Pollination in the Tropics
1. Pollination Basics
A.
B.
Biotic Pollination
Abiotic Pollination
2. Pollination Syndromes
A.
B.
C.
D.
E.
F.
Bees
Flies and Beetles
Moths
Butterflies
Bats
Birds
3. Weird Reproduction
4. Pollination in major
tropical ecosystems
5. Humans and Pollination
The “perfect” flower:
Pollination basics
• Pollination = the transfer of pollen
(male microgametophyte) to receptive
female stigmas for reproduction.
• Plants may be hermaphroditic,
dioecious or monecious.
• Some plants are self-compatible, while
others are obligate outcrossers.
• Pollen may be transferred by abiotic
vectors (wind, water) or biotic vectors
(animals such as insects, birds, bats).
Abiotic Pollination
• No need to attract pollinators
• No production of nectar, no loss of
pollen, no production of flowers or
aromas
• The plant can invest all of its energy
into making lots of pollen
• In tropical regions, usually in
seasonally dry areas, such as in
savannas where grasses form an
herb layer.
• Not very common in rainforests
Wind
pollination
Wind pollination is
usually seen in
grasses, sedges,
pines, some palm
trees, and other
open area species.
Why wind pollination doesn’t work well in tropical wet
forests:
•It is a passive process, and
depends on environmental
conditions to be successful
• Lack of consistent wind
makes it ineffective in a
rainforest
•High diversity makes it
unlikely that a pollen grain will land on a conspecific stigma
•Lack of a leafless stage: it’s hard for pollen to get around
•High humidity and rainfall reduce amounts of pollen in the air
Biotic Pollination
• Mutualistic relationship benefits both the plant and the animal
• Animals:
– Benefit from an easy source of food (pollen or nectar)
– Get as much as they can at each stop
– Prefer lots of flowers close together, or a few big ones (expend
less energy on foraging)
• Plants:
– Benefit from dispersal of pollen to as many conspecifics as
possible: the further the better
– Do not benefit from investing too much in showy flowers,
scents, attractants
– Benefit from providing as little “reward” (pollen, nectar) as
possible for animal consumption
Pollination Evolved from Pollinivory in early seed plants
• 250 + MYA
(late Paleozoic, Mesozoic)
• e.g. Cycadales, seed ferns
• Probably Beetles
• Pollination perhaps inadvertent initially,
but floral traits that increased chances of
pollination and encouraged visits by most
efficient pollinators were favored by
selection
• The carpel (female reproductive structure)
was originally leaf-shaped. It became folded
on itself to enclose and protect the ovule
from being eaten by the pollinators. Plants
with protected ovules would have a
selective advantage - angiosperms
Taxonomic Distribution
2/3 + of Angiosperms are animal pollinated + a small
proportion of Gymnosperms (e.g. Ephedra, cycads)
Pollinators include:
•Flies (Diptera), Ants, bees, and wasps
(Hymenoptera), Beetles (Coleoptera), Butterflies and
moths (Lepidoptera)
•Hummingbirds, sunbirds, honey eaters
•Bats, rodents, small marsupials
• Oddities: Frogs, slugs, earthworms
Honey guides
Pollination Syndromes
Often, plants that are visited by particular types of
pollinators will have things in common, especially
in their flowers, such as certain colors, shapes,
smells, etc.
These are generalizations though, not hard and fast rules!
Flower Flower
Pollinator Color Shape
Bees
Scent
Landing
Sweet
platform,
corolla tube
Beetles
Blue,
yellow,
have UV
pattern
Drab
Open (flat)
Strong; spicy,
fruity, or smelly
Flies
Drab
Open (flat)
Moths
Light
(white or
cream)
Dull
Tubular
corolla or
spur
Very long
tubes
Red or
orange
Tubular
Strong; spicy or
smelly
Strong, sweet;
produced in
evening
Very strong
fermenting or
fruity
Little or none
Bats
Birds
Rewards
Usually nectar,
pollen, resin, or
hormone
precursors
Nectar, petals, or
specialized food
bodies
Nectar
Lots of nectar
and pollen; flower
parts
Nectar, flower
parts, insects
Bees
• Bees are important in all tropical
communities.
•In rainforests, bees alone pollinate
almost half of all canopy trees and
lianas.
•Bee pollinated flowers:
•are often blue or yellow
•have “guide marks” that are
visible in UV light
•have a landing pad
Flies and Beetles
Many fly- or beetle-pollinated plants mimic the
odor and/or appearance of dung or rotting flesh
to entice insects for feeding or oviposition.
They tend to be
brown or dull-colored.
Traps and windows are common. There
is often no nectar. This is called deceit
pollination.
Moths
•Mostly nocturnal
•Moth pollinated flowers tend to be pale
•Petals tend to be flat or recurved
•Very strong, sweet scent
•May only be open or producing scent or
nectar at night
•Many moths have extremely long tongues,
and feed on nectar from flowers with very
long corolla tubes, matching the their
tongue length.
Some moths that fly in
the day can be mistaken
for hummingbirds!
Butterflies
• Diurnal, good vision - see the color
red
• Flowers pollinated by diurnal
butterflies are often colorful and
odorless
• Many butterfly flowers occur in
clusters - Asteraceae, milkweed
Bats (Chiropterophily)
Nocturnal nectar feeding bats have long
muzzles and weak teeth, and long tongues
to scoop pollen. Their flowers are often
pale, mustily scented, with long tubes and
wide “mouths”.
Pollen from these plants is
often high in protein and
important amino acids.
Birds
•Bird pollination is extremely important
in the tropics.
•Birds are visually oriented, and so their
flowers often are red, orange, purple or
yellow.
•They tend to be unscented, with long
tubes and recurved petals.
Pollinator Specialization
Generalist plants: a variety of small
insects visit the flowers
Specialists: the plant is pollinated by a particular
assemblage of animals. Examples: orchids and
euglossines, Heliconia and hummingbirds.
Extreme specialists: almost one-to-one
host specificity, exemplified by figs and
fig wasps. This is rare.
Freaky Reproduction
• Examples of highly specialized plant-pollinator
interactions in the tropics are ubiquitous. However, some
plants have co-evolved with their pollinators to extremes
that seem almost bizarre.
Aroids
•2,500 described species,
most pantropical.
•Produce a huge variety of
scents, from nauseating to
blissful.
•Many have heatproducing structures: this
helps diffuse the odors.
•Often pollinated by flies
or beetles.
Some aroids use modified leaves to trap
pollinators. When insects are attracted to the
dung-odor of Arum nigrum, they fall into a
“dungeon” and are prevented from leaving by
one-way filaments. If the insects are carrying
pollen it is transferred to
the receptive female
flowers. Nectar is
produced to feed the
insects. Twenty-four
hours later, the male
flowers mature. The
filaments shrivel and
the insects escape but are covered with
pollen as they exit.
http://www.youtube.com/watch?v=4P8YhP5_oig&feature=related
This Titan Arum can be 12 feet
tall, and emits a strong smell of
decay! People used to believe it
was pollinated by elephants.
The stench attracts insects,
perhaps carrion beetles, for long
distances to lay their eggs. They
enter and transfer or receive
pollen.
Male and female flowers mature
at separate times to avoid self
pollination.
Sauromatum guttatum
Orchids
•Over 25,000 species
described.
•Nearly all orchids are
pollinated by insects notably bees and wasps,
but also butterflies, ants,
flies and others.
•However, almost every
orchid species is
pollinated by just one or
two kinds of insects.
•Tight relationship with
pollinator: a species of
orchid may go extinct if
its pollinator insect dies
out.
Orchids as pollinator traps
Coryanthes gernotii
• Pollinators of Coryanthes sp. fit
exactly to the size of a tunnel
formed by the lip and the column.
• Approaching male euglossine
bees are excited by the fragrance,
and fall into the liquid-filled
bucket. The only way out is to
climb up the callus and squeeze
past the lip, first passing the
stigma (where pollinia are scraped
off) and then the pollinarium
which is stuck onto the body of
the departing bee.
http://www.youtube.com/watch?v=CP1A6TLDQLQ&NR=1
Pseudocopulation
Ophrys is pollinated by several genera of
solitary bees and wasps. It emits a
pheromone that mimics the scent of a
female pollinator, and even looks like one.
Males are highly attracted to the flowers.
Their repeated attempts at copulation
transport the pollinaria between orchids.
Often these orchids bloom prior to the
emergence of the real females.
Pseudoaggression
This orchid (Oncidium planilabre) mimics a male bee.
When a real bee spots this orchid he attacks it, attempting
to drive the intruder away. He strikes the inflorescence,
and pollinia are stuck on his head. When he attacks
another orchid the pollinaria are transferred.
Figs and Fig Wasps
• ~1000 species of Ficus (Moraceae), each with own wasp
pollinator
• fig “fruit” is a synconium: the inside is full of male and female
flowers.
Male and female fig wasp
(Pleistodontes imperialis). The
male has a greatly reduced body
with two primary purposes: (1)
Inseminating the female and (2)
Drilling exit tunnels through the
syconium wall.
• Very
precisely timed interaction between pollinators and male and
female flowers.
• Female wasps enter a fig with receptive female flowers, oviposits
in sterile flowers and dies.
• Males hatch first, mate with unborn females. Then they chew exit
tunnels out of the fig before dying. Male flowers are starting to
mature and produce
pollen.
• Newly hatched
females leave through
the tunnels, but pick
up pollen in doing so.
When they enter a
new fig they deposit
the pollen on
receptive female
flowers as they search
for oviposition sites.
Pollination in major tropical
ecosystems
•
•
•
•
•
•
•
Dry Forest - Santa Rosa
Lowland Rainforest - La Selva
Moist Forest - BCI
Montane Forest - Yanayacu
Mangrove - Milne Bay
Savannah - Serengeti
Desert - Sahara
Dry forest - Santa Rosa
• Lower species diversity than other
forest types
• High degree of seasonality
restricts most pollination activity
to rainy seasons
• Bees and moths most important
pollinators, some bats
• Beetle, butterfly, and
hummingbird pollination are rare
Lowland rainforests - La Selva
• Very high diversity of trees plants are widely distributed, but
locally rare
• Pollination syndromes and
coevolution are common
• Large, showy bracts are common
• Many tree species are
outcrossers, some understory
species are self-compatible
• Mostly pollinated by bees,
especially the canopy
• Flowering time is variable
Moist Forest - BCI
• Has a more pronounced
dry season
• More seasonal flowering
Sequential blooming and simultaneous
fruiting in 6 species of Shorea
Montane forests - Yanayacu
• Wet and cold with greater
seasonality than lowland rainforest
• Weather fairly unpredictable
• Lower overall diversity than
lowland rainforest
• Relatively higher diversity of
epiphytes
• Many tree species are selfcompatible or dioecious, long
lasting flowers
• More hummingbird pollinators,
fewer bees
Mangroves
• Old world mangroves
tend to be more
diverse than those in
the new world.
• Diverse pollination
mechanisms,
including bats, birds,
bees and wind.
• Some bear propagules
rather than seeds;
similar to bearing live
young.
Savannah and Desert
• Many plants found in grasslands and deserts
are wind pollinated, which is possible in
these open, often windy habitats.
• Vegetation includes perennial
grasses, shrubs, and trees at
oases.
Desert - Sahara
Euphorbiaceae - same ecological niche as the
cacti of the New World deserts
• produce milky latex
• small flowers in complex inflorescences
(cacti usually have large single flowers)
• flowers often surrounded by large,
colorful bracts - pollinator attraction
Humans and pollination
• Efficient pollination is critical for agriculture.
• Most food crops require animal pollination
• Beekeepers have used European honeybees for this in many
places.
• 1/3 of human food is derived from plants pollinated by wild
pollinators
• In the US, the value of wild, native pollinators is in the
billions of dollars each year.
References:
– Bawa, K.S. 1990. Plant-pollinator interactions in tropical rain
forests. Annu. Rev. Ecol. Syst. 21:399-422
– Bawa, K.S., and M. Hadley (eds). 1990. Reproductive Ecology of
Tropical Forest Plants. UNESCO.
– Kricher, J. 1997. A Neotropical Companion. Princton Univ
Press.
– Meeuse, B. and S. Morris. 1984. The Sex Life of Flowers.
Rainbird Pub. Grp. Ltd., London UK
– Proctor, M., P. Yeo, and A. Lack. 1996. The natural history of
pollination. Timber Press, Portland OR.
– Raven, P.H., R.F. Evert, and H. Curtis. 1976. Biology of Plants,
2nd ed. Worth Pub., New York NY