[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: COMPETING BATS, BIRDS & PTEROSAURS



Dear people of the list,

I shall now go on about the ecological struggle of the hairy, membraneous,
echolocating bats and the sharp-sighted, feathery birds. I too hope that no
one gets offended if the topic hasn't got enough to do with dinosaurs.

I said:

> > But anyway, the historical constraint of having become a
> > nocturnal, color blind animal with dull vision results in an inability
to
> > evolve into a diurnal flier, when there are birds around.

Adam Britton said:

> Haven't we come full circle here? You originally argued that vision was
> superior to echolocation and hence bats were unable to exploit the daylit
> skies, whereas I responded that echolocation is just as effective as
vision
> in its ability to provide the bat with the information it needs to get
> around. I'm not sure whether I succeeded in my argument, although I
enjoyed
> trying, but it brings me back to the idea that other factors were
> responsible for bats not exploiting the daylit skies. For example, flying
at
> night avoids diurnal predators, and it also neatly gets around
> thermoregulatory problems during the heat of the day. Megabats, which use
> vision and not echolocation, also have similar thermoregulatory problems
> forcing them to roost during the heat of the day.

I'm not sure if I completely understand what you are meaning here with your
statement of us making a full circle. However, my original statement really
was that vision is superior to echolocation and so bats can't compete with
diurnal birds. You have made me more convinced that echolocation is indeed a
very good way of detecting insects. But still, as you seem to think too,
vision is in overall a better way of perception - when there is light, of
course. And in daytime, there is light. In the night, there isn't.

Then, we may ask how we have come to this situation - why have bats evolved
echolocation, and why birds use their eyes? I think the reason is that the
ancestral mammals somehow couldn't compete with diurnal dinosaurs (and I'm
not going to start guessing why), and so started to adapt into living in the
night. Their cones got sparser, and they lost the ability to see colors and
little details - while gaining the ability of seeing in almost complete
darkness.

Then, for some reason, some of these mammals started to evolve into flying
forms. However, the skies were already swarming birds, equipped with very
good eyes. They could see many colors, and they could see very far. The
early bats, in turn, had the eyes of nocturnal animals (no color sight, dull
vision, though very sensitive to light), and probably already some kind of
primitive echolocation system. The most natural path of evolution they could
take, then, was to become nocturnal fliers. That's what I think.

I agree with you that the sensory system adopted by the ancestors of bats
and passed on to the bats in a more sophisticated form may not be the only
constraint making bats lose to diurnal birds. But I think it is an important
factor.

Best wishes,
Henri Rönkkö