Abstract
Life-history traits represent organisms' strategies to navigate the fitness trade-offs between survival and reproduction. Eric Charnov developed three dimensionless metrics to quantify fundamental life-history trade-offs. Lifetime reproductive effort (LRE), relative reproductive lifespan (RRL) and relative offspring size (ROS), together with body mass can be used to classify life-history strategies across the four major classes of tetrapods: amphibians, reptiles, mammals and birds. First, we investigate how the metrics have evolved in concert with body mass within tetrapod lineages. In most cases, we find evidence for correlated evolution among body mass and the three dimensionless metrics. Second, we compare life-history strategies across the four classes of tetrapods and find that LRE, RRL and ROS delineate a space in which the major tetrapod classes occupy mostly unique subspaces. These distinct combinations of life-history strategies provide us with a framework to understand the impact of major evolutionary transitions in energetics, physiology and ecology.
Highlights
Life-history traits quantify the two crucial components of fitness: survival and reproduction
Since results did not differ based on the value of body mass used, we present results using the maximum body mass in the body of the paper and include the results of the average mass converted from SVL in the electronic supplementary material
relative offspring size (ROS) demonstrated a similar pattern to Lifetime reproductive effort (LRE): mean natural log ROS differed across all four classes (Tukey HSD; p < 0.05), increasing by 98.1% from amphibians to birds
Summary
Life-history traits quantify the two crucial components of fitness: survival and reproduction. Organisms cannot optimize both individual survival and reproductive investment, so allocation to one component of life-history necessitates trade-offs in other areas [4,5]. Organisms navigate these constraints in a variety of ways to maximize overall fitness, creating an astonishing diversity of life-history strategies. Endotherms can attain greater metabolic power and rates of production [15] and exploit a wider range of environments [16], but they face energetic costs that limit their minimum size Without these constraints, ectotherms can potentially display a wider variety of life-history strategies in response to their local environmental conditions. We consider how they may influence the position of amphibians, reptiles, mammals and birds in life-history trait space
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