Correlation of some environmental variables with adaptive net-spinning strategies in stream larval Hydropsychids (Trichoptera) in Garhwal Himalaya (Short Communication)

Abstract

Introduction



The Hydropsychidae (Trichoptera) being the master spinners of freshwater rapids spin the net s of various sizes required during different seasons, and for different instars. Also they adopt strategies for coexistence between similar and different species by selecting various mesh sizes, current regimes, and habitat modes. The paper highlights the results of the study on the various net spinning strategies and associated environmental variables. In two larval hydropsychids from a small stream ‘Malethagaad in the Garhwal, Central Himalaya (India). Among net – spinning Hydropsychidae, the effect of certain seasonal environmental variables was studied and the most influencing ones recognised were water temperature changes, current speed, and increase in resource particulate concentration downstream.



It was observed that in response to increase in all the above parameters (except temperature) net – spinning activity increases, reducing the size of mesh and thus successfully enabling the animal to adjust to the drag of the water current and particle filtration requirements with relation to the body size and microclimate of the dwelling mode.



Certain anomalies were observed in hydropsychid capture nets from lotic sidewater pools and an increase in temperature probably also triggered an increase in net – spinning activity during summer, but the mesh shapes and sizes vary. Also probably the behavioural and morphological differences of various instars considered, facilitated in adaptive strategies for coexistence between similar and different species.



Summary



1. The Hydropsyche k1 and Hydropsyche k2 divide up net spinning sites by partial differences in water velocity preferences, use of different dwelling crevices and modes of habitat.



2. The catch net mesh was found to be related to current speeds, resource particle requirements and the morphological stages of various instars and the combination of these variables may be taken as deciding factor as to how the mesh size is determined in a particular species to facilitate coexistence among different and similar instars of the same and different putative species.



3. Also the correlation of body size and net dimensions along with the distribution on the stream, with the increased resource particle concentration downstream and larger instars downstream point towards a natural distributional strategy enabling a successful species propagation for instars associated.



Tropical Freshwater Biology VOL. 8 1999, pp. 27-30