The Biosphere, Biomes and Ecosystem Relationships

Class Notes Summary


Ecology is the study of the relationship between organisms and their environment. Ecologists study not only how an organism act together but also how they are adapted to their environments. Ecology is divided in levels of organization starting with the biosphere, ecosystems, communities, populations, organism, cell, atom, and matter. The biosphere is the area surrounding the earth that can support life. The biosphere is made of different ecosystems. Ecosystems are made of different communities. A community includes all the populations in an area. Population in made of the same species that live in the same area and make up a breeding group. So populations are made of organisms. Organisms are made of cells, cells are made of atoms, and all atoms are made of matter.


An ecosystem is an ecological unit that includes at the interacting parts of an environment in an area. Ecosystems consist of abiotic and biotic factors. Abiotic factors are the nonliving components of an ecosystem.


Abiotic factors can be divided into man-made and natural factors. Examples of man-made abiotic factors include automobiles, buildings, planes, boats, bridges, roads, cities and towns. Examples of natural abiotic factors include sunlight, precipitation (rain or snow), temperature, slope and drainage of the land (erosion), chemistry of soils and atmosphere, volcanic activity, earthquakes, and storms (hurricanes, tornados, sand storms).


Biotic factors are the living components of the ecosystem. Examples of biotic factors include plants, animals, protists, humans, bacteria, and all other living organisms. Biotic factors may interact with each other in 3 ways. Competition for food, living space, or mates. The relationship between predators and prey. And finally in symbiosis.


Abiotic and biotic factors can interact. For example climate and soil conditions determine which plants will live in a certain area. The availability of land for predators to hunt and live is affected by the increasing number of housing being built for humans.


Biotic relationships are all the relationships among organisms living in a given area. There are 3 types of biotic relationships: competition, predation, and symbiosis.


Organisms interact through competition. Competition is the use or defense of a resource by one individual that reduces the availability of that resource to other individuals. In other words, competition is the use or defense of food source, living space, or mates so that others cannot have it. There are two main types of competition: intraspecific and interspecific competition.


Intraspecific competition is the competition between organisms of the same species. Usually competing over mating rights. For example: male deer with fight for the right to mate with a female. The male that wins the fight gets to mate and the loser has to fight a different male or wait another year to mate. This insures that the healthiest individual best adapted to their environment will pass on their genes to offspring at a greater rate than individual less fit. Intraspecific competition is one of the driving forces of evolution. Evolution is the change in a species over time. This change occurs by mutations that may occur that can cause a species to become better adapted to their environment.


Interspecific competition is competition between organisms of different species. Interspecific competition is often less intense than intraspecific competition because individuals of different species do not compete for exactly the same kinds of food, space, or mates. An example of interspecific competition is the competition between predators for the same kind of prey. The competitive exclusion principle states that two competitors cannot coexist on the same limiting resource. Meaning that if the availability of a resource such as food decreases, two competitors cannot compete for that same resource. Both competitors will be negatively affected by the decrease resource. Organisms can develop behavior to limit the effects of competition. For example three species of warblers (birds) eat similar types of food and can occupy the same forest, but they differ in their feeding pattern. One feeds from the tops of trees, another from the middle and the last feeds on the bottom portion of trees. Another behavior that has developed to limit the effects of competition is diurnal and nocturnal animals. Diurnal organisms sleep at night and are active in the daylight. Nocturnal organisms sleep during the day and are active at night. Such behavioral adaptations greatly reduce, but do not entirely eliminate the competition for food.


Predation is the act of one organism feeding upon another organism. The predator is the organism that kills, and the prey is the organism that is killed. The population size of predator and prey are related and dependent on each other.

                        If the predator population decrease, the prey population increases.

                        If the prey population decreases, the predator population also decreases.

                        If the prey population increases, the predator population increases.

The prey and predator populations are equal in size, but a new predator enters and begins feeding on the prey. This would cause the prey population to decrease, which would cause both predator populations to decrease.


Symbiosis is a biological relationship in which two dissimilar organisms live together in a close association. There are 3 types of symbiosis: parasitism, commensalism, and mutualism.


Parasitism is a close long term symbiotic relationship in which one organism obtains its nutrition from another organism. The parasite is the organism receiving the benefits and the host is the organism that is providing the nutrients and is weakened or harmed in the process. Examples of parasitism are: fleas or ticks on animals, tapeworms, roundworm, ringworms, leaches etc.


Commensalism is a form of symbiosis in which one organism benefits and the other neither benefits nor suffers harm. For example orchids (a flower) grow high in the trees in tropical forest. The trees provide the orchids with the support to grow and allow them to capture more sunlight than they would on the forest floor. The trees are not harmed since the orchids neither feed on their tissues nor prevent significant amounts of sunlight from reaching the leaves of the tree. However, the tree gains nothing from the orchid.


Mutualism is a form of symbiosis in which both organisms benefit form living together. For example enzymatic action of bacteria that living in the digestive tracts of cattle enables the cattle to digest grasses. By breaking down the cellulose in the grasses the bacteria make it possible for the cattle to use the nutrients the grass contains. At the same time the bacteria take in nutrients for themselves but do not harm the cattle.


Biomes are major biological communities that occur over large areas of land. There are two categories of biomes, terrestrial biomes and aquatic biomes. Terrestrial biomes include polar (arctic and antarctic), tundra, coniferous forests (taiga, coniferous belt, & southern pine), deciduous forest, grass lands (prairie in N. America, steppes in Asia, pampas in S. America, and veldt in S. Africa) and savanna, Desert (true desert and chaparral), and rain forest (tropical and temperate). Aquatic biomes include the ocean zone, intertidal zone, and estuaries and also freshwater lakes and rivers. Read your text for descriptions.


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