Men turn from penny-pinching savers to big spenders if they think there is a shortage of women around them according to new research.

When men believe that competition for wives and girlfriends is increasing they become impulsive with their money and even increase their borrowing.

To test their theory that sex ratios affect economic decisions, researchers at Minnesota University"s Carlson School of Management told volunteers to read articles that described their local population as having more men or more women.

They were then asked to indicate how much money they would save each month from a pay cheque, as well as how much they would borrow with credit cards for immediate expenditures.

When led to believe women were scarce, the savings rates for men decreased by 42 percent.

Men were also willing to borrow 84 percent more money each month.

In another study, participants saw photographs showing more men, more women or were neutral.

After looking at the photographs, participants were asked to choose between receiving some money tomorrow or a larger amount in a month.

When women were scarce in the photos, men were much more likely to take an immediate $20 rather than wait for $30 in a month.

Study leader Vlada Griskevicius said: "What we see in other animals is that when females are scarce, males become more competitive. They compete more for access to mates.

"How do humans compete for access to mates? What you find across cultures is that men often do it through money, through status and through products.

"It turns out we have a lot in common with other animals. Some of our behaviours are much more reflexive and subconscious. We see that there are more men than women in our environment and it automatically changes our desires, our behaviours, and our entire psychology."