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Journal Article

Seasonal Phytoplankton Demographic Processes and Experiments on Interspecific Competition

Heath J. Carney, Peter J. Richerson, Charles R. Goldman and Robert C. Richards
Ecology
Vol. 69, No. 3 (Jun., 1988), pp. 664-678
Published by: Wiley on behalf of the Ecological Society of America
DOI: 10.2307/1941015
Stable URL: http://www.jstor.org/stable/1941015
Page Count: 15
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Seasonal Phytoplankton Demographic Processes and Experiments on Interspecific Competition
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Abstract

Population dynamics of Lake Tahoe phytoplankton species were studied during 1985. Four dominant diatoms were examined: Cyclotella glomerata, Cyclotella ocellata, Synedra amphicephala, and Synedra radians. The role of interspecific resource-based competition during spring and summer was tested in three ways: (1) species distribution patterns along the vertical gradient (upper 100 m of the water column), (2) measurements of in situ growth and loss (sinking, grazing, natural death, diffusion) processes, and (3) transplants of assemblages between depths. All three tests indicated that resource-based competition was important. Species clearly segregated with thermal stratification and nutrient depletion in the epilimnion. C. glomerata peaked within the epilimnion (0-20 m), S. radians became dominant in the deep chlorophyll maximum region (60-90 m), and the other species peaked at intermediate depths. Resource-limited growth was a dominant process during this time, and sinking and natural death were significant losses. Experimental transplants of assemblages between two depths (15 and 75 m) demonstrated competitive interactions in the phosphate-limited region near the surface, but there was no evidence of competition in the deeper light-limited region. This suggested asymmetrical competition along the vertical gradient. Primary productivity nutrient-enrichment bioassays and growth kinetic assays (phosphate, nitrate, light) also indicated that phosphate and light limitation were important bases of species interactions.

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