3: Drivers of diversification

Question 1

If diversification rates vary across the Tree of Life (causing unevenness), what are the causes?

Answer 1

• Speciation rates
• Extinction rates

Question 2

Describe the ‘pull of the present’

Answer 2

• As we aproach the present, the no. of observed extinctions declines (as young linages are less likely yo go extinct)
• In the past we observe net diversification
• In the present we observe only speciation

Question 3

What did Ernst Mayr (1963) argue the rate of speciation depends upon?

(3 things)

Answer 3

1. Formation of geographic barriers
2. Aqusition of reproductive isolating barriers
3. Ecological differentiation, coexistence and range expansion

Question 4

Rate of geographic isolation

The chance of geographic isolation may be greater in…

Answer 4

• Species with larger range sizes (more chance of subdivision)
• Species with larger area available for colonisation (more opportunity for long-distance dispersal)

Question 5

Why does the geographic scale of speciation depend on levels of gene flow?

Answer 5

• Non-dispersive organisms (e.g snails, certain plants) with low gene flow between pops can speciate over smaller spatial scales
• More dispersive groups require require larger geographic areas in order to achieve isolation

Question 6

Rate of reproductive isolating barriers

Are rates of genetic differentiation correlated with speciation rates?

Answer 6

Yes, lineages which experience faster rates of genetic differentiation might tend to accumulate genetic incompatibilities faster than other species

= therefore accumulating reproductive isolating barriers more quickly

Question 7

Is mating differentiation correlated with speciation rates?

Answer 7

• Yes: Ellis & Oakley (2016) studied whether lineages with bioluminescent courtship displays (sexually selected) have more species than non-bioluminous relatives
• Found that luminous lineage had a greater species richness than non-luminous linages (not true for groups that used luminescene as camo = must be courtship related!)

= supports idea that rapid evolution of sexually selected traits might accelerate evoltuion of reprodutive isolation = higher species richness

Question 8

Does ecological differentiation facilitate species coexistence?

Answer 8

Yes, if closely related species are able to become ecologically differentiated then they are more likely to be able to expand their ranges and stably coexist

Example:
- Study into Island bird bill shape found that pairs that achieved secondary sympatry the fastest where those with the most highly differentiated bill shapes

Question 9

Compare the importance of dispersal ability vs ecological differentiation traits in determining whether newly speciated species can coexist

Answer 9

Pigot et al. (2018):
- Found disersal ability (blue) can be important in determining initial range overlap
- But, at higher levels of range overlap, ecological differentiation traits (red) become more important in determining whether they can coexist stably

Question 10

Polyploid plant suffer high extinction rates and low speciation rates.

So, why are they so common?

Answer 10

High frequency of polyploids speciation
= high number of young polyploid species (have not had time to go extinct)
But most often these lineages go extinct quickly