Wednesday, December 28, 2011

What's down there?

Beyond the bounds of the scientific questions I like to ask about biological communities, I frequently just want to know what organisms live where. In shallow streams and ponds I can simply reach down with a net for the answer. Deeper lakes present a slightly larger challenge. Biologists before me have risen to the challenge and designed an array of amazing devices to get to the bottom of things.

A collaborator recently needed benthic samples from 5m deep in Lake Champlain. My petite Ponar dredge was the obvious tool for the job. It's called 'petite', because the full size version must be lifted using a winch. The petite version can be lifted, deployed, and recovered with just a little elbow grease.

The device is lowered on a line into the lake and consists of two weighted jaws held apart by a sprung pin. When the sampler embeds in the lake floor and the line goes slack, the pin springs out. A tug on the retrieval line brings the jaws together and a sample of the lake floor is collected. The lake floor organisms can be seen after some washing in a sieve bucket to remove the fine sediment.

So what's down there? Well, the sample I took in November was overwhelmingly dominated by striped mollusks native to the Baltic region of Europe. Zebra mussels came to Lake Champlain via the Laurentian Great Lakes. Because of their filter feeding activity, they shift food resources from the water column to the lake floor. One result of this is increased abundance of other benthic organisms. The other organisms in my sample included the larvae of midges, caddisflies, and mayflies along with 2 snail species. That's quite a bit of diversity for a square of lake floor measuring just 9cm on each side.

An important lesson can be learned from this sample. Zebra mussels are extraordinarily abundant and can easily attach to any equipment used in an infested lake. To contain these invaders, it is essential to clean and then dry all equipment between uses in different water bodies.

Monday, October 31, 2011

Birds eat pumpkins?

This seemed like an appropriate posting for today. My family and I carved pumpkins yesterday and left them outside overnight for the big day. At around lunch time today I noticed that most of our pumpkins had been attacked! I found small triangular dents, suggestive of bird beaks on most of them. The gourds that form the eyes of one pumpkin had fairly deep holes in them; I actually liked the effect. One pumpkin lid was entirely missing.

I took a quick look around online to see if this is a widespread phenomenon and it does not seem to be the case. A host of six-legged pests is listed along with snails and slugs on several pest management sites, but I can find no mention of birds. Perhaps the birds have focused just on me......or not.

I found a couple of blogs discussing pumpkin seeds as bird food with an array of advice (cook them ; don't cook them; sprout them...). One site recommended pumpkins as a source of beta carotene for birds. I can't say I have ever tried to feed pumpkin to birds, but it seems that the birds have helped themselves to them. My kids seemed oblivious to the vandalism, so all was well for the festivities.

Has anyone else had birds feasting on their pumpkins? I see that one person has had squirrels eating his pumpkins and with rather convincing documentation

Thursday, October 13, 2011

Spied a spider?

I recently had the pleasure of spending the night on an island in Indian Lake in the Adirondacks. While foraging for firewood on the northeast end of our island, my son and I found a large fishing spider sitting on a rock. She was carrying an egg mass under her body and sat still for some photographs.

Somewhere I had read that fishing spiders ran across the water surface to prey upon invertebrates trapped in the surface film. I assumed that with a 6.7 cm leg span, this must be the largest spider in our region. But with a little digging, I learned that at least one local wolf spider species is larger.

Far more interestingly, the fishing spider does not limit its menu to invertebrate prey. While they typically consume invertebrates, they are occasionally true to their name and can actually catch fish more than four times their body weight (Bleckmann and Lotz 1987). The spiders use ripples on the water surface to detect prey, including water striders. They move rapidly across the water surface by rapidly retracting their legs and then gliding before again making water contact. All of this happens so rapidly that Gorb and Barth (1994) who described the behavior could see it only using high-speed photography.

View Indian Lake in a larger map

Wednesday, October 12, 2011

Foot prints

How can biologists efficiently collect enough observations to draw conclusions about mammal abundance or diversity in a habitat? This is exactly the problem my students and I tackled in the Saint Michael's College Community Ecology course in the last two weeks. Attempting to observe shy mammals can be disappointing, particularly when moving through a habitat as a group of 20. Instead, our approach was to record mammal footprints at track stations.

Our track stations included a layer of powdered black chalk to blacken the feet of the mammals and a sheet of sticky contact paper to collect each chalky print. All of this was sheltered from rain in a plastic tunnel-shaped structure with an opening at one end. Students determined which habitats to study and we left several track stations in each habitat. We convinced the mammals that walking through chalk and onto contact paper was a good idea by baiting the stations with peanut butter or dog biscuits.

We recorded a total of 355 visits to our 31 track stations over a two week period. We have indeed confirmed that the campus is a grey squirrel and chipmunk haven! Prints were also left by skunks, raccoons, muskrats, and mice. One of the stations with rather smudged prints also contained several black hairs. Microscopic scale patterns on the hairs confirmed our suspicions that the nocturnal visitor was a skunk. Perhaps most interesting, the traps set by the Winooski River were visited by mink; perhaps many mink, or perhaps just one extremely well fed mink with a deep fondness for peanut butter and dog biscuits.