Transcript Plant Ecology - Chapter 7

Plant Ecology - Chapter 7
Growth & Reproduction
Plant Growth - Modular
Plant Growth - Modular
Apical meristems
Intercalary
meristems
Axillary meristems
Vascular cambium
Plant Architecture
Raunkaier
classification system
of perennial growth
forms
>25 cm
<25 cm
At ground level
Below ground level
Plant Architecture
Plasticity can
change plant shape
in response to
environmental
conditions
Sun vs. shade
Self-pruning
Clonal Plants
Spatial distribution
of ramets affected
by:
Competition among
genets
Spatial variation in
resource distribution
Clonal Plants
Two growth forms
Phalanx - tightly
grouped advancing
front
Guerilla - isolated
ramets penetrating
competitors’ turf
All in the
perspective
Clonal Plants - Why variation?
Mechanics of clonal
spread
“Foraging” for
resources
Following the
resource distribution
Integration within
clone to minimize
environmental
variation
Vegetative Reproduction
Apomixis general term for
asexual
reproduction
Can take on
many different
forms
Vegetative Reproduction
Stolons - runners
- branches that
spread at surface
of the soil,
generate new
ramets
Vegetative Reproduction
Rhizomes underground
horizontal stems
growing near soil
surface
Many grasses
(like bamboo)
Vegetative Reproduction
Bulbs underground
rosette stems that
store nutrients
Tulips, onions,
daffodils
Vegetative Reproduction
Suckers - bud
formation on
some of nearsurface roots
Quaking aspen
clones can cover
many hectares
Vegetative Reproduction
Clonal
fragmentation pieces break off,
are capable of
rooting to form
new plants
Mother of
thousands
Vegetative Reproduction
Bulbils - bulblike
organs produced
in leaf axils
Seeds Produced Asexually
Agamospermy partial meiosis
without reduction
division - new
embryos are
clones
Seeds Produced Asexually
Grasses,
raspberries,
nettles
Sexual Life Cycles
Alternation of
generations
Gametophyte
Sporophyte
Lower plants gametophyte
dominant
Higher plants sporophyte
dominant
Pollination Ecology
Pollination of typical,
showy flowers done
by birds or insects
But many flowers
not showy, and likely
are pollinated by
wind
Pollination Ecology
Pollen transfer in
most grasses and
temperate-zone
trees is by wind
Human allergies to
pollen (hay fever)
due to huge
amounts of pollen in
air
Pollination Ecology
Wind-pollinated
flowers are not showy
Waste of energy to
produce big, colorful
petals, scents, nectar
Grasses often lack
petals, sepals
(interfere with pollen
transfer by wind)
Pollination Ecology
Wind-pollinated
plants produce
massive quantities
of pollen
Little influence
over where pollen
goes
Pollination Ecology
Wind-pollinated
plants have higher
pollen:ovule ratios
than their animalpollinated relatives
Pollination Ecology
Wind pollination most
common in plants of
open habitats
Usually flower before
leaves emerge in
spring
Also windiest time of
year
Pollen can travel 100s
of miles
Pollination Ecology
Wind pollination might
be evolutionarily
primitive
But wind pollination is
common in both “old”
and “new” taxa
Both can be present
in same group
Visual Displays
Flower shape and
color are
advertisements of the
rewards an animal
can expect to receive
from the flower
But both sides cheat
Visual Displays
Insects usually see
colors at shorter
wavelengths than
humans (e.g.,
ultraviolet)
Birds more sensitive to
colors in middle and red
parts of spectrum
Birds may not see or be
attracted to flowers
bees can see
Visual Displays
Many bee-pollinated
flowers are yellow
Bird-pollinated flowers
often orange or red
Moths: white to pale
yellow
Bats: white to brown
Visual Displays
Some flowers reflect
light in several
different wavelengths
- can be seen by
different pollinators
Contrasting colors
may help guide
pollinator - nectar
guide
Visual Displays
Some plants have
modified other plant
parts to attract
pollinators
Poinsettias - red
bracts, leaves more
attractive than small,
yellow flowers
Visual Displays
Some plants arrange
flowers into various
aggregations inflorescences
Increase the size of
the attractive display
without altering the
flowers themselves
Floral Odors
Scents act as
attractants over
longer distances than
visual attractants
First locate generally
by scent, then locate
specifically by sight
Floral Odors
Odors can vary
independently of
colors
Odors of different
species can be highly
variable, to attract
different pollinators
Floral Odors
Bees attracted to
sweet odors (like we
are)
Bats like musty odors
Flies like rotting flesh
and dung odors
Restricting Visitors
Adaptations to attract
right visitor, repel
unwanted visitors
Change flower shape
from unspecialized bowl
to something else
Only long
tongues/mouthparts can
access rewards
The Reward
Usually nectar
(sugars) or pollen
(protein)
Can also be oils,
scent
Timing of reward
also changeable
(day vs. night)
Nectar robbers
Pollination Syndromes
Certain combinations
of flower color, shape,
odor, reward type,
timing of rewards
often associated with
certain types of
pollinators
Tightly coevolved
mutualisms
Pollination Syndromes
Bee-pollinated flowers
- yellowish, sweetsmelling, broad to
allow bee contact with
anthers, stigma,
produce nectar during
daytime
Pollination Syndromes
Bird-pollinated flowers
- red or orange, little
scent, produce lots of
nectar during the day,
shape with long tubes
or spurs
Pollination Syndromes
Strength, generality of
pollination syndromes
may be overstated
Syndromes are
tendencies rather than
laws
Animals “outside”
syndrome can
accomplish significant
pollination
Pollination Syndromes
Syndromes emphasize
specialist pollinators,
but neglect the
generalist pollinators,
which may be more
important
Complex Interactions!
St. Johnswort on shores
of Florida ponds
Plants growing by fishfree ponds more pollenlimited than those
around fish ponds
Aquatic Pollinators?
Most aquatic plants
bear flowers above
water surface
Plants pollinated by
insects or wind
Aquatic Pollinators?
Large numbers of
aquatic plants have
underwater flowers
One strategy: make
pollen dispersal units
bigger,
disperse/receive at
surface (Vallisneria)
Others: sticky pollen
in rafts, elongated
pollen
Plant Mating Systems
Factors that govern
who can mate with
whom
Many complications
because of widely
varying gender
expression
Plant Mating Systems
Obligatory selffertilization - inbreeding
- individuals can only
pollinate themselves
Outcrossing mechanisms preventing
self-fertilization
Something in between
Gender Issues
Some individual plants are
cosexual - function as
both males and females
simultaneously
Hermaphroditism - most
common type of gender
expression in plants
Individuals have perfect
flowers containing both
functional stamens and
functional stigmas
Monoecy
Individual plants
have some flowers
with functional
stamens only
(staminate flowers)
and some with
functional stigmas
only (pistillate
flowers)
Monoecy
All individuals have
both types of flowers
Monoecy
Dioecy
At least some plants
in a population have
only pistillate or only
staminate flowers
Function as female
only or male only
Mixed gender expression
3 systems of gender
expression can exist
in combination with
one another
E.g., gynomonoecy,
androdioecy
Mixed gender expression
Sequential
hermaphroditism often begin life as
male, then gradually
switch to female
Self-fertilization
Cosexual plants
may or may not be
capable of selffertilization
25% of windpollinated cosexual
plants are mainly
inbreeding remainder strongly
outcrossing
Self-fertilization
Animal-pollinated
cosexual plants
evenly divided
among strongly
inbreeding, strongly
outcrossing, and
mixtures of
inbreeding and
outcrossing
Confusion
Different forms of
gender expression
can occur at same
time within a
population
Difficult to determine
how they actually
function
Competition for Pollinators &
Pollen
Plants produce
excess ovules that
never produce
viable seeds
Competition for
pollinators, pollen?
Too few pollinators,
or very inefficient at
transferring pollen
Sexual Selection
Differential success
at mating among
plants
Male-to-male
competition
Female choice
Sexual Selection
Male-to-male
competition results in
extremes of floral
displays
Large inflorescences
where most flowers
function only to attract
pollinators
Functionally male reproduce only by
having pollen taken
elsewhere
Sexual Selection
Female choice occurs
at site of pollination
Competition among
pollen grains
Female flower
“chooses” pollen via
biochemical interactions
Affect pollen
germination, rate of
pollen tube growth
May selectively abort
certain seeds
Pollen Dispersal
Inbreeding common
in plants
Most matings occur
among neighbors,
which tend to be
relatives
Pollen Dispersal
Animal-pollinated
plants
Plants are clumped,
pollinators don’t
move much
Pollen Dispersal
Wind-pollinated plants
Most pollen grains fall
nearest their source
Plants releasing single
pollen grains most likely
to mate with most
distant individuals
Clumped pollen mating with nearest
neighbors
Assortative Mating
Plants with similar
phenotypes mate with
one another more
often than they would
by chance
Time of flowering,
flower color, influence
the pollinator
Negative Assortative Mating
Plants with dissimilar
phenotypes mate with
one another more
often than they would
by chance
Heterostyly styles/stigmas of
different lengths cause obligate
outcrossing
Fruits and Seeds
Fruit - mature ovary
with seeds - great
variety
Two functions protect developing
seeds, affect
dispersal of seeds
Fruits and Seeds
Compromise between
protecting seeds from
being eaten, and
attracting animal
consumers to aid in
seed dispersal
Fruits and Seeds
Wind dispersal - float,
flutter based on mass,
surface area, shape
Fruits and Seeds
Animal dispersal attract/reward
disperser, but protect
seeds
Thick, hard seed
coats
Spit out, regurgitated,
pass with feces
Seed Banks
Dispersal in time
Seedbank - collection
of seeds in the soil
Short-lived plants
tend to have longlived seeds, and vice
versa