Growth model of the reared sea urchin Paracentrotus ... - SciViews
Growth model of the reared sea urchin Paracentrotus ... - SciViews
Growth model of the reared sea urchin Paracentrotus ... - SciViews
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quantifies maximum speed growth, k2 represents <strong>the</strong> speed at which<br />
inhibition is released with time. All parameters in this <strong>model</strong> carry a clear<br />
biological meaning, considering hypo<strong>the</strong>ses that were formulated to build<br />
it.<br />
Usually, a fuzzy <strong>model</strong> is treated with fuzzy arithmetic. The output is<br />
<strong>the</strong>n "defuzzified" by one <strong>of</strong> several methods (Cox, 1999) to provide a<br />
crisp number (<strong>the</strong> most probable size <strong>of</strong> an individual at a determined age).<br />
Being simple enough, <strong>the</strong> current <strong>model</strong> can also be transformed into a<br />
classical analytic equation:<br />
D( t') = M ( t') ⋅ S( t') + M ( t') ⋅ L( t')<br />
(28)<br />
S L<br />
which gives, after combination <strong>of</strong> eqs 24-28 and simplification:<br />
Dt' ( ) = D +∆D<br />
Part IV: A growth <strong>model</strong> with intraspecific competition<br />
0<br />
1−e 1+ l ⋅e<br />
−k1⋅t' ∞ −k2⋅t' (29)<br />
This way <strong>the</strong> <strong>model</strong> can be treated with classical (crisp) arithmetic that<br />
<strong>of</strong>fers a larger panel <strong>of</strong> statistical tools than fuzzy arithmetic.<br />
Fitting <strong>the</strong> dataset<br />
Since echinoids are not tagged individually, it is not possible to track<br />
animals across measurement sets. Consequently, one will consider virtual<br />
individuals according to <strong>the</strong>ir relative position in <strong>the</strong> entire size<br />
distribution at each sampled time, that is, virtual individuals corresponding<br />
to fixed quantiles (or percentiles) in each size distribution. It should be<br />
noted also that, if mortality is not randomly distributed among individuals,<br />
actual growth speed could be different from <strong>the</strong> one calculated on virtual<br />
individuals. This means that if mortality preferably affects small<br />
individuals, growth speed is overestimated; conversely, if mortality affects<br />
ra<strong>the</strong>r larger animals, growth speed is underevaluated. In absence <strong>of</strong><br />
individual tagging, we will thus consider <strong>the</strong> apparent growth speed <strong>of</strong> <strong>the</strong><br />
virtual individuals as defined here above.<br />
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