In every environment you will find many organisms that depend on each other and their surroundings. Diversity in populations is a key element to maintaining a healthy environment. However, when you study an ecosystem, you will notice that some populations are much larger than others even though food, water, and energy sources seem plentiful. You might also notice that changes or disruptions in an ecosystem can change the sizes and types of populations either very quickly or over time.
It may be difficult to determine what type of ecosystem you live in, especially if you live in a city or a suburb. But, before the land was developed for human use, it was most likely a balanced ecosystem. Find out about the region you live in, and compare the species that once lived there to those that live there today, Use the information in this chapter to help you identify and describe any changes that might have occurred to the ecosystem.