Mammal life‐history evolution: a comparative test of Charnov's model

Abstract

We present a comparative test of Charnov's recent theoretical model of mammalian life‐history evolution. Phylogenetic analysis of life‐table data from 64 species, ranging across nine orders. supports all of Charnov's assumptions and most of his predictions. The allometries of time from independence to maturity (a), annual fecundity, and adult and juvenile mortality rates are in agreement with previous work and with the theory, as are the signs of the relationships among these traits when body size is controlled for. As predicted, the non‐dimensional products of a and each of the other three traits are independent of adult body size, as is survivorship to maturity. However, we find that the ratio of weaning weight to adult weight (δ) is correlated with adult weight, in contradiction with the theory, and we do not find the predicted relationships between δ and the three non‐dimensional products. The discrepancies could be because we have equated independence with weaning, or because the model assumes determinate growth: they could arise if large mammals have relatively longer periods of post‐weaning care, or continue to grow after starting to reproduce. There is some evidence that δ is influenced by the nature of mortality around independence (density‐dependent or density‐independent), and we suggest this as a possible area for further work. In general, the areas of agreement between Charnov's theory and the data are more impressive than the differences, indicating that it could be a major breakthrough in understanding the evolution of life histories in placental mammals.

Life-history phenotypes in populations of Brachyrhaphis episcopi (Poeciliidae) with different predator communities

“…Although causality is always uncertain, when similar trends repeatedly emerge across taxa, and plausible selective mechanisms are known, our confidence in specific adaptive scenarios increases (Harvey and Pagel 1991). Crude attempts to rank average mortality rates across species have had considerable success in predicting lifehistory features (Charnov 1993;Purvis and Harvey 1995;Jennings et al 1998;Gemmill et al 1999). Within-species comparisons of poeciliids showing convergent patterns of population differentiation provide similar supporting evidence.…”

Adult and offspring size in the ocean over 17 orders of magnitude follows two life history strategies

“…The Mammalia group slope was slightly but significantly less than 1 (0.90; Table 1) and not significantly different from the slope of the relation for terrestrial mammals (0.95; Purvis andHarvey 1995, Falster et al 2008; likelihood ratio testing, P ¼ 0.086). For groups showing the proportional strategy, the average ratio of adult-tooffspring size mainly varied between 10 2 and 10 3 , with the Euphausiids deviating significantly from this pattern by having much smaller eggs, relatively (ratio ;10 Invariant offspring size was found in the Cephalopoda, Cnidaria, Sagittoidea, teleosts, and possibly Ctenophora, though the latter is data-limited with n ¼ 3 (Tables 1 and 3; Appendix: Fig.…”

“…Groups that demonstrate the proportional offspring size strategy are Crustaceans, Elasmobranchii, and Mammalia (Table 3). In earlier work, offspring vs. adult size relationships significantly different from 0 were found for sharks (Freedman and Noakes 2002), foraminifera (Caval-Holme et al 2013), and terrestrial mammals (Purvis andHarvey 1995, Falster et al 2008). The offspring-adult slope for marine mammals (this study) was not different from that of terrestrial mammals (Falster et al 2008) but was significantly less than 1.…”

Circadian Rhythms of Urinary Cortisol Levels Vary Between Individuals in Wild Male Chimpanzees: A Reaction Norm Approach

“…There is however evidence for some genetic predisposition of glucocorticoid excretion mechanisms (Linkowski et al, 1993;Oswald et al, 2004;Pflüger et al, 2016). Furthermore, a multitude of species has prolonged phases of intensive maternal care (e.g., Purvis and Harvey, 1995), rendering priming of glucocorticoid excretion patterns possible (e.g., Plotsky and Meaney, 1993, but see Aizer et al, 2015;Berghänel et al, 2016;Murray et al, 2016;McCormick et al, 2017). Therefore, exposure to differential levels of parental care and differences in genetic makeup could generate glucocorticoid trait repeatability among adult individuals in mammals.…”