Biology Chapter 4- Population BiologyPopulation

Limiting factorExponential growthCarrying capacity

Life-history patternsDensity

R strategyK strategy

Competition

More Vocabulary

• Stress

• Crowding

• Demography

• Birthrate

• Deathrate

• Doubling time

• Age structure

Population Growth

• J Curve

• http://cauchy.math.colostate.edu/Applets/ExponentialGrowth/exponentialgrowth.htm

• Limits to growth (Limiting Factors y’all)– Biotic and abiotic

• Carrying Capacity

• Exponential growth

• Page 94 growth graph and explaination

More graphing

• Add carrying capacity

• http://cauchy.math.colostate.edu/Applets/LogisticGrowth/logisticgrowth.htm

Life History patterns

• Rapid Life history

• Slow life history

• K reproduction strategy (but intrinsic, not conscious)

• R reproduction strategy

• http://www.sumanasinc.com/webcontent/animations/content/tradeoffs.html

Population DensityPatterns

– Random– Clumped– Uniform

Limiting Factors

• Density-dependent– Disease– Competition

• Density-independent– Usually abiotic

Organism interactions

• Predation– Graph p 98

• Interspecies competition

• Intraspecies competition

• Effects of crowding

Addendum

• An S shaped curve is logistic growth

• This is the more common representation of population growth

Basic Characteristics of Populations

• The suitability of habitats influences the geographic distribution of a species.

• Insights can be gained by studying the spatial distributions of populations within habitats.

Population Age Structure

• Differences in environmental conditions and past history may cause populations to differ in their age distributions.

• The future growth of a population depends on its current age distribution.

Density-Independent Population Growth

• Simple models describe how idealized populations would grow in an infinite environment.

• In these models, populations increase to infinity or decrease to zero.

• Continuous Model – Reproduction occurs in the

population at all times.

• Discrete Model – Populations reproduce only at

certain times.

Density-Dependent Population Growth

• In density dependent population growth, the per capita growth rate decreases as the population approaches a carrying capacity.

• When population growth rate depends on current population size, the population smoothly approaches carrying capacity.

• When there is a delay such that population growth depends on past population sizes, the population may cycle or have chaotic dynamics.

Dynamics of Lagged Logistic Growth Models

• As growth rate increases, populations overshoot carrying capacity (K).

• Further increases cause the population to cycle.

Human Population Growth

• Human population growth does not currently show density effects that typically characterize natural populations.

• In natural populations, per capita population growth rate decreases with population size, whereas global human population growth rate has a positive relationship.

• Human population growth rate has been growing more than exponentially.

• Limited resources eventually will cause human population growth to slow, but global human carrying capacity is not known.

Density-Dependent and Density-Independent Effects on

Populations• In many habitats, the forces that limit population

sizes are independent of population density. For example, extreme weather events may decrease populations.

• For most species, density-dependent factors limit birth rates or increase death rates at least some of the time. This type of population determination often is referred to as “regulation.”

• Disease outbreaks and starvation are two factors that may increase with population density.

r-selected Reproductive Strategy

• r-selected Species: – have high

reproductive rates– tend to occur in

unpredictable environments

– typically have type III survivorship curves

K-selected Reproductive Strategy

• K-selected Species: – occur near carrying

capacity – experience effects of

population density – have low

reproductive rates, high parental care

– have type I survivorship curves.

Populations

• Groups of organisms of the same species that live within a given area

• Key characteristics:– Dispersion patterns– Population density – Growth rate

Ostriches are nomadic, wandering

in small groups.

Aspen trees are quick to pioneer areas that have been disturbed

by fire.

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Dispersion Patterns Within Populations

Three common patterns of population distribution are:

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Population Density• Population density is total population size per unit of

area.

• Population densities depend on:– Interactions within the environment

– Quality of habitat

– Density dependent factors

– Density independent factors

• Carrying capacity is the maximum number of organisms that can be supported in a given habitat.

• Population size can be measured by several sampling techniques.

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Population Growth

Exponential vs. Logistical Growth

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Survivorship in Populations

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Reproductive Strategies

• r- Selected (maximum growth rate, below carrying capacity)– Early reproduction– Short life span– High mortality rate– Little or no parental care– Large investment in

producing large numbers of offspring

– Below carrying capacity– Examples:

• Bony fish• Grasshoppers

• K-Selected (maximizes population size near carrying capacity)– Late reproduction– Long life span– Low mortality rate– Extensive parental care– Greater investment in

maintenance and survival of adults

– At or near carrying capacity– Examples:

• Sharks• Elephants

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Limits on Population Growth

• Density Dependent Limits– Food– Water– Shelter– Disease

• Density Independent Limits– Weather – Climate

Water and shelter are critical limiting factors in

the desert.

Fire is an example of a

Density independent

Limiting factor.BioEd Online