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The feeding relationships of two invertebrate predators in a New Zealand river
Author(s) -
DEVONPORT B. F.,
WINTERBOURN M. J.
Publication year - 1976
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.1976.tb01601.x
Subject(s) - predation , chironomidae , invertebrate , biology , ecology , predator , larva , cannibalism , habitat , population , detritus , caddisfly , diel vertical migration , demography , sociology
Summary The size frequency distributions and foods of the larvae of Archichauliodes diversus (Megaloptera: Corydalidae) and Stenoperla prasina (Plecoptera: Eustheniidae) were studied for a year in the Glentui River, South Island, New Zealand. These two species are the largest invertebrate predators inhabiting streams and rivers in New Zealand, where they are the only carnivorous members of their respective orders. Both species occupied the same habitat with A. diversus being slightly more abundant in most months. Many small larvae occurred within the sediments of the stream bed, whereas more larger larvae were found on stones lying on the surface. A wide size range of larvae was present throughout the year and the median size (in terms of head width) of both species was similar in most months. Larval growth could not be determined from field data and the life cycles of both species can be described as non‐seasonal. Quantitative sampling in 5 months provided estimates of population densities. These were maximal in December when values of 136/m 2 for A. diversus and 114/m 2 for S. prasina were obtained. Larval Chironomidae and mayflies of the genus Deleatidium were the most frequently taken prey of both predators in all months, and no strong relationship between size or species of predator and size of prey was found. Caseless trichopteran larvae formed a less important component of the diets of both species and detritus was ingested by some individuals. No instances of cannibalism and only one example of cross‐predation by each predator was seen. Diel sampling in November showed that large Deleatidium larvae were relatively more abundant in the guts of insect predators and in nocturnal drift samples than in the benthos. This suggests that their greater activity at night may increase their susceptibility to predation by nocturnal feeders. No clear ecological segregation of the two species with respect to habitat or prey utilization was found and there was no obvious interspecific competition for food, which appeared to be abundant at all times. Finally, the prevalence of non‐seasonal life cycles in New Zealand aquatic insects is discussed in relation to the low degree of speciation in several groups.