Accounting for demography in the assessment of wild animal welfare

Abstract

Welfare is experienced by individual animals, but the quantity and average quality of welfare an individual is likely to experience in their lifetime is bounded by population demography; namely, age-specific survivorship and the ecological forces that shape it. In many species, a minority of the individuals who are born survive to adulthood, meaning that the lives of those we observe in nature are often unrepresentative of the typical individual born into their population. Since only living animals are capable of experiencing welfare, lifespan is effectively an upper bound on the amount of affectively positive or negative experience an animal can accrue. Life history strategies that increase the probability of a long life are therefore more permissive of good welfare; but even holding life expectancy constant, specific patterns of age-specific mortality may enable a larger proportion of individuals to live through periods characterized by above-average welfare. I formalize this association between demography and welfare through the concept of welfare expectancy, which is applied to published demographic models for >80 species to illustrate the diversity of age-specific mortality patterns and entertain hypotheses about the relationship between demography and welfare.