Changes in evolved lifespan and maturation age are accompanied by corresponding shifts in juvenile energetic investments.

<p>Under classical (<b>A–C</b>) and non-classical conditions (<b>D–F</b>), the percentage of per-iteration energy devoted to somatic maintenance, reproduction, and metabolism by juveniles is shown. In both cases, the majority of energy was devoted to reproduction, followed by metabolism, followed by somatic maintenance (<b>A–F</b>). Under classical conditions, rising levels of predation, , caused juveniles to invest less in somatic maintenance (<b>A</b>), more into early peak fertility (<b>B</b>), and less into metabolism (<b>C</b>). Under non-classical conditions, larger values of caused juveniles to devote less energy to early peak fertility (<b>E</b>) and more towards somatic maintenance (<b>D</b>). Investments in metabolism were comparable for various values of predation modifier, (<b>F</b>).</p

Overview of the modeling and optimization procedures.

<p>An agent-based stochastic model was implemented in which individuals invest energy foraged from a common pool toward maturation, metabolism, mating, and maintenance and are subject to random, density-dependent predation, starvation, and aging. Maturation and intrinsic death times are inheritable traits used to determine maturation, and maintenance costs. A flowchart depicts the simulations scheme (<b>A</b>). Sample simulation solution depicting changes in observed statistics with time is shown (<b>B</b>). To find appropriate values for six simulation-invariant parameters for the classical and non-classical evolutionary response to increased predation a simulated annealing optimization approach was used (<b>C</b>). See methods for model and optimization details.</p

Classical and non-classical conditions identified by simulated annealing optimization.

<p>A simulated annealing optimization scheme was used to find values for six simulation-invariant parameters that would predispose populations toward either increased or decreased maintenance in response to increased extrinsic mortality. The fit score stochastically improved over the course of the optimization (<b>A and C</b>). The optimal starvation modifier (ε), growth efficiency (), initial energy of individuals (), mating energy (), mating energy threshold (<i>mateThreshold</i>), and death cost function type () for the classical (<b>B</b>), and non-classical (<b>D</b>) effect are shown as a function of optimization duration. D_type: 0 = Sigmoidal Low, 1 = Linear Low, 2 = Asymptotic Low, 3 = Sigmoidal High, 4 = Linear High, 5 = Asymptotic High. Colored dots indicate that the intrinsic death effect was monotonic.</p

Higher predation impacts parameters related to density dependence under classical conditions.

<p>Under classical conditions, increased predation reduced population size (<b>A</b>) and enlarged the total energy pool that could be foraged (<b>B</b>). Average normalized birth rates increased (<b>C</b>) and, concomitant with this, average individual energy decreased (<b>D</b>).</p

Higher predation impacts parameters related to density dependence under non-classical conditions.

<p>Akin to classical conditions, higher predation under non-classical conditions resulted in smaller population sizes (<b>A</b>) and a large shared energy pool (<b>B</b>). Unlike classical conditions, however, average normalized birth rates decreased (<b>C</b>) and the average mature individual energy was increased (<b>D</b>).</p

Summary of key model parameters and quantities.

<p>Populations were modeled explicitly using stochastic agents to represent individuals subject to shared resources, mating, and both extrinsic and intrinsic death.</p

Disparate effects of high predation on the evolution of lifespan and maturation age.

<p>Under classical conditions of relatively low food availability and relatively inexpensive mating costs, increased values of predation modifier, x, caused mean T_die to decrease (<b>A</b>) and mean T_mat to decrease (<b>C</b>) over time. Conversely, under the non-classical conditions of relatively abundant food but relatively expensive mating costs, higher values of predation modifier, , caused the mean T_die to increase (<b>B</b>) and the mean T_mat to increase (<b>D</b>). In (<b>E</b>) and (<b>F</b>), the population distribution of T_die is shown under classical (<b>E</b>) and non-classical (<b>F</b>) conditions at the end of 300,000 model iterations.</p