Ecological Archives A024-063-A1

Manuel Hidalgo, Esben M. Olsen, Jan Ohlberger, Fran Saborido-Rey, Hilario Murua, Carmen Piñeiro, Nils C. Stenseth. 2014. Contrasting evolutionary demography induced by fishing: the role of adaptive phenotypic plasticity. Ecological Applications 24:1101–1114. http://dx.doi.org/10.1890/12-1777.1

Appendix A. Sensitivity analysis of maturation reaction norms to a range of somatic growth rates scenarios.

To estimate the most likely somatic growth scenarios in the pre-truncated period at each population subunit, we analyzed the sensitivity of maturation reaction norms to a range of somatic growth rates scenarios. To do that, we run simulated scenarios of a range of values of the Bertalanffy growth parameters inlineEq for the pre-truncated period using growth parameters of the truncated period as reference. We thus assumed that for the truncated period fish within a cohort followed, on average, the von Bertalanffy growth parameter used in the assessment groups: K = 0.175/yr for the north deme and K = 0.163/yr for the south deme, with L = 130 cm and t0 = 0 for the two demes (ICES 2009) Though the two parameters K and L are correlated we run our simulations modifying K given the higher sensitivity of the growth performance to K variation at young ages (i.e., pre-spawners) compared to L (Stearns 1992). Given the opposed trends of lengths at 50% of probability of being mature (Fig. 1d), we tested whether higher values of length at 50% maturation probability for north deme in the pre-truncated period could be a consequence of higher somatic growth by increasing the K parameter from 5% to 50% of the value in the truncated period. For the south deme, by contrast, we tested whether lower values of length at 50% maturation probability in the pre-truncated period could be a consequence of lower growth rate by decreasing the K parameter from 5% to 50%.

We expect to obtain a unique range of variation in K for age-2 and age-3 in which we observe minimal variability of maturation reaction norm midpoints and no significant variation in the mean values. We will interpret this percentage of K as the most likely growth pattern during the pre-truncated period. A variation in K close to zero would indicate low variation in the mean somatic growth between periods.

The simulations show that, for the north deme during the pre-truncated period, increasing somatic growth simulated for age-2 individuals did not significantly influence the reaction norm midpoints (Fig. A1a). These estimates did not overlap with those of the truncated period, displaying a difference of around 8 cm. By contrast, pre-truncated reaction norm midpoints for age-3 overlapped with the truncated period when the K parameter was increased above 10% (Fig. A1b). Highly uncertain and variable values of age-3 midpoints beyond a 10% increase of K imply that the most likely growth scenario was similar between periods (between 0–10% increase of K) suggesting low phenotypic plasticity in somatic growth. Maturation reaction norms presented in the main document (Fig. 3) were constructed averaging the most likely growth scenarios determined by the simulations (gray bars, Fig. A1a, A1b).

The south deme displayed higher dependency on the somatic growth compared to the north deme. Combining the growth simulations for age-2 (Fig A1a) and age-3 (Fig A1b), the percentage of decrease on K that stabilizes mean estimates of reaction norms and minimizes their uncertainty was between ca. 15–35%. These results suggest higher phenotypic plasticity in the somatic growth compared to the north deme. Thus, maturation reaction norms presented in the main document (Fig. 3) were constructed averaging information for this growth scenario (gray bars, Fig. A1a, A1b).

 

FigA1

Fig. A1. Midpoints of the probabilistic maturation reaction norm for age-2 (a) and age-3 (b) estimated for the pre-truncated period under growth scenarios of increasing (for north deme, left column) and decreasing (for south deme, right column) values of the Von Bertalanffy growth coefficient (K) from 5% to 50%. Red lines (mean: solid line, ± SD: broken lines) indicate estimated values for the truncated period. Vertical lines indicate ± SD. Gray areas represent the most likely growth scenarios for the pre-truncated period, whose average is plotted for age-2 and age-3 (Fig. 3 of the main document).


 

Literature Cited

ICES. 2009. Report of the Working Group on the Assessment of Southern Shelf Stocks of Hake, Monk, and Megrim [WGHMM]. 5–11 May 2009, ICES CM 2009/ACOM:08.

Stearns, S. C. 1992. The Evolution of Life Histories. Oxford University Press, Oxford, 249 pp.


[Back to A024-063]