I went on an interpretive trail today and came across a wild flower sign. It said that some flower species evolved such that they can not be pollinated by humming birds as they are shaped such that only an insect proboscis could get into it. Why would a flower evolve in such a way? Wouldn't it be advantageous to take any pollinator?

An interpreter in the visitor center suggested it might be that the flower wants to save it's limited pollen for pollinators most likely to visit other families of its species. I'm not completely sure I buy this, as a pollinator willing to visit one flower of a species is likely to visit another flower of the same species. That said, I think he might have been on to something. Alternatively, this link made me think perhaps certain pollinators might damage the flower and it would want to discourage them.

This question goes beyond a flower co-evolving such that a particular organism could specialize in pollinating it; I'm curious why a flower would specifically evolve such that it could not be pollinated by a particular organism.

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    Could you tell us specifically what species you are talking about. Otherwise this is an unclear question. – James Sep 14 '16 at 8:21
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    It's two sides of the same coin, by specialising to have one specific pollinator, you have to exclude others – ELL Sep 14 '16 at 10:04
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    Probability. A rare flower got a larger chance of successful pollen transfer if the pollinator searches specifically for other members of its species. The previous comment describes one option to achieve that. Typically, what we observe today is the result of coevolution. The pollinator gets access to a food source not accessible to others and the flower gets a specific pollinator. – Roland Sep 14 '16 at 10:33
  • The interpreter's explanation was also the one that immediately came to my mind. There is also some evidence that high specialization (and therefore low pollinator sharing) increases pollination probabilty: ncbi.nlm.nih.gov/pubmed/19909087 – Hav0k Sep 14 '16 at 12:14
  • @James, I was afraid someone would ask that (: I looked a lot online and could not find the species. I believe it was a type of Elephant Flower indigenous to Utah but am not sure. – chessofnerd Sep 14 '16 at 17:49
up vote 0 down vote accepted

I think the explanation by the interpreter is most appropriate. The definition of species is a particular category of organisms capable of reproduction among themselves. Thus pollen of a particular species must fall on the stigma of the same species. But pollinators visit all species of flowers (as they never visit Biology Stock Exchange, thus ignorant of the definition of species) which bears nectar and the entrance is big enough to let them in.

The flowers in your question increase their chance of pollination by reducing the varieties of flowers a particular pollinator can visit. Lets make it simpler (or even more difficult for those who don't like mathematics!)...

Suppose there lives 4 humming birds and 4 bees in a oasis...both are too lazy to visit other oasis in search of nectar. One morning 4 flowers bloom in that oasis...2 wild flowers you mentioned and 2 wide mouthed flower of some other species. Now 1 flower of the wild species can be visited by 4 bees (as humming birds can't enter the flower). One flower of the other species can be visited by 4 bees and 4 humming birds. This large number of pollinators for the second type of flower reduces its chance to be visited by a pollinator that visited a flower of the same species. Whereas for the wild type flower the possible number of pollinators are very few (only 4)...so the chance of one bee visiting two flowers of the same species is very common and so is the chance of it getting pollinated.

In this way these flowers increase their chance of pollination by modification of their shape.

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    I think the OP is asking why a flowering plant might evolve to exclude pollination by some species of pollinators, rather than why it might evolve to special adaptations to allow some specific pollinator – ELL Sep 14 '16 at 15:03
  • I answered by considering "species" of pollinator...humming birds and bees are examples of species only. – Arnb Sep 14 '16 at 16:17
  • I think this is correct. To repeat but also perhaps flesh out your example, suppose a flower only has enough pollen to be visited by 5 pollinators each day. If a hummingbird only has a 10% chance of visiting another flower of the original flower's species but a bee has a 50% chance of visiting the original flower's species, it is advantageous for the flower to not "waste" pollen on the bird. – chessofnerd Sep 14 '16 at 17:48

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