SS3 Biology Lesson Note on Balance in Nature

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TOPIC: BALANCE IN NATURE

CONTENT:

1. Factors affecting a population
2. Dynamic population
3. Family planning

SUB-TOPIC ONE: FACTORS AFFECTING A POPULATION

In ecology, the interaction between plant and animals in an environment produces a stable and a balance system. A population is referred to as stable if the population size remains relatively constant.

There are many factors that contribute to the balance in nature; these factors are either abiotic or biotic

Abiotic factors these factors are:

• Availability of space
• Light
• Heat
• Oxygen (air)
• Water
• Food

Biotic factors: these factors are

• Predation
• Competition
• Parasitism
• Diseases
• Natality
• Mortality
• Territorial behaviour
• Dispersal

EVALUATION

1. List five factors (abiotic) that contribute to the balance in nature
2. List five factors (biotic) that contribute to the balance in nature.

Gaza, Gaza Strip

Palestinian fishers celebrate the Israeli withdrawal from the city of Gaza (background) and the Gaza Strip in 2005. Decades of political instability and a massive influx of Palestinian refugees have produced extreme overcrowding, large-scale unemployment, and poor living conditions in Gaza and the Gaza Strip. The Palestinian National Authority is headquartered in Gaza.

SUB-TOPIC 2: DYNAMIC EQUILIBRIUM

The biotic community in each ecosystem is composed of population of many species. An ecosystem with a stable climax community, the population sizes of the various species are constant. For each species the population size fluctuates around the carrying capacity of the habitat for that particular species. The various populations in a climax community are said to be in balance or in dynamic equilibrium. The equilibrium is said to be dynamic because though the population remain constant, new individuals are being added while the existing ones are removed all the time. Rate of addition is equal to the rate of removal.

Dynamic equilibrium is maintained by two major factors that relate to density

Density –independent factors: some factors affecting growth of a population irrespective of its population density.

Examples of such factors are:

• Sudden changes in weather conditions
• Natural disaster like flood, fire, drought, earthquakes, volcanic eruptions, tsunamis, storm, presence of pollutants, etc.

These events may wipe out large number of individuals in a population and are independent of the number of individuals in a population

Density dependent factors: these are factors that affect the growth of a population and are dependent on the number of individual in a population.

Examples Of density dependent factors are

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