Figure 1. Relationships between the empirical parameters 
and 
.
The reproductive ratio is plotted against the rate of growth. The downward trend is not well described by the linear model with negative angular coefficient (
) and an intercept (
) (dotted blue line). In addition, the model prediction with 
fixed (dashed-dot black line) fails to precisely represent the data, even if it provides a more reasonable relationship (notice that high stable prions, such as MK4985, would always be associated to positive 
values). Introducing one more degree of freedom (exponent 
) yields a higher 
value (red line, 
). This result corresponds to a prediction of 
. In addition, we tested a further simplified model version (where 
is considered to be much smaller than 
) according to which 
(i.e. 
, shown in green). Similar conclusions could be drawn.