Making use of data gathered from a 10-year field study, scientists report in Nature today that saiga antelope, which rank in the World Conservation Union's category of most endangered species, are being pushed closer to extinction because there are not enough male antelopes to mate with the females - despite the male's polygynous practice of maintaining a harem of 12-30 females.
Selective hunting of the male for its horns, for use in traditional Chinese medicine, has led to a gender bias where females outnumber males by a ratio of 100:1.
Dr E.J Milner-Gulland, lead author of the study, based in the Department of Environmental Science and Technology, Imperial College London, explains:
"Until now, in polygynous systems, it has been assumed that even when males are in short supply their ability to inseminate many females secures the viability of the population.
"Our observations indicate that if the percentage of males in the population falls below one per cent, reproductive collapse will result."
Even more striking, field observations of saiga behaviour in the year 2000 suggest that the crash in male numbers appear to have disrupted the species' in-built reproductive strategy, which is exacerbating their decline.
"Normally, a male defends his harem of females from other males," said Dr Milner-Gulland. "We found dominant females were aggressively excluding the younger females from the males and preventing them from getting pregnant.
"Once you get these indirect effects causing population decline through fecundity you can not be sure whether the population will recover.
"At present, the saiga population is halving each year and the species could soon be lost. Action must be taken now to provide a sustain
Contact: Judith H Moore
Imperial College London