24 - Symbiosis* Flashcards
Host
the organism harbouring the other
Symbiont
Usually microscopic or harboured partner
mutualism
Both benefit, obligate association. Often based on protection and nutrient/waste exchange
Cooperation/synergism
Both benefit, no obligatory. Often based on satisfaction of nutritional requirements
Commensalism
One benefits, other is unaffected. Shelter, resources, habitat modification
Predation
One engulfs the other
Parasitism
Co existence, usually to detriment of one partner
Amensalism
One produces an inhibitor of the other. E.g. antibiotics, alcohol formation by yeasts, acid formation
Competition
Both compete for limited resource
Consortia
Complex communities of diverse interacting
populations
Ectosymbiosis
The symbiont is associated with host surfaces
Endosymbiosis
Symbiont is internal to host
Example of mutualism
- Reef building corals and zooxanthellae.
- Reef building corals satisfy most of their energy requirements using zooxanthellae
- Zooxanthellae receive nitrogenous compounds, phosphates, CO2 and protection.
Syntrophism
Growth of one organism depends on or is improved by growth factors or nutrients provided by another organism growing nearby
Marine food webs
depend on predation by predator protists on phytoplankton and bacteria
Examples of predatory microbes
Bdellovibrio, Vampirococcus, Daptobacter
What can parasitism lead to
genomic reduction and parasite dependence on host
Benefit of parasitism
Population control
Example of parasitism
Bacteriophages. Lysogenic cycle may add useful genes to host (mutualism?)
Example of mutualism maintained by amensalism
- Fungus growing ants maintain fungal gardens as food source (mutualism)
- Gardens subject to infestation by parasitic fungus.
- Ants co-cultivate bacteria that produce inhibitors of the parasite (amensalism)
Four likely outcomes of competition
- Reduced growth: coexistance but neither achieves maximum potential growth (-/-)
- Competitive exclusion: one is eventually eliminated from the habitat (+/-)
- Niche separation: the competitors occupy different niches in the habitat (0/0)
- Temporal resource sharing: the competitors occupy the habitat at different times (+/- and -/+ cycle)
Competitive exclusion
The populations with the higher growth rate
ultimately exclude competitors from a niche
Negative interactions of symbiosis as a driving force in evolution
- Limit population density
- Prevent individual dominance
- Drive increased genetic diversity
positive interactions of symbiosis as a driving force in evolution
- Promote more efficient use of resources
- Enable organisms to colonise habitats they could not colonise alone
- Enhance **growth/survival **of benefiting populations
