Plant Eco Pollen & Dispersal

Male parts of flowers: stamens, Produce pollen. Made of a filament and an anther (pollen producing part)

Female parts of flowers: pistil, produce seeds. It has three parts, stigma which is the receptive surface. Style which is the tube leading to the ovary. Ovary which is the chamber holding ovule.

Some flowers have male and female parts: bisexual

Some are only male or female, unisexual, staminate or pistillate

Pollination-transfer of pollen grains from anther to a stigma. Can occur without fertilization, since fertilization requires same species

fertilization- union of sperm and egg in plants 

Pollination syndrome: floral characteristics associated with pollination by biotic or abiotic means

Bee-pollinated, bird-pollinated, etc.

Many plant species are wind pollinated 

For example, most grasses

Wind pollination: Small, light pollen grains. Smooth pollen or grains with air compartments. Generally have small flowers and do not have petals for wind pollination.

Wind pollination is unusual in the tropics, too humid and too many leaves. But common in temperate forests. Pollen shed before leaves develop. Pollen timed to avoid rain.

Water pollination is fairly rare but does occur. About 150 angiosperm species, pollen transported above, on, or below water

Species with water pollination may have folamentous pollen. Long stalk.

Also just because a plant grows in the water does not mean it is water pollinated.

Some plants that grow underwater release their male flowers that float. Female flowers rise on long stalks, create depression in water which makes male flowers fall in.

Animal pollination:

Animals often transport pollen more efficently than wind. allows pollination even when there is little wind, and movement between flowers causing cross pollination. Many plant species have coevolved with their pollinators.

Bee pollination: flowers brightly colored, blue or yellow. 

• Uv markings

• Other markings leading bee to nectar 

• Offer nectar and/or pollen reward.

Butterfly pollination: 

• Flowers brightly colored

• may have landing platform

• Nectar reward (nectar spurs)

Moth pollination:

• flowers open at dusk/night

• Sweet odor

• White or pale covered

• Nectar reward

Fly pollination:

• Flowers light colored if they offer nectar reward

• Flowers red, brown or purple If they smell like carrion

Beetle pollination:

• Flowers white or green

• Strong smells, often yeasty, spicy, or fruity

• Nectar or pollen reward

Bird pollination:

• Flowers brightly colored, often red

• No scent

• Tube-shaped petals

• Nectar reward

3/5/25:

Bat Pollination:

• Flowers showy and whitish colored

• Strong musky scent

• Flowers open at night

• Nectar or pollen reward

Non-flying mammals Pollination:

• Flowers dull colored

• Varying scents

• Flowers open at night

• Nectar and pollen reward

• Examples being lemurs or chipmunks.

Pollination can also occur in two different ways:

1. Self-pollination

   1. Advantage: pollen doesn’t have to go far for it to reproduce. Disadvantage: inbreeding, limited gene flow. This leads to reduced fitness due to accumulation of deleterious alleles

2. Cross-pollination

   1. Advantage: Plants have gene flow and reduced risk of inbreeding. Disadvantage, relies on nearby plants

Self-pollination= pollination within an individual plant

Geitonogamy=breeding between flowers from one individual plant

Autogamy=breeding within a single flower

Cleistogamy=flower that never opens; pollination only occurs within a flower, and does not require a pollinator. 

Some plants use both cleistogamy and chasmogamy (flowers that open), and sometimes both types are on the same plant. 

Henbit are an example of this, they can either be cleistogamous or chasmogamous

Many plants avoid self-pollination through spatial separation of gametes, or temporal separation of gametes.

Dioecious plants have unisexual flowers on separate individuals. Each plant is either entirely male or female so cross pollination must occur. 

Monoecious plants have both male and female flowers.

• May be bisexual flowers (hermaphrodite)

• May be unisexual flowers

• Requires a different method to avoid self-pollination, such as temporal separation. 

protogyny=stigmas receptive before pollen shed. 

Protandry=pollen shed before stigmas receptive

Self-incompatibility= inability of bisexual plant to produce zygotes with its own pollen. Genetically controlled by the S gene. Unsuccessful mating when pollen/pistil have the same S allele. 

3/7/25:

Self-incompatibility can also be due to the separation of anthers and stigmas, called hercogamy. This decreases self-fertilization but not completely stop it. 

• Heterostyly

• Enantiostyly

• Movement hercogamy

Heterostyly- involving floral differences in stigma and stamen position. Most flowers are homostylous, which means the height of stigmas and stamens are constant/equal. 

Distylous- two types of differences in stigma and stamen positions, i.e, pin and thrum. 

Tristylous, where there are three different types of differences in stigma and stamen positions, i.e, long mid and short.

Enantiostyly- curvature of style to left or right away from stamen. 

• “Left-handed” and “right-handed” flowers.

Movement hercogamy- movement of floral parts.

• Rapid closure of stigmas responding to touch

• Trigger mechanisms- pollinator triggers sudden movement of stamens, which dusts them with pollen. Smacks pollinators without harming the pollinator. 

Fruit and Seed Dispersal:

Dispersal:

• Most plants cannot move, so they need something else to disperse the next generation

• Dispersal- moving seeds away from parent plant

• Dispersal affects various aspects of plant ecology

  • Population genetics

  • Inter- and intraspecific competition

  • Migration patterns

Diaspores= “dispersal units” of plants. Aka fruits of flowering plants. Fruits are what the ovary turns into. 

A fruit has two major functions

1. Protect the seeds

2. Help with seed dispersal

Dispersal can be short-distance or long-distance.

“Long distance’ is relative to plants. It usually means far enough distance to not interact with parent population. It could only be a few hundred meters. 

Long-distance dispersal is often required for establishment in recently disturbed areas or islands.

Dispersal is not always beneficial: for instance in patchy habitats, not all areas are suitable for growth. Often a problem in deserts. 

Types of dispersal:

Wind Dispersal: usually fruit and seeds are light and fluffy and float in the air, or have wings to flutter to the ground. 

Water dispersal: a few fruits and seeds are dispersed with water.

• Trapped air for flotation

• Example being coconuts or america lotus 

Animal Dispersal: many fruits and seeds are dispersed by animals.

• Internally- pass through digestive tract

• Externally- adhere to fur or feathers

• Some attract ants 

Problem: seeds are not mature in unripe fruit,  and need to keep animals from eating it. Because it is a wasted seeds otherwise.

The solution: no attractive color, odor in unripe fruit. Unripe fruit often makes animals sick.

Another Problem: fruit cannot be too attractive. Animals will stay there and eat all of it, meaning no dispersal.

Solution: asynchronous fruit ripening- animals will move from plant to plant. Or having slightly toxic fruit=animals won't eat too much at once. 

Ant dispersal usually requires the seeds to have elaiosomes.

• Fats, proteins, sugars attaches to outside of seed

• Ants carry seeds to nest, eat elaiosomes, discard seeds outside. An example being spring beauty plants. 

3/12/25:

Further elaboration on animal dispersal:

• Seeds dispersed by animals also need to not be destroyed in the process

• Externally dispersed seeds (burs, etc.) are usually well protected. 

• Seeds that are eaten need to survive the digestive tract, however.

Seeds dispersed by frugivores (animals that eat fruit) often have:

• Hard, thick seed coats

• Fruits that contain a mild laxative (so the seeds do not spend as much time in the digestive tract)

Many seeds dispersed this way actually require passage through an animal to stimulate germination

• Indicates they have been dispersed from parent plant

• May weaken tough seed coat, making germination easier

Seeds that have hard, thick seed coats may require scarification (abrasion) if they are not dispersed by animals

• weakens/breaks open seed coat

• Usually done by animal digestion 

A seed bank is the collection of seeds in the soil

• Single species

• Entire community

Seed banks allow plants to disperse their seeds through time

Seed Banks:

• Many seeds can remain dormant in the seed bank for long periods of time

• Wait to germinate until conditions are favorable

  • Rain,light, temp, etc.

  • Some need disturbed soil

Some seeds remain viable long enough in the soil that the seed bank does not represent the plants currently growing in the area

• Eg: plant grew when light available, but now in shade of taller trees

• May bring back genes from previous years

There is a wide range of how long seeds remain viable in seed banks. 

• Some only last a few years (1-5 years)

• Others last more than a hundred years

Viability depends on the specific conditions in which the seeds are kept.

• Human made seed banks are kept cold, for example. 

Some seed banks are above ground. Such as pines.

• Seronitous fruits/cones are sealed shut with resin

• Only open in high temps, but usually require fire. 

Seeds dispersed via serotiny will only germinate when conditions are favorable.

• High temps to remove resin

• Low competition

• Bare soil