Youth in the study of comparative physiology: insights from demography in the wild
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Youth in the study of comparative physiology: insights from demography in the wild Richard W. Hill1 · David A. Sleboda2 · Justin J. Millar3 Received: 4 May 2020 / Revised: 7 September 2020 / Accepted: 20 September 2020 © The Author(s) 2020
Abstract Of all the properties of individual animals of interest to comparative physiologists, age and stage of development are among the most consequential. In a natural population of any species, the survivorship curve is an important determinant of the relative abundances of ages and stages of development. Demography, thus, has significant implications for the study of comparative physiology. When Edward Deevey published his influential summary of survivorship in animal populations in the wild seven decades ago, he emphasized “serious deficiencies” because survivorship curves for natural populations at the time did not include data on the earliest life stages. Such data have accumulated over intervening years. We survey, for the first time, empirical knowledge of early-age survivorship in populations of most major animal groups in a state of nature. Despite wide variation, it is almost universally true that > 50% of newly born or hatched individuals die before the onset of sexual maturity, even in species commonly assumed to exhibit high early-age survivorship. These demographic facts are important considerations for studies in comparative and environmental physiology whether physiologists (i) aim to elucidate function throughout the life cycle, including both early stages and adults, or (ii) focus on adults (in which case early-age survivorship can potentially affect adult characteristics through selection or epigenesis). We establish that Deevey’s Type I curve (which applies to species with relatively limited early mortality) has few or no actual analogs in the real, natural world. Keywords Juveniles · Immatures · Young · Life tables · Survivorship · Mortality · Ontogeny · Development · Deevey
Introduction In the study of comparative physiology, an important dimension is comparison of the sequential stages of postnatal development within species. Already in the early nineteenth century, Edwards (1824) observed that young mammals and birds—compared with adults of their species—are less capable of maintaining a high body temperature in cold surroundings. In more recent decades, comparative studies of the stages of development have become more detailed, and Communicated by G. Heldmaier. * Richard W. Hill [email protected] 1
Department of Integrative Biology, Michigan State University, East Lansing, MI 48824, USA
2
Department of Physiology, McGill University, Montreal, QC H3G 0B1, Canada
3
Big Data Institute, University of Oxford, Old Road Campus, Oxford OX3 7LF, UK
they have addressed a wide diversity of animals and levels of organization. To illustrate with a few examples, Hill (1976) detailed the radical changes in metabolic rate and thermoregulatory competence that take place as newborn mice (Peromyscus leucopus) mature to adulthood—including the r
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