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Ecology Notes

ecology: the study of the interactions of living things with each other and their physical environment

[Ecological Organization]

population: all the members of a species inhabiting a given location

community: all the interacting populations in a given area

ecosystem: the living community and the physical environment functioning together
                 as an independent and relatively stable system

biosphere: that portion of the earth where life exists

** The biosphere is composed of numerous complex ecosystems.

** An ecosystem involves interactions between abiotic (physical) and biotic (living) factors.  The members of the community in the ecosystem and environment must interact to maintain a balance.

An ecosystem is self-sustaining if the following requirements are met:

1. A constant source of energy and a living system capable of incorporating
    this energy into organic molecules.

2. A cycling of materials between organisms and their environment.

In all environments, organisms with similar needs may compete with each other for resources, including food, space, water, air, and shelter.  

Abiotic factors: those physical and chemical factors which affect the ability of
                        organisms to survive and reproduce

Some Abiotic Factors:

1. intensity of light         
2. range of temperatures
3. amount of moisture
4. type of substratum (soil or rock type)
5. availability of inorganic substances such as minerals
6. supply of gases such as oxygen, carbon dioxide, and nitrogen
7. pH

** Each of the prior listed abiotic factors varies in the environment and,
as such, may act as a limiting factor, determining the types of organisms
that exist in that environment.

Some examples:

1. A low annual temperature common to the northern latitudes
determines in part the species of plants which can exist in that area.

2. The amount of oxygen dissolved in a body of  water will help
    determine what species of fish live there.

3. The dry environment of desert regions limits the organisms that can live there.

carrying capacity -- the maximum number of organisms the resources of an area can support

The carrying capacity of the environment is limited by the available abiotic and biotic resources, as well as the ability of ecosystems to recycle the residue of dead organisms through the activities of bacteria and fungi.

Biotic factors: all the living things that directly or indirectly affect the environment

** Thus, the organisms, their presence, parts, interaction, and wastes are all biotic factors.

[Nutritional Relationships]

autotrophs: can synthesize their own food from inorganic compounds and a usable
                  energy source

heterotrophs: can NOT synthesize their own food and
                     are dependent on other organisms for their food

[Types of Heterotrophs]

saprophytes: include those heterotrophic plants, fungi, and bacteria which live on dead matter  AKA decomposers

herbivores: plant-eating animals

carnivores: meat-eating animals

omnivores: consume both plants and meat

(Types of Carnivores)

predators: animals which kill and consume their prey

scavengers: those animals that feed on other animals that they have not killed

[Symbiotic Relationships]

symbiosis: living together with another organism in close association

Types of (symbiosis): mutualism, commensalism, parasitism

commensalism: one organism is benefited and the other is unharmed (+,0)
                        ex. barnacles on whales, orchids on tropical trees

mutualism: both organisms benefit from the association
                ex. nitrogen-fixing bacteria on legume nodules,
                        certain protozoa within termites (also ruminants)

parasitism: the parasite benefits at the expense of the host
                ex. athlete's foot fungus on humans, tapeworm and heartworm in dogs

** Recent experimental research indicates that lichens may represent a controlled
parasitic relationship of the fungus on an algal host.

** If an ecosystem is to be self-sustaining it must contain a flow of energy.

** Those life activities that are characteristic of living organisms require an expenditure of energy.

** The pathways of energy through the living components of an ecosystem are represented by food chains and food webs.

** Producers convert the radiant energy of the sun into the chemical energy of food.

Food chain: involves the transfer of energy from green plants through a series of organisms with repeated stages of eating and being eaten

Food web: In a natural community, the flow of energy and materials is much more complicated than illustrated by any one food chain.

Since practically all organisms may be consumed by more than one species, many interactions occur along the food chains of any community
Food Web interactions)

producers: (plants) -- the energy of the community is derived from the organic compounds in plants  (grass in the web above)

primary consumer: (always a herbivore) -- feeds on plants (mice, grasshoppers, and rabbits in the web above)

secondary consumer: (always a carnivore) -- feeds upon other consumers (frogs, sparrows, snakes, and foxes above)  (The hawk is a secondary or 3rd level consumer depending on the availability of food.)

** Omnivores may be primary or secondary consumers.

decomposers: break down organic wastes and dead organisms to simpler substances (ex. bacteria of decay)

** Through decomposition, chemical substances are returned to the environment where they can be used by other living organisms.

Energy flows through ecosystems in one direction, typically from the Sun, through photosynthetic organisms, including green plants and algae, through herbivores, to carnivores, and finally decomposers.

** There is a decrease in the overall energy in each level as you move up the food web. This means that there is much more energy in the producer level in a food web than at the consumer levels.  Also, this means that there is more energy at the primary consumer level than at the secondary consumer level.

** Each consumer level of the food pyramid utilizes approximately 10% of its ingested nutrients to build new tissue. This new tissue represents food for the next feeding level.

** The remaining energy is lost in the form of heat and unavailable chemical energy.   Eventually, the energy in an ecosystem is lost and is radiated from the earth.

** Thus, an ecosystem can not survive without the constant input of energy from the sun.

biomass: amount of organic matter

** The decrease of energy at each successive feeding level (trophic level) means that less biomass can be supported at each level.

*** Thus, the total mass of carnivores in a particular ecosystem is less than the total mass of the producers. (A pyramid of biomass illustrates this.)



level D = producers

level C = primary consumers  

level B= secondary consumers

level A = tertiary consumers



Above is a typical representation of a NY State terrestrial energy pyramid.

succession: replacement of populations in habitat as it moves toward a stable state
                 (determined by changes in plants)

The environment may be altered in substantial ways through the activities of organisms, including humans, or when the climate changes.   Although these alterations are sometimes abrupt (ex. natural disasters), in most cases species replace others, resulting in long-term gradual changes in ecosystems.

** Ecosystems tend to change with time until a stable system is formed.
The type of ecosystem that is formed depends on the climatic limitations of a given geographical area.

pioneer organisms: the first organisms to inhabit a given location
                             (ex. lichens on bare rock)

** Pioneer organisms modify their environment -- thus establishing conditions
under which more advanced organisms can live.

(ex. seasonal dieback and erosion, for example, would create pockets of "soil" in the crevices and hollows of the bare rock inhabited by the lichen)

** Each community modifies its environment, often making it more difficult for itself and, apparently, more favorable for the following community which infiltrates the first
community over a period of years.

primary succession: the development of plant communities on newly formed habitats that previously lacked plants (ex. a lava flow)

secondary succession: return of an area to its natural vegetation following
                                  a disruption or removal of the original climax community

(ex. An example of a PRIMARY SUCCESSION  ex. (Adirondack Bog Succession)

1. water plants at pond edge
2. sedges and sediments begin to fill pond
3. sphagnum moss and bog shrubs fill pond  (Labrador tea & cranberries)
4. black spruce and larch
5. birches, maple, or fir


1. plowed field
2. annual grasses
3. shrubs and briers
4. cherries, alders, and birches
5. climax community -- Northern N.Y. (hemlock, beech, maple)
                               -- Southern N.Y. (oak, hickory)



climax community: a self-perpetuating community in which populations remain stable and exist in balance with each other and their environment

** The climax community of a region is always its dominant plant species.

**  Altered ecosystems may reach a point of stability that can last for hundreds or thousands of years.

** A climax community persists until a catastrophic change of a major biotic or
abiotic nature alters or destroys it.

(ex. forest fires, abandoned farmlands, floods, areas where the topsoil has been removed)

** After the original climax community has been destroyed, the damaged ecosystem is likely to recover in stages that eventually result in a stable system similar to the original one.

** Ponds and small lakes, for example, fill in due to seasonal dieback of aquatic vegetation and erosion of their banks, and eventually enter into a terrestrial succession terminating in a terrestrial climax communit



flora -- plant species -- dominate in the sense that they are the most abundant food sources

** Plant succession is a major limiting factor for animal  succession.

** Climax communities are identified by the dominant plant species -- the one that exerts the most influence over the other species present.

Competition: occurs when two different species or organisms living in the same environment (habitat) utilize the same limited resources, such as food, water, space, light, oxygen, and minerals.

** The more similar the requirements of the organisms involved,
the more intense the competition.

(Competitive Exclusion Principle)

If two different species compete for the same food source or reproductive sites,
one species may be eliminated. This establishes one species per niche in a community.

niche: the organism's role in the community


** In a self-sustaining ecosystem, materials must be cycled among the organisms
and the abiotic environment. Thus the same materials can be reused.

1. Carbon-Oxygen Cycle -- involves the processes of respiration and photosynthesis


3. Water Cycle: involves the processes of photosynthesis, transpiration, evaporation
                         and condensation, respiration,  and excretion

Evolutionary processes have resulted in a diversity of organisms and a diversity of roles in ecosystems.

biodiversity -- the differences in living things in an ecosystem

Increased biodiversity increases the stability of an ecosystem.

Increased biodiversity increases the chance that at least some living things will survive in the face of large changes in the environment.

monoculture -- planting one species over a huge area

Monoculture leaves an area more vulnerable to predation or disease.

What are some other reasons biodiversity is valuable?

1.   Biodiversity ensures the availability of a rich variety of genetic material that may lead to future agricultural or medical discoveries with significant value to humans.  (if this is lost we lose the sources of these materials for discovery)

2.  Biodiversity adds aesthetic qualities to the environment.