Download CB098-008.36_Plant_Ecology_A

Plant Ecology:
Plant
Populations,
Communities, &
Ecosystems
Plant Ecology – The study of plants interacting with their
nonliving and living environment. Plant ecology
includes nutrient acquisition, deterring herbivores,
competition with other plants, reproduction,
disseminating seeds, fighting disease, disturbances to
ecosystem such as fire, hurricanes, human changes
and local tree falls.
Environment – Environment is the sum of all biotic and
abiotic elements that surround and influence an
organism. Environment is often synonymous with
“ecosystem” and “habitat.”
Biotic Elements – Plants, animals, soil microbes, fungus, etc.
Abiotic Elements - Temperature, moisture, wind, sunlight, soil
nutrients, fire etc.
Biotic and abiotic elements affect an individual plant in
its environment.
Plant Population - a group of freely interbreeding plant
individuals belonging to the same species and occupying
the same area (dependent on scale). Populations can be
large or very small. Individuals of the same species could
potentially interbreed. Plant Population Example: All
white oak (Quercus alba) trees at Ben Hawes State Park.
Plant Community - all the plant populations within a given
habitat; a plant community includes different plant species
living together in the same area.
Plant Community Example: White oak, sugar maple,
poison ivy, glade fern, and club moss all living together in
an area.
Ecosystem - an inclusive term for a living community; an
ecosystem includes all the living and nonliving factors in
an area. If you take a plant community and other forms of
life in an area plus the nonliving component then you have
an ecosystem. Ecosystem Example: Oak-Hickory Forest.
A 1-Year-Old
Conifer Seedling
During its life span of
several hundred years,
the plant that grows from
this seedling must
successfully budget time
and resources to satisfy
the demands of growth,
maintenance,
reproduction,
competition and
herbivore defense.
Plant
Distribution
Plants vary in their distribution. Plant species can be
common, uncommon or rare. Red maple (common) is
found throughout the eastern United States. Coast
redwood (uncommon) is found along the pacific coast.
Tecate cypress (rare) is only found in a small localized
area in the southwestern U.S.
Life History Patterns
Annuals – Annual plants go from seed to seed in less than
one year. After they develop mature seed, annuals eventually
wilt and die. Their work is done. Some annuals cycle
between 10-14 days but many have a 3 to 8 month life cycle.
Annual Examples: Corn, other grains, legumes, cosmos,
many wildflowers.
Perhaps the
term ephemeral
is more
appropriate
than annual,
because it does
not imply a full
year of life.
(& Seed Production)
Biennials – Biennial plants live for 2 years.
During the
first year, growth in the root system occurs and a basal
rosette of leaves forms (often during the fall). During the 2nd
year, the shoot elongates, produces flowers, then seeds form
and then the individual dies.
Biennial Examples: Carrot, Lettuce, Thistle, Radish, Beets,
weeds found in yards.
Beets and carrot are biennials, but we harvest them in their first year and so
missing seeing their flowers. Why do we harvest them the first year?
Musk Thistle, An example biennial
Shoot and Inflorescence found in 2nd year’s
growth.
A rosette found in 1st year’s growth
Perennials – Perennial plants live for some to many
years and usually flower repeatedly. Perennials can be
herbaceous (nonwoody) or woody (subshrubs, shrubs,
vines or trees).
Herbaceous Perennials die back to their underground parts each
winter. Their bulbs, corms, roots or rhizomes are the true
perennial parts of the plant. These plants are nonwoody. They
don’t have wood.
Some herbaceous perennials can live up to 20-30 years.
Herbaceous Perennial Examples: Iris, onion, potato, ferns, many
wild grasses, black-eyed Susan, most of the spring-flowering
herbs of the eastern deciduous forest.
Jack-in-the-pulpit
(Arisaema triphylla), an
herbaceous perennial,
which flowers in the spring
in the deciduous forests of
western Kentucky.
Woody Perennials accumulate above ground woody stem tissue
year after year. These woody perennials have secondary growth
(Their woody stems thicken year after year). Woody Perennial
Example Categories include Subshrubs, Shrubs, Vines & Trees.
Subshrubs are multibranched and
genetically dwarfed, seldom becoming
taller than 30 cm. At the end of each
growing season, their stems die back
partially, but not all the way to the soil
surface.
A Subshrub , rabbitbrush
(Chrysothamnus nauseosus)
Shrubs are multibranched but their stems do
not die back annually. They vary in life span,
some can live to greater than 100 years.
A Shrub, Creosote bush
(Larrea tridentata) found in warm deserts of North
American can live more than 100 years.
Vines (called lianas in the tropics) have
weak, single trunks. They require
support form neighboring shrubs, trees
or structures, obtaining that support by
twining about the host’s trunk or literally
sprawling on top of the host’s leafy
canopy. Vines can have secondary
growth. Vine examples include
dutchman’s pipe, grape, greenbriar.
Trees have strong, single trunks and an
elevated branch system that does not die back
annually. Angiosperm trees are typically
considered hardwoods. Gymnosperm trees
are typically considered softwoods.
Angiosperms and gymnosperms both have
evergreen and deciduous species in their
divisions.
A Vine , Virginia Creeper
(Parthenocissus quinquefolia)
Deciduous Trees
If a tree has deciduous leaves,
it loses all of its leaves with the
seasons. Deciduous
leaves have less than 1 year
life spans and all leaves fall
roughly at the same time. A
gymnosperm deciduous tree is
the bald cypress. An
angiosperm example is the
white oak.
Bald Cypress Foliage
Evergreen Trees
If a tree has evergreen leaves, it has green leaves all
year. Evergreen leaves have life spans greater than 1
year. A gymnosperm example is eastern white pine. An
angiosperm example is Southern Flowering Magnolia.
Reproduction Can Be Iteroparous or Semelparous
An Iteroparous plant is a perennial plant that is capable of flowering repeatedly
throughout its lifespan. They do have a juvenile period before the first
reproductive event. Some iteroparous species reproduce at a constant rate
once the juvenile period is over. Others such as oak, pine, and fir reproduce
more abundantly some years than other years. The years of high reproduction
are called mast years. Mast indicates years of high reproduction due to certain
environmental conditions. During a mast, seed eaters are overwhelmed with
seeds. This ensures that some seeds will survive and germinate.
A Semelparous plant flowers only once at the
end of its life span. Semelparous reproduction
can be found in various life history strategies
(annual, biennial or perennial).
Our Lord’s candle (Yucca whipplei ), a
semelparous perennial plant. It flowers only
once, at the end of its 20-year life span. This
species grows in coastal hills of central and
southern California.
Plant Demography: Population Age Structure Over Time
Plant Demography –
The study of
changes in plant
population age
structure over time.
The width of trunks are
measured by D.B.H.
D.B.H. stands for
diameter breast height.
This is the diameter of
the trunk at average
breast height. So trees
with greater DBH are
older trees.
Age distribution (on the basis) of trunk diameters at breast
height) for pines and hardwoods in a forest near Gainesville,
FL. The pine population is senescent (growing old), and the
hardwood population is invading (and young). The green line
(dashes and dots) shows the expected age distribution of a
stable population, in contrast to the pines and hardwoods.
A Simulated Energy Budget of A Leaf
Energy budget of a leaf. Incoming solar radiation is given a value
of 100% energy. 1% of this energy is used for photosynthesis.
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Reradiation involves the
plant releasing infra red
heat (> 740 nm in the
electromagnetic
spectrum). With special
sensors, these long
wavelengths are best
seen at night, when the
temperature of the leaf
decreases.
Convection – is the transfer
of heat energy back to
air.
Transpiration is very
expensive for the plant
but is less costly for
CAM plants in the
desert. Why?
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Fire Can Be a Natural Part of the Environment
Fire is an important factor in some
ecosystems. Fires set by lighting, Native
Americans or land managers today alter and
determine plant community types. Fire is an
important disturbance factor in ecosystems.
Some forests are dependent on fire (Periodic
ground fires are necessary to preserve the
balance of pine forests. Such fires remove
excessive fuels, kill competing species and
help seeds germinate). Fires can help
increase diversity within a forest. It can help
some plant species flourish and suppress
other plant species. When fires are set by
land managers (prescribed burns) only a
fraction of the land that should burn, actually
burns. Fires can be spotty. This can provide
plant diversity.
Fire Climax Ecosystems are ecosystems
that are dependent on the recurrence of fire
to maintain their existence. Prairies, or
grassland ecosystems are fire climax
ecosystems because fire prevents growth of
shrubs and trees.
Interaction Among Neighboring Plant Populations
1). Competition - Competition occurs when there is a common required resource
that is also in limited supply. Competition can occur between 2 different species
or within the same species. Competition can result in decreased growth rates
because of insufficient supplies of necessary resources. To name a few, plants
will compete for light, moisture, space, nutrients, pollinators, etc. Competition
affects how plants are distributed. In a young forest, there may be many
saplings but as that forest ages, there are fewer trees but they are bigger.
Competition caused some trees not to make it to greater ages. Competition can
cause divergent evolution, which would result in decreased competition.
2). Amensalism - Amensalism is the inhibition of one plant by another through
the addition of something to the environment. Walnut trees suppress plants
around them. Decay and leaf litter decomposition can suppress the growth of
other plants.
Possible amensalism between sage
shrubs (Salvia and Artemisia species)
and grasses in the coastal areas of
southern California. (a) Aerial
photograph of a patch of sage. Note the
bare soil benthea the shrubs and for
some distance away from them. (b)
View along the edge of a patch of
shrubs, showing a zone of bare soil and
stunted grasses several meters in width.
Some researchers speculate that a
volatile chemical exuded by shrub
leaves prevents the grasses from
germinating or growing normally.
3). Herbivory – Herbivory is the consumption of plant biomass by animals.
These plant eaters eat part of the plant and sometimes kill the plant. Plants
have defenses against herbivory:
1) Physical Barriers - Spines, prickles, thorns, thick bark, hard fruit
2) Chemical Defenses – Toxins and bad tasting Tannin and Turpentine compounds.
3) Complex Ecological Relationships Help Deter Herbivory.
Caterpillars are notorious for eating great amounts of plant material. Parasitic wasps lay
eggs inside these caterpillars. Wasp larvae eat the caterpillar inside. The wasp larvae
emerge and form pupae. The adult wasp will emerge from these pupae (cocoons).
Recruitment of a parasitic wasp in response to
an herbivore (caterpillar).
Tomato hornworm caterpillar
with many braconid wasp
cocoons (Pupae).
3). Mutualism – Mutualism occurs when two species interact and they both
benefit. Examples include Biotic Pollinators (Plant and Insect Both Benefit),
Seed Dispersal (Plant and Fruit-eating Bird Benefit), Lichen (Fungi and Algae in
close relationship.
4). Commensal – One individual receives a benefit while the other is neither
harmed nor benefits (neutral). A epiphyte (a plant that grows on another) is
helped by the host tree by being higher in the canopy to reach sunlight. The
host tree does not benefit but also is not harmed.
Epiphytes on Branch in Costa Rica
BIO 141 Botany with Laboratory
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