a.Acacia and ants

(1) 90% of Acacia contain potent secondary chemicals

(2) The remaining species lack secondary chemicals, but have special features such as swollen thorns, extra-floral nectaries, and Beltian bodies.

(a) These species are defended by ants, which get rid of herbivores and any plants that touch

(b) The ants receive food and shelter from the tree

(3) Acacia trees in the mid-Caribbean lack these special features and ants, even though their ancestors had them.

2. Your mutualist will cheat you

a. Example: orchids and pollinators

(1) Many orchids offer no nectar or other reward, but the pollinators keep coming.

(2) These orchids attract male pollinators by resembling females of their species.

b. Example: Yucca buccata and the Yucca moth

(1) The plant depends on the moth for pollination

(2) The moth depends on viable ovules for raising larvae

(3) Many plants "cheat" by producing flowers with low numbers of ovules.

(a) These plants get pollinated, but the larvae don't survive.

(b) As many as 70% of plants in a population "cheat"

(c) They "cheat" the other plants as well as the moth.

3. Your whole world could collapse

a. Suppose that an obligate mutualism exists, and then one of the mutualists goes extinct

(1) Example: Tambalacoque tree

(a) Thirteen trees remain

(b) All trees are >300 years old

(c) Trees produce fruits, but the seeds don't germinate.

(d) The dodo went extinct in 1861

i) it ate Tambalacoque fruits

ii) germination can be induced by scarifying the seeds