Thirty-five per cent of the world's crop production is dependent on pollinators such as bees, birds and bats, suggests a study published this week.

In Wednesday's edition of the Proceedings of the Royal Society B: Biological Sciences,researchers say that biodiversity loss could directly affect global food crops.

The study comes a week after another report found a decline in populations of key North American pollinators, which help spread the pollen needed for fertilization of such crops as fruits, vegetables, nuts, spices and oilseed.

"There's a widely stated phrase in agriculture that you can thank a pollinator for one out of three bites of food you eat," said Claire Kremen, an assistant professor at University of California Berkeley and co-author of this new study.

"However, it wasn't clear where that calculation came from, so we set out to do a more thorough and reproducible estimate, and we wanted to look at the impact on a global scale," said Kremen.

The international research team led by Alexandra-Maria Klein, an agroecologist from the University of Goettingen in Germany, conducted an extensive review of scientific studies from 200 countries and for 115 of the leading global crops.

Out of the 115 crops studied, 87 depend to some degree upon animal pollination, accounting for one-third of crop production globally. Of those crops,researchers found 13 are entirely reliant upon animal pollinators, 30 are greatly dependent and 27 are moderately dependent.

The crops that did not rely upon animal pollination were mainly staple crops such as wheat, corn and rice.

The study looks at what's at stake if steps to improve pollinator biodiversity are not taken.

"Passion fruits in Brazil are hand-pollinated through expensive day-labourers as the natural pollinators, carpenter bees, are hardly available because of high insecticide use in the agricultural fields and the destruction of the natural habitats," said lead author Klein.

The researchers say that the loss of key pollinators could boost the cost of production of some crops.Klein points to cities in Brazil, where the high prices for fruits and vegetables are pushing people to turn to less healthy alternatives.

"The stability of crop yields not only depends on pollination, but also on further ecosystem services," Klein added. "Therefore, we need landscapes carefully managed for a diversity of functionally important groups of organisms that sustain many important ecosystem services such as pollination, pest, pathogen and weed control, and decomposition."

The study was supported by the Sixth European Union Framework program.