BIOL LECT 12

Large-scale evolutionary change; evolution at or above the level of species

macroevolution

large-scale patterns of evolution

stasis & gradualism

(patterns of evolution)

• the fossil records should consist of a long sequence of continuous & intermediate forms linking ancestors and descendants

• morphological gaps are due to imperfections in the geological records

gradual

(patterns of evolution)

• species arise by splitting

• new species develop rapidly, especially on geological time scales

• a small subpopulation of the ancestral form gives rise to the new species

• the new species originates in very small part of the ancestral species’ geographic extent- in an isolated area at the periphery of the range

• The fossil record should consist of a sharp morphological break between species (punctuation)

• Migration of the descendant from the peripherally isolated area into its ancestral range

• Rarely discover the actual event of speciation in the fossil record

• Many morphological breaks in the fossil record are real

stasis

evolution of morphological diversity occurs during speciation, with periods of stasis in between

punctuated equilibrium

stasis is __ change and introduces diversity

no morphological

in stasis, organisms look __ after long time

identical

rapid burst of morphological or ecological diversity

evolutionary radiation

(triggers evolutionary radiation)

• unfilled or vacated ecological niches

• unoccupied niche with few competitors + lots of resources to exploit

• removal of competitors or predators = open ecological resources

• affects many independent species in the ecosystem

ecological opportunity

(triggers evolutionary radiation)

• evolution of highly beneficial adaptation

• exploit a new resource or ecological niche (e.g., aerial nocturnal insectivore)

• possibly an evolutionary response to competition with other species

• affects a single clade, often referred to as adaptive radiation

key innovation

the process by which the number of species in a lineage changes

lineage diversification

the birth of new lineage

speciation (λ)

the death of linages

extinction (μ)

net diversification (r)=

speciation - extinction (λ-μ)

expect initial diversification to be __

fast

measures the relative position of nodes within a phylogeny

gamma statistic (γ)

(measuring diversification)

• balanced node depth

• γ=0

constant-rates model

(measuring diversification)

• excess of old nodes

• γ will be negative

• evidence for adaptive radiation

• skewed to left

early & rapid branching model

(measuring diversification)

• excess of young nodes

• γ will be positive

• skewed to the right

late branching

(Visualizing lineage diversification) accumulation of lineages through time

lineage through time plot (LTT)

the slope of the plot

net diversification

• speciation increases exponentially

• extinction= 0

pure-birth process

• extinction unlikely to affect __ lineage

• __ in diversification towards the present = pull of the present

• old lineage more likely to extinict

• requires fossil records

young, increase