unit 5

• Abiotic factors


  Physical factors such as light, heat and moisture that determine the environment in which an organism lives
• Biotic factors


  The influence of other living organisms on an organism
• Biotic factors that affect the survival and distribution of an organism

  • Intraspecific interactions
  • Interspecific interactions
  • Humans
• Intraspecific interactions


  Interactions between members of the same species, such as competition for food and territory
• Interspecific interactions


  Interactions between members of different species, such as predator-prey and host-parasite interactions
• Important interspecific associations


  • Predation
  • Symbiosis
  • Competition
• Predation


  The consumption of one species (the prey) by another (the predator)
• Symbiosis


  The living together, in close association, of two or more organisms of different species, usually involving nutrition
• Mutualism


  A symbiotic relationship in which both partners benefit
• Examples of mutualism


  • Nitrogen fixing bacteria and legumes
  • Clown fish and sea anemone
• Commensalism


  A type of symbiosis in which one organism (the commensal) benefits while the other is neither harmed nor helped
• Example of commensalism


  • Epiphytes (mosses, orchids, ferns) living on tropical trees
• Parasitism


  A symbiotic relationship in which one member (the parasite) benefits and the other (the host) is adversely affected
• Ectoparasites


  Parasites that live on the outer surface of a host, e.g. ticks, fleas, leeches
• Endoparasites


  Parasites that live within a host, e.g. tapeworms
• Competition


  When two species have overlapping fundamental niches, leading to one species being excluded from the niche
• Competitive exclusion


  One species is excluded from a niche by another as a result of competition between species
• Resource partitioning


  The adaptation of species to separate or partition the available resources amongst themselves to avoid competition and survive
• Fundamental niche


  The potential ecological niche of an organism
• Realized niche


  The lifestyle that an organism actually pursues and the resources that it actually uses
• Evolution


  The theory that various types of animals and plants have their origin in other pre-existing types, and that the distinguishable differences between them are due to modifications in successive generations
• Natural selection


  The fundamental concept in Darwin's explanation of evolution, where organisms with favourable variations are more likely to survive and reproduce
• Without constraints, populations will grow exponentially
• Population numbers remain near equilibrium, fluctuating above or below some mean value
• Resources are limited, leading to a struggle for existence
• Individuals are unique, with individual variation within a population
• Much of the individual variation is hereditable
• Example of natural selection


  • Peppered moths in industrial England
• Succession


  The orderly replacement of one ecosystem by another
• Primary succession


  Succession occurring in essentially lifeless areas, such as lava flows, newly formed sand dunes, or rocks left from a retreating glacier
• Secondary succession


  Succession occurring in areas where a community that previously existed has been removed, such as after a fire or storm
• Many plant species in fire-prone environments have seeds that remain dormant within the soil until the heat of a fire stimulates them to germinate