Transcript Plant Ecology - Chapter 8

Plant Ecology - Chapter 8
Plant Life Histories
Life History Strategies
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
Type III survivorship curve
Type I or II survivorship curve
Grime’s Triangular Model
Grime’s Triangular Model
Grime’s Triangular Model
Dealing with Variation
“Hedging their bets” to
maximize fitness in a
varying environment
Spread reproduction
more evenly among
years
Increase seed dispersal
area
Increase dispersal time
via seed banks
Dealing with Variation
When should seeds
germinate?
Controlled by
temperature, light,
moisture, others
Can plants evolve
predictable germination? depends on predictability
of environment
Fire?
Dealing with Variation
Masting - large and
erratic variation
among years in the
size of the seed crop
produced
Synchronized among
plants within the
population
Dealing with Variation
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
May actually be
adaptation in windpollinated plants to
reduce pollen
limitations
Many plants are
pollen-limited, and
increasing pollen
densities increases
pollination efficiency
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
Vegetative Phenology
Forest floor plants in
temperate regions grow,
flower before tree leaf
expansion
Get sunlight before
canopy closes, but
much colder than trees
experience for their
growth, flowering
Vegetative Phenology
Plants use temperature
(degree-days) and
photoperiod to
determine phenologies
Photoperiod prevents
growth during midwinter warm periods
Vegetative Phenology
In warmer climates,
moisture is major
controller of vegetative
phenology
Grow leaves, lose
leaves in response to
changes in moisture
Reproductive Phenology
Flowering regulated by
many abiotic factors:
temperature, light
availability, moisture
Belief that moisture
limitation and related
stressors induce
flowering not fully
supported: not in
annuals, weak in
perennials
Reproductive Phenology:
biotic factors
Biotic factors can
influence reproductive
phenology, especially
pollinators
Pollen-limited, animalpollinated plants may
be strongly controlled
Reproductive Phenology:
biotic factors
Two structuring forces
possible:
Competition for
pollinators may lead to
temporal separation of
flowering, or
Similar phenologies
may attract more
pollinators than
separate flowering
Little evidence for either
Reproductive Phenology:
biotic factors
Fruit or seed eaters
more likely to be
affected by plant
phenology than to
affect it
Crowding by
neighbors delays
flowering, may select
for faster growth or
earlier flowering
Reproductive & Vegetative
Phenologies: linked?
Link generally weak,
especially for longerlived plants like forest
trees
Plants can store
products of
photosynthesis at one
time and use them at
another
Temperate trees flower
when leafless