Mutualistic dependence seminar

Question 1

virtually every species on earth is involved in one or more mutualisms; this type of relationship may represent … of the interactions in communities

Answer 1

~50%

Question 2

Mutualisms provide essential ecosystem services (e.g. … is worth 30 billion a year to the US economy alone)

Answer 2

pollination

Question 3

Assumptions of the tit for tat model:

• no … differences between species
• The services exchanged cannot evolve
• The payoffs associated with cooperation, defection, cheating and being cheated are …
• Partners need to … previous interactions

These assumptions are not met in most mutualisms

Answer 3

ecological, constant, remember

Question 4

Mutualistic … varies a lot.

Answer 4

dependence (e.g. none, facultative, obligate)

Question 5

Does mutualistic dependence affect mutualism breakdown at the geological scale?

Answer 5

Ant plants phylogeny - facultative generalist is intermediate ancestral state. There were 4 increases in dependence (obligate) and 12 losses of dependence (non-mutualists). The non-mutualist state NEVER evolved from the specialised obligate state, only the facultative

• the level of dependence of mutualism affects the likelihood of breakdown at an evolutionary scale

Question 6

Does mutualistic dependence affect the efficiency of the service provided?

Answer 6

Small clade of ant plants - do obligate ant-plants get more nitrogen from ants than facultative ant-plant species?

The facultative type has limited nitrogen uptake capacity and no apparent selection on the location of defecation (pretty much even throughout plant). The obligate type has a very clear differentiation - the ants exclusively defecate in the warty (rather than the smooth) chambers and uptake here is significantly higher.

Removing the ants from both types and measuring the amount of nitrogen in the plants 16 months later showed that the obligate ant-plants get 2.5-fold more nitrogen from ants than facultative species - so yes, they are more efficient

Question 7

How are high versus low dependence mutualisms stabilised?

Answer 7

Obligate - fitness alignment between partners and partner choice (making rewards exclusive to partner - nectaries that only symbiotic species can access) - two different ways to stabilise this system

Facultative - different species can live in the same domatium - goes against theory. Found that obligate species have one cavity (connected to outside) whereas facultative have multiple - physical separation of ant species is enough to maintain coexistence (most species fight when you introduce workers from another species) - optimal number of cavities increases with number of invading ant colonies arriving at plant while nest develops - reducing physical contact is the very simple mechanism