Wednesday, October 17, 2007

Plethodon survey

Tuesday in Field Biology Lab we performed the annual survey of Slim Jim woods for Plethodon cinereus, the good ol' Red-backed Salamander. The survey consisted of forming three groups, survey three adjacent 50m-wide swaths up and down the slope of forest in the the Cornell Plantations. We partitioned the data by: Red-backed vs. Lead-backed, wood vs. rock cover, and upper slope vs. lower slope.

The game plan

Charlie outlining the game plan

Game time!

Since I could let the minions students do all the work, I focused my attention on getting some good pics of P. cinereus, in particular leadbacks, which I had none of. I feel I succeeded.

[A note: in case you haven't noticed this, you can click on the pictures to view them full size. I highly recommend it, to fully appreciate them (not to be vain about my photography skills! I just like seeing more detail in the pictures).]



Pattern variants

Melanistic patches on the back
Cream-backed with varying amounts of melanin

Now on to some of the finds. You can't turn 25 people loose on the woods without digging up some cool stuff. The first up is this:

I have previously identified these egg masses as Plethodon eggs. I did so again on this treck, showing them my group. Looking at this picture, I began to wonder, what is that slug doing? A closer examination brought doubt to my mind. Don't Plethodon attend their eggs? A few quick googles and I had my answer: a Plethodon nest vs. a Slug nest. These are slug eggs, and that slug is currently laying more. You learn something new every day!

Another neat find: a large Wolf Spider

This one also gets an explanation. While surveying the top of the slope, I found these fragments of a wing:

If you're thinking Pheasant, I'd agree with you. I've seen plenty of those feathers from the time when my Grandpa used to raise them for eating. Now the really fun part. 40 minutes later at the bottom of the slope, I found this:

A Pheasant skull, with blinder still attached! What a quirky find, given that I had found other remains 40 minutes earlier up the slope. I'm guessing this Pheasant was taken by a Red-tail or other large predator from the game farm just up the road from the forest lot we were surveying. Other students reported finding blinders too, so maybe its the preferred food source of one of the forest inhabitants?

After just over an hours' worth of sampling, we returned to the lab to compile our results. Drumroll.... 732 Plethodon cinereus! Our table-ized results follow:

A few things can be gleaned from our partitioning of the data:
- Lead-backed forms comprise ~10% of the population
- More cinereus were found in the top half of the slope. That could be due to effort (we searched the top half first and rushed the second half) but also less cover on the lower half.
- P. cinereus were found overwhelmingly more often under rock cover rather than wood cover. We can't infer much from that, though, without measures of the abundance and area cover of the wood vs. rock in the forest.
- Our measure of effort was 0.25 salamanders/minute/searcher. Given 64 minutes of searching, the whole group found cinereus at a rate of ~11/minute.

Doing some learning

Survey Data from previous classes

Date Number
1-Oct-98 312
7-Oct-99 248 * Mid-20's the night before
5-Oct-00 573
4-Oct-01 575
3-Oct-02 696
9-Oct-03 1641 *Whole slope sampled
7-Oct-04 771
18-Oct-05 608
17-Oct-06 460
16-Oct-07 732

These are the data from previous years' surveys. Excepting the year the entire slope was surveyed, we had the second highest total! Awesome!

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