In the mid-eighteenth
the Swedish botanist Carolus von Linné (1707-1778) better known
as Linnaeus, invented the classification scheme of the living world that
we still use. Early scholars such as Aristotle and Pliny had also invented
such classifications, some of which still hold. For example, Aristotle
first classified dolphins as mammals! Pliny (23-79 AD) wrote a 37-volume
Natural History, classifying all reported living beings! Linnaeus'
scheme gave every living being two names. The first is its genus,
the group to which it belongs, and the second the species, describing
the subclass in the genus. Thus the present species of humans are Homo
sapiens, others like Homo erectus and Homo habitis being
extinct. The genus and species have Latin names, with the genus term written
members of the same species in a particular area at the same time constitute
a population, and the area is called the habitat of the
species. Different species may live together in a habitat, forming a community.
The different species in a community might interact through a food web
or exist in symbiosis. Symbiosis is a state
in which members of different species live in physical contact, mutually
benefiting from each other's presence. Lichens that occur on exposed rocks
throughout the world are a wonderful example of symbiosis: They are usually
a fungus and an algae (or bacterium) living symbiotically. The photosynthetic
algae provide nutrients for the fungus. The fungus seems to provide support
and the ability to extract essential minerals from the rock. Because of
this pairing, lichens can colonize extreme environments where the fungi
or algae alone cannot exist. These include the rocks of Antarctica and
of Donegal, Ireland. The lichens scraped off from rocks in Donegal is
used to color the woolen material called Donegal tweed.1
are the several habitats that co-exist in a particular climatic area.
Tropical rainforests and coniferous forests are examples of biomes. Biosphere
is the general term for the highest organizational level in which life
exists, ranging from the very depths of the oceans to several thousand
meters into the tropospheric region of the atmosphere, and including land
and Ecological Balance
are living and nonliving components of an area that include the habitat
and the physical and chemical environment. The classic definition of an
ecosystem was stated in 1953 by Odum: any unit that includes all organisms
(i.e., community) in a given area interacting with the physical environment
so that a flow of energy leads to a clearly defined structure, biotic
diversity, and materials cycles. [INDIRA - I don't
have a reference for this, because it came from Sharon's modules. Should
we just take it out?]
do we mean by "ecological balance," "balance of nature,"
or "ecosystem stability"? Balance and stability in this context
are different from a static condition in which there is no change. Nature
is continuously changing, and especially over periods of thousands of
years, changes substantially. In his book, Discordant Harmonies,
Daniel Botkin writes, "...every thousand years a substantial change
occurred in the vegetation of the forest, reflecting in part changes in
the climate and in part the arrival of species that had been driven south
during the ice age and were slowly returning."2
The forest he is referring to is in the western region of northern Minnesota
and southern Ontario, which Botkin studied in detail.
this difficulty of defining balance, and the fact that balance or stability
occurs over different time scales, ecologists talk of "ecological
stability" or "resilience." For each of these terms, one
may focus on one or two species and their change over time. Most ecologists
study population ecology or community ecology. In general, the stability
of 10 to 100 species over time scales of 10 to 1000 years is considered
when talking of stability. Over this time, populations may remain in an
equilibrium. Population resilience is defined as the rate at which the
population return to equilibrium after it is disturbed.
1A-D show a representation of the progress of the Earth's ecosystems as
we progress from prehistoric times, through hunter-gatherer societies
and agricultural societies, to an ecosystem in which industrial activities
dominate. In Figure 1A, the different levels of the ecosystem depend upon
the plants, the primary producers of nutrients from H2O and
CO2 using the sun's energy. As we go from 1A to 1D the role
and impact of humans increase. In Figure 1D, human industrial activity
and pollution dominate. As the human-dominated fraction of the system
increases, we see the shrinking of the other levels, representing loss
in biodiversity and even species extinction.3
1A: Trophic levels in an ecosystem.
1B: Ecology of a hunting-gathering economy.
1C: Ecology of an agricultural economy.
1D: Ecology of an industrial economy.
Clark, Mary E. Ariadne's Thread. St. Martin's Press, New
York, 1989. Reprinted with permission of Macmillan Ltd..
Johnjoe. Quantum Evolution, Norton: New York, 2000.
Botkin, Daniel. Discordant Harmonies, Oxford University Press:
New York, 1990. p. 62
Clark, Mary E.. Ariadne's Thread, St. Martin's Press: New York,