How widespread is Euryopis formosa's relationship with pines?

Click to enlarge. [source]

Rod Crawford and I noted in our recent paper that virtually every Euryopis formosa (Theridiidae) specimen collected in Washington state has been collected in the vicinity of ponderosa pines (Pinus ponderosa) (see map, right).  Our observation was consistent with Gillette et al. (2008), who identified E. formosa as a significant indicator of old-growth status in a pitfall study of the ground-dwelling spiders in P. ponderosa stands in the Cascade Range of California.

Since Euryopis formosa occurs from "Central California north to British Columbia and east to Wyoming" according to Levi (1954), these findings left me wondering whether E. formosa is associated with pines over its entire range, or whether the apparent association is only a Cascades phenomenon.  To begin answering this question, I decided to do a back-of-the-envelope analysis by mapping E. formosa specimen locations reported in Levi (1954) and Bennett at al. (2014) along with those Rod Crawford and I reported on from Washington.

Presence or absence of pine
(Pinus) at E. formosa collection sites

I obtained coordinates for the published locations from USGS's Graphic Names Information System and Google maps, then determined the presence/absence of pines (of any species that drops open, intact cones) in the area using a combination of Google Street View, E-flora B.C. and Calflora.  I mapped the results using GPSVisualizer.  Note that since the specimens listed in Levi (1954) were collected in the late 19th or early 20th century, sometimes from poorly defined locations (e.g. "Jackson County"), I can't be certain that I've correctly identified every location or correctly guessed the forest type growing there at the time of collection.  Hence, "back-of-the-envelope".  Given those caveats, here is the result.  Green markers indicate specimens collected in places where pines were likely to be present at the time of collection.  Collection sites within about 5 miles of pine-containing forests are marked in blue, while sites thought to be devoid of pines are marked in red.

It appears that the spider-pine relationship holds true in the core of E. formosa's range, but less reliably so on the edges. Of course, no firm conclusion can be drawn from this surface analysis.  For that, one would need to get updated specimen data from relevant spider repositories and superimpose it on range maps of pines that drop open, intact cones.  It would be a fair amount of work, but it looks like a worthwhile project.