Essential Principles of Ecology and Population Dynamics

Fundamental Ecological Laws

Liebig's Law of the Minimum

Established in 1840, this law states that plant development depends on the minimum quantity of a specific element present (e.g., water, gas).

Shelford's Law of Tolerance

This principle dictates that the existence and prosperity of an organism depend on the deficiency or excess of factors approaching its tolerance limits. Organisms vary in their ability to tolerate environmental conditions.

• Stheno: Organisms with narrow tolerance ranges.
• Eury: Plants and animals with wide tolerance ranges.

Biotic Interactions

Biotic factors include diseases, predation, and parasitism.

Types of Relationships

• Interspecific Relationships: Interactions between different populations.
• Intraspecific Relationships: Interactions between individuals of the same species.

Interaction Categories

• Positive Interactions: Beneficial effects such as cooperation, mutualism, and commensalism.
• Negative Interactions: Interactions affecting development and survival, such as predation and parasitism.
• Neutralism: Two populations associated without affecting one another.
• Competition: Two individuals competing for space or resources.
• Mutualism: Both populations benefit in development and survival.
• Cooperation: Both populations benefit, but the relationship is not mandatory.
• Commensalism: One population benefits while the other remains unaffected.
• Parasitism or Predation: Interactions where one species negatively affects another.

Population Dynamics

Key Definitions

• Population: Groups of organisms of the same species inhabiting a specific geographical area.
• Population Size: The total number of individuals in the study population.
• Density: The size or magnitude of the population relative to a unit of space.
• Gross Density: Number of organisms or biomass per unit of total space.
• Specific Density: Number of organisms or biomass per unit of habitable area.

Growth and Mortality Factors

• Birth Rate: The percentage of population increase; the number of individuals born and integrated into the population over a period.
• Maximum Birth Rate: The theoretical maximum production of new organisms.
• Ecological Birth Rate: The real or specific growth of organisms in a population.
• Mortality: The percentage of population decrease due to deaths.
• Minimum Mortality: Deaths occurring under ideal physiological conditions.
• Ecological Mortality: Deaths occurring under real-world limiting factors like climate or predators.
• Migration: The movement of individuals to disseminate seeds, spores, or elements.

Growth Rate: The net population growth resulting from the balance of birth rates, mortality, and migration (+, -, or 0).