Observations on the biology of nymphs of Povilla Adusta Navas (Ephemeroptera: Polymitarchidae) in Lake Kainji, Nigeria
✍ Scribed by A. Bidwell
- Publisher
- Springer
- Year
- 1979
- Tongue
- English
- Weight
- 741 KB
- Volume
- 67
- Category
- Article
- ISSN
- 1573-5141
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✦ Synopsis
Observations on Povilla adusta Navas nymphs in Lake Kainji revealed that seasonal fluctuations in abundance were due to a shortage of food during the period of rising lake level rather than a depletion of oxygen in the water column ; this shortage was caused by the increased turbidity of the flood waters restricting the growth of both planktonic and periphytic algae. Planktonic algae apparently formed the diet of nymphs < 4-6 mm and also of larger nymphs if their preferred diet of periphytic algae was in short supply . Both depth distribution and individual size of the nymphs were closely related to the distribution of periphytic algae . Depth distribution patterns of the nymphs revealed a peak between 2-4 m below the surface .
The dimensions of the nymphs and the duration of the aquatic stages (3-4 months) in Lake Kainji correspond closely with results obtained elsewhere as does the mean percentage of males in the population (28% ± 1o%). Seasonal fluctuations in the sex ratio were apparently caused by variations in the intensity of predation .