Page 1 - MICHAUX2002

P. 1

Global Ecology & Biogeography (2002) 11, 427–436

RESEARCH LETTER

BodyBlackwellScience,Ltd size increase in insular rodent populations:
a role for predators?

JOHAN R. MICHAUX*†, JOËLLE GOÜY DE BELLOCQ‡, MAURIZIO SARÀ§ and SERGE MORAND‡

*Unité de recherches zoogéographiques, University of Liège, Quai Van Beneden, 22, 4020 Liège, Belgium; †Laboratoire de Paléontologie, cc064,
Institut des Sciences de l’Evolution, 34095 Montpellier cedex 05, France; ‡Laboratoire de Biologie Animale (UMR 5555 CNRS), Centre de
Biologie et d’Ecologie Tropicale et Méditerranéenne, Université de Perpignan, Avenue de Villeneuve, 66860 Perpignan Cedex, France;
§Dipartimento di Biologia Animale, via Archiraﬁ, 18 90123 Palermo, Italy

ABSTRACT predator species — to changes in body size of the woodmouse
(Apodemus sylvaticus) in the Western Mediterranean
Insular mammalian populations living in areas of small Sea. Our results, based on a comparative analysis using the
size are often characterized by a drastic change in body phylogenetic independent contrasts method, indicate that the
mass compared to related continental populations or species. increase in body size is related both to the decrease of island
Generally, small mammals (less than 100 g) evolve into size and to the lower number of predator species. A decrease
giant forms while large mammals (up to 100 g) evolve into of competitor species does not seem to have an important
dwarf forms. These changes, coupled with changes in other effect.
life, behavioural, physiological or demographic traits are
referred to generally as the insular syndrome. We tested in Key words Apodemus sylvaticus, body size, comparative
this study the relative contribution of three factors — area analyses, genetic distances, insular syndrome, islands,
of island, numbers of competitor species and number of rodents, predators, Western Mediterranean.

INTRODUCTION according to Brown (1995), a single species living on a tiny
island should tend to approach the optimum mean body size
The distribution of animal body size and the changes in body of 100 g.
size of insular populations compared to mainland populations
have stimulated a large number of theoretical and empirical Gigantism is observed generally in rodents and insectivores,
studies (Case, 1978; Brown, 1984, 1995; Lomolino, 1985; whereas dwarﬁsm concerns larger species such as artio-
Angerbjörn, 1986; Brown et al., 1993; Damuth, 1993; Adler dactylids or perissodactylids (Thaler, 1973; Vigne et al., 1993).
& Levins, 1994). These changes in body mass seem to occur very quickly. Roth
(1990) reported that elephants on Sicily and Malta decreased
Island populations live in small areas isolated from con- in body mass by an order of magnitude in a few thousand
tinental populations. The degree of isolation, i.e. the decrease years. In the same way, Atchley et al. (1982) showed that it
in genetic exchanges, may lead these populations to differen- was possible to select giant forms of Rattus rattus in only 23
tiate greatly from their closely related continental populations, generations in the laboratory. These changes, which involve
giving rise to new species. The main characteristic of island modiﬁcations in life history, behavioural (Gliwicz, 1980;
mammal populations is the often drastic change in body Takada, 1985; Granjon & Cheylan, 1988, 1990; Perret &
mass compared to that of related continental populations or Blondel, 1993; Adler & Levins, 1994; Blondel, 1995), physi-
species. Insular populations of mammals that on continents ological or demographic (Poitevin, 1984; Blondel et al., 1992;
are smaller than 100 g evolve typically into giant forms, Fons et al., 1995) traits are referred to generally as the insular
whereas those that are larger than 100 g on continents evolve syndrome. The determinism of these modiﬁcations is probably
into dwarf forms (Van Valen, 1973; Lomolino, 1985). Thus, complex and involves numerous factors, which are difﬁcult to
dissociate. Nevertheless, several general hypotheses have been
Correspondence: Johan R. Michaux, Unité de recherches zoogéo- proposed to explain these phenomena.
graphiques, University of Liège, Quai Van Beneden, 22, 4020 Liège,
Belgium. E-mail: Johan.Michaux@ulg.ac.be Grant (1985) suggested that founder events, i.e. the colon-
ization by a low number of immigrants, could play an important

1 2 3 4 5 6