Thursday, October 18, 2007


Today, we learned how to read and interpret demographics. Demography is used to measure factors that affect the growth and decline of a certain population. These factors are used to measure risk and are used to impliment laws such as restrictions on land use, ect.

The diagram to the left shows the average life expectancy of each cohort, or group that travels through life together, of male and female belding ground squirrels. Females generally live longer lives than males and produce mor offspring than can survive, a theory introduced by Darwin.

The graph to the right shows the maximum life spans of the human, the hydra, the oyster. Humans are generally type 1 ( high death rate in post-reproductive years). Hydra are type two (constant mortality rate throughout the life span). Oysters are type 3 (very high early mortality but the few survivors then live long and stay reproductive). Because of this situation, oysters make a ton of babies but do not provide any care for them while humans make few babies and yet invest a lot in raising them. We call the behavior of the oysters "r-selected' and the humans "k-selected".

1 comment:

KB Foglia said...

Love the moving Earth!
It's like its revolving through our classroom. Yes, that's it... our classroom is the center of the Universe!