Ecology of a Population

By:Tara Hill

Population Defined

A population is:

A group of organisms of the same species

occupying a particular space at a particular

time

Population Characteristics:

Distribution:where organisms are found on earth, determined by biotic/abiotic factors

Dispersion: spatial distribution of individuals of a population -- three general kinds of patterns:

clumped (aggregated) dispersion -- individuals clumped together -- resources in a habitat may be patchy in distribution which causes organisms to form "clumps"

Uniform-individuals are about equal distance from one another

-caused by competition among individuals in the same population

Random-habitat is relatively uniform so individuals are neither repelled or attracted to one another.

Population Size

A balance between:

• Natality=birth rate (b)

• Mortality=death rate (d)

(b)>(d)=population size increases

(b)<(d)=population size decrease

(b)=(d)=population size is constant

Factors affecting population size besides natality/mortality

• Immigration rate (i) (increases pop. size)

• Emigration rate (e) (decreases pop. size)

Growth rate equation:

r=(b-d) + (i-e)

Population Growth

Biotic Potential=

-promotes positive growth

-intrinsic factors(litter size, gestation)

Environmental Resistance=

-limits growth

-extrinsic factor(weather, food supply)

Patterns of growthExponential growth (J shaped curve)

• biotic potential(rm)=maximum value

Logistic growth (S shaped)

K=carrying capacity=population size that is based on number of resources available

Limiting factors:

Density dependent:

-competition

-disease

-predation

-food

Density independent:

-weather

-catastrophes

-natural disasters (typhoons, volcanoes)

Natural Selection:

• limiting factors place stresses on a population

• the best adapted organisms will survive and get to reproduce and pass on their genes with the adaptation to their offspring

• over long periods of time this can lead to a change in species

Population Growth

Biotic Potential=

-promotes positive growth

-intrinsic factors(litter size, gestation)

Environmental Resistance=

-limits growth

-extrinsic factor(weather, food supply)

Patterns of growthExponential growth (J shaped curve)

• biotic potential(rm)=maximum value

Logistic growth (S shaped)

K=carrying capacity=population size that is based on number of resources available

Limiting factors:

Density dependent:

-competition

-disease

-predation

-food

Density independent:

-weather

-catastrophes

-natural disasters (typhoons, volcanoes)

Natural Selection:

• limiting factors place stresses on a population

• the best adapted organisms will survive and get to reproduce and pass on their genes with the adaptation to their offspring

• over long periods of time this can lead to a change in species

• proportionally massive eyes

making vision acute for locating

prey

• movable ears for better hearing

making them good nocturnal

hunters

• can rotate their heads a full 180

degrees to help them avoid

predators such as wild cats

• Long back legs to help them

jump twenty feet, an important

survival skill in the jungle

• Long tail providing power for

jumping and holding onto tree

branches for stability

Ex:Phillipine Tarsier

Survivorship curves:

-based on a cohort of individuals from birth until death

-cohort=a group of individuals of the same age

-survivorship curves are meant to show the number of individuals surviving at each age for a particular species

-three types of curves

Type 1=good early survival, die of old age, low birth rates, provide lots of parental care (humans)

Type 2=die at constant rate regardless of age (birds, lizards)

Type3 =poor early survival,survival thatimproves with

age, lots of offspring, low parental care(fish,plants)

Life History Patterns:

r selected species: species inhabiting fluctuating or unpredictable environments-environments keep populations below carrying capacity (lots of predation, competition over resources)

k selected species-species inhabiting stable, predictable environments-keep population size near carrying capacity and resources are scarce