Ecology Notes

Biotic Environment

• Biotic (living) components interact with each other and abiotic (non-living) components in an environment.
• Populations in a community interact with each other and abiotic factors in their habitat, affecting population sizes.

Factors Affecting Population Size

• Availability of food: Ecosystems with rich food supplies support more species (higher biodiversity).
• New predators, pathogens, and parasites: Introduction can have devastating effects.
• Competition between organisms: Influences population growth.

Indigenous vs. Alien Species

• Indigenous (native) species: Evolved and are an integral part of the natural system (e.g., Carob tree).
• Alien/exotic species: Introduced into an ecosystem, potentially causing disruptions and displacement of native organisms (e.g., Geranium Bronze Butterfly).
• Alien species reduce biodiversity through competition, predation, or transmission of pathogens.

Producers and Consumers

• Producers (autotrophs): Convert inorganic molecules into organic compounds (e.g., plants, algae).
• Consumers (heterotrophs): Rely on other living organisms for food (e.g., animals, bacteria, fungi, parasitic plants).
  • Herbivores: Primary consumers that eat plants.
  • Carnivores: Secondary consumers that feed on herbivores.
  • Omnivores: Eat both plants and animals; may be secondary or tertiary consumers.
• Decomposers (detritivores): Decompose plants, animals, and faeces, returning nutrients to the environment.

Endemic Species

• Living organisms found only in one area with specialized adaptations (e.g., Maltese Wall Lizard).
• Environmental disturbances endanger endemic species.
• Native/indigenous species evolved in an area and may be found in surrounding areas. Endemic species are native species found only in a specific habitat within a given area.

Symbiosis

• Close association between two organisms where one or both benefit.
• Mutualism: Beneficial to both organisms.
• Commensalism: One species benefits, the other is neither harmed nor helped.
• Parasitism: One species (parasite) benefits, the other (host) is harmed.

Parasitism

• Parasite lives inside or on the surface of a host for food and shelter.
• Endoparasites: Live inside the host (e.g., tapeworms).
• Ectoparasites: Live outside the host (e.g., leeches, ticks).
• Parasites have adaptations (e.g., hooks, enzyme-resistant covering) for survival.
• Humans control parasites by interrupting their life cycle.

Mutualism Examples

• Bacteria and roots of leguminous plants: Bacteria convert nitrogen to nitrates; plants provide carbohydrates.
• Algae and Fungi (Lichen): Fungus extracts minerals; algae provide food through photosynthesis.
• Sea anemone and hermit crab: Anemone protects crab from predators; crab provides transportation and food for anemone.

Competition

• Occurs when organisms depend on a common resource that is in short supply.
• Plants compete for light, water, mineral salts, and root space.
• Animals compete for food, nesting space, water, mates, or shelter.
• Intraspecific competition: Between organisms of the same species.
• Interspecific competition: Between organisms of different species.
• Competition influences population growth; successful organisms survive and breed.

Populations

• A group of organisms of the same species living together in the same habitat and capable of interbreeding.

Population Growth

• Depends on food supply, predation, and disease.
• Sigmoid (S-shaped) growth curve:
  • Lag Phase: Population grows slowly as organisms acclimatize.
  • Exponential Phase: Rapid population increase due to minimal limiting factors.
  • Equilibrium/Stationary Phase: Growth slows as environmental resistance increases; birth rate equals death rate; population reaches carrying capacity.
  • Death Phase: Population decreases due to unsuitable conditions.
• Carrying capacity: The maximum number of individuals of a species that can be supported by available resources.
• Unlimited population growth cannot be supported due to finite resources.

Predator-Prey Cycles

• Predators regulate prey populations.
• Prey increase first, followed by an increase in predator numbers (delayed reaction).
• Prey numbers decrease due to higher environmental resistance.
• Predator numbers decrease once prey numbers are low.
• Predation is a density-dependent factor regulating population sizes.

Human Population Growth

• Increased due to disease prevention, improved nutrition, lack of predators, controlled climatic conditions, and competition with pests.
• Potential consequences of uncontrolled increase: resource depletion, soil degradation, pollution, overcrowding, spread of disease.

Pest Control

• Pests compete with humans for resources and spread disease.
• Chemical Pest Control: Effective but harmful to the environment and humans.
• Biological Pest Control: Uses other organisms (predators, parasites, pathogens) to limit pest numbers; less harmful to the environment.