Latitudinal diversity gradients are underlain by complex combinations of origination, extinction, and shifts in geographic distribution and therefore are best analyzed by integrating paleontological and neontological data. The fossil record of marine bivalves shows, in three successive late Cenozoic time slices, that most clades (operationally here, genera) tend to originate in the tropics and then expand out of the tropics (OTT) to higher latitudes while retaining their tropical presence. This OTT pattern is robust both to assumptions on the preservation potential of taxa and to taxonomic revisions of extant and fossil species. Range expansion of clades may occur via "bridge species," which violate climate-niche conservatism to bridge the tropical-temperate boundary in most OTT genera. Substantial time lags (∼5 Myr) between the origins of tropical clades and their entry into the temperate zone suggest that OTT events are rare on a per-clade basis. Clades with higher diversification rates within the tropics are the most likely to expand OTT and the most likely to produce multiple bridge species, suggesting that high speciation rates promote the OTT dynamic. Although expansion of thermal tolerances is key to the OTT dynamic, most latitudinally widespread species instead achieve their broad ranges by tracking widespread, spatially-uniform temperatures within the tropics (yielding, via the nonlinear relation between temperature and latitude, a pattern opposite to Rapoport's rule). This decoupling of range size and temperature tolerance may also explain the differing roles of species and clade ranges in buffering species from background and mass extinctions.biodiversity | biogeography | climate | macroecology | macroevolution T he latitudinal diversity gradient (LDG), meaning the decrease in the number of species and higher taxa from the equator to the poles, is as pervasive among marine organisms as it is on land (1, 2). Although the marine LDG is increasingly well documented, we are only beginning to understand the evolutionary and biogeographic dynamics of speciation, extinction, and distributional shifts that generate and maintain it. Here we evaluate these dynamics in marine bivalves, a group that not only parallels diversity patterns of the overall marine biota (1-3), but permits the integration of biogeographic, phylogenetic, and spatially explicit paleontological data (4, 5) and has thus become a model system for macroecological and macroevolutionary analysis. Extending our previous work, we show that clade origination in the tropics and range expansion out of the tropics [the OTT model (5)] are major factors in the origin and maintenance of the bivalve LDG. We reanalyze and update paleontological data on the OTT dynamic and present evidence that at least some bridge species, whose ranges cross the tropical/extratropical boundary, are important in the expansion of lineages along the LDG. Although bridge species violate niche conservatism with their expanded thermal ranges, we find that species with narrow th...
Summary1. Priority question exercises are becoming an increasingly common tool to frame future agendas in conservation and ecological science. They are an effective way to identify research foci that advance the field and that also have high policy and conservation relevance. 2. To date, there has been no coherent synthesis of key questions and priority research areas for palaeoecology, which combines biological, geochemical and molecular techniques in order to reconstruct past ecological and environmental systems on time-scales from decades to millions of years. 3. We adapted a well-established methodology to identify 50 priority research questions in palaeoecology. Using a set of criteria designed to identify realistic and achievable research goals, we selected questions from a pool submitted by the international palaeoecology research community and relevant policy practitioners. 4. The integration of online participation, both before and during the workshop, increased international engagement in question selection. 5. The questions selected are structured around six themes: human-environment interactions in the Anthropocene; biodiversity, conservation and novel ecosystems; biodiversity over long time-scales; ecosystem processes and biogeochemical cycling; comparing, combining and synthesizing information from multiple records; and new developments in palaeoecology. 6. Future opportunities in palaeoecology are related to improved incorporation of uncertainty into reconstructions, an enhanced understanding of ecological and evolutionary dynamics and processes and the continued application of long-term data for better-informed landscape management. 256-26750 priority research questions in palaeoecology 257 7. Synthesis. Palaeoecology is a vibrant and thriving discipline, and these 50 priority questions highlight its potential for addressing both pure (e.g. ecological and evolutionary, methodological) and applied (e.g. environmental and conservation) issues related to ecological science and global change.
Analyses of how environmental factors influence the biogeographic structure of biotas are essential for understanding the processes underlying global diversity patterns and for predicting large-scale biotic responses to global change. Here we show that the large-scale geographic structure of shallow-marine benthic faunas, defined by existing biogeographic schemes, can be predicted with 89-100% accuracy by a few readily available oceanographic variables; temperature alone can predict 53-99% of the present-day structure along coastlines. The same set of variables is also strongly correlated with spatial changes in species compositions of bivalves, a major component of the benthic marine biota, at the 1°grid-cell resolution. These analyses demonstrate the central role of coastal oceanography in structuring benthic marine biogeography and suggest that a few environmental variables may be sufficient to model the response of marine biogeographic structure to past and future changes in climate.bivalves | climate | macroecology | sea-surface temperature B iogeographic units (BUs), such as provinces or biomes, have been essential for understanding the macroecological and evolutionary processes underlying global biodiversity patterns (1-4) and are increasingly being incorporated in conservation planning (5-8). BUs are also becoming important from a global change perspective as components in models of biotic responses to global climate change in terrestrial settings (9). However, the factors that determine the biogeographic structure of benthic marine species in shallow-water habitats, where marine biodiversity is best documented and environmental changes are projected to be most severe (10-12), remain poorly understood, limiting our ability to model systems-level responses of marine biodiversity to environmental change. Here we use global datasets (Datasets S1, S2, S3, S4, and S5) to show that, in contrast to the more complex relationship between species richness and environment (13,14), the biogeographic structure of coastal and continental shelf habitats can be predicted using just a few oceanographic parameters. This robust first-order link between specific environmental factors and large-scale biotic patterns establishes the importance of climate and oceanography in structuring marine faunas and provides important insights into modeling past and future responses of marine biogeography to global change.We evaluate the correspondence between BUs and oceanographic variables using a model-fitting approach (Materials and Methods) to determine which oceanographic variables (individually or in combination) are most strongly correlated with biogeographic structure at both the ocean-basin and coastline scales (Table 1 and Tables S1 and S2). Our models focus on mean annual values and seasonal ranges of sea surface temperature, salinity, and productivity (hereafter TSP) because these variables have been previously hypothesized, separately or together, to affect taxonomic compositions and species richness in benthic marine system...
Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8-1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2-0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50-80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale. O rogenesis reflects the balance of crustal material entering a mountain belt to undergo shortening and uplift versus material leaving the orogen through exhumation, erosion, and sediment transport (1-5). Perturbations in the influx/efflux from the orogen are expected to result in predictable changes in deformation within the orogen as it attempts to reestablish equilibrium (3). The long-term sink for sediment transported out of mountain belts is often in the deep sea, particularly in large submarine fans where sediments accumulate at anomalously high rates (>10 cm/ky) compared with deep-sea pelagic sedimentation (6-8). Even higher sedimentation rates (>100 cm/ky) proximal to glacially eroded regions (9-14) imply that wet-based glaciers are extremely efficient agents of erosion. Observations and modeling have argued that erosion rates can influence tectonic processes (15)(16)(17)(18)(19), but the timescales of adjustment, and the role of landscape disequilibrium, remain unclear. For example, exceptionally high local sedimentation rates (100-1000 cm/ky) recorded on the century timescale (13) SignificanceIn coastal Alaska and the St. Elias orogen, over the past 1.2 million years, mass flux leaving the mountains due to glacial erosion exceeds the plate tectonic input. This...
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