[Taxacom] Geodetic datums do matter

Jim Croft jim.croft at gmail.com
Mon Mar 23 20:33:40 CDT 2009

Yours is a particularly animal view of the world Doug.  Plants, as a
rule, generally don't get up and move around and it is not uncommon
for botanists to want to recollect the exact same population (and even
exact same individuals) and not uncommon for them to have reasonable
success in this, given an accurate and precise locality for the
original collection.  A variable 20-200m offset may not make the task
impossible, but it makes it a lot more difficult, especially in thick
vegetation and complex terrain.

In plants, patches or populations tend to be the rule rather than the
exception, and many (most?)  of these patches would be (much?) less
than 200 m (an approximate datum error in this part of the world)
across and often times they can be less than 200 m apart.  The study
of variation within an between populations has been critical to the
sorting out of taxonomy of certain complex groups and a near enough is
good enough approach doesn't really cut it these days.  But if the
mobility of your organism exceeds the precision of you instrumentation
(e.g. with larger vertebrates), then 'near enough' is probably more
than adequate.

A collateral benefit of precise and accurate geolocation is that
occurrence records defining populations can be used for climate
climate change studies at a finer resolution, at least in plants.
For many plants to get up and move 200 m is a big deal and one not
undertaken lightly and without careful consideration of imperative.

Compared to zoologists, botanists have it easy.  We have the single
geostochastic variable of a collector stumbling around in the bush.
We do not have to deal with an equally mobile prey taking evasive
action.  There is little luck involved - if you can get to the right
place, you expect the plant, in many cases the same one, to be there.
If it is no there, either you are not in the right place, or there is
a story there needs telling.


On Tue, Mar 24, 2009 at 9:47 AM, Doug Yanega <dyanega at ucr.edu> wrote:
> I would have hoped it was clear that I was not implying that you or I
> couldn't come up with dozens of scenarios where precision is
> important - but rare plants, rare fungi, rare sessile snails, and
> invasive plants that only occur in a SINGLE PATCH, are all *extremely
> exceptional* cases. There are not going to be very many species on
> this planet that will be found ONLY in an area that is less than 50m
> in diameter, never straying beyond that boundary. Just because there
> are exceptional cases doesn't invalidate the existence of a general
> pattern, and the general pattern is that if you give a biologist a
> GPS reading and let them go in search of an organism, even a 200m
> error is almost never - *in and of itself* - going to make it
> impossible for them to find what they're after, because most
> organisms don't occur as isolated individuals or "particular patches"
> that could never be found unless you go back to the exact square
> meter they were first seen (and most biologists wouldn't give up
> looking after searching only a 20m radius). Certainly, if you happen
> to work on organisms that *are* in that exceptional category, then by
> all means you should take all necessary steps to record your
> geolocations as precisely as possible, but for the vast majority of
> cases, that level of precision is meaningless.
> Peace,
> --
> Doug Yanega        Dept. of Entomology         Entomology Research Museum
> Univ. of California, Riverside, CA 92521-0314        skype: dyanega
> phone: (951) 827-4315 (standard disclaimer: opinions are mine, not UCR's)
>              http://cache.ucr.edu/~heraty/yanega.html
>   "There are some enterprises in which a careful disorderliness
>         is the true method" - Herman Melville, Moby Dick, Chap. 82
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Jim Croft ~ jim.croft at gmail.com ~ +61-2-62509499

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