ECOSYSTEMS and BIOMES

Ecosystems vary according to the predominant types of living and nonliving elements available. Ecosystems may be classified along two major types:

• natural or those which have existed and are regenerated through natural processes; and


• man-made or those which have been formed through man's intervention.

Whether natural or man-made, ecosystems are basically characterized by the continuity of life processes brought about by the presence of life support systems that move around in cyclic paths.

Most of us are confused when it comes to the words ecosystem and biome. What's the difference? There is a slight difference between the two words. An ecosystem is much smaller than a biome. Conversely, a biome can be thought of many similar ecosystems throughout the world grouped together. An ecosystem can be as large as the Sahara Desert, or as small as a puddle or vernal pool.

Ecosystems are dynamic interactions between plants, animals, and microorganisms and their environment working together as a functional unit. Ecosystems will fail if they do not remain in balance. No community can carry more organisms than its food, water, and shelter can accomodate. Food and territory are often balanced by natural phenomena such as fire, disease, and the number of predators. Each organism has its own niche, or role, to play.

The types of marine ecosystems commonly used by fisheries and aquaculture are: coastal waters (including estuaries and lagoons), coral reefs, soft bottom continental shelves, upwelling continental shelves, open oceans and polar oceans.

ESTUARY

Coastal waters

(including estuaries and lagoons) constitute the interface between the marine and the freshwater environments, and between the continents and the oceans. Estuaries are broad portions of rivers or streams near their outlet, influenced by the marine water body into which they flow. As such, estuaries are semi-enclosed coastal bodies of brackish water with free connection to the open sea. The demarcation between an estuary and the sea is generally the mean tidal level. Similar to coastal ponds or lakes, lagoons are shallow brackish water bodies with one or more restricted outlets to the sea. Estuaries and most lagoons receive water from land and therefore can be heavily impacted by land-based sources of pollution through inland runoffs. Coastal waters are the main area of development for artisanal fisheries and play a key role as nursery grounds for a wide range of marine species and are the principle cause of conflict between artisanal and industrial fisheries.

Coral reefs

Coral reefs are the dominant type of ecosystems in tropical areas with low upwelling or freshwater inputs. Coral reef ecosystems occur in areas where sunlight can reach reef-building corals on solid surfaces and stable sediments. They are fragile, vital for island countries, richest in biodiversity and heavily impacted by inland runoffs and inland activities (e.g. deforestation or inappropriate agricultural practices). Coral reefs are particularly sensitive to destructive fishing methods using explosives and poisons. They are mainly used by artisanal fisheries.

In the warm, shallow waters around the islands, we find the corals and the coral reefs. Corals are micro organisms, so, they are the smallest animals you can imagine. These 'microscopic small' organisms produce (secrete) lime which form miniscule small holes (cavities). These miniscule small holes serve as their living room. The corals use their tentacles to trap passing plankton. Plankton is the food for corals. As generations of corals die, the lime skeletons of the dead micro organisms will build-up the coral reefs. It takes a coral reef 5 years to grow one inch. The forms of the reefs we can see today, are the result of a natural process of millions of years. These limestone forms are the environment (the habitat) for the many different en coloured tropical fish.

Marine bio-diversiy

The coral reefs in the Western Pacific have the highest marine biodiversity in the world. In the waters of the Philippines there are more than 2000 different kinds of fish. This area is one of the most unique in the Pacific Ocean. The coral reefs are very beautiful, ideal for divers and snorkelling tourists. Moreover, they also protect the shoreline by acting as a wave breaker.

Threats for the coral reefs?

Its very sad that many coral reefs have been damaged in the past by fishermen. Many fishermen used cyanide and dynamite to get fish in a more easy and fast way. To use the cyanide was an effective way not to kill but paralyze (put them to sleep) the fish for some time. It was then easy to collect the fish in a relative short time. The fish was sold to traders. Using the dynamite by the fishermen caused a lot of damage to coral reefs.

Soft-bottom continental shelves appear in front of major river systems and deltas from which they receive their characteristic fine sediments (e.g. gravel, sand and mud). Extending up to a depth of 200 metres, they are usually strongly influenced by the riverine effluents from which they draw their high productivity and which govern their natural variability. These ecosystems are exploited with a variety of fishing methods and are particularly suitable for bottom trawling. Artisanal fisheries are generally restricted to the shallower areas of these shelves, while semi-industrial and industrial fleets (with which artisanal fisheries often conflict) can exploit both the nearshore and offshore areas.

Upwelling continental shelves are very productive continental shelves found mostly at the eastern boundaries of the oceans, often in front of arid zones or deserts. The usually wind-driven, upwelling process brings cold, nutrient-rich water from deep layers into the euphotic zone where photosynthesis uses sunlight and the upwelled nutrients to produce the organic matter that is the basis of the marine food chain. These ecosystems are affected by strong inter-annual variability (e.g. El Niño and La Niña, off Peru-Chile). They represent areas of especially high concentrations of small pelagic species usually exploited by surface fisheries using purse seiners and mid-water trawls.

Open oceans

Open oceans (Pelagic) represent the largest area and volume of marine ecosystems, although their biological and fisheries production per unit of area is far less than the other ecosystems. The depth of open oceans varies from about 200m, where in theory the continental shelf ends and the continental slope starts, to 11 500m in the deepest trenches. Seamounts are noticeable elements of the open ocean ecosystem and host some long-living and fragile deep-sea resources (e.g. orange roughies) on which fisheries have recently expanded - causing concern for the conservation of these poorly known ecosystems. Upper layers are exploited mainly with wide opening midwater trawls (e.g. for horse mackerel) and longlines (e.g. for tuna, billfishes and sharks).

Polar oceans (i.e. the Arctic and Antarctic oceans) are particular, highly-productive ecosystems with great seasonality, characterized by active, current-driven, enrichment processes that sustain important fishery resources (e.g. fish, krill, whales, small cetaceans) and other species (e.g. seabirds, seals). Some doubts have been raised that in some years krill production might be insufficient to support the demand of seals, penguins and albatross for the food needed to raise their offspring.

WETLANDS

Wetlands are defined as land areas that are at least partially covered with water for all or part of the year. Wetlands are wet, of course! There are many different types of wetlands each with its own characteristics. They serve many roles and functions and are full of life!

There are many different types of wetlands found throughout the world. They are found everywhere in the world except Antarctica. Wetlands all have common characteristics, yet each are unique in their hydrology and biodiversity

MARSHES

A marsh is another type of wetland. There are salt water marshes and fresh water marshes. Marshes have shallow water and floating leafed plants and grasses. A great many animals like marshes because it is a very good place for protection from predators, food supply, and nesting sites. Migratory birds and waterfowl depend on marshes as resting places as they migrate.

Fresh water marshes are dependent upon rainfall, runoff, and flooding that occurs during certain seasons. Fresh water marshes support many species of animal, such as frogs, turtles, ducks, egrets, heron, hawks, muskrat, mink, otter, and in some regions alligators.

Salt marshes are generally influenced by wind and tides and have special plants that have adapted to the salty life of a salt marsh. They are useful commercially for speckled trout, crabs, and shrimp.

SWAMPS

Swamps are one type of wetland. They hold many different types of plants and animals. They fall into two categories; forested swamps and shrub swamps.

Forested swamps are dominated by the bald cypress and tupelo gum trees. They also have other varieties of trees and plants. They provide homes to many animals like deer, beaver, otter, muskrat, fox, black bear, frogs, snakes, turtles, and a large variety of birds. The difference between the forested swamp and the shrub swamp is that the forested swamp has lots of trees and is often covered by a layer of old leaves.

A shrub swamp is a swamp that has mostly shrubs in it rather than trees. It is dominated by grass, algae, reeds, and many types of shrubs. Herons and other birds like shrub swamps because of the abundant food supply.

BOGS

Bogs can be found all over but they are usually in cold regions of the world. Bogs form from shallow lakes, slowly moving water, and where there is bad water run off. They usually have no inflow or outflow.The plants decay slowly so there is lots of peat in bogs. The soil is generally poor and quite acidic. Unique plant life grows in bogs. Carnivorous plants such as the venus flytrap and pitcher plant grow in bogs. Also seen in bogs are a variety of wildflowers, grasses, rushes, and sedges. There is often an abundance of mosses and sphagnum moss. Bogs do not usually have a lot of different types of animals, other than insects, because the water is very acidic too. Migratory birds, however, often stop off at bogs to rest along their journeys. Some bogs will also have certain fish species such as the smallmouth bass. Some reptiles and amphibians are also found in bogs; frogs, salamanders, turtles, and snakes.

Freshwater Ecosystems

Only 3% of the world's water is fresh. And 99% of this is either frozen in glaciers and pack ice or is buried in aquifers. The remainder is found in lakes, ponds, rivers, and streams.

Lakes and Ponds

Deep lakes contain three distinct zones, each with its characteristic communities of organisms.

Littoral zone

The zone close to shore. Here light reaches all the way to the bottom. The producers are plants rooted to the bottom and algae attached to the plants and to any other solid substrate. The consumers include:

• tiny crustaceans


• flatworms


• insect larvae


• snails


• frogs, fish, and turtles.

Limnetic zone

This is the layer of open water where photosynthesis can occur. As one descends deeper in the limnetic zone, the amount of light decreases until a depth is reached where the rate of photosynthesis becomes equal to the rate of respiration. At this level, net primary production no longer occurs.
The limnetic zone is shallower is turbid water than in clear and is a more prominent feature of lakes than of ponds.

Life in the limnetic zone is dominated by

• floating microorganisms - called plankton


• actively swimming animals - called nekton.

The producers in this ecosystem are planktonic algae.

The primary consumers include such animals as microscopic crustaceans and rotifers - the so-called zooplankton.
The secondary (and higher) consumers are swimming insects and fish. These nekton usually move freely between the littoral and limnetic zones.

Profundal zone

Many lakes (but few ponds) are so deep that not enough light reaches here to support net primary productivity. Therefore, this zone depends for its calories on the drifting down of organic matter from the littoral and limnetic zones.

The profundal zone is chiefly inhabited by primary consumers that are either attached to or crawl along the sediments at the bottom of the lake.

Such bottom-dwelling animals are called the benthos.

The sediments underlying the profundal zone also support a large population of bacteria and fungi. The decomposers break down the organic matter reaching them, releasing inorganic nutrients for recycling.

Fall overturn

Where there is a pronounced change of seasons, the warming of the surface of the lake in the summer prevents this water from mixing with deeper water. This is because warm water is less dense than cold.
The surface water becomes enriched in oxygen

• some from the air above it


• the rest - because it is in the limnetic zone - from photosynthesis.
  

But the water in the profundal zone - being removed from both these sources - becomes stagnant.

In the fall, however, as the surface water cools, it becomes denser and sinks to the bottom - carrying oxygen with it.

A similar phenomenon occurs when the ice melts in the spring.

Rivers and Streams

The habitats available in rivers and streams differ in several ways from those in lakes and ponds.
Because of the current, the water is usually more oxygenated.
Photosynthesizers play a minor role in the food chains here; a large fraction of the energy available for consumers is brought from the land; e.g., in falling leaves.

Rivers are flowing bodies of waters. There are rivers on every continent (except Antarctica). Rivers are an important part of the Earth's water cycle and the sculpting of the Earth's topography as they carry huge quantities of water from the land to the sea.

The early course of a river is often in steep, mountain areas, with rapidly-flowing cold water. As a river continues along its course (which is always changing), the surrounding terrain flattens out and the river widens. Rivers often meander (follow a winding path) along their middle course. Tributaries (smaller rivers or streams) and runoff flow into the river, increasing the river's volume (the amount of water it has). Rivers often have increased volume and water speed in the spring, as snow at the river's source melts.

Most rivers end when they flow into a large body of water. The end of the river is called the mouth. At the mouth, there is usually a river delta, a large, silty area where the river splits into many different slow-flowing channels that have muddy banks. New land is created at deltas. Deltas are often triangular-shaped, hence the name (the Greek letter 'delta' is shaped like a triangle).

The Water in a RiverAt the source of a river, the water is relatively pure. As the water flows downstream, it picks up silt and minerals (including mineral salts) from the soil and rock in the river bed. Many other chemicals enter river water as it flows downstream, including animal waste, human sewage, agricultural (farm) runoff, urban runoff, and mining/factory effluent.

The course of a river changes over time, as erosion caused by the flowing water and sediment sculpts the landscape around the river. Rivers erode land and carry it downstream towards the sea or lake it flows into. This kind of erosion can even form canyons, like the Grand Canyon (eroded by the Colorado River), waterfalls, like Victoria Falls (formed by the Zambezi River), oxbow lakes, and other formations.
As eroded soil is carried downstream, it is deposited at areas where the river slows, especially where the river meets the body of water it flows into (often the ocean or a lake), forming a fertile river delta that has muddy swamps and/or sandbars.

River Extremes

The longest river in the world is the Nile River (4,157 miles long); it is located in northeastern Africa, and flows into the Mediterranean Sea. The second-longest river is the Amazon River (3,915 miles long); it is located in northeastern South America, and flows into the Atlantic Ocean. The third-longest river is the Chang (Yangtse) River (3,434 miles long); it flows across south-central China into the East China Sea.
The river with the biggest volume (the most water flowing in it) is the Amazon River.

What is a Biome?

A biome is a large area with similar flora, fauna, and microorganisms. Most of us are familiar with the tropical rainforests, tundra in the arctic regions, and the evergreen trees in the coniferous forests. Each of these large communities contain species that are adapted to its varying conditions of water, heat, and soil. It is characterized by a given assemblage of plants and animals that interact with each other within a given natural enironmental setting. Global climate patterns, plant and animal relationships and their evolution and migration, movements of continents and, to a high degree, human a ctivities, determine the distribution of species of plants and animals. For instance, polar bears thrive in the arctic while cactus plants have a thick skin to help preserve water in the hot desert.

The word "biome" is used to describe a major vegetation type such as tropical rain forest, grassland, tundra, etc., extending over a large geographic area (Figure 1). It is never used for aquatic systems, such as ponds or coral reefs. It always refers to a vegetation category that is dominant over a very large geographic scale, and so is somewhat broader than an ecosystem.

The major biomes are:
(a) deserts
(b) tundra
(c) grassland
(d) savanna
(e) coniferous forests
(f) deciduous forests
(g) tropical forests

Figure 1. The Distribution of Biomes

Tropical Rain Forests

Rainf forests are found in the tropics. Forming a thick, lush carpet of vegetation with a stunningly diverse array of species, tropical rain forests of the world once covered an area about the size of the United States. Today, tropical rain forests have been reduced by half, and logging continues at a feverish pace in many areas. Some experts think that tropical rain forests in all but a few places could be virtually obliterated early in the next century if nations do not enact strict measures to protect them.

A forest is that portion of the public domain where there is a predominant growth of trees. It is an area of land where plants and animal live together in close association, bound by specific and recognizable patterns of interdependence. Philippine forests are called tropical rain forests because of the country's tropical location and the amount of rainfall received (over 200 cm a year).

Of all the world's forests, it is those in the tropics that face the greatest threat from mankind. Tropical rainforests are one of nature's treasures, and many of them are now at risk. We have already destroyed half of the world's original tropical rainforests! Just in a few decades, we can possibly witness the complete elimation of the world's rainforests. Technically, this type of forest can be defined as a forest in the tropics receiving 4-8 meters of rain each year. Tropical rainforests are found in Central and South America, Southeast Asia and islands near it, and West Africa. There are smaller rainforests in northern Australia and other small islands. All tropical rainforests are found along the equator where the temperatures and the humidity is always high, with the days being equal to the nights.

Tropical Rainforest Layers

Tropical rainforests have four layers:

Emergent Layer
These giant trees thrust above the dense canopy layer and have huge mushroom-shaped crowns. These trees enjoy the greatest amount of sunlight but also must endure high temperatures, low humidity, and strong winds.

Canopy Layer
The broad, irregular crowns of these trees form a tight, continuous canopy 60 to 90 feet above the ground. The branches are often densely covered with other plants (epiphytes) and tied together with vines (lianas). The canopy is home to 90% of the organisms found in the rain forest; many seeking the brighter light in the treetops.

Understory
Receiving only 2-15% of the sunlight that falls on the canopy, the understory is a dark place. It is relatively open and contains young trees and leafy herbaceous plants that tolerate low light. Many popular house plants come from this layer. Only along rivers and roadways and in treefall and cut areas is sunlight sufficient to allow growth to become thick and impenetrable.

Forest Floor
The forest floor receives less than 2% of the sunlight and consequently, little grows here except plants adapted to very low light. On the floor is a thin layer of fallen leaves, seeds, fruits, and branches that very quickly decomposes. Only a thin layer of decaying organic matter is found, unlike in temperate deciduous forest.

Did you know that enough rainforests are being destroyed every minute to fill 50 football fields? We need to preserve these valuable resources because they are the lungs of our planet, and can possibly hold cures for many of our most deadly diseases. The tropical rainforests are a critical link in the ecological chains of our our earth's biosphere.

Despite covering only 2% of our planet's surface, over half of the earth's animal, insect species, and flora live there. Within a four mile square area of a tropical rainforest, you would find:

• Over 750 species of trees


• 1500 different kinds of flowering plants


• 125 species of mammals


• 400 species of birds


• 100 reptiles


• 60 amphibians


• countless insects


• 150 species of butterflies
  

**Only 1% of these species has ever been studied**

Important Facts

• Amazon rainforests produce about 40% of the world's oxygen


• One in four pharmaceuticals comes from a plant in the tropical rainforests


• 1400 rainforest plants are believed to offer cures for cancer


• 40% of tropical rainforests have already been lost in Latin America and Southeast Asia
  

Forest ecosystems have protective, regulative and productive functions. These functions can acquire utlity value for man and become functions of the cultural ecosystem. The effects of these functions on the environment are called forest influences. The more important of these are:

Protective functions

• soil protection by asorption and deflection of radiation, precipitation and wind;


• conservation of humidity and carbon dioxide by decreasing wind velocity; and


• sheltering and providing required conditions for plant and animal species.
  

Regulative functions

• absorption, storage and release of CO2, O2 and mineral elements.


• absorption of aerosols and sound;


• absorption, storage and release of water; and


• absorption and transformation of radiant and thermal energy.

Productive functions

• efficient storage of energy in utilizable form in phyto- and zoo mass;


• self-regulating and regenerative processes of woods, bark, fruit and leaf production; and


• production of a wide array of chemical compunds, such as resins, alkaloids, essential oils, latex pharmaceuticals, etc.

These functions can be utilized by man for:

Protection

• sheltering agricultural crops against drought, wind, cold and radiation;


• conserving soil and water; and


• shielding man against nuisances (noise, sights, smells and fumes)

Regulation

• improvement of atmospheric conditions in residential and recreational areas;


• improvement of temperature regimes in residential areas (roadside trees and parks); and


• improvement of the bio type value and amenity of landscapes.

Production

• supply of a wide array of raw materials to meet man's growing demands;


• source of employment; and


• creation of wealth

BIOGEOCHEMICAL CYCLES

Elements and inorganic compounds that sustain life tend to circulate in the earth's biosphere in regular paths from the atmosphere to the lithosphere (soil) or hydrosphere (water) into living things and then back into these environments. These are called biogeochemical cycles.Thus, all of the elements that function in animals or plants follow some of cyclic paths. The following are the important cycles of materials found in ecosystems.

1. Hydrologic or Water Cycle - water is collected, purified and distributed on the earth's fixed supply of water.

2. Carbon - Oxygen Cycle - depends on photosynthesis and respiration

3. Nitrogen Cycle - relies heavily on bacteria

4. Phosphorus Cycle - depends on the weathering of rock

THE WATER CYCLE

The Water Cycle (also known as the hydrologic cycle) is the journey water takes as it circulates from the land to the sky and back again. The Sun's heat provides energy to evaporate water from the Earth's surface (oceans, lakes, etc.). Plants also lose water to the air (this is called transpiration). The water vapor eventually condenses, forming tiny droplets in clouds. When the clouds meet cool air over land, precipitation (rain, sleet, or snow) is triggered, and water returns to the land (or sea). Some of the precipitation soaks into the ground. Some of the underground water is trapped between rock or clay layers; this is called groundwater. But most of the water flows downhill as runoff (above ground or underground), eventually returning to the seas as slightly salty water.





Carbon Cycle

The movement of carbon, in its many forms, between the biosphere, atmosphere, oceans, and geosphere is described by the carbon cycle, illustrated in the adjacent diagram. The carbon cycle is one of the biogeochemical cycles. In the cycle there are various sinks, or stores, of carbon (represented by the boxes) and processes by which the various sinks exchange carbon (the arrows).

We are all familiar with how the atmosphere and vegetation exchange carbon. Plants absorb CO2 from the atmosphere during photosynthesis, also called primary production, and release CO2 back in to the atmosphere during respiration. Another major exchange of CO2 occurs between the oceans and the atmosphere. The dissolved CO2 in the oceans is used by marine biota in photosynthesis.

Two other important processes are fossil fuel burning and changing land use. In fossil fuel burning, coal, oil, natural gas, and gasoline are consumed by industry, power plants, and automobiles. Notice that the arrow goes only one way: from industry to the atmosphere. Changing land use is a broad term which encompasses a host of essentially human activities. They include agriculture, deforestation, and reforestation.

The adjacent diagram shows the carbon cycle with the mass of carbon, in gigatons of carbon (Gt C), in each sink and for each process, if known. The amount of carbon being exchanged in each process determines whether the specific sink is growing or shrinking. For instance, the ocean absorbs 2.5 Gt C more from the atmosphere than it gives off to the atmosphere. All other things being equal, the ocean sink is growing at a rate of 2.5 Gt C per year and the atmospheric sink is decreasing at an equal rate. But other things are not equal. Fossil fuel burning is increasing the atmosphere's store of carbon by 6.1 Gt C each year, and the atmosphere is also interacting with vegetation and soil. Furthermore, there is changing land use.

The carbon cycle is obviously very complex, and each process has an impact on the other processes. If primary production drops, then decay to the soil drops. But does this mean that decay from the soil to the atmosphere will also drop and thus balance out the cycle so that the store of carbon in the atmosphere will remain constant? Not necessarily; it could continue at its current rate for a number of years, and thus the atmosphere would have to absorb the excess carbon being released from the soil. But this increase of atmospheric carbon (in the form of CO2) may stimulate the ocean to increase its uptake of CO2 .

THE NITROGEN CYCLE

All life requires nitrogen-compounds, e.g., proteins and nucleic acids.
Air, which is 79% nitrogen gas (N2), is the major reservoir of nitrogen. But most organisms cannot use nitrogen in this form. Plants must secure their nitrogen in "fixed" form, i.e., incorporated in compounds such as:

• nitrate ions (NO3−)


• ammonia (NH3)


• urea (NH2)2CO

Animals secure their nitrogen (and all other) compounds from plants (or animals that have fed on plants). Four processes participate in the cycling of nitrogen through the biosphere:

• nitrogen fixation
• decay
• nitrification
• denitrification

Microorganisms play major roles in all four of these.

Nitrogen Fixation
The nitrogen molecule (N2) is quite inert. To break it apart so that its atoms can combine with other atoms requires the input of substantial amounts of energy. Three processes are responsible for most of the nitrogen fixation in the biosphere:

• atmospheric fixation by lightning
  
• biological fixation by certain microbes — alone or in a symbiotic relationship with some plants and animals


• industrial fixation

Atmospheric Fixation

The enormous energy of lightning breaks nitrogen molecules and enables their atoms to combine with oxygen in the air forming nitrogen oxides. These dissolve in rain, forming nitrates, that are carried to the earth.
Atmospheric nitrogen fixation probably contributes some 5– 8% of the total nitrogen fixed.

Industrial Fixation

Under great pressure, at a temperature of 600°C, and with the use of a catalyst, atmospheric nitrogen and hydrogen (usually derived from natural gas or petroleum) can be combined to form ammonia (NH3). Ammonia can be used directly as fertilizer, but most of its is further processed to urea and ammonium nitrate (NH4NO3).

Biological Fixation

The ability to fix nitrogen is found only in certain bacteria and archaea.
Some live in a symbiotic relationship with plants of the legume family (e.g., soybeans, alfalfa).
Some establish symbiotic relationships with plants other than legumes (e.g., alders).
Some establish symbiotic relationships with animals, e.g., termites and "shipworms" (wood-eating bivalves).
Some nitrogen-fixing bacteria live free in the soil.
Nitrogen-fixing cyanobacteria are essential to maintaining the fertility of semi-aquatic environments like rice paddies.
Biological nitrogen fixation requires a complex set of enzymes and a huge expenditure of ATP. Although the first stable product of the process is ammonia, this is quickly incorporated into protein and other organic nitrogen compounds.

Decay

The proteins made by plants enter and pass through food webs just as carbohydrates do. At eachtrophic level, their metabolism produces organic nitrogen compounds that return to the environment, chiefly in excretions. The final beneficiaries of these materials are microorganisms of decay. They break down the molecules in excretions and dead organisms into ammonia.

Nitrification

Ammonia can be taken up directly by plants — usually through their roots. However, most of the ammonia produced by decay is converted into nitrates. This is accomplished in two steps:
Bacteria of the genus Nitrosomonas oxidize NH3 to nitrites (NO2−).
Bacteria of the genus Nitrobacter oxidize the nitrites to nitrates (NO3−).
These two groups of autotrophic bacteria are called nitrifying bacteria. Through their activities (which supply them with all their energy needs), nitrogen is made available to the roots of plants.
Many soils also contain archaeal microbes, assigned to the Crenarchaeota, that convert ammonia to nitrites. While more abundant than the nitrifying bacteria, it remains to be seen whether they play as important a role in the nitrogen cycle.
Many legumes, in addition to fixing atmospheric nitrogen, also perform nitrification — converting some of their organic nitrogen to nitrites and nitrates. These reach the soil when they shed their leaves.

Denitrification

The three processes above remove nitrogen from the atmosphere and pass it through ecosystems.
Denitrification reduces nitrates to nitrogen gas, thus replenishing the atmosphere.
Once again, bacteria are the agents. They live deep in soil and in aquatic sediments where conditions are anaerobic. They use nitrates as an alternative to oxygen for the final electron acceptor in their respiration.
Thus they close the nitrogen cycle.
Are the denitrifiers keeping up?Agriculture may now be responsible for one-half of the nitrogen fixation on earth through
the use of fertilizers produced by industrial fixation
the growing of legumes like soybeans and alfalfa.This is a remarkable influence on a natural cycle.
Are the denitrifiers keeping up the nitrogen cycle in balance? Probably not. Certainly, there are examples of nitrogen enrichment in ecosystems. One troubling example: the "blooms" of algae in lakes and rivers as nitrogen fertilizers leach from the soil of adjacent farms (and lawns). The accumulation of dissolved nutrients in a body of water is called eutrophication.

PHOSPHORUS CYCLE

Phosphorus enters the environment from rocks or deposits laid down on the earth many years ago. The phosphate rock is commercially available form is called apatite. Other deposits may be from fossilized bone or bird droppings called guano. Weathering and erosion of rocks gradually releases phosphorus as phosphate ions which are soluble in water. Land plants need phosphate as a fertilizer or nutrient.

Phosphate is incorporated into many molecules essential for life such as ATP, adenosine triphosphate, which is important in the storage and use of energy. It is also in the backbone of DNA and RNA which is involved with coding for genetics.

When plant materials and waste products decay through bacterial action, the phosphate is released and returned to the environment for reuse.

Much of the phosphate eventually is washed into the water from erosion and leaching. Again water plants and algae utilize the phosphate as a nutrient. Studies have shown that phosphate is the limiting agent in the growth of plants and algae. If not enough is present, the plants are slow growing or stunted. If too much phosphate is present excess growth may occur, particularly in algae.

A large percentage of the phosphate in water is precipitated from the water as iron phosphate which is insoluble. If the phosphate is in shallow sediments, it may be readily recycled back into the water for further reuse. In deeper sediments in water, it is available for use only as part of a general uplifting of rock formations for the cycle to repeat itself.

Human influences on the phosphate cycle come mainly from the introduction and use of commercial synthetic fertilizers. The phosphate is obtained through mining of certain deposits of calcium phosphate called apatite. Huge quantities of sulfuric acid are used in the conversion of the phosphate rock into a fertilizer product called "super phosphate".

Plants may not be able to utilize all of the phosphate fertilizer applied, as a consequence, much of it is lost form the land through the water run-off. The phosphate in the water is eventually precipitated as sediments at the bottom of the body of water. In certain lakes and ponds this may be redissolved and recyled as a problem nutrient.

Animal wastes or manure may also be applied to the land as fertilizer. If misapplied on frozen ground during the winter, much of it may lost as run-off during the spring thaw. In certain area very large feed lots of animals, may result in excessive run-off of phosphate and nitrate into streams.

Other human sources of phosphate are in the out flows from municipal sewage treatment plants. Without an expensive tertiary treatment, the phosphate in sewage is not removed during various treatment operations. Again an extra amount of phosphate enters the water.

SULFUR CYCLE

Sulfur is one of the components that make up proteins and vitamins. Proteins consist of amino acids that contain sulfur atoms. Sulfur is important for the functioning of proteins and enzymes in plants, and in animals that depend upon plants for sulfur. Plants absorb sulfur when it is dissolved in water. Animals consume these plants, so that they take up enough sulfur to maintain their health.Most of the earth's sulfur is tied up in rocks and salts or buried deep in the ocean in oceanic sediments. Sulfur can also be found in the atmosphere. It enters the atmosphere through both natural and human sources. Natural recourses can be for instance volcanic eruptions, bacterial processes, evaporation from water, or decaying organisms. When sulfur enters the atmosphere through human activity, this is mainly a consequence of industrial processes where sulfur dioxide (SO2) and hydrogen sulphide (H2S) gases are emitted on a wide scale.When sulfur dioxide enters the atmosphere it will react with oxygen to produce sulfur trioxide gas (SO3), or with other chemicals in the atmosphere, to produce sulfur salts. Sulfur dioxide may also react with water to produce sulphuric acid (H2SO4). Sulphuric acid may also be produced from demethylsulphide, which is emitted to the atmosphere by plankton species.All these particles will settle back onto earth, or react with rain and fall back onto earth as acid deposition. The particles will than be absorbed by plants again and are released back into the atmosphere, so that the sulfur cycle will start over again.

Population Ecology

A population is a group of individuals of the same species living in the same geographic area. The study of factors that affect growth, stability, and decline of populations is population dynamics. All populations undergo three distinct phases of their life cycle:
1. growth
2. stability
3. decline

Population growth occurs when available resources exceed the number of individuals able to exploit them. Reproduction is rapid, and death rates are low, producing a net increase in the population size.

Population stability is often proceeded by a "crash" since the growing population eventually outstrips its available resources. Stability is usually the longest phase of a population's life cycle.
Decline is the decrease in the number of individuals in a population, and eventually leads to population extinction.

Characteristics of Population:

1. SIZE - pertains to the number of individuals in a population.

Factors affecting size:

• NATALITY - refers to the number of ndividuals added to the population thru REPRODUCTION. Birth rate - refers to the number of individuals born per year 1,000 individuals per year.
• MORTALITY- refers to the number of individuals that die in a given time. Death rate - is the number of individuals die per 1,000 individuals per year.
• C. IMMIGRATION- pertains to individuals of the population moving into an area in a particular time.
• D. EMIGRATION - pertains to individuals of the population moving out from an area in a particular time.

2. Population density

(a) Given that a population is defined in terms of some natural or arbitrarily defined geographical range, then population density may be defined as simply the number of individual organisms per unit area
(b) Different species, of course, exist at different densities in their environments, and the same species may be able to achieve one density in one environment and another in a different environment
(c) Population densities may additionally be determined in terms of some measure other than population size per unit area such as population mass per unit area.

3. DISPERSION PATTERN

The dispersion pattern of a population refers to the way individuals are spaced withthin their area. These patterns are important characteristics for an ecologist to study, since they provide insights into the environmental effects and social interactions in the population.

The Three Main Types of Population Dispersion
Population dispersion is the observation of where individuals are found in a habitat. How individuals "disperse" themselves.

There are three main types of dispersion: clumped, uniform and random.

Clumped Dispersion
Is the tendency for populations to be found in tight clusters, dispersed across a large landscape. In between these population hubs, very few to no individuals are usually found. This sort of a dispersion can be caused by a number of factors. Some species cluster together for protection, while others group around natural resources necessary to their survival. For instance, fish are often clumped in schools which may reduce predation risks and increase feeding efficiency. Mosquitoes often swarm in great numbers, increasing their chances for mating.

Uniform Dispersion
Is the tendency for populations to be found evenly distributed about their habitat. This is generally caused by a species ability to survive anywhere in their habitat - they use the resources found immediately around them, and spread out as to use all of the available resources. Examples are uniform disperson of nesting king penguins and human habitations. Plant plantations are another examples.

Random Dispersion
Is the tendency for populations to be found randomly about their habitat. In immobile species, this is usually caused by their ability to live anywhere in a given habitat, except, they are limited to growing wherever they are first set root (which is usually caused randomly, from spores drifting in the wind to seeds falling and tumbling on the ground). In motile populations, individuals are able to move about their habitat, so that at any given instance, they can be found anywhere about their environment. Desert cacti are examples.

4. DOMINANCE - describes the most abundant individual of the population.

5. SEX RATIO - refer to the relative number of males and females.

6. AGE DISTRIBUTION -pertains to the number of individuals belonging in each age group of a population.

Different age groups:

a. REPRODUCTIVE JUVENILES - individuals of the population who are not yet capable of reproducing.

b. REPRODUCING ADULTS - individuals of the population who are capable of reproducing.

c. POSTREPRODUCTIVE ADULTS - individuals of the population who are no longer capable of reproducing.

SPECIES INTERACTIONS

DOMINANCE

Not all species in anecosystem are equally important in determining the nature and function of the entire ecosystem. Every community has one or two dominant species, being the most abundant or containing the most biomass. Dominant species however may not be necessarily essential to a community. The most essential species in the ecosystem are the so-called keystone species as their activities determine the structure of the entire community and consist of species that often turn out unexpectedly to be the ones essential to the survival of the community. In communities controlled by a keystone species, its removal can have dramatic consequences whereas, in communities controlled by competition, removal of one or a few species may not be noticed.

SPECIES INTERACTIONS

The different organisms in the ecosystem each occupies a certain ecological niche, which is described as all the physical, chemical and biological factors that a species needs to live, grow and reproduce in an ecosystem.

Specialized niche - species that can tolerate only a narrow range of climatic and other environmental conditions and feed on a limited number of different plants and animals. This limits them to specific habitats in the ecosphere.

Generalist niche - adaptable organisms which can live in many different palces, e ait a wide variety of foods, and tolerate a wide range of environmental conditions. This explains why they are usually in less danger of extinction that a species with a specialized niche.
Examples of generalist species : flies, cockroaches, mice, rats and human beings.

The ecological niches of species include how they interact with other species in an ecosystem. The major types of species interaction are interspecific competition, predation, parasitism, mutualism and commensalism.

Interspecific competition happens when two or more species in the same ecosystem use the same scarce resources such as food, water, oxygen, sunlight, soil nutrients, space and shelter or anything required for survival. The most obvious form of species interaction in food chains and webs is predation. An organism of one species, known as the predator, feeds on parts or all of an organism of another species, the prey, but does not live on or in the prey. Together, the two kinds of organisms involved, such as frogs and insects, are said to have a predator-prey relationship. Another example is the picture with the lynx chasing a hare.

Another type of species interaction is parasitism. Parasites feed off another organism, called their host, but unlike predators, they live on or in the host for a good part of their life cycle. The parasite draws nourishment from and gradually weakens its host. This may or may not kill the host. Pathogens are disease-causing organisms like bacteria, viruses, or protists that could be thought of as microscopic parasites. Unlike, most parasites, however, many pathogens inflict lethal harm on their hosts. Example is the photo below of a roundworm may affect dogs and puppies.

Animals, just like humans, can become infected with parasites. Internally, contaminated water and food can spread the problem to our pets. Externally, animals become infected by parasites on their bodies, especially on their fur, because of exposure to infected animal wastes. Forgetting to wash your hands even one time after handling or cleaning up after your animal can transmit the parasite to you. Pets are a wonderful part of our lives. They provide comfort, companionship, protection, amusement, and unconditional love for their owners. Yet, pets, like humans, are often victims of serious infections that can unintentionally be passed on to their owners. In fact, there is a whole set of diseases classified as 'zoonoses' (animal-transmitted diseases) in parasitology textbooks. Animals are major carriers of parasites, and most physicians, let alone the general public, are unaware of this fact. Experts have projected that of the 110 million pet dogs and cats in this country, over half may be infected with at least one or more different kinds of parasites. Considering these numbers, the potential for transmission of parasitic infection from animals to humans is extremely high.

In some cases two different types of organisms interact directly in ways that benefit each species. Such a mutually beneficial interaction between species is called mutualism. e.g., the honeybees and birds and certain flowers. The honeybee/bird feeds on the flower's nectar and in the process picks up pollen and pollinates female flowers when it feeds on them.

Commensalism, on the other, is a type of species interaction where one type of organism benefits while the other is neither helped nor harmed to any great degree. Algae that grow on the shells of sea turtles and false clownfish hiding in anemone (photo below) are examples of this interaction.Another example, epiphytic plants (which grow on other plants but are not parasitic) gain an enormous ecological benefit from living on larger plants, because they gain access to a substrate upon which to grow relatively high in the canopy. The host trees, however, are not affected in any significant way by this relationship, even in cases when they are supporting what appears to be a large population of epiphytes. Some plants are specialized as epiphytes, for example, many species of airplants or bromeliads (family Bromeliaceae), orchids (Orchidaceae), and ferns (Pterophyta). Many lichens, mosses, and liverworts are also epiphytes on trees. There are also animal analogues of this relationship. Sometimes sea anemones will gain a benefit in terms of food availability by growing on the upper carapace of a hermit crab (crustacean infraorder Anomura) which is apparently unaffected by the presence of the epiphyte.

MORE ECOLOGICAL CONCEPTS

The variety of life on Earth, its biological diversity is commonly referred to as biodiversity. The number of species of plants, animals, and microorganisms, the enormous diversity of genes in these species, the different ecosystems on the planet, such as deserts, rainforests and coral reefs are all part of a biologically diverse Earth.

Species diversity is the extent to which an ecosystem possesses differences in spcies in terms of genetic variation and distribution. Species diversity or BIODIVERSITY is directly related to the stability of ecosystems. Communities consist of populations each of which is a group of interbreeding organisms belonging to the same species. Populations increase through births or seed production and the addition through movememnt into a population called immigration. On the other hand, populations decrease through deaths and emigration or movement out of a population.

Biodiversity actually boosts ecosystem productivity where each species, no matter how small, all have an important role to play and that it is this combination that enables the ecosystem to possess the ability to prevent and recover from a variety of disasters. This is obviously useful for mankind as a larger number of species of plants means more variety of crops and a larger number of species of animals ensure that the ecosystem is naturally sustained.

Higher diversity results in longer food chains and more cases of interactions among species.


DISTRIBUTION:

Individuals in a population are either distributed randomly, uniformly, or clumped. Random distribution is rare and occurs only when the environment is so uniform that there is no use to stay together for reasons of security, access to food or whatever.

Desert cacti are examples of plants with random distribution. Restriction of distribution of species occurs when barriers to the dispersal of the species exist. Land, water and mountains can set the broad limits to distribution of species on a global scale.

In areas where are uniformly distributed species, there is severe competition among individuals. In other cases, there is antagonism that promotes even spacing among animals or plants. Mice or even chicken tend to exhibit uniform distribution. Among plants, plantation species need to be evenly distributed so as to get nutrienst and water evenely.

Any introduced activity, wheter it be massive grazing, road building or power projects, disrupt the natural distribution of species. This may eventually lead to species extinction unless special attention is given to the nature of species distribution in an ecosystem.

RELATED ECOLOGICAL CONCEPTS

LIMITING FACTORS

A major reason why organisms do not spread everywhere is that each species and each individual organism of a species has a particular range of tolerance to variations in chemical and physical factors in the environment, such as temperature.
The tolerance range includes an optimum range of values within which population of a species thrive and operate most efficiently. This range also includes values slightly above or below the optimum level of each abiotic factor- values that usually support a smaller population size. When values exceed the upper limits or fall below the lower limits of tolerance, few if any organisms of a particular species survive.
The law of tolerance states that the existence, abundance and distribution of a species in an ecosystem are determined by whether the levels of one or more physical or chemical factors fall above or below the levels tolerated by the species.

Related to the law of tolerance is the limiting factor principle. Too much or too little of any abiotic factors can limit or prevent growth of a population of a species in an ecosystem even if all other factors are at or near the optimum range of tolerance for a species.
A single factor, such as temperature, water, light or soil nutrients in terrestrial ecosystems and
salinity, temperature, sunlight or dissolved oxygen content in marine ecosystems, found to be limiting the population growth of a species in such ecosystem is called a limiting factor.


The Law of the Minimum
Justus von Liebig, generally credited with being the "Father of the Fertilizer Industry", propounded the "Law of the Minimum" which states that if one crop of the nutritive elements is deficient or lacking, plant growth will be poor even when all the other elements are abundant. Any deficiency of a nutrient, no matter how small an amount is needed, will hold back plant development. If the deficient element is supplied, growth will be increased up to the point where the supply of that element is no longer the limiting factor. Increasing the supply beyond this point is not helpful, as some other element would then be in a minimum supply and become the limiting factor.

The figure at the left exlains that the yield potential of a crop is like a barrel with staves of unequal length. The capacity of the barrel is limited by the length of the shortest stave (in this case, nitrogen), and can only be increased by lengthening that stave. When that stave is lengthened, another one becomes the limiting factor.

The concept of the law of the minimum has been modified as additional elements have proved to be essential in plant nutrition. It has been extended to include other factors such as moisture, temperature, insect control, light, plant population and genetic capacities of plant varieties.

Carrying capacity refers to the number of individuals who can be supported in a given area within natural resource limits, and without degrading the natural social, cultural and economic environment for present and future generations. The carrying capacity for any given area is not fixed. It can be altered by improved technology, but mostly it is changed for the worse by pressures which accompany a population increase. As the environment is degraded, carrying capacity actually shrinks, leaving the environment no longer able to support even the number of people who could formerly have lived in the area on a sustainable basis. No population can live beyond the environment's carrying capacity for very long.
In fact, the criterion for determining whether a region is overpopulated is not land area, but carrying capacity.