Lecture 3: Ecology of Seed Germination Flashcards
Highbush cranberry
Viburnum opulus
- attracts Cedar Waxwings
Seed Disperal: Fruits
- 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
Fruit
ripened ovary
What type of fruiting don’t humans want?
Humans don’t want asynchronous fruiting so they can collect fruits all at one time
Other dispersal mechanisms
- wind - surface area of seed to help seed dispersal
- animals: frugivores (those specializing in fruit) & granivores (those specializing in seeds)
- water
water
- ethanobotany ( how humans use plants) - when trying to discover where they come from, seeds dispersed via water, can be hard to track
Elaiosomes on Sanguinaria canadensis
- sticky/sweet coating
- nutrient rich reward for seed dispersal animal
- favored by ants
- Blood root (Sanguinaria canadensis)
Frequency distribution of seeds dispersed over given distance classes - seed dispersal kernel
- what these graphs show
- overall there are fewer seeds dispersed far away from the parents
- mammals are the most important for carrying the seeds long distances from parent
Seed Bank: Temporal dispersal
- 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
Prunus pennsylvanica
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
William J. Beale’s jar experiments
- 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
bet hedging
- 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
Seed dormancy (I think in relation to Beale’s experiment?)
- 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
Why do habitats with frequent disturbance also promote genetic variability?
- 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
Seed bank and genetic diversity:
Linanthus parryae of Mojave Desert
- 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
Germination timing:
see graph handout!
- 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
Seed size tradeoffs:
Why don’t they all have big seeds?
- 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
Microtopographical Variation
- variation in soil conditions/topographical features
Safe sites
- 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
nurse log
- 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
seed “sinks”
- seeds that don’t remain in seed bank
Why do only a tiny fraction of seeds reach the seedling phase?
- predation; digested to the point where seed is no longer viable
Summary - factors affecting germination
- 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
Epigeous germination
cotyledons pulled out of ground -> where cotyledons are when germination occurs