Another word for positive interactions

Facilitation

Mutually beneficial interaction
between individuals of two species (+ / +
relationship)

Ex. Gut microbiota (plant mycorrhizae)

Mutualism

individuals of one species benefit; individuals of the other species do not benefit but are not harmed (+/0 relationship).

Ex. follicle mites

Commensalism

Two species live in close physiological contact with each other.
• Symbioses can include parasitism (+/–),
commensalism (+/0), and mutualism (+/+).

Symbiosis

Two major types of Mycorrhizae

Fig 15.4

Ectomycorrhizae

Arbuscular mycorrhizae

What does fungi help do?

Protect the plants from pathogens

Improve plant growth and survival

Supply plants with carbs

Corals form a mutualism
with symbiotic algae
(zooxanthellae) by

The coral provides the alga with a home, nutrients and the alga with carbs

relationships that have coevolved where each organism depends on the other (not optional

Ex. fig and fig wasps

Obligate interactions

relationships that are optional (not obligate) and show few signs of coevolution

Ex. deer and seed dispersal

Facultative interactions

In a mutual interaction, the partners do what?

net effect is advantageous

Not altruistic

Take actions to promote their own best interests

Mutualist receives energy or nutrients from its partner

Ex. ants and fungus, mycorrhizae

Trophic mutualisms

One partner provides the other with shelter, living space, or favorable habitat.

Habitat mutualisms

One partner performs an ecological service for the other

ex. fig-fig wasp

Service mutualisms

In a mutualism, net benefits must exceed net costs for

both partners

n if the environment change and benefit is reduced or cost increase, outcome may change

Great-spotted cuckoos and carion crows went from parasitism to mutualism how?

Cuckoos are brood parasites – they
lay eggs in another species nest for
them to raise.
• Canestari et al. showed that this
parasitism can actually benefit the
crows in areas of high predations

individuals that increase offspring
production by overexploiting their mutualistic
partner.

occurs, interaction wont persist

Cheaters

The benefits from mutualism and commensalism can ultimately increase

growth, survival, or reproduction of the interacting species

How would you experimentally determine the
benefits that the trees get from the ants?

set up plots with ants present and absent
and measure different aspects of the acacia tree (abundance, size, percent mortality, growth, etc

Fig 15.19 Many coral reef fish have service mutualisms with smaller organisms (cleaners)
that remove parasites from
the fish (clients)

The benefit the client
receives is greater than the
energy benefit it could gain
by eating the cleaner

Increase ocean temp can lead to

coral bleaching resulting in death

Bee colony collapse disorder (CC) threatens ecosystems dependent on

their pollination services