xxxii The Environmental Debate
driving these now harder-to-find fish to the brink of extinction. With fishermen harvesting fewer and
smaller fish, governments are struggling both to protect the fish and to keep fishermen employed. Con-
flicts over how best to manage regional fisheries pit biologists who propose catch limits to allow the
replenishment of fish stocks against fishermen who need to earn a living.
There is now no question that the growing quantity of CO2 in the atmosphere has resulted in a huge
increase in the acidity of the ocean.^10 While organisms that construct carbonate shells (such as shellfish)
and other calcifying species (such as corals) are undoubtedly being affected by this acidification, many
of its other consequences for marine life are still unknown.
Also not yet known are the long-term consequences of oil spills and leaks such as the Deepwater
Horizon-British Petroleum leak in the Gulf of Mexico.
THE LOSS OF BIODIVERSITY
The earth is populated with billions of different species of living things, ranging from an enormous vari-
ety of bacteria to hundreds of species of orchids to a multitude of different kinds of primates, including
humans. Where and how each species lives is a product of geologic and climatic factors as well as its
interactions with other living things in its habitat.
The biologically diverse organisms in a habitat are dependent on one
another for both food and the well-being of the ecosystem that they share. This complex interde-
pendence of living things results in there being a maximum and a minimum number of each species that
can exist within a particular ecosystem without upsetting what has been called the “food chain”, the
“web of life”, and the “balance of nature.”
Changes in the populations of member species that live in particular habitats have occurred naturally
since the beginning of life on Earth. Climatic factors, such as fluctuations in rainfall and temperature,
and geologic upheavals, such as volcanic eruptions and earthquakes, can cause the decline, extinction, or
movement of species. The introduction of invasive foreign species, which can be brought as seeds in the
feathers, fur, or feces of migrating species or result from animal migrations caused by geological upheav-
als or climatic changes, may also cause species extinction and result in disruptions in the food chain.
Invasive species can also be brought by people, who may carry an organism from a native habitat where
it has numerous enemies to a new setting where it has few or no predators.
Humans, by making major alterations in the natural environment and by replacing a varied environ-
ment with one that is much more uniform, have been responsible for the extinction of numerous species.
Towns and cities replace wild habitat; farmers, seeking to maximize food supply or income, grow only
edible or cash crops and may eliminate all other plants from the land; the timber industry clear-cuts
whole forests of diverse species of trees and then plants new forests that contain only a single species. As
the habitat becomes more homogeneous, the number and variety of species that can be sustained by it
grows smaller. The rate of species extinction, which has accelerated as the human population has grown
and as human civilization has developed and expanded around the world, is unparalleled in the recent
history of the Earth.
There are multiple reasons for concern about species extinction and the resultant loss of biodiversity.
First, as diversity is lost, the population balance is disturbed and the resilience of the remaining species in
the entire area is reduced. As a result, their population may decrease. Then, if some kind of blight occurs
that affects a particular species, the loss of that species is likely to have a much more devastating effect
on the whole area. Second, the loss of biodiversity results in the loss within species of individuals that
carry varied genetic material. The wild strains of many domesticated plants retain genetic material that