Data from: Changes in age-structure over four decades were a key determinant of population growth rate in a long-lived mammal

1. A changing environment directly influences birth and mortality rates,
and thus population growth rates. However, population growth rates in the
short-term are also influenced by population age-structure. Despite its
importance, the contribution of age-structure to population growth rates
has rarely been explored empirically in wildlife populations with
long-term demographic data. 2. Here, we assessed how changes in
age-structure influenced short-term population dynamics in a semi-captive
population of Asian elephants (Elephas maximus). 3. We addressed this
question using a demographic dataset of female Asian elephants from timber
camps in Myanmar spanning 45 years (1970-2014). First, we explored
temporal variation in age-structure. Then, using annual matrix population
models, we used a retrospective approach to assess the contributions of
age-structure and vital rates to short-term population growth rates with
respect to the average environment. 4. Age-structure was highly variable
over the study period, with large proportions of juveniles in the years
1970 and 1985, and made a substantial contribution to annual population
growth rate deviations. High adult birth rates between 1970-1980 would
have resulted in large positive population growth rates, but these were
prevented by a low proportion of reproductive-aged females. 5. We
highlight that an understanding of both age-specific vital rates and
age-structure is needed to assess short-term population dynamics.
Furthermore, this example from a human-managed system suggests that the
importance of age-structure may be accentuated in populations experiencing
human disturbance where age-structure is unstable, such as those in
captivity or for endangered species. Ultimately, changes to the
environment drive population dynamics by influencing birth and mortality
rates, but understanding demographic structure is crucial for assessing
population growth.