experimental evidence for tradeoffs. survival vs. fecundity (astrocaryum mexicanum) photo copyright...
TRANSCRIPT
Experimental Evidence for
Tradeoffs
Survival vs. Fecundity (Astrocaryum mexicanum)
Photo copyright © 1998, Jody Haynes
Size vs. Fecundity (Poa pratensis)
Fecundity vs. Fecundity (Poa pratensis)
Tradeoffs
“If two processes require the use of a limiting resource, then allocation of the resource to one process requires de-allocation to the second.”
The Bottom Line
IdealPlant
Key Stages in the Life-History of a Plant
Growth
Flowering
Pollination
Seed Maturation
Dispersal
Dormancy
Germinationse
ed
ph
ase
Growth in Plants
Growth
Apical meristems
Source of plant elongation; often acting to suppress lateral growth from other
nodes
Growth
Apical meristems
Axillary meristems at nodes
Gives rise to leaves and flowers; can also form lateral branches when not suppressed by apical meristem
Growth
Apical meristems
Axillary meristems at nodes
Growth between adjacent nodes
Internodes
Growth
Apical meristems
Axillary meristems at nodes
Cambium in many perennial plants (not monocots) allows them to increase in girth over time
Secondary growth
Internodes
Ecology and Plant Architecture
The Raunkier system of classification
snowpack
Plant growth is generally a Modular Process
Clonal Growth
Pros and Cons of Clonal Growth
Advantages Disadvantages
• Rapid growth
• More widespread foraging
• Lower mortality than seedlings
• Greater competitive ability
• Avoid cost of sexual repro.
• Resource sharing
• No recombination
• Limited dispersal range
• Disease accumulation
Forms of Clonal Growth
Phalanx Guerilla
Phalanx Growth: Aspen Example
Guerilla Growth: Solidago Example
Modes of Foraging Behavior
Ramet size (S)
Shoot
Root Branch angle ()
Number of Branches (n)
Optimal Foraging?
Nutrient Rich Nutrient Poor
Nutrient Rich
Optimal Foraging: Rich Habitat
X
Optimal Foraging: Poor Habitat
X
Optimal Foraging through a Plastic Response
Predictions
Nutrient Rich Habitat Nutrient Poor Habitat
• Short internodes
• Profuse branching
• Acute branch angles
• High shoot:root
• Long internodes
• Few branches
• Obtuse branch angles
• Low shoot:root
An Experimental Test of
Optimal Foraging
The plant: Glechoma hederacea
Slade, A. J., and M. J. Hutchings. 1987. The effects of nutrient availability on foraging in the clonal herb Glechoma hederacea. Journal of Ecology 75:95-112.
General Growth Pattern
Experimental Design
LegendNutrient poor
Nutrient rich
Mixed
Predictions
Nutrient Rich Habitat Nutrient Poor Habitat
• Short internodes
• Profuse branching
• Many large ramets
• High shoot:root
• Long internodes
• Few branches
• Few small ramets
• Low shoot:root
and Results
Predictions and Results
Nutrient Rich Areas Nutrient Poor Areas
• Short internodes
• Profuse branching
• Many large ramets
• High shoot:root
• Long internodes
• Few branches
• Few small ramets
• Low shoot:root
Mixed Treatment
Intermediate growth in all locations
General Interpretation
• Glecoma hederacea exhibits a plastic growth response to nutrient conditions • This response is not localized, but represents an average to conditions encountered across the clone
What role does physiological integration play?
Physiological Integration through Movement of Resources
Xylem: Transport of raw materials, e.g., H20
and soil nutrients
Phloem: Transport of products of photosynthesis
Experimental Examination of Integration through Xylem
Price, E. A. C., C. Marshall, and M. Hutchings. 1992. Studies of growth in the clonal herb Glechoma hederacea. I. Patterns of physiological integration. Journal of Ecology 80:35-38.
Experimental design
• Cut leaf off
• Inject fuchsin dye into xylem
Leaf with dye
Leaf without dye
Experimental Examination of Integration through Xylem
Experimental results
• Complex pattern of nutrient flow, depends on xylem architecture
• Apparent unidirectional flow of nutrients
Experimental Examination of Integration through Phloem
Leaf labeled with 14C
Experimental Examination of Integration through Phloem
Leaf labeled with 14C
Resulting radiograph
Experimental Examination of Integration through Phloem
Interpretation
• Photosynthate stays in leaf or is transported to young developing tissues
• Source-sink relationship
General Interpretation of Experiments
• Patterns of physiological integration can be shown
• Resource sharing seems to be in the direction of younger ramets
• Optimal foraging is an ideal that is only partially met
Forms of Asexual Reproduction
in Plants
Clonal Growth (revisited)Rhizome
Stolon
Suckers
Plantlets
Bulbils
Fragmentation: jumping cholla
Agamospermy
Production of seeds with no fertilization
Key Stages in the Life-History of a Plant
Growth
Flowering
Pollination
Seed Maturation
Dispersal
Dormancy
Germinationse
ed
ph
ase
Sexual
Reproduction in
Plants
Typical Angiosperm Lifecycle
Alternation of generations
• Sporophyte (2n)
• Gametophytes (1n)
Typical Angiosperm Lifecycle
Alternation of generations
• Sporophyte (2n)
• Gametophytes (1n)
Fertilization
♂♀
Hermaphrodites
Gender Expression in Plants
Sequential Hermaphrodism
Jack-in-the-pulpet (Arisemea triphyllum)
Some plants change sex over time!
Distribution of Flower Types
Variability in Flowering Patterns
• Semelparity
• Iteroparity
Flower once and die
Flower many times
Semelparity: A closer look
Annuals
Biennials
Biennial plant
Year 1 Year 2
© R. Jackson © R. Jackson
Semelparity: A closer look
Big bang perennials
Bet Hedging
Big bang
Vegetative reproduction
Semelparity vs. Iteroparity
Tradeoffs in Phenology of Flowering
Annuals PerennialsBig Bang
Advantages
• Quick reproduction
• Protected as seed
Disadvantages
• High environmental risk
• Poor competitors
Special Circumstances
• Poor conditions for extended time periods
• Strong signal for breaking seed dormancy
Advantages
• Increased size
• Reproduce when resources are plentiful
Disadvantages
• Slower initial population growth
• Require relatively stable habitats
Special Circumstances
Advantages
• Increased fecundity*
• Predator satiation
Disadvantages• Delayed reproduction
• “All eggs in one basket”
Special Circumstances• Can succeed in situations with high stress, low resources
• Better competitor*
* (vs. annuals)
• Unpredictable resource for seed predators
A Majority of Plants are Iteroparous Perennials