Food Webs of Lake George
Image courtesy of USDA
A food web is a complex system of several food chains. Food webs show the eating relationships between the species that live in an ecosystem or a particular living place. An essential part of a food chain is that each individual organism is of equal importance to the ecosystem. Thus, the organisms are interdependent.
In a simple food chain, aquatic bugs eat the plants, and small fish eat the bugs. Big fish eat the little fish, and people catch and eat the big fish. However, organisms often feed on more than one species. This interaction is important, because if one organism declines or disappears, the organisms that feed on it are not necessarily lost; they can find other sources of food.
In Lake George, the food chain begins with the primary producers. These plants and plant-like algae, or phytoplankton, take in carbon dioxide and water and, with the sun's energy, produce their own food in the form of a sugar. They then give off oxygen, an extremely important element for all aquatic animals.
Cyclops sp. is a common copepod zooplankton found in Lake George. Photo courtesy of: Department of Biological Science, University of New Hampshire
Bosmina longirostris is a common zooplankton in Lake George. It is only about 0.5mm in size. Photo courtesy of: Department of Biological Science, University of New Hampshire
Next in the chain are the primary consumers, otherwise known as herbivores. These animals, small or large, eat the primary producers. Ducks, tadpoles, mayfly nymphs, and small crustaceans are all considered primary consumers.
The most populous of the primary consumers are the zooplankton. These tiny animal-like organisms consume phytoplankton in large quantities.
Zooplankton slowly propel themselves up and down the water column, grazing on the phytoplankton and avoiding predators.
The two main kinds of Crustacean zooplankton found in Lake George are the Cladocerans and the Copepods. A crustacean zooplankton survey in the 1980s found eleven species of cladocerans and eight species of copepods.
An abundance of copepods is typical for an oligotrophic lake like Lake George, and they dominate the zooplankton community. Copepods are torpedo-shaped with antennae. They dart quickly through the water.
Cladocerans come in a variety of shapes, but they tend to be more round, and have lots of little legs, so they look more like they are swimming around. The most abundant cladoceran zooplankton in Lake George is Bosmina longirostris. Daphnia sp. is another common cladoceran, while Diaptomus sp. and Cyclops sp. are two of the common copepods. Copepods such as Diaptomus might live for six to twelve months, while Cyclops might only live for only one to two months. Still, that is better than most cladocerans – which only live for one to two weeks!
An example of a type of zooplankton found in the Lake that is not a crustacean is Asplancha, which is a rotifer. No matter what they are, crustacean, insect, or rotifer, all zooplankton provide an important food source for many invertebrates and for most fish in the food chain, at least at some point in the fish's development.
Crayfish eat both plants and small insects or fish, making them an omnivorous secondary consumer.
Next in the chain are the secondary consumers. Those that eat other animals are called carnivores. Those that eat both plants and animals are called omnivores. Examples of secondary consumers are: small fish such as minnows, crayfish, and the young of larger species. These animals consume zooplankton and insects as their source of energy.
The tertiary consumers eat the secondary consumers. Tertiatry consumers may include salmon, trout, bass and otter.
Lastly, an essential component in the food web is that of the decomposers. Decomposers grow as they break down dead and decaying organisms into nutrients, which are the essential elements of life. These nutrients, such as nitrogen and phosphorus, are then accessible to many forms of life around.