Research by a UK-based scientist suggests that African elephant breeding rates are determined by their environment.

Contrary to popular belief, he says, the elephants do not breed beyond the carrying capacity of their habitat.

Before they can reach that point, their reproductive capacity is automatically checked. And the result is a finely balanced system which avoids any need for human adjustments.

The researcher is Raphael Ben-Shahar, of the University of Oxford, UK. He spent 10 years researching elephants' habitats in the Chobe and Okavango area of northern Botswana, close to the border with Namibia. The area is home to 60,000 to 100,000 elephants, about 10% of Africa's total.

Finely tuned

Dr Ben-Shahar's findings are potentially very significant, because several southern African countries, Botswana among them, argue that they have too many elephants, and that the animals' habitats and the species that share them are suffering as a result.

Conservationists often argue that in these circumstances it is best to control the elephants' numbers, either by moving them elsewhere or by killing them, before they starve.

But Dr Ben-Shahar says that in large nature reserves it is the environment that regulates elephant numbers rather than the reverse, with a stable but finely tuned ecosystem of plants and animals that works perfectly well on its own.

"There is no need to cull elephant herds to maintain an ecological equilibrium," he says. "Long before elephant populations exceed the carrying capacity and threaten the environment, their breeding rate falls.

"This seems to be determined by a fall in nutrients in their food supply, suppressing the elephants' reproduction systems."

Other threats

Elephants have been known to breed at up to 5% a year, a rate which intensifies the risks of contact with growing human populations. And an adult elephant can eat from 150 to 220 kg (330 to 440 pounds) of plant matter daily.

Dr Ben-Shahar said: "A staggering amount of biomass passes through the guts of northern Botswana's elephants.

"In the worst scenario, scientists fear that elephants could destroy their habitats and then die of hunger as they are unable to migrate across human settlements in search of alternative food supplies."

But his research persuaded him that vegetation was much more capable of withstanding large numbers of elephants than anyone had supposed. He found that many plants were in any case suffering much less damage than supposed from elephants and much more from fire, insects and disease.

Analysing the different pressures on the plants, Dr Ben-Shahar compiled a comprehensive life history cycle of different species. And he concluded that in the study area the elephants were "nowhere close" to becoming a threat to the vegetation.