Hydropsychidae are represented in Newfoundland by only 8 species compared to 145 species in North America. It was predicted that these 8 widely distributed hydropsychids would differ in their distribution and ecology here because of the reduced species diversity and the broad diversity of lotic habitats available in the glacial-fluvial morphology of Newfoundland streams. Specifically, that Newfoundland species would differ in their physical niche and that water temperature and food resources would influence their distribution.

Distribution of Newfoundland Hydropsychidae was strongly influenced by lake outlets, which had higher nutrient concentrations and warmer temperatures than downstream sites. All species occurred in forested and barren landscapes. Densities of hydropsychids were elevated at outlets and in forested streams. Parapsyche apicalis was restricted to cooler streams. Stream size also influenced the distribution of some species. Other physical factors did not correlate with densities. The hypothesized reduced spatial and nutritional competition between species because of the impoverished fauna did not translate into an expanded habitat range in Newfoundland.

A logistic model was derived to provide a basis of comparison for the longitudinal abundances of hydropsychids and their potential food sources (phytoplankton, zooplankton and periphyton) below lake outlets in streams of differing sizes. The model was used to establish 5 sampling stations that were relatively equidistant from outlets in streams of varying sizes. Across stream comparisons showed rapid changes near outlets. Abundances of C. pettiti and H. betteni declined rapidly below outlets, H. slossonae had a fairly constant longitudinal abundance and H. sparna increased in abundance downstream. Overall the logistic model was an excellent tool for studying the influence of outlets on longitudinal organism abundance in streams of different sizes. Zooplankton, H. betteni and total hydropsychid abundance showed statistically significant similar longitudinal trends. Phytoplankton and zooplankton abundances and those of certain hydropsychid species showed similar trends in individual streams. Although there were similar trends, this did not indicate what elements were being utilized, or whether food sources were being partitioned among hydropsychid species

Lipid and fatty acid analyses allowed a more detailed examination of the feeding ecology of Newfoundland hydropsychids. All hydropsychids had high proportions of a storage lipid and a fatty acid composition dominated by 14 fatty acids. The fatty acid composition of P. apicalis was the most distinctive from the other species, followed by A. ladogensis, D. modesta and H. alternans. Discrimination of four commonly occurring and most abundant species (C. pettiti, H. betteni, H. sparna, H. slossonae) was more difficult indicating the similarity in their fatty acid composition. Little research has been conducted on seston lipid and fatty acid composition. There was a seasonal shift in both the hydropsychid and seston fatty acid composition suggesting an influence of lake seston on the lotic community. Fatty acid markers compared seston composition to that of hydropsychids, showing selective feeding by hydropsychids. Seston composition differed among streams and between outlets and downstream sites but there were no consistent trends. This demonstrated the ability of hydropsychids to adapt to differing food sources among and within streams, showing that hydropsychids are opportunistic generalists. w02clf@mun.ca