Lecture 3: Ecology of Seed Germination

Question 1

Highbush cranberry

Answer 1

Viburnum opulus

- attracts Cedar Waxwings

Question 2

Seed Disperal: Fruits

Answer 2

• attracts organisms to move seeds for them
• often attract frugivores
• asynchronous fruiting - plants tend to do this in the wild, all fruits don’t ripen at the same time, and dispersed seeds will be different age groups and success increases -> this enhances overall survival
• toxic fruits

Question 3

Fruit

Answer 3

ripened ovary

Question 4

What type of fruiting don’t humans want?

Answer 4

Humans don’t want asynchronous fruiting so they can collect fruits all at one time

Question 5

Other dispersal mechanisms

Answer 5

• wind - surface area of seed to help seed dispersal
• animals: frugivores (those specializing in fruit) & granivores (those specializing in seeds)
• water

Question 6

water

Answer 6

• ethanobotany ( how humans use plants) - when trying to discover where they come from, seeds dispersed via water, can be hard to track

Question 7

Elaiosomes on Sanguinaria canadensis

Answer 7

• sticky/sweet coating
• nutrient rich reward for seed dispersal animal
• favored by ants
• Blood root (Sanguinaria canadensis)

Question 8

Frequency distribution of seeds dispersed over given distance classes - seed dispersal kernel
- what these graphs show

Answer 8

• overall there are fewer seeds dispersed far away from the parents
• mammals are the most important for carrying the seeds long distances from parent

Question 9

Seed Bank: Temporal dispersal

Answer 9

• pool of buried seeds (definition of seed bank) - stored underground
• ‘Memory’ of the site - things will grow that were not known to be there
• long-lived seeds in seed bank, but short-lived plants - do well in disturbed environment

Question 10

Prunus pennsylvanica

Answer 10

Pin cherry

• Pin cherry seeds were dormant in the seed bank, and grew when forest was clear-cut - it wasn’t present in this area until it was clear-cut
• it resided in the seed bank and has some longevity in there

Question 11

William J. Beale’s jar experiments

Answer 11

• He wanted to know how long seeds lasted
• 20 jars
• 50 seeds of 19 species
• examined viability every 5-10 years -> grew a portion of the seeds out - if grew then seed was viable; if not then death in seed bank
• 120 yr. old (Malva pusilla) and (Verbascum spp.) seeds remained viable
• bet hedging - purpose for the seed - if seed can last long in seed bank, then it can wait until favorable conditions -> ensures seeds will be successful when plants disperse them -> basically so the seed can pick the best time to germinate

Question 12

bet hedging

Answer 12

• purpose for the seed
• if seed can last long in seed bank then it can wait until favorable conditions to germinate
• ensures seeds will be successful when plants disperse them

Question 13

Seed dormancy (I think in relation to Beale’s experiment?)

Answer 13

• buried seed of “Verbascum thapsiforme” survived 850 yrs. of dormancy
• dormant seeds produced in large numbers by populations subject to periodical local extinction
• sometimes local extinctions of a gene pool of seeds but they may also exist somewhere else because of dispersal

Question 14

Why do habitats with frequent disturbance also promote genetic variability?

Answer 14

• frequent recruitment from gene pool - seed bank
• disturbance reduces plant-plant competition
• genetic variability of seed bank if seeds are long-lived
• areas with frequent disturbance pull from the seed bank periodically, which increases genetic diversity

Question 15

Seed bank and genetic diversity:

Linanthus parryae of Mojave Desert

Answer 15

• seed banks of mixed genetic origins
• emerging cohorts draw from seeds originating at different times
• ratio of purple to white flowers determined by spatially variable natural selection
• used color as a substitute for genomes to see the forms of natural selection
• seed pool buffers genetic changes in plant populations

Question 16

Germination timing:

see graph handout!

Answer 16

• seedlings that emerge earlier (correlate with earlier germination) tend to have higher survival rates
• research question: order of emergence more important than date of emergence
• research question: deteriorating environmental condition OR older plants capture more resources

Question 17

Seed size tradeoffs:

Why don’t they all have big seeds?

Answer 17

• graph on left shows that bigger seeds have lower death rates - have better chance of producing a seedling that survives
• graph on right shows the energy allocated between growth and reproduction - trade-offs in creating seeds with growth
• energy costs - trade offs -> large seeds might be produced in late-successional situations, whereas several smaller seeds might be more cost effective in situations with high disturbance, shorter plant life, etc.
• dispersal ability
• ability to produce more seeds

Question 18

Microtopographical Variation

Answer 18

• variation in soil conditions/topographical features

Question 19

Safe sites

Answer 19

• the lab is not the field
• seed germination responsive to fine-scale differences in physical environment
• nurse logs
• flat seeds of Achillea millefolium germinate best on even surface
• Prunella vulgaris prefers 20 mm grooves

Question 20

nurse log

Answer 20

• important sites for germination especially in forested situations, mature forests, late-succesional forests, temperate, and tropical forests
• some smaller seeds will grow on logs because there is not litter accumulation there- this occurs a lot in places with a lot of leaf litter
• i.e. small seeds like birch and hemlock can get buried sometimes in leaf litter
• i.e. a trees root system growing over a large log
• i.e. tree roots growing over large log

Question 21

seed “sinks”

Answer 21

• seeds that don’t remain in seed bank

Question 22

Why do only a tiny fraction of seeds reach the seedling phase?

Answer 22

• predation; digested to the point where seed is no longer viable

Question 23

Summary - factors affecting germination

Answer 23

• species composition of seed bank
• seed looses in the field
• physical characteristics of seed bed
• physical characteristics of seeds
• Physiological Cues:
  - light intensity, photoperiod, light quality, temperature, temperature fluctuations, nitrates, O2, CO2, pH, moisture, physical abrasion

Question 24

Epigeous germination

Answer 24

cotyledons pulled out of ground -> where cotyledons are when germination occurs

Question 25

Hypogeous germination

Answer 25

cotyledons remain in soil

Question 26

common monocots

Answer 26

• 1 cotyledon

- onions and corn

Question 27

Hypocotyl hook

Answer 27

hook breaks the ground open and pulls the seed behind it, protects the embryo in the seed, and pulls it out cotyledons out of the ground

Question 28

Next after seed has germinated?

Answer 28

leaves, nodes, internodes, apical meristems -> overall morphology and how photosynthesis fits in

Question 29

Epicotyl

Answer 29

the young shoot that is developing