Standard Set 6.  Ecology
Ecology is the study of relationships among living organisms and their interactions with the physical
environment.  These relationships are in a constant state of flux, and even small changes can cuse effects
through the ecosystem.  Students in grades nine through twelve can be taught to think of ecology as
changing relationships among the components of an ecosystem. Students also need to recognize that
humans are participants in these ecosystem relationships, not just observers. A goal of classroom teaching
should be to develop a strong scientific understanding of ecology to establish the basis for making in-
formed and valid decisions.

6.  Stability in an ecosystem is a balance between competing effects. As a basis for
understanding this concept:
6. a.    Students know biodiversity is the sum total of different kinds of organisms and is affected
by alteration of habitats
Biodiversity refers to the collective variety of living organisms in an ecosystem. This structure is influenced
by alterations in habitat, including but not limited to climatic changes, fire, flood, and invasion by organisms
from another system. The more biodiversity in an ecosystem, the greater its stability and resiliency. The
best way for students to learn about ecology is to master the principles of the subject through careful study
and then to make firsthand observations of ecosystems in action over time.
Although field trips are the ideal way to implement this process and should be encouraged, even career
scientists often use models to study ecology. Local ecologists from government, private industry, or
university programs may also be willing to serve as guest speakers in the classroom. Viewing the Internetâ
€™s many virtual windows that show actual ecological experiments can also help students understand the
scientific basis of ecology.

6. b. Students know how to analyze changes in an ecosystem resulting from changes in climate,
human activity, introduction of nonnative species, or changes in population size.
Analysis of change can help people to describe and understand what is happen¬ing in a natural system
and, to some extent, to control or influence that system. Understanding different kinds of change can help
to improve predictions of what will happen next. Changes in ecosystems often manifest themselves in
predictable patterns of climate, seasonal reproductive cycles, population cycles, and migrations. However,
unexpected disturbances caused by human intervention or the introduction of a new species, for example,
may destabilize the often complex and delicate balance in an ecosystem.
Analyzing changes in an ecosystem can require complex methods and techniques because variation is not
necessarily simple and may be interrelated with changes or trends in other factors. Rates and patterns of
change, including trends, cycles, and irregularities, are essential features of the living world and are useful
indicators of change that can provide data for analysis. Often it is important to analyze change over time, a
process called longitudinal analysis.

6. c. Students know how fluctuations in population size in an ecosystem are determined by the
relative rates of birth, immigration, emigration, and death.
Fluctuations in the size of a population are often difficult to measure directly but may be estimated by
measuring the relative rates of birth, death, immigration, and emigration in a population. The number of
deaths and emigrations over time will decrease a population’s size, and the number of births and
immigrations over time will increase it. Comparing rates for death and emigration with those for birth and
immigration will determine whether the population shows a net growth or a decline over time.

6. d. Students know how water, carbon, and nitrogen cycle between abiotic resources and
organic matter in the ecosystem and how oxygen cycles through photosynthesis and respiration.
Living things depend on nonliving things for life. At the organism level living things depend on natural
resources, and at the molecular level, they depend on chemical cycles. Water, carbon, nitrogen,
phosphorus, and other elements are re-cycled back and forth between organisms and their environments.
Water, carbon, and nitrogen are necessary for life to exist. These chemicals are incorporated into plants
(producers) by photosynthesis and nitrogen fixation and used by animals (consumers) for food and protein
synthesis. Chemical recycling occurs through respiration, the excretion of waste products and, of course,
the death of organisms.

6. e. Students know a vital part of an ecosystem is the stability of its producers and
decomposers.
An ecosystem’s producers (plants and photosynthetic microorganisms) and decomposers (fungi and
microorganisms) are primarily responsible for the productivity and recycling of organic matter,
respectively. Conditions that threaten the stability of producer and decomposer populations in an
ecosystem jeopardize the availability of energy and the capability of matter to recycle in the rest of the
biological community. To study the interaction between producers and decomposers, students can set up
a closed or restricted ecosystem, such as a worm farm, a composting system, a terrarium, or an aquarium.

6. f. Students know at each link in a food web some energy is stored in newly made structures
but much energy is dissipated into the envi¬ronment as heat. This dissipation may be
represented in an energy pyram
id.
The energy pyramid illustrates how stored energy is passed from one organism to another. At every level
in a food web, an organism uses energy metabolically to survive and grow, but much is released as heat,
usually about 90 percent. At every link in a food web, energy is transferred to the next level, but typically
only 10 percent of the energy from the previous level is passed on to the consumer.

6. g.* Students know how to distinguish between the accommodation of an individual organism
to its environment and the gradual adaptation of a lineage of organisms through genetic change.
Living organisms may adapt to changing environments through nongenetic changes in their structure,
metabolism, or behavior or through natural selection of favorable combinations of alleles governing any or
all of these processes. Genetic and behavioral adaptations are sometimes difficult to identify or to
distinguish without studying the organism over a long time. Physical changes are slow to develop in most
organisms, requiring careful measurements over many years. Examining fossil ancestors of an organism
may help provide clues for detecting adaptation through genetic change. Genetic change can institute
behavioral changes, making it all the more complicated to determine whether a change is solely a
behavioral accommodation to environmental change.
Through the use of print and online resources in library-media centers, students can research the effects of
encroaching urbanization on undeveloped land and consider the effects on specific species, such as the
coyote (not endangered) and the California condor (endangered). Such examples can illustrate how some
organisms adapt to their environments through learned changes in behavior, and others are unsuccessful in
learning survival skills. Over a long time, organisms can also adapt to changing environments through
genetic changes, some of which may include genetically determined changes in behavior. Such changes
may be difficult to recognize because a long time must elapse before the changes become evident. Studies
of the origins of desert pup fish or blind cave fish may help students understand how gradual genetic
changes in an organism lead to adaptations to changes in its habitat.