Blackwell Science, Ltd
Cladistic biogeography of the Mexican transition zone
C. J. Marshall and J. K. Liebherr Department of Entomology, Comstock Hall, Cornell University, Ithaca, New York 14853–0901, U.S.A.
Biogeographic relationships among nine montane areas of endemism across the transition zone between North and South America areanalysed cladistically based on phylogenetic hypotheses of thirty-three resident monophyletic taxa of insects, ﬁsh, reptiles, and plants.
Areas of endemism include the Arizona mountains (AZ), Sonoran Desert (SD), Sierra Madre Occidental (OCC), southern Sierra Madre Occidental (SOC), Sierra Madre Oriental (ORI), Sierra Transvolcanica (TRAN), Sierra Madre del Sur (SUR), Chiapan-Guatemalan Highlands(CGH), and Talamancan Cordillera (TC). Area relationships are summarized using Brooks Parsimony Analysis and Assumption 0, with the former resulting in more defensible biogeographic hypotheses. Areas of endemism are dividable into two monophyletic groups; a northern group including AZ, SD, OCC, and ORI, and a southern group consisting of TC, CGH, TRAN, SUR, and the isolated southern regions of theSierra Madre Occidental (SOC). The northern set of areas are characterized by recent, probably Pleistocene, isolation and prevalent widespread species, whereas the southerly areas probably diverged after Pliocene closure of the Panamanian isthmus. The southern areas are redundantly represented on many of the taxon-area cladograms by endemic species, indicative of much higher levels of endemism inthe Sierra Transvolcanica and further south. Use of a general area cladogram in such a transition zone permits explicit exploration of biogeographic patterns and establishes a predictive framework for taxonomy and conservation prioritization.
Keywords Vicariance, areas of endemism, montane biota, Mexico, Central America.
INTRODUCTION Mexico and Central America comprise one of the mostbiologically diverse regions of the world. This diversity, in conjunction with a complex geological history, has held the attention of biogeographers for more than a century. Soon after the recognition of the major biogeographic regions of the world (Sclater, 1858; Wallace, 1876), this area was recognized as a transition zone between the Nearctic and Neotropical biotas (Heilprin, 1887). Transition zoneshave been traditionally thought to be populated by groups exhibiting disparate distributional patterns. Because these disparate patterns have been the focus of most studies, distributions in one taxon have not been thought predictive or informative for other unrelated taxa. We utilize cladistic biogeography to simultaneously derive a general summary of patterns in a variety of groups occupyingMexico and Central America.
Correspondence: C. J. Marshall, Department of Entomology, Comstock Hall, Cornell University, Ithaca, NY14853– 0901, U.S.A.
We then demonstrate the utility of this general pattern for understanding the biotic diversiﬁcation in the region. A complete and detailed geological history for Mexico and Central America is not at hand. In general terms, however, we know thatsubduction of the Paciﬁc and Cocos Plates under the North American Plate during the Cretaceous has produced most of the extensive orogenic activity, volcanism and uplifting characteristic of the region. Geologists paint a dynamic, almost mosaic, history of the terrestrial (emergent) topography (Morán-Zenteno, 1994). More recently, the opening of the Gulf of California as well as Pleistocene glaciationfurther modiﬁed the biotic patterns, especially in the north (Martin & Klein, 1984; Betancourt et al., 1990; Van Devender, 1990a). Proponents of cladistic biogeography hold that the distributions of different taxa are related historically, and that they should display common patterns resulting from orogenic and widespread ecological events. Common patterns of this type are what this study seeks...