Notes

ch 44 population ecology

A population consists of all the individuals of a given species that live and reproduce in a particular place and time.
Population size can respond to changes in the physical and biological environment.
The age structure of a population helps ecologists understand past changes and predict future changes in population size.
The dynamics of populations are influenced by the colonization and extinction of smaller, interconnected populations that make up a metapopulation.

ecology - study of the relationships of organisms to one another & the environment
abiotic factors - climate & nutrient availability
biotic factors - competitors, predators, parasites, & prey

-populations - consists of all the individuals of a species that live & reporduce in a particular place; defined by three key features: size, range, & density
-natural selection enables populations to adapt to the physical & biological compenents of their environment;
-population size - # of individuals of all ages alive at a particular time in a particular place

geographic range - how widely a population is spread & the factors that determien its distributiion; range of a species reflects the range of climates a population can tolerate & how many other species it encounters
population density - population size/population range; measures how crowded or dispersed the individuals in the population are

population distribution
a) random - no clear pattern to distribution of individuals; the location of one individual has no influence on where another is located
b) clumped - indiviudals cluster together in a small space; occurs when resources are clustered or proximity to others enhances chances of survival
c) uniform - individuals are distributed more evenly (farther spread) than predicted by chance; occurs if all iresources are limited or if predators target a single species

estimating population size
-sessile (sedentary) organisms can be counted within a defined area & total population can be extrapolated from that count
-mark-&-recapture is used to count mobile organisms; organisms are captured, marked, & released on 2 successive days; population size = organisms marked & unmarked on the second day/recaptures * organisms caught on the first day

factors affecting population size
-increasing: immigration & birth
-decreasing: emigration & death

population growth equation: changeN = N2 - N1 = (B - D) + (I - E)
N1 = time 1, N2 = time 2
B = births, D = deaths
I = immigration, E = emigration

per capita growth rate - proportional increase/decrease over time per individual
per capita growth rate: r = (changeN/changet)/N1 or Nt =N1(1+r)^t

r = per capita growth rate
changeN = change in population size, changet = per unit of time
N1 = # of individuals at start, initial population size
Nt = population size after t = years

exponential growth - pattern of population increase that results when the per capita growth rate is constant, but the # of individuals added per unit of time increases as the population grows due to new individuals reproducing; cannot continue for long since # of individuals eventually outgrow resources available
-competition for resources limtis population growth:
-intraspecific (within-species) compeition results in natural selection
-interspecific (between-species) competition results in increase/decrease in population size

carrying capacity - max # of individuals any habitat can support; grwoth rate is maximal when population size is half of the carrying capacity & decreases as it approaches due to crowding & competition for resources

logistic growth: dN/dt = r [K-N/K]N
-at first, growth reflects the rate at which indiviudals can reproduce themselves (rises steeply) then it levels off to reflect decreasing availabiltiy of food & space
population at any time t: Nt = N1 + rN1 [(K-N1)/K]

density-independant factors - influence population size w/o regard for the population's density; include resources & predation & events like severe drought or a prolonged cold period

age structure - # of individuals within each age group of the population; some individuals contribute more to population growth than others (younger populations increase faster); birth/death rates vary /w age & environment

demography - study of the size, structure, & distribution of populations over time; includes changes in response to birth, aging, migration, & death

cohor - the individuals born at a given time
survivorship - proportion of indiviudals from the initial cohort that survive to each successive stage of the life cycle; different organism exhibit different survivorship curves

3 types of survivorship:
1. most mortality late in life (large animals)
2. consistent levels of mortality throughout life (birds & small mammals)
3. high mortality at earliest stages of life (small plants & animals & organisms that grow fast & reproduce early)