16 September 2012

Highlights of Field Season 4: The Final Release

Good evening lizard-lovers,
I hope you enjoyed the last post in which I got a little off-topic of summing up the field season with a tonne of baby pictures...
Anyway, this time I promise to actually write a concluding blog this time.

First off, as I may or may not have mentioned before, we decided to exclusively catch S. undulatus this time. The reasoning behind this was mainly that mark-recapture of the sort that measures natural selection requires one initial capture, and at least two more recaptures following. We already have this completed for H. maculata... May/June 2011, August 2012, and May/June 2012. Because we decided to add the second species, S. undulatus, May/June of this year we decided to focus on them this season (July/August) because we had under a month and needed to increase our sample size... (yes this also means we'll be going back next spring for our last recapture!)

Well, unfortunately, recapture-rates (from lizards marked in the spring of this year) weren't nearly as good as they were for H. maculata.

       The release of a little S. undulatus that certainly
got going as soon as we let him go!

Overall, of the over-200 lizards we caught, only ~10% showed elastomer marks from the spring. This is surprising since after the summer last year, we had a 60% recapture rate for H. maculata. We can think of two possible reasons behind this low recapture rate. The first is that perhaps the elastomer tags are falling out. Perhaps I am not tagging the lizards deep enough and they are shedding their tags with their skin. We thing this is unlikely because we'd see a number of lizards with some, but not all of their tags remaining- i.e. the ones that were not deep enough. This doesn't seem to be the case... either lizards had tags, or they didn't. We hope that with all the photographs, scans, and gps coordinates we took, we can match up the lizards determine if they really did lose their tags.

Our "field schedule" including person-hours, lizards-captured, and some other... interesting drawings that show up after four people have been living in close proximity for far too long.
Of course, it is also possible that the population size of S. undulatus is much larger than we had anticipated (this is what mark-recapture calculations should tell us)... and this species is far more elusive. Considering what we know about the fence lizards... they do seem to be elusive. They are more arboreal than the lesser-earless lizards, and hide extremely well in vegetation (such that we often have to wait for an hour for the little fellows to re-emerge).

Sometimes we mistake this species, the side-blotched lizard (Uta stansburiana) for S. undulatus when it flashes by through a bush. These little ones are only found on the very edge of White Sands... often only the first dune off the dark soil desert. As of yet, it's a mystery why the side-blotched lizard hasn't colonized and adapted to White Sands.
Regardless of the extra patience it required to catch S. undulatus and the lower recapture rate, the field season was a great success with an average of 13 lizards per day. We even got a chance to head over to the Jornata Long Term Ecological Research Site (one of our dark-soils sites) and take a look at some of the species there:

One of the cutest/fattest lizards of all- a Texas horned lizard (Phrynosoma cornutum)

Lizard food? Unlikely... in all the lizard guts I've dissected.. I've never seen evidence of them having eaten an Anisoptera.
Recognize this little guy? My supervisor likes to call them the "junk lizard" of the desert. I took this action shot just after we let this one go... 
Well with that I will finally sign off for this year. Hopefully soon I will be able to post some results regarding the direction and magnitude of natural selection on the two White Sands lizard species- the lesser-earless lizard (Holbrookia maculata) and the Eastern-fence lizard (Sceloporus undulatus). Is natural selection still acting? What form does it take? Is it similar in both species? What about the population dynamics? Is there a fifty-fifty sex ratio? What is juvenile recruitment? How far do lizards disperse and do both species overlap in habitat use?
So many questions... only one dissertation (for now!)

Thank you everyone for following! Thank you to my great field assistants (Jackie Howells, Isaiah Hoyer, and Michaela Brinkmeyer), and especially the lizards for their reluctant participation in the noosing, prodding, flattening, and injecting that is my project!
Until next time, good night herps and herpetologists of the world!
-S. Des Roches

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