Dynamic Equilibrium or Balance in Nature.
Factors which affect population size include abiotic factors such as temperature, water, space etc and biotic factors such as food, competition, parasite etc. When these factors are favourable, growth is promoted but when they are scarce or unfavourable, growth is retarded.
Population density is defined as the number of individual or organisms per unit area or volume of the habitat. Mathematically, population density is expressed as:
: Total Population/Area of Habitat
Population density can be used to estimate the total number of individual species of a population or population size.
CLASSIFICATION BASED ON LIFE CYCLE
i) Annuals: Plants which complete their life cycle within one growing season, or within a year e.g. melon, maize, cowpea.
ii) Biennials: Plants which complete their life cycle within two years e.g. onion, banana.
iii) Perennials: Plants that persist over two years and above e.g. oil palm, mango, orange, guava etc.
EFFECTS OF AGRICULTURAL ACTIVITIES ON ECOLOGICAL SYSTEMS
1. BUSH BURNING
i) It leads to loss of soil fertility by destroying the humus on the soil surface.
ii) It destroys useful organism in the soil that brings about decay causing loss of fertility.
iii) It exposes the soil and encourages soil erosion.
iv) It destroys vegetation.
v) It causes migration of some animals.
vi) It produces smoke which pollutes the atmosphere.
i) It breaks up the soil surface and loosens the soil for roots of young plants.
ii) It mixes humus in the soil.
iii) It removes plant covering the soil and increases soil erosion.
iv) It could lead to the compaction of soil, due to the movement of heavy equipment.
3. FERTILIZERS APPLICATION
i) It may kill useful organisms that have direct contact with fertilizers.
ii) If washed into nearby water bodies, fertilizers pollutes the water affecting aquatic life.
iii) It leads to eutrophication (excessive richness of nutrients in a lake or other body of water, frequently due to runoff from the land, which causes a dense growth of plant life and death of animal life from lack of oxygen).
iv) Prolonged use of chemical fertilizers may lead to development of poor soil structure.
v) Salination pH is altered.
3. HERBICIDES / PESTICIDES APPLICATION
i) Pollution of the atmosphere since most of the chemicals are aerosols.
ii) They may kill useful insects such as butterflies that pollinate flowers.
iii) They may accumulate in the soil to levels harmful to crops
4. FARMING PRACTICES
i) Mono culture
ii) Continuous cropping
iii) Shifting cultivation
iv) Crop rotation
v) Mixed cropping
For further reading visit Wikipedia Balance of Nature