Latitudinal‐diversity gradients can be shaped by biotic processes: new insights from an eco‐evolutionary model

Abstract

The processes involved in shaping latitudinal‐diversity gradients (LDGs) have been a longstanding source of debate and research. Climatic, historical and evolutionary factors have all been shown to contribute to the formation of LDGs. However, meta‐analyses have shown that different clades have LDG slopes that may vary in more than one order of magnitude. Such large variation cannot be explained solely by climatic or historical factors (e.g. difference in surface area between temperate and tropical zones) given that all clades within a geographic region are subject to the same conditions. Therefore, biotic processes intrinsic to each taxonomic group could be relevant in explaining rate differences in diversity decline across latitudinal gradients among groups. In this study, we developed a model simulating multiple competing species subjected (or not) to a demographic Allee effect. We simulated the range expansion of these species across an environmental gradient to show how these two overlooked factors (competition and Allee effects) are capable of modulating LDGs. Allee effects resulted in a steeper LDG given a higher probability of local extinction and lower colonization capacity compared to species without Allee effects. Likewise, stronger competition also led to a steeper decline in species diversity compared to scenarios with weaker species antagonistic interactions. This pattern occurred mostly due to the strength of priority effects, wherein scenarios with strong competition, species that dispersed earlier in the landscape were able to secure many patches whereas late‐arriving species were progressively precluded from expanding their ranges. Overall, our results suggest that the effect of biotic processes in shaping macroecological patterns could be more important than it is currently appreciated.

Niche breadth and species richness: Correlation strength, scale and mechanisms

“…This supports the conclusion of Vazquez and Stevens () that latitude and niche breadth are probably associated indirectly, via species richness. Our results support the growing perception that local interactions may significantly affect large‐scale biogeographical patterns (Gotelli et al, ; Henriques‐Silva, Kubisch, & Peres‐Neto, ; Russell, Wood, Allison, & Menge, ; Wisz et al, ).…”

Global geographic patterns of heterospecific pollen receipt help uncover potential ecological and evolutionary impacts across plant communities worldwide

“…HP pollen receipt is thus an untested mechanism that might contribute to overall patterns of pollen limitation. Even though the importance of biotic interactions in contributing to global patterns of diversity has been well documented for a large number of antagonistic and mutualistic interactions 42,43 , the potential for HP transfer interactions in contributing to these patterns has so far been overlooked.…”

“…Thus, selection on traits that maximize reproductive success by avoiding or tolerating HP effects can be expected to be stronger in species-rich areas, leading to further diversification and contributing to observed latitudinal patterns of plant biodiversity. Biotic interactions have long been predicted to play a key role in generating latitudinal patterns of biodiversity 42,43 , and plant-plant interactions via HP transfer may not be the exception.…”

Priority effects and the macroevolutionary dynamics of biodiversity

“…We note that these different competition scenarios could arise through a variety of demographic and ecological routes. For instance, local priority effects may arise because residents have a numerical advantage (Hubbell, 2001), modify niche space (Odion et al, 2010; Westoby et al, 1989), or because invaders are subject to Allee effects (Henriques‐Silva et al, 2019). Invaders may have a transient competitive advantage if they have escaped from their natural enemies (enemy release hypothesis (Colautti et al, 2004; Keane & Crawley, 2002)) or carry novel weapons (e.g.…”