Bo. Wolf et Cm. Del Rio, Use of saguaro fruit by white-winged doves: isotopic evidence of a tight ecological association, OECOLOGIA, 124(4), 2000, pp. 536-543
We report the use of stable isotope and crop content analyses to quantify t
he use of saguaro (Carnegiea gigantea) nectar and fruit by migratory desert
white-winged doves (Zenaida asiatica mearsnii). Saguaro resources had char
acteristically C-13-enriched CAM values (delta(13)C=-12.8+/-0.7 parts per t
housand SD VPDB and -13.1+/-0.5 parts per thousand SD VPDB for nectar and f
ruit, respectively) relative to other food plants used by doves (delta(13)C
(C3)=-24.9+/-3.3 parts per thousand SD VPDB). The water contained in saguar
o nectar and fruit was deuterium enriched (delta D=19.6+/-2.0 parts per tho
usand SD VSMOW and 48.4+/-1.6 parts per thousand SD VSMOW for nectar and fr
uit, respectively) relative to other water sources (ranging from -41 to -19
parts per thousand VSMOW). During the fruiting season, there was a positiv
e correlation between delta(13)C in dove liver tissues and percent of sagua
ro in crop contents. A two-point mixing model indicated that during the pea
k of saguaro fruit use, most of the carbon incorporated in dove tissues was
from saguaro. Desert white-winged doves appear to be saguaro specialists.
Averaged over the period when doves were resident, saguaro comprised about
60% of the total carbon incorporated into dove tissues. Tissue delta(13)C a
nd delta D of body water showed a significant positive correlation, indicat
ing that doves were using saguaro as a source of both nutrients and water.
However, at the peak of saguaro utilization, the doves' body-water delta D
was more positive (by about 20 parts per thousand) than saguaro fruit water
. We hypothesize that this enrichment is due to fractionated evaporative wa
ter losses by doves. Using dove carbon isotope data and a two end-point mix
ing model we estimate that, on average, doves consume the equivalent of 128
saguaro fruits per season; each fruit contains on average 26.0+/-14.8 g SD
of pulp (wet mass) of which 19.4 g is water. Stable isotopes have been use
d to produce qualitative re-constructions of animal diets. Our study shows
that they can be used to provide quantitative estimates of the now of nutri
ents from resources into consumers as well.