Overall, this is very well written and engaging paper that uses a superb set of data from diverse soecies to tackle a topic of wide interest: understanding the diversity of demographic life history traits and strategies.

The authors examine the existence of continua of life history both among species and within species (the first time I have seen this done). This is nice work, though I have a few comments.

While the authors emphasize the existence of a single dominant fast-slow continuum of life history, the among-species analysis seems to show two axes, not one. This aligns with findings from similar analyses (cited in this manuscript) by Healy and Salguero-Gomez. It is true that the fast-slow continuum has a dominant role, but I feel that this manuscript overemphasises the "simple" single-axis story. Incidentally, Bielby (2007) also found more than one axis using different methods.

Furthermore, I would like to see more discussion about how data quality, such as recapture rate, heterogeneity, and selective disappearance, might influence the results. These issues might be very important for some species but not others and could influence the results. Relatedly, these PCA analyses do not account for uncertainty in the input variables. THese uncertainties probably vary across species and it would be useful if this could be accounted for in some way, or at least discussed. I wonder if bootstrapping the PCA to recalculate the PCA and get a distribution for the % variation explained/loadings etc could help in this regard.

Finally, I think the discussion could be improved with some consideration of the processes involved at the two levels considered: among and within species. At the former level the differences are likely driven by natural selection and differences in trait optima among species. In contrast, the differences among individuals within a species may be a reflection of phenotypic plasticity/development or within-species genotypic/phenotypic variation (which may vary across species). It would be interesting to see a careful discussion of these processes and what they mean for the POLS idea and other investigations into life history strategy.

Specific comments:

L. 68: It would be good to cite the work of Reznick, who shows experimentally that changes in LH can be driven very quickly by changes to extrinsic mortality risk (in Trinidadian Guppies).

L. 70: "Accelerating their life cycles due to disturbance." Please explain the mechanism for this change.

L. 73: "Trade-offs are not always detected." Please briefly explain why.

L. 87: The analysis accounts for the phylogeny, and this should be mentioned here.

L. 112: Please explain why "respecting dimensionality" is imperative.

L. 138: I'm a bit confused about the use of individual generation time. Is this used in addition to age at first reproduction, or as an alternative? (maybe I missed that)

L. 141: Covariable -> Covariate?

L. 435. Do you mean "individual traits" or "traits of individuals"?

Figure 2. This figure implies that there are two axes: a dominant one which we can interpret is the fast slow continuum and another access which might be largely influenced by distribution of reproduction through the life course? In any case it is interesting that the loading for breeding frequency is at right angles to the loadings for the other traits.

References

Healy, K. et al. (2019) Animal life history is shaped by the pace of life and the distribution of age-specific mortality and reproduction. Nat. Ecol. Evol. 3, 1217–1224

Salguero-Gómez, R. et al. (2016) Fast-slow continuum and reproductive strategies structure plant life-history variation worldwide. Proc. Natl. Acad. Sci. U. S. A. 113, 230–235

Bielby, J. et al. (2007) The fast-slow continuum in mammalian life history: an empirical reevaluation. Am. Nat. 169, 748–757