Ch. 15 Flashcards
Hutchinson’s view: ecology…
provides the selective environment within which evolution acts.
At the time ecologists viewed evolutionary processes occurring over long time periods and
thus contemporary evolution could not influence population dynamics or outcomes.
We now know that this isn’t entirely true for two reasons:
Evolution can occur over very short time scales.
High degree of interplay between ecological and evolutionary forces that result in
eco-evolutionary feedbacks.
community phylogenetics:
a field that examines community ecology
from a phylogenetic perspective.
What is an eco-evolutionary dynamic?
“The cyclical interaction between ecology and evolution such that changes in ecological
interactions drive evolutionary change in organismal traits that, in turn, alter the form of
ecological interactions.”
Theory suggest that alterations in prey vulnerability will affect
predator-prey interactions
and cycling.
Trade-offs may occur that may also influence predator-prey cycling. ex.?
If a trait reduces vulnerability to predation, it might come at a cost of reduced population growth
for prey populations.
Hairston et al.
developed an experimental system to test this idea ( trade offs of trait and populaiton size) using
freshwater plankton.
Phytoplankton can evolve traits that reduce their susceptibility to
predation by zooplankton such as:
Spines, toxic chemicals, gelatinous coatings, increased size
Chlamydomonas ( Plankton) with trait trade offs
usually is biflagellated, but when zooplankton
populations are present in high quantities Chlamydomonas can clump
into colonies (unflagellated) and become too large for rotifers to eat
There is a cost though, clumping Chlamydomonas has a lower resource
competitive ability when compared to bilagellated Chlamydomonas.
If low genetic diversity started in the population….
if high genetic diversity oscillatory dynamics resulted
with dominant algal genotypes….
If low genetic diversity started in the population, there was directional selection towards one,
moderately well-defended genotypes;
if high genetic diversity oscillatory dynamics resulted
with dominant algal genotypes alternative over time between well-defended large colonies
and small colonies or single cells.
phylogeny.
We can examine evolutionary (historical) relationships between extant species by creating a phylogeny
A phylogeny describes the hypothesized pattern of evolutionary relationships among a set of
organisms.
phylogeny or phylogenetic trees infer evolutionary relationships based on
descent from a common ancestor.
A phylogenetic node represents a
a taxonomic unit
terminal nodes vs internal nodes
terminal nodes are existing taxa, internal nodes
represent shared ancestors.
branch length could have no meaning or represent
amount of time diverged between species (molecular
clocks),
A monophyletic lineage is one that includes
one common ancestor and all of its descendants
and that entire group is called a clade.
phylogenetic outgroup
a distantly related taxon – this helps to establish the group’s
common ancestor or root)
Two species that originate from the same ancestor are called
sister taxa
Phylogenetic effects
strong phenotypic similarity among closely related species.
The competitive-relatedness hypothesis or phylogenetic limiting similarity hypothesis
If species with similar traits, use similar resources, and in similar habitats then one would
expect to observe strong interspecific competition and this would lead to very few similar
species inhabiting one ecosystem.
Alternatively, species might be ecologically limited to specific sets of characteristics and as
a result might undergo
habitat filtering
habitat filtering,
more
similar species inhabiting particular communities than by chance.
Phylogenetic Overdispersion
If strong interspecific competition
determines species coexistence
Species are more evenly dispersed in
phylogenetic space than would occur by
chance
This data would support the
competitive-relatedness
hypothesis/phylogenetic limiting similarity
hypothesis
Phylogenetic Clustering
Closely related species share similar
environmental requirements
Communities contain more closely related
species than would occur by chance
This data would support the habitat filtering
hypothesis
Conserved =
= traits that are
ancestral in origin
Convergent =
traits that are similar due to similar
environmental circumstances.
ARE CLOSER RELATED
SPECIES STRONGER COMPETITORS?
Tests of the competitive-relatedness hypothesis have yielded mixed results.
Few direct tests of the assumption that closely related species are stronger competitors than
distantly related species.
DOES PHYLOGENETIC
OVERDISPERSION OCCUR?
Significant phylogenetic overdispersion is rare, which is surprising given the strong effects
of interspecific competition.
But, an interesting result: Graham et al. (2009) analyzed spatial distribution of communities
that fell in the top 10th percent for dispersion vs. the lowest 10th percent (clumped).
where did Graham find phylogenetically dispersed and cluster communites
Graham et al. (2009) found that phylogenetically dispersed communities were found in most
lowlands; phylogenetically clustering occurred in harsh environments.
harsh environments =
stronger environmental filter = phylogenetic clustering.
the first person to draw a phylogenetic tree
Darwin - on the orgin of species
The competitive-relatedness hypothesis or phylogenetic limiting similarity hypothesis
predicts
strong interspecific competition and high overdispersion of highly related species.
The habitat filtering hypothesis or phylogenetic clustering hypothesis predicts
that
closely related species would be clustered due to sharing similar environmental
requirements.
The evidence for competitive-relatedness hypothesis is
MIXED
there is strong evidence
for
habitat filtering particularly in harsh environments.
