Page 305 - Environment: The Science Behind the Stories

ThE SCIENCE BEhIND ThE STORY

Wildlife Declines world’s fastest rates of human popula-
in African Reserves tion growth, and this has intensified
pressures on wildlife and ecosystems:
Tanzania and Kenya have some of the • Settlements have increased as
largest and most famous parks and nomadic Maasai herders have be-
protected areas in the world, with the come sedentary and as people from
greatest variety and density of large elsewhere have moved in.
mammal species to be found any- • Farmers convert grasslands to crops
where. The parks are generally well Zebras in Serengeti National Park (especially wheat), and this destroys
managed and well funded. Yet even habitat for grazers such as antelope
these places of refuge are not immune and wildebeest and for the preda-
to pressures from rising human popula- Population declines were greater tors that follow them.
tion, development, and resource use. outside of parks and in areas that • Livestock are competing with wild
For several decades, biologists received less protection. However, even grazers for food on the grasslands.
and park managers have censused within the boundaries of well-protected • People are killing animals for food.
wildlife in and around the parks and reserves, many species decreased in Impoverished residents poach ani-
reserves. In recent years, researchers number. mals for their own subsistence, but
have begun to analyze these long-term Why are animals declining? For “bushmeat” is also sold to wealthy
data sets to assess population trends decades East Africa has had one of the diners in cities as far away as Europe.
of the large mammals of the East
African savanna. These studies are In Kenya, researchers are see-
finding that most animals are declin- 60 Declining ing similar patterns. As in Tanzania,
ing in number—inside the parks and Increasing Kenyan scientists and park managers
reserves as well as outside. 50 have been censusing wildlife by air-
In Tanzania, several government plane, road, and foot for decades, and
agencies and nonprofit groups have 40 recently researchers have taken a hard
collaborated to census mammals by look at the accumulated data.
airplane. These aerial surveys began in Percent of species significantly declining or increasing In 2009, conservation biologist
Serengeti National Park in the 1970s 30 David Western and two colleagues
and expanded to other parks in the reviewed 30 years of data from aerial
1980s. In 2006, Chantal Stoner and 20 surveys conducted from 1977 to 2007
six colleagues from Tanzania and from across Kenya’s rangelands, which
the University of California at Davis 10 comprise three-quarters of the nation’s
compiled and analyzed data on land area. In most locations, Western’s
25 species over a 10-year period 0 group found downward trends in the
(roughly 1990–2000) from eight regions, Wet season Dry season populations of most species. Cycles of
each centered on a major park. rainfall and drought affect grazing mam-
Across the eight regions in wet and Figure 1 across Tanzania’s protected mals, but statistical analysis of the data
dry seasons for all species, this team areas, more animals have decreased in indicated that the long-term declines
number than have increased. Data are
found that population declines outnum- combined from six locations, from Stoner, C., et transcended short-term effects due to
bered increases by more than 10 to 1 al., 2006. Changes in large herbivore populations rain or drought.
(Figure 1). In the Serengeti region, five across large areas of Tanzania. African Journal of Moreover, the populations sur-
species declined while two increased. Ecology 45: 202–215. veyed by Western’s team were trending

Invasive species Introduction of non-native species intentional. In Lake Victoria west of the Serengeti, the Nile
to new environments, where some may become invasive perch was introduced as a food fish. Within years it spread
(pp. 106–107), can push native species toward extinction throughout the vast lake, preying on and driving extinct doz-
(Table 11.2). Some introductions are accidental. Examples ens of native species of cichlid fish from one of the world’s
include aquatic organisms, such as zebra mussels, transported most spectacular adaptive radiations of animals. The Nile
in the ballast water of ships (Chapter 4); animals that escape perch is providing people food, but at a significant ecologi-
from the pet trade; and weeds whose seeds cling to our socks cal cost. People everywhere have long brought food crops and
304 as we travel from place to place. Other introductions are animals with them as they colonized new places, and today

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