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

Citation

Peláez Beato, Marta et al. (2022), Using retrospective life-tables to assess the effect of extreme climatic conditions on ungulate demography, Dryad, Dataset, https://doi.org/10.5061/dryad.fn2z34tvd

Abstract

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.

Methods

This database contains data on 4176 known-age females culled (or found dead) mostly from October to February during the years 2000-2019. These females were a random subsample of the popula­tion (i.e. no hunting selection was performed because of the objective was culling as much females as possible).

For each individual culled, the first incisor (I1) was removed to assess its age, although for younger ones, still with milk incisors, the age was assessed by tooth replacement and succession method (Mitchell, 1967; Azorit et al., 2002a). Histological examinations of incisors were performed by staff at the Los Quintos de Mora’s laboratory by counting cementum annuli (Low & Cowan, 1963; Azorit et al., 2002b).

After extraction of the incisors, each tooth was placed into labeled plastic containers filled with water. They were left in the plastic containers for around four weeks to let the soft tissue rot away and thus, help eliminating any remaining soft tissues before decalcification. Subsequently, incisors were placed in a 5% nitric acid solution for two or three days (Morris, 1972). Once decalcified, each tooth root was placed in a cryostat where several longitudinal cuts of 25 μm were made at a temperature of -18ºC. The different sections were stained using diluted haematoxylin and then, several sections of each tooth were mounted on a glass microscope slide. Finally, the dental cementum annuli were count by using a 20x magnification microscope (ZEISS MC 100).

Usage Notes

This database has 3 columns:

DATE_CAPTURE indicates the date when females were culled (mm/dd/yyyy)

AGE: The age of females in years (ranging from 0-15 years).

SEX: Sex is always "Female"

Funding

Organismo Autónomo Parques Nacionales