Ecology - Population Dynamics

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Demography

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study of how the vital rate of individuals (birth, death, growth) affect structure and dynamics of populations

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Population

Back 2

group of potentially interbreeding individuals (same species, co-occur in time and space)

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Properties of Populations

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density: number of individuals per area or volume

size structure: proportion of individuals in various size categories

age distribution: proportion of individuals in various age categories

sex ratio: number Males: number Females (not always 1:1)

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Life Tables

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summary of age (or size) specific rates of survival and fecundity (progeny per individual)

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Cohort

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a group of individuals of the same age, from birth until they all die

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Bide equation

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N(t) = N(0) e^rt

r = b - d = per capita rate of population growth (time^-1)

N = Births + immigration – deaths – emigration (open population)

If r > 0, population grows exponentially. If r < 0, population declines exponentially (until it goes extinct). If r = 0, population is in a stable equilibrium (zero population growth), although individuals 'turn over' (some die, and are replaced by new births)

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K

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the carrying capacity, or the population limit because of overexploitation of resources

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r

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per capita rate of population growth

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r-selected traits

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Usually those with r-selected traits will be abundant in newly-dispersed areas.

short life span
small size
high predator vulnerability
weak competitor
good disperser
many small offspring
early reproduction

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K-selected traits

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Usually those better at competing as time has gone on, when population is dense.

large life span
large size
low vulnerability to predators
strong competitor
slower disperser
fewer but better provisioned offspring
late reproduction

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Density dependence

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When the survivorship curve follows the logarithmic equation which predicts an initial exponential growth curve, which then gradually flattens out (carrying capacity).

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Density independence

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Changes in population that have nothing to do with the carrying capacity.

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Limiting factor

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An aspect that can determine the carrying capacity. For example, for a grass species, the shade of the tree may limit the amount of light that comes through, and therefore how many grasses can live on that light.

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Regulation

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how tight are the fluctuations around the average stable density that is the population carrying capacity. Loose regulations = high amplitude fluctuation.

Population stability based on how regulated population is to the carrying capacity. Overcompensating density dependence (strong density-dependent feedback) or time lags in feedbacks can destabilize population growth.

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Ecological footprint

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estimate of land and water area needed to produce all resources a nation consumes, and to absorb all the waste in generates.