Unit 5: The structure of the ecosystems                      1   2   3   4   5   6

2. The physical environment

Abiotic factors are the variables of the physical environment (light, temperature, humidity, etc) that affect living beings.

The most important abiotic factors are:

   - Temperature.

         It has an enormous importance in the development of life.

         Freezing occurs below certain temperature values and all cellular activity stops

         above certain limits.

         Temperature depends on altitude, latitude and the season or day hour.

         Its influence is bigger in land than in water. Aquatic environments have usually

         a constant temperature, while in terrestrial environments, temperature

         changes a lot.

   - Light

         The amount of solar radiation that arrives to the plants depends on the altitude,

         the latitude and the time of the year and the hour of the day.

         For plants, light is essential to perform photosynthesis. On the other hand,

         light affects animals’ sleep patterns and other biological activities.

         It is difficult for light to penetrate an aquatic environment and it can only

         enter until certain depth.

   - Humidity

        Water is essential for all living beings. The presence or absence of water or

        the precipitations amount and its distribution determine the type of living beings

        we can find in an ecosystem.

   - Salinity

        It is the concentration of salt in water. In aquatic environments, water can be

        freshwater or salt water depending on the amount of salts it contains.

   - Pressure

        It does not vary very much with altitude in terrestrial environment

        but it increases considerably with depth in aquatic environment.

The influence of the abiotic factors can be more or less intense depending on the environment:

      - The most influential ones in terrestrial environment are temperature

         and humidity.

      - The most influential ones in aquatic environments are light, salinity

         and pressure.

These factors determine the types of living beings which develop in an ecosystem. They have a tremendous impact because they influence the ecosystem in many ways. For example, climate or water supply, affects the behavior and the vital functions of the organisms.

Tolerance limits are the maximum or minimum values of a variable which a species can tolerate. When variables exceed these limits, organisms cannot survive. In this case, this factor is called limiting factor.

In order to survive, living beings adapt to their environment.

Adaptation is the progressive adjustment of a species to the special conditions of the environment where it lives.

Animation: Animal adaptations (Study jams)

Animation: Plant adaptations (Study jams)

2.1. Look at the graph showing the temperature tolerance for a species

        and answer:

2.2. Indicate what abiotic factor correspond each one of these adaptations:

a. Large leaves.

b. Fur and feathers.

c. Hibernation and migration

e. Storing of nutritive substances in roots

f. Reduced leaves or transformed into spines.

g. Skin with scales and without glands