Vertical stratification influences global patterns of biodiversity

Abstract

Species distributions in terrestrial ecosystems are three‐dimensional, spanning both the horizontal landscape and the vertical space provided by the physical environment. Classical hypotheses suggest that communities become more vertically stratified with increasing species richness, owing to reduced competition or finer niche subdivision. However, this assertion remains untested in the context of the broader realm of biogeography. Here, integrating traits and distribution data for amphibians globally, we show how vertical strategies interact with the physical and climatic environments to govern global patterns of species richness and community composition. Our results reveal a marked latitudinal shift in strategies of vertical habitat use, from highly arboreal assemblages in the tropics to highly fossorial assemblages in sub‐tropical and temperate regions. Arboreality is strongly associated with precipitation, vegetation structure and climatic stability, whereas fossoriality is more common in dry environments with high diurnal temperature range and low vegetation structure. These analyses shed light on the importance of vertical stratification for species coexistence in species‐rich regions. As certain tropical habitats become drier from climate change, the rich biological diversity that is emblematic of the tropics may transition from vertically stratified to ‘flattened’, with future communities living mostly on or beneath the ground.

Vertical stratification collapses under seasonal shifts in climate

“…As such, these microgeographic processes in the vertical dimension are increasingly recognized as an influential contributor to macroecological patterns. For example, the exploitation of above-ground habitat is more common in tropical than temperate regions (Oliveira & Scheffers, 2019) where aboveground conditions are more physiologically challenging (Lowman & Rinker, 2004). Multidimensional species distributions that arise from the partitioning of niche space should therefore be susceptible to shifts in niche components both in space and time.…”

Effects of Forest Fragmentation on the Vertical Stratification of Neotropical Bats

“…60% of all known animal and plant species in only 8% of the planet's surface [1]. This diversity is largely mediated by the complex stratification and multidimensionality of tropical forest canopies, which allow for additional niche space and facilitate the coexistence of a large number of species in the same geographical area [2][3][4]. However, biological assessments across the tropics tend to be largely limited to understory-level surveys that under-represent species associated with higher forest strata [5].…”

Canopy height explains species richness in the largest clade of Neotropical lianas

“…In addition, biotic interactions (such as competition or facilitation) may influence species richness by increasing habitat specialization or reducing extinction due to species coexistence (Gotelli, Graves, & Rahbek, 2010). Finally, environmental heterogeneity (e.g., topographic, edaphic and 3-D ecosystem heterogeneity) also contributes to diversification, species specialization and coexistence and ultimately increases species richness (Oliveira & Scheffers, 2019;Stein, Gerstner, & Kreft, 2014). Apart from the individual effect of each factor, these factors interact and influence species richness in a complex way (Rangel et al, 2018), making it difficult to formulate a unique explanation of richness patterns.…”

“…One possibility is to use proxies of vegetation structure such as canopy height, which can be derived from spaceborne light detection and ranging (LiDAR; Lefsky, 2010;Simard, Pinto, Fisher, & Baccini, 2011). Such canopy height estimates can then be used to test hypotheses concerning the relationship between 3-D habitat structure and the distribution and diversity of organisms (Couvreur et al, 2015;Gouveia et al, 2014;Oliveira & Scheffers, 2019).…”