[R] Singling out observations

[Kurt_Helf at nps.gov]

Greetings
     I am attempting to plot observations of a cave aquatic invertebrate
dating from 1901-2004.  I can come up with a nice lattice plot of the eight
sites from which I have data easily enough.  However, I'd like to be able
to highlight the 0 observations on the plots, i.e., attempts to find it at
the site were unsuccessful.  I'd like to be able to highlight these
observations with either a symbol or a color.  Here's a sample of the data
(Reach=site):
 (Embedded image moved to file: pic17437.jpg)

Here's my code for the plot:
xyplot(No.Invert~Year|Reach, data=Invert.Coll.1901.2004,
         layout=c(4,2),
       ylab="No. Invert 'collected'",
       scales=list(x=list(rot=45)))

***************************************************************
Kurt Lewis Helf, Ph.D.
Ecologist
EEO Counselor
National Park Service
Cumberland Piedmont Network
P.O. Box 8
OR
NPS Warehouse
61 Maintenance Rd.
Mammoth Cave, KY 42259
Ph: 270-758-2163
Lab: 270-758-2151
Fax: 270-758-2609
Cumberland Piedmont Network (CUPN) Homepage:
http://tiny.cc/e7cdx
***************************************************************
Science, in constantly seeking real explanations, reveals the true majesty
of our world in all its complexity.
-Richard Dawkins

[Scientific] theories are passed on not as dogmas but rather with the
challenge to discuss them and improve upon them.
-Karl Popper

...consider yourself a guest in the home of other creatures as significant
as yourself.
-Wayside at Wilderness Threshold in McKittrick Canyon, Guadalupe Mountains
National Park, TX

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CUPN Cave Cricket Monitoring Website:
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CUPN Cave Aquatic Biota Monitoring Website:
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