EVOLUTION OF BIODIVERSITY Flashcards
Is biodiversity evenly distributed?
No, it varies across the tree of life, in space, and through time.
What methods are used to study diversification patterns?
Fossil data: Reveals long-term patterns but is coarse (families, not species) and incomplete.
Molecular phylogenies: Calibrated with fossil dates to infer diversification.
How do traits affect diversification?
Traits associated with diversification often haven’t evolved enough to clarify their role.
Testing requires independent replicates.
What is a sister clade comparison?
Compares clades sharing a common ancestor.
Focuses on differences that evolved after divergence.
Example: Herbivorous clades are often more species-rich than their sister clades.
Why is a large sample (N) needed?
To identify meaningful associations between traits and diversification rates.
What is the importance of dated phylogenies?
Enables plotting the number of lineages through time.
Observed surviving lineages (N) are usually fewer than the actual lineages.
What is co-speciation?
When two groups (e.g., host and parasite) speciate in tandem due to close ecological or evolutionary relationships.
One species’ divergence drives a corresponding split in the other.
Why does co-speciation occur?
Dependency: A species depends on another for survival.
When the host speciates, the dependent species is affected, leading to parallel diversification.
Examples of co-speciation:
Host-Parasite Systems: Lice diverging alongside bird species.
Plant-Pollinator Relationships: Specific fig trees and their wasp pollinators.
Symbiotic Relationships: Termites and their gut protozoa.
Evidence for co-speciation:
Mirror phylogenies: Similar branching patterns in associated lineages.
Genetic correlation: Parallel evolutionary patterns.
What is the diversification rate (D)?
D = S - E (Speciation rate - Extinction rate).
On a log scale:
Steeper slopes indicate higher diversification rates.
Pull of the present: Reflects the ratio S/E.
Expectation vs. observed lineages:
Expectation: Assumes all species in phylogeny are sampled, with constant speciation/extinction rates.
Observed: Often shows a slowdown in diversification due to limited niches.
What does a constant positive diversification rate imply?
Exponential growth in the number of species.
Do taxa diversify at the same rates?
No, taxa show high variation in diversification rates.
What is the evidence for clade-specific limits?
Many clades show:
Initial burst of diversification.
Later slowdown due to ecological limits.
