Shaping the Latitudinal Diversity Gradient: New Perspectives from a Synthesis of Paleobiology and Biogeography

Abstract

An impediment to understanding the origin and dynamics of the latitudinal diversity gradient (LDG)-the most pervasive large-scale biotic pattern on Earth-has been the tendency to focus narrowly on a single causal factor when a more synthetic, integrative approach is needed. Using marine bivalves as a model system and drawing on other systems where possible, we review paleobiologic and biogeographic support for two supposedly opposing views, that the LDG is shaped primarily by (a) local environmental factors that determine the number of species and higher taxa at a given latitude (in situ hypotheses) or (b) the entry of lineages arising elsewhere into a focal region (spatial dynamics hypotheses). Support for in situ hypotheses includes the fit of present-day diversity trends in many clades to such environmental factors as temperature and the correlation of extinction intensities in Pliocene bivalve faunas with net regional temperature changes. Support for spatial dynamics hypotheses includes the age-frequency distribution of bivalve genera across latitudes, which is consistent with an out-of-the-tropics dynamic, as are the higher species diversities in temperate southeastern Australia and southeastern Japan than in the tropical Caribbean. Thus, both in situ and spatial dynamics processes must shape the bivalve LDG and are likely to operate in other groups as well. The relative strengths of the two processes may differ among groups showing similar LDGs, but dissecting their effects will require improved methods of integrating fossil data with molecular phylogenies. We highlight several potential research directions and argue that many of the most dramatic biotic patterns, past and present, are likely to have been generated by diverse, mutually reinforcing drivers.

The global latitudinal diversity gradient pattern in spiders

“…Although this latitudinal diversity gradient pattern is confirmed by a broad sweep of taxa, many previous studies were done in the Northern Hemisphere, and in particular North America (Gaston, ), but a number of more recent studies have taken a broader perspective (Jablonski, Huang, Roy, & Valentine, ; Lamanna et al., ; Rolland, Condamine, Beeravolu, Jiguet, & Morlon, ; Vasconcelos et al., ). In addition, for animals, many previous studies focused on the megafauna in part because the taxonomy of such groups is largely complete, thus allowing a shift in research to ecological and population studies, and perhaps also because the species are easier to monitor.…”

Biodiversity and Topographic Complexity: Modern and Geohistorical Perspectives

“…Biogeographers have analyzed variation in biologically relevant properties along gradients of latitude, elevation, depth, and topographic complexity, although the processes that generate and maintain diversity gradients remain unresolved. Ecological, evolutionary, and geohistorical processes all contribute [2,3], but no agreement has emerged on which processes dominate, how processes interact, or whether different geographic and geohistorical manifestations of each kind of gradient emerge from a common cause.…”

“…To date, landscape history, diversification history, the spatial dynamics of diversity, and ecological traits have been studied largely in isolation, yet their integration is critical for advancing our understanding of diversity gradients over space and time [3,4]. Testing scenarios of different biogeographic processes acting separately and in combination (e.g., Box 2) can clarify the historical consequences of different processes and the phylogenetic and geographic diversity patterns that result.…”

A review of phylogeography: biotic and abiotic factors

“…They observed distribution patterns of AAPs along the latitudinal gradient which might be due to the small-scale environmental conditions formed along the axis. The only impediment to assess the dynamics of latitudinal diversity gradient is the tendency to focus narrowly on single casual factor when a more integrative approach is required (Jablonski, Huang, Roy, & Valentine, 2017).…”