Ecology Predicts Levels of Genetic Differentiation in Neotropical Birds

Abstract

Despite the theoretical link between the ecology and the population genetics of species, little empirical evidence is available that corroborates the association. Here, we examined genetic variation in 40 codistributed species of lowland Neotropical rain forest birds that have populations isolated on either side of the Andes, the Amazon River, and the Madeira River. We found widely varying levels of genetic divergence among these taxa across the same biogeographic barriers. Our investigation of the extent to which ecological traits predicted the amount of cross-barrier divergence revealed a strongly significant relationship between the forest stratum at which a species forages and the level of cross-barrier genetic differentiation. Canopy species had statistically lower genetic divergence values across the Andes and the two Amazonian rivers than did understory birds. We hypothesize that the association reflects an effect of dispersal propensity, which is greater in canopy birds, on the movement of alleles among demes (i.e., migration) and, consequently, on the interdemic proportion of the genetic variance. Differences in dispersal propensity may also explain the observation that understory species contain a significantly greater number of subspecies than do canopy species. This result indicates that higher rates of diversification may occur in lineages with lower dispersal propensity.

High dispersal ability inhibits speciation in a continental radiation of passerine birds

“…This result is consistent with population-level studies, which have found a negative association between gene flow and genetic differentiation [2,32,51]. Although range expansion certainly plays an important role in diversification [6], the potentially stimulating effects of colonization and range expansion [7,52] may have been overshadowed by the inhibitory effect of increased levels of gene flow in the Furnariidae.…”

“…Empirical evidence supports the hand-wing index as a valid surrogate for flight and dispersal ability in birds. Flight performance (see the electronic supplementary material), migratory behaviour [29,30], natal dispersal distance [31] and genetic differentiation [32] are all correlated with this index. Because the index varies on a continuous scale, it can be used to study higher order relationships between dispersal and diversification like the intermediate dispersal model.…”

Dispersal and the transition to sympatry in vertebrates

“…By contrast, we show that differences in intrinsic dispersal potential provide the best explanation for the failure of many terrestrial vertebrate species to attain sympatry even millions of years after speciation. This makes sense because barriers to dispersal in terrestrial systems have extremely protracted effects that vary according to dispersal limitation, for example when rivers, mountain ranges or narrow regions of unsuitable climate and vegetation cause longstanding disjunctions in the geographical ranges of sister species in lineages with low dispersal ability, but not those with high dispersal ability [19,45,48].…”

Functional traits reveal the expansion and packing of ecological niche space underlying an elevational diversity gradient in passerine birds

“…For example, the higher number of habitat strata in lowland tropical forest may allow vertical segregation of ecological competitors with similar traits, facilitating coexistence without direct contact [6,27]. However, because ecological adaptations to different vegetation strata are also associated with consistent biometric differences in traits such as tarsus or wing length [25,42], we expect that these effects should also be detected in our analyses.…”