Key Concepts

Population pertains to the number of organisms of the same species living in a certain place.

Biodiversity refers to the variety of life in an area.

Communities with many different species (a high index of diversity) will be able to withstand environmental changes better than communities with only a few species (a low index of diversity).

Populations can be of the same size, but they may have different densities. When we consider the number of individuals per unit area, we are referring to the density of the population. Differences in population density in any community may be attributed to many factors. Population sizes change when new members move into the ecosystem. They decrease when members move out of an ecosystem. The birth and death rates can also affect a population's size. Anything that limits the size of a population like certain environmental conditions are called limiting factors. Limiting factors keep a population from increasing in size and help balance an ecosystem. Examples of limiting factors are the availability of food, water, and living conditions. Light, temperature and soil nutrients are also limiting factors because they help determine the types of organisms that can live in an ecosystem. The maximum population size an environment can support is called its carrying capacity. If the population size rises above the carrying capacity, organisms die because not all their needs can be met.

Key Concepts:

Population sizes vary among organisms. They change with the number of births and when they move into an ecosystem. They also change when members die or move out of an ecosystem.

Limiting factors are environmental conditions that keep a population from increasing in size and help balance ecosystems.

The carrying capacity is affected by changes in the environment.

Life depends on life. Animals cannot exist without green plants. Living things create niches for other living things. But what happens if the living conditions of these organisms are not ideal for their survival? What do you think are the major causes of pecies extinction?

When a species' population becomes so low that only a few remain, the species is considered endangered and will possibly become extinct. In the Philippines, some terrestrial species like the tamaraw in Mindoro, mouse deer in Palawan, Philippine deer, Monkey-eating eagle, and aquatic species like the dugong found in Negros, Batangas, and Leyte are in danger of extinction.

Sometimes, there is a particular species that declines so fast that it becomes endangered and is said to be threatened. In a study conducted by field biologists on population size and distribution of Philippine fauna, they reported that as of 1991, 89 species of birds, 44 species of mammals, and eight species of reptiles are internationally recognized as threatened. These include also the Philippine Eagle or Monkey-eating Eagle in the list of Philippine Endangered Species. (Source: cf. Rabago, L. et.al. Functional Biology: Modular Approach. 2nd edition)

Extinction is the disappearance of a species when the last of its members die. Changes to habitats can threaten organisms with extinction. As populations of people increase, the impact of their growth and development is altering the face of the Earth and pushing many other species to the brink of extinction.

Key Concepts:

Extinction occurs when the last member of that species dies.

When the population of a species begins declining rapidly, the species is said to be a threatened species.

A species is endangered when its population has become so low that it is possible of becoming extinct.

Human actions have resulted in habitat loss and degradation that have accelerated the rate of extinction.

Many changes take place in the communities. You may have noticed that the natural vegetation in the area has been cleared. Concrete structures and increasing populations of people and other organisms gradually take over the area. Perhaps some areas were destroyed by natural disasters or by human activities. Just as vegetation changes, animal populations also change. These may have major effects on the ecosystem causing replacement of communities or development of a new environment.