Ecology: The Biotic Environment

Biotic Environment

• Ecology: Study of interactions between biotic (living) and abiotic (non-living) components of an environment.
  • Populations in a community interact with each other and abiotic factors.
  • Population size changes due to:
    • Availability of food.
    • New predators, pathogens, and parasites.
    • Competition between organisms.

Species Classification

• Indigenous (Native) Species: Evolved and are an integral part of the natural system. E.g., Carob tree (Ceratonia siliqua).

• Alien (Exotic) Species: Introduced into an ecosystem, causing disruptions. E.g., Geranium Bronze Butterfly (Cacyreus marshalli).

• Endemic Species: Found only in one specific area. E.g., Maltese Wall Lizard (Podarcis filfolensis).

  • Native/indigenous species evolved in an area and may be found there as well as in the surrounding areas.
  • Endemic species are native species that are found only in a specific habitat within a given area.

Trophic Levels

• Producers (Autotrophs): Convert inorganic molecules into organic compounds. E.g., plants, algae.
• Consumers (Heterotrophs): Rely on other living organisms for food.
  • Herbivores: Primary consumers that eat plants.
  • Carnivores: Secondary consumers that eat herbivores.
  • Omnivores: Eat both plants and animals; can be secondary or tertiary consumers.
• Decomposers (Detrivores): Decompose plants, animals, and faeces, returning nutrients to the environment.

Symbiosis

• Close association between two organisms.
  • Mutualism: Both species benefit. E.g., bacteria and roots of leguminous plants.
  • Commensalism: One species benefits, the other is unaffected.
  • Parasitism: One species (parasite) benefits, the other (host) is harmed.
    • Endoparasites: Live inside the host. E.g., tapeworms.
    • Ectoparasites: Live outside the host. E.g., leeches, ticks.

Competition

• Occurs when organisms depend on a common resource in short supply.
  • Intraspecific Competition: Between organisms of the same species.
  • Interspecific Competition: Between organisms of different species.

Populations

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

Population Growth

• Rate of growth depends on food supply, predation, and disease.
• Sigmoid (S-shaped) Growth Curve:
  • Lag/Establishment Phase: Slow growth as organisms acclimatize.
  • Exponential/Log Phase: Rapid growth with little limiting factors.
  • Equilibrium/Stationary Phase: Growth slows due to environmental resistance; birth rate equals death rate; reaches carrying capacity.
    • Carrying Capacity: The maximum number of individuals of a species that can be supported by available resources.
  • Death Phase: Population declines due to unsuitable conditions.
• Unlimited growth cannot be supported due to finite resources.

Predator-Prey Dynamics

• Predators regulate prey populations.

• Predator-Prey Graph Interpretation

  • Prey numbers increase first when environment is lacks predators and have food, space.
  • Predator numbers rise after the numbers of prey has increased and competition for prey exists.
  • Prey numbers will start to decrease after environmental resistance takes effect.
  • Predator numbers will start to decrease once prey numbers are low or decreasing rapidly.
  • Local Examples between Snakes and Mice and Hedgehogs and Beetles.

Human Population Growth

• Increased due to disease prevention, improved nutrition, lack of predators, controlled climate, and pest control.
• Consequences of uncontrolled growth: diminished resources, soil degradation, increased pollution, overcrowding.

Pest Control

• Pests compete with humans for resources and spread disease.
• Methods to reduce alien species:
  • Enforcing laws.
  • Screening imports.
  • Monitoring infestations.
  • Eradication of new species.
• Control Methods:
  • Chemical: Effective but harmful to the environment.
  • Biological: Uses predators, parasites, or pathogens; less harmful.