JAMB Biology Note- Ecology of Populations

Topics:

(a) Population density and overcrowding.
(b) Adaptation for survival
i. Factors that bring about competition
ii. Intra and inter-specific competition
iii. Relationship between competition and succession.
(c) Factors affecting population sizes:
i. Biotic (e.g. food, pest, disease, predation, competition, reproductive ability).
ii. Abiotic (e.g. temperature, space, light, rainfall, topography, pressure, pH, etc.
(d) Ecological succession
i. primary succession
ii. secondary succession

Table of Contents

• Topics:
  • 1. Population Density and Overcrowding
    • Formula to Calculate Population Density:
  • 2. Adaptation for Survival
    • Factors that Bring About Competition:
    • Intra-specific Competition:
    • Inter-specific Competition:
    • Relationship Between Competition and Succession:
  • 3. Factors Affecting Population Sizes
    • Biotic Factors:
    • Abiotic Factors:
  • 4. Ecological Succession
    • Primary Succession:
    • Secondary Succession:
    • Climax Community:
  • Conclusion

1. Population Density and Overcrowding

Population density refers to the number of individuals of a species per unit area or volume. Overcrowding occurs when the population exceeds the carrying capacity of an area, leading to insufficient resources, which can cause various ecological and social issues.

Formula to Calculate Population Density:

Population Density =
Number of Organisms / Unit Area or Volume

Overcrowding Consequences:

• Increased competition for resources (food, space, mates).
• Spread of diseases due to closer contact.
• Reduced reproductive success due to stress and resource scarcity.

---

2. Adaptation for Survival

Adaptations are traits that help organisms survive and reproduce in their specific environment. These can be behavioral, physiological, or structural. Competition for resources plays a significant role in shaping these adaptations.

Factors that Bring About Competition:

• Food Availability: Lack of food leads to competition.
• Space: Limited space can cause organisms to compete for shelter or territory.
• Mating Opportunities: Competition for mates can lead to evolution of traits that improve reproductive success.

Intra-specific Competition:

• Occurs between individuals of the same species. It results from limited resources and can lead to:
  • Natural Selection: Organisms with better adaptations survive and reproduce.
  • Niche Differentiation: When members of the same species evolve to occupy different ecological niches to reduce competition (e.g., different feeding times or food types).

Inter-specific Competition:

• Occurs between different species. For example, different species of birds may compete for the same nesting sites.

Relationship Between Competition and Succession:

• Competition influences the progression of ecological succession. Species that are better adapted to a particular environment tend to dominate in the early stages of succession. As succession progresses, the competitive advantage of certain species may change, leading to a shift in the dominant species.

---

3. Factors Affecting Population Sizes

Biotic Factors:

• Food: Abundance or scarcity of food affects reproduction and survival.
• Pests/Disease: Outbreaks can reduce population sizes.
• Predation: The number of predators can influence the prey population.
• Competition: Both intra- and inter-specific competition regulate population sizes by limiting resources.

Abiotic Factors:

• Temperature: Organisms have an optimal temperature range for survival; extreme temperatures can limit population sizes.
• Space: Space for habitation, feeding, and reproduction can limit populations.
• Light: Light intensity is crucial for photosynthetic organisms and thus affects plant and herbivore populations.
• Rainfall: Availability of water affects plant growth, which in turn affects herbivore and carnivore populations.
• Topography: The physical features of an area (mountains, valleys, rivers) can affect the distribution of populations.
• Pressure, pH, and other factors: Extreme conditions, like high pressure or low pH, can limit the growth of certain populations.

Example of Biotic and Abiotic Interaction:
A drought (abiotic) leads to a shortage of water, which reduces the food supply for herbivores (biotic), ultimately impacting the predator population.

---

4. Ecological Succession

Ecological succession is the process by which ecosystems change and develop over time, leading to a climax community. It occurs in two stages: primary succession and secondary succession.

Primary Succession:

• Occurs in areas where no soil or living organisms previously existed, such as after a volcanic eruption or glacier retreat.
• Pioneer Species: Organisms like lichens and mosses begin the process by colonizing the bare rock.
• Stages:
  1. Pioneer species arrive.
  2. Soil formation occurs through the breakdown of rock and the accumulation of organic material.
  3. More complex plants, like grasses and shrubs, begin to grow.
  4. Eventually, a stable, mature community (climax community) forms.

Secondary Succession:

• Occurs in areas where an ecosystem has been disturbed but soil and some organisms remain (e.g., after a forest fire or abandoned agricultural land).
• Faster Process: Since soil and seeds are already present, secondary succession proceeds more rapidly than primary succession.

Climax Community:

• The final, stable community in succession that remains relatively unchanged unless disrupted by external forces (e.g., a fire, flood).
• In temperate regions, the climax community might be a deciduous forest, while in tropical areas, it could be a tropical rainforest.

---

Conclusion

The ecology of populations examines the factors that influence the size and distribution of populations, how organisms adapt to their environment, and the dynamic processes of ecological succession. By understanding these concepts, we can better manage natural resources, protect biodiversity, and mitigate the effects of human activities on ecosystems.