Common latitudinal gradients in functional richness and functional evenness across marine and terrestrial systems

Abstract

Functional diversity is an important aspect of biodiversity, but its relationship to species diversity in time and space is poorly understood. Here we compare spatial patterns of functional and taxonomic diversity across marine and terrestrial systems to identify commonalities in their respective ecological and evolutionary drivers. We placed species-level ecological traits into comparable multi-dimensional frameworks for two model systems, marine bivalves and terrestrial birds, and used global speciesoccurrence data to examine the distribution of functional diversity with latitude and longitude. In both systems, tropical faunas show high total functional richness (FR) but low functional evenness (FE) (i.e. the tropics contain a highly skewed distribution of species among functional groups). Functional groups that persist toward the poles become more uniform in species richness, such that FR declines and FE rises with latitude in both systems. Temperate assemblages are more functionally even than tropical assemblages subsampled to temperate levels of species richness, suggesting that high species richness in the tropics reflects a high degree of ecological specialization within a few functional groups and/or factors that favour high recent speciation or reduced extinction rates in those groups.royalsocietypublishing.org/journal/rspb Proc. R. Soc. B 286: 20190745

Functional diversity of reef molluscs along a tropical-to-temperate gradient

“…Unlike previous studies on bivalves (Edie et al 2018;Schumm et al 2019), gradients in functional richness were not associated with latitude over the spatial scale of our study. Instead, it is the difference between species in communities that is associated with the changes in functional diversity, as functional dispersion declines at subtropical latitudes (Fig.…”

“…5), high variability suggests that our analyses do not capture the full picture of functional redundancy change. Evidence of functional redundancy is lacking for many subtropical marine species and to our knowledge has not been directly addressed in marine mollusc assemblages (Schumm et al 2019). Fishes are best studied and despite reports of low functional redundancy for many systems (Micheli and Halpern 2005), there is evidence of functional redundancy in tropical assemblages (Mouillot et al 2014).…”

“…Trait and functional understanding of marine mollusc assemblages is limited globally, though there is evidence for contrasting trends in functional richness and functional evenness with increasing latitude in marine bivalves (Edie et al 2018;Schumm et al 2019). Molluscs play important roles in the marine environment such as food and habitat provision, predation, and grazing (Przeslawski et al 2008).…”

Traits and depth: What do hydroids tell us about morphology and life‐history strategies in the deep sea?

“…Trait-based approaches are increasingly being used to help understand the processes that regulate large-scale diversity patterns (e.g. Lamanna et al, 2014;Schumm et al, 2019). Traits affect the abilities of individuals and species to occur in different habitats by mediating responses to biotic and abiotic conditions.…”

“…Therefore, it is important to incorporate intraspecific variation into macroecological studies because it relates to niche occupation by individuals or populations of the same species (Messier, McGill, & Lechowicz, 2010). In general, analyses of trait variations across large spatial and environmental gradients have the potential to reveal mechanisms not evident from species richness alone (Barton et al, 2013;Bremner, 2008;Connell & Irving, 2009;Frainer et al, 2017;Henriques et al, 2017;Lamanna et al, 2014;Monro & Marshall, 2015;Schumm et al, 2019;Stahl, Reu, & Wirth, 2014;Violle, Reich, Pacala, Enquist, & Kattge, 2014).…”