[OANNES Foro] Geographic patterns of diversification and the latitudinal gradient of richness of rocky intertidal gastropods along the eastern Pacific coast

[Mario Cabrejos]

Global Ecology and Biogeography

 <http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1466-8238/earlyview>
Early View (Online Version of Record published before inclusion in an issue)

Article first published online: 25 MAY 2015

DOI: 10.1111/geb.12328


 


Geographic patterns of diversification and the latitudinal gradient of
richness of rocky intertidal gastropods: the ‘into the tropical museum’
hypothesis


1.     Marcelo M. Rivadeneira1,*, Alex H. Alballay1, Jaime A. Villafaña1,
Peter T. Raimondi2,Carol A. Blanchette3 and Phillip B. Fenberg4

1 Laboratorio de Paleobiología, Centro de Estudios Avanzados en Zonas Áridas
(CEAZA) & Universidad Católica del Norte, Coquimbo, Chile 2 Department of
Ecology and Evolutionary Biology, Long Marine Laboratory, University of
California, Santa Cruz, CA, USA 3 Marine Science Institute, University of
California, Santa Barbara, CA, USA 4

Ocean and Earth Science, National Oceanography Centre, University of
Southampton, Southampton, UK. * Correspondence:  E-mail:
<mailto:marcelo.rivadeneira en ceaza.cl> marcelo.rivadeneira en ceaza.cl


 


Abstract


Aim


To evaluate the existence of a latitudinal gradient of richness (LGR) in
rocky intertidal gastropods and the role of evolutionary processes in
shaping the LGR.


Location


The entire eastern Pacific coast, from Alaska to Tierra del Fuego,
encompassing ca. 120° latitude.


Methods


The LGR was assessed using field surveys and a comprehensive literature
dataset from 308 rocky intertidal sites, representing 328 species and 159
genera. The importance of geographic patterns of diversification in shaping
the LGR was assessed using three complementary approaches. First, we used
the fossil record to evaluate the region of origination of genera (tropical
vs. extra-tropical). Secondly, we used a nestedness analysis to compare
present-day biogeographic distributions of genera with their region of
origin. Finally, we evaluated the importance of biogeographic dynamics for
shaping the LGR using a projection matrix and estimating transition
probabilities among different biogeographic states.


Results


Eastern Pacific rocky intertidal gastropods follow the canonical latitudinal
gradient of richness (higher richness in the tropics). Originations were
similar in the tropics and extra-tropics, a pattern that was robust to
geographic differences in fossil sampling. The biogeographic distribution of
genera was significantly nested, irrespective of the region of origin of
genera. The distribution dynamics model accurately reproduced the LGR and
showed that key-transitions are low extinction in the tropics and high
dispersal of taxa from the extra-tropics to the tropics.


Conclusions


The existence of a canonical LGR in rocky intertidal gastropods can be
explained by the combined effect of reduced extinction rates in the tropics
and the range expansion of taxa from the extra-tropics toward the tropics,
in what we have called the ‘into the tropical museum’ hypothesis.

 



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