Scales of Ecological OrganizationScales of Ecological Organization

Organism

Population

Community

EcosystemBiosphere

DefinitionDefinition Population ecologyPopulation ecology is the study of births, deaths, is the study of births, deaths, and the dynamics forces which regulate the and the dynamics forces which regulate the number of individuals in a population.number of individuals in a population.

•DensityDensity

–Is the number of individuals per Is the number of individuals per unit area or volumeunit area or volume

•DispersionDispersion

–Is the pattern of spacing among Is the pattern of spacing among individuals within the boundaries of individuals within the boundaries of the populationthe population

Density and Dispersion

Population dispersionPopulation dispersion

Population dispersionPopulation dispersion

spatial patternsspatial patterns

spacedspaced -- may indicate competing individuals-- may indicate competing individuals

clumpedclumped -- may indicate social patterns or -- may indicate social patterns or resource distributionresource distribution

•A random dispersionA random dispersion

–Is one in which the position of each individual is Is one in which the position of each individual is independent of other individualsindependent of other individuals

(c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

•A uniform dispersionA uniform dispersion

–Is one in which individuals are evenly distributedIs one in which individuals are evenly distributed

–May be influenced by social interactions such as territorialityMay be influenced by social interactions such as territoriality

Figure 52.3b

(b) Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.

•A clumped dispersionA clumped dispersion

–Is one in which individuals aggregate in patchesIs one in which individuals aggregate in patches

–May be influenced by resource availability and behaviorMay be influenced by resource availability and behavior

Figure 52.3a

(a) Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory.

•Density is the result of a dynamic interplay between processes that add individuals to a population and those that remove individuals from it.

Births and immigration add individuals to a population.

Births Immigration

PopuIationsize

Emigration

Deaths

Deaths and emigration remove individuals from a population.

•The life table of Belding’s ground squirrels

–Reveals many things about this population

•A survivorship curve

–Is a graphic way of representing the data in a life table…

Figure 52.4

1000

100

10

1

Num

ber

of s

urvi

vors

(lo

g sc

ale)

0 2 4 6 8 10

Age (years)

Males

Females

•The survivorship curve for Belding’s ground squirrelsThe survivorship curve for Belding’s ground squirrels

–Shows that the death rate is relatively constantShows that the death rate is relatively constant

PopulationPopulation

patterns in age structurepatterns in age structure

r- vs K-selectionr- vs K-selectionr- vs K-selectionr- vs K-selection

r-selection K-selectionr-selection K-selection

A.A. DisturbanceDisturbance Common, irregularCommon, irregular Rarer, more regularRarer, more regular

B.B. MortalityMortality Variable, unpredictableVariable, unpredictable Constant, predictableConstant, predictable

C.C. CompetitionCompetition Low or variableLow or variable High, constantHigh, constant

D.D. Pop. sizePop. size Variable, below KVariable, below K Rel. constant, near KRel. constant, near K

E.E. ConsequenceConsequence High rHigh r Good competitorsGood competitors

r is the rate of a population’s

increase K is a population’s carrying capacity

Small sizeSmall size

Rapid growthRapid growth

Early reproductionEarly reproduction

Many, small offspringMany, small offspring

Large sizeLarge size

Slow growthSlow growth

Late reproductionLate reproduction

Few, large offspringFew, large offspring

A. Body size and rA. Body size and rOn average, small organisms have higher rates of per capita increase and more variable populations than large organisms.On average, small organisms have higher rates of per capita increase and more variable populations than large organisms.

K vs. r selection: K vs. r selection: extremes in parental careextremes in parental care

K vs. r selection: K vs. r selection: extremes in parental careextremes in parental care

Sea urchinsSea urchins

Humpback whales

K vs. r selection: extremesK vs. r selection: extremes

Population GrowthGeometric growth vs. exponential growth vs

logistic growth.

Population GrowthGeometric growth vs. exponential growth vs

logistic growth.

When there are no limits, populations When there are no limits, populations grow faster, grow faster,

and FASTERand FASTER

and and FASTERFASTER!!

When there are no limits, populations When there are no limits, populations grow faster, grow faster,

and FASTERand FASTER

and and FASTERFASTER!!

Bottom line:

Invasive Invasive Cordgrass Cordgrass ((SpartinaSpartina) in ) in Willapa BayWillapa Bay

The Simple Case: Geometric Growth

The Simple Case: Geometric Growth• Constant reproduction rate

• Non-overlapping generations (like annual plants, insects)• Also, discrete breeding seasons (like birds, trees, bears)Suppose the initial population size is 1 individual. This indivual reproduces once &

dies, leaving 2 offspring. How many if this continues?

• Constant reproduction rate• Non-overlapping generations (like annual plants, insects)• Also, discrete breeding seasons (like birds, trees, bears)Suppose the initial population size is 1 individual. This indivual reproduces once &

dies, leaving 2 offspring. How many if this continues?

Exponential GrowthExponential GrowthAssumes continuous breeding life history strategy and

overlapping generations.Assumes continuous breeding life history strategy and

overlapping generations.

Human Population GrowthHuman Population GrowthHuman Population GrowthHuman Population Growth

www.smalltownproject.org/

Logistic Growth:Logistic Growth:The sigmoidal curve--carrying

capacity (K) plays a role in determining population growth.

The sigmoidal curve--carrying capacity (K) plays a role in determining population growth.

What happens if there ARE limits? (And eventually there ALWAYS are!)

Human populationHuman population

patternspatterns in age structure in age structure

Exponential growth modelExponential growth model

Exponential growthExponential growth