Exponential and Logistic Growth Curves
When resources are unlimited, populations demonstrate exponential growth where there is no limit to their sizes. When resources are scarce, populations show a logistic growth. This is when they begin to grow, but stop when resources become limited and the population hits the carrying capacity.
In a logistic growth ecosystem, there will come a point where the limited resource has become scarce. This means that the ecosystem cannot support any more of that species - which then halts the increase in population. The limit to the population of a species in a logistic growth ecosystem is called the carrying capacity.
There are three simple types of pyramids to demonstate population growth and decay: expansive, constrictive, and stationary.
Expansive - this pyramid has a broad base and a rapid population growth. The population of older organisms is small and the population of young organisms is very big.
Constrictive - this pyramid shows a low death rate and a low birth rate. The population is mostly of older organisms.
Stationary - this pyramid shows somewhat equal numbers for almost all ages. The birth and death rate are roughly the same here.
Environmental Limits to Population Growth. Boundless Biology. Retrieved from https://courses.lumenlearning.com.
(8 Aug. 2015). Population Pyramid. Geography of India and The World. Retrieved from http://www.drishtiias.com/upsc-exam-gs-resources-Population-Pyramid.
