1. There are many reasons human activities cause imbalance in biogeochemical cycling. Fish kills can be caused by eutrophication and an increased growth of algae. Algae causes a loss of available oxygen, called anoxia. Anoxia can kill fish and other aquatic organisms. Algae does produce oxygen but only when there is enough light. Eutrophication reduces the clarify of water so in eutrophic lakes, algae is starved of light. When algae do not have enough light, instead of producing oxygen, algae consume oxygen.

2. Opportunistic species exhibit aggressive growth. They have a short-life span, are small in size and they produce numerous offspring that they show little care to. They are typically found in unpredictable and variable environments and their population can survive anything that threatens it. Most insects are examples of an opportunistic species. Equilibrium species exhibit a strategic growth. They are opposite of opportunistic, meaning they are large with a long-life span. They have few offspring to whom they give more care to, but they are more likely to become extinct. Birds are examples of equilibrium species.