Food Chain Definition
The food chain begins with a producer organism that got energy from the Sun, used it to perform its functions and stored elsewhere as reserve.
When the frog eats the caterpillar, it gets the energy it had stored.
In the end, the snake gets indirectly part of the stored energy of the above organisms.
The exchange of energy in ecosystems is not so simple, because the same body can be a food to several others. Thus there are naturally occurring networks or food webs, linking an organism to another as if they were the threads of a spider web.
Ecosystems: Populations and Communities
The set of individuals of the same species that share a given area causes the population , as a population of violet, for example.
The set of populations shape the communities , eg a plant community that is made up of different types of plants. One way to assess the characteristics of an ecosystem is to know how to categorize the size of the populations.
The population growth depends on some conditions of the ecosystem, eg the amount of food, space, water, weather, etc..
Similarly, diseases can change the number of individuals in a population.
Human activities can also affect the size of populations, eg when building roads, highways or cities. Only some of the original populations of plants and animals can survive the changes in their environment. Some will go to other sites looking for better conditions or some will perish.
When all members of a population die, we can say that organisms are extinct. One example of this is the dodo bird.
These unique birds living on a certain island in the Indian Ocean, for 100 years were hunted by sailors, who did eat them or their eggs.
In the year 1680, they were declared extinct, which means there were no individuals alive in that population.
Nowadays some animal populations are threatened or endangered due to human activities. African elephants,for example, are still being hunted for their tusks and ivory figures.