Belg. J. Zool., 135 (supplement) : 21-29 December 2005 Investigating the role of natural gallery forests outside the Congolese rainforest as a refuge for African forest shrews Patrick Barrière 1,2 , Rainer Hutterer 3 , Violaine Nicolas 4,2 , Sophie Quérouil 5,2 and Marc Colyn 1,2 1 Laboratoire Ecobio : Ecosystèmes, Biodiversité et Evolution, UMR 6553 - CNRS, Université de Rennes 1, Station Biologique, F-35380 Paimpont, France. 2 Laboratoire EVE : Ethologie, Evolution et Ecologie, UMR 6552 - CNRS, Université de Rennes 1, Station Biologique, F-35380 Paimpont, France. 3 Zoologisches Forschungsmuseum Alexander Koenig, Adenauerallee 160, D-53113 Bonn, Germany. 4 Museum National d’Histoire Naturelle, Département de Systématique et Evolution, UMR 5202 - CNRS, USM 601, Labora- toire Mammifères et Oiseaux, 55 rue Buffon, F-75005 Paris, France. 5 Instituto do Mar (IMAR), Departamento de Oceanografia e Pescas, cais Santa Cruz, 9901-862 Horta, Portugal. Corresponding author : P. Barrière, e-mail : Patrick.Barriere@laposte.net ABSTRACT. Conditions that prevailed in rainforest faunal refuges during glacial periods of the Pleistocene, partic- ularly their size, position and habitat characteristics, remain little investigated. After the peak of the last interglacial period of the Holocene (7000 years B.P.), the Guineo-Congolese rainforest has been reduced in size and isolated gallery forests emerged in the peripheral Northern Congo forest-savanna mosaic, mainly because of the reduction in rainfall. In the north of the Central African Republic, 400 km north of the present rainforest zone, up to the Sudano- Sahelian savannas, such gallery forests harbour several forest species of plants, birds and mammals related to West and/or East Congo faunal regions. This suggests that since the catastrophic destruction of central African rainfor- ests, that culminated about 2500 years ago, these galleries could have mimicked the conditions that occurred in the Pleistocene refuges. We tested whether these natural gallery forests, outside the Congolese rainforest, could act as refuges for small forest mammals such as shrews. Composition and structure of shrew communities were studied in three main regions belonging to three river basins and two distinct phytoregions. They were compared to two other shrew communities located within the main Congolese rainforest, also in C.A.R.. None of the typical rainforest shrew species was collected within the studied isolated gallery forests. Thus, climatic and habitat characteristics within these gallery forests were presumably not suitable for these forest patches to act as climatic refuges for the forest shrew fauna. KEY WORDS : Soricidae, Crocidura, Suncus, Central African Republic, Community structure, Biogeography, Refuge theory. INTRODUCTION In the Quaternary period (from 1.8 My B.P. to present), Africa underwent climatic oscillations resulting in several phases of forest fragmentation and extension. During the last glacial maximum of the Pleistocene (between about 20000 and 15000 years B.P.), as a result of the very cold and dry climate, tropical rainforest decreased in size and became fragmented. Paleontological and biogeographic data suggest that it was limited to lowland forest patches in the downstream zone of the large rivers and on lower slopes of mountains (HUTTERER et al., 1987; MALEY, 1987; COLYN, 1991; COLYN et al., 1991; MALEY, 1996; MALEY & BRENAC, 1998). According to HAFFER (1969), these forest patches may have acted as refuges for the for- est flora and fauna. In contrast, during the inter-glacial periods, the warmer and wetter climate favoured an extension of the rainforest. The last inter-glacial period culminated at 7000-8000 years B.P., during the Holocene (MALEY, 2001). The central African rainforest extended to the north, up to the present Sudano-Sahelian savanna zone. Since 5000 years B.P., the reduction in rainfall (BERTAUX et al., 2000), associated with climatic distur- bance, resulted in contraction of the central African rain- forests that culminated about 2500 years ago (MALEY, 2001). In the north of the Central African Republic (C.A.R.), since 7000 years B.P., the extension of the savannas (MALEY & BRENAC, 1998) resulted in the isola- tion of gallery forests outside the Congolese rainforest. Despite a new phase of forest extension that began 2000 years ago (MALEY, 2001), it is probable that these Holocene gallery forests remained isolated from the Con- golese rainforest and could have acted as forest refuges. It is hypothesised that Pleistocene and Holocene refuges probably formed a network of forest isolates within a for- est-savanna mosaic zone rather than small homogenous forest isolates (LEAL, 2000; MALEY, 2001). The principal refuges of the Pleistocene were probably located in the downstream zone of the large rivers, within the present rainforest zone. However, the conditions that prevailed in