Keyi Cui

Two Yale scientists have made major strides in avian ecological research.

A recent publication in the journal Nature from Yale’s Jetz Lab examines the rates at which species of birds evolve at different altitudes. The researchers used widely accepted data from the Andes Mountains, the Himalayas and other regions and summits to amalgamate many local studies into one comprehensive publication.

Ecology and Evolutionary Biology professor Walter Jetz and Ignacio Quintero GRD ’19 published research, the most comprehensive in their field to date, on Feb. 21. They concluded that avian species diversify — or develop and go extinct — at the highest rates in locations where current species richness — the concentration of a species in a given area — is lowest. This means that new species of birds evolve most readily in areas with a low variety, or richness, of bird species.

“The decrease of species richness toward higher elevations is arguably the most ubiquitous ecological pattern, yet one that has neither been fully captured globally nor seen general macroevolutionary scrutiny,” Jetz said.

The researchers initially hypothesized their results would support the commonly accepted belief that species richness decreases as altitude increases. The research affirmed the ecological principle that species richness decreases at higher altitudes, but the scientists discovered an odd correlation: As species richness decreased, diversification rates increased.

Given the accepted notion that species richness decreases at higher altitudes, it should follow that the rate of species diversification should also decrease. But the study’s results revealed opposite trends, with low species richness at high altitudes causing high species diversification.

“This shatters the existing paradigm about higher diversification rates necessarily supporting the build-up and maintenance of greater richness,” Jetz said. “It is to our knowledge the first general demonstration of such an inverse relationship worldwide.”

Jetz and Quintero speculated that the unexpected results could have to do with climate. Historical climatic stability, which allowed the accumulation of species over time, may have resulted in this greater diversification at high altitudes.

Prior research analyzing diversification of birds at varying altitudes has struggled to reach meaningful conclusions, according to Quintero. Studies have been halted by a lack of technology, low data standards and a general lack of scientific effort. Quintero explained that the discrepancies between the data the Yale team used and low-standard data could be accounted for by considering the effort that produced each data set.

Some researchers have rushed collecting data in the past, he said, sometimes spending only a few days in certain areas.

A better understanding of ecology can result in more efficient conservation efforts, Quintero said. According to the study, considering the effects of previous climate change can help predict potential effects of future climate volatility on high-altitude species.

For Jetz, the hope is that the study may also be used to bridge the gap between empirical research and broader ecological trends.

“We expect our study to invigorate the integration of macroecological and evolutionary dynamics in the biodiversity research broadly,” he said.

Research conducted in 2016 by the American Natural History Museum found that there are approximately 18,000 species of birds in the world today.

Nick Tabio |