction

Reproductive Isolation

prevent breeding with other species

Introduced Species

Organisms brought to an ecosystem as a result of human actions

Invasive Species

Introduced species that begin to out-compete native species