ABSTRACT
Email: mferrer@uady.mx 2 Department of Biology, University of Winnipeg. 515 Portage Avenue. Winnipeg, MB.
R3B2E9. Email: s.good-avila@uwinnipeg.ca 3 Acadia University, 24 University Drive, Wolfville, Nova Scotia, B4P 2R6. Email: gpcruiser@hotmail.com * Corresponding author
Understanding why rates of speciation and extinction, and therefore net diversifi cation rates, change over geological time and among lineages is one of the fundamental goals of evolutionary biology (Stanley 1979; Raup and Sepkoski 1984; Erwin and Anstey 1995; Heard and Hauser 1995; Nee 2006; Jablonski 2007). Furthermore, it has been suggested that rates speciation and extinction may be affected by long-term macroevolutionary changes such as plate tectonics, climate change and/or episodic catastrophic events (extrinsic factors), as well as by the presence of traits that affect the probabilities of speciation and extinction in species over micro and macroevolutionary time scales (intrinsic factors) (Slowinski and Guyer 1993; Purvis 1996). There is strong paleontological evidence that rates of speciation and extinction have changed over geological time (Stanley 1979; Raup and Sepkoski 1984; Erwin and Anstey 1995; Niklas 1997; Jablonski 2007), and molecular phylogenetic analyses of extant groups point to climate change and other physical (extrinsic) factors as being associated with shifts in diversifi cation rates in the recent past (Erwin and Anstey 1995; Zink and Slowinski 1995; Kadereit et al. 2004).
