Sympatric Speciation in Birds Is Rare: Insights from Range Data and Simulations

Abstract

Sympatric speciation is now accepted as theoretically plausible and a likely explanation for divergence in a handful of taxa, but its contribution to large-scale patterns of speciation remains contentious. A major problem is that it is difficult to differentiate between alternate scenarios of geographic speciation when species ranges have shifted substantially in the past. Previous studies have searched for a signal of the geographic mode of speciation by testing for a correlation between time since speciation and range overlap. Here we use simulations to show that the proportion of species showing zero or complete range overlap are more reliable indicators of the geography of speciation than is the correlation between time since speciation and overlap. We then apply these findings to the distributions of 291 pairs of avian sister species. Although 49% of pairs show some overlap in their ranges, our simulations show that this is not surprising under allopatric models of speciation. More revealingly, less than 2% show complete range overlap. Our simulations demonstrate that the observed patterns are most consistent with a model in which allopatric speciation is dominant but in which sympatric speciation is also present and contributes 5% of speciation events.

Evidence of linked selection on the Z chromosome of hybridizing hummingbirds*

“…Variations on this debate occur at all levels of biological hierarchy—from population genetic studies asking if genetic variation is adequately explained by neutral processes (Kimura ; Kern and Hahn ), to phylogeographic studies that ask if speciation has proceeded with or without gene flow (Nosil ), to macroevolutionary analyses that seek to estimate the ratio of sympatric to allopatric speciation by studying range overlap across whole taxonomic classes (Phillimore et al. ). At the level of the genome, a similar question arises: what process explains variation in differentiation across the genome?…”

Evolution of sympatric species: a case study of the coral reef fish genus Pomacanthus (Pomacanthidae)

“…ARC analysis has been questioned on the basis that substantial changes to species geographical ranges can effectively eliminate the relationship between the geography of speciation and contemporary geographical distributions (Barraclough & Vogler, ; Losos & Glor, ), especially in highly mobile species (Phillimore et al ., ). Despite this, ARC analysis has been shown to be capable of detecting when the predominant mode of speciation is sympatric (Phillimore et al ., ).…”

“…ARC analysis has been questioned on the basis that substantial changes to species geographical ranges can effectively eliminate the relationship between the geography of speciation and contemporary geographical distributions (Barraclough & Vogler, ; Losos & Glor, ), especially in highly mobile species (Phillimore et al ., ). Despite this, ARC analysis has been shown to be capable of detecting when the predominant mode of speciation is sympatric (Phillimore et al ., ). Further improvements have been made as a result of simulation studies, including: independent comparisons to determine overlap between clades, and Monte Carlo methods to test the relationship between phylogenetic relatedness and geographical range overlap (Fitzpatrick & Turelli, ); and the proportion of species showing zero or complete range overlap as a more reliable indicator of the geography of speciation (Phillimore et al ., ).…”

“…Despite this, ARC analysis has been shown to be capable of detecting when the predominant mode of speciation is sympatric (Phillimore et al ., ). Further improvements have been made as a result of simulation studies, including: independent comparisons to determine overlap between clades, and Monte Carlo methods to test the relationship between phylogenetic relatedness and geographical range overlap (Fitzpatrick & Turelli, ); and the proportion of species showing zero or complete range overlap as a more reliable indicator of the geography of speciation (Phillimore et al ., ). All of these methods require a robust phylogeny within a temporal framework (Fitzpatrick & Turelli, ) and generally work best when applied to geographical relationships among sister species (Phillimore et al ., ; Fitzpatrick et al ., ).…”

Using phylogenies to trace the geographical signal of diversification

“…In this approach, the observed patterns between sympatry and node age are compared with the expected patterns of range overlap under alternative modes of speciation (Barraclough & Vogler, ; Fitzpatrick & Turelli, ; Perret, Chautems, Spichiger, Barraclough & Savolainen, ). The assumption is that the amount of overlap between the geographical ranges of sister species or clades depends initially on the geography of speciation, but becomes randomized over time due to subsequent range shifts (Barraclough & Vogler, ; Berlocher & Feder, ; Lynch, ; Phillimore et al., ; Pigot, Owens & Orme, ).…”