Effects of fan morphology and habitat on feeding performance of blackfly larvae
Archiv für Hydrobiologie Volume 149 Number 3 (2000), p. 365 - 386
published: Nov 14, 2000
ArtNo. ESP141014903002, Price: 29.00 €
The labral fan morphology of blackfly larvae (Diptera: Simuliidae) can influence the efficiency of suspension feeding which in turn might affect their ecological success in different habitats. According to a cost-gain model, in slow-flowing streams, larvae develop large labral fans for feeding, because drag acting on the fans is small and the cost of feeding performance increases slowly with increasing fan area. In streams and rivers with high current velocities, larvae possess small labral fans to decrease the sharply increased cost of drag. Due to a high delivery rate of currents, sufficient food is acquired with a small fan area. The gradient of the slopes of the fan area-feeding rate relationship increases with current velocity. To test this model, I studied the relationships between labral fan structure, body size, and suspension feeding of five species of blackfly larvae in two small streams and a large river with different velocity regimes. Feeding observations were conducted at five localities: slow (11-18 cm/s), fast (47-60 cm/s), and very fast (140-180 cm/s). The results showed that the relationship between larval body size and feeding rate did not reflect different velocity-related habitat. The ontogenetic relationship between fan area and feeding rate did reflect the current velocity-related habitat use. Fast-current species (M. lyra and S. tuberosum) had very steep slopes for the relationship, where the feeding rate rapidly increased as fan size increased. A slow-current species (S. lundstromi) had the gentlest slope of the regression. In habitats with moderately fast currents, the larvae of S. ornatum and P. ferrugineum had intermediate slopes for the relationship. This study supported the cost-gain model describing the relationship between the fan morphology of different blackfly species and the success in the microhabitats. The association between labral fan morphology and the habitat is apparently mediated by hydrodynamic features affecting the efficiency of the labral fan at different current velocities.