Factors Affecting the Distribution of Organisms

The distribution of organisms refers to how individuals of a species are spread across a particular geographical area or habitat. This distribution is determined by two main categories of factors: Abiotic (non-living) and Biotic (living) factors.

1. Abiotic Factors

Abiotic factors are physical and chemical elements in the environment that influence the survival and reproduction of organisms.

• Temperature: Influences metabolic rates and enzyme activity. Most organisms have an optimum temperature range. For example, polar bears thrive in cold regions, while cacti are adapted to high desert temperatures.
• Rainfall (Precipitation): Determines the availability of water. In Nigeria, the tropical rainforest receives high rainfall, supporting diverse species, whereas the Sahel savanna has limited rainfall, supporting drought-resistant shrubs.
• Relative Humidity: Affects the rate of transpiration in plants and evaporation in animals. High humidity reduces water loss.
• Wind Speed and Direction: Wind aids in the dispersal of seeds and pollen (anemophily). It also influences the rate of transpiration and can cause physical damage to plants in high-velocity areas.
• Altitude: As altitude increases, temperature and atmospheric pressure decrease. This leads to distinct vegetation zones on mountains (montane vegetation).
• Salinity: The concentration of salt in water. High salinity in marine habitats requires specialized adaptations in organisms (halophytes). Freshwater organisms cannot survive in high salinity due to osmotic pressure.
• Turbidity: Refers to the cloudiness of water caused by suspended particles. High turbidity reduces light penetration, thereby limiting photosynthesis in aquatic plants.
• pH: The acidity or alkalinity of soil or water. Most organisms prefer a neutral pH (around 7), though some are adapted to acidic (low pH) or alkaline (high pH) environments.
• Edaphic Factors: These are soil-related factors including soil texture, structure, organic matter content, and pH, which determine the types of plants that can grow in an area.

2. Measuring Abiotic Factors

Ecologists use specific instruments to measure these factors accurately:

• Thermometer: Measures temperature.
• Rain Gauge: Measures the amount of rainfall.
• Hygrometer: Measures relative humidity.
• Anemometer: Measures wind speed.
• Wind Vane: Determines wind direction.
• Secchi Disc: Measures turbidity and light penetration in aquatic habitats.
• Barometer: Measures atmospheric pressure (affected by altitude).
• pH Meter / Litmus Paper: Measures acidity or alkalinity.
• Photometer: Measures light intensity.

3. Biotic Factors

Biotic factors involve interactions between living organisms that affect their distribution.

• Human Activities: Deforestation, urbanization, pollution, and bush burning can destroy habitats, leading to the migration or extinction of species. Conversely, conservation efforts can expand habitats.
• Competition: Organisms compete for limited resources like food, space, and mates. Intense competition can lead to the exclusion of weaker species.
• Predation: The presence of predators controls the population and distribution of prey species.
• Parasitism: Parasites can weaken or kill hosts, limiting the host population in certain areas.
• Symbiosis: Mutualistic relationships (e.g., nitrogen-fixing bacteria in root nodules) allow organisms to survive in otherwise nutrient-poor soils.