Tree and plant species will go all out to make sure
their genes are passed on. This has lead to the development of various methods of
pollination and seed dispersal, adopted by various tree species. Some of these methods may
be very intriguing.
Features that help in pollination
Plants evolve accordingly to make sure that pollination is
effective. This goes hand in hand with their method of pollination. For example, for
wind-pollinated plant species such as pine and grass, their strategy is to produce large
amount of pollen so that the chance of pollen getting to the female is higher.
Others depend on animals to help pollinate their flowers. However
not any animals can pollinate a specific plant species. Pollinators such as birds,
butterflies, moths, bats and bees are able to pollinate certain types of plants. In this
mutual relationship between flower and animals, each party benefits. The main purpose why
some flowers only allow a specific pollinator is so that the chances of the pollen getting
to the same species of flower are higher. For those flowers that allow a greater variety
of pollinators to pollinate their flowers, they face the risk of having their pollen
delivered to a different type of flower on the pollinators next visit.
Some species of flowers and pollinators has even taken a step
further whereby the plant and the pollinator totally depends on each other. The term for
this is coevolution, where there is a joint evolution between plant and its animal
pollinator. An example of a coevolution would be the relationship between the yucca plant
and the yucca moth. The female yucca moth lays her eggs in the flower and simultaneously
pollinates the flowers. The caterpillars hatch within the seeds in the ovary. The flowers
may lose some of their seeds, but it is worthwhile to ensure pollination.
For plants that
requires animal pollinators, it is important that the plants:
- Supply some reward for the pollinators (nectar, etc)
- Advertise their presence
- Have a way to implanting pollen onto the pollinator
One interesting orchid has evolved such that it looks and
smells like a female of a wasp species. Males of this wasp species emerge one week before
the females, but the orchids are already blooming. When a male finds this orchid, it
thinks it has just found a mate and tries to copulate and instead it ends up having
pollens stuck to its body.
All flowers requiring a pollinator are
designed to attract. For bee-pollinated flower,
they tend to be mostly yellow with slight blue and an ultraviolet nectar guide. These
flowers also tend to have a sweet scent, which the bees are able to smell. The nectars
found in these flowers are usually situates in the far end of the flowers, at the end for
a narrow tube. The position of the nectar is such that only a specific species of bees are
able to reach it. Even so the bees are forces to struggle a bit to get to the nectar and
during this slight struggle the pollens tend to adhere to the body of the bee.
orchid has a very interesting and complex method to fix pollen onto a
bee. At the lower petal, there is a pot-looking structure which holds fluid is that
dripped from gland above. The fluid is filled to a depth of 5mm. Orchid bees are attracted
to the scent of this flower and attempt to collect oils from the gland area. However, as
the sides of the flower are slippery, the bee slides into the fluid. The design on the pot
is such that the bee is able to escape. However just as the bee tries to escape through a
small exit tunnel on the side of the flower, the tunnel end is shut and the bee is trapped
again. When this happens, pollens are fixed onto the bees back. A few minutes later,
the bee is released and it flies off.
Butterflies, unlike bees are able
to see most colours but are not able to smell. Thus butterflies tend to pollinate flowers
are brightly coloured but are odourless. Butterfly
pollinated flowers are usually found in clusters where it provide a
landing ground for the butterflies.
Those species of plants that require bats for pollination often have their
flowers along high erected stalks or on stalks that hangs downwards from the branches. And
many of the flowers are white and give out musty odor that attracts bats. One example of a
bat pollinated tree is the Parkia pendula. The flowers of this tree are in a cluster and
hangs down from a stalk. That way, the flower is easily accessible.
Fruits function to protect and disperse seeds whose function is to
continue the next generation on plants. Plants adopt different methods to disperse their
Wind dispersed fruits are usually from emergent trees where their
crowns are high up where there are wind. These fruits are light and have fluff or wings to
carry them away as far as possible the wind can take them.
For water dispersed fruits, they are floatable and waterproof to
prevent damage from the water.
For animal dispersed fruits,
- some have structures to attach themselves onto animals, such as sharp
barbs or hooks, or just being sticky
- Some are small enough to be eaten and excreted by animals. The seeds
are passed through the animals digestive tract unharmed and deposited in a moist
- Have brightly coloured flowers and fruits like the ginger
Some plants resort to mechanical dispersal to release their seeds.
Once dried and mature, the fruits of these plants pop out and release an explosion of
seeds. Such trees include the rubber.
Fruits and seeds provide one of the most important concentrated
resources to many invertebrates and vertebrate. Thus, to survive the seeds must be able to
escape from predation. Some do so by being dispersed by specialized animals.
Some seeds even resort
to being poisonous to escape from predators. The toxins that are developed
by these plants are powerful and may include chemicals such cyanide, latexes and
alkaloids. To counterstrike, insects have developed their own defenses against these
poisons. Some of them even use the poison themselves! Many legumes for example produce
canavanine, which halt the animals ability to manufacture protein. The bruchid
beetles can however not only identify this chemical, but also eat it.