Appendix B. Summary of the hypotheses evaluated and how they were supported by our study.
TABLE B1. Summary of hypotheses, predictions, and the evidences of support provided by our study.
Hypotheses |
Predictions |
Results |
Support |
Conservative reproductive tactic |
Stronger influence of maternal traits on allocation strategies than offspring traits |
Offspring traits had an influence but the greatest variation in maternal allocation and in the probability of future reproduction was explained by mother mass, age, and previous reproductive status |
Yes |
Reproductive senescence |
Offspring mass, relative maternal allocation, and/or reproductive success decline with mother age |
Mass of offspring produced progressively declined from age 8 (age at which asymptotic mass is reached) until death; probability of reproduction declined importantly from age 12 until death; maternal allocation showed a slight but nonsignificant decline from age 3 until death |
Yes* |
Terminal allocation |
Offspring mass, relative maternal allocation, and/or reproductive success decline with mother age |
Mass of offspring produced progressively declined from age 8 (age at which asymptotic mass is reached) until death; probability of reproduction declined importantly from age 12 until death; maternal allocation showed a slight but non-significant decline from age 3 until death |
No* |
Terminal investment |
Fitness costs of reproduction, i.e., probability of future reproduction after allocating to current reproduction, increase with mother age |
Costs of reproduction did not vary with age |
No* |
Reproductive constraint |
Offspring mass, relative maternal allocation and reproductive success increase with age in young females, and/or are greater in multiparous than primiparous females |
Calf mass and maternal allocation were low in 2-year-old mothers and increased dramatically in the ensuing years; probability of reproducing in successive years increased with age in young females; primiparous mothers allocated more to their offspring but produced offspring of similar mass |
Yes |
Individual quality |
Heavy females reproduce successfully at each reproductive occasion and produce heavier offspring by providing less relative maternal allocation than light females |
Large residual variance in calf mass, maternal allocation, and probability of future reproduction explained by mother identity; heavy mothers produced heavier offspring by providing less relative allocation than light mothers; heavy mothers had a higher probability of reproducing successfully in successive years; the level of allocation provided was positively correlated among the offspring a mother produced |
Yes |
Costs of reproduction |
Females allocating more to reproduction show a reduced probability of reproducing at the next occasion and/or produce lighter future offspring than females allocating less to reproduction |
Previously reproductive females produced lighter future offspring and allocated less to their new offspring than previously barren females, but mothers allocating more to reproduction did not have a reduced probability of reproducing again compared with mothers allocating less |
Yes† |
* Very old and barren females were removed from the population. This selective culling very likely underestimated the senescence patterns and overestimated terminal investment or allocation processes.
† Indirect costs of reproduction in terms of the quality of the future offspring produced as a result of reproduction per se, but no cost as a result of variation in the amount of allocation provided when reproduction occurs.