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Re: Evidence for bat predation on birds
Googling around on stuff like "chiroptera, altitude" gleans 3000m
foraging for t. braziliensis... I was mainly wondering about maximum
observed reproductive altitude.
That's the figure I found as well, and seems to be what Dann Pigdon
came up with.
As usual the most interesting stuff is accidental-- e.g., it seems
species richness in birds and bats "declines smoothly" w/ increasing
altitude (in the Andes) whereas species richness in local mice does
not. Further, the mouse species are more 'discretely zonated' than the
volants. Encouraging and unsurprising to a functionalist like myself,
who assumes that the gradual change in flight medium density has
shaped the bird/bat species profile... in all the ways you might
theoretically expect. I hasten to add that as near as I can tell, the
authors listed below don't necessarily share my locomotively based
assumption. Hard to tell until I get the whole article.
I just took a very quick look through the paper; it's pretty
interesting. One thing I note is that the species richness decline
isn't really that smooth in birds, though it is in bats. Given the
spike around 2500 m for bird diversity, and the high mid-range
amplitude, it might be that changes in arboreal habitat are more at
work than air density for the species richness change. The evidence
for density effects looks (at first glance) to be a bit better for bats
than birds. One bit of help would be to include some larger-bodied
volant species; they should be less affected by density changes (though
they would tend to be less affected by habitat gradients, as well).
This is a little surprising if you just paste it into a black/white
cartoon world-- "Highland bat species occupy broader elevational
ranges than lowland bat
species, but for both birds and mice, species at intermediate
had the broadest amplitudes."
It is a bit counter-intuitive. Maybe intermediate elevation bird
species have wider habitat preferences, or maybe they are adapted to
flight at both highlands and lowlands, and just happen to roost at
intermediate elevations. Hard to say, but just a couple of ideas to
toss out there. Thanks for posting the reference.