[Odonata-l] Morphology and niche overlap

[Roy v. Grunsven]

Testing the niche theory is very difficult. It is always possible that 
species differ in a characteristic you did not check, no matter how well 
you've looked.

In dragonflies the larvae are the real playing field, that's where the 
species compete. Looking at habitat preference a lot of species can be 
separated on pH, oxygen concentration and different sediments or vegetation 
needed. But if two species are in the same pond does not mean they 
automatically compete, they can be in different places (in clusters of 
plants or in the open) active at different times of the day or year or have 
different food preferences.
An example of this is A. juncea and A. subarctica. These two are very alike, 
both as adults and larvae. They often co occur and (at least in The 
Netherlands) A. juncea is much more common. When looking more closely the 
larvae of A. subarctica live in sphagnum mats and have an advantage over 
juncea in this specific microhabitat. Probably competition with juncea keeps 
it restricted to these sites but it does allow them to coexist.

Another aspect is temporal change. A lot of species are weak competitors and 
are out competed all the time if a stronger competitor arrives. But in new 
sites (after drought for instance) they have a temporal safe haven until out 
competed again. So they can coexist although it's temporary.

All in all we can not really answer this question. Maybe we’ll get the data 
to show differences but will never have enough data to show that there is no 
difference between two species.


Roy van Grunsven.


>From: Joshua Stuart Rose <opihi at mindspring.com>
>To: Odonata-l <odonata-l at listhost.ups.edu>
>Subject: Re: [Odonata-l] Morphology and niche overlap
>Date: Wed, 29 Mar 2006 23:54:05 -0600
>
>At 02:40 PM 3/26/2006, Dennis Paulson wrote:
>
> >Niche theory has always predicted that there should be some
> >difference in two closely related species to allow them to coexist,
> >yet that doesn't seem to be the case in many odonate genera. Are
> >odonates examples of animals that can be used to refute the
> >absolutes of both niche theory and allopatric-speciation theory?
>
>I do not think the data exist yet to allow us to make this claim. I
>tried to apply niche theory to odonates in my dissertation, and even
>restricting myself to a fairly narrow set of populations, the
>challenge was formidable. And I just worked on adults; to really work
>out the problem would require data on larvae as well. Maybe things
>have progressed a lot in the last year or two, but I did not see any
>ecological niche data on larva except at the coarsest scales: pH,
>plant/aquatic community, seasonal phenology.
>
>I haven't read Mark McPeek's latest stuff - I'm out of academia now
>and so do not have ready access to a decent library - but I think
>short-term, fine-scale allopatry is still a much more likely method
>of speciation, especially for insects with relatively limited
>dispersal and specialized habitat, than simultaneous mutation of male
>and female lock-and-key structures in sympatry. There is relatively
>extensive evidence among birds, and I think Hawaiian Drosophila too,
>that species get much less picky about mates when mates are in very
>short supply; and it is very difficult to figure out patterns of
>sympatry/allopatry in the past.
>
>Would love to hear if there have been some big new publications in
>the above areas that I've missed...
>
>Cheers,
>
>Josh
>
>Joshua S. Rose, Ph.D.
>http://www.duke.edu/~jsr6/
><mailto:opihi at mindspring.com>opihi at mindspring.com
>
>Bird Program Specialist
><http://www.worldbirdingcenter.org/>World Birding Center
>Bentsen-Rio Grande Valley State Park
><mailto:joshua.rose at tpwd.state.tx.us>joshua.rose at tpwd.state.tx.us
>956-584-9156 x 236
>
>Duke Natural History Society
>http://www.biology.duke.edu/dnhs/
>
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