Net-building of a caddis fly (Hydropsyche siltaiai) in a French stream: relations with larval density and physical conditions
Statzner, Bernhard; Bretschko, Gernot
Archiv für Hydrobiologie Volume 144 Number 1 (1998), p. 87 - 102
published: Dec 22, 1998
ArtNo. ESP141014401006, Price: 29.00 €
The net-spinning behaviour of caddis larvae, in particular of hydropsychids, receives increasing interest in functional or applied considerations of running waters. Evaluations of the functional role of hydropsychid nets face two problems: (1) observed natural net-building rates (proportion of nets to larvae) are very variable and (2) net-building responses to current velocity, temperature, oxygen, starvation and intra- or interspecific hydropsychid aggression under experimental laboratory conditions are very diverse. Using correlation, regression and Monte Carlo simulation we exploited a large number of benthic samples (n = 89) to relate potential net-building variability of Hydropsyche siltalai Döhler to gradients in its larval density and the environment across a riffle of the French Furan stream. In this stream, the slope of the regression of net versus larval density defined the average net-building rate as 0.344. The most important relations affecting net-building were that (1) larval density increased with velocity; (2) net density increased with larval density; and (3) potential aggressive encounters reducing net-building rates probably increased with both, larval density and current velocity. However, predictions of net density could be simply made from larval density, which enabled us to predict 63 % of the variability in the observed net density. Therefore, the diversity of clear net-building responses of Hydropsyche described in laboratory studies seems to be of minor relevance for field situations such as ours (i.e. for a given date and a stream reach being homogeneous in temperature and oxygen but heterogeneous in flow characteristics and substrate rugosity). This would simplify future studies on functional and applied aspects of the net-building activity of these larvae as net density could be simply predicted from larval density.