Ecology Ch 20 Notes April 23, 2014
Properties of Populations
Density
Dispersion
Size
Ch. 20-1
Ch. 20-2
Growth Rate- the amount by which a population's size changes in a given time
-can increase OR decrease
• birth rate• death (mortality) rate• immigration• emigration
Change in pop size=(birth + immigration) - (death + emigration)
-usually assume no immigration/emigration when calculating growth rate
Ecology Ch 20 Notes April 23, 2014
MODELS *not accurate representation of reality, but useful tool
Exponential growth model• rapid increase after a few generations• "J" curve• usually happens under rare conditions (new habitat, new food supply) for short periods of time
Why can't it keep increasing indefinitely?
LIMITING FACTORS
• Factors that restrain the growth of a population • Two types- density-independent & density dependent • Regulate the population size (limits the numbers)
Leads to a different model...
Ecology Ch 20 Notes April 23, 2014
Logistic Growth Model• population stabilizes after a period of exponential growth• includes the carrying capacity- the number of individuals the environment can support over a long period of time• certain limiting factors control population size
TWO TYPES OF LIMITING FACTORS
1. Density-independent• can affect population regardless of density• affects pop. no matter what it's density • example: natural disaster, etc
2. Density-dependent• factor related to density• can affect population size only when population density is high• example: resource limitations
Ecology Ch 20 Notes April 23, 2014
Sawtooth Curve Model
• predator- prey cycle• each species cause of other's cycle• maybe, but not necessarily- prey might be dependent on some other factor
Ecology Ch 20 Notes April 23, 2014
SMALL POPULATIONS vulnerable to extinction
• environmental disturbances • disease outbreaks• inbreeding (descended from few individuals)
- decreased genetic variability- uniform traits- decreased ability to adapt to changing environmental
conditions
20-3 HUMAN POPULATION GROWTH
• Hunter-gatherer lifestyle• Agricultural revolution
http://ngm.nationalgeographic.com/7-billion7 BILLION IS A BIG NUMBER
Ecology Ch 20 Notes April 23, 2014
THE FACE OF 7 BILLION http://ngm.nationalgeographic.com/2011/03/age-of-man/face-interactive
http://galen.metapath.org/popclk.html
Ecology Ch 20 Notes April 23, 2014
http://ngm.nationalgeographic.com/2011/03/age-of-man/map-interactive
HOW & WHERE WE LIVE
Developed countries- industrialized, better economy, education & health, longer life span
Undeveloped/developing countries- not
