Monday, 21 October 2013
Ponds are a family favourite. Give a child a net and just wait for all the mysterious creatures that will turn up: fearsome water tigers and skittish pond skaters, leggy hoglice and shining snails. The remarkable variety of life that makes mini-beast hunts such a great lucky dip is also a beautifully familair version of the richness and diversity of ponds when compared to other freshwater habitats in more systematic, scientific comparisons. The treasury of creatures suddenly revealed from under the water is special. A recent paper in the Journal of Animal Ecology is a neat demonstration that the mix of creatures really does matter, a point often lost in more anonymous counts of species, metrics of diversity and abstractions of foodwebs. Jan Klecka and David Boukai compared the mortality of prey such as tadpoles, midge and mayfly larvae when hunted by larvae and adults of diving beetles, adult bugs and dragonfly larvae. The different hunting methods of the predators and escape responses of the prey resulted in different outcomes: it matters which species live together and what they do. This harks back to classic definitions of ecological niches by the British Ecologist Charles Elton who captured the idea of the niche by comparing the idea to the various roles found amongst the inhabitants of a village: policeman, butcher, teacher. The most voracious predators were instar 3 larvae of the Great Diving Beetle, Dytiscus marginalis, and their larvae certainly are fearsome. I avoid putting my fingers anywhere near them. Wave a twig in their direction and they rush in, hypodermic jaws agape. Larvae of another beetle, Acilius canaliculatus, were also used, extraordinary creatures which stalk through the open water, their elongated heads and thorax lending a slightly plesiosaur look, although only a centimetre or two long. Ecology is very good at creating useful models and abstract visualisations of pond-life. Nice to see the precise animals trying to sink its teeth into your finger still matters (J. Anim., Ecol, Vol 82, pp 1031-1041 doi 10.111/1365-2656.12078).