On 5/13/2010 12:31 PM, Josh Donlan wrote:
I would argue the answer to this question is not so cut and dry. Recent genetic
evidence paints a more complicated story, and suggests quite close relationship
- at least genetically.
Weinstock et al. 2005. PLOS Biology
Evolution, Systematics, and Phylogeography of Pleistocene Horses in the New
World: A Molecular Perspective
The rich fossil record of horses has made them a classic example of
evolutionary processes. However, while the overall picture of equid evolution
is well known, the details are surprisingly poorly understood, especially for
the later Pliocene and Pleistocene, c. 3 million to 0.01 million years (Ma)
ago, and nowhere more so than in the Americas. There is no consensus on the
number of equid species or even the number of lineages that existed in these
continents. Likewise, the origin of the endemic South American genus Hippidion
is unresolved, as is the phylogenetic position of the “stilt-legged” horses of
North America. Using ancient DNA sequences, we show that, in contrast to
current models based on morphology and a recent genetic study, Hippidion was
phylogenetically close to the caballine (true) horses, with origins
considerably more recent than the currently accepted date of c. 10 Ma.
Furthermore, we show that stilt-legged horses, commonly regarded as Old World
migrants !
related to the hemionid asses of Asia, were in fact an endemic North American
lineage. Finally, our data suggest that there were fewer horse species in late
Pleistocene North America than have been named on morphological grounds. Both
caballine and stilt-legged lineages may each have comprised a single,
wide-ranging species.
On May 13, 2010, at 10:12 AM, James J. Roper wrote:
You do remember that the horses that went extinct in North America are not
the same ones that came back with the Spaniards? So, yes, they are
introduced.
However, horses are not really the issue with introduced species, although
they are causing animated debates in the few states that have feral herds.
On Thu, May 13, 2010 at 10:16, Randy K
Bangert<[email protected]<mailto:[email protected]>> wrote:
Are horses exotic or native if they evolved in North America and then
subsequently reintroduced?
======================================
Randy Bangert
C. Josh Donlan MA PhD
Director, Advanced Conservation Strategies | http://www.advancedconservation.org
Fellow, Cornell University | http://www.eeb.cornell.edu/donlan
M: +1 (607) 227-9768 (GMT-6)
E: [email protected]<mailto:[email protected]>
P: P.O. Box 1201 | Midway, Utah 84049 USA
u
Excuse me while I butt in... I haven't read every word of every email in
this thread, but I have a comment. Isn't it more interesting to ask
questions directed at the biological differences between exotic species
that have become successful invaders and those that have not? Since
only a small percentage of introduced species establish populations, and
of those only a small percentage become invasive (even when they are
closely related phylogenetically), isn't it better to focus on why? It
seems like there are some key differences here. Also, if we compare
genotypes of invasive exotic species here to genotypes in its native
range, we could also ask interesting questions. These are the kinds of
questions I am asking for my thesis, and seem to allow for both
ecological and evolutionary conceptual frameworks to be used. Now if we
think about the native communities of grasses to which these species
invade, Tillman has done tons of work in this field.
Invasive species are, by definition, exotic species that have a negative
effect on the environment, economy, or human health. So it is a
human-created concept. I think what we should argue about is if
invasiveness is binary. Which I'm sure none of us would agree with.
This is also something I'm working on, creating a more continuous scale
of invasiveness.
Kyle
--
Kyle Hernandez
Ph.D. Candidate
Department of Biological Sciences
Purdue University
West Lafayette, IN 47907
