Page 80 - Environment: The Science Behind the Stories

Hakalau and many other ecosystems throughout the world. animals in the area that it scavenges for food. For a whale,
As new technologies allow scientists to learn more about the water temperature, salinity, and the density of marine
complex dynamics of natural systems at a global scale, ecolo- microorganisms might be critical characteristics. Each spe-
gists are increasingly expanding their horizons beyond eco- cies assesses habitats differently because each species has
systems to the biosphere as a whole. different needs.
In the remainder of this chapter we explore ecology up Habitat use is important in environmental science because
through the population level. In Chapter 4 we examine com- the availability and quality of habitat are crucial to an organ-
munity ecology, and in Chapter 5 we consider ecology at the ism’s well-being. Indeed, because habitats provide everything
levels of the ecosystem and biosphere. an organism needs, including nutrition, shelter, breeding sites,
and mates, the organism’s very survival depends on the avail-
Each organism has habitat needs ability of suitable habitats. Often this need results in conflict
with people who want to alter or develop a habitat for their
At the level of the organism, each individual relates to its own purposes.
environment in ways that tend to maximize its survival and
reproduction. One key relationship involves the specific envi- Niche and specialization are key
ronment in which an organism lives, its habitat. A species’
habitat consists of the living and nonliving elements around it, concepts in ecology
including rock, soil, leaf litter, humidity, plant life, and more. Another way in which an organism relates to its environment is
The ‘akiapo¯ la¯ ‘au (Figure 3.12) lives in a habitat of cool, moist, through its niche. A species’ niche reflects its use of resources
montane forest of native koa and ‘o¯ hi‘a trees, where it is high and its functional role in a community. This includes its con-
enough in elevation to be safe from avian malaria. sumption of certain foods, its role in the flow of energy and
Each organism thrives in certain habitats and not in oth-
ers, leading to nonrandom patterns of habitat use. Mobile matter, and its interactions with other organisms. The niche is
a multidimensional concept, a kind of summary of everything
organisms actively select habitats in which to live from among an organism does. The pioneering ecologist Eugene Odum
the range of options they encounter, a process called habitat once wrote that “habitat is the organism’s address, and the
selection. In the case of plants and of rooted animals (such as niche is its profession.”
sea anemones in the ocean), whose young disperse and settle Organisms vary in the breadth of their niches. Species
passively, patterns of habitat use result from success in some with narrow breadth, and thus very specific requirements, are
habitats and failure in others. said to be specialists. Those with broad tolerances, able to use
Habitats are scale dependent. A tiny soil mite may use less
than a square meter of soil in its lifetime. A vulture, elephant, a wide array of resources, are generalists. A native Hawaiian
honeycreeper like the ‘akiapo¯ la¯ ‘au (see Figure 3.12) is a
or whale, in contrast, may traverse miles upon miles of air, specialist, because its unique bill is exquisitely adapted for
land, or water in just a day. Species also may have different feeding on grubs that tunnel through the wood of native trees.
habitat needs in different seasons; many migratory birds use In contrast, the common myna (a bird introduced to Hawai‘i
distinct breeding, wintering, and migratory habitats. from Asia) is a generalist; its unremarkable bill allows it to
The criteria by which organisms favor some habitats
over others can vary greatly. The soil mite may assess avail- eat many types of foods in many types of habitats. As a result,
the common myna has spread through virtually all areas of
able habitats in terms of the chemistry, moisture, and texture the Hawaiian Islands where native birds have disappeared and
of the soil and the percentage and type of organic matter. where human development has altered the landscape. Today it
The vulture may ignore not only soil but also topography is one of Hawaii’s most numerous birds.
and vegetation, focusing solely on the abundance of dead
Specialists succeed over evolutionary time by being
extremely good at the things they do, but they are vulnerable
when conditions change and threaten the habitat or resource
on which they have specialized. Generalists succeed by being CHAPTER 3 • Ev ol u T i on, Bi odiv ER si T y, A nd Po P ul AT i on E C ology
able to live in many different places and to withstand vari-
able conditions, but they may not thrive in any one situation
as much as a specialist would. An organism’s habitat prefer-
ences, niche, and degree of specialization each reflect adapta-
tions of the species and are products of natural selection.

Population Ecology

Individuals of a species that inhabit a particular area make up
Figure 3.12 The ‘akiapo¯ la¯ ‘au lives in a habitat of cool, a population. Species may consist of multiple populations that
moist, native forest on the slopes of Hawaiian volcanoes. are geographically isolated from one another. This is the case
It fills a unique niche by virtue of its odd bill, whose short, straight with Hawaii’s state bird, the ne¯ne¯ , a goose that grazes in open
bottom half, and long, curved top half allows it to specialize on grassy areas (see Figure 3.1d). Originally common throughout
digging grubs out from native trees. the Hawaiian Islands, the ne¯ne¯ (pronounced “nay-nay”) was 79

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