Update: Of refugia and colonization, an innovative use of biogeography for climate studies

Abstract

ISSN 1948-6596 require a careful consideration of exactly what constitutes a random and a structured matrix with respect to species nesting and spatial turn- over. But they should be conducted before at- tempting a meta-analysis of published empirical matrices. Second, this index, like most other meas- ures of nestedness and beta diversity, assumes that island censuses are complete and there are no undetected species. Anne Chao and colleagues have recently modified classic similarity indices to take into account undetected shared species. The presence of undetected species biases the un- modified indices towards underestimating shared species (and hence over-estimating beta diver- sity). It is not yet clear how serious of a problem this is for Baselga's (2009) proposed partition. news and update Baselga (2009) has made an innovative contribu- tion that deserves further exploration. Baselga, A. (2009) Partitioning the turnover and nest- edness components of beta diversity. Global Ecology and Biogeography, doi:10.1111/j.1466- 8238.2009.00490.x. Nicholas J. Gotelli Department of Biology, University of Ver- mont, USA e-mail: Nicholas.Gotelli@uvm.edu http://www.uvm.edu/~ngotelli/ homepage.html Edited by Thiago F. Rangel update Of refugia and colonization, an innovative use of biogeography for climate studies A beautiful sight in Glacier National Park is found along the Trail of the Cedars, a stand of western red cedar (Thuja plicata) replete with mossy rocks and cold running waters. This tree, and western hemlock (Tsuga heterophylla), are emblematic of the northern coastal temperate rainforests of the western US and Canada. However, they are also found over 160 kilometers to the east, across a large expanse of sagebrush steppe, on the west- ern flank of the Rocky Mountains. This well known disjunct rainforest distribution is the subject of a new biogeographic study titled, “The coastal- disjunct mesic flora in the inland Pacific Northwest of USA and Canada: refugia, dispersal and disequi- librium” by Daniel Gavin, professor of Geography at the University of Oregon. Dr Gavin analyzed the patterns of biodiversity between the coastal populations and northern and southern interior populations of 67 vascular plant species, all com- ponents of the temperate rainforest group. He used the biogeographic patterns to explore the possible interactions between species richness, climate change, and glaciation. The study exam- ines how species richness varies with climate; how distribution patterns may have been affected by glaciated versus un-glaciated areas in the interior; and whether life history characteristics such as seed dispersal mode and growth habit help ex- plain the current extent of the species analyzed. Dr. Gavin mapped each plant’s range distri- bution to 50x50 km grid cells using a variety of reference materials. He then examined patterns of species richness, according to life history char- acteristics and climate as defined in the PRISM data sets. The study used regression models of species richness as a function of Actual Evapotran- spiration (AET) in the coastal regions (most mesic and specious) to develop expected levels of spe- cies richness for the AET of more recently suitable interior regions. This permitted regional quantifi- cation of the level of disequilibrium from expected species richness, an indication of incomplete colo- nization by the regional flora. The northern inte- rior was most in disequilibrium, indicating that many species have yet to disperse into the area. Since several sources of colonizers exist, the impli- cation is that some plant species may have a diffi- cult time dispersing into newly suitable habitats across a fragmented landscape under future cli- mate change. frontiers of biogeography 1.2, 2009 — © 2009 the authors; journal compilation © 2009 The International Biogeography Society