Post on 31-Mar-2015
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