Population Population Ecology Ecology
Population Population EcologyEcology
What is a populationWhat is a population
A group of individuals of a species A group of individuals of a species that live in an area and rely on the that live in an area and rely on the same resources for survival often same resources for survival often interacting and breeding with one interacting and breeding with one anotheranother
Population Population CharacteristicsCharacteristics
Density Density DispersionDispersion DemographyDemography
Life TablesLife Tables Survivorship curvesSurvivorship curves Reproductive ratesReproductive rates
Life Histories-Trade off Life Histories-Trade off between survival and between survival and reproductive traits reproductive traits
When reproduction beginsWhen reproduction begins How often the organism reproducesHow often the organism reproduces How many offspring are produced How many offspring are produced
during each reproductive episodeduring each reproductive episode
Reproduction TypesReproduction Types
Semelparity/Big Semelparity/Big Bang ReproductionBang Reproduction Ex. Pine Looper Ex. Pine Looper
MothMoth
Iteroparity/Iteroparity/Repeated Repeated ReproductionReproduction LizardsLizards
Why choose one over the other?
Studying PopulationsStudying Populations Exponential growth model – the rate of Exponential growth model – the rate of
expansion of a population under ideal expansion of a population under ideal conditionsconditions
Population-limiting factors – hunting, amount Population-limiting factors – hunting, amount of space suitable for breeding, restricted of space suitable for breeding, restricted population growth, food availabilitypopulation growth, food availability
Logistic growth model – idealized populationLogistic growth model – idealized population growth slowed by limiting factors as the growth slowed by limiting factors as the
population size increasespopulation size increases Carrying capacity – the maximum population Carrying capacity – the maximum population
size that an environment can support at a size that an environment can support at a particular time with no degradation to the particular time with no degradation to the habitathabitat
Exponential GrowthExponential Growth
G= growth of population over time (dN/dt)
r=tells if the population is growing (per capita rate of increase) r=0 with ZPG
N= population size
Logistic growth and Logistic growth and exponential growth comparedexponential growth compared
K= carrying capacity
K-N= the number of additional individuals the environment can accommodate
(K-N)/K= fraction of K that is still available for population growth
Growth of a population of Growth of a population of fur sealsfur seals
What does the logistic growth What does the logistic growth model suggest about real model suggest about real
populations in nature?populations in nature? A population’s growth rate will be small A population’s growth rate will be small
when the population size is either small or when the population size is either small or large and highest when the population is large and highest when the population is at an intermediate level relative to the at an intermediate level relative to the carrying capacity.carrying capacity.
Limiting factors make the birth rate Limiting factors make the birth rate decrease, the death rate increase or bothdecrease, the death rate increase or both
Eventually the population will stabilize at Eventually the population will stabilize at the carrying capacity when the birth rate the carrying capacity when the birth rate equals the death rateequals the death rate
These are mathematical models and no These are mathematical models and no population fits either perfectlypopulation fits either perfectly
Some factors that limit population Some factors that limit population growthgrowth
As density of song As density of song sparrows increase, the sparrows increase, the number of eggs laid number of eggs laid decreases because of decreases because of food shortagesfood shortages
Plants grown under Plants grown under crowded conditions crowded conditions tend to be smaller and tend to be smaller and less likely to surviveless likely to survive
Disease transmission Disease transmission or accumulation of or accumulation of toxic waste products toxic waste products can increase mortalitycan increase mortality
Continued……Continued…… A predator may capture A predator may capture
more of a particular more of a particular kind of prey as the prey kind of prey as the prey becomes abundantbecomes abundant
White-footed mice stop White-footed mice stop reproducing at a colony reproducing at a colony size of 30-40 even when size of 30-40 even when food and shelter are food and shelter are provided. Stress?provided. Stress?
The graph shows aphids The graph shows aphids which feed on the which feed on the phloem sap of plants phloem sap of plants increase in population increase in population in the summer and then in the summer and then die-off in the fall and die-off in the fall and winterwinter
Continued….Continued…. Some populations Some populations
remain fairly stable in remain fairly stable in size close to carrying size close to carrying capacitycapacity
Most populations Most populations fluctuate as seen at the fluctuate as seen at the leftleft
This graph shows song This graph shows song sparrow populations, sparrow populations, with periodic with periodic catastrophic reductions catastrophic reductions due to severe winter due to severe winter weatherweather
Boom and bust cyclesBoom and bust cycles Hare cycles may be Hare cycles may be
caused by increasing caused by increasing food shortages during food shortages during winter caused by winter caused by overgrazingovergrazing
They may be due to They may be due to predator-prey predator-prey interactionsinteractions
Cycles could be Cycles could be affected by a affected by a combination of food combination of food resource limitation and resource limitation and excessive predationexcessive predation
Predators reproduce Predators reproduce more slowly than their more slowly than their prey so they always lag prey so they always lag behind prey in behind prey in population growth.population growth.
Regulation of Regulation of PopulationsPopulations Density IndependentDensity Independent
Birth and death rate does not change with Birth and death rate does not change with population densitypopulation density
Density DependentDensity Dependent Death rate that rises as population density risesDeath rate that rises as population density rises
Competition for resourcesCompetition for resources TerritorialityTerritoriality HealthHealth PredationPredation Toxic WasteToxic Waste Physiological factorsPhysiological factors
Population DynamicsPopulation Dynamics Complex interactions between biotic and abiotic Complex interactions between biotic and abiotic
factorsfactors Population CyclesPopulation Cycles
Boom and bust cyclesBoom and bust cycles Snowshoe hare and lynxSnowshoe hare and lynx
Survivorship curvesSurvivorship curves Type I curve – Type I curve –
produce few produce few offspring and give offspring and give them good carethem good care
Type III curve – Type III curve – high death rates for high death rates for very young then a very young then a period when death period when death rates are lower for rates are lower for those who survive those who survive to a certain ageto a certain age
Logistic Model & Life Logistic Model & Life HistoriesHistories
K-Selection K-Selection Occur near carrying Occur near carrying
capacitycapacity Density dependentDensity dependent Low reproductive rates Low reproductive rates
and high careand high care Type I Survivorship CurveType I Survivorship Curve
r-Selection r-Selection High Reproductive RatesHigh Reproductive Rates Unpredictable Unpredictable
environmentsenvironments Density IndependentDensity Independent Type III Survivorship Type III Survivorship
CurveCurve
Life tables – compiled by Life tables – compiled by life insurance agentslife insurance agents
Human carrying capacity Human carrying capacity estimatesestimates
Ecological footprint Ecological footprint with multiple with multiple constraints such as constraints such as food, fuel, water, food, fuel, water, housing, and waste housing, and waste disposal used.disposal used.
Calculates current Calculates current demand on resources demand on resources by each country in by each country in hectares of land per hectares of land per personperson
World ecological World ecological capacity is 1.7 ha per capacity is 1.7 ha per person alive in 1997person alive in 1997