Using retrospective life-tables to assess the effect of extreme climatic conditions on ungulate demography

In Mediterranean areas, severe drought events are expected to intensify in
forthcoming years as a consequence of climate change. These events may
increase physiological and reproductive stress of wild populations
producing demographic changes and distribution shifts. We used
retrospective life tables to understand demographic changes on a wild
population after severe drought events. We studied the impact of two
extreme events (2003 and 2005) on the population dynamics of our model
species, the red deer (Cervus elaphus). During both years, population
density was high (40 and 36 ind/100 hectares, respectively). Thus, we
reconstructed retrospectively the age-structure of the female part of the
population for the period 2000-2010 by using data of known-age individuals
culled during the period 2000 to 2019 (n = 4176). Also, based on previous
studies results, we aimed to validate this methodology. Both extremely dry
years, 2003 and 2005, produced marked and lasting cohort effects on
population demography. Age pyramid the following years (2004 and 2006)
revealed that the extreme drought caused the female fawn cohort to be
similar or even smaller than the yearling cohort. Furthermore, these
cohort effects were still perceptible 3 years after theses severe events.
Results agree with previous findings that showed a negative effect of
severe drought events on female pregnancy rates and conception dates.
Although simple, this study provides an empirical
quantification of the demographic effects of severe drought
events for a wild population which might be useful to understand future
demographic changes under the context of climate change.