D1- The fast-slow continuum of life history

Fast and slow life histories of mammals, Stephen Dobson and Madan Oli, 2007

• Previous studies→ compare species to discern patterns in the evolution of traits, first major component in variation in life histories is body size

• Aim→ test whether the second major component of variation in life histories of mammals is a continuum from species with short lives to long lives, the “fast–slow continuum.”

• Method→ 144 mammalian populations representing 109 species were examined, and life histories were summarized using 5 key variables that reflect reproduction and survival.

• Results→

  • Body size and phylogeny were significant influences on life histories→ were removed statistically, a major axis of life history variation that reflected the fast–slow continuum was revealed in a principal components analysis. This component of life history was poorly but significantly associated with indices of the fast–slow continuum, such as the ratio of reproduction to age at maturity and generation time.

  • Fast and slow species were identified among several orders and families of mammals, and one species exhibited fast and slow populations.

  • Degree of precociality did not appear to be a third major component of life histories.

• Conclusion→ these results may indicate that fast and slow life cycles are highly phenotypically plastic

• life histories are significant to understand allocations of energy, categorising species due to their periods and breaks

• comparative analysis- mammalian species, life history traits, insights into evolutionary factors shaping histories

• body mass explained 36% of variation, smaller mammals have faster whilst larger have slower, phylogeny explained 85% of the variation, fastest and slowest were in the same family- lots of variation

• continuum is more evolutionary- adapts to environments

Life histories are not just fast or slow, Iain Stott et al., 2024

• Life history strategies, which combine schedules of survival, development, and reproduction, shape how natural selection acts on species’ heritable traits and organismal fitness.

• Previous studies→ comparative analyses have historically ranked life histories along a fast–slow continuum, describing a negative association between time allocation to reproduction and development versus survival.

• New studies→

  • higher-quality, more representative data and analyses have revealed that life history variation cannot be fully accounted for by this single continuum

  • studies often do not test predictions from existing theories and instead operate as exploratory exercises

• Future→ offer three recommendations for future investigations:

  • standardizing life history traits

  • overcoming taxonomic siloes (that isolate from others)

  • using theory to move from describing to understanding life history variation across the Tree of Life

• critiques that the continuum is not common and oversimplified and biased→ can’t use to make evolutionary inferences very well

• should use hypotheses rather than ideas, current studies are more correlational not causational, should integrate multiple axes of variation

Further Research-

• needs more environmental context

• applies between species but not between conspecifics

• can be seen at the level of communities