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Fig. 3 | Movement Ecology

Fig. 3

From: Size-dependent tradeoffs in seasonal freshwater environments facilitate differential salmonid migration

Fig. 3

a Crossing points where the difference in migratory timing between larger and smaller individuals is within the empirical range of 20 ± 10 days observed in our study system. Colors represent different values of differential growth ΔG(M) (increasing from black to red, magenta, dark blue and light blue dots). The ratio for predation over growth for the migratory environment is on the y-axis and the ratio for the natal environment on the x-axis. For both axes, the ratio is lowest at the intersection of the axes, meaning no predation risk with positive growth potential, and increases when moving away from this intersection. This means that an increase in predation risk is not matched by an increase in growth potential. For the y-axis, a growth differential of ΔG(M’) is applied to model growth differences between natal and migratory habitat and specific growth for a fish of a given size is calculated using the same formula based on size-specific growth rate for both environments. The black line represents the theoretical 1:1 relationship where P/G is equal for both environments. The temporal differences between large and small migrants occur most often at low values of growth differential between the two habitats (red dots). This result suggests that it is not merely high growth potential but rather the tradeoff between predation and growth that shapes differential migration patterns. b The number of runs in our simulation that predict earlier crossing points for given ΔG(M’) values. At low values of ΔG(M’), the predation in the migratory environment outweighs the growth potential for most fish regardless of size, leading to a lower number of predicted values. Differential migration within the empirical range happens most often at intermediate values, then decreases again as the migratory environment becomes profitable enough for small fish to risk predation because of the high growth potential, allowing them to move as early as large fish.

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