@article {1714, title = {The responses to current flow of two stream dwelling triclads, Crenobia alpina (Dana) and Polycelis felina (Dalyell)}, journal = {Oecologia}, volume = {10}, year = {1972}, month = {1972 Dec}, pages = {313-320}, abstract = {

An apparatus is described which allows triclads to choose between the fast and slow regions of a stirred tank. In the absence of a stone substratum Crenobia alpina preferred or tolerated higher current speeds than Polycelis felina, this effect was enhanced when a stone substratum was added to the apparatus. These results indicate that the absence of Polycelis felina from the steep gradient regions of streams could be accounted for by its preference for slower micro-currents. Conversely the presence of Crenobia alpina in steep gradient regions could be accounted for by its preference for or tolerance to higher micro-currents.

}, issn = {1432-1939}, doi = {10.1007/BF00345735}, author = {Lock, Maurice A} } @article {1713, title = {The effects of electrofishing on the invertebrates of a Lake District stream}, journal = {Oecologia}, volume = {9}, year = {1972}, month = {1972 Mar}, pages = {1-11}, abstract = {

The experiments were performed in Dale Park Beck, a stony stream in the English Lake District. Two operators electrofished the sampling area (length 20 m in April and July 1970, and 40 m in May 1971) three times (runs 1, 2, 3) in each experiment.Electrofishing caused a marked increase in the number of invertebrates drifting out of the sampling area, and nearly all taxa taken in the bottom samples were also found in the drift samples. The fish shocker was chiefly responsible for the increased drifting of Plecoptera, Ephemeroptera and Gammarus pulex, and these taxa were dislodged from the substratum more easily than Trichoptera, Coleoptera, Diptera and Polycelis felina. The increased drifting of the latter taxa was chiefly due to the disturbance of the substratum by the two operators.Most of the invertebrates drifting from the upstream end of the experimental section returned to the bottom within the sampling area. The invertebrate drift out of the sampling area came chiefly from the downstream end of the section, and was equivalent to a loss of only 5\% from the total benthos in the sampling area (losses varied between \<1 and 13\% for individual taxa).

}, issn = {1432-1939}, doi = {10.1007/BF00345239}, author = {Elliott, J M and Bagenal, T B} } @article {1712, title = {The distances travelled by drifting invertebrates in a Lake District stream}, journal = {Oecologia}, volume = {6}, year = {1971}, month = {1971 Dec}, pages = {350-379}, abstract = {

The distances travelled by drifting invertebrates of 18 taxa were investigated at sites 3 and 4 in the Wilfin Beck, a small stony stream in the English Lake District. Fifty invertebrates of the same taxon were released into the stream at increasing distances upstream from a large net which caught all invertebrates drifting downstream.The relationship between the catch in the net (Y x ) and the distance from the release point to the net (X m) was well described by the regression equation:[Formula: see text] whereR is the constant relative rate of return of invertebrates to the bottom of the stream, andA=Y 0=number of invertebrates released at each point=50. Values ofR, the mean drift distance ([Formula: see text] m), and the distance (X p m) travelled byP\% (1\%, 10\%, 50\%) of the drifting invertebrates were calculated for each taxon at different modal water velocities. Values ofR,[Formula: see text] andX p were fairly constant for each taxon at a particular modal water velocity, and were not significantly affected by the source of the experimental animals (benthos or drift), by changes in illumination (daylight or darkness), or by seasonal changes, including water temperature.The experimental taxa at site 4 were divided into the following three groups according to their ability to return to the bottom: 1. Polycelis felina, Ancylus fluviatilis, Chironomidae, Eliminthidae, andAmphinemura sulcicollis. Values ofR,[Formula: see text],X p not significantly different from those obtained for dead invertebrates, which were removed from the drift by chance effects. 2. Protonemura meyeri, Leuctra spp.,Chloroperla spp.,Rhithrogena semicolorata, Simulium spp. Values ofR,[Formula: see text],X p not significantly different from those obtained for dead invertebrates at modal water velocities ≧19 cm/sec. At low velocities (10-12 cm/sec),R was significantly greater and[Formula: see text],X p significantly smaller than values obtained for dead invertebrates. 3. Erpobdella octoculata, Gammarus pulex, Hydropsyche spp.,Ecdyonurus venosus, Ephemerella ignita, Ba\ëtis rhodani. Values ofR,[Formula: see text],X p significantly different (R greater,[Formula: see text] andX p smaller) from those obtained for dead invertebrates. The exponential law was not a good model for experiments with cased caddis larvae (Agapetus fuscipes and a mixed group ofSericostoma personatum, Drusus annulatus, Potamophylax cingulatus). Larvae sank rapidly after release and drifted over very short distances.Values ofR for each taxon were significantly higher at site 3 than at site 4, and the more rapid return at site 3 was presumably due to dense stands of aquatic macrophytes. The increase inR was greatest forSimulium spp. andE. ignita.The relationship between[Formula: see text] and modal water velocity (V cm/sec) was well described by the regression equation:[Formula: see text] wherea andb are constants. The relationship betweenR andV, orX p andV, was described by similar equations. Values ofa andb were calculated for each taxon at sites 3 and 4.The drift distance was also investigated by blocking the total drift and taking drift samples at several stations downstream from the blockage. Drift rate was markedly reduced immediately below the blockage and then gradually increased downstream until it was similar to that recorded before blocking. The mathematical model developed from the detailed experiments was a good fit to the results of the blocking experiments.The behaviour of the drifting invertebrates and their ability to return to the bottom are discussed. From the results of the present study and those of other workers, it is concluded that the mathematical model is a good model for invertebrate drift. The implications of the model are discussed, especially the relationship between drift rate and water velocity, and the proportion of the benthos in the drift.

}, issn = {1432-1939}, doi = {10.1007/BF00389109}, author = {Elliott, J M} }