Download Ecological evolution

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Evolutionary Ecology
Evolutionary Ecology
•  In what ways do plants adapt to
their environment?
•  Natural selection is a constant
•  Individuals are continuously challenged by
their environment
•  Populations are constantly undergoing
selection (directional, stabilizing, divergent)
Perspective on evolution
•  Tendency to think of evolution as
phylogenies and speciation
•  Considerable selection without speciation
Ecological Selec+on Alterna+ve phenotypes Alterna+ve species Alterna+ve life histories, physiology, life form Differen+al Performance Individuals and their environment
Light and temperature
? Wind, fire, damage
Neighbors and their impact
on resources
Mutualists involved in reproduction or dispersal
Herbivores and
pathogens
Other conspecifics for reproduction
Differen+al Fitness Soil moisture patterns and Soil geology and chemistry
Mineral nutrients
Soil mutualists and action of soil
organisms on mineral cycling
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Selection->Differential Success
•  ‘Selection’ is a concept incorporating the
probabilistic success of individuals or
populations in a given environment
•  ‘Success’ refers to survival and reproduction
Geographic differences in coevolution:
example of an invasive species,
Centaurea diffusa
This native of central Eurasia
was introduced to western North
America. It associates with similar plants
in both places (genera).
In central Eurasia this is a
relatively uncommon plant.
But in North America this has
become a terrible invasive.
Root exudates directly affect neighbors, and
directly affect soil microbes and mycorrhizae,
influencing NAm native hosts
Selection on Centaurea
•  In North America, Centaurea was selected
to produce more root exudates
More exudate in N. Am.
More invasion w/ N. Am. Natives & soil
Phenotypes with differen+al rates of exudate produc+on Centaurea evolved in the context of
new plants and soil organisms
•  The changes in Centaurea increased the
success of its populations Differen+al Fitness of those phenotypes 2
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Diffuse reciprocal evolution of the
physiology of plants and soil
organisms to each other
•  The Centaurea example also shows that
local communities may reciprocally evolve
tolerances to each other’s impact on the
environment (in this case chemical root
exudates)
Selection->Differential Success
•  For example, a population adapted to an
unusual soil type that contains toxic metals
should differentially be successful (compared
to other non-adapted populations): –  Invading and establishing on those soils –  Reproducing and maintaining populations on
those soils
While many of these
species are restricted to
serpentine, others are
not and represent
populations that have
adapted to this soil.
Arctostaphylos montana
Calamagrostis ophitidis
Serpentine soils act as an environmental constraint to plants
because of their low N & P and high heavy metal %. These soils,
therefore, “select” from available species, those that can tolerate
their conditions.
The Pygmy Pine forest occurs on very acidic soils that are
low in nutrients, with a clay pan beneath the surface. A
number of species are found only in these soils.
Calachortus uniflorus
Organisms can act as agents of
ecological selection, as in the trees
invading a chaparral area, shading
out the shrubs.
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In some cases,
ecological
evolution refers
to specific cases
of speciation or
patterns of
evolution within
a population.
Selection can be positive as well. The Douglas-fir above invaded shrubs
that share the same mutualist fungi for mycorrhizae.
Arctostaphylos gabilanensis is
adapted to a habitat
intermediate between its two
ancestral parents, A. glauca
and A. luciana.
Adaptation
•  Adaptation is a change in the characteristics of a
population that leads to higher probabilities of
survival and reproduction
Dimensions of Adapting
•  Physiologically
–  Shifts in aspects of metabolism, biochemistry,
or sensitivity to environmental conditions
•  Structurally
–  Size and shapes of leaves, density of wood,
aspects of flower size, color or display, size of
plant or location of buds
•  Life History variations
–  Relative proportion of life span spent in one
stage or another
•  Physiology
•  Life form/
Structure
•  Life History
These are not independent categories
because plants are integrated organisms.
Keep that in mind even while we focus
on these independently.
But they are the sources of
differential responses
1. Physiological Adaptations
•  Qualitatively –  (as in C3 vs C4 vs CAM PS)
•  Quantitatively –  (as in shade vs sun-adapted leaves = shifts in
proportions of light reactions vs dark reactions
Plants are a world of hormone gradients, each hormone
influenced by different factors, such as light, mineral
status, temperature, drought, daylength, damage. Plants
are constantly responding to their world in this way.
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2. Structurally
•  Variation in shape/thickness of leaves
•  Variation in density of wood in trees
•  Variation in life form (annuals vs
perennials; tree vs shrubs; deciduous vs
evergreen)
Long-term, this is a sorting process of the
habitat. Short-term, as plants develop,
structurally each node/internode/leaf unit
adjusts to their local environment.
3. Life Histories
•  Life history is the different stages of
development of individuals
•  Because life history patterns involve
multiple generations, these usually reflect
long-term selective forces on populations
Adaptation
•  Different components of fitness may be under
conflicting selective pressures •  Resolution of compromises in the allocation of
energy and materials to competing demands
means more than one ‘solution’ exists for any
environment
Contrast Annuals vs Perennials
•  Perennial life histories are favored by high
and relatively constant adult survival
•  Annual life histories are favored by high
fecundity and habitats in which adult
survival is difficult or seedling
establishment rates can be high
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Interactive nature of Life Histories usually
yields collections of adaptations selected to be
synergistic with other adaptations.
r-selection and K-selection as an
example
•  These can be thought of as life history
syndromes.
•  Ultimately, think of this as a resolution of
conflicting demands, an allocational tradeoff.
J. P. Grime incorporated R. H.
Whittaker’s ideas about stress-selection
in his R, S, C system
Life History Evolution
•  Stages of a life cycle interact which means
that stage-specific survival will influence
evolution of life history patterns
•  Imagine two populations:
–  adults have high survival rates
–  adults have low survival rates
–  selection will be strongly different on seeds and
juveniles for these two populations
Interaction among Life History Stages
leads to the Principle of Allocation
•  Assume there are finite resources of energy
and materials available to individuals
•  Assume that different stages of life history
sometimes represent competing demands
(e.g. maximizing seed production may
minimize adult survival)
•  Allocation occurs among competing
demands (trade-offs?)
Semelparity (big bang reproduction) vs.
Iteroparity (multiple reproductive cycles)
•  If seedling establishment has a low
probability while adult survival is high, then
slow frequent reproduction may be favored.
•  If seed establishment has a high probability
while adult survival is low, then “big-bang”
reproduction may be favored.
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Other examples of ‘trade-offs’
Patterns observed among plants:
•  Seed size vs seed number
•  Increasing seed size may reduce the time
from seedling to reproduction (and the
reverse).
•  Increasing seed # comes at the expense of
reducing or parental survival
•  trade-offs between growth rate and shade
tolerance
•  trade-offs between seed number and seed size
•  monocarpic (semelparous) vs polycarpic
(iteroparous) reproduction
•  wood density (strength) increases at a cost to
growth rates
•  chemical defenses to herbivory can be produced at
a cost to growth rates
What patterns do assemblages
display?
•  Do all species at a site have the same life
form, physiology, life histories?
•  At the other extreme, are life histories or
life forms randomly dispersed across a
landscape?
Conclusions
1.  Natural selection constantly impacts ecological
systems
2.  Sorting occurs at the scale of individuals,
populations and communities
3.  Organisms are selected by differential fitness
Conclusions
4. Different components of fitness may be under
conflicting selective pressures
5. Resolution of compromises (trade-offs) means
more than one ‘solution’ exists for any
circumstance
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