Monday, August 6, 2012

Did You Know? Animals and Food

by Jim Northrop, GSWA Volunteer

The diversity of plant and animal life in the Great Swamp area is great. Probably none of us can experience it completely in our lifetimes, but many have tried. In fact, a branch of science called Zoology attempts an orderly classification of animal life, from the simplest to the most

Although it is easy to see that a bear is an animal and that a pine tree is a plant, some of the smaller animals and plants are not obviously members of their respective kingdoms. Most animals can be distinguished by their ability to move; yet there are microscopic water plants that swim as freely as animals do.

All animals large enough to be seen with the naked eye obtain energy by eating plants or other animals. Surprisingly, a few microscopic animals are like green plants because they also capture energy from sunlight through the process of photosynthesis, and use simple chemical compounds dissolved in water as food.

Thus, it seemed that some consistent method must be developed to distinguish animals from plants, and to separate one kind of animal from another. One useful way to do this is an analysis of food habits.

The food habits of an animal will give information concerning its structure and function, some of the animals related to it, and a general idea of the environment in which it lives. Sometimes a broad category of food habits will cover a wide variety of creatures.

Herbivores.  Any animal that eats only vegetable matter is a herbivore, or plant-eater. Herbivores eat grasses, leaves, twigs, succulent plants, and other types of vegetation. The classification encompasses such different creatures as caterpillars and cows.

Carnivores.  Animals that eat the flesh of other animals are called carnivores, meat-eaters. Animals as different as lions and ladybird beetles appear in this category. When a cat pounces on a mouse, kills it, and eats it, the cat becomes a predatory carnivore. Animals such as the vulture and hyena are also carnivores, although they usually prefer to feed on dead animals, so they are referred to as scavenger carnivores. Domestic animals also become scavengers at times, such as when a dog rummages through refuse.

Omnivores.  The most familiar omnivores, creatures that eat both animal and vegetable matter, are human beings and the domestic pig. Some aquatic omnivores subsist on food so small that they must strain it from the water. Clams and oysters are examples. Even giant whales, which may be as long as 110 feet, filter their food. They swim mouth open, until small crustaceans, plankton, and other types of food are caught between thin plates known as whalebone (or baleen) that hang down in the mouth cavity. Then they close their mouths and swallow the contents.

Symbionts.  Animals that form a beneficial partnership with animals of some other kind or a similar partnership with a living plant are symbionts. If both partners in a symbiotic arrangement benefit equally, the relationship is mutualistic. If one benefits without harming the other, it is a commensal relationship; if one gains at the expense of the other, it is parasitic.

Many termites illustrate mutualism. They chew and swallow wood but cannot digest the wood fibers until they are predigested by minute animals that inhabit the termites' digestive tract. These minute animals could not obtain wood fibers without the termites; the termites could not utilize the wood fibers if the minute animals did not first digest them.

Certain minute insects parasitize plants by producing chemicals that irritate the plants into forming unnatural swellings on the leaf or stem, producing deformed terminal buds. These galls provide a place for the insects to live while they suck sap from the plant. Each type has a distinctive shape and inner structure.

Organizing animal creatures into categories based on their food habits has value because all animals must eat to survive. What's amazing is the diversity of ways animals satisfy this survival need.

Before your next meal, appreciate how the human animal's food habits, while so diverse, are satisfied so much better than the needs of many other animals in our Great Swamp area! For example, while food for most animals is plentiful in the warm seasons, winter's food supply for most animals is meager, and there is not much that non-human animals can do about it.  For human animals in winter, however, their Great Swamp Watershed area food stores simply shift suppliers to those in California, Mexico or other warmly bountiful locations.

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