ESS 2.1.4-5

• Predation is where one organism (the predator) hunts and kills another (the prey) in order to provide it with the energy for survival and reproduction.

  • Predation can be by an individual, a group or by a plant.
• In the short term predation is obviously only beneficial to the predator. However the interaction creates a negative feedback loop in which the predator and prey populations are kept in balance 
• The predator prey relationship produces a very typical graph The graph shows a number of things:

  1. Prey numbers are, on average higher than predator numbers. This is to do with the laws of thermodynamics and loss of energy. 
  2. The populations peak are out of sync - this is due to the time lag between the numbers of prey decreasing and the numbers of predators decreasing. 
• Herbivory is the consumption of plant material by an animal (Herbivores).

  • Plants evolve defense mechanisms to cut down herbivory, these are either structural/mechanical or chemical. The herbivores evolve coping mechanisms to continue eating.
  • These make eating and digestion difficult and painful, herbivores will browse for a while but then move on to something less difficult to eat.
• Parasitism is when an organism (the parasite) takes nutrients from another organism (the host).

  • Parasites may live on the outside of their host, for example tick and fleas (ectoparasites). The parasites that live on the inside of the host are called endoparasites for example tapeworms spend part of their lives in the gut of their host.
• Mutualism is where two organisms of different species exist in a mutually beneficial relationship.

  • Mutualism is vital to ecosystem functioning and it is believed that nearly 50% of all terrestrial plants rely on the fungi around their roots to enable them to absorb inorganic compounds from the soil.
• Disease is a departure from the normal state of functioning of any living organism – plant, animal or human. It can affect the whole body or just part of it. 
• Competition is where organisms compete for a resource that is in limited supply (water, food, territory, mates, habitat, etc.)

  The resource must be limited for competition to occur, if it is plentiful there is no need for competition and the population will grow exponentially giving the J-shaped curve.

  Unlimited resources are rare so competition becomes important and population growth will slow resulting in the S-shaped curve.
• Intraspecific competition occurs when members of the same species compete for a limited resource – water, space, mates, food etc. Most species will demonstrate this type of competition, depending on the environment they are in. 
• Interspecific competition is where members of different species compete for a resource that they both need. The resources fought over will be the same as in intraspecific except for mates and maybe habitat. Members of different species do not compete for mates because they can not mate. Also, in some cases different species have different habitats. 
• Interspecific competition has more impact on species survival and population dynamics than intraspecific competition. If members of the same species are fighting for the same resource the end result is likely to be a slight drop in population numbers as the weaker members of the species are out competed. But if one species out-competes the other than extinction may be the result.