Pool- A major receiver of an element or compound. There is continuous movement of the element or compound in and out of the pool. Sink- A depository of an element or compound that is not recycled. A certain amount of the chemical passes in and is not recycled. A sink can become a limiting agent on the continued growth or health of an ecosystem, unless it can be tapped again. The retapping of a sink is usually through geological action such as movement or erosion.

Two examples of biochemical cycles:

A: Carbon Cycle Carbon is a vital element in all life systems, it is the basis of organic chemistry and is a major part of all sugars, proteins, fats, etc. Carbon Dioxide is abundant in water in the forms of carbonic acid and bicarbonate. Plants "fix" the carbon from the water into organic compounds through the process of photosynthesis. This carbon is transferred to animals by herbivory and predation. Respiration and bacterial action return the carbon to the pool. When carbon is deposited into the skeletons of corals or the shells of mollusks, it does not return to the pool. The coral skeletons and shells are a "sink". B: Nitrogen Cycle Nitrogen is also a major constituent in organic chemistry found in many of the basic amino acids and a required element in photosynthesis. Air is the major pool reserve of nitrogen, but in its raw form it is unusable to most organisms. Nitrogen must first be converted into a nitrogen compound, "fixing" by plants. This is done through a symbiotic relationship between bacteria and plants. Once the bacteria and plants have "fixed" the nitrogen, the nitrogen compounds are available for all the other organisms to use in their biological processes.

COMMUNITY STRUCTURE

The species that make up the communities in ecosystems varies tremendously worldwide. While there are always the same trophic levels in every ecosystem, the species that constitute those trophic levels vary both regionally and temporally (in time). The individuals of the species are in constant competition for the limited resources in their environment. All the species in an ecosystem must deal with each other and the local environmental stresses placed upon them such as floods or droughts, changing weather patterns, fires, earthquakes, and all the other natural disaster we can think of. The different species have their particular strengths and weaknesses in regard to dealing with these environmental stresses. The group of species that are the best suited for dealing with a particular ecological stress are generally those that survive to face the next environmental stress. If a particular species survives in an environment for a long enough period of time, natural selection of its best suited individuals will make the species better adapted for its local environment. Natural selection does not remember past successes though; if the individuals of a species face changing environmental conditions that they are not adapted for, they may not survive, and the species may go extinct, to be replaced by a species that is better suited at that time for the environment.

Two general ecological success strategies have evolved for the continued propagation of species. These strategies are known as Equilibrium and Opportunistic, and they are most concerned with how frequently the species will face environmental disturbances.

The Equilibrium success strategy is best suited for ecosystems with few environmental disturbances. The species which follow the equilibrium success strategy are usually the larger organisms. They have few reproductive periods per year, slow development, low death rate, are highly mobile, but they have low recruitment into and later colonization time of newly disturbed environments. As they survive in an environment for a long time, natural selection of the individuals can make the species highly adapted to their environment. In the oceans, these species are usually Lecithotrophic, with larger, fewer, more costly and less dispersed eggs. The problem with the equilibrium success strategy is when environmental stress or change does occur, its followers are not able to adapt to the stress through natural selection of the best suited individuals. The infrequent reproductive periods and slow development slows down the evolution process. The species may become extinct before it has had the opportunity to adapt to the new environment. The Opportunistic success strategy is best suited for ecosystems with frequent environmental disturbances. The opportunistic species are usually small compared to the equilibrium species. They have many reproductive periods, a fast development time, a high rate of recruitment into new environments, and are the first to colonize a freshly disturbed environment. These species also face high death rates, low mobility, and have small body sizes. The high rate of reproduction and development allows these species to quickly become better adapted to new environments. In the oceans, these species are usually Planktotrophic, with smaller, more numerous, easy to produce and highly dispersed eggs. The opportunistic species are the first to find and colonize a freshly disturbed environment and enjoy early success in the environment. With their high rate of evolution, they are able to continually survive in environments which face frequent environmental stresses. If the environment does not face another environmental stress for a long time after the opportunistic species have settled, then equilibrium species will usually gain the upper hand and soon crowd out the opportunistic species. Opportunistic species have much lower juvenile and adult death rates so they are the better competitors in a non-changing environment. As soon as there is environmental stress, the opportunistic species gain the upper hand, and the battle for species survival continues.

The way that each species happens to go about getting its necessary resources and how it deals with other organisms it encounters is known as the species Niche. A Niche is the role an organism plays in a community, the sum of the characters that determine the position of an organism in its ecosystem. This includes all chemical, physical, spatial, and temporal factors required for survival of that species and which limits its distribution and growth. A niche is characteristic of a species, and no two species occupy the same niche in the same environment in the presence of each other. However, a different species may occupy the same niche in the absence of the normal occupant from that habitat. The Fundamental Niche is the range within which a species can exist. Whereas the Realized Niche is the actual distribution of the species in the real world. The Habitat is the part of the environment occupied by an animal.

Leibig's Law of the Minimum Each species in a community has certain tolerances with respect to environmental factors. If the limit of tolerance is exceeded by a given factor (ie. Temperature) the species will be absent in the community.Each species requires a certain minimum amount of materials. If the concentrations of these necessities (ie. Nitrate) falls below the minimum then the species disappears.The above is true even if all other factors and substances are favorable for the species.

GENERALISTS AND SPECIALISTS

A species fundamental niche can be wide or narrow, meaning that it can have great latitude in what kind of actual environment it can exist in, or it can have very specific needs that the environment must posses in order for the species to exist in that environment.
A generalist has a very wide fundamental niche, and can exist in many different local environments. Generalists make great opportunistic species, as their widely dispersed eggs can settle and succeed in many of the new environments they may reach.
A Specialist has a narrow fundamental niche. The number of environments a specialist can occupy is much lower than that of a generalist. Specialists are often equilibrium species; a long period without environmental disasters allows them to become very well adapted to a particular environment, which can enable them to outcompete the generalists in resource allocation as long as the environmental conditions remain constant.

There is room and need in the world for both generalists and specialists.


SPECIES DIVERSITY

Some communities have only a few resident species, such as the tundra on a high mountain top. Other communities have literally hundreds of species per square meter, such as a rainforest or a coral reef. Most communities have a characteristic species structure that consists of a few numerically abundant species, known as the Dominants, and many rare species.

Species structure in ecological communities can be measured by:

Species Richness: the total number of species in a community.

Species Diversity: combines into a single index a measure of both the number of species [Richness] and the distribution of the total number of individuals among the species [Evenness].

Knowing an ecosystem's richness and diversity is very important for understanding its complexity and health. These indexes can be compared from location to location, and a great deal of information can be inferred about the frequency and severity of the stresses placed upon the ecosystem just from the indexes. By following the indexes for a location temporally [through time] we can judge the general health change of the ecosystem.



HIGH SPECIES DIVERSITY MAINTENANCE

There are two major competing schools of thought on how high species diversity can be maintained for an environment.

EQUILIBRIUM:

Species composition in a community is usually in a state of equilibrium.

I.

High diversity is due to a large number of habitats and/or finely divided narrow niches maintained by various feedback mechanisms (i.e., Niche Diversification).

II.

Stable nature of the physical environment allows equilibrium to be maintained.

INTERMEDIATE DISTURBANCE:

Communities and species are rarely in a state of equilibrium.

I.

High species diversity is maintained through continual or gradual environmental change and disturbance.

II.

Promotes a changing species composition through the presence of many species that are not highly specialized.

Predictions of Intermediate Disturbance Model:

I.

Communities which experience very frequent disturbances that kill most or all of the resident species would tend to be colonized by only those few species that happen to have the ability to attain maturity and reproduce quickly before the next catastrophic event.

II.

Areas experiencing infrequent or small disturbances on long time intervals would also have low diversity; the most efficient competitors have had time to eliminate most or all other species and take over the community.

III.

Only when the disturbances are intermediate in frequency does species diversity increase; enough time is available to permit establishment of a variety of slower growing and reproducing species, and the interval between disturbance events is short enough to avoid competitive exclusion.

** Ample evidence exists for both schools of thought, depending on the particular environment and the methods used to investigate the models.

** On a global scale, our biospheres richness and diversity indexes have started into a major downward trend as we loose many species to extinction and cover vast areas with monoculture crops [crops of the same species]. This has happened five previous times in the Earths history, and is known as a major extinction event, such as the way the dinosaurs departed.



COMMUNITY SUCCESSION

Communities of organisms are not static units, they change in structure and composition with season and over longer periods of time. Some communities change in an orderly fashion over periods of many years until they reach a stage that perpetuates itself indefinitely as long as the climate does not change or there is no disturbance.

There are three major models as to how this community change takes place.


Facilitation Model of Succession:

Each community modifies the environment in turn making it suitable for the next community. Orderly change to the physical environment is known as Ecological Succession, and the terminal, persistent community is the Climax community.

Inhibition Model of Succession:

No species is competitively superior, whichever species gets to a site first holds it against later settlers. The succession is not an orderly predictable process, and generally proceeds from short lived to long lived species. There is no climax community.

Tolerance Model of Succession:

This model is intermediate between the other two. Early colonizing species are not necessary, any species can start succession. Community change occurs as species that are more tolerant, or more competitively superior, prevail.

**Marine Environments tend to follow the second and third models. In many cases the initial occupier does not modify the environment to make it unsuitable for them and more suitable for subsequent organisms. They may even prevent the occupation of an area by more competitively superior organisms, and their is no climax community.

SYMBIOSES


POSETIVE SYMBIOSES

SYMBIOSIS :The living together of two organisims of different species.

MUTUALISM : A symbiotic relationship between two species that is benificial to both (host and symbiont).

COMMENSALISM : A symbiotic relationship between organisms of two different species in which one species benefits and the other is unaffected

NEGATIVE SYMBIOSES (ECOLOGICAL CONTROL AND REGULATION)

The makeup of populations, communities, and ecosystems are all regulated by various factors.

-Energy -Environment [Climate] -Interactions among component species -Tolerance limits on population ranges

All systems on earth are limited by the amount of energy available from the sun. This is the greatest limitation of all.


Limits on populations

All species possess the reproductive potential to produce much larger populations than are observed under natural conditions. Given unlimited resources, a population could quickly grow to exponential proportions. Nature has control mechanisms so that if a population explosion occurs, it is quickly reduced.

POPULATION CONTROLS:

I. Competition II. Predation III. Parasitism IV. Disease

Competition: interaction among organisms for a necessary resource that exist in short supply.

    I. Intraspecific - among individuals of the same species.

    II. Interspecific - among individuals of different species, usually two closely related species.

The organisms could be competing over light, food, nutrients, water, or space, etc.

Options:

A. Share limited resource, both individuals are hampered, which inhibits their growth, development, and reproduction. B. One excludes the other, controlling population. Competition Exclusion Principle: No two species with the same requirements can coexist in the same place at the same time. Complete competitors cannot coexist. This leads to niche diversification, where the competitors will diverge on their similar needs, a major factor in the formation of additional species.

As population increases, competition increases as a limited resource becomes scarcer. Increased competition increases the stress on organisms, absorbing energy used for growth and reproduction, effectively limiting populations.


Predation:The consumption of one species by another. Consumer is the predator, victim the prey.

I.

A predator may be most the important factor in the regulation the #'s of prey species. Removal of the predator will have a marked effect on prey population, causing it to increase dramatically.

II.

The predator may have little effect on prey population. The predator may not be the main factor limiting the preys population. The prey may be missing other elements in its environment that prevent a population explosion. In some communities, the existence of Keystone species has been shown. A keystone species is one of the most important species populations in a community; its affects are felt by most of the other populations in the community. Removal of the keystone species can cause great changes in the community structure even though most species are not the prey of the keystone species.

Parasitism and Disease: As populations expand, the opportunity for parasitism and disease greatly increases as the organisms will be living closer together, polluting their local environment with waste and competing strongly over resources. They will become weakened and highly susceptible to the effects of parasitism and disease, lowering their populations. Little is known about the specifics of these effects in the marine environment, but we all know how it is affecting man.



Ecology

Biotic Factors