Symbiosis

Question 1

What is symbiosis?

Answer 1

Describes a wide variety of close, often beneficial interactions

Question 2

What are the types of symbiosis

Answer 2

Mutulism - both organisms benefit from the relationship

Commensalism - one organism benefits from the relationship whilst the other is neither helped nor harmed

Parasitism - one organism benefits at the expense of another

Question 3

Give some examples of symbiosis

Answer 3

Mutualism:

• Mycorrhizas is a symbiotic plant-fungal partnership
  -90% plants form mycorrhizas
  -increases plant access to nutrients and plant can have nutrients back to fungus

Commensalism:

• barnacles attach themselves to whale skin and live there their whole lives
• whales provide stable surface for them to catch food
• whales also protect them from predators
• whales unaffected by presence of barnacles

Parasitism:

• mistleote lives on trees
• derives nutrients, shelter and other needs from host but also photosynthesises
• modified roots penetrate bark and extract nurtients and water for parasite
• spread through bird droppings
• heavy infestation weakens host and makes it more suceptible to disease

Question 4

Is symbiosis neatly divided?

Answer 4

No, more like a continuum

Symbioses dont have to be static, can operate across continuum within lifetime

Question 5

Why study the mechanisms of symbiosis?

Answer 5

Important for understanding how symbioses evolve and persist over time

Can gain insight into the ways species interact and depend on each other and how these relationships can shape ecological and evolutionary processes

Question 6

What is coevolution?

Answer 6

Two or more species evolve together in response to each other’s adaptations

Often seen in mutualisms

E.g. plants evolved to produce nectar and their pollinators

Question 7

What is horizontal transfer?

Answer 7

Genetic material is transferred between different organisms that are not related by descent

Can be through viral-mediated gene transfer

Question 8

What is endosymbiosis?

Answer 8

One organism lives inside another and is often mutualistic

Question 9

What are the implications of symbiosis?

Answer 9

Can have significant effects on functioning and stability of ecosystems

E.g. nutrient cycling, ecosystem resillience, species diversity and evolutionary innovations

Question 10

What is nutrient cycling?

Answer 10

Exchange of nutrients between partners

E.g. legumes form symbioses with nitrogen fixing bacteria which converts nitrogen gas to ammonium for plant hosts to use

Question 11

What is ecosystem resilience?

Answer 11

Help maintain resilience and stability of ecosystem by providing buffering mechanisms against environmental stressors

E.g. coral reefs rely on coral-algae symbioses

Question 12

How is symbiosis linked to species diversity?

Answer 12

Can allow organisms to occupy new niches or exploit new resources

Question 13

What are ant-plant mutualisms?

Answer 13

Ants often receive food and shelter from the plant and in return they provide protection for the plant

Some ants farm by actively planting and fertilising the seedlings of plants who provide shelter for the ants

Evolved by the primary driving factor being shelter and not food due to limitations of nesting space in forest canopies