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.

Options:• choice between large and small -

which is available to an annual vs a perennial plant?

• 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?

Use of seeds for Dispersal

dispersalUse 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???

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.

Ways to use fewer seeds. Get them further away or to a good place.

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

• 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

or don’t play the game – use wind pollination or self pollination

So how come some desert plants have tiny flowers??

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.

When should you flower in the tropics?? When can you flower?

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)

ProtectionHow 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

http://www.zooomr.com/photos/shirleytwofeathers/5446188/

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

• 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