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Vol. 52, 2013
An alternative kernel-based method for estimating copepod
growth rates from multimodal biomass distributions in artificial cohort
experiments
Kuan-Yu
Lin1, Akash R Sastri2 and Chih-hao Hsieh1,3*
1Institute
of Oceanography, National Taiwan University, 1 Roosevelt Road, Sec. 4,
Taipei 106, Taiwan
2Department of Biological Sciences, Université du
Québec à Montréal, Montreal H3C 3P8, Canada
3Institute of Ecology and Evolutionary Biology,
National Taiwan University, 1 Roosevelt Road, Sec. 4, Taipei 106, Taiwan
Abstract
Background: Elucidating copepod
growth and production rates is important in understanding the trophic
role of copepods in marine systems. One of the most commonly used field
methods for measuring copepod growth rates is the artificial cohort
method.
Results: An ‘artificial cohort’ is established by
limiting the incubated animals to relatively narrow size ranges or
developmental stages. Thus, one can measure the change in body weight
(BW; attributed to body growth) between the start and conclusion of
incubation by following the shift in the biomass distribution. The
critical issue here is determining how to describe the biomass
distribution before and after incubation in a mathematically concise
manner. Traditionally, the mean value of the biomass distribution is
used as the representative BW, which assumes that the biomass
distribution follows a unimodal distribution. However, in practice, the
complex composition of copepod communities can commonly yield
observations of multimodal distributions. To overcome this difficulty,
we suggest that the representative BW of copepod communities be
estimated by multiple-peak consideration instead of using the average
value. Specifically, we used a kernel-based approach to determine peak
values; as such, only BW values associated with a high frequency were
used to determine the representative BW.
Conclusions: Through a comparison
of different methods, we show that the multiple-peak consideration
yielded a higher proportion of realistic growth rate values. In
addition, we noted that growth rates estimated with the multiple-peak
method were more closely aligned with predictions based on the
metabolic theory of ecology.
Key words: Copepod community; Artificial
cohort method; Metabolic theory of ecology; Multimodal distribution.
*Correspondence: E-mail: chsieh@ntu.edu.tw
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