Blackfly larvae

 

Blackfly larvae at the outlet (upper or left picture) have first access
to the food particles drifting from the lake.
They grow much faster and pupate and emerge as adult flies earlier than larvae
which happen to live only a few hundred meters further
downstrem (lower or right picture).

See how this downstream gradient in blackfly larvae
affects the behaviour of the Barrow's Goldeneyes,
which compete for the best feeding patches.

 

REFERENCES

Gísli Már Gíslason 1985. The life cycle and production of Simulium vittatum Zett. in the River Laxá, North-East Iceland. Verh. Internat. Verein. Limnol. 22: 3281-3287.

Gísli Már Gíslason 1991. Lífið í Laxá. Bls. 218-235 í: Náttúra Mývatns. Ritstj. Arnþór Garðarsson & Árni Einarsson. Hið íslenska náttúrufræðifélag, Reykjavík.  (Life in the river Laxá.  In: The Natural History of Mývatn. Published by the Icelandic Natural History Society, Reykjavík, in Icelandic).

Gísli Már Gíslason 1994. River management in cold regions: a case study of the River Laxá, North Iceland. Pp. 464-483 in: The Rivers Handbook. Hydrological and Ecological Principles. Vol. 2. Eds.: P. Calow & G.E. Petts. Blackwell, Oxford. 483 pp.

Gísli Már Gíslason & Arnþór Garðarsson 1988. Long term studies on Simulium vittatum Zett. (Diptera: Simuliidae) in the River Laxá, North Iceland, with particular reference to different methods used in assessing population changes. Verh. Internat. Verein. Limnol. 23: 2179-2188.

Gísli Már Gíslason & Vigfús Jóhannsson 1985. Bitmýið í Laxá í Suður-Þingeyjarsýslu. Náttúrufræðingurinn 55: 175-194.

Gísli Már Gíslason & Vigfús Jóhannsson. 1991. Effects of food and temperature on the life cycle of Simulium vittatum Zett. (Diptera: Simuliidae) in the River Laxá, N-Iceland. Verh. int. Verein. Limnol. 24: 2912-2916.