Plant Community Ecology
Plant Life Histories
Life History- A plant’s schedule of birth, mortality, and
growth
Life Cycles:
Annuals,
Biennials,
Perennials
Idea of Trade-offs—limiting resources is central to
thinking about natural selection on life histories
e.g. root-shoot ratios, fast growing vs
wood density
What would an ideal plant species look like (life
history traits) if there were no trade-offs?
What are the
trade-offs
between large,
few seeds vs.
small,
numerous
seeds?
MacArthur’s Life History Selection-r vs K species
r strategist
K strategist
Unstable environment,
density independent
Stable environment,
density dependent
Small size of organism
Large size of organism
Much energy for reproduction
Little energy for reproduction
Many offspring produced
Few offspring produced
Early maturity
Late maturity (often after parental
care)
Short life expectancy
Long life expectancy
Semelparous
Iteroparous
Productivity-idea at low population densities, selection is strongest on traits
that increase population growth (r), high densities, selection strongest on
Type III survivorship curve
Type I or II survivorship curve
traits that increase population size on carrying capacity K
Grime’s Triangular Model
Grime’s Model-extended r-k selection theory to plants;
plant populations face consistent selective pressures
mainly from physiological stress (all external factors to
a plant that limit growth)
1) stress-tolerators—slow-growing species that inhabit
low-fertility, low-disturbance sites (conservation of
captured resources)
2) competitors—fast-growing species that inhabit high
fertility, low disturbance sites (maximize captured
resources)
3) ruderals-fast-growing species that inhabit highfertility, high-disturbance sites (high seed production)
Grime’s Triangular Model
Grime’s Triangular Model
Dealing with Variation—seed
germination
Try to maximize fitness (how an organism apportions
resources among competing demographic functions
(survival, growth, reproduction) in a varying environment
Spread reproduction more evenly among years
Increase seed dispersal area
Increase dispersal time via seed banks
When should seeds germinate?
Controlled by temperature, light, moisture, others
Can plants evolve predictable germination? - depends on
predictability of environment
Dealing with Variation
Masting - large and
erratic variation
among years in the
size of the seed crop
produced
Synchronized among
plants within the
population
Often explained as a response to avoid seed
predators
Overwhelm abilities of predators to eat all the
seed - some survive to germinate
Dealing with Variation
Synchrony achieved
by low reproduction
one year (bad
weather, low pollen),
low resource
expenditures, greater
likelihood of more
reproduction next
year
Plant Phenology
Timing of growth and reproduction within a year
Much variation among species, populations,
individuals
Constrained mostly by temperature, moisture
http://www.youtube.com/watch?v=8Ks5IG6Mu9g
What influences
leaf expansion in
deciduous trees?
 canopy is elevated
 late spring frosts
 individual
metabolic enzymes
have defined temp
ranges over which
they can operate
and are most
efficient at
particular temps
Reproductive Phenology: abiotic factors
Reproductive Phenology: biotic factors
Pollinator interactions; pollen-limited,
animal-pollinated plants may be strongly
controlled
Herbivory; flowering time delayed
Reproductive Phenology: biotic factors
Fruit or seed eaters
more likely to be
affected by plant
phenology than to
affect it
Crowding by plant
neighbors delays
flowering, may select
for faster growth or
earlier flowering