Le problème de la détermination de l’âge : une source d’erreur négligée dans le calcul des tables de vie transversales

Abstract

We demonstrate in the present work that wrong assessment of age can markedly affect the interpretation of vertical life tables. We built such a life table from a sample of known age roe deer considered as representative of a fictional population. Mean survival rate in adult stage was then 0.51, leading to a decreasing population (-10 % per year) by using a demographic model. Conversely, 5 out of 8 age structures estimated by different people (3 specialists, 3 well-trained and 2 inexperienced people) from wear tooth criteria well-defined for roe deer led to overestimate survival. In these cases, estimates led to conclude that the fictional roe deer population was either stable (1 case) or increasing (4 cases). This outcome was independent on the relative experience of observers : age assessment by 2 specialists, 1 well-trained and 1 inexperienced people led to increasing population. Because most previous works focussed on large mammals were based on similar wear tooth criteria, wrong age assessment is likely to occur. This may invalidate interpretations of vertical life tables as well as the violation of both stationarity of the population and representativity of the sample that have received much more attention.Resume. -Nous d£montrons dans ce travail que des erreurs de determination de Tage peuvent avoir des consequences importantes dans l'interprotation des tables de vie transversales. Ainsi, une table de vie transversale construite ä partir d'un echantillon de chevreuils d'age connu indique un taux de survie adulte moyen £gal ä 0,51. L'utilisation d'un modele demographique conduit alors ä une population fictive de chevreuils declinante au taux moyen de 10 % par an. Au contraire, 5 des 8 structures d'age estim^es par des observateurs diff&ents (3 spocialistes, 3 habitues et 2 bootiens) ä partir des criteres d'usure dentaire bien e*tablis pour le chevreuil conduisent ä surestimer le taux de survie et par la concluent ä la stabilite* (l cas) ou ä la croissance (4 cas) de cette meme population fictive. Ceci apparait independant du niveau d'exp£rience des observateurs: les structures d'age determine'es par 2 spe"cialistes, l habituo et l bootien conduisent ä des populations croissantes. Comme la grande majorite* des travaux realisos sur les tables de vie transversales de grands mammiferes reposent sur des criteres d'usure dentaire similaires ä ceux utilises dans notre otude, des erreurs de determination d'äge sont probables et pourraient invalider les conclusions au meme titre que le non-respect des hypotheses de stationnarito de la population et de representativite de l'e*chantillon prelev6 plus classiquement evoquees. , t. 58, n° 2,1994 : 293 · 299. Mammalia

Can Dental Microwear Textures Record Inter-Individual Dietary Variations?

“…From 5 deer per 100 ha in 1980, their density increased to 25 individuals per 100 ha in 1988. The feeding, sexual and breeding behavior, as well as the social organization of this population were then studied [23] , [39] , [40] , [41] . After this 10-year period, 120 individuals were slaughtered following strict procedures.…”

Variation in cohort mandible size as an index of roe deer (Capredus capreolus) densities and population trends

“…The age of 45 of the 120 culled animals was known precisely as they had been marked as juveniles (kids, in their first year, are readily distinguished from older animals from patterns of tooth eruption, Ratcliffe & Mayle, 1992;Angibault et al, 1993). For the remaining animals, age was estimated from tooth wear (Van Laere, Boutin & Gaillard, 1989;Vincent et al, 1994). Although this technique is inexact (Vincent et al, 1994), it was considered sufficiently precise to assign animals to a birth year within 1 of 3 defined periods over the course of the study.…”

“…For the remaining animals, age was estimated from tooth wear (Van Laere, Boutin & Gaillard, 1989;Vincent et al, 1994). Although this technique is inexact (Vincent et al, 1994), it was considered sufficiently precise to assign animals to a birth year within 1 of 3 defined periods over the course of the study. For further confirmation, these estimated ages were also checked against estimates derived from eye lens weight, a reliable index of roe deer age (Angibault et af., 1993).…”

Aging through growth marks in teeth of Spanish red deer

“…Consequently, we suggest using the first lower molar for deer aging in Sierra Morena, to avoid age underestimation errors that can lead to overestimation of population growth rates. Further, it can lead to cohort misidentification and life-table misinterpretation, with the subsequent risk of erroneous management decisions, leading to serious negative effects on wildlife populations and environment (Roseberry 1980, Vincent et al 1994. Regression likely is more efficient than the SCM for aging when using incisors.…”