Ecology of Ecosystems

Free Response

Compare and contrast food chains and food webs. What are the strengths of each concept in describing ecosystems?


Food webs show interacting groups of different species and their many interconnections with each other and the environment. Food chains are linear aspects of food webs that describe the succession of organisms consuming one another at defined trophic levels. Food webs are a more accurate representation of the structure and dynamics of an ecosystem. Food chains are easier to model and use for experimental studies.

Describe freshwater, ocean, and terrestrial ecosystems.


Freshwater ecosystems are the rarest, but have great diversity of freshwater fish and other aquatic life. Ocean ecosystems are the most common and are responsible for much of the photosynthesis that occurs on Earth. Terrestrial ecosystems are very diverse; they are grouped based on their species and environment (biome), which includes forests, deserts, and tundras.

Compare grazing and detrital food webs. Why would they both be present in the same ecosystem?


Grazing food webs have a primary producer at their base, which is either a plant for terrestrial ecosystems or a phytoplankton for aquatic ecosystems. The producers pass their energy to the various trophic levels of consumers. At the base of detrital food webs are the decomposers, which pass this energy to a variety of other consumers. Detrital food webs are important for the health of many grazing food webs because they eliminate dead and decaying organic material, thus, clearing space for new organisms and removing potential causes of disease. By breaking down dead organic matter, decomposers also make mineral nutrients available to primary producers; this process is a vital link in nutrient cycling.

How does the microcosm modeling approach differ from utilizing a holistic model for ecological research?


In a microcosm model, an ecologist recreates an ecosystem in a controlled environment. Since the ecologist is populating the environment, he can control the variables and the different species involved in the study to ask specific questions.

How do conceptual and analytical models of ecosystems compliment each other?


Conceptual models allow ecologists to see the “big picture” of how different components of the ecosystem interact with each other, energy sources, and resources. However, this approach is more descriptive than quantitative, so it is difficult to make conclusions about the resistance or resilience of a system. Analytical modeling creates a model that can predict how the ecosystem’s relationships will change in response to disturbances, but does not convey the complexity of the relationships seen with conceptual modeling.