Lecture 15 Flashcards
(22 cards)
what is ubiquitous throughout the tree of life?
uneveness in diversity both across groups and across different hierarchies - e.g. 400,000 species of beetles compared to 5,000 species of mammals
what is the definition of phylogenetic tree imbalance?
relative numbers of descendent tips
(usually species) on the branches that originate at the focal node
- maximum imbalance = unequal numbers of descendants on each side of the focal node
- perfect balance = equal numbers of descendants on each side of the focal node
3 reasons why species richness varies
1) chance alone
2) variation in clade age
3) variation in net diversification rate
describe the equal-rates Markov model
- species arise from other species
- probability of speciation per unit time is constant across all linages
- can be extended to include extinction e.g probability of extinction per unit time is also constant across all lineages
are real trees more imbalanced than expected by chance?
- experiment done with data from 120 phylogenies
- found imbalanced trees a more common than expected under the ERM model
- fewer balanced trees than expected by chance
what was the results of the hypothesis about variation in clade age?
- experiment proved clade age and species richness are uncorrelated
what was the results of the hypothesis about variation in net diversification rate?
net diversification rate in a strong predictor of species richness at any taxonomic level across the tree of life
what is net diversification rate?
the net rate of lineage splitting
what is the equation for net diversification?
R = S-E speciation rate (s) - extinction rate (E) (lineage birth rate) - (lineage death rate)
what does it mean if speciation rate is lower than extinction rate?
diversification rate will be negative implying that clades are actually getting smaller
how do you measure net diversification rates?
- make a lineage through time plot (LTT)
- if speciation rate is constant and extinction rate is zero then clade growth is exponential
e. g. Hawaiian silverswords
species traits that may influence diversification rates
- dispersal ability
- range size
- body size
- mutation rate
- sexual selection and conflict
environmental factors that might affect diversification rates
- climate
- habitat heterogeneity
- biogeography
environmental productivity - area
2 species trait/environmental factor affecting diversification rates
- population size
- ecological opportunity
if the probability of extinction and speciation are constant through time then as we approach the present what will happen?
the number of observed extinctions will decline
in the past we observe net diversification what do we observe in the present?
only speciation
how can extinction be calculated?
by comparing the recent slope with the past slope
what is self incompatibility and the advantage of it?
- the ability of hermaphrodites to enforce outcrossing
- avoids inbreeding depression
describe an example of trait dependent diversification
- night shades - large family of flowering plants
- 57% are self - compatible and 41% are self - incompatible
- SI if often lost to become SC (SI can never be regained)
- loss of SI enables self fertilisation
how is the distribution of SI and SC maintained?
by balancing the short term (within species ) advantaged of SC with the long term (between species) advantages of SI
describe speciation, extinction and net diversification rates in SC and SI lineages
speciation and extinction rates are both higher in SC lineages but net diversification is higher in SI lineages
SC lineages are heading towards extinction but why are they maintained?
SC is maintained because SI lineages speciate more often but then transition into SC
