Tag Archives: species

What is a species? Bird expert develops a math formula to solve the problem

(Pennsoft Publishers: Thomas Donegan, Blanca Huertas, Christian Olaciregui, 10 May 2018)
Whether co-habiting populations belong to the same species is only as tough as figuring out if they interbreed or produce fertile offspring. On the other hand, when populations are geographically separated, biologists often struggle to determine whether they represent different species or merely subspecies. To address the age-long issue, a British bird expert has developed a new universal mathematical formula for determining what is a species.

Nature is replete with examples of identifiable populations known from different continents, mountain ranges, islands or lowland regions. While, traditionally, many of these have been treated as subspecies of widely-ranging species, recent studies relying on molecular biology have shown that many former “subspecies” have in fact been isolated for millions of years, which is long enough for them to have evolved into separate species.

Being a controversial matter in taxonomy — the science of classification — the ability to tell apart different species from subspecies across faunal groups is crucial. Given limited resources for conservation, relevant authorities tend only to be concerned for threatened species, with their efforts rarely extending to subspecies.

Figuring out whether co-habiting populations belong to the same species is only as tough as testing if they can interbreed or produce fertile offspring. However, whenever distinct populations are geographically separated, it is often that taxonomists struggle to determine whether they represent different species or merely subspecies of a more widely ranging species.

British bird expert Thomas Donegan has dedicated much of his life to studying birds in South America, primarily Colombia. To address this age-long issue of “what is a species?,” he applied a variety of statistical tests, based on data derived from bird specimens and sound recordings, to measure differences across over 3000 pairwise comparisons of different variables between populations.

Having analyzed the outcomes of these tests, he developed a new universal formula for determining what can be considered as a species. His study is published in the open-access journal ZooKeys.

Essentially, the equation works by measuring differences for multiple variables between two non-co-occurring populations, and then juxtaposing them to the same results for two related populations which do occur together and evidently belong to different “good” species. If the non-co-occurring pair’s differences exceed those of the good species pair, then the former can be ranked as species. If not, they are subspecies of the same species instead.

The formula builds on existing good taxonomic practices and borrows from optimal aspects of previously proposed mathematical models proposed for assessing species in particular groups, but brought together into a single coherent structure and formula that can be applied to any taxonomic group. It is, however, presented as a benchmark rather than a hard test, to be used together with other data, such as analyses of molecular data.

Thomas hopes that his mathematical formula for species rank assessments will help eliminate some of the subjectivity, regional bias and lumper-splitter conflicts which currently pervade the discipline of taxonomy.

“If this new approach is used, then it should introduce more objectivity to taxonomic science and ultimately mean that limited conservation resources are addressed towards threatened populations which are truly distinct and most deserving of our concern,” he says.

The problem with ranking populations that do not co-occur together was first identified back in 1904. Since then, most approaches to addressing such issues have been subjective or arbitrary or rely heavily upon expert opinion or historical momentum, rather than any objectively defensible or consistent framework.

For example, the American Herring Gull and the European Herring Gull are lumped by some current taxonomic committees into the same species (Herring Gull), or are split into two species by other committees dealing with different regions, simply because relevant experts at those committees have taken different views on the issue.

“For tropical faunas, there are thousands of distinctive populations currently treated as subspecies and which are broadly ignored in conservation activities,” explains Thomas. “Yet, some of these may be of conservation concern. This new framework should help us better to identify and prioritize those situations.”

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New Peruvian bird species discovered by its song

(Florida Museum of Natural History, ScienceDaily 23 oct 2017;Photo Andy Kratter)

A new species of bird from the heart of Peru remained undetected for years until researchers identified it by its unique song.

In 1996, a group of Louisiana State University and Florida Museum of Natural History researchers traveled to the Cordillera Azul, an isolated mountain ridge in Peru, where they discovered a previously unknown manakin species.

With its bright yellow front feathers, the bird was different from the local subspecies of striped manakin, but nearly identical to the subspecies Machaeropterus regulus aureopectus found in the distant Venezuelan tepuis. But it has a completely different voice.

The newly discovered manakin’s song lacks undertones and has a one-noted rising vocalization, rather than two-noted falling vocalization with undertones or a falling monosyllabic vocalization with undertones.

It was given the name Machaeropterus eckelberryi, commemorating the 20th century bird illustrator Don Eckelberry.

Andy Kratter, a museum ornithology collection manager, said the differences went unnoticed for years because the research team didn’t have vocalizations for all of the bird species.

“We kind of sat on it for a long time because we didn’t have vocalizations of the birds in Venezuela, and this bird is different from the local birds but close enough to the Venezuelan birds that it might have been considered the same species,” he said. “In manakins, it’s often subtle clues that might be different among species.”

The discovery of the new species and details of the expedition were recently published in Zootaxa.

Kratter said finding the new species and the isolated mountain ridge were important for the scientific community, in part because the discovery spurred Peru to preserve the area.

“The Peruvian government established a national park in the area in the early 2000s, mainly as a result of finding this novel diversity in this area, which our expedition did,” he said. “Finding these guys opened up a little more inventory and exploration, which led to the formation of this gigantic national park.”

Dan Lane, leader of the expedition and a research associate at LSU, was the first to record the new species, and he said it is one more bird for the ornithological community to include in their studies.

“Even if we weren’t discovering new species, just exploring regions of the world that are sse this knowledge to preserve them is a worthwhile activity,” he said. “Peru still has many till poorly known and getting a better picture of where species are distributed, what habitats they use and how we may utreasures hidden in unexplored nooks and crannies, and I’d be lying if I said I didn’t enjoy the opportunity to uncover them. To this day, it may be some of the most virgin terrain I’ve ever visited.”

A grant from the National Geographic Society’s Fund for Research and Exploration funded the research in 1996.

Dance Moves Support Evidence for New Bird-of-Paradise Species

Western New Guinea form of the Superb Bird-of-Paradise

(Cornell LoO 29 June 2017; Photo Tim Laman)

Ithaca, NY—The Superb Bird-of-Paradise—the shape-shifting black bird of central New Guinea that woos its mate with an iridescent blue “smiley-face” dance—has an equally superb cousin in the isolated mountains of Indonesia’s Bird’s Head Peninsula in the island’s far west. Scientist Ed Scholes and photographer Tim Laman, with the Cornell Lab of Ornithology’s Birds-of-Paradise Project, have now visually documented the distinct differences between the western population in the Arfak Mountains and the more common form found elsewhere on the island. Both believe the western form should be considered a new species.

“The courtship dance is different. The vocalizations are different. Even the shape of the displaying male is different,” says Scholes. “For centuries, people thought the Superb Bird-of-Paradise in the mountains of the Bird’s Head region was a little different from the other populations throughout the rest of New Guinea, but no one had ever documented its display in the 200 plus years this bird has been known to occur there.”

“Even after many trips to the region, we’d never seen the Arfak birds do their courtship display,” says Birds-of-Paradise Project co-leader Tim Laman. “When we finally located a display site and saw a male open his cape for the first time, what we saw was a complete surprise!”

When expanded for courtship display, the western male’s raised cape creates a completely different appearance—crescent-shaped with pointed tips rather than the oval shape of the widespread form of the species. The way the western male dances for the female is also is distinctive, being smooth instead of bouncy.

           
The raised cape of the western male (left) is crescent shaped and unlike the oval shape of the widespread Superb Bird-of-Paradise (right) found throughout most of New Guinea. Left image by Tim Laman/Macaulay Library. Image on right is from video by Ed Scholes/Macaulay Library.

Scholes and Laman have been studying and filming birds-of-paradise behavior in the Arfak Mountains for the past 13 years. They first uncovered this population’s unique courtship behaviors in June 2016 and returned again this year to gather additional documentation for a forthcoming scientific paper.

A recently published independent genetic study confirms the visual and behavioral evidence collected by Scholes and Laman. A team of researchers from Sweden and Australia used DNA samples from museum specimens to examine the evolutionary relationships among Superb Bird-of-Paradise forms throughout New Guinea. Their research, published online in the Zoological Journal of the Linnean Society, found that the western form is more genetically distinct from the widespread form than previously thought. They, too, say the western population should be recognized as a full species called Lophorina neidda inopinata. 

“The timing of this DNA-based study is perfect,” said Ed Scholes, “because it is great to have our field observations supported by solid genetic evidence. We really appreciate this in-depth study of the evolutionary relationships among the different forms of Superb Bird-of-Paradise.”

The Cornell Lab’s Birds-of-Paradise Project (birdsofparadiseproject.org) is a research and education initiative to document, interpret, and protect the birds-of-paradise, their native environments, and the other biodiversity of the New Guinea region—one of the largest remaining tropical wildernesses on the planet.