The reproductive advantages of a long life: longevity and senescence in wild female African elephants

Abstract

Long-lived species such as elephants, whales and primates exhibit extended post-fertile survival compared to species with shorter lifespans but data on age-related fecundity and survival are limited to few species or populations. We assess relationships between longevity, reproductive onset, reproductive rate and age for 834 longitudinally monitored wild female African elephants in Amboseli, Kenya. The mean known age at first reproduction was 13.8 years; only 5 % commenced reproduction by 10 years. Early reproducers (<12.5 years) had higher age-specific fertility rates than did females who commenced reproduction late (15+ years) with no differences in survival between these groups. Age-specific reproductive rates of females dying before 40 years were reduced by comparison to same-aged survivors, illustrating a mortality filter and reproductive advantages of a long life. Overall, 95 % of fertility was completed before 50, and 95 % of mortality experienced by age 65, with a mean life expectancy of 41 years for females who survived to the minimum age at first birth (9 years). Elephant females have a relatively long period (c. 16 years) of viability after 95 % completed fertility, although reproduction does not entirely cease until they are over 65. We found no evidence of increased investment among females aged over 40 in terms of delay to next birth or calf mortality. The presence of a mother reproducing simultaneously with her daughter was associated with higher rates of daughter reproduction suggesting advantages from maternal (and grandmaternal) co-residence during reproduction.

Can We Sustainably Harvest Ivory?

“…EXPERIMENTAL PROCEDURES Demography Demographic parameters were estimated from individual follows in Amboseli, southern Kenya, from 1972 to 2014 and ongoing (Table S3) [19]. The study was entirely observational and had full clearance from relevant authorities.…”

“…At the same time, we cannot brush aside the fact that poaching has reached industrial scale fuelled by an increase in consumer demand driven by the rise of the middle class in countries like China [5]. We must urgently work on finding ways to change consumer behaviour as the only avenue by which we can resolve the ivory trade tragedy.EXPERIMENTAL PROCEDURES Demography Demographic parameters were estimated from individual follows in Amboseli, southern Kenya, from 1972 to 2014 and ongoing (Table S3) [19]. The study was entirely observational and had full clearance from relevant authorities.…”

General conclusion to the special issue Moving forward on individual heterogeneity

“…Thus, the most appropriate distribution for their annual fecundity (sensu Allainé et al 1987) is a Poisson or generalized Poisson regression (Kendall and Wittmann 2010). Conversely, long-lived mammals, like elephants, whales, or humans, usually produce only a single offspring per reproductive attempt, with long inter-birth intervals (Kraus et al 2001, Hayward et al 2015, Lee et al 2016). In such cases, annual fecundity is usually modelled with a logistic regression.…”

Nearby grandmother enhances calf survival and reproduction in Asian elephants

“…Although elephants lack menopause, Asian elephant ( Elephas maximus ) females which survive to old age can have relatively long lives after last reproduction, at the population level, 17 years after age 47 (when 95% of population fecundity has been realized) and at the individual level 11 years for those females living beyond 40 years3. Similarly, African elephant ( Loxodonta africana ) females live 16 years on average after age 4929. Increasing evidence supports the importance of older females for group wellbeing/survival273031, allomothering/grandmothering among elephant groups2932333435 and recent evidence shows enhanced reproduction of daughters with longer living mothers in African elephants29.…”