A remarkable paper led by Julius Bright Ross delves into WildCRU’s 32-year long badger demographic data
Having devoted 32 years to gathering data on the births, deaths, and marriages of badgers in Oxfordshire, it has been exciting to see a pay-off to our doggedness, writes David Macdonald in celebration of a remarkable paper led by Julius Bright Ross.
Julius, a talented doctoral student who arrived at WildCRU from Easter Island via Harvard, has delved with deep originality into our 32-year long badger demographic data, asking how inter-individual differences arise in the trade-off between survival and reproduction. This question grows out of the so-called “pace-of-life syndrome” hypothesis, which proposes that individual differences along various correlated axes represent an optimisation of energy allocation trade-offs, the costs and benefits of which can change depending on prevailing environmental conditions. Almost nobody has been able to study this in biggish wild mammals, because almost nobody has spent 32 years gathering the data! The key thing is to analyse exactly which environmental conditions are most influential to setting these differences in the speed at which individuals live their lives, or when in an individual’s life history they have the greatest impact.
Julius and our badger team found strikingly different effects of environmental conditions on male and female badgers. While weather strongly affected how early males would start breeding, harsh weather conditions continued to determine year-to-year reproduction in females. In short, weather—and its role in setting food availability—affected males’ race to the starting line whereas it affected females’ pace once they were in the race. Meanwhile, social conditions strongly affected both sexes as they paced their lives: at higher population densities, female pace-of-life slowed with the increasing competition for reproductive opportunity. In contrast, it seems that amongst males faced with elevated mating competition, the race to start breeding earlier is even more intense; in line with the all-too-human epithet of “live fast, die young”, early-breeding males do just that, and their higher mortality likely contributes to a heavily female-skewed sex ratio in the later (higher density) years of the Oxford study.
Finally, prevailing wisdom has it that early-life conditions tend to set individual success trajectories, and much pace-of-life research has therefore focused on early-life environment. However, Julius and the team found that in badgers, early-life conditions contributed relatively little to pace-of-life, with changing conditions later in life instead playing a large role in the population’s overall pace-of-life. This exemplifies the notion that in long-lived animals, behavioural plasticity–the ability to “pivot” when faced with new conditions—is likely to be an important component of withstanding the effects of human-induced rapid environmental change.
This study, published in Global Change Biology, not only emphasises the importance of long-term studies (this one started before climate and its change was a hot topic in wildlife research) but also reveals life history as a particularly important facet of behavioural plasticity: in this case, the badgers illustrate population-level effects wrought by sex-specific life-history responses.
Young Badger (Appleton Wildlife Diary)