2Population ecology Population ecology is the study of populations. Population = group of individuals of the same species occupying a common geographical areaHabitat = where a species normally livesDensity = The number of individuals in a population per unit area.
3Exponential Growth Indicated by a J-shaped growth curve growth in which the population increase in a period is a fixed percentage of the size of the population at the beginning of the period;the number of individuals increases over time logarithmically (e.g. bacterial cultures).
4Components of an exponential growth pattern for a given population Time Zero - time of establishment of a population; for bacterial culture, time that the culture was inoculatedLag Phase - time that it takes for the population to start growing; resources must be obtained; habitat and microhabitat establishment; niche definition; population prepares for reproduction (for bacterial cultures: time that the cells need to begin their specific type of metabolism before cell division can occur).
5Log Phase - period of exponential (logarithmic) growth. Stationary Phase - period following exponential growth where number of deaths equals the number of new individuals.Death Phase - period following the stationary phase where the population is dying due to depletion of resources and or contamination of habitat with waste products.
6EXPONENTIAL/ LOG PHASE STATIONARY PHASEDEATH PHASEEXPONENTIAL/ LOG PHASELAG PHASELABEL THE PHASES OF EXPONENTIAL GROWTH
7Logistic growth (S-shaped curve) Because of limiting factors, populations rarely exhibit J-shaped growth curves.When growth encounters environmental resistance, populations experience an S-shaped or logistic growth curve.Early on populations will exhibit very rapid growth, but as they near the carrying capacity they will level off.Logistic growth is density dependent.High density and overcrowding put individuals at greater risk of being killedPredators, parasites and pathogens have greater numbers of prey and hosts in a smaller area to interact with
8Components of a Logistic Growth Curve Lag PhaseLog/ Exponential Growth PhaseDeceleration PhaseStable, Equilibrium Phase
10Growth curve of a laboratory population of yeast cells. STABLE EQUILIBRIUM PHASEDECELERATION PHASEEXPONENTIAL/ LOG PHASELAG PHASE
11Growth curve of the sheep population of Southern Australia Growth curve of the sheep population of Southern Australia. The smooth curve is the hypothetical logistic curve about which the real curve seems to fluctuate.
12Effects of population density on growth in open systems: Density-independent growth - size of population is not a factor in determining the resulting population size overall;population size, however, stays about the same as when it began.Most density-independent factors are abiotic.Examples: temperature, storms, floods, drought, habitat destruction
13Effects of population density on growth in open systems: Density dependent growth - size of the population is a factor in determining the resulting population size overall;exponential growth can occur if adequate resources are available and range expansion can occur as in an open system.Disease is spread more quicklyStress can lead to aggression
14Population growthPopulations grow, shrink, or remain stable, depending on rates of birth, death, immigration, and emigration.(birth rate + immigration rate) –(death rate + emigration rate)= population growth rate
15Exponential growthUnregulated populations increase by exponential growth:Growth by a fixed percentage, rather than a fixed amount.Similar to growth of money in a savings account
16Exponential growth in a growth curve Population growth curves show change in population size over time.Scots pine shows exponential growthFigure 5.10
17Limits on growthLimiting factors restrain exponential population growth, slowing the growth rate down.Population growth levels off at a carrying capacity—the maximum population size of a given species an environment can sustain.Initial exponential growth, slowing, and stabilizing at carrying capacity is shown by a logistic growth curve.