CH 15-Mutualisms

Define mutualism in the context of facilitation and symbiosis.

• Mutualism is a type of interation where both species benefit (+/+)

• Not all mutualisms are symbiotic

  • Symbioses just broad term to describe any close long term interaction bw 2 diff species

  • → symbioses can include parasitism, commensalism and mutualism such as bacteria and plants

• Mutualism is always facilitation 

  • Facilitation is a broader term for any positive interaction between species that benefits at least one indiv

    • mutualism +/+ and commensalism +/0).

Use examples to explain the ecological importance of mutualisms

• many organisms depend on mutualists to grow or reproduce 

  • ex: bees and flowering plants: bees get nectar and plants get pollinated, without bees many plants fail to reproduce

• Can help move/fix nutrients essential to ecosystems

  • ex: mycorrhizal fungi and plant roots

  • fungi increase plants ability to absorb P and nitrogen 

  • plants give fungi sugar

Define and give examples of different types of mutualisms: a) trophic

Trophic 

• Mutualism where partners help each other get energy/nutrients, atleast one gets food directly from the other.

• ex: mycorrhizae→ plant roots. fungi help plant take up water + nutrients and get sugar in return 

• ex: coral and symbiotic photosynthetic algae 

  • Algae gets home coral gets sugar 

b) Defense Mutualism 

• 1 mutualist defends the other and receives resources in return 

  • ex: Acacia trees provide housing and ants defend the tree from herbivores 

  • clownfish and anemones. Anemone provides protection and clownfish chase away anemone predators + bring nutrients

c) Cleaning Mutualism 

• 1 animal removes ectoparasites/fungi from another 

  • ex: cleaner shrimp and reef fish. Shrimp removes parasites and fish tolerate their presence + don’t eat them

d) Transport and Dispersal Mutualism 

• Animal moves pollen or seeds for plants and gets nutritional award 

• ex: bees and flowering plants → pollinators get nectar plants get their pollen transported

• ex: seed dispersal by birds/mammals, animals eat it and dropping disperse seeds 

Explain how mutualisms vary in inter-dependency. Give examples of obligate vs facultative mutualisms.

• Mutualisms vary from obligate to facultative 

Obligative 

• a mutualist cannot survive without its partner 

• ex: tropical figs pollinated by fig wasps. The two coevolved neither can reproduce without the other 

Facultative mutualisms 

• mutualism can survive in absence of its partner 

• ex: mot pollination mutualisms. Many plants can be pollinated by other insects/wind and bees can get nectar from other plant species. 

Interpret examples and explain why mutualisms vary in space and time.

• Mutualisms not always equally beneficial everywhere or at every moment 

• their strength (or if they occur at all) depends on envt conditions, resource levels, community composition, seasonal patterns 

• ex: in nutrient poor soils plants depend heavily on fungi to get phosphorus→ strong mutualism. But in rich soils plants gain little from fungi and can stop associating→ weak/absent mutualism 

• ex: vary in time bc conditions change (pollination during flowerinig season mutualism strong outside flowring season mutualism temporarily disappears)

Give examples of conflict and cheating in mutualisms. Explain why "evolutionary arms races" may also apply to mutualism

• Cheaters= individuals that increase offspring production by overexploiting their mutualistic partner (selfish)

• Conflict because each species is trying to maximize its own fitness

• ex: acacis trees that give ants nectar, but the ant may use the plants resources and give little defense against herbivores

Evolutionary arms race 

• 1 mutualism evolved a way to punish cheaters/poor partners 

• the other mutualism evolves a way around this (to keep taking advantage)

Given the strong selection for cheating, explain what mechanisms can maintain mutualistic interactions in evolutionary time

• mutualists can choose/prefer good partners and avoid cheaters

  • plants reward the fungi that supply the most nutrients 

• Partners punish individuals that cheat 

Explain, with examples, how mutualisms can impact populations and communities

• community→ nitrogen fixing bacteria help plants grow→ supports the rest

• population→ help them survive and grow like below the ants decrease abundance of nearby plants but increase the acacia trees

• contribute to biotic resistance by preventing colonization by invasive species

Population impacts

• Acacia trees enlist ants as private gardeners without ants they are often killed by herbivores

• Ants can’t survive without the trees

• Interaction between the two increases survival of acacia trees while decreasing the abundance of nearby plants

Community impacts 

• Cleaner fish remove parasites from their clients 

• reefs with cleaner fish have higher abundance of fish species ( bc if removed the fish moved to place with cleaner fish) and more stable communities