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

Y
1
Y•
0.8
0.6
Y•êH1+bL
0.4
0.2
General introduction
1
i
2 4 6 8 10 t
t
Figure 13. Examples of Jolicoeur curves with m = 3, 1 (bold curve) and 0.5 respectively from
highest to lowest curve; Y∞ = 0.95 and b = 0.9. When m > 1, the curve is sigmoidal.
h. The Johnson model, a heavily asymmetrical sigmoid
Y
Y
1
Y• 0.8
0.6
0.4
0.2
The Johnson growth curve (see Ricker, 1979) uses 1/t instead of t:
Yt () Y e
2 4 6 8 10 t
1 k⋅( t−t0) = ∞ ⋅ (15)
Figure 14. Example of a Johnson curve, with k = 0.7, Y∞ = 0.95 and t0 = 0.
It is sigmoidal with a very strong asymmetry, the inflexion point being
very low and close to 0 (and thus hardly visible in Fig. 14).
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