Unit 2: Mutualism and Commensalism

Facultative

each partner gains a benefit but is not dependent

Obligate

each partner gains a benefit and is dependent

Symbiosis

A close ecological relationship between individuals of two species.

Symbiotic Mutualism Example 1

Rhizobium fixes nitrogen from the air (N2) into a form that both species can use. The bacteria gain carbon from the plant.

Non-symbiotic mutualism Example 1

Plant and pollinators, pollinators gain nectar/pollen and plants can reproduce

Mutualisms played key roles

• Evolved early on in multi-cellular lineages and in evolution of terrestrial organisms

• Are ubiquitous

  • Mutualisms cover the land surface of the earth

  • mutualisms are a key component of many aquatic communities

Mutualisms evolved early on

• Bacterial origins of mitochondria and plastids

  • probably originated as a mutualistic relationship

• relationship is obligatory

  • incomplete genome

Mycorrhizae

Plants form mutualistic associations with soil fungi

• Increase uptake water and nutrients

Mycorrizae - Advantages to the plant

• Phosphorous uptake

  • Surface area

  • Acid phosphates

• Nitrogen uptake

  • Digestion of organic material

• Water uptake

• Protection from diseases

Mutualism in the ocean

• Coral and Eel

  • Gains sugar and oxygen for the algae

• Zooxanthellae

  • Gain nitrogen, carbon dioxide, physical structure, and protection from the coral

Trophic mutualism

A mutualist receives energy or nutrients from it partner

Habitat mutualisms

one partner provide the other with shelter, a place to live, or favorable habitat

Service mutualisms

interactions in which one partner preforms an ecological services for the other

Cheaters

Are individuals that increase offspring production by overexploiting their mutualistic partner

Lotka Volterra Equations for Mutualisms Species 1

\frac{dN_1}{\differentialD t}=r_1N_1\left(\frac{K_1-N_1+aN_2}{K_1}\right)

Lotka Volterra Equations for Mutualisms Species 2

\frac{dN_2}{\differentialD t}=r_2N_2\left(\frac{K_2-N_2+\beta N_1}{K_2}\right)

Commensalism

An interaction between two species in which one benefits and the other neither benefits nor is harmed