What looks like two species might actually be the male and the female of one.
If there are only two species of elephant, African and Indian, losing one matters a lot.
Two species of fish are immediate beneficiaries: the federally threatened leopard darter and the Ouachita-strain smallmouth bass.
This increased encounters between the two species and left more old moose and calves available to wolf predation.
While the two species will co-exist, eventually they hybridise and the native with its rich blue is displaced.
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The two species had lived separately since splitting off from a common ancestor, Homo heidelbergensis, 160, 000 years earlier.
About two decades later, two French biologists described two species of giant tortoises.
The two species are thought to have diverged over one million years ago.
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Moreover, the argument that the two species were interbreeding over such a long time is, to say the least, controversial.
Half of the gestures Dr Pollick and Dr de Waal regularly observed seemed to have completely different meanings in the two species.
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And as the two species slug it out for Antarctic dominance, Rambo appears to be losing, declining 65% in the last few years.
They also said they were able to differentiate between two species of bacteria and two different strains of the same P. aeruginosa bacterium.
The two species of mice were successively bred, and those hybrids built long, two-tunnel burrows like oilfield mice - showing that the behaviour is a "dominant" trait.
Over most of their ranges, the two species look quite similar to each other: the females are brown and the males are black with small, white patches.
"But the fact that two species have the same song is actually a pretty weird finding, " said Joe Tobias from Oxford's Edward Grey Institute, who led the research.
In only two species, robins and goldcrests, was there no discernible difference in size between the spleens of those pounced on by cats and those killed in collisions.
Dr. Rakel and his colleagues used pills made from the roots of two species of echinacea, Echinacea purpurea and Echinacea angustifolia, which are found in most commercially available echinacea products.
By analysing where these differences occur in the animals' genomes, it is possible to get an insight into the two species' histories - the timing of key events in their evolution.
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In a study comparing 22 organic farms with nearby conventional ones, birds did better on organic farms in 50 out of 68 cases, though the numbers were significant for only two species.
But his new data add weight to the theory that the more sophisticated idea of fair shares, which underpins collaborative behaviour, appeared in the hominid line only after the ancestors of the two species split from one another.
Since the last common ancestor of the two species lived more than 400, 000 years ago (see following story) fire-control is probably at least as old as that, for they lived in different parts of the world, and so could not have copied each other.
Other small carnivores caught on camera were the Sunda stink-badger (Mydaus javanensis), and two species of mongoose, the very common Short-tailed mongoose (Herpestes brachyurus) and the Collared mongoose (H. semitorquatus), and all three Bornean otter species, the Smooth-coated otter (Lutrogale perspicillata), Asian small-clawed otter (Aonyx cinereus) and the extremely elusive Hairy-nosed otter, considered to be the world's rarest otter.
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There seem to have been two hominid species present at Swartkrans around two million years ago.
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At least two other species of goose existed there until people arrived and, presumably, ate them.
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Males of the two antbird species have evolved the same call to keep other males off their patch.
Two other species of threatened shark will be voted on later on Monday.
"We have two different species (Hawksbill and Olive Ridley) hatching in Perancak Beach, " said Ketut Putra of the WWF.
The researchers from Oxford University believe this is the first evidence of two separate species having evolved the same territorial song.
Fifty-two butterfly species saw populations decline in 2012 compared with 2011, with 13 experiencing their worst year in records dating back to 1976.
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