Practice Questions: Essay topics 1.) The biological communities of lakes have often between greatly impacted by human activities, and these can lead to declines in water quality associated with excessive algal through both bottom-up and top-down mechanisms. Explain the difference between these two mechanisms, the types of human induced changes that lead to them, and how one might distinguish between them using characteristics of the food web. 2.) The river continuum concept had a major effect on our view of biological processes in rivers, their links to the underlying physical environment, and the way we study them and compare them to each other. Explain the concept, and show how and why it gave rise to new ideas, methods and approaches. 3.) Fisheries managers typically use population based models to attempt to make decisions regarding sustainable exploitation. However, populations of organisms are “embedded” within complex ecosystems and their carrying capacities and rates of increase are determined by interactions with other species and with the physical environment. Explain how the parameters of fish population models can be influenced by community interactions and how these interactions should influence the decisions that fish managers make.