31 August 2011
28 August 2011
We left Montreal Friday morning and a couple of hours later left Canada near Rouses Point, New York. After exiting the U.S. border station, we took Route 2 that crosses Lake Champlain into Vermont. While still on the bridge, we stopped for lunch at a convenient parking lot facing north.
After I finished my sandwich, I had my customary quick walk along the shore of the lake to check out the local mollusk fauna. These small mussels were abundant on the rocks at the edge of the water.
If I am not mistaken, they are the infamous zebra mussels (Dreissena polymorpha) that have been present in Lake Champlain at least since 1993.
These mussels are native to southeast Europe. They were 1st seen in North America in 1988. Despite its small size, the zebra mussel is a nuisance species, because it is invasive and often present abundantly (more info from the USDA).
Posted by AYDIN ÖRSTAN at 20:19
25 August 2011
I spent part of my last full day in Montreal photographing and filming the snails I found in my sister's garden. One of them was the following.
The diameter of the shell was 8.7 mm. Note the hairs visible along the edge of the body whorl. Based on the descriptions in Identifying Land Snails and Slugs in Canada – Introduced Species and Native Genera, I have identified this specimen as Trochulus hispidus (the other candidate is T. striolatus). It is a native of Europe that has been introduced to Canada.
Posted by AYDIN ÖRSTAN at 21:41
24 August 2011
Yesterday on our way to Ottawa we stopped at the village of Bishop's Mills and paid a visit to our naturalist friend Fred Schueler. Our sojourn culminated with a search for the snail Cepaea nemoralis. Our expedition was brief, though, and barely extended beyond the lily patch across the road from Fred's house.
We did find several of our favorite snails on the soil under the lily leaves and among the grass.
How these snails, which are native to Europe, came to be in Bishop's Mills is a question we will leave unanswered for the time being.
Posted by AYDIN ÖRSTAN at 08:44
22 August 2011
This week I am in Canada. Yesterday morning on our way to Niagara Falls thru New York, we stopped at the northern shore of Skaneateles Lake for a short walk along the lake and on the pier that extends into it.
These operculated snails were abundant on the shore.
I suspect they are a non-native species of apple snail (family Ampullariidae). A more definite identification will hopefully follow after I've had a chance to send their pictures to more knowledgeable people.
Posted by AYDIN ÖRSTAN at 08:48
18 August 2011
In the previous post, I presented a histogram for the heights of a sample of 131 adult shells of an Albinaria species. Now here is a bivariate plot of shell heights (H) against shell diameters (D) for the same sample.
Height and diameter are about equally variable and they are also correlated with each other. What could this mean?
If the snails were under strong selective pressure to conserve their shell volumes, we would expect a negative correlation between H and D: when H became large, D would be smaller and vice versa. So a plot of D against H would look like this:
I obtained this plot by calculating a hypothetical value of D for each measured value of H at a constant volume. I obtained the volume from the mean H and D values for the sample assuming that the shell shape was a cylinder. Of course, in a real-life sample there would be scatter arising from biological variation and measurement error.
The positive correlation between H and D in my sample (1st plot) indicates that shell volume is not conserved. What is under selection is probably the shape of the shell. But what is the significance of shell shape?
Let this be tonight's food for thought. I will probably return to this topic in the future.
Posted by AYDIN ÖRSTAN at 20:49
16 August 2011
Regular readers may have noticed that one of my passions is to measure snail shells. I have written about the variability of shell dimensions on several occasions, for example here. Naturally, I have pages and pages of data waiting to be analyzed and made sense out of.
Today, I entered a set of measurements from 2004 into the computer. They belong to a sample of 131 shells of an Albinaria species that we had collected in 2002 in Turkey. Here is the histogram for shell heights.
I haven't run any statistical tests, but the distribution looks roughly normal. The 2 specimens making up the right-hand tail seem to be outliers. However, the relative coefficient of variation* is 5.8%, which is quite ordinary for shell heights of tall-shelled land snails. So those 2 shells actually lie within the expected range of variation for a sample of this size.
The 2nd entry in this series is here.
Posted by AYDIN ÖRSTAN at 19:42
14 August 2011
And now for something completely different: the video of an inchworm looping on my deck.
As you can imagine, it wasn't easy to follow this little guy with the camera while keeping it in focus and at the same time without shaking the camera too much. It was about 16 mm long.
Posted by AYDIN ÖRSTAN at 19:36
11 August 2011
I bought a new camera recently that can take high resolution videos, which I intend to use to film my favorite creatures. The ultimate aim is to better understand their behavior and functional anatomy.
I am more or less a novice at this and still learning the tricks of video photography, especially of the close-up, hand-held camera kind. The experience I have gained from years of still photography helps, though.
Here is one of my 1st attempts at snail cinematography. The subject was an adult Euxina circumdata with a shell length of 11.7 mm.
Do remember that at such high magnifications the depth of field is very short as it would be in any kind of close-up photography. As a result, not everything is in focus simultaneously. But the nice thing about using a hand-held camera is that I can move it back and forth to bring different parts of the subject in focus.
Notice how short the snail's foot is relative to its shell. Because of that size discrepancy, the snail can't lift its shell up when crawling on a horizontal surface. I have written about this before in this post. Nevertheless, the adhesion provided by the short foot is more than enough to support the weight of the snail's body and its shell when it's crawling sideways as you can see in the video or even upside down.
I had to reduce the resolution of the file to be able to upload it here. The original uncut version is 225 MB.
Posted by AYDIN ÖRSTAN at 09:20
09 August 2011
This was probably a Laudakia stellio, a relatively large lizard that inhabits rock outcrops, ruins and even the walls of houses in western Turkey and elsewhere.
I saw this one on one of the surviving walls of Magnesia on the Meander last July in Turkey. They are quite skittish, as are most lizards, and quickly disappear inside a crevice as soon as they spot an approaching human.
A telephoto lens would have produced a better picture, but I didn't have one with me.
Posted by AYDIN ÖRSTAN at 18:32
07 August 2011
I am into making videos these days. Here is a carpenter bee I filmed this morning.
I am still in the learning phase. I hope to get better as I get more practice and develop my techniques in the art and science of close-up moving pictures, my primary interest.
So expect more video clips on this blog from now on.
Posted by AYDIN ÖRSTAN at 21:19
05 August 2011
On very hot days it's not unusual to chance upon flattened squirrels on sidewalks or streets. The 1st time I saw a squirrel like that it was so flat that I thought it had been run over by a car. But when the squirrel noticed me it got up and ran to the nearest tree.
After the squirrel in the picture above ran away, I walked over to the shady spot where it had been lying and flattened my palm on the asphalt. It felt cool. Apparently asphalt and concrete conduct heat well. So by flattening its belly against such a surface, a squirrel loses body heat and lowers its body temperature. That's a good thing to achieve on a hot day.
Initially I thought the belly-cooling behavior had probably originated among the city-dwelling squirrels within the last 200 years or so. But when I searched the internet for more information, I saw pictures of squirrels lying on soil or wood chips. The behavior may in fact be an ancient one.
Posted by AYDIN ÖRSTAN at 21:20
03 August 2011
The eastern North America has been under the influence of a heat wave that hasn't quite abated yet. For about 3 weeks now, the daytime temperatures have been hovering around at least 30ºC (what's that on the Fahrenheit scale?).
July 22nd was an exceptionally hot day. At 1545 a few centimeters above the soil in my backyard, I measured an air temperature of 39.3ºC. When I put the probe of the thermistor in contact with the surface of a rock that had been baking in the sun, it shot past 46ºC*.
It eventually went up to 46.7ºC and would have gone up even higher if I hadn't gotten too hot from squatting out there and escaped inside.
My underlying purpose was to figure out how the snails and slugs that normally inhabit the undersides of those rocks were faring with the heat. I could not find any Vertigo to run a test, though. Had they all retreated deep into the soil?
*Admittedly, this was not a good measurement. The thermometer probe, being unshielded, was probably exposed to radiation. On the other hand, it would have been difficult to shield it while measuring the temperature of the surface of a rock.
Posted by AYDIN ÖRSTAN at 14:26
01 August 2011
Following the American Malacological Society's annual meeting in Pittsburgh last week, a group of us went on a field trip on Thursday. The location was the biological research station of Carnegie Museum of Natural History, Powdermill Nature Reserve, near Rector, PA.
We spent about 2 hours in the woods searching for snails and slugs. Some of the finds included this slug, a Pallifera sp.
And there were several individuals of Mesodon thyroidus. This one was climbing a tree, something they often do on warm and humid days.
The next snail, Ventridens intertextus, was the highlight of the trip for me, for I had never seen this species before.
After field work, we had lunch, sorted and identified the specimens collected and socialized. Here is the group photo after lunch.
Posted by AYDIN ÖRSTAN at 11:58