2Population EcologyThe study of populations in relation to their environmentMembers of a population rely on the same resources, are influenced by similar environmental factors, and are likely to interact and breed with one another3 fundamental characteristicsDensityDispersionDemographics
3Density The number of individuals per unit or volume The number of oak trees per square kmCounting all individuals is impractical so there are a variety of surveying methods to make a viable estimateSample plotsUse of an indicator (nests, burrows, tracks)Mark-recapture methodThis is dynamic and is under constant change via birth, emigration, immigration, death, etc.
4DispersionThe pattern of spacing among individuals within the boundaries of the populationClumped – most common pattern; organisms group together based on needs (i.e. food, mate, etc.)Uniform – evenly spaced patternRandom – the position of each individual is independent of other individuals
5DemographicsThe study of the vital statistics of populations and how they change over timeBirth and death rates are particularly importantLife tables look at the survival patterns of a given population based on cohort groups (age groups)Data in a life table can then be represented graphically using a survivorship curveClassified into 3 types: Type I, II and III
6Life HistoryTraits that affect an organism’s schedule of reproduction and survival (from birth to death)When reproduction beginsHow often the organism reproducesHow many offspring are produced during each reproductive episodeSeveral kinds of life historiesBig bang reproduction (semelparity)Repeated reproduction (iteroparity)There is a trade off between reproduction and survivalReproduction can lower the chance of survival for the parent
7Exponential Model Change in population size (ΔN/Δt) = rNΔN = the change in population sizeΔt = the time intervalr = per capita rate of increase (annual per capita birth rates – annual per capita death rates)Under ideal conditions, population will increase exponentiallyThe resulting curve is J shaped
8Logistic ModelActual populations have limitations to population growth known as the carrying capacity (K)Limited by a variety of resources including energy, shelter, predators, nutrient availability, water, etc.The resulting curve is an SNot uncommon for populations to overshoot K and then fall back
9Population DensityDensity independent – a birth rate or death rate does not change with population densityDune fescue grass mortality is due to physical factors such as drought, rather than densityDensity dependent - death rate will rise as population density rises; birth rate will fall as density increases
10Density DependentDensity dependent is a type of negative feedback loop that works to halt population growth as density increasesCompetition for resourcesTerritorialityDiseasePredationToxic WastesIntrinsic factorsNatural drop in reproduction via aggression, hormonal changes, delay in maturation, immune system depression
11Population DynamicsFocuses on the complex interactions between biotic and abiotic factors that cause variation in the size of populations.Populations are not generally stable, they fluctuate for a variety of reasonsHarsh weather can weaken the organism and diminish food supply causing a higher death rate. The fewer number of animals allows the food source to rebound and become plentiful causing a higher birth rate.
12Population CyclesSome organisms undergo boom-and-bust cycles with average time lengthsVoles and lemmings 3-4 yr cyclesRuffed grouse and ptarmigans 9-11 yr cyclesEx: Lynx and snowshoe hare populations are connected because of their predator prey relationship; they rise and fall togetherThis cycle is thought to be related to predator-prey interactions and sunspot activity, which effects the quality of the hare’s food
13Human PopulationIn 1650, human population was 500 million, 1850 reached 1 billion, today almost 7 billion.The human population was experiencing exponential growth, but in the 1960s the growth rate began to declineWe are still growing, but at a slower rate (currently ~1.15%)This is largely due to new diseases and population controls
14Population Dynamics Populations vary widely from region to region Many areas are in the process of moving from high birth rate, high death rate to low birth rate, low death rateThis is demographic transitionThis is related to healthcare and education, especially for women
15Population DynamicsAge structure is very important in determining growth trendsPopulations with many more children than adults will find population increasingUnderstanding age structure and its potential effects can help countries plan accordinglyInfant mortality and life expectancy play a role in planning at the family level
16Global Carrying Capacity Estimates for carrying capacity vary widely, but average in the billion rangeEstimate can be based on a variety of information such as extrapolation of current data or limiting factors such as the potential of available food based on dietMust be realistic about our needs/wantsScientists have also come up with the ecological footprint which accounts for the amount of land and water area required by each person to produce the resources consumed