[Odonata-l] what a difference a wing makes
ethanbr at umich.edu
Tue Nov 11 10:33:21 PST 2008
Dennis Paulson wrote:
> A recent paper published in the journal Fisheries concludes that
> nearly 40 percent of all species of freshwater and anadromous fishes
> in North America (Canada, US, Mexico) are in jeopardy.
> Details here: http://www.ens-newswire.com/ens/sep2008/2008-09-09-02.asp
> On the other hand, it is possible that odonates are also more
> resistant to the numerous environmental problems encountered by fish.
> One I can think of is fishing pressure. There isn't much of a fishery
> revolving around any species of odonate! Dragonfly larvae could also
> be more resistant to pollution, siltation, reduced oxygen levels,
> and/or temperature fluctuation. They could have greater habitat
> breadths than fishes, species for species. Or does it all come down to
> those two pairs of wings?
What might be more of concern are the indirect effects upon odonates -
and other aquatic macroinvertebrates - due to the loss of anadromous
fish populations. I would hypothesize that the effects upon lotic
odonates might be more pronounced in oligotrophic streams, where
migrating fish often represent a significant input in nitrogen and
phosphorus nutrients upon their death after spawning. (Essentially there
is a net transfer of biomass and nutrients from regions of somatic
biomass growth, e.g., the oceans or very large lakes). These fish are
often important indirect contributors to primary productions in
naturally nutrient-poor systems, and when these fish die one can see
both an increase in bacterial, fungal and algal biomass as well as
macroinvertebrates grazing on the dead bodies as well as the
previously-mentioned micro-organisms. Yes, there might be a direct
predator release due to the loss of foraging fish, but then again there
might be subsequent decline due to the loss of prey organisms that
depend on the products of fish decomposition.
Would make for a great study. Any money?
More information about the Odonata-l