OUTSTANDING QUESTIONS
• Is there a universal characterisation of life histories across the tree of life?
• Does the fast-slow continuum explain the majority of life-history variation across all taxa? It does in Tetrapods (especially mammals and birds), which are relatively over-studied, and only in recent years has the fast-slow continuum been shown to be important in sessile and clonal organisms (vascular plants, corals). Whether the fast-slow continuum is the major structuring axis of life history variation has not been studied in most invertebrates other than insects, where the fast-slow continuum was identified [6], but seems to be less structuring than in tetrapods [7].
• Are other axes of life history variation consistent among taxa? Traits relating to reproductive or developmental tactics have repeatedly emerged as the second most important axis of life history variation. However, heterogeneity in the set of traits analysed so far prevents us from concluding taxonomic universality.
• What, if any, are the implications of particular choices of data and analytical approaches? Certainly the choice of multivariate data to analyse, and the availability of particular measures by taxa, will vary. If the impact of these choices on research outcomes is significant, cognisance of such consequences is of paramount importance.
• Are there clearly defined clusters and boundaries of life history variation across taxa that occupy distinct spaces in multidimensional life history trait space? Biomechanical constraints limit the range of covariation among life history traits [62]. Intuitively, certain life history strategies should not exist if they defy physical or evolutionary laws. How will human actions and climate change alter these boundaries and shape rates of extinction/invasion?
TABLE 1 - Comparison of different types of demographic data in the context of life history strategy comparative analyses.