Monday, October 22, 2007

Ecology Part II

Ecology Part II

Population Growth

Change in population= births-deaths
Today we were indroduced to the exponential model of population growth. The exponential model is based upon having ideal conditions within population growth.
The exponential model has five variables:

N= number of individuals
r= rate of growth
ri= intrisic rate (maximum rate of growth)
t= time
d= rate of change

the formual is: dN/dt=riN
If a pair reproduces two offspring no population growth will be seen because those two offspring will only be replacing that one pair. If a pair produces four offspring not only will there be a replacement for the pair but an added two more into the population, thus increases the population size.

Exponential Growth Rate

- characteristics of a population without any factors limiting it.
- Some factors that may limit a population are an organisim being introduced to a new enviorment or it having to rebound from a catastrophe.
- Exponential Growth Rate can be seen through the growth in population of both the African Elephant and the Whooping crane which barely survived exctintion, but are slowly fighting there way back.

Regulation of Population Size

There are factors in which limit the regualtion of a population size. These factors can be categorized in to two selections; density dependent and density independent or biotic and abiotic factors.The density dependent factors are food suppy, competition, predetors and disease.The density independent factors are sunlight, temperature, and rainfall.

Introduced New Species

-Non native species are when a population is put into and new area and the population exponentially grows
- When these non native species are put into this new area, though it may seem benifical, at times placing a species to a new surronding backfires. These species now no longer have there native predetors such as diseases or other organisims, they now lack competitors, and there is a lack of natural controls leaving them to do as they please since there is no longer anything that can hinder their growth or activites. There also becomes a reduction in diversity again due to the fact that there usually are no other organisims to surpress their activites.

A good example of this are the zebra mussels which after being introduced to a new enviorment very rapidly spread and cling on to any found objects.

The purple loosestrife is a very good example of how introductiong a new species in to an enviornment can also reduced diversity. Overtime the loosestrife spreads itself and seems to over take its surronding areas.

No comments: