Body Size Variation of Mammals in a Fragmented, Temperate Rainforest MARK V. LOMOLINO ∗ AND DAVID R. PERAULT† ∗ Department of Environmental and Forest Biology, SUNY College of Environmental Science and Forestry, Syracuse, NY 13210, U.S.A., email island@esf.edu †Environmental Science Program, Lynchburg College, Lynchburg, VA 24501, U.S.A. Abstract: Body size is perhaps the most important trait of an organism, affecting all of its physiological and ecological processes and, therefore, fundamentally influencing its ability to survive and reproduce in different environments, including those that have been modified by human activities. We tested the hypothesis that anthropogenic transformation of old-growth forest landscapes can result in significant intraspecific changes in body size of resident biotas. We collected data on five species of nonvolant mammals (common deer mouse [Per- omyscus maniculatus], northwestern deer mouse [P. keeni], southern red-backed vole [Clethrionomys gapperi], montane shrew [Sorex monticolus], and Trowbridge’s shrew [S. trowbridgii]) to test whether body size (mass and length) of these species varied across types of land cover (macrohabitats) and along elevational gradients of the fragmented, temperate rainforest of Olympic National Forest (Washington, U.S.A.). We measured 2168 and 1134 individuals for body mass and body length, respectively. Three species (P. keeni, S. monticolus, and S. trowbridgii) exhibited significantly different body size among macrohabitats: individuals from fragments were smaller than those in old-growth corridors and those in more extensive stands of old-growth forest. Body size of P. keeni was significantly correlated with elevation along corridors, peaking near the medial reaches of the corridors. The effects of anthropogenic transformations of this landscape of old-growth, temperate rainforest, although not universal among the five species, were significant and rapid—developing in just a few decades following tree harvests. Thus, anthropogenic fragmentation may influence not only the diversity, species com- position, and densities of local biotas, but also one of the most fundamental and defining characteristics of native species—their body size. Keywords: corridors, elevation, forest fragmentation, old-growth forest, rainforests Variaci´ on del Tama˜ no del Cuerpo de Mam´ ıferos en un Bosque Lluvioso Templado, Fragmentado Resumen: Probablemente, el tama˜ no corporal es la caracter´ ıstica m´ as importante de un organismo, ya que afecta todos sus procesos fisiol´ ogicos y ecol´ ogicos y, por lo tanto, influye fundamentalmente en su ha- bilidad para sobrevivir y reproducirse en ambientes diferentes, incluyendo los que han sido modificados por actividades humanas. Probamos la hip´ otesis de que la transformaci´ on antropog´ enica de paisajes con bosque maduro puede resultar en cambios intraespec´ ıfios significativos en el tama˜ no corporal de biotas residentes. Recolectamos datos de cinco especies de mam´ ıferos no voladores (Peromyscus maniculatus, P. keeni, Clethrion- omys gapperi; Sorex monticolus y S. trowbridgii) para probar si el tama˜ no corporal ((masa y longitud) de estas especies variaba a trav´ es de diferentes tipos de cobertura de suelo (macroh´ abitats) y a lo largo de gradientes de elevaci´ on en el bosque lluvioso templado Olympic National Forest (Washington, E. U. A.). Medimos la masa corporal y la longitud total de 2168 y 1134 individuos respectivamente. Tres especies (P. keeni, S. monticolus, and S. trowbridgii) mostraron diferencias significativas en el tama˜ no corporal entre macroh´ abitats: los indi- viduos de fragmentos eran m´ as peque˜ nos que los de corredores de bosque maduro y los de ´ areas extensas de bosque maduro. El tama˜ no corporal de P. keeni se correlacion´ o significativamente con la elevaci´ on a lo largo de corredores, con pico cerca de los alcances intermedios de los corredores. Los efectos de las transformaciones Paper submitted May 2, 2006; revised manuscript accepted January 4, 2007. 1059 Conservation Biology Volume 21, No. 4, 1059–1069 C 2007 Society for Conservation Biology DOI: 10.1111/j.1523-1739.2007.00727.x