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BIOL 103 Lecture Notes - Population Ecology, Logistic Function, Exponential Growth

Course Code
BIOL 103
Peter T Boag

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Population Ecology
- Ecology is the study of how organisms interact with and adapt to the
o Environment includes abiotic (rainfall, soil type) and biotic factors
(competitors, predators)
- Population ecology is the study of how and why the number of individuals in
a population changes over time or space
o Requires knowledge of population size and composition (sex ration,
age structure, condition of individuals, etc)
- Population density is the number of individuals of a species per unit area at a
given time
- Population dispersion (spacing) gives clues about population processes and
relations with local environment
o Clumped dispersion
o Uniform dispersion
o Random dispersion
o Distinguish from dispersal*****
- Dispersion of population members may depend on:
o Density
o Interactions between conspecifics
o The distribution of other species that are competitors
o Predators or prey
o Environmental features such as moisture, temperature, soil type, wind
direction, etc.
- Relative importance of four processes affects population growth, sizem and
o Natality (birth rate b)
o Morality (death rate d)
o Immigration (i)
o Emigration (e) usually assume i = e so they cancel out)
o These may be influenced by other factors such as the age of
individuals, density, environmental quality, etc
- Growth rates given by r, the per capita rate of increase (or decrease) of a
o r > 0 = increase, r < 0 = decrease, r = (b-d); if immigration and/or
emigration also occur then r = (b d) + (i e)
o The intrinsic rate of increase (rmax) is the maximum rate a population
can increase at, under ideal conditions
- Two models of population growth
o Exponential growth (J-shaped curve)
Applies in an idealized, unlimited environment
Rare in nature except for brief periods in a new environment
or seasonally abundant food
o Logistic growth (S-Shaped curve)
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