Published online 24 September 2008 | Nature | doi:10.1038/news.2008.1127

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Competition for sex hampers endangered species' recovery

Study challenges conservation management methods.

birdThe Seychelles magpie robin: making too much war and not enough love.NHPA/ M. HARVEY

The battles for reproductive supremacy between individuals of an endangered species can significantly hamper the population's recovery rate, according to a study that measured the effects of this competition on conservation. The research suggests that some aspects of conservation practice, such as supplementary feeding of threatened species, should be re-evaluated to take account of this effect.

Fighting for the right to reproduce is well known to benefit individuals more than groups, and can sometimes have negative effects on the population as a whole. But the impact of such fighting on efforts to conserve whole populations is not thought to have been explored before now, according to biologists led by Andrés López-Sepulcre from the University of California, Riverside.

His team based the analysis on Seychelles magpie robins (Copsychus sechellarum), which in 1988 were judged to be one of the world's most endangered birds. The researchers found that breeding competition slowed the birds' recovery out of critically endangered status by 33%.

That conclusion came from detailed computer modelling of the population's growth under two different scenarios. A control scenario simulated growth in real-life conflict conditions whereas an alternative scenario modelled population growth in a conflict-free environment.

Scientists have extensive records of the birds: every individual in the population had been monitored between 1988 and 2004, including records of mating behaviours, allowing very precise modelling. Indeed, the control simulation correctly predicted the population's actual observed growth rate, with the birds eventually being downgraded to merely 'endangered' status after 11 years.

But in the conflict-free scenario, the models showed that the population would have reached that level more than 32 months earlier. The findings are published in the Journal of Animal Ecology1.

Frequent fighters

Non-reproducing subordinate individuals are generally thought to benefit populations by feeding others' chicks. But team member Hanna Kokko of the University of Helsinki says that while the presence of subordinate robins helps in some ways, the overall effect in their simulations was negative. The robins live in groups of between 2 and 10 individuals, with a single dominant breeding pair, and there are frequent fights over breeding territory within the group, with subordinate individuals trying to overthrow the dominant pair.

"The presence of same-sex subordinates alongside dominant individuals makes them fight more, feed less and increases monthly takeover in territory," she says. "You could say this does not matter because when one pair does not breed then the other will. But these birds take a long time before dominance is clearly established after a fight, and so breeding is affected."

"We found it took them 33% more time to recover — you could say that is a 33% increase on the extinction rate," she adds.

Basic lessons

Understanding these behaviours could improve conservation management techniques. For example, some management methods, such as supplementary feeding, could increase conflict over territory, thus hampering recovery rates.

Conservation biologist Guy Cowlishaw of the Institute of Zoology in London says that the study illustrates how important individual behaviour can be for population persistence and conservation management.

"It's a nice analysis, and it shows how important it is to monitor and understand the behavioural ecology of the species that is the subject of conservation," he says. "There have been lots of theoretical looks at how individual behaviour could affect conservation of a species, but this paper is unique in demonstrating this in a real-life species that has been critically endangered."

"There are some basic lessons for conservation here," he adds. "As a conservationist you may think you are doing enough by protecting the habitat or stopping hunting."

But this research, he says, shows that studies of individuals' behaviour could show if endangered populations are recovering more slowly than expected — and point conservationists in the right direction to alleviate this. 

  • References

    1. López-Sepulcre, A., Norris, K. & Kokko, H. J. Anim. Ecol. doi:10.1111/j.1365-2656.2008.01475 (2008).
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