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The distribution of aquatic invertebrate egg masses in relation to physical characteristics of oviposition sites at two Victorian upland streams

Authors


Paul Reich, School of Anthropology, Geography & Environmental Studies, The University of Melbourne, Victoria, Australia 3010. E-mail: preich@unimelb.edu.au

Summary

1. Various physical variables were measured at rocks potentially used by lotic macroinvertebrates as oviposition sites at multiple locations on two occasions along the Acheron and Little Rivers, south-eastern Australia. The associations between these parameters and the presence/absence and abundance of aquatic insect egg masses were explored as well as the small-scale distribution of egg masses on individual rocks.

2. Physical features that characterise oviposition sites of 17 different aquatic taxa are presented. No obvious differences in patterns of oviposition site selectivity were apparent between multiple sampling times or locations. For some common taxa, multivariate analyses revealed that measurements of rock size and local current speed were positively related to the likelihood of an egg mass being present. However there were no consistent relationships between the abundance of egg masses and either of these variables.

3. The small-scale distribution of egg masses on individual rocks revealed patterns in relation to surfaces that clearly differed as oviposition habitat, such as the underside, upstream and downstream surfaces. Presumably, these patterns are the result of small-scale variation in flow conditions that characterise these particular rock surfaces.

4. The results of this study indicate that the oviposition strategies of a number of aquatic taxa may be reasonably predictable based on measurable physical parameters. These findings have important implications for future studies wanting to incorporate the adult and egg life history stages of lotic insects into studies of population dynamics.

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