population ecology chapter 53. population ecology the study of populations in relation to their...
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Population EcologyChapter 53
Population 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 characteristicsDensity DispersionDemographics
DensityThe 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.
DispersionThe 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
DemographicsThe 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
Life HistoryTraits that affect an organisms 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 histories Big bang reproduction (semelparity)Repeated reproduction (iteroparity)There is a trade off between reproduction and survival Reproduction can lower the chance of survival for the parent
Exponential ModelChange in population size(N/t) = rNN = the change in population size t = 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
Logistic 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
Population 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
Density Dependent Density 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
Population 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.
Population 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 hares food
Human 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
Population DynamicsPopulations vary widely from region to regionMany 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
Population 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
Global Carrying CapacityEstimates for carrying capacity vary widely, but average in the 10-15 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