Evol Ecol Res 20: 317-329 (2019)     Full PDF if your library subscribes.

Within-niche pace of life acceleration as a fundamental evolutionary principle:
a mammal pilot test case

Marcus Clauss¹, Dennis W.H. Müller² and Daryl Codron²

¹Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland,
²Zoological Garden of Halle, Halle (Saale), Germany and ³Department of Zoology and Entomology, University of the Free State, Bloemfontein, South Africa

Correspondence: M. Clauss, Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstr. 260, 8057 Zurich, Switzerland. email: mclauss@vetclinics.uzh.ch

ABSTRACT

Background: A mechanism by which a taxon or clade might prevail is by reproducing faster than its competitors — or, in other words, by a faster life history. Hence, for organisms that share a niche space, there should be strong directional evolution of life-history characteristics towards faster reproduction. One reason why this mechanism is rarely considered may be the conceptualization of life-history strategies as a set of trade-offs subject to fixed overall physical laws, rather than as a set of morpho-physiological adaptations that might evolve a higher efficiency.

Hypothesis: Among extant taxa, directional evolution towards faster reproduction should be reflected by higher diversity in those clades of a niche that have a faster pace of life. Assuming phylogenetic inertia in the pace of life, fossil representatives of clades whose extant representatives are characterized by a slower pace of life should have been replaced in the niche space by representatives of clades whose extant representatives have a faster pace of life.

Data description: We use life-history data from extant eutherian mammals from the PanTheria data base, and examples from the mammalian fossil record, focusing in particular on large herbivores.

Pilot results: We show case examples that indicate differences in offspring production per unit time in eutherian mammals of similar niches. For example, the sequence of gestation period length in which cattle, horses, dromedaries, and okapis produce offspring of similar number, size, and maturity (280, 340, 390 and 440 days, respectively) reflects the current species diversity and past displacement sequences of bovids, equids, camelids, and giraffids.

Conclusions: The demographic mechanism of the ‘survival of the fittest’ can be expected to have consequences for the evolution of properties determining demographic life history. Considering life history as clade-specific, and life-history characteristics of extant species as a snapshot in evolutionary time, can prominently enhance interpretations of clade turnovers and species diversity.

Keywords: competition, directional evolution, displacement, escalation, key innovation, life history, mammal.

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