Biotic vs. Abiotic
Organisms with similar needs may compete with one
another for resources, including food, space, water, air, and
shelter. In any particular environment, the growth and survival of organisms depend on the physical
conditions including light intensity, temperature range, mineral availability,
soil type, and pH. Physical or non-living factors
such as these which influence living things are called abiotic
factors. Living factors which influence living
things are called biotic factors. Some
examples of biotic factors include disease and predation.
flows through ecosystems in one direction, typically
from the Sun, through photosynthetic organisms or
producers, to herbivores to carnivores and
decomposers. The chemical elements that make
up the molecules of living things pass through food webs
and are combined and recombined in different ways. At
each link in a food web, some energy is stored in newly
made structures but much energy is lost into the
environment as heat. Continual input of energy from
sunlight is required to keep this process
going. Energy pyramids are often used to
show the flow of energy in ecosystems.
The atoms and molecules on the Earth cycle among the living
and nonliving components of the biosphere. Carbon dioxide and
water molecules used in photosynthesis to form energy-rich
organic compounds are returned to the environment when the
energy in these compounds is eventually released by cells
through the processes of cell respiration and other life
activities. The number of organisms any
environment can support is called its carrying capacity.
The carrying capacity of an environment is limited by the
available energy, water, oxygen, and minerals, and by the
ability of ecosystems to recycle the remains of dead organisms
through the activities of bacteria and fungi. Living
organisms have the capacity to produce populations of
unlimited size, but available resources in their environments
are finite. This restricts the growth of populations and
produces competition between organisms.
Organisms interactions may be competitive or
beneficial. Organisms may interact with one
another in several ways. Some of these
relationships include producer/consumer, predator/prey,
or parasite/host relationships. Other organisms
interactions include those in which one organism may
cause disease in, scavenge, or decompose
to evolution, there is a great number of different organisms
which fill many different roles in ecosystems. The
number of different organisms in an ecosystem is called
biodiversity. Increased biodiversity increases the
stability of the ecosystem. Biodiversity also
ensures the availability of diverse genetic material that may
lead to future discoveries with significant value to
humans. As diversity is lost, potential sources of these
materials for these discoveries may be lost with it. A great diversity of species provides for variations which
increase the chance that at least some living things will
survive in the face of large changes in the environment.
environment may be changed greatly through the
activities of organisms, including humans, or when
climate changes. Although sometimes these changes occur
quickly, in most cases species gradually replace others,
resulting in long term changes in
ecosystems. These changes in an
ecosystem over time are called ecological succession.
Ecosystems may reach a point of stability that can last
for hundreds or thousands of years. If a disaster
occurs, the damaged ecosystem is likely to recover in
stages that eventually result in a stable system similar
to the original one.
This page and the links at the left are designed to aid students in
reviewing the following topics pertaining to ecology which will appear on the New
York State Living Environment Regents Examination; biotic vs.
abiotic factors, energy flow, material cycles, organism
relationships, biodiversity, and ecological
succession. In addition, students may test their knowledge of the material presented here by accessing multiple-choice questions from past Regents Exams.