In general, populations have the ability to increase exponentially, but why do you think that most populations are fairly constant in size?

Answer 1

You might want to question that question!

http://www.globalchange.umich.edu/globalchange2/current/lectures/human_pop/human_pop.html

and others: http://www.google.com/search?q=population+growth&rls=com.microsoft:en-us:IE-SearchBox&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7SUNA