In lieu of an abstract, here is a brief excerpt of the content:

29 CHAPTER 2 Lake Ecology Ecology is the study of the relationship of organisms to one other and to their physical environment. Natural selection, predator–prey interactions, and population dynamics are all included within the framework of ecology. Like other disciplines of biology , ecology is based on the fundamental science of physics. Within ecosystems, the laws of science, such as the thermodynamic laws are often hidden to the casual observer by the complexity of species interactions and the environment. The first thermodynamic law states that energy in an isolated system is conserved, and the second law states that energy disperses in an isolated system. As with theories of physics, most theories in ecology have been around for a long time. In 1942, Raymond Lindeman related the second law of thermodynamics to energy flow in Cedar Bog Lake of central Minnesota and Lake Mendota of Wisconsin. Lindeman used the then newly defined concepts of ecosystems and food webs and tied them to energy flow. Lindeman documented the flow of energy through lake food webs, from primary producers (algae and other plants) to herbivores (zooplankton) to predators (fish and humans). As energy moves through the food web, a large amount is unavailable to organisms. On average , only about 10 percent of the energy from one level of the food web transfers up a level (for example from herbivores to predators). Animals use energy to survive and reproduce; the end result is that there must be substantially fewer predators than prey. The law of conservation of energy states that energy can neither be created nor destroyed. This holds true within ecosystems, where energy is not truly lost, but just lost into the environment, typically in the form of heat that is unavailable to organisms at higher trophic levels. Given this energy dissipation between trophic levels, the overall shape of a food web is a pyramid. It also follows that a food web cannot extend more than a small number of levels. Conversion of food must follow chemical and thermodynamic laws. Species do not exist because of magic. Lindeman’s research on lake ecosystems proved this to be true. These laws of nature, along with the theory of natural selection, population dynamic concepts , community succession, and predator–prey theory, provide the theoretical framework of ecology. Lakes and wetlands follow these general laws of nature, and so should their management . Several principles of nature follow from this framework. Here are four core principles. Principle #1: The law of the minimum applies to organisms and populations within ecosystems . Every individual and population has space and condition requirements, and the size of that niche influences their fate. While an organism is dependent on a number of different resources, at a single point in time one of those resources will limit its growth—the limiting factor. The scarcest resource determines the rate of growth for an individual or a population. For example, lake algae growth is dependent on carbon, nitrogen, phosphorus, and other 30| North American Lakes essential nutrients, but phosphorus is often the scarcest and its availability therefore generally determines algae abundance. There is always a limiting factor. Principle #2: Organisms and ecosystems have histories that constrain the future. Through genetic variation (random mutation and recombinations) and natural selection, every organism has evolved from something similar. Evolution is a bottom-up process. An organism may evolve in the future, but in many ways it will be quite similar to its recent evolutionary ancestors. We evolved from earlier hominids several hundred thousand years ago. Our needs are similar to those of our ancestors. If, in the future, another species evolves from us, its needs are likely to be similar to our own. Every ecosystem also had a past with a community of species and physical resources. The character and function of an ecosystem in the future is constrained by its present condition. An undisturbed ecosystem will operate in the future much as it did in the past. Species and ecosystems are not created out of thin air. The future will likely be similar to the past. Principle #3: Processes and interactions within ecosystems occur at many different scales. From the molecular scale that determines walleye egg survival on the shore of a lake to the walleye population dynamics in a lake to the range and distribution of walleye in North America, the study of walleye ecology is scale dependent. Scale matters. Principle #4: Many things are connected to many other things. Organisms are dependent on other organisms, and...

Share