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Scales of Ecological Organization Organism Population Community EcosystemBiosphere

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Definition Population ecology is the study of births, deaths, and the dynamics forces which regulate the number of individuals in a population.

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DensityDensity – Is the number of individuals per unit area or volume DispersionDispersion – Is the pattern of spacing among individuals within the boundaries of the population Density and Dispersion

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Population dispersion

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spatial patterns spaced-- may indicate competing individuals spaced -- may indicate competing individuals clumped-- may indicate social patterns or resource distribution clumped -- may indicate social patterns or resource distribution

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A random dispersionA random dispersion – Is one in which the position of each individual is independent of other individuals (c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

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A uniform dispersionA uniform dispersion – Is one in which individuals are evenly distributed – May 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.

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A clumped dispersionA clumped dispersion – Is one in which individuals aggregate in patches – May 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.

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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. BirthsImmigration PopuIation size Emigration Deaths Deaths and emigration remove individuals from a population.

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The life table of Belding’s ground squirrels – Reveals many things about this population

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A survivorship curve – Is a graphic way of representing the data in a life table… Figure Number of survivors (log scale) 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 constant

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Population patterns in age structure

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r- vs K-selection r-selection K-selection A.DisturbanceCommon, irregularRarer, more regular B.MortalityVariable, unpredictableConstant, predictable C.CompetitionLow or variableHigh, constant D.Pop. sizeVariable, below KRel. constant, near K E.ConsequenceHigh rGood competitors r is the rate of a population’s increase K is a population’s carrying capacity

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Small size Rapid growth Early reproduction Many, small offspring Large size Slow growth Late reproduction Few, large offspring

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A. Body size and r On average, small organisms have higher rates of per capita increase and more variable populations than large organisms.

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K vs. r selection: extremes in parental care Sea urchins Humpback whales

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K vs. r selection: extremes

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Population Growth Geometric growth vs. exponential growth vs logistic growth. When there are no limits, populations grow faster, and FASTER and FASTER and FASTER! When there are no limits, populations grow faster, and FASTER and FASTER and FASTER! Bottom line: Invasive Cordgrass (Spartina) in Willapa Bay

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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?

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Exponential Growth Assumes continuous breeding life history strategy and overlapping generations.

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Human Population Growth

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Logistic 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!)

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Human population patterns in age structure

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Exponential growth model

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Exponential growth

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