The Big Four of An Ecosystem

Ecologists recognize at least four components in an ecosystem, each of which is essential and probably has been essential since the beginning of life. A discussion of each component will provide background for reconstructing mid-Pleistocene conditions and events.

The Physical Environment

We are fairly certain that during the Pleistocene epoch the earth rotated on its axis as it revolved around the sun-as it does today.  Phases of the moon preceded and succeeded each other than as now.  Atmospheric pressures and temperatures were influenced by the same physical factors in existence today and produced winds, clouds, fogs, rains, thunder, lightning, dew, and humidity.  Rains were seasonal, but the amount of rainfall was probably greater during the summer months. 

Water and wind erosion reduced elevations and filled depressions.  Streams were muddy or clear, depending upon the amount of runoff from seasonal rains and the amount and kind of sediment.  As water percolated through the soil, it dissolved mineral substances such as lime, phosphate, and potash and carried them, together with other mineral substances, into larger bodies of water which contained  such organisms as plankton.

Amount the plankton were diatoms-microscopic, free-moving plants that extracted silica from their environment and incorporated it into their cell walls, transforming them into protective test.  Grasses, reeds, and other plants obtained silica, which as generally deposited along the edge of the leaves.  Mineral-containing water was absorbed through plant roots by osmosis and capillarity.  Because these processes and organism exist today, we assume that they also existed in the past.

Produce Organisms 

A second component of ecosystems is plant life.  Plants extract minerals from water and carbon dioxide from the air to manufacture food.  Aided by sunlight in this process, they produce food not only for themselves but for other organisms as well.  In this food is the energy used by all animals, from paramecia to elephants.  This is why ecologists refer to plants as producers.

We were not in California some 1.3 million years ago, but we have fossil evidence to prove that plants were there and that they were producers.  Even without plant fossils, we have to assume that plants were there.  If carnivores (meat-eaters) were the only fossilized animals found, we would have to assume that herbivores (plant-eaters) had been an essential part of the meat-eaters' environment.  Without such assumptions, could anyone reconstruct an ecosystem of the past?

Consumer Organisms

Animals are the chief consumers.  herbivores are first-order consumers-they consume producers.  Mice, deer, horses, camels, and other plant-eating animals are in this group.  Carnivores are second-order consumers if they eat consumers of the first order.  For example, a fox is a second-order consumer if he eats a mouse.  If a wolf eats the fox, the wolf is a third-order consumer, and so on.  Higher orders of consumers exist, but each higher order moves a step farther from the producers.  Try to imagine a Pleistocene situation in which a wolf is eaten by a sabercat.  In which consumer order would you place the cat?

Although remains of insects have not been found in the California deposits, we assume that both carnivorous and herbivorous insects were there  We assume that tree leaves were eaten by leaf-eating insects, wood and bark by boring insects.  Predatory insects consumed other predators and herbivores.  Today, throughout California, different species of ladybird beetles feed extensively on aphids, scales insects and mites.  There is no evidence to prove that this did not happen during the Pleistocene epoch. 

Assuming that there were mid-Pleistocene insects, do you suppose that honeybees were among them?  If so, would it be illogical to further assume that bears were there to raid the beehives?  Wouldn't the presence of honeybees require the presence of flowering plants?

Decomposer Organisms

The fourth major component of an ecosystem, represented by bacteria and fungi, is a group known as the decomposers.  These organisms break down the complex organic materials of dead protoplasm (both plant and animal) and release simpler substances that can be used by producers.  For example, certain kinds of bacteria convert dead plant and animals proteins into ammonia.  Other kinds, called nitrifying bacteria, convert the ammonia into nitrates that will be used by a new generation of plants.  Can you imagine ancient ecosystems without fungi and bacteria?  If they had not been present, wood would not have rotted, and dead flesh would not have putrefied.