Ecology of Acorn Dispersal by Small Mammals in Montane Forests of Chiapas, Mexico

Abstract

The highlands of central and eastern Mexico are the major centre of diversity (60–75 species) for the genus Quercus (Nixon 1993; Chap. 1). Oaks are canopy dominants in many forests in the mountains of Mexico, and provide a wide range of biological resources for insect, mammal and bird species (QuintanaAscencio et al. 1992; Tovar-Sanchez et al. 2003; Chaps. 14, 16 and 20). The occurrence of temporal fruiting synchronicity in oak populations (usually termed masting or mast seeding) has cascading effects in acorn consumers. Understanding such mast-dependent ecological chain reactions is important for predicting, managing and conserving montane forests. In more northern temperate forests, small mammal populations rely on acorns as an important food source (Wolff 1996), and acorns rely on small mammals as potential seed dispersers (Price and Jenkins 1986; Steele and Smallwood 2002). However, there is little information available on the extent to which oaks rely on dispersal in Neotropical montane forests. Most oak species suffer reproductive failure under their own canopies (Crow 1988; Lorimer et al. 1994; Figueroa-Rangel and Olvera-Vargas 2000; Chap. 28), relying instead on the dispersal of acorns to forest edges or clearings where establishment success is increased (Lopez-Barrera 2003, see Chaps. 14 and 16). In the Chiapas Highlands, the traditional land use of slashand-burn agriculture, existing since pre-Columbian times, has resulted in forest mosaics comprised of small clearings (0.5–2 ha; pastures, cornfields and shrublands), surrounded by fragments of secondary forest, evergreen cloud forest, oak forest, and pine–oak forest with various levels of disturbance (see Chap. 16), and resulting in the creation of different forest edge types varying in sharpness, such as hard and soft edges (Fig. 13.1). Oak regeneration in this landscape of small-scale, scattered forest disturbances (Gonzalez-Espinosa et al. 1991; Chap. 16) is primarily due to oak resprouting ability and the activity of acorn dispersers. This landscape con-