Abstract
The geography of speciation is one of the most contentious topics at the frontier between ecology and evolution. Here, building on previous hypotheses, I propose that ecological constraints on species co-existence mediate the likelihood of speciation, via a trade-off between competitive and dispersal abilities. Habitat stability, as found in the tropics, selects for the evolution of stronger competitive abilities. Since resource investment in competitive and dispersal abilities should trade off, high competition in stable habitats reduces species dispersal ability, decreasing effective population sizes. In smaller local populations, higher fixation rates of molecular substitutions increases the likelihood of speciation. Higher species diversity triggers more speciation by further increasing the spatial structuring of populations and decreasing effective population sizes. Higher resource specialization also trades-off with dispersal ability and could account for speciation at higher trophic levels. Biotic interactions would therefore promote parapatric speciation and generate spatial patterns in diversity such as the latitudinal diversity gradient. I discuss the main evidence for this mechanism and emphasize the need for studies coupling ecology and speciation theory within landscapes.
Highlights
The extraordinary diversity of species on earth provides infinite motivation to unravel the underlying ecological and evolutionary rules
Stable habitats reunite the theoretical conditions expected to fuel speciation, including lower effective population size, local mating linked to dispersal limitation and high levels of local genetic variation (Gavrilets, 2004)
Together this suggests that molecular evolution fuelling speciation is faster under stable conditions, high competition and limited dispersal, which is characteristic of the tropics
Summary
The extraordinary diversity of species on earth provides infinite motivation to unravel the underlying ecological and evolutionary rules. Classic examples of exceptional events of speciation, including Darwin’s finches (Grant and Grant, 2011), Anolis lizards (Losos, 1998) or African cichlids (Schliewen et al, 1994; Barluenga et al, 2006), took place in confined spatial areas such as islands or lakes Together, this suggests that the rate of species diversification is strongly linked to the spatial distribution and connectivity of meta-populations. Building on Fedorov’s observations, I propose the hypothesis of a possible direct link between biotic interactions, connectivity among populations, and speciation that may explain the higher diversity in the tropics (Mittelbach et al, 2007). Five decades after the publication of Federov’s observations and based on new molecular evidences (e.g., Lasso et al, 2011), I hypothesize that the ecological trade-off between resource use efficiency and dispersal abilities promotes higher speciation rates in the tropics
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