Vocabulary: limiting factors, ecological succession, symbiotic, parasitism, mutualism, commensalism, pioneer species, climax community

Abiotic Factors
Abiotic factors are those non-living physical and chemical factors which affect the ability of organisms to survive and reproduce.   

Some Abiotic Factors

  • light intensity
  • temperature range
  • type of soil or rock
  • pH level
    (acidity or alkalinity)
  • water availability
  • dissolved gases
  • level of pollutant

Abiotic factors vary in the environment and determining the types and numbers of organisms that exist in that environment. Factors which determine the types and numbers of organisms of a species in an ecosystem are called limiting factors. Many limiting factors restrict the growth of populations in nature. An example of this would include low annual average temperature average common to the Arctic restricts the growth of trees, as the subsoil is permanently frozen.

Biotic Factors
Biotic factors
are all the living things or their materials that directly or indirectly affect an organism in its environment. This would include organisms, their presence, parts, interaction, and wastes. Factors such as parasitism, disease, and predation (one animal eating another) would also be classified as biotic factors.

Some Biotic Factors

  • parasitism
  • disease
  • predation

Ecological Succession
The environment may be changed greatly through the activities of organisms, including humans, or when climate changes. Although sometimes these changes occur quickly, in most cases species gradually replace others, resulting in long term changes in ecosystems. These changes in an ecosystem over time are called ecological succession.   Ecosystems may reach a point of stability that can last for hundreds or thousands of years. If a disaster occurs, the damaged ecosystem is likely to recover in stages that eventually result in a stable system similar to the original one.

Feeding Relationships
Organisms may interact with one another in several ways.  One example of an organism interaction is that of a producer/consumer relationship. A producer is any organism capable of making its own food, usually sugars by photosynthesis. Plants and algae are examples of producers. A consumer is any organism which eats another organism. Several different types of consumer organisms exist. A herbivore is a consumer which eats primarily plant material. A deer is an example of a herbivore. A carnivore consumes primarily animal material. An omnivore eats both plant and animal matter. Humans are examples of omnivorous organisms.

A predator is a type of carnivore that kills its food. The organism the predator feeds upon is called its prey. A wolf and rabbit would provide an example of a predator/prey relationship. Scavengers feed upon organisms that other organisms have killed. A crow feeding off dead carrion in the highway would be an example of scavenger in this instance. 

Scavengers Feeding

The cartoon above represents a typical situation where vultures are acting as scavengers feeding on a dead rhinoceros.

Symbiotic Relationships
Close living associations are called symbiotic relationships.  Parasitism is an example of such a relationship. In this situation, the parasite feeds upon the tissues or fluids or another organism, but usually does not kill the organism it feeds upon, as this would destroy its food supply. The organism the parasite feeds upon is called the host organism. An example of this sort of relationship would be fleas on a dog or athlete's foot fungus on a human.

Types of Symbiosis

  • parasitism: the parasite benefits at the expense of the host
  • mutualism: both organisms benefit from the association
  • commensalism: one organism is benefited and the other is unharmed

Other Relationships
Some organisms such as certain pathogenic bacteria may cause disease in other organisms. Decomposer organisms use the energy of dead organisms for food and break them down into materials which can be recycled for use by other organisms. Bacteria of decay and many fungi are examples of decomposer organisms.

Ecosystem Stability
The interrelationships and interdependencies of organisms affect the development of stable ecosystems. The types of animal communities found in an ecosystem is dependent upon the kinds of plants and other producer organisms in that ecosystem.

The environment may be altered in substantial ways through the activities of humans, other living things, or when natural disasters occur, such as climate changes and volcanic eruptions. Although these changes are sometimes occur very quickly, in most cases species replace others gradually, resulting in long-term changes in ecosystems.   These gradual long term changes in altered ecosystems are called ecological successions. Ecosystems tend to change with time until a stable system is formed. The type of succession which occurs in an ecosystem depends upon climatic and other limitations of a given geographical area.

A Typical New York State Succession

Pioneer organisms are the first organisms to reoccupy an area which has been disturbed by a disruption. Typical pioneers in a succession include grasses in a plowed field or lichens on rocks. These pioneer organisms modify their environment, ultimately creating conditions which are less favorable for themselves, but establishing conditions under which more advanced organisms can live. Over time, the succession occurs in a series of plant stages which leads to a stable final community which is very similar to the plant community which originally existed in the ecosystem.   This final stable plant community is called a climax community. This community may reach a point of stability that can last for hundreds or thousands of years.

A Pond Succession Sequence

It has been observed that when natural disasters occur, such as a floods or fires, the damaged ecosystem is likely to recover in a series of successional stages that eventually result in a stable system similar to the original one that occupied the area.

A Typical New York State Succession

This chart represents a typical succession which is observed in New York State. The annual grasses represent the pioneer or first organisms in this succession. The beech-maple forest would represent a typical Northern New York climax community. The climax community will last hundreds or thousands of years unless again disrupted. A forest containing oak and/or hickory trees would be a more typical Southern New York climax community.

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