 Density = # of ind per unit area or volume  3 ways to measure › Aerial count of herds, tall trees in savanna › Random (sample) plots to count individuals or nests, burrows, tracks › Mark-recapture  Capture, mark, release, recapture  Pop size = total recaptured X (marked & released) marked & recaptured

 Clumped – individuals in patches › Most common  Uniform – territoriality  Random › Ex – wind blown seeds

 Age at 1 st reproduction  # of offspring/year – natality (birth rate)  Life expectancy – death rate  Movement of organisms › Immigration › emigration

Type I – human – greatest survival to old age Type II – squirrel – medium survival Type III – clam – greatest deaths early

 Opportunistic species (r-selection)  Density-independent › Population densities tend to fluctuate below carrying capacity or have little competition so overshoot & crash › Many offspring quickly › No parental care › Short lifespan › Small offspring › Weeds, salmon, insects, starfish, mice

 Equilibrium species (k-selection)  Density dependent › Few young › Parental care › Reproduce at more mature age › Long lifespan › Large offspring › Birds, whales, elephants, humans, hardwood trees

 Exponential model – typical of populations introduced to a new area or whose # have been reduced › Ex – single pair of elephants produce 19 million in 750 years › Single bacterium divides every 20 mins, can cover the earth 1 ft deep in 36 hours › Begin with a few individuals and unlimited resources, but can lead to crash as resources become limited

 Logistic Model › The per capita rate of growth is reduced as the population nears the carrying capacity › Carrying capacity – maximum population size that can be maintained in a particular area

 # of population that can be maintained indefinitely in the ecosystem › dN = rN(K-N) dt K If population (N) is small, equation works as if it were just rN As N increases, growth slows b/c it is being multiplied by a fraction If N=K, growth is zero

 Density dependent LFs – only come into play or intensify when the population becomes denser › Food › Disease › Sunlight for plants › Hormonal changes › Space, nesting sites › predation

 Density-independent LFs – affect both large & small populations the same › Climate, weather › Disasters – flood, drought, fire