Literature Review: Bluets

by Carl Strang

One of the papers I found most interesting in this year’s literature review had to do with damselflies (Siepielski, Adam M., Ken-Lou Hung, Eben E.B. Bein, and Mark A. McPeek. 2010. Experimental evidence for neutral community dynamics governing an insect assemblage. Ecology 91:847-857).

Familiar bluet. I can believe that this one is ecologically interchangeable with most of the others.

In particular they focused on the 34 species of North American bluets that live in lakes with fish in them (among both dragonflies and damselflies there are a few species that live only in the relatively few bodies of water in which nymphs are free of predation pressure by fishes). Using a variety of experimental, observational and comparative methods, the researchers concluded that the nymphal stages of all these species are completely interchangeable. Competition, separation into different chunks of niche space, differential avoidance of predation, none of these processes apparently separate these bluets ecologically.

Tule bluet. This species, on the other hand, in my experience sticks to the larger, more open lakes.

These bluets as a group are, however, separated from the forktails, a different group of similar-sized damselflies. Bluets are better at avoiding predators, while forktails are more efficient “at converting prey into their own biomass.” I’m not entirely sure what that means; perhaps being more predation prone, they need to be able to get by on less food and so minimize their own exposure.

Eastern forktail. The authors seem to believe that the forktails likewise are ecological equivalents. Someone needs to get the data.

If the larvae are all alike, perhaps the adults are ecologically subdivided? Siepielski et al. didn’t look into this, but they pointed out that the damselflies live in their adult stage for an average of only 4 days, compared to most of a year as nymphs. The diversification of bluet species “seem[s] to have been driven primarily by sexual selection for differentiation in reproductive structures and little else.”

Slender bluet. Another question is, why are some species much more common than others? I run into a lot more familiar bluets than slender bluets.

They suggest that similar neutral community dynamics may operate commonly among insects, given the many sibling species groups. This raised my own metaphoric antennae, as many singing insects (cicadas, crickets and katydids) belong to clusters of sibling species. Along the way, Siepielski et al. mentioned the interesting fact that dragonfly nymphs have been shown elsewhere to feed negligibly on bluet nymphs.

Orange bluet. On the whole I accept these results, but as hinted in the above captions, there may be a little more complexity to this story.

A related theoretical paper published this year (Van Doorn, G. Sander, Pim Edelaar, and Franz J. Weissing. 2009. On the origin of species by natural and sexual selection. Science 326:1704-1707) developed a model that supports the possibility of sympatric speciation where female selection of mates produces divergence. It requires the appearance of identifiers (e.g., color patches) that correlate with the different subpopulations. Females in the different environment patches then are favored to the extent that they identify and mate with the appropriate local males.

Dragonfly Monitoring Update

by Carl Strang

Earlier I described  my first venture into dragonfly and damselfly monitoring by kayak. I have been out on the Des Plaines River twice since then. There has been some variation in the count of species and individuals each time, but most seems unremarkable. I’ll focus on a couple high points. The biggest surprise was a transition in the damselflies. The slender bluet was the common black type bluet my first time around.

Slender bluet 5JL 1b

Bluets are a group of small to medium sized damselflies. Black type bluets are so called because their abdomens are nearly all black as viewed from above. On my second and third outings, the slender bluets were replaced by stream bluets as the common black type bluets. Here is one of the latter I rescued from the water.

Stream bluet 23JL09 1b

Note that, in contrast to the slender bluet in the top photo, the stream bluet has a slender blue shoulder stripe with a wider black stripe below it. “Eye spots” on the back of the head are smaller in the stream bluet, and there is less blue in the abdomen tip. Stream bluets were largely in tandem pairs and actively laying eggs on floating vegetation during both recent outings.

Stream bluets tandem b

The other surprise is the relatively large number of orange bluets. Here is one sharing a photo with a stream bluet.

Orange and stream bluet b

I’m not saying that the river is swarming with them, but in my experience a count of 13 orange bluets in a 2-hour outing is a lot. A final note is that eastern amberwings have become the most abundant dragonflies, despite my seeing none on the first outing. Here is a photo of one from 2007.

Eastern amberwing male 2b

I have decided to limit my monitoring to the stretch of river that bounds Waterfall Glen Forest Preserve. This gives me a span of stream between the launch ramp and the preserve in which I can practice another type of inquiry, to be featured tomorrow.

Dragonflies on the Deck

by Carl Strang

I have been part of the regional dragonfly monitoring program since it began in 2003. I started counting dragonflies and damselflies at Willowbrook, Songbird Slough and Waterfall Glen Forest Preserves, in recent years focusing on the last two. Though I continued to find new species from time to time, the past couple of years I have felt the need to try something new. The major gap in my knowledge was in river species, so this year I decided to combine my loves of kayaking and dragonfly monitoring by trying out a river route. Water levels have been high, and cool weather has been suboptimal for monitoring, so I didn’t make my first excursion until last weekend. I launched my sea kayak from the forest preserve boat ramp at Des Plaines Riverway, and headed downstream into Waterfall Glen Forest Preserve.

Des Plaines monitor view b

Experienced kayakers know to tie everything to the boat. I didn’t want to risk wetting my digital voice recorder, so I tied a waterproof notebook to a deck line, tied two pencils to the notebook, wore my waterproof small camera and binoculars, and tucked everything else into my yellow deck bag.

Monitor deck 1b

I used the strongest current in the center of the river to go downstream, taking moments along the way to enjoy sights such as scattered great blue heron nests.

GB heron nest Des Plaines b

The only American rubyspot of the day made it easy by landing on my bow.

American rubyspot kayak b

Dragonflies were tougher, however. The low, seated vantage point made flying dragonflies look different, and it took a while to recognize even familiar species. They were flying fast over the center of the river, making photography impossible, and even tracking them with binoculars was very difficult. My frustration was limited by the low number of insects active in the center of the river that day. I reached a convenient turn around point after an hour, and started back following the sunlit north shore. (Current is slower near the bank, making the upstream paddling easier.) Odonata were much more abundant along the edge. Some damselflies continued to land on the boat. Here a powdered dancer and a blue-fronted dancer chose to land on the deck bag, providing a comparison shot.

Dancers kayak 1b

Other damselflies kept their distance, landing on sticks or debris. The small camera’s telephoto was adequate to get shots of the abundant blue type bluets, which proved to be familiar bluets.

Familiar bluet 5JL 1b

There also were many black type bluets, which I identified as slender bluets.

Slender bluet 5JL 1b

The most abundant dragonflies were jade clubtails, some of which liked my deck.

Jade clubtail kayak b

I was pleased to see a Cyrano darner along the way, though I was unable to get a photo. Toward the end I got a nice view of some Illinois roses.

IL roses Des Plaines b

All in all there was a nice variety of species, most of them familiar but some I missed. I look forward to a continuing learning experience as I return to this route on future weekends.

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