Data from: From gestation to weaning: combining robust design and multi-event models unveils cost of lactation in a large herbivore

1. The cost of current reproduction on survival or future reproduction is
one of the most studied trade-offs governing resource distribution between
fitness components. Results have often been clouded, however, by the
existence of individual heterogeneity, with high-quality individuals able
to allocate energy to several functions simultaneously, at no apparent
cost. 2. Surprisingly, it has also rarely been assessed within a breeding
season by breaking down the various reproductive efforts of females from
gestation to weaning, even though resource availability and energy
requirements vary greatly. 3. We filled this gap by using an intensively
monitored population of Pyrenean chamois and by expanding a new
methodological approach integrating robust design in a multi-event
framework. We distinguished females that gave birth or not, and among
reproducing females whether they lost their kid or successfully raised it
until weaning. We estimated spring and summer juvenile survival,
investigated whether gestation, lactation or weaning incurred costs on the
next reproductive occasion, and assessed how individual heterogeneity
influenced the detection of such costs. 4. Contrary to expectations if
trade-offs occur, we found a positive relationship between gestation and
adult survival suggesting that non-breeding females are in poor condition.
Costs of reproduction were expressed through negative relationships
between lactation and both subsequent breeding probability and spring
juvenile survival. Such costs could be detected only once individual
heterogeneity (assessed as two groups contrasting good vs poor breeders)
and time variations in juvenile survival were accounted for. Early
lactation decreased the probability of future reproduction, providing
quantitative evidence of the fitness cost of this period recognized as the
most energetically demanding in female mammals and critical for neonatal
survival. 5. The new approach employed made it possible to estimate two
components of kid survival that are often considered practically
unavailable in free ranging populations, and also revealed that
reproductive costs appeared only when contrasting the different stages of
reproductive effort. From an evolutionary perspective, our findings
stressed the importance of the temporal resolution at which reproductive
cost is studied, and also provided insights on the reproductive period
during which internal and external factors would be expected to have the
greatest fitness impact.