A Beetle Out Of Water

First (outdoor) insect shot of the year:

Hydrobius fuscipes, Van Patten Woods Forest Preserve,
Lake Co, IL  3/29/2014

I think this is Hydrobius fuscipes, one of the water scavenger beetles of the family Hydrophilidae. Some members of this family, most likely including this one, undergo dispersal flights in the spring, (1) which would explain why this guy fell out of the sky right in front of me. Unfortunately for him, I suppose, he missed the water, landing on the boardwalk instead.

This species was part of a field study in Scotland examining changes to aquatic macroinvertebrate faunas in a mixture of temporary and permanent ponds. Jeffries found that even permanent ponds had a considerable turnover, which suggests that dispersal flights must be very important in maintaining a population of these beetles. Surprisingly, they also found that extinction rates were similar in temporary and permanent ponds, indicating that factors other than the loss of water were responsible for most local extinctions. (2)

Another interesting result throws a significant wrinkle into that story, though. Working in experimental tanks in Illinois, Resetarits found that another member of this family, Tropisternus lateralis, actively avoided colonizing tanks with fish in them. (3) This suggests that some of the colonization/extinction dynamic found by Jeffries in Scotland was based on interactions between species, in many cases interactions that took place generations ago, rather than the simple incidence models he was using. Trying to tease all of this apart is a tricky task indeed!

Biology is sometimes called a "soft" science. This is in contrast to chemistry or (especially) physics, which are "hard" sciences. This doesn't refer to difficulty, but rather to the degree that the field is dependent upon mathematical descriptions. While there are fewer mind-bending calculations in biology, there is no reason for a physicist to consider the ancient history of a photon. In biology, though, ignoring the evolutionary history of your subjects is bound to lead you astray, no matter how seductive your calculations may look.

(1) Landin, J. (1980). Habitats, life histories, migration and dispersal by flight of two water‐beetles Helophorus brevipalpis and H. strigifrons (Hydrophilidae).Ecography, 3(3), 190-201.

(2) Jeffries, M. (1994). Invertebrate communities and turnover in wetland ponds affected by drought. Freshwater biology, 32(3), 603-612.

(3) Resetarits, W. J. (2001). Colonization under threat of predation: avoidance of fish by an aquatic beetle, Tropisternus lateralis (Coleoptera: Hydrophilidae).Oecologia, 129(1), 155-160.