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Biol 121- 2010.04.07- Ecology- Demograpy and Population Growth (Ch. 52).docx

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University of British Columbia
BIOL 121

Biol 121 225 Freeman 1173-1183 Apr 7, 10 Population Ecology (how to study?) -population ecology is the study of how and why the number of individuals in a population change over time -look at distribution patterns: -measure changes in abundance and distribution -identify causes of these changes What is a population? -a group of individuals of the same species that live in the same area at the same time Characteristics of populations -individuals in one population tend to rely on the same resources (ie. Food, water, nesting sites) -they are influenced by similar environmental factors -they behave in a similar way -they have a high likelihood of interbreeding How (what terms used) to describe -abundance populations? -distribution: what areas they are in and how many? -(population) density (number per unit area) -pattern of spacing in habitat (3): a. clumped (e.g. a few schools of fish) b. Uniform (e.g. penguins) c. Random (e.g. trees) Demography -is the study of vital statistics that affect population size -the number of individuals depends on (4): -births, deaths, immigration and emigration (emigration is leaving) How to measure population density? -count the whole population (most accurate but time consuming) -sample (e.g. quadrats) -index of population size (indirect counting: e.g. count nests, burrows, droppings) -marked recapture (method): -traps placed in study area, trapped animals are marked with tags bands or tracking devices -then allow some time for them to mix randomly with the unmarked population -recapture (set traps a second time) and look at the proportion of recaptured animals N(total population) = Problems: 1. Individuals leaving or entering the population 2. Probability of catching individuals might not have been the same on both the 1 and 2 times (can be due to different setup, or environmental change, or perhaps intelligence/learning behaviour of the species) 3. Experimenter bias 4. Loss of eggs 5. Location What affects change in population size? 1) Survivorship (3) 2) Fecundity 3) Role of life history 1) 1) Survivorship -how many individuals of each age come out alive (after each year)? -how likely is it that individuals survive to the next year? Biol 121 225 Freeman 1173-1183 Apr 7, 10 -how many offspring does each female have? -note: a cohort is a group of individuals of same age that can be followed through time -survivorship can be shown by a life table showing year (0, 1, 2...) and survivorship and fecundity as the columns -survivorship x fecundity = average number of offspring produced per female born -survivorship can be shown by a survivorship curve of number of survivors vs. age (three types of survivorship) st -1 type is high survivorship at first and then very low survivorship at a later age (humans) -2 is a steady survivorship (so constant negative slope of the survivorship curve) (e.g. rodents) rd -3 is low survivorship at a very young age but afterwards a high survivorship (e.g. fish, sea turtles) 2) 2) Fecundity -the number of female offspring produced by each female in the population a. female offspring per female -calculate age-specific fecundity – average # female offspring produced by a female in age class x, where age class is a group of individuals at a specific age (e.g. lizards between 4 and 5 years old) b. Fertility rate -in humans, the fertility rate is highest near 20 and then decreases at a constantly increasing rate (concavity is negative) 3) 3) Role of Life History -time to mature sexually? -how many offspring? -survivorship
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