Transcript Introduction, Consequences of being a plant

03-55-468 – Plant Ecology
Basic Information:
Lectures MWF
Labs
W
11:30 – 12:20
2:30 – 5:20
Room 2126 Erie Hall
Room 322 Biology
Professor
Dr. I. Michael Weis
Office
Room 202 Biology
Contact information
Email: [email protected]
Office phone: x2724
Office Hours:
To be determined (T/Th afternoons are initially likely). Electronic
communications will almost always be answered within 24 hours.
Text: Gurevich, J., S.M. Scheiner and G.A. Fox. 2006. The Ecology of Plants. 2nd ed.
Sinauer Assoc., Sunderland, MA.
Grade Components:
Proportion of final grade
Midterm exam (TBA)
Lab/discussion participation
Term paper
November 30
Final exam
December 16, 2011
30%
5%
25%
due
40%
Final grade assignment, drawn from scores on these
components and weighted as indicated, will use the
university conversion scheme to code letter grades from
final numeric grades, e.g. 70.0 – 72.99 = B-, 73.0 –
76.99 = B, 77.0 – 79.99 = B+.
Marking and Exam Policy:
Late submission of the term paper will be penalized 5%
per calendar day
Make-up examinations will only be conducted for valid
and documented medical reasons, or for faith-based
conflicts.
Application for Aegrotat standing (marks appeal,
missed examination) must be made to the Associate
Dean of Science ASAP after the occurrence.
Application for examination exemption for faith-conflict
reasons must be made to the Registrar, within 4 weeks
following commencement of classes.
Date
Sept. 9
Sept.
Sept.
Sept.
Sept.
Sept.
Sept.
Oct.
Oct.
Oct.
Oct.
Oct. 10
Oct.
Oct.
Oct.
Oct.
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Oct.
Lecture Subject
Associated text chapter(s)
Introduction, Consequences of being a plant
Chapter 1
Photosynthesis and alternate pathways
Evolution of alternate pathways
Chapter 2
Water relations
Chapter 3
Energy balance
Soil relations
Chapter 4
Population growth and demography
Chapter 5
Matrix methods in demography
Variation and evolution
Chapter 6
Mechanisms in variability
Heritability
Mutation and selection and breeding systems
Chapter 8
Life history strategies cont.:
selfing and self-incompatibility
Chapter 8
Seed and pollen dispersal
Chapter 7
Catch up
Thanksgiving
Catch up
Evolution of life histories
Evolution of life histories: fixing the theory
Exceptions prove the rules
Community Ecology
Chapter 9
Diversity – measures and approaches
Chapter 13
Nov.
Nov.
Nov.
Competition: First look
Competition cont.
Plant defenses against herbivory
We’ll see how fast we get to this point, then adjust
Chapter 10 pp.226-242
Chapter 11 pp.258-273
The first step is to define the outlines of the subject.
You know what a plant is.
Review: a population is a group of individuals belonging
to the same species and living in ‘close enough
proximity’ to make the potential for interbreeding high.
Every population has structure. That structure will be
critical in most of what we examine in this course.
There are a number of components to that structure:
genetic structure: gene frequency and
genotypes
spatial structure: variation in density within a
population
age structure: numbers distribution of different
age classes
size structure: relative distribution of large and
small individuals
How do we examine the structure:
Genetic structure - evolution examines changes in
genetic makeup that occur over time. Various
molecular techniques provide the tools.
Spatial structure – distribution and density variation are
studied by field sampling and mapping.
Age structure – is the basic information for
demography, the age structure and size of
different age classes. Mathematical tools can
then project population size and age structure into
the future.
Size structure – in population biology we examine
interactions within and among populations.
Size is a key factor in the interactions.
Finally, it is also important to note what makes plant
population biology different from that for animals.
Animals are mostly (exceptions being organisms like
coelenterates that are colonial) unitary organisms,
surviving and growing as integrated wholes. Plants are
metameric, comprised of repeating modules.
Therefore, there is an important dynamics of metamers,
as well as individuals.
Following the order in the text –
Demography - is the key to understanding population
dynamics. The first step is understanding what
processes affect population size.
If a population begins at time t at a size Nt, then the
population size one time unit later is:
Nt+1 = Nt + B – D + I – E
B is births over the time interval
D is deaths
I is immigrations
E is emigrations
All of these factors are important in the local dynamics of
plants.
Immigration and emigration are normally disregarded in
animal population dynamics, but plants disperse their
offspring (seeds) more or less widely, and seeds from
other areas disperse into the area more or less
frequently. Immigration and emigration are important.
The presence of particular alleles may affect the
dynamics of populations at different latitudes or in
different climatic zones…
The figures show the change in
allele frequency of acid
phosphatase in Picea abies
(Norway spruce) with latitude in
northern Europe in the top part and
with altitude in the Austrian Alps
the middle figure.
Correlation between allele
frequency and distribution do not
necessarily mean these alleles are
the causes of the distribution.
They do indicate environmental
differences in fitness associated
with APH alleles.
Palynology (study of the pollen
record found in deposited
sediment) can reveal the history of
a species’ distribution, as in (a) at
right:
Neutral genetic markers can
assess how a distribution arises.
In Picea abies two sources of
post-glacial spread have distinct
chloroplast markers that permit
study of how the current
distribution arose. This type of
study is called phylogeography.
Fitness and natural selection – with genetic structure
now clearly important to local demography, how do we
assess fitness and the occurrence of natural selection?
The genetic structure of a population is influenced by:
gene flow: changes in allele frequency caused by
migration
natural selection: Natural selection occurs when:
1. there is variation among individuals
2. the variation is heritable, and
3. there are fitness differences among
variants
What is fitness?
Fitness is the relative contribution of a genotype or
phenotype to the next generation. It is traditionally given
the symbol w (or W), but is measured by the finite rate of
increase, , for some particular phenotype versus
another. Generally, we set the fitness of the ‘adapted’
type to 1, and those for other phenotypes are <1.
We measure the  for each allele separately. The
relative values, determined by the separate values for
Nt+1, are the measure of fitness.
Looking back at APH in Norway spruce, in southern
Scandinavia and at low elevation in the Alps the WL is 1,
and the allele common at high elevation has a WH < 1.
Selection can produce local changes in members
of the same population.
Eg. The annual Veronica peregrina that grow in and around
vernal pools in the Central Valley of California
• Plants in the centre differ
from those in the periphery,
and are more tolerant of
flooding
• They are also tolerant of
intense intraspecific
competition and complete
their life cycle more rapidly.
• Plants in the periphery
have different
adaptations to cope
with competition with
grasses.
Life tables and age dependence
Both the probability of survival (or mortality) and the
likelihood of reproduction change with age. A life table is
the catalog of a cohort from birth to death.
This is the same data an insurance company uses to
figure out the premiums to charge for life insurance. Life
styles and environment influence human life tables.
Environment, phenotype, and other factors also
influence plant life tables.
In plants (more than in animals) phenotypic expression
is influenced by the environment. The variation is called
phenotypic plasticity. Identical alleles and genotype
may appear (and function) differently in different
environments.
When events in the life of a plant population occur as a
fixed program with respect to age, a life table and the
calculations that can be drawn from it can provide good
estimates of what the population will look like (age
structure, population size) in future generations.
However, many plant species survive and reproduce
according to schedules determined by individual size.
When age alone determines the survival and
reproduction, this is the life cycle graph that describes it:
When, in species like teasel (Dipsacus sylvestris), it isn’t
age, but stage determined by the diameter of a rosette
of leaves, the life cycle is called stage dependent, and
the life cycle graph looks like this:
In reality, however, the life cycle graph for teasel is more
complicated. Rapid growth may lead to one or more
stages being ‘skipped’. In other cases there may even
be backward movement (loss of size). Here is the real
life cycle graph for teasel – stage classified but complex:
Meristems and metamerism
Plant growth occurs in and from specific places called
meristems. Meristems occur in multiple places – typically
at the apices of shoots, in the axils of leaves, in buds, at
the tips of roots, and in the cambium of woody plants.
The meristematic cells are, initially at least,
undifferentiated.
There are both primary and secondary meristems.
Secondary meristems arise in flowering plants from cells
that have suspended division, then later resume.
The architecture of a plant results from the positions of
meristems. Because there are many, plant growth is
sometimes called modular construction, or
metamerism.
A bud that produces a shoot usually multiplies its
meristems, since each shoot develops its own
meristems.
If the bud develops into a flower (or an entire
inflorescence), the meristem is “used up”, and further
growth, at least along this axis, ceases.
Think of a grass. The growth meristems are at ground
level. But the flowering of a stem
(a tiller) results in the death of that
tiller. Others may develop from the
ground level meristem or from
meristems along rhizomes, so that
the genetic individual (the genet)
survives into subsequent years.
The tiller (a ramet) dies.
Meristems along roots, runners and rhizomes make
clonal growth possible, not just in many grasses, but
also in plants like the goldenrod Solidago canadensis.
Clonal plants can spread through stolons (aboveground creeping stems), rhizomes (below-ground
creeping stems), tubers (potato), bulbs (tulip or onion),
or corms (crocus).
Clonal growth makes it
possible for a genet to spread.
Connections among ramets
may be short-lived, or longlived. One text claims the
largest ‘tree’ on earth is a
clone of a banyan tree that is
>200 years old, has >1000
connected trunks, and covers
>1.5 ha.
Behaviour
You probably think of plants as sessile and passive.
Plants do respond to environmental conditions with
various responses that can only be called ‘behaviours’.
Many plants are ‘sun-followers’ – they re-orient
themselves throughout the day to point towards the sun.
Properly this is called heliotropism.
Plants also respond to their light environment by altered
growth. In low light, many plants etiolate, elongate the
length of shoot (or stolon) between nodes. If stolons
elongate, the genet is, in effect, moving until it enters a
‘better’ light environment. They also modify the sizes of
leaves.
The tropical liana, Ipomoea phillomega modifies
internode length and leaf size in response to the light
environment.
Lines are stolons, circles represent places where the
liana has ascending shoots. At straight ends the liana
has lost its meristem. Ys indicate continuing growth.
Note the number of stolons that have reached the
clearing and grow vertically with larger leaves
Other plants, like railroad vine and sagebrush, similarly
have mobility, even though it is slower and not much like
animal mobility.
Plant defenses
Collectively, plants have many types of defenses. There
are also many ways to classify them. My approach:
Chemical defenses – toxins, digestive inhibitors,
hormone analogues
Structural – hooks, prickles, spines, toughened layers
Apparance and distribution – potential herbivores and
predators must find plants.
Dispersal – seeds leave the region of the parent
Structural defenses:
Chemical defenses
Toxin-based defenses generally involve no more than
one or two-step modifications of normal metabolic
processes to produce defensive chemicals.
Among the chemicals are: glycosides – cyanogenic (link
cyanide to a sugar. Digestive enzymes break the link
and release the poisonous cyanide), cardiac (e.g.
milkweed leaves contain a cardenolide glycoside
Also various neuro- and neuromuscular toxins, e.g.
Alkaloids, amine-containing molecules (the diagram is of
ephedrine) usually derived as secondary products of
amino acid metabolism.
Some alkaloids are viciously poisonous, like coniine
from hemlock that killed Socrates or strychnine that
blocks neuron chloride
channels (from
Strychnos nox-vomica
Strychnos spp.),
and curare, that blocks acetylcholine receptors on postsynaptic nerve and muscle cells. Curare is really a
group of toxins from Strychnos toxifera and
Chondrodendron tomentosum. Synthetic curares are
now used as anaesthetics.
Hormone analogues – Some plants modify hormones to
structures that mimic insect hormones (and were the
original source of human birth control pills). They are
“devious” – some mimic insect juvenile hormone. The
immature insect, feeding on a plant, is continuously
signaled not to go through a molt to mature and
become capable of reproduction. Others mimic molting
hormone. The insect is signaled to molt prematurely,
fails to grow, and may molt to mature body plan without
sufficient resources to reproduce.
Digestive inhibitors
Tannins and phenols both bind to proteins and tend to
prevent their digestion by consumers. The amount of
tannin or phenol required can be large. More than 30%
of the dry weight of oak leaves is tannins.
In at least one well documented example insects (locust
species) have evolved the ability to circumvent
inhibition, and digest the tannins as an energy source.
The broad ability is rare. However, it is interesting that
closely related species (e.g. maples, Acer spp.) evolve
to contain different tannins, so that the consumer faces
different detoxification challenges when eating different
species.
Apparance and dispersal
Some plants have critical tissues active only for short
periods, e.g. buds and flowers, or have unpredictable
timing and distribution. Specialist herbivores that could
decimate these tissues (or worse) have trouble finding
them.
Others depend on seed dispersal to escape severe
damage. There are many means to achieve dispersal,
basically separated into passive and active dispersal.
Passive dispersal generally means that seeds are
carried on currents of air or water.
Active means dispersed through the activities of
animals.
Passive:
Active:
By forced expulsion
In the gut
Attached
to fur