AN ASSESSMENT OF LONG-TERM FOOD-HABITS OF TSAVO ELEPHANTS BASED ON STABLE CARBON AND NITROGEN ISOTOPE RATIOS OF BONE-COLLAGEN
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Stable carbon and nitrogen isotope ratios of bone collagen from elephants that died in the Tsavo National Park, Kenya, between 1975 and 1980, were determined in an attempt to establish possible changes in past diets. Individuals ranged from one to fifty years old at the time of death, and possessed a mean 13C value of 184 018 and a mean 15N value of 138018. These values for carbon were independent of age at the time of death, which suggests that these elephants assimilated similar proportions of C3 (shrub and tree) and C4 (grass) vegetation during the sixtyyear period covered by these specimens. Faecal analyses showed high interindividual variation in the proportion of C3/C4 food eaten, but the mean intake was similar (around 75% trees and shrubs) to that estimated from the isotopic composition of bone collagen. These data suggest that in the Tsavo National Park, elephants have maintained similar proportions of C3 and C4 vegetation in their diet over the past fifty years even though woodlands were being converted to grasslands. We suggest that this resulted from the high mobility of elephants or immigrations of individuals from similar woodland areas. On a dtermin le taux d'isotopes de carbone et d'azote dans le collagne osseux des lphants morts au Pare National du Tsavo (Kenya) entre 1975 et 1980 pour relever d'ventuels changements dans les rgimes alimentaires entrieurs. Les individus furent classs de un cinquante ans selon l'ge de leur mort et possdaient un delta 13C moyen de 184 018, etun 15Nde 13.8 018. Pour le carbone, ces valeurs taient indpendantes de l'ge au moment de la mort, laissant supposer que ces lphants ont absorb des proportions semblables de vgtation de type C3 (arbres et arbustes) et C4 (plantes herbaces) durant toute la priode de soixante ans o ont vcu ces individus. L'analyse des excrments montrait de grandes variations individuelles dans la rapport C3/C4 mais la consommation moyenne tait similaire (environ 75% d'arbres et arbustes) celle qui avait t estime partir de la composition en isotopes du collagne osseux. Ces donnes suggrent qu'au Tsavo, les lphants ont conserve un rgime alimentaire de composition similaire en type C3 et C4 durant les cinquante dernires annes, mme lorsque les rgions boisees se sont transformes en savanes herbeuses. Nous suggrons que ceci est le rsultat soit d'une grande mobility des lphants, soit de l'immigration d'individus provenant de rgions boises semblables. Copyright 1989, Wiley Blackwell. All rights reserved
