Sensitivity of Crab-Crab Interactions

Appendix A.5.3 describes how interactions between crabs are modeled. Given that little is known empirically about crab-crab interactions, a sensitivity analysis was conducted to determine the importance of the assumptions made. One part of the algorithm utilizes a maximum interaction distance (Appendix A.5.3). Since this parameter has the largest impact on the rate of crab cannibalism, three interaction distances are considered in Scenario III in the paper. The other possibilities considered here include shifting the function in Eqn (A.26) to the Left and Right from the Default position ( $\mu = 1.5 , 2.0, 2.5$), changing the width of the function by altering $\sigma$ to 0.4, 0.5, and 0.6 and changing the overall height of the function by setting $\alpha_$inter to 0.7, 0.8, and 0.9.

Shifting the function Left or Right (i.e., changing the ratio of crab sizes at which death due to aggression is most likely) had the largest effect of the two possibilities considered. Shifting Left (crabs 1.5 times smaller experience maximum mortality due to aggression) lead to a higher overall survival than shifting Right (Fig. B16). This counter-intuitive result is caused by differences in the density of 7-12 instar crabs leading to differences in survival, as discussed in the paper. Changing the width or height of the function had little influence on survival, gut fullness or average food quality of 18+ crab densities.