Human Population Growing in Many Species-Rich Habitats

GIS Powers Population Action International Report

With the dawn of the new millennium come new environmental concerns. Species—from birds and frogs to insects and plants—are becoming extinct at least 1,000 times faster today than they did in the planet's prehuman past. Alarmingly, scientists expect the rate of species loss to accelerate during the 21st century. Indications are that human population and growth, which has increased dramatically over the past century, is a significant contributor to species extinction. But even with this understanding, many questions still exist.

In what ways can human population density and growth pose a risk to populations of other species and the ecosystems in which these species live, reproduce, and evolve? Where among the world's most species-rich ecological regions is population still growing, and where has human settlement in these zones become exceptionally dense? And can development policies and programs influence current population trends—particularly those that are putting the natural world at risk, without removing the right of individuals to make their own decisions about having a family?

More than a year and a half ago, Population Action International (PAI) set out to explore these questions by investigating the relationship between the ongoing growth of the human population and the dynamics of plant and animal life. As an organization, PAI advocates strategies that promise to improve the lives of individual women and their families while slowing the world's population growth, improving access to voluntary family planning and other reproductive health services, getting more girls into the classroom, and opening up greater economic opportunities to women. Its staff of 40 work in four areas: research, media, political affairs, and international advocacy. PAI's publication, Nature's Place: Human Population and the Future of Biological Diversity, is an all-purpose report; it serves as a handbook of facts and figures on species and habitat loss and features a guide to modern human demography, reviewing the scientific evidence that implicates human activity in the great extinctions of the recent past. But its most effective and attractive section-the centerpiece of the report—is a GIS analysis that generates the first-ever estimates of population size and growth in the most threatened, biologically rich regions of the terrestrial world—the 25 biodiversity hot spots.

map as described below
World population density (1995) and the 25 global biodiversity hot spots (outlined in red, numbered) and three major tropical wilderness areas (outlined in green, lettered).

What is a biodiversity hot spot? The concept was originated by British Ecologist Norman Myers over a decade ago and has been refined through collaboration with American Primatologist Russell Mittermeier and other scientists at Conservation International. To qualify as a hot spot, a region must be home to a high number of plant species unique to one particular place and found nowhere else in the world. Hot spots also must have 30 percent or less of their original vegetation left intact. Mittermeier and Myers have also mapped another set of less-threatened tropical forest regions that are biologically important. These regions—known as the major tropical wilderness areas—represent the last three remaining stretches of extensive, intact tropical forest: the Upper Amazon, the Congo Basin, and New Guinea. PAI's report looks at human population in the biodiversity hot spots as well as these three deep-forest regions.

2 maps of Madagascar--1995 and 2000 years ago
Madagascar is one of the most biologically unique spots in the world. Because of a lack of urban jobs and severe land shortages, Malagasy farmers have moved further upslope, burning the island's remaining tropical forests from the hillsides of its eastern region. Madagascar's woodlands now cover less than 20 percent of what existed from 15 centuries ago.

"We first realized that this part of the report would be possible," Jennifer Wisnewski, PAI's GIS specialist, told ArcNews, "when two important GIS events occurred nearly simultaneously. First, geographers at the National Center for Geographical Information Analysis (NCGIA) at the University of California, Santa Barbara, and the Center for International Earth Sciences Information Network (CIESIN) produced the Gridded Population of the World, 1995, which is a global population density data set. The second event—the completion of a hot spot boundary data layer by Conservation International—occurred soon after. When these two layers became available, we knew we had an opportunity to visually and numerically show the importance of ongoing human population growth as a factor in global biodiversity conservation."

Half the problem—the population density estimates—was solved using ArcView GIS and ArcView Spatial Analyst. To estimate population growth rates, the PAI research team searched through libraries, the Web, and foreign census sources to locate subnational population data corresponding to the political units that were identified using ArcView GIS and country maps.

2 maps of Lake Victoria, Africa, area, showing changes over past 50 years in national parks' isolation
Tanzania's Serengeti and Kenya's Maasai Mara national parks have become, over the past 50 years, isolated by agricultural settlement. To maintain Serengeti's mix of plant and animal species under conditions of increasing population density will likely demand greater efforts and financial resources.

How important is population? By 1995 more than 1.1 billion people were living in what are flagged as biodiversity hot spots. Perhaps even more significant for the future, the population density levels and growth rates within these species-rich ecoregions significantly exceed world averages. Population densities are still low in the major tropical wilderness areas, but these irreplaceable expanses of tropical forest are experiencing extremely rapid population growth—around two and a half times the world average. Apparently this growth is driven principally by intense migration, with help from rapid natural population growth occurring in the surrounding regions.

"Though most demographers might not even bat an eye after reviewing these findings, they caught biologists and environmental policy makers by surprise," said Richard Cincotta, an ecologist at PAI and a co-author of the report with Research V.P. Robert Engelman. "Biologists are now aware that where the planet's biological wealth is the most concentrated and the most threatened, human population is either denser than the world as a whole or growing faster than the world as a whole, or both. And if they read the report, some may connect basic development issues in the poorest countries of the world, such as reproductive health and girls' education, with the future of the orangutan, the harpy eagle, and the dragon orchid. We want policy makers to realize what we've realized—that the future of many of today's species rests, in part, on how much the world's governments decide to invest in the female of our own species."

This means both conservation programs and sound population policies will need to work in tandem in order to minimize both the loss of species and the impacts that such losses will have on human generations yet to come. The biodiversity hot spot concept and the GIS mapping featured in Nature's Place give development policy makers a guide to where their efforts might be best directed. One glimmer of hope: although world population is now over six billion and is still growing by 78 million annually (roughly a population the size of Germany's), its rate of annual growth is slowing dramatically and world population size could reach a plateau by the middle of this century. According to Cincotta and Engelman, this modern reproductive transition is well underway and could be speeded up if the richer nations meet their financial commitments to help the poorest nations of the world educate their girls, improve and promote their family planning programs, and elevate the status of women.

For more information contact Richard Cincotta, ecologist, PAI (tel.: 202-557-3406; e-mail:

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