Single way of living creates new danger for wildlife

www.guardian.co.uk Rise in individual households bodes ill for biodiversity, say scientists Tim Radford, science editor Monday January 13, 2003 The Guardian

The planet's wild creatures face a new threat - from yuppies, empty nesters, singletons and one parent families.

Biologists studying the pressure on the planet's dwindling biodiversity today report on a new reason for alarm. Although the rate of growth in the human population is decreasing, the number of individual households is exploding.

Even where populations have actually dwindled - in some regions of New Zealand, for instance - the numbers of individual households has increased, because of divorce, career choice, smaller families and longer lifespans.

Jianguo Liu of Michigan State University and colleagues from Stanford University in California report in Nature, in a paper published online in advance, that a greater number of individual households, each containing on average fewer people, meant more pressure on natural resources.

Towns and cities began to sprawl as new homes were built. Each household needed fuel to heat and light it; each household required its own plumbing, cooking and refrigeration.

"In larger households, the efficiency of resource consumption will be a lot higher, because more people share things," Dr Liu said.

He and his colleagues looked at the population patterns of life in 141 countries, including 76 "hotspot" regions unusually rich in a variety of endemic wildlife. These hot spots included Australia, New Zealand, the US, Brazil, China, India, Kenya, and Italy.

They found that between 1985 and 2000 in the "hotspot" parts of the globe, the annual 3.1% growth rate in the number of households was far higher than the population growth rate of 1.8%.

"Had the average household size remained at the 1985 level," the scientists report, "there would have been 155m fewer households in hotspot countries in 2000. By 2015, 233m more households are likely to be added to hotspot countries as a result of continued reduction in average household size alone."

Paradoxically, smaller households do not mean smaller homes. In Indian River county, Florida, the average area of a one-storey, single family house increased 33% in the past three decades, from about 1,800 sq ft before 1970 to an average 2,400 sq ft for those built since 1970.

Dr Liu's work grew from the alarming discovery that the giant pandas living in China's Wolong reserve were more at risk now than they were when the reserve was first established.

The local population had grown, but the total number of homes had increased more swiftly, to make greater inroads into the bamboo forests.

Only around 1.75m species on the planet have been named and described. Biologists estimate that there could be 7m, or even 17m, as yet to be identified.

But human numbers have grown more than sixfold in the past 200 years, and humans and their livestock are now the greatest single consumer group on the planet.

The world population will continue to soar, perhaps levelling off at around 9 billion in the next century. Environmental campaigners have claimed that between a quarter and a half of all the species on earth could become extinct in the next century.

Gretchen Daily of Stanford, one of the authors, said: "We all depend on open space and wild places, not just for peace of mind but for vital services such as crop pollination, water purification and climate stabilisation.

"The alarming thing about this study is the finding that, if family groups continue to become smaller and smaller, we might continue losing biodiversity - even if we get the aggregate human population size stabilised."