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The effect of growth pattern, sampling interval and number of size classes on benthic invertebrate production estimated by the size‐frequency method
Author(s) -
MOTHIVERSEN TORBEN,
DALL PETER
Publication year - 1989
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.1365-2427.1989.tb01105.x
Subject(s) - statistics , population size , mathematics , population , sample size determination , reproduction , biology , production (economics) , sampling (signal processing) , cohort , ecology , demography , macroeconomics , sociology , economics , filter (signal processing) , computer science , computer vision
SUMMARY. 1. A hypothetical leech population with known initial density, initial weight, final weight and cohort production interval (CPI) was established. Production estimated by the size‐frequency method for various growth patterns, mortalities, number of samples per CPI and number of size classes was compared with actual production estimated from daily growth and mortality by the increment‐summation method. The population had either perfectly continuous reproduction or a perfectly synchronous cohort. 2. When size‐classes were delimited in order to equalize the time spent in each size class, the deviations from actual production increased with decreasing number of size‐classes and increasing mortality. For a population with perfectly continuous reproduction, production was only overestimated by 32% with an extreme mortality of 2.0% day −1 and three size‐classes. For a perfectly synchronous cohort, production was either underestimated or overestimated, depending on the first day of sampling. The deviations from actual production increased considerably with decreasing number of size‐classes, increasing mortality and decreasing number of samples per CPI. 3. Differences between actual and assumed growth patterns may give underestimates or overestimates of more than one order of magnitude at high mortalities and few size‐classes. It is concluded that knowing the actual growth pattern, the size frequency method will give realistic estimates of production in cases when normal cohort methods cannot be used. The estimate can be improved significantly by increasing the number of size classes and the number of samples per CPI.