Growth model of the reared sea urchin Paracentrotus ... - SciViews

Y
1
Y• 0.8
0.6
Y•-d.e 0.4
-k
0.2
Y0
General introduction
1
i
2 4 6 8 10 tt
Figure 12. Examples of Weibull curves for m = 5, 2, 1 and 0.5 respectively, with k = 0.6,
Y∞ = 0.95 and Y0 = 0.05. In bold, the curve with m = 1, equivalent to a von Bertalanffy 1
model. All curves start from Y0 and pass by Y∞ - d·e -k which is also the inflexion point for the
sigmoidal curves when m > 1.
g. The Jolicoeur curve, another flexible model
Another curve that can possibly be sigmoid or not is Jolicoeur model
(Jolicoeur, 1985). It is derived from a logistic curve, but using the
logarithm of time instead of time itself:
Y∞
Yt () =
1+
bt ⋅
−m
(14)
Like the Weibull function, it is sigmoidal when m > 1, but with an
asymmetry between the limbs of the S that can vary independently,
according to the value of parameter b. When m ≤ 1, there is no inflexion
point (Fig. 13).
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