ВУЗ:
Составители:
Рубрика:
Because of the diverse approaches required to study organisms in their environment, ecology draws upon
such fields as climatology, hydrology, oceanography, physics, chemistry, geology, and soil analysis. To study
the relationships between organisms, ecology also involves such disparate sciences as animal behavior, taxon-
omy, physiology, and mathematics.
An increased public awareness of environmental problems has made ecology a common but often misused
word. It is confused with environmental programs and environmental science. Although the field is a distinct
scientific discipline, ecology does indeed contribute to the study and understanding of environmental problems.
The term "ecology" was introduced by the German biologist Ernst Heinrich Haeckel in 1866; it is derived
from the Greek "oikos" ("household"), sharing the same root word as "economics". Thus, the term implies the
study of the economy of nature. Modern ecology, in part, began with Charles Darwin. In developing his theory
of evolution, Darwin stressed the adaptation of organisms to their environment through natural selection. Also
making important contributions were plant geographers, such as Alexander von Humboldt, who were deeply
interested in the "how" and "why" of vegetation distribution around the world.
The thin mantle of life that covers the earth is called the biosphere. Several approaches are used to classify
its regions.
The broad units of vegetation are called "plant formations" by European ecologists and "biomes" by North
American ecologists. The major difference between the two terms is that "biomes" include associated animal
life. Major biomes, however, go by the name of the dominant forms of plant life.
Influenced by latitude, elevation, and associated moisture and temperature regimes, terrestrial biomes vary
geographically from the tropics through the arctic and include various types of forest, grassland, shrub land,
and desert. These biomes also include their associated freshwater communities: streams, lakes, ponds, and
wetlands. Marine environments, also considered biomes by some ecologists, comprise the open ocean, litto-
ral (shallow water) regions, benthic (bottom) regions, rocky shores, sandy shores, estuaries, and associated
tidal marshes.
A more useful way of looking at the terrestrial and aquatic landscapes is to view them as ecosystems, a
word coined in 1935 by the British plant ecologist Sir Arthur George Tansley to stress the concept of each lo-
cale or habitat as an integrated whole. A system is a collection of interdependent parts that function as a unit
and involve inputs and outputs. The major parts of an ecosystem are the producers (green plants), the consum-
ers (herbivores and carnivores), the decomposers (fungi and bacteria), and the nonliving, or abiotic, compo-
nents, consisting of dead organic matter and nutrients in the soil and water. Inputs into the ecosystem are solar
energy, water, oxygen, carbon dioxide, nitrogen, and other elements and compounds. Outputs from the ecosys-
tem include water, oxygen, carbon dioxide, nutrient losses, and the heat released in cellular respiration, or heat
of respiration. The major driving force is solar energy.
Ecosystems function with energy flowing in one direction from the sun, and through nutrients, which are
continuously recycled. Light energy is used by plants, which, by the process of photosynthesis, convert it to
chemical energy in the form of carbohydrates and other carbon compounds. This energy is then transferred
through the ecosystem by a series of steps that involve eating and being eaten, or what is called a food web.
Each step in the transfer of energy involves several trophic, or feeding, levels: plants, herbivores (plant eat-
ers), two or three levels of carnivores (meat eaters), and decomposers. Only a fraction of the energy fixed by
plants follows this pathway, known as the grazing food web. Plant and animal matter not used in the grazing
food chain, such as fallen leaves, twigs, roots, tree trunks, and the dead bodies of animals, support the de-
composer food web. Bacteria, fungi, and animals that feed on dead material become the energy source for
higher trophic levels that tie into the grazing food web. In this way, nature makes maximum use of energy
originally fixed by plants.
The number of trophic levels is limited in both types of food webs, because at each transfer a great deal of
energy is lost (such as heat of respiration) and is no longer usable or transferable to the next trophic level. Thus,
each trophic level contains less energy than the trophic level supporting it. For this reason, as an example, deer
or caribou (herbivores) are more abundant than wolves (carnivores).
Energy flow fuels the biogeochemical, or nutrient, cycles. The cycling of nutrients begins with their release
from organic matter by weathering and decomposition in a form that can be picked up by plants. Plants incor-
porate nutrients available in soil and water and store them in their tissues. The nutrients are transferred from
one trophic level to another through the food web. Because most plants and animals go uneaten, nutrients con-
Страницы
- « первая
- ‹ предыдущая
- …
- 74
- 75
- 76
- 77
- 78
- …
- следующая ›
- последняя »
