Population Ecology Notes

Ecology

Definition

  • Ecology: Study of living organisms in relation to their environment.
  • Studied at levels: species, population, community, ecosystem, biosphere.

Ecological Hierarchy

  • Species: Interbreeding organisms producing fertile offspring.
  • Population: Same species in a defined area.
  • Community: All organisms in an area affecting each other, made up of two or more populations.
  • Ecosystem: Community interacting with physical/chemical environment.
  • Biosphere: All Earth's ecosystems.

Environment vs. Habitat

  • Environment: Sum of external factors affecting life.
  • Habitat: Characteristic physical locality where organisms live.

Maltese Terrestrial Habitats

  • Garigue (Xagħri): Commonest habitat over karst, chemical erosion of calcium carbonate
  • Maquis (Makkja): Small patches with deeper soil, shrubs/low trees (carob, olive trees).
  • Steppe: Treeless grassland, Garigue degenerated due to overgrazing/burning.
  • Woodland: Deeper soil, limited, mostly planted, typical plants (Aleppo pine, Holm Oak).
  • Cliffs (Rdum): Support rupestral communities.
  • Sand dunes (Għaram tar-ramel): Salty air environment, deep roots needed.
  • Salt Marshes (Bwar Salmastri).

Population Characteristics

  • Population size determines survival, small populations result in inbreeding.
  • Size depends on natality, mortality, emigration, immigration.

Sigmoid (S-shaped) Growth Curve

  • Lag Phase: Slow growth, acclimatisation.
  • Log Phase: Rapid (Exponential) growth, Natality >> Mortality, maximum growth potential rate of the population (r).
  • Deceleration: Natality > Mortality, competition sets in.
  • Stationary Phase: Population stops growing, maximum size reached, Natality = Mortality.

Limiting Factors

  • Environmental resistance: overcrowding, lack of food/nutrients/oxygen, toxic materials, lack of light, disease.
  • Biotic potential (r) : maximum reproductive potential.
  • Environmental resistance: limiting factors preventing biotic potential.

Carrying Capacity (K)

  • Maximum individuals supported without increasing/decreasing.
  • Populations tend to overshoot (K), oscillate around it, die-off occurs, then oscillates again.

J-shaped Growth Curve

  • Exponential growth continues, sudden crash occurs.
  • Factors: establishing in new environment, recovery from exploitation, transient favorable conditions.

Factors Influencing Carrying Capacity

  • Abiotic: Non-living components (temperature, water, soil, pH, light, climate, space, nutrients, pollution).
  • Biotic: Interactions with other organisms (competition, predator-prey, parasitism).

Competition

  • Intraspecific: same species.
  • Interspecific: different species.

Predation

  • Predator population increases, more prey eaten.
  • Prey population decreases, less food for predators.
  • Predator numbers decrease.
  • Fewer prey eaten, prey numbers increase.
  • Cycle begins again.

Parasitism

  • Parasite obtains food from host while alive, harming it.
  • Ectoparasites: on host surface (fleas, mosquitoes).
  • Endoparasites: inside host (tapeworm, viruses).
  • Greater effect on dense populations, increases death rate, similar cycles to predator-prey.