3: Phylogeny & diversity

Question 1

What is a phylogeny?

Answer 1

The history of descent of a group of taxa (e.g species from their common ancestor)

Question 2

What is phylogenetic tree imbalance?

Answer 2

A difference in the number of descendant tips (usually species) either side of a focal node

Question 3

Give 2 reasons why species richness varies

Answer 3

1. Chance alone
2. Variation in diversification rate

Question 4

Why does species richness vary?

Describe the equal rates Markov model

Answer 4

Null model:
- Species arise from other species (bifurcation)
- Prob of speciation per unit time is constant across all lineages

Question 5

Chance alone model for variation in species richness

Describe the findings of Guyer & Slowinski (1991)

Answer 5

= Found fewer balanced trees than expected by chance
= Found more imbalanced trees than expected by chance

Question 6

Does clade age (i.e. time for diversification) explain species richness patterns across taxa?

Answer 6

• Would assume that there would be a positive relationship between clade age and species richness
• But, (Rabosky et al. 2012) found that clade age and species richness are uncorrelated across 1,397 clades of multicellular eukaryotes
  = no relationship between clade age and species richness

Question 7

What is Net diversification rate (R)

Answer 7

Net rate of species accumulation

Question 8

Fill in the blank

The Tree of life is more ———– than expected by chance

Answer 8

Imbalanced

Question 9

What can be used to estimate diversification rates?

Answer 9

Dated phylogenies and Linage Through Time (LTT) plots

Question 10

What is a strong predictor of species richness across the Tree of Life?

Answer 10

Net diversification rate

Question 11

What is the equation for Net diversification rate (R)?

Answer 11