Biology Lecture 22: Human Ecology
Demographic transition model:
o The demographic transition model is based on historical patterns of changes in birth
rates, and death rates; and we observe changes in r
o For Western Europe and North America: over time human societies become more
technologically advanced (this is associated with increasing levels of wealth per capita).
Over time we tend to transition from the pre industrial societies, in which birth and
death rates are high, which mean that population size and r is low. Over time
populations move into the transitional stage (people are moving into the city, increase
in economic development). When this occurs, we see a decrease in death rates, but the
birth rates are still high. Therefore capita birth rates continue to increase through the
transitional stage. This is where values of r are at their maximum. When individuals start
to move more and more into the cities, death rates decrease and birth rates start to
decrease, which is known as the industrial stage. As a result little r starts to decrease.
The post industrial stage is defined as reaching zero population growth.
o These models were designed to explain what was occurring in Europe and North
America. We are not sure how this model can apply to other areas in the world that are
still developing. Overall, this how we determine predictions on how human population
size is going to change over lifetimes.
Population size isn't everything!
o It may more important to know what is happening with the resources use per person
o The impact humans have on the earth will not decrease with decreasing population size
o Decreasing our impact on the earth will likely require reductions in population size and
resource use per capita
o Community: a set or assemblage of populations that interact with each other
o Community ecology is concerned with the interactions between populations