Model results under different levels of extrinsic mortality.

<p>The horizontal axis represents the values of extrinsic mortality used to run the model(;). A) and B) show the optimized parameters (, ,) from our model. In C)–F) the solid lines indicate the results when the optimal values of and , The dashed lines indicate results if the colony did not change the maintenance investments () or the switching time () with increasing extrinsic mortality ( = 0.38 = 84). A) Optimal investment into workers () decreases with increasing extrinsic risk. B) Denotes the switching time (), where the colony switches to the production of sexuals. C) The number of sexuals alive at the end of the season (maximized by finding optimal values for switching time () and maintenance investments into workers ()) decreases with increasing extrinsic mortality. D) Worker mortality combines intrinsic and extrinsic mortality (). The dashed line denotes the increase of extrinsic mortality. The difference between the dashed and solid lines shows the effect of the changing investment in worker maintenance. E) Worker life expectancy at the beginning of the season with different levels of extrinsic mortality. F) Worker life expectancy at switching time. At switching time, the worker population reaches its maximum. The difference in worker life span between e) and f) is due to the reduction of foraged resources caused by density dependency. Used parameters: = 0.15, = 0.005, = 0.0024, = = 0–0.06.