D3- Body size and life history variation

Effects of body size and lifestyle on evolution of mammal life histories, Richard Sibly and James Brown, 2007

• previous studies→ life-history evolution is subject to a fundamental size-dependent constraint which limits the rate at which biomass can be produced so that production per unit of body mass is inevitably slower in larger organisms than in smaller ones. Here we

• aim→ derive predictions for how changes in body size and production rates evolve in different lifestyles subject to this constraint.

• methods→ predictions are tested by using data on the mass of neonate tissue (brain, spinal cord, heart, tendons, and skin) produced per adult per year in 637 placental mammal species

• results→ predictions are generally supported

  • compared with terrestrial insectivores with generalized primitive traits, mammals that have evolved more specialized lifestyles have divergent mass specific production rates:

    • increased mass specific production rates in groups that specialize on abundant and reliable foods: grazing and browsing herbivores (artiodactyls, lagomorphs, perissodactyls, and folivorous rodents) and flesh-eating marine mammals (pinnipeds, cetaceans)

    • decreased mass specific production rates in groups that have lifestyles with reduced death rates: bats, primates, arboreal, fossorial, and desert rodents, bears, elephants, and rhinos.

    • convergent evolution of groups with similar lifestyles is common, so patterns of productivity across mammalian taxa reflect both ecology and phylogeny.

  • conclusions→ groups with different lifestyles have parallel but offset relationships between production rate and body size. Variation occurs along two axes corresponding to body size and lifestyle.

• fast-slow continuum, trade offs and energy allocation

• question→ what would favour live slow, die old lifestyles? abundant/low resources, low predation rates, sociality

• rule linking production rate and body size, use terrestrial insectivores as a baseline

• all mammals have same pattern, of high body mass and low specific production rate, when looking at orders, but when grouping by lifestyle, see differences between each e.g. arboreal, herbivores, marine

• is important to take into account phylogeny and lifestyles

Universal rules of life: metabolic rates, biological times and the equal fitness paradigm, Joseph Burger et al., 2021

• aim→ to review and extend the equal fitness paradigm (EFP) as an important step in developing and testing a synthetic theory of ecology and evolution based on energy and metabolism.

• EFP→ states that all organisms are equally fit at steady state, because they allocate the same quantity of energy, ~ 22.4 kJ/g/generation to the production of offspring.

  • On the one hand, the EFP may seem tautological (using two words or phrases that express the same meaning), because equal fitness is necessary for the origin and persistence of biodiversity.

  • On the other hand, the EFP reflects universal laws of life: how biological metabolism – the uptake, transformation and allocation of energy – links ecological and evolutionary patterns and processes across levels of organisation from: (1) structure and function of individual organisms, (2) life history and dynamics of populations, and (3) interactions and coevolution of species in ecosystems.

• The physics and biology of metabolism have facilitated the evolution of millions of species with idiosyncratic anatomy, physiology, behaviour and ecology but also with many shared traits and tradeoffs that reflect the single origin and universal rules of life.

• all use same amount of energy to produce offspring, solar energy passed on in biomass

• steady state assumption→ birth rate = death rate, biodiversity always stays the same, but natural selection still occurs so is not true

• other theories→

  • metabolic theory of ecology- scaling metabolic rates across body size and temperature, explains why animals have more/less offspring, links well to the first theory

  • dynamic energy budget→ biochemical and physiological aspects of metabolism, broad range of parameters, too specific, hard to link to other two theories

• are very theoretical models, theoretically systems all have an equilibrium

• specifics vs universal rule

• body size and lifestyles vs metabolic rates and biomass