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