Living Things and the Environment

What is Ecology?


Ecology is the study of how living things relate to each other and their environment.


            All living things and non-living things in an environment are independent.  Living things such as plants and animals are called biotic factors.  The nonliving things in an environment like soil, water, light, and temperature are called abiotic factor. 

  • Biotic Factors interact with the abiotic factors in order to survive.  Changes in the environment are brought about by the interaction between the biotic and abiotic factors.



What is an Ecosystem?

Ecosystem – a group of living things in an area that interact with each other, together with their nonliving environment.

  • An ecosystem can be as tiny as a drop of pond water or a few square meters of a garden. 
  • It can be as large as a forest or an ocean.
  • The entire Earth is also an ecosystem.


In an ecosystem, the different factors are interdependent.  The plants, animals, and the nonliving parts of the ecosystem all interact with one another.




            All the different organisms that live together in an area make up the living part, or community, of any ecosystem.  A pond community has plants, fish, insects, frogs and turtles.  In a forest ecosystem, the trees, birds, snakes, insects, and small animals make up a community.


            The living things in the community are interdependent.  In a pond community, frogs eat insects, and fish eat tadpoles.  Some fish also eat plants as the insects do.  In a forest ecosystem, insects and birds feed on plants.  Other animals such as lizards feed on insects.  Larger animals eat lizards.


            The plants in the community are the source of food for the plant-eating animals.  The other organisms feed on plant-eaters and on other animals.  Animals in this community cannot live without plants, the same way plants cannot live without these animals.  They depend on each other in order to survive.




            A population is a group of organisms of the same kind that live together in the same area.        


The water lilies in a pond make up the water lily population in that pond.

The group of frogs make up the frog population in the pond.



            Populations do not live alone.  You can find many different populations in a given place.  These populations live together and interact with each other.

Example:          A forest includes separate populations of trees, birds, insects, worms, and fungi.  These population interact with each other in different ways.


                        Birds depend on insects and worms for food.  They also build nests on branches of tress.


                        Fungi help in the decaying process of dead plants and animals in the forest.


            A community may be composed of hundreds of populations.  Of the many populations in a community, a few would stand out more than the others.  These have the largest number of organisms or are the dominant populations in the community.  In a forest, the tall tress make up the dominant population in the community.  In a grassland, the dominant plant population are the grasses.


            All the living and nonliving things in an ecosystem must interact successfully in order for the ecosystem to survive.  All the living things must be able to obtain food, water, and shelter from their environment.  The plant and animal populations can reproduce and increase their numbers given the right conditions.  Certain living and nonliving factors in the environment can stop population from increasing its size.  These are called the limiting factors.  The food, space, temperature, and disease are examples of limiting factors.  Sometimes the growth of a population is limited as a result of its relationship with other organisms.  Relationship between organisms include mutualism, commensalism, parasitism, predation, competition, and cooperation.  These relationships are either beneficial or harmful to the interacting populations.


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