Sheet nº 238
March 2006
Adaptive strategies of monkeys
in the struggle for survival
Red colobus are tree-dwelling
primates that live in the tropical
forests of Africa. The IUCN, the
World Conservation Union,
classifies them as Endangered
on its Red List of Threatened
Species. They cannot be successfully kept in captivity and
are therefore highly dependent
on the conservation of their
habitats.
In Senegal and the Gambia, an
IRD primatology team studied
Red colobus
some residual groups of red
©IRD/Anh
GALAT-LUONG
colobus (Procolobus badius
ssp. temmincki) in West Africa
over a long period. The northernmost population, situated in the Fathala Forest
(Saloum Delta National Park and MAB Reserve, Senegal), has been faced with severe degradation of its environment. However, censuses conducted over a lengthy period of time, organized jointly with IUCN and Senegal National Parks authority and
Forestry Commission (DPN Eaux et Forêts) have shown that the numbers of these
colobus have not regressed in the same proportions as the density and diversity of
the trees they depend on. Observed behavioural changes in these primates showed
they have developed surprising and effective adaptive responses to meet changes in
their environment, thus enabling them to ward off the threat of extinction.
or most primates the overriding threat to
survival is habitat degradation. The
Saloum Delta National Park in Senegal
embraces a marine environment consisting of
islands and mangrove swamps, as well as a
mainland portion, the Fathala Forest. The latter is
made up of a plateau of savannah with substantial numbers of trees and gallery forest along the
sides of rivers (which are now dry for more than
ten months per year) on its mainland part and
mangrove swamps in its marine zone.
F
IRD primatologists examined changing trends in
vegetation that occurred between 1969 and
2002, particularly modifications to cover and
diversity of woody species (the area occupied by
trees and large creeper species), tree density
and biodiversity (assessed as specific indices).
Three-quarters of gallery forest, the red colobus’
main habitat, have disappeared and tree species
diversity has plummeted by half. Human activities such as overgrazing, excessive extraction of
timber and uncontrolled fires, which compound
../...
the effects of a large deficit in rainfall (300 mm over the
past 30 years), are responsible for such drastic deterioration of the Fathala Forest.
In parallel investigations, from 1974 to 1976 and from
1988 to 2002, scientists have been monitoring red
colobus populations. Numbers in fact did not recede
dramatically, the total falling from about 600 to 500 individuals. The research team observed colonization of
new forest areas. They sought clues as to the factors
that enabled the population to survive in such difficult
conditions.
Findings indicated that conservation of these red
colobus depended on five major behavioural adaptations.
The oldest one is an increased consumption of fruit
(frugivory) and the use of plant species not hitherto
drawn upon: graminae, herbaceous plants and seeds,
in spite of their folivore metabolism. The second significant change is an increased terrestriality, the time spent
on the ground, although their morphology is adapted to
movement in the canopy of the highest trees (this
includes an extreme reduction in size of the thumb
which was ideal for jumping and swinging from branch
to branch). The colobus are now therefore vulnerable to
predators at ground level such as hyenas and dogs.
The next two adaptations are elements of behaviour
Redaction – IRD : Aude Sonneville
Translation : Nicholas Flay
that appeared more recently in this population: a trend
for polyspecific association, cooperation with other
species, especially with the green monkey
(Cercopithecus (aethiops) sabaeus) and frequentation
of more open habitats.
The fifth and most recent adaptation is the unprecedented use of mangrove swamps, in the first instance
as a refuge, then for nesting and foraging.
These important changes were more likely to be interlinked than independent from one another. The most
plausible hypothesis would involve a chain of causes
and effects. The loss of trees led to the necessity to
move around on the ground, which in parallel raised the
hazards represented by terrestrial predators.
Modifications to the habitat, plus predator pressure,
induced the tendency to associated with other species,
as if the red colobus seemed to trust in the green
monkeys’ knowledge about ground-level predators,
food resources and other habitats like the mangrove
swamps. These changes made it possible for them to
extend their ecological niche to mangrove swamps.
These five complementary adaptations have
become established in less than 30 years, a very short
period on the scale of evolution. Their effectiveness
emphasizes the importance of behavioural strategies in
the survival of higher vertebrates like primates.
These results bring into relief the need to protect the
Fathala Forest and to create a conservation area for the
red colobus of Saloum. IUCN and UNESCO have
incorporated the conclusions of this research in the
Management Plan for the Saloum Delta Biosphere
Reserve.
For futher information
CONTACTS:
Anh GALAT-LUONG, IRD UR 136, "Aires protégées, écosystèmes, gestion et fonctions périphériques"
IRD Orléans, 5 rue du Carbone - Technoparc, 45072 Orléans cedex 2, France
Tel.: 33 (0)2 38 49 95 55, Email : luong@orleans.ird.fr , Web site : http://www.orleans.ird.fr/UR_US/airepro.htm
IRD Communication :
Aude Sonneville (editor), Tel.: +33 (0)1 48 03 76 07, Email: fichesactu@paris.ird.fr ;
Sophie Nunziati (press officer), Tel.: +33 (0)1 48 03 75 19, Email: presse@paris.ird.fr
REFERENCES
GALAT-LUONG, A., GALAT G. (2005). Conservation and survival adaptations of the Temminck's red colobus, (Procolobus badius
temmincki), in Senegal. International Journal of Primatology, 26 (3): 585-603.
L'espoir qui venait des singes. (1996). Reportage TV. Magazine Têtes chercheuses. Réalisation Alain LABOUZE et Robert
CLARKE. Coproduction: Cinquième - CNDP - Gédéon - CNRS audiovisuel - ORSTOM . Soutien: Centre national de la
Cinématographie. Participation: Ministère de l'Education nationale, de l'Enseignement supérieur et de la Recherche; Secrétariat
d'Etat à la Recherche; Ministère des Affaires étrangères. Prix des 10 meilleurs films au Festival International du Film Médical
1996, meilleur film scientifique.
GALAT-LUONG, A., (1988). - Monkeys in the Pirang forest. In: Pirang. Ecological Investigations in a Forest Island in the Gambia.
Ellenberg, H., Galat-Luong, A., Von Maydel, H. -J., Mühlenberg, M., Panzer, K. F., Schmidt-Lorenz, R. S., Sumser, M., Szolnoki,
T. W. Eds. Stiftung Walderhaltung in Afrika, Hamburg, und Bundesforschungsanstalt für Forst- und Holzwirtschaft, Hamburg,
Warnke Verlag, Reinbek: 187-208.
GALAT G., GALAT-LUONG, A. (1976). - La colonisation de la mangrove par Cercopithecus aethiops sabaeus au Sénégal. Revue
d'Ecologie (Terre et Vie), 30 (1): 3-30.
ILLUSTRATIONS
Contact Indigo Base, IRD picture library, Claire Lissalde or Danièle Cavanna, Tel.: +33 (0)1 48 03 78 99, Email : indigo@paris.ird.fr
The illustrations can be viewed on: www.ird.fr/us/actualites/fiches/2006/fiche238.htm