Transcript Ecological Issues for Plants

Ecological Issues for Plants
Problems of being a sessile organism.
dispersal
finding a good living space
mating
protection
deal with harsh conditions.
Clue ; look for variety of solutions, and alternative strategies or bet hedging
strategies, – in the same plant
Remember about biological “rules” They apply except when they don’t =
many variables, alternative strategies.
Dispersal
• Why bother? If you are living in a good
place, why not stay there??
Conditions change = disease, fire, flood
Spread to new areas
Get offspring best chance of survival = find a good habitat away from parent.
Use of seeds for Dispersal
Options:
• choice between large and small which is available to an annual vs a
perennial plant?
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Choice of how many seeds –
annual vs perennial
In all cases, have seed designed to
germinate only when conditions
are good. What are the problems
of waiting?? Large seeds vs small?
dispersal
Use of wind
no choice about where seed goes
must be small seed – light weight
not much nutrient
So need to make lots of seeds –
guarantee that some find a good area.
Who uses this strategy??
Annuals, ferns (use spores, not seeds)
In what environments should it work best?? (where are randomly
placed seeds most likely to survive?? Where is their no choice???
Ways to use fewer seeds.
Get them further away or to a good place.
Animal transport: cocklebur – stick in fur of passing animal
Bigger seed; still no control over
where it goes – need a lot, but can
store more energy in seed.
Coconut – large seed – floats, water
dispersal from beach
Fewer seeds, lots of energy storage
Will land on a beach
Seychelles Island Palm nut
Fruits: get someone to eat the seed – carry it
elsewhere, and deposit in dung (fertilizer)
Get dispersal, get fertilizer. Still no guarantee of
where it will go
And must make fruit – fewer seeds and more
energy per seed
Seed disperser
For large tropical seeds
What happens when disperser
Dies out??
Finding a good place to live
How to guarantee seeds get to a good spot.
1. long lasting seeds – can wait to germinate
until conditions are good
2. Lots of seeds – heavy loss.
3. Pass through a gut as seed – get
deposited with dung (manure)
4. Growth variation – stem vs leaves in case
of shade.
Bet hedging strategies in reproduction
1. Can always reproduce by a clone - aspen groves
Aspen; each grove changes
color simultaneously, why?
All same clone, same genes.
Problems: if a fire??
Won’t work in tropics. Why?
Mating in plants
• primitive – motile sperm, advanced, pollen
•
dependent on wind or luck to find female; need
lots of them
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Advanced - use a flower
bet hedging = clone or self pollinate
can still, in some cases use wind
but can use insects, birds, etc. to carry pollen to
another flower.
• Allows for production of less pollen – more efficient
transfer.
Pollination: how to play the game
alternatives.
Some flowering plants have
reverted to use of wind. Flowers
very minimal
Ultraviolet patterns (right) that insects can see.
Red trumpet shaped flowers designed for hummingbirds.
Tropical Heliconia – flower designed to match hermit (hummingbird) bill
shape.
CP51: Perhaps the most
striking of all orchid flower
mimics are the Ophrys family
members that grow in Europe.
This specimen from Turkey
has flowers whose lips look
like the abdomen of a female
bee. The male bee's energetic
efforts to mate with it scatters
the pollen everywhere. The
orchid gets pollinated and the
frustrated bee gets nothing.
Natural selection has molded the flowers of
these orchids (many in the genus Ophyrys)
into mimics of the insects that pollinate
them. Horny male insects, thinking that the
petals are a female, land on them and
engage in fruitless attempts to copulate
(“pseudocopulation”). During the barren act,
the insects’ heads or bodies contact the
orchids’ pollen sacs, which break off and
attach to the insect. The frustrated insect
flies off, but soon tries to copulate with
another orchid, which puts the hitchhiking
pollen in contact with the new orchid’s
stigma. In such a way the bees/wasps
serve as “flying penises,” helping the
orchids have sex. Here are some
specimens:
Ophyrys insectifera (fly orchid), which deceives male digger
wasps.
Meat smelling flower – attracts flies
as if to carrion – a specialty
pollinator.
When is the best time to flower??
in desert?? In tropics??
What determines flowering time in the desert??, in temperate region?
The economics of flowering
Desert: must be synchronous of all annuals – after rain or after winter.
= lots of competition for insect pollinators = buyers market
big reward to attract a few insects.
Plant choices:
big showy flowers, lots of nectar
So how come some desert plants have tiny flowers??
or don’t play the game – use wind pollination or self pollination
When should you flower in the tropics?? When can you flower?
Flowering times of 41 tropical trees;
If you want to cross pollinate – and there are few trees, and no
change in day length (seasonality) how do you synchronize flowering
time within a species?
Answer – use time of sunset, sun rise.
Top of page
Abstract
In tropical rainforests, 30−65% of tree species grow at densities of less than one
individual per hectare1. At these low population densities, successful cross-pollination
relies on synchronous flowering. In rainforests with low climatic seasonality,
photoperiodic control is the only reliable mechanism for inducing synchronous
flowering2, 3. This poses a problem because there is no variation in day length at the
Equator. Here we propose a new mechanism of photoperiodic timekeeping based on the
perception of variation in sunrise or sunset time, which explains and predicts the
annually repeated, staggered, synchronous and bimodal flowering of many tree species
in Amazonian rainforests near the Equator.
In tropics – conditions always good, so can flower at any time
No synchrony ; sellers market – one seller, lots of buyers
so small reward = low nectar, etc. to attract insects.
Flowering of annual vs perennial
Which has the biggest flowers – all things being equal?
Wind vs insect pollination; which has the biggest flowers?
Why are there exceptions??
Tiny flowers of grass (use wind)
And some trees (use wind)
Protection
How does a plant protect itself from being eaten??
Fence off the enemy – plant galls.
Develop poisons in tissue; most efficient way – only in response to injury
Out grow whoever is eating you. – new leaves
Mechanical devices; thorns, etc.
Find bodyguards – ants and acacia
Oak galls – wasp egg in oak walled off by gall.
ocotillo
Madagascar thorn forest
Madagascar thorn forest when wet
Madagascar elephant bird; extinct soon after humans arrived
about 1000 ad
Acacia tree with ants and hollow spine homes for them.
Harsh conditions
Mostly a perennial problem
Dry – store water, loose surface area when dry – cactus, etc.
chlorophyl in stem – palo verde
Need to protect self (and water supply) = cactus thorns, poisons, etc.
Local coastal sage
Size of leaves compared
to well watered area
Waxiness of leaves
Deciduous leaves.
All reasons for fire danger.
Many mosses can grow in desert conditions because they can dry up and
then, when water returns, expand their cells again.
Other harsh conditions
Cold: avoid it (annuals)
: low surface area, no freezing
: oils to avoid freezing
Salt: adapt
Pickleweed – salt tolerant
Human caused problems for plants
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Fire ( frequency)
Water supply
lowering of water table in Arizona
Diseases
dutch elm disease
new insects.
New Competators
Fire: if an area regularly burns, all plants
living there have a way of surviving.
- annuals as seeds
- perennials – resistant bark
- underground storage roots.
Number of fires has gone down
But severity of fires has gone up.
Reason: wood is a resource to be protected = prevent fires
Get fuel build up – now fires more severe that before.
Frequent fires keep fuel from building up – get rid of small plants, fire burns on
ground and does not crown (get to top of trees)
Natural forest
Widely spaced trees,
older trees. Ground fire
cannot reach branches.
If fuel buildup – trees burn –
If frequent fires – forest becomes
grassland
Local chaparral after fire; everything burns. If too hot,
sterilizes the ground.
In deserts, little soil moisture.
Plants must reach ground water for
supply. How deep is it??
Ground water use.
No rules about saving
any for organisms.
Western U.S.; less rain = more use of ground water, especially in
southwest.
Result: streams dry up, ground water is deeper – new seedlings cant reach it.
Desertification.
Result of lowering water table
Winners: annual plants and drought resistant (cactus)
Losers: trees and perennials
So savannas and dry area forests slowly turn into grasslands.
Arizona desert community – lots of perennials, can reach ground water
Arizona grasslands; annuals replace perennials when water table drops
Plant diseases - introduced
• Movement of plants from other continents
– brings diseases never seen before by
native plants.
• These diseases are in closely related
plants and can infect our plants.
Dutch elm disease in the U.S.
A fungus spread by bark beetles.
Even as a kid, there was something about the story of the American
Chestnut tree that made me yearn for a past I never knew. The blight
first appeared in Brooklyn in 1904, and within 50 years they were gone.
Millions of trees stretching from New England to Georgia, along the
spine of the Appalachians, spilling across the Great Lakes into Ontario,
and along the Ohio Valley, gone. Mere ghost trees, whose trunks still
exist, stumps ten foot in diameter, slowly succumbing to rot over
generations.
The Passenger Pigeon, once probably the most numerous bird on the
planet, made its home in the billion or so acres of primary forest that once
covered North America east of the Rocky Mountains. Their flocks, a mile
wide and up to 300 miles long, were so dense that they darkened the sky for
hours and days as the flock passed overhead. Population estimates from
the 19th century ranged from 1 billion to close to 4 billion individuals. Total
populations may have reached 5 billion individuals and comprised up to 40%
of the total number of birds in North America (Schorger 1995). This may be
the only species for which the exact time of extinction is known.
Chestnut blight; killed American chestnut.
Chinese resistant.
Another fungus
Red Gum eucalyptus – CMC campus
Lerps = an infectious aphid like organism (psyllid), finally arrived in California
from Australia
Lerps suck out plant juice – kill leaves, tree gets sick and less resistant to
disease as no leaves for photosynthesis.
Solution: bring in a parasitic wasp from
Australia to kill the lerps
Or ignore it. Why?
Native grassland is
mostly bunchgrass
European grasses and weeds grow faster = 50% + of ground cover
Ok to farmer because its edible