Biology Lecture No. 22: Community Ecology
Monday, November 21 , 2011
Human Population Growth:
-Human population size (worldwide) is still increasing because we have succeeded in increasing our
Human Populations Vary In R:
-E.g. while some continents are projected to increase in population size, some are projected to
decrease, or stay the same.
“R” Reflects Age Structures:
-E.g. growth rate in United States is zero; growth rate in Mexico is rapid; all due to age structure.
Increasing “N” (Population), But Decreasing “R” (Growth Rate):
-Globally, r = 0.011 or 1.1 % (per person per year)
-Population sizes won’t decrease until r becomes negative.
Demographic Transition Model:
-Over time, human societies get wealthier and throughout the industrial age, human birth rates and
death rates are subject to tremendous variation.
Population Size Isn’t Everything:
-The interactions within a population and between other populations are sometimes more significant
than population size.
-Community: A set of assemblage of populations that interact with each other.
Why Are Populations Distributed The Way They Are? :
-Some species are limited by a single critical factor (e.g. temperature, water abundance, daylight, etc.)
-Many species have multidimensional toler