Ecology is the study of the interactions between organisms and the living and nonliving components of their environment. In other words, ecology is the study of ecosystems.

The science of ecology involves collecting information about organisms and their environment, looking for patterns, and seeking to explain these patterns.

The Four Laws of Ecology:

1. Everything is connected to everything else.
    
2. Everything must go somewhere.
    
3. Nature knows best.
    
4. There is no such thing as a free lunch.

world population.

All organisms fit into:

• Habitat - the physical area in which an organism lives.
   
• Niche - the way of life of a species, population, or organism.

  There can be many ecological niches in one geographical area. An animal's niche is determined by all the ways the animal interacts with its environment, including what it eats, how it obtains its food, what physical and chemical conditions it will tolerate, what conditions are optimal for its well-being, and how it interacts with its predators and parasites.

Trophic levels (from the Greek for "nourishment") represent the flow of energy through an ecosystem. Only stored food energy is available to higher trophic levels. The energy an organism uses for its own respiration and heat energy is lost. This energy goes to fuel cellular processes and maintain life.

For instance, average human body temperature is 98.6 ^oF. It takes fuel to maintain this temperature! Because of this, less and less energy is available to successively higher trophic levels.

• Producers - autotrophic organisms using solar or chemical energy to produce the organic nutrients for an ecosystem.

  Although less than 1% of the solar energy that enters Earth's atmosphere is converted into chemical energy by photosynthesis, the energy stored by producers represents 100% of the energy available to the other trophic levels!

• Consumers - heterotrophic organisms that cannot make their own food. They get energy from the chemical bonds in the food they eat.
   
  • Primary consumers (herbivores) - eat primary producers (plants).

    Conversion efficiency: only 10 to 20 percent of the available energy passes from producers to primary consumers.
     

  • Secondary consumers (carnivores) - eat primary consumers (herbivores).

    Conversion efficiency: only 5 to 10 percent of the available energy passes from primary consumers to secondary consumers.
     

  • Tertiary consumers (carnivores) - eat secondary consumers (carnivores).

    The conversion efficiency for tertiary consumers may be as low as 1%.
     

  • Omnivores - eat both plants and animals.
   
• Decomposers - break down dead tissues and wastes. Bacteria and fungi are the most common decomposers.

Primary productivity of an ecosystem is the rate at which solar energy is converted into organic compounds. The units of productivity are kilocalories per square meter per year.

• Gross primary productivity is the total amount of energy produced, including the energy used by plants for their own respiration.
   
• Net primary productivity is the rate at which plants store energy that is not used in plant respiration.

CONCEPTS (continued)  

The number of organisms in an area is directly related to the productivity of the area.

A food chain is the specific sequence in which organisms obtain energy within an ecosystem.

A food web represents the interrelated food chains within an ecosystem.

The diagram above represents a simple food web. Natural food webs are very complex - with many more linked food chains.

Within any ecosystem, some organisms use resources and reduce the availability of those resources to other organisms. This is called competition.

• Intraspecies competition is between organisms of the same species.
   
• Interspecies competition is between organisms of different species.

Predator and prey are often closely tied together. Each has traits that attempt to take advantage of the traits of the other.

Moths are a good meal for many birds. Most moths are active at night, a time when most birds are not hunting. But the moth has to hide during the day to escape the birds. The protective coloration of some moths allow them to hide in plain view.

Would the moth above be as well hidden on just any tree?

Have you ever seen a rabbit or squirrel run onto the road in front of a car and suddenly stop? While this is not a good reaction at the time, it is the behavior that will most often save the animal from being caught by a predator. How?

Even predator and prey populations are related. If the predator population is low, the numbers of the prey species will increase.

Most predator species will reproduce in larger numbers if food is abundant. As the numbers of the predator species increase, the prey population begins to decline.

 
Symbiosis is the close association between two dissimilar organisms. There are three basic types of symbiosis:

• Parasitism - one organism obtains its nutrition from another organism to the harm of the host.
   
• Commensalism - one organism benefits from another organism while that organism neither benefits nor is harmed.
   
• Mutualism - the relationship benefits both organisms equally.