Ecology Primer: Biological Interactions

1. Ecology Primer: Biological Interactions Nicklaus Kruger NISL nicklaus@webmail.co.za An Optional Graphic can go here

2. Biological Interactions • 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

3. Interspecific Interactions

4. Competition • 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

5. Competition (cont) • 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

6. 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

7. Predator/Prey Dynamics • 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)

8. 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

9. Herbivores and Plants • 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

10. Herbivores and Plants (cont) • 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

11. Parasitism • 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

12. Parasitism: The malaria parasite

13. Mutualism • 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

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

15. Endosymbiosis • 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

16. Commensalism • 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)

17. Coevolution • 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

18. Coevolutionary arms races • 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

19. Bibliography • Dark green font Arial at least 18 point this colour is 70 70 0 • Use animation and the effects of BLINDS for TEXT and DISSOLVE for IMAGES– they are quick and effective and bring in by paragraph and then dim after mouse click to a mid grey colour 150 150 150 • Give your presentation a header … there is space in the top and it also uses the colour 150, 150, 150 this uses Word Art and can be stretched. Use VIEW / MASTER/ SLIDE MASTER to access • If you need to hyperlink such as this is the URL for NISL if you use this as a template the colour is already set and is 96 132 113. For a visited Hyperlink use this colour which is 204 102 0 • Keep within the frame … this ensures it will not get clipped when projecting. • Use Bullet Points as indicated (Square colour is 128 128 0 )