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ecology final notes

ecology final notes - ECO Test 4 Ch 10 Population Dynamics...

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ECO Test 4 4/11/11 Ch. 10 Population Dynamics Densities of many populations fluctuate greatly over time E.g. many insect populations show great density changes Often due to climatic factors or Changes in food availability Or predator or parasite densities There has been a study that hopefully will allow the use of wasps to decrease pests Many insect pests of crops show periodic outbreaks followed by decline and periods of low abundance (see the graph on the notes of this day) Many disease organisms show outbreaks (=epidemics) medicine ecology=epidemiology Example: Influenza virus killed 20-40 million people in 1918-1919, another is cholera a deadly bacterium Temporal variation in population density may be reflected in the population age structure – the relative numbers in each age class. Typical of populations in which few strong year classes dominate population For example, marine fish stocks, like cod Cohort – same age group of individuals in a population (all from the same year) Marine fish – high fecundity (egg count) or forest trees are long lived from the same process Dominant year classes also are observed in tree populations following a disturbance such as fire (The disturbance actually allows establishment of new seedlings –result same – age strands) Most organisms that have high fecundity most eggs die unless recruitment takes place To determine the age structure of a population – we must be able to estimate the ages of individuals These are the various methods Fish scales and oliths – annual growth rings Mammals – tooth morphology and condition Tree trunks – annual growth rings Bird plumage (feathers) – color pattern, condition Population density and distribution are influenced by the movement of individuals Movement between populations: Emigration (leaving) Immigration (entering) The best way to study animal movements is to mark the individual (e.g., bird bands, fish tags, mammal radio collars) To project a population dynamics (change), we need to know: 1. # of individuals in each age class 2. Their probability of survival (survival rate) 3. Their rates of fecundity (birth rate) 4. Rates of emigration and immigration A compilation of these population vital statistics is referred to as a life table. Life tables deal with a handful of population variables: one designated by x (measured in years, months, or days) Age – specific survivorship – designated by l x The probability that a new born will be alive at age x
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I 0 = 1.0 first age class I w = last age class Expectation of life – probable number of additional age classes that an individual of age x will live ( age specific and designated by e x ) Age specific fecundity – probable number of offspring born to an individual during age class x (designated by m x ) ** Generation time (Time between generations) Formula is T ~(a+w)/2 A is the age of first reproduction W is the age of last reproduction Survivorship curve (a plot of l x vs x) Can be characteristic for certain kinds of organisms
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