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

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.

Zoogeographic patterns of pelagic oceanic cephalopods along the eastern Pacific Ocean

“…Along the coast of the eastern Pacific Ocean several studies have reported latitudinal patterns of species richness in northern or southern hemispheres (Roy, Jablonski, Valentine, & Rosenberg, ; Valdovinos, Navarrete, & Marquet, ; Rex, Crame, Stuart, & Clarke, ; Rivadeneira et al., ). So far, the few studies focused on inter‐hemispheric trends have documented similar patterns to those observed in terrestrial environments, with a marked poleward decrease in species richness (Hillebrand, ; Lyons & Willig, ; Rex et al., ; Roy et al., ; Willig & Lyons, ), and other studies have reported trends in species range sizes related to Rapoport's pattern (Mora & Robertson, ; Tomašových & Jablonski, ; Tomašových et al., ).…”

Explaining Ocean Warming: Causes, scale, effects and consequences

“…The distribution of species on rocky shores around the world is largely driven by broad-scale climatic regimes, associated with latitude and modified by ocean currents and upwelling regimes (Hutchins, 1947;Helmuth et al, 2006b;Fenberg et al, 2015). There are warm-and cold-water adapted species, leading to different species pools able to live in different biogeographic areas.…”

“…There are warm-and cold-water adapted species, leading to different species pools able to live in different biogeographic areas. The species pool is ultimately determined by phylogeographic processes associated with the evolutionary origin of species and their subsequent spread in response to tectonic and climatic processes over long geological timescales, including opening and closing of ocean basins (Rivadeneira et al, 2015). Natural biogeographical processes have been altered, however, by humanmediated transport of species around the world.…”

“…In these regions, nutrient-rich water is brought to the surface and fuels production within intertidal and nearshore communities. Where upwelling is particularly intense, for example around headlands, reductions in sea-surface temperature can also be important in structuring species distribution and abundance patterns at regional scales (Blanchette et al, 2008;Fenberg et al, 2015;Reddin et al, 2015). Under future climate change projections, it is predicted that land temperatures will increase faster than coastal waters, creating a scenario favouring stronger upwelling-producing winds (Bakun et al, 2010;Di Lorenzo, 2015;Wang et al, 2015).…”

“…The balance of processes will also vary with regional modulation by upwelling or enclosure of seas/bays, and by other local environmental gradients and microhabitat variation. Furthermore, the region of evolutionary origin of species may predetermine their responses to interacting climate-driven processes (Rivadeneira et al, 2015). Long-term contextual monitoring of natural systems (Hawkins et al, 2013;Mieszkowska et al, 2014b), coupled with experimental investigation of multi-stressor effects on species and communities (e.g.…”