SS1 Biology Lesson Note on Ecological Factors Affecting Terrestrial Habitats

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Ecological Factors Affecting Terrestrial Habitats

(1) Topographic Factors: These factors are associated with the structure of the habitats e.g. effects of hilts, valleys, plains mountains and rivers. These factors bring about variation in the vegetation and types of animals in an area.

Topographic factors include:

(a) Altitude (elevation): This refers to height of the land above sea level. This affects the growth of plants and the level of erosion in an area. As altitude increases, temperature falls by approximately 1ºc per 150metres, as a result of this, mountain tops are generally cold places cold air causes clouds to condense and fall as rain, thus the annual rainfall on mountains is high especially on the windward side. As one ascends a mountain, the air become less dense, there is less of it to filter the sun’s rays, so organisms at the top of mountains are exposed to intense solar radiation.

(b) Slope: Water flows faster on a steep slope than on a gentle slope as such, run-off  is greater and less water sinks into the soil on steep slopes. Also, erosion tends to be more. Gentle slopes are more favourable to plant growth.

(c) Exposure: This refers to the extent to which living things are not protected from climatic factors such as rainfall, sunshine and wind. Exposure is usually high on mountains and low within a forest. Winds tend to be stronger in exposed habitats and relative humidity is lower than in sheltered habitats. Low degree of exposure ensures the availability of nutrients to plants.

(2) Edaphic Factors: These are factors related to the nature of soil particles. The word edaptic refers to the influence of soils on plants and animals. Differences in the soil of a locality usually produce difference in vegetation since plants are dependent on the soil and the type of plants determine the type of animals that will be found in the habitat. Edaphic factors include:

(a) Soil Types: this could be sand, loam or clay. The type of soil determines the fertility of the soil, its porosity and water retaining capacity.

(b) Soil Texture: The amount of sand, silt and clay in a soil affects its water retaining capacity. Soil texture refers to the degree of fineness or coarseness of soil particles. It also affects leaching and erosion.

(c) Soil structure: This refers to the arrangement of the various soil particles in soil. This affects the level of soil aeration and percolation and the type and level of soil organisms in the soil.

(d) Soil pH: The pH of soil also affects the type of plants in the habitat e.g. some plants grow best in acid soils while others prefer alkaline conditions.

(3) Atmospheric factors (Relative Humility): This is a measure of the amount of moisture in the air. It affects the rate of transpiration from plants and evaporation from animals. As relative humidity falls, evaporation and transpiration rise as such organisms that live in areas where humidity is low must prevent water loss from their body surfaces. E.g. in deserts, the leaves of plants like the cactus are reduced to spines to prevent loss of water.

Ecological Factors That Affect Aquatic Habitats

(1) Salinity: This refers to the concentration of salts in the water. Salinity affects the movement of water and salts across the body tissues of aquatic organisms. Salinity is low in fresh water, high in sea water and moderate in brackish water. Aquatic organisms have to maintain the osmotic balance between their body fluids and their aquatic surroundings in order to survive. Those living in fresh water have adaptive features which enable them get rid of excess water that enters their bodies; those living in sea water have body fluids with almost the same salt concentration as the sea water while those living in brackish water have body tissues that can tolerate wide and sudden fluctuations in salt concentration of their body fluids.

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