Energy flow in populations of stream invertebrates has attracted much attention in the northern hemisphere but little in Australia. I am going to deal with two studies of energy flow, one I carried out at the beginning of my career and one towards the end. My aim is to show how knowledge of energy flow can provide insights into the dynamics of invertebrate populations in streams; and to encourage further studies of energy dynamics.
My early study of the production and feeding ecology of a gammarid amphipod (Gammarus pseudolimnaeus) took place in the Credit River in southern Ontario. Gammarus amphipods are classic examples of shredders and are dominant members of the invertebrate fauna of many rivers in western Europe and North America. Although their diet is well known, the rate at which they feed in nature and their annual consumption of organic matter had not been measured. I will describe how feeding rates were estimated in the field, the bearing these rates have on assimilation efficiency and the degree to which these rates varied seasonally.
My later study examined invertebrate production and its availability for the platypus, a major predator. This study was carried out in the upper Shoalhaven River in NSW at a site whose platypus population has been monitored for 40 years. Platypus diet was established by sampling cheek pouches over 12 months. Benthic production was calculated over 2 years and compared with the known energy requirements of the platypus. This enabled estimation of the number of platypus that could be supported by a given length of river. Despite the fact that the catchment of the river had been disturbed by agriculture, productive foraging habitat has persisted in the upper Shoalhaven for many decades.