Marine latitudinal diversity gradients, niche conservatism and out of the tropics and Arctic: Climatic sensitivity of small organisms

Abstract

Aim The latitudinal diversity gradient (LDG) is a consequence of evolutionary and ecological mechanisms acting over long history, and thus is best investigated with organisms that have rich fossil records. However, combined neontological‐palaeontological investigations are mostly limited to large, shelled invertebrates, which keeps our mechanistic understanding of LDGs in its infancy. This paper aims to describe the modern meiobenthic ostracod LDG and to explore the possible controlling factors and the evolutionary mechanisms of this large‐scale biodiversity pattern. Location Present‐day Western North Atlantic. Taxon Ostracoda. Methods We compiled ostracod census data from shallow‐marine environments of the western North Atlantic Ocean. Using these data, we documented the marine LDG with multiple metrics of alpha, beta (nestedness and turnover) and gamma diversity, and we tested whether macroecological patterns could be governed by different environmental factors, including temperature, salinity, dissolved oxygen, pH and primary productivity. We also explored the geologic age distribution of ostracod genera to investigate the evolutionary mechanisms underpinning the LDG. Results Our results show that temperature and climatic niche conservatism are important in setting LDGs of these small, poorly dispersing organisms. We also found evidence for some dispersal‐driven spatial dynamics in the ostracod LDG. Compared to patterns observed in marine bivalves, however, dispersal dynamics were weaker and they were bi‐directional, rather than following the ‘out‐of‐the‐tropics’ model. Main conclusions Our detailed analyses revealed that meiobenthic organisms, which comprise two‐thirds of marine diversity, do not always follow the same rules as larger, better‐studied organisms. Our findings suggest that the understudied majority of biodiversity may be more sensitive to climate than well‐studied, large organisms. This implies that the impacts of ongoing Anthropocene climatic change on marine ecosystems may be much more serious than presently thought.

Truncated bimodal latitudinal diversity gradient in early Paleozoic phytoplankton

“…These results strongly contrast with the unimodal nature of other LDGs found for Paleozoic organisms, such as brachiopods and bryozoans ( 5 , 11 ). It seems that no single model of LDG prevails, but rather that several models, which vary in amplitude and shape in space and time, as well as according to the ecological characteristics and life traits of organisms [such as size; ( 71 – 73 )], have coexisted at least since the early Paleozoic.…”

The Subhabitat Dependence of Biogeographic Pattern

“…For instance, many biogeographic surveys have focused only on specific groups of organisms, such as birds (Hazzi et al, 2018), fish (Cowman et al, 2017), trees (Dick and Pennington, 2019), algae (Stekoll, 2019), crustaceans (Brun et al, 2020), or ants (Maravalhas and Vasconcelos, 2020), to name just a few. To some extent, however, different groups of organisms may differ in biogeographic pattern within a region, as the various drivers of species distribution may vary in importance among the groups (Qian et al, 1998;Hart and Chen, 2006;Chiu et al, 2020). Hence, distribution data for subsets of organisms may not properly reveal the biogeographic pattern for a regional biota as a whole.…”

Missing in the Middle: A Review of Equatorially Disjunct Marine Taxa

“…Therefore, anti-tropical divergence events between clades should date to approximately 17-15 mya for this hypothesis to be supported in the strictest sense. A secondary assumption that anti-tropical marine taxa resulting from the mid-Miocene climatic optimum event should be physiologically restricted to cooler water temperatures may also be valid if niche conservatism operates on extended time scales (Romdal et al, 2013;Chiu et al, 2020). This all-encompassing hypothesis has received criticism.…”