Available at Ecology Primer: Biological Interactions Nicklaus Kruger NISL An Optional Graphic can go here

  Ecology is the study of the interactions between living organisms and their environments   Other organisms are part of that environment   The interactions between organisms are numerous, but they can all be fitted into a framework of a handful of interactions Biological Interactions

Interspecific Interactions RelationshipEffect on species 1Effect on species 2 Competition - (competitor) Predation + (predator)- (prey) Mutualism + (partner) Commensualism + (epiphyte)O (host) Amensalism + (secretor)- (other) Parasitism + (parasite)- (host)

  The concept of competition is fundamental to the science of ecology   Competition occurs when two (or more) organisms require the same limiting resource   Intraspecific competition refers to competition between conspecifics   Interspecific competition refers to competition between members of different species   The more similar the fundamental niche of two organisms, the more potential for competition between them Competition

  Competition leads to niche differentiationn or competitive exclusion   Competitive release occurs when one of the competitive species is removed the area, and its competitor species expands its niche and occupation of the habitat   Laboratory experiments demonstrate that two species cannot coexist if they require similar resources Competition (cont)

  Closely related species rarely coexist for long in the laboratory   If two species are forced to live off the same resource, inevitably one persists and the other dies out   The competitive exclusion principle holds that two species cannot coexist on the same limiting resource   Only resources that limit population growth can provide the basis for competition   Non-limiting resources are superabundant compared to the needs of organisms Competition (cont…)

  Organisms must consume food to survive   Some organisms are able to derive chemical energy from inorganic molecules   Other organisms get their carbon from living organisms   Predation has received more attention from ecologists than any other form of biological interaction (except competition) Predator/Prey Dynamics

  When prey is plentiful, predator numbers can increase   But predators have an obvious adverse effect on prey population numbers   Ecologists debate whether ecosystems are regulated more by the dynamics within predator populations, or the dynamics within the populations of their prey   Individual predators tend to be larger than their prey, and also less abundant Predator/Prey Dynamics

  While we often view herbivore relationships differently from classic predator/prey relationships, functionally they are rather similar   Herbivores tend to be larger than carnivores, or to have larger populations, as a result of the way energy flows through an ecosystem Herbivores and Plants

  The nature of the plant has profound effects on the evolution of its herbivores   Plants also adapt to the pressures of herbivory, and develop strategies to escape predation   Plants and herbivores are locked in a coevolutionary arms race Herbivores and Plants (cont)

  Parasitism is similar to predation, except that the parasite tends not to kill its host as swiftly (if at all)   Endoparasites live within the tissues or their hosts   Ectoparasites live outside the tissues of their hosts, but attached to them   Epiparasites are parasites that parasitise parasites   Social parasites exploit the interactions between members of their host species Parasitism

Parasitism: The malaria parasite

  In mutualism, both of the interacting species benefit   When the species form a lifelong association in close physical and biochemical content, this form of mutualism is known as symbiosis   Obligate mutualism occurs when both species are dependent on their partners, and cannot survive without them   Facultative mutualism occurs when the partners are capable of surviving separately under certain conditions Mutualism

Symbiois: Lichens Lichens are symbiotic associations between algae and fungi Lichens are symbiotic associations between algae and fungi They are more successful together than apart They are more successful together than apart Many lichens are obligate mutualists Many lichens are obligate mutualists

  Obligate mutualism can sometimes lead to the evolution of a new unity   Endosymbiogenesis is the theory that this has happened several times in the evolution of the eukaryotic cell   The mitochondria that power our cells are thought to have once been bacterial endosymbionts Endosymbiosis

  In this form of interaction, one species benefits, while the other is not affected at all   Real and well-attested examples of commensalism are hard to come by   Certain epiphytes are thought to be involved in commensal relationships with their hosts (algae covering barnacles, for example) Commensalism

  Co-evolution is the mutual evolutionary influence between two or more species   In a co-evolutionary relationship, organisms exert selective pressure on one another   Effectively, co-evolution refers to biological interactions on an evolutionary timescale Coevolution

  Co-evolutionary arms races are positive feedback loops   The evolution of one participant leads to the evolution of the other, which in turn feeds back to the original participant   The classic example of this is in predator-prey relations   Below is an illustration of positive feedback and its involvement in the greenhouse effect Coevolutionary arms races

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