
The Features of Plants
The annuals (such as cheat grass) avoid drought by growing
only when there is adequate moisture. Shrubs have numerous branches arising
from a short basal trunk, and small, thick leaves that may be shed during
dry periods. They survive by their ability to become dormant before wilting
occurs. In cooler areas, the shrubs develop very long root systems to tap
deep moisture that remains available after the surface completely dries
out.In such cases the leaves and stems may remain green and active throughout
the summer. The succulents, such as cacti, store water in their tissues.
Microflora, such as mosses, lichens, and blue-green algae, remain dormant
in the soil but are able to respond quickly to cool or wet periods.
Food Web
Ecosystems
on land have five major biotic components-- autotroph, herbivore, carnivore,
omnivore and saprovore. Generally, green plants constitute the autotrophic
component. Green plants, such as Gushua, are able
to convert and concentrate light energy and manufacture food from simple
inorganic substances( e.g., water, carbon dioxide, nitrates) by the process
of photosynthesis. Piebald is the herbivore, which
feeds on plants; Sargo is the carnivore, which
feeds on other animals; Dadi is omnivore, which
feeds on both plants and animals; and microorganisms, such as Q3, primarily
are saprovores, which feed on decaying organic materials.
Energy and Trophic Levels
There
is a tremendous loss of energy between one trophoc level and the one above.
For one thing, every kind of animals needs to consume several kcals-worth
of energy in order to build one kcals-worth of flesh. The picture shows
part of trophic levels on land. It takes an enormous amount of vegetation
to support one herbiore; and a lot of herbivores to support one predator.
So big predators need vast territories. Inevitably, then, the big animals
are few in number; and so they are easily driven to extinction.