9.2 - Population Ecology

Population ecology is the study of the interactions between a population with its environment. A population distribution in a habitat shows how a certain species of the same kind are spread.

Factors Affecting Population Distribution

Figure 8 - Factors that can affect the population distribution of plants. The optimum temperature of plants lies between 25°C to 30°C. Higher temperature will destroy the enzymes and affect the biochemical processes in plants. As a result, their growth will become stunted, the rate of photosynthesis will decrease and the rate of transpiration will increase. Water is also an important source in enzyme activities, photosynthesis, transport and support in herbaceous plants. Dry regions will reduce the population distribution and density of plants. Light energy is also needed for photosynthesis process. Areas with low light intensity will have less plants growth. The value soil pH is also important for the absorption of nutrients. Acidic or alkaline soil can reduce nutrients absorption and affect the growth of plants. Mineral content can have an impact on the absorption of water. The high concentration of salt can lead to water loss via osmosis. Important minerals are crucial for the synthesis of proteins, nucleotides, vitamins and other compounds.

Figure 9 - Factors that can affect the population distribution of animals.

---

There are 3 specific patterns of population distribution – clumped, random and uniform.

Clumped

• Separated groups formed.
• Caused by uneven distribution of resources in the area.

Random

• Organisms are distributed freely in an area.
• Less interaction between the species.

Uniform

• Organisms are spread throughout the area inhabited.
• Species compete for limited resources in an area.

Estimation of Organism Population Size

Population ecology can be affected by 2 factors which are population size and population density.

• Population size means the number of organisms present in a population.
• Population density refers to the number of individual species per unit area of the habitat.

Figure 10 - A quadrat sampling technique is used to estimate the population size of less active or slow-moving land plants and animals. The number of organisms in all the quadrats will be the estimated population in the area of study. Quadrat is a square-framed structure, made from wood, metal or plastic. Normally, a quadrat will be divided into several parts of the same size to estimate the coverage percentage of a species. The size of the quadrat depends on the types and size of the organisms, the area of study, distribution and density of the plants to be studied. For example, a quadrat of 1 m2 is suitable to be used for the estimation of plants population in school fields.

This technique can estimate the frequency, density and coverage percentage of a studied plant species.

Frequency

• Refers to the probability of obtaining an individual of a plant species in each quadrat.
• Formula:

Density

• Average number of individual species per unit area of study.
• Formula:

Coverage percentage

• Surface area covered by the studied plant species.
• Coverage percentage is the percentage surface area of soil covered by the plants.
• Formula:

---

For organisms that can move freely, a capture-mark-release-recapture technique can be used to estimate the population size of the organisms in an area. Normally, this technique is used on foxes, sharks, snails, millipedes, insects and butterflies. Below are the steps of the technique: