FOUR main kinds of species interactions; all play a role in the formation of community structure...

Competition (-,-)

Predation, parasitism (+,-)

Mutualism (+,+)

Commensalism (+,0)

Mutualism:

Any long-term association between twospecies that confers mutual fitness benefitsto individual members of both species.

Facultative mutualisms: Each species gains a benefitfrom the presence of the other, but each can still survive without the other. “Generalist” mutualisms.

Obligate mutualisms: Each species can only livein the presence of the other. “Exclusive” mutualisms.

A) Plant-animal mutualisms:

- most common (90%)

1. defensive / protective mutualisms

2. dispersive mutualisms

1. Defensive / protective mutualisms

-animal species receives food and/or shelterfrom mutualistic plant species in return for defending plant

e.g. ants and “swollen thorn” acacias

-acacia plants save energy by notproducing expensive alkaloids

- ants protect acacias by attacking herbivores and other plants

- ants gain shelter and food

2. Dispersive mutualisms

i) seed dispersal

ii) pollination

i) Seed dispersal mutualisms

- birds and mammals disperse seeds via defecation- seed burial by mammals

- animals benefit from fruitthat surrounds seed

-plants benefit by havingseeds moved to favorablegermination sites

Most seed dispersal mutualisms are facultative; however, a few are obligate…

Obligate seed dispersal mutualisms:

e.g. Mistletoe Bird

An obligate mutualism is an interaction in which at least one species cannot survive without the presence of the other species; a facultative mutualism is an interaction that benefits both species but is not required by either species. One reason facultative mutualisms are more common is that

A) in an obligate mutualism, if the partner becomes extinct, the obligate mutualist will also become extinct.

B) in a facultative mutualism, if the partner becomes extinct, the facultative mutualist will also become extinct.

C) in an obligate mutualism, the obligate mutualist is obliged to support its partner.

D) in a facultative mutualism, neither partner can depend on the other partner.

E) facultative mutualisms require longer periods of time to evolve.

e.g. Dodo and Calvaria Tree

- extinction of Dodo once thought to threaten Calvaria tree

Historical obligate seed dispersal mutualism?

Problem for plants:

- many seed dispersers are also seed predators

Solutions:

-‘mast’ seeding

- ‘choose’ dispersal agent

Mast seeding:

- all trees of a particular species in a given areaproduce large seed crops simultaneously

- alternating years of high and low production

e.g. Oak tree production of acorns-squirrels can’t retrieve all

Toxic or distasteful fruits are one way for a plantto ‘choose’ its dispersal agents.

e.g. chili peppersand birds

Capsaicinoids distasteful to mammals, but very tasty to birds!

Phlox family adaptationsto many different pollinators

ii) Pollination mutualisms

What are the advantages of exclusive pollination mutualisms?

For plants?

For animals?

What are the disadvantages of exclusive pollination mutualisms?

If one member goes extinct, the other will too.

STDs!

e.g. nostril mites

Insects are the most specialized pollinators andhave evolved more obligate mutualisms than birds or mammals. Why?

A) Because there are so many different species, they are able to pollinate a greater variety of flowering plants.

B) Because they have short life cycles, short generation times, and many offspring.

C) Because they have small brains and therefore cannot learn to recognize many different plant species.

D) Because they can move quickly from plant to plant and therefore can remember the last species visited.

Species-specific Coevolution:

A mutual evolutionary influence between only two interacting species.

Two classic examples of species-specificcoevolution:

Madagascar Star Orchid

-discovered by Du Petit-Thouars (1822)-white, night-scented-nectar tube 30 cm long-Darwin predicted moth pollinatorwith proboscis slightly shorter

Predicta hawkmoth- discovered 40 yrs later- proboscis 25 cm long

Nilsson (1988) experimentally shortened nectar tubes.Moth’s head does not contact pollen; so flower producesfewer seeds.

Another classic example of species-specific coevolution:

Figs and Fig Wasps...(video clip)

B) Animal-animal mutualisms:

1. cleaner mutualisms

a) aquatic

b) terrestrial

Cleaner Wrasse plus “clients”

Aquatic Cleaner System: Cleaner Fish

Do cleaner fish really clean?

1) Exclusion experiment on coral reef:

-fish on reefs without cleaners had4.5X more parasites

YES

2) Diet choice experiment:

- choice of fish mucus or parasites- cleaners preferred client mucus

NO

Red-billed Oxpecker on Impala

Terrestrial Cleaner System: Tickbirds

Do oxpeckers really clean?

Commensalism: +, 0

Shark with remora Cape buffalo with cattle egrets

Commensalism: +, 0

e.g. Antbirds and army ants