Latitudinal biodiversity gradients at three levels: Linking species richness, population richness and genetic diversity

Abstract

Motivation Theory describing biodiversity gradients has focused on species richness with less conceptual synthesis outlining expectations for intraspecific diversity gradients, that is, broad‐scale population richness and genetic diversity. Consequently, there is a need for a diversity–gradient synthesis that complements species richness with population richness and genetic diversity. Review methods Species and population richness are the number of different species or populations in an area, respectively. Population richness can be totalled across species, within a species or averaged across species. Genetic diversity within populations can be summed or averaged across all species in an area or be averaged across an individual species. Using these definitions, we apply historical, ecological and evolutionary frameworks of species richness gradients to formulate predictions for intraspecific diversity gradients. Review conclusions All frameworks suggest higher average population richness at high latitudes, but similar total population richness across latitudes. Predictions for genetic diversity patterns across species are not consistent across frameworks and latitudes. New analysis methods Species range size tends to increase with latitude, so we used empirical data from c. 900 vertebrate species to test hypotheses relating species range size and richness to population richness and genetic diversity. New analysis conclusions Species range size was positively associated with its population richness but not with species‐specific genetic diversity. Furthermore, a positive linear relationship was supported between species richness and total population richness, but only weakly for average population richness. Overall conclusion Through the lens of species richness theories, our synthesis identifies an uncoupling between species richness, population richness and genetic diversity in many instances due to historical and contemporary factors. Range size and taxonomic differences appear to play a large role in moderating intraspecific diversity gradients. We encourage further analyses to jointly assess diversity–gradient theory at species, population and genetic levels towards better understanding Earth’s biodiversity distribution and refining biodiversity conservation.

Life history, climate and biogeography interactively affect worldwide genetic diversity of plant and animal populations

“…This may suggest that (i) contemporary processes are more important than postglacial recolonization dynamics in explaining population genetic diversity, and/or (ii) microrefugia that are uncoupled from general macroclimatic clines contribute more than macrorefugia to past population dynamics 59 . Importantly, our results are in line with a recent study that could not find clear latitudinal patterns in population genetic diversity for 600 vertebrate species 60 . The strong discrepancy between studies assessing latitudinal gradients in genetic diversity (ref.…”

“…The strong discrepancy between studies assessing latitudinal gradients in genetic diversity (ref. 60 and our study vs refs. .…”

“…The strong discrepancy between studies assessing latitudinal gradients in genetic diversity (ref. 60 and our study vs refs. .44,48,51 ) calls for a new paradigm regarding the worldwide distribution of population genetic diversity.…”

The conservation utility of mitochondrial genetic diversity in macrogenetic research

“…Perhaps unsurprisingly then, we have seen an increased interest in this area of research Lawrence and Fraser 2020;. This new work has led to a coalescence of ideas around the emerging subdiscipline of macrogenetics .…”

Flight demand and environmental niche are associated with molecular evolutionary rates in a large avian radiation

“…The furnariid miners ( Geositta ) and palm creepers ( Berlepschia ) are examples of taxa with a high hand-wing index that are also likely to have low population density. Similarly, tropical regions have previously been associated with lower population density compared with regions with lower environmental energy (Lawrence and Fraser 2020). Some alternatives that might disentangle effects of selection and population size on molecular evolution in future research include the incorporation of independent estimates of population size, or an extensive exploration of the relative impacts of the two factors on molecular evolutionary rates.…”