microevoltion Flashcards
whats the rate of evolution
-Steady change over time
-Expected outcome from microevolution
-Does not mean smooth change, but rather the accumulation of small stepwise changes over time
whats the problem with the rate of evolution
-The fossil record generally lacks transitional forms.
-New taxa appear abruptly in the fossil record.
-Major morphological innovations sometimes appear suddenly in the fossil record, often preceded and followed by periods of relative stasis.
Why do we observe apparent bursts of change?
-The fossil record is incomplete- not everything is preserved
-Transitional forms extremely unlikely to be found in the fossil record- because process of fossilisation is complex
Why are there gaps in the fossil record?
-Recall that fossilisation requires:
Death- inevitable
Burial with organism (mostly) intact- rare due to scavenging and decay
Sedimentation- rare in terrestrial environments
Survival of sedimentary rocks- rare, geologic processes repeatedly destroy sedimentary layers
whats punctuated equilibrium with rates of evolution
-Stephen J Gould and Niles Eldredge suggested an alternative model
-They proposed that rates of evolutionary change during and between speciation were different because different processes were at work.
-Proposed that speciation took place in small populations
and that a genetic revolution took place due to a process other than natural selection
-Implies that evolution is fast during speciation and slow between speciation events
-Widely discussed but not fully accepted
-But let’s assume that variation in rate is real, even if not necessarily related to speciation we can flip the question…
-Can selection explain the fastest rates of evolution and the slowest?
-Any explanation needs to be able to cope with:
=Periods of rapid divergence
=Periods of stasis
whats stasis
-no observable change between 2 end points
-Stasis is fully compatible with selection
-If selection pressures do not vary greatly over time, then net change should be minimal
why does Rates of (macro)evolution vary among species
-What if stasis between bursts is not the absence of change but instead the absence of consistent directional change over geological time?
-Recent studies show that rates of evolutionary change are just as high for fossil time series with net stasis as those with net change
patterns of evolution
-With divergent evolution…
lineages split and seperate
-With convergent evolution…
Lineages that are not closely related evolve similar adaptations because they live in similar environments
whats convergent evolution
-Convergent evolution is the process where unrelated or distantly related species independently evolve similar traits as they adapt to similar environments or lifestyles
Anolis ecomorphs
-Six ‘ecomorphs’
-Different microhabitats occupied by different species
-Morphologically & behaviourally distinct
-description of idea that species arise in different micro habitats and morphologies
-Repeated evolution of ecomorphs on different islands - phylogenetically clustered but phenotypically overdispersed (or convergent)
whats historical contingency
-Related species share evolutionary history
-Closely related species tend to be similar
-repeated evolution of ectomorphs and different islands
-phylogenetically clustered but over dispersed and non conserved
whats adaptive radiation
-Adaptive radiation is the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage
-Requires differentiation of a single ancestor into multiple species and…
-variation in morphological traits that allow exploitation of range of environments
What causes adaptive radiation
-Ecological opportunity: many examples of diversification in the apparent absence of ecological (competitive) constraint
what are ecological releases from antagonist
-End Cretaceous extinction of the dinosaurs
-Vacant niches filled by mammals
-mammals diversified over a period of time
hats the Morphological expansion of the Acanthomorpha
-Spiny finned teleost fish (Acanthomorpha)
-Low morphological diversity before the Cretaceous-Palaeogene boundary (blue polygon)
-Extinction of non-Acanthomorph competitors (pink polygon)
-Expansion of morphospace into vacated niches
