Wednesday, December 16, 2015

15-Dec-2015 U-W Campus, Washington

Site location. Click to enlarge.
The weather forecast wasn't looking promising for a full day in the field at any of Rod Crawford's target sites, so instead I spent an hour tapping cones on the nearby University of Washington campus in Seattle.  The campus sports numerous eastern white pines (Pinus strobus) as well as other exotic pine species.  In some places their fallen cones are allowed to accumulate, creating habitat for spiders and other invertebrates.

Sample site, Hutchinson Hall on right.
The fallen cone microhabitat, with
cigarette butts.
For years I've been developing a mental map of pine cone deposits on campus.  The site I sampled this day, located between Hutchinson Hall and the adjacent tennis courts, was one of the first I noted years ago as I walked through campus from the Burke Museum to my bus stop by the HUB.  Four mature eastern white pines stand in a row along the sidewalk that runs the length of the area.  No shrub layer or ground cover grow here, and the litter consists of a thin veneer of pine needles and the occasional oak leaf.  The area seems to have two main functions: as a pedestrian shortcut through the tennis courts, and as a place for people in Hutchinson Hall to grab a smoke.  Cigarette butts outnumbered fallen cones near the hall's southeastern door, and there were a lot of cones...

Female Tachygyna ursina (left)
and T. vancouverana (right)
Juvenile theridiid
Air temperature never exceeded 40 F while I was there (brrr!), but this didn't seem to impede the movement of the linyphiids that hit my net.  Of the 6 spiders I tapped from 50 cones, 4 of them were linyphiids: Tachygyna vancouverana and probably Tachygyna ursina (still to be confirmed).  The other two spiders were a juvenile dictynid and a juvenile theridiid that could very well be a Platnickina tincta (=Theridion tinctum).  These are all spider species that I've tapped previously from pine cones in western Washington.

Interestingly, I found no spiders in the cones I tapped in the middle of the plot.  All spiders came from cones lying within a few inches of the building or the tennis court wall.  Was this random chance, or was it due to differences between the "inner" and "edge" cones in microclimate or predation pressure or some other factor?
Another view of the sample site.

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