31 terms

Macroevolution

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mass extinction
by definition extinction terminates lineages and thus removes unique genetic variation and adaptation but over geological time scales it can reshape the evolutionary landscape in more creative ways via the differential survivorship of lineages and the evolutionary opportunities afforded by the demise of dominant groups and the postextinction sorting of survivors
a mass extinction
refers to the wholescale loss of many group of organisms over a broad geographic range.
ded clade walking
to describe clades that survived a period of mass extinction only to go extinct some time inthe following geological time period
the cretaceous teritiary (K-T) mass extinction
this mass extinction occurred gradually over the course of millions of years likely as a result of gradual changes
permian mass extinction
greatest mass extinction.
the longer a taxon has existed
species longevity had no effect on the probability of extinction how well species in a taxon had adapted in the past was irrelevant to the probability of extinction in the future. that is the biotic and abiotic environments are always changing and extinction is a function of how well individuals in a species adapt to the current environment not how well they adapted to past environmental conditions.
whatever the cause of extinction may be
the wider the geographical range the less likely that species will go extinct
rates and patterns of evolutionary change
phyletic gradualism model =- darwin and that adaptations that arise within a species are the result of a slow gradual process, where any variant that provides the slightest net benefit slowly increases
the theory of phyletic gradualism hypothesized that
new species arise from a gradual transformation of an ancestral species through slow constant change.
cladogenesis
branching speciation events
anagenesis
gradual modification of form over evolutionry time without branching speciation
when the lineage being studied has changed enough
through the slow grdual accumulation of adaptive and nonadaptive changes it is considered a new species. the earlier forms no longer occur in the fossil record and it appears as if this earlier species has gone extinct-pseudoextinction
punctuated equilibrium
major evolutionary changes do not occur through a slow gradual process instead some minor degree is always occuring within this lineages
stasis
the absence of change is the rule during the vast majority of alineage history. when evolutionary change does occur in lineages it is not only rapid but leads to branching speciation cladogenesis. thus periods of rapid morpholoical change coincied with bursts ofc rapid branching speciation
if speciation occurs in small peripheral populations
we are likely to see large scale evolutionary changes arising out of rapid punctuated bursts of change becuae of natural selection combined with drift
Looking over macroevolutionary timescales, evolutionary biologists sometimes
note trend
patterns of directional change over time—in the clades that they are
studying

or example, what is called Cope's rule asserts that species
in mammalian clades tend to increase in body size over evolutionary time

a number
of researchers have argued in favor of a general increase in organismal complexity—
measured in any number of ways—over the history of lif
passive versus active trends
These graphs provide a way to think of change in
a clade over time. The y-axis represents time, while the x-axis represents a character state that we are
interested in—body size, in this example. In each, a species starts at some point in character space, and
over time, evolutionary changes and speciation events lead to increasing diversity in the character states
represented within the clade. (A) Here we have no evolutionary trend. Different lineages diffuse out in
both directions from the original ancestor. (B) Here again there is no directional tendency to the evolution
of any individual lineage, but our precursor species starts at a boundary—a minimum value—beyond
which a lineage cannot go. As a result, all derived lineages have body sizes at least as large, and often
larger, than that of the ancestor. This generates a "passive trend" in which the mean size within the
clade increases over time, even though at any point away from the boundary, the evolutionary process is
equally likely to lead to an increase or a decrease in size. (C) Here we see an active trend, in which each
lineage tends to increase in the character state. Adapted from McShea
active trends can arise from two distinct processes
The
most straightforward is a process by which the distribution of trait values (for
example, size) in a clade shifts because the trait values within each subclade shift
in parallel. Alternatively, the average trait value may increase due to species
selection: speciation and extinction rates that vary according to the value of the
trait in question. For example, if species with larger body size are more likely to
speciate and/or less likely to go extinct, species selection can result in a shift of the
distribution of trait values across specie
the fossil record shows that
many kinds of organisms that were once common no longer exissts
Fossilization is a rare event. Very few, if any, individuals of
most species ever leave remains that become fossilized.
• Species with hard body parts are best preserved Species with hard body parts are best preserved - shells,
plates, bones fossilize well - soft bodied organisms are not
well represented in the fossil record
• Erosion, weathering, metamorphic processes destroy fossils
and have made the fossil record more incomplete - older time
pp p eriods are less well represented than newer time periods
extinctions ar emost easily seen in species that
have restricted distributions endemic species
mass extinction events change diversity
major atmospheric change, volcanic and asteroid related catastrophes causing mass extinctions subsequently promoting species and higher taxa diversity
extinction and origin of species
appear closely related
species selection
some lineages are more successful not all species radiate at the same rate
this may be related to the pattern through anagenesis and cladogenesis
punctuated equilibrium ctd
paleotologist- trained in geology classifying and indexing fcossil stata have one empirical rule, in the fossil record a great majority of species appear suddenly then undergo a period of stasis then they go extinct quite suddenly 3 phases of macro evolution through punctuated equilibrium
using random walk asnul model hunt found that gradual directional chnge
was the best supported model o evolutionary chnge in only 5 percent and 95 git a random walk or stasis this supports a key prediction in punctuated equilibrium
on geological time scales directional evolution is brief, stabilizing selection or
drift is long term.
the analysis begins with the first appearance followed by rapid evolution leading to fluctuations around the optimum

gould and eldrigde suggest that punctuation and stasis depend on the establishment and break down of genetic constraints
ev idence for macroevolutionary change
A. Biogeography (analysis of distribution of organisms on large spatial scales, e.g., globally)
B. Fossil Record
1. Change over long time periods
2. Link to biogeography (e.g., continental drift; marsupial patterns)
3. Most taxa are exinct
C. Comparative Biology
1. Homology: a character shared between two or more species that was present in their common ancestor.
2. Analogy: "shared" character not present in common ancestory (i.e., the character evolved twice, independently): convergent evolution.
macroevolution
is the origin of new taxonomic groups as opposed to microevolution which is genetic variation between generations within a species
two models of macroevolution
The Gradualism model suggests that change is gradual with the accumulation of unique morphological adaptation.

The Punctuated Equilibrium model suggests that rapid change occurs, with a new species "erupting" from the ancestral lineage and then staying the same thereafter.
LTEE figure out if its punctutated or gradual def in final
several hallmarks of macroevolutionary dynamics, including periods of rapid evolution and stasis, altered functional relationships between traits, and concordance of anagenetic and cladogenetic trends. Our results support a Wrightian interpretation, in which chance events (mutation and drift) play an important role in adaptive evolution, as do the complex genetic interactions that underlie the structure of organisms.
LTEE continued
Thus, our experiment
recreates one of the major features taken as evidence for the
theory of punctuated equilibrium. We believe the explanation
for this concordance of anagenetic and cladogenetic rates is
that environmental change (i.e., introduction of the study
organism into the experimental environment) radically perturbed
the adaptive landscape. This perturbation precipitated
rapid adaptive evolution, while diversification resulted from
the stochastic effects of mutation and drift that pushed
replicate populations into the domains of attraction of different
adaptive slopes and fitness peaks
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