What's the gist of pollination?
Think of pollination as plant sex by proxy. Or if this makes you uncomfortable, think of it as the transfer of pollen (male sperm) to the female part of the plant. After pollination, the plant forms seeds. They, in turn, once the opportunity arises, germinate into a new plant and the cycle of plant life continues.
While sex in general is fun, plant sex is especially fascinating. Plants evolved a number of ingenious ways to ensure successful pollen transfer. Since they can not move, meeting up and rubbing of parts together like in so many animals rarely is an option. Plants, instead often use mediators to “complete the gene transaction”.
Not all plants are into sex.
To be clear – not all plants reproduce by pollination. This is the so-called sexual type of reproduction – duh! However, there are plenty of plant species which do not care for sex at all and prefer other, more secure, but simple ways to propagate.
Many plants rely on the so-called asexuall reproduction, where the plant divides by fragmentation of its body, which in turn give rise to whole new plants. This is also known as vegetative reproduction.
Others chose the formation of vegetative spores. Pine cones for example are a collection of individual spores attached to each cone “scale”, which can grow a whole new tree.
Why is it that some plants evolved to depend of unreliable pollinators such as insects, other animals, water or wind for their reproduction? Clearly there are easier ways of the “doing it yourself” as described above.
Like in many animals, plant species often opt in for sexual reproduction, however complicated it might be. It advantage is that it provides variety! And no, I don not mean promiscuity, although, this also is an evolutionary favored factor in some cases. I mean genetic variability. This link leads to a detailed explanation of why is genetic variability important for evolution – from the University of Berkley.
To put it simply – having male sperm and female eggs randomly get together and fuse in order to produce the new plant allows the gene pool to be mixed up well. That way at least some of the population’s new plants are bound to be lucky in the gene lottery and carry the plant lineage successfully into the future.
Which plants rely on pollination?
All flowering plants have sexual reproduction. That’s the whole point of them having flowers – they carry their sexual organs. This brings a whole new meaning to the act of “smelling flowers”… The important thing is that in order for pollination to occur, the male and female sex-cells have to meet and fuse.
In some cases, a flower hosts both the male and female reproductive organs and the process tends to be relatively easy. A whiff of wind or a drop of morning dew can be sufficient to transfer one to the other and allow the fusion to happen. Such flowers are called bisexual or perfect flowers. Such are for example the lilies and roses, apples, cherries and many others.
In other cases, each flower carries only one of the sexual organs – male or female. They are, surprise, called imperfect flowers. The number of plants having two different types of flowers include, but is not limited to begonias, corn, hazelnuts and squashes.
To make things complicated, many flowering plant can reproduce asexually too, but that’s for another post.
Who's the third wheel in plant sex?
As already mentioned, sexual reproduction in plants usually involves a middleman.
Some of the world’s most important crops are pollinated by wind – wheat, rice, corn, rye, barley, and oats.
Water pollination is the trademark of many water plants like seaweed and eel-weeds.
The more interesting ones though, are the ones which use animals as pollinators. Those can be anything from bees, insects, butterflies, birds, mammals – you name it.
Picky pollinators and picky plants
If you’ve learned anything from my Amazing Parasites series, I hope it is that Nature is amazing and if you look hard enough, you’d find the weirdest things in it!
When talking plant sex, there’s nothing kinky (that I know of). However, there are some very picky players, which are such high-maintenance that one might wonder how are they still around!
One such species is the Brazil nut. It can only be pollinated by one single species of bee – the Euglossine bee. Not only that, but the nut only allows the females to enter it’s flowers. To make things more complicated, the male bees of the species need to woo the females in order for the bee colony to be sustained. But female euglossine bees pay attention only to males which have gone the extra mile. In this bee case, this involves a visit to a specific fragrant species of orchid, which is found in the same ecosystem. Once the Brazil nut itself is formed it requires yet another species – a local rodent, to spread and actually plant it for it to grow into a new Brazil nut tree.
Also, some species of fruit flies and mosquitoes would pollinate only exclusively single species of orchids.
The danger of BEEing exclusive
The danger of being so picky (either as plant or as a pollinator) is that if the collapse of one of the populations due to say environmental stress, directly threatens the co-dependent population. This article and video illustrate this very well in the case of squash and squash bees).
Luckily, most plants rely on more than just one species for their pollination, which is why the the disappearance of some one insect pollinator would most probably not be as cataclysmic as often portrayed in mass-media.
Nonetheless, each species has its place in the ecosystem. Ecosystems are very complex network of tens, sometimes thousands of species, and you never know what might be the knock-on effects of removing one (seemingly non-vital) species from the network, until it’s too late.
Which is why so many scientists caution for protection of habitats and ecosystems as intact and complete as possible – we’re far from being that skilled in geo- and eco-engineering yet, to allow ourselves the destruction of our ecosystem.