primary and secondary production, landscape ecology and ecological modeling

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PRIMARY PRODUCTION & ENERGY FLOW LANDSCAPE ECOLOGY & ECOLOGY MODELLING SUBMITTED BY: 1. Ateeqa Ijaz 2. Ayesha Basheer 3. Farzeen Anwar. 4. Hina Hameed. 5. Nimra Rafique 6. Summan INTRUCTOR NAME :

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Page 1: Primary and secondary production, landscape ecology and ecological modeling

PRIMARY PRODUCTION & ENERGY FLOW

LANDSCAPE ECOLOGY & ECOLOGY MODELLING

SUBMITTED BY:

1. Ateeqa Ijaz

2. Ayesha Basheer

3. Farzeen Anwar.

4. Hina Hameed.

5. Nimra Rafique

6. Summan

INTRUCTOR NAME :

Dr. Hamid Saeed.

Page 2: Primary and secondary production, landscape ecology and ecological modeling

Primary production & energy flow

In ecology the word production refers to the rate of making of a biomass or new organic matter

in an ecosystem. For example when a new plant i.e. wheat plant grows, photosynthesis create a

new organic molecule, which converts the light energy into the chemical energy stored in the

plant tissue. This energy is then used by plants metabolic machinery and as a results plant

perform different functions and grow in size. This increases the biomass of an ecosystem.

Ecology divides production as primary and secondary production.

PRIMARY PRODUCTIVITY:

The amount of the production of organic biomass produced by an organism, community,

population or ecosystem during a given period of a time is called as productivity. Primary

productivity is the fixation of energy by autotrops i.e. plants, algae etc. in an ecosystem. As sun

shines down the canopy of a forest, it cause some of the light energy to be absorbed by the plants

chlorophyll while some of them is reflected back and some is absorbed by the soil, water etc. that

cause the increase in the kinetic energy of the forest. This absorbance of the light with some of

the carbon dioxide from the atmosphere causes the synthesis of organic molecule which is aided

by the process known as "Photosynthesis". The biochemical formula that describes the

photosynthesis process is,

Page 3: Primary and secondary production, landscape ecology and ecological modeling

Photosynthesis is a principle key factor of a primary production. But sometimes this is carried

through chemosynthesis as well, which is an oxidation or reduction of chemical compounds and

acts as a source of energy. The organisms responsible for this productivity refer as autotrops and

form the base line of the food chain. If it's terrestrial region then plants would be the autotrops

and if it is aquatic then algae would be the autotrops.

Ecologists distinguish between net and gross primary production. Gross primary production is

the total amount of solar energy converted into the chemical energy by the green plants through

photosynthesis. Abbreviated as GPP. A certain amount of energy is used by plants for its own

use i.e. respiration etc and its maintenance and its reminder are known as NET primary

production (NPP). This energy is used for the increase in the biomass of an ecosystem and is

used by the consumers. The NPP can be described by the given equation:

GPP - Energy lost by respiration and maintenance = NPP

Primary production is a key of an ecosystem. All organisms depend on the primary producers for

their existence as they can change inorganic molecule into organic one, which is then used by

them as a food source. Primary production occupies the first position in the trophic level of an

ecosystem because of their ability. Because of the significance and the varying rate of primary

production in an ecosystem, ecosystem ecologist studies the different pattern of primary

productivity in different ecosystems.

PATTERN OF PRIMARY PRODUCTIVITY IN TERESSTERIAL ECOSYSTEM:

EFFECT OF TEMPERATURE AND MOISTURE:

The temperature and moisture are the major variables highly correlated with the variation in

primary productivity. Highest rate of primary productivity occurs at the moist and warm

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conditions. The influence of moist and temperature can be determined by the annual net primary

production and annual actual evapotranspiration (AET). AET is the total amount of water that

transpires and evaporates off a landscape in a year and measured in millimeters in that particular

year. This process is affected by both temperature and precipitation. The ecosystems showing the

highest levels of primary production are those that are warm and obtain great amounts of

precipitation. On the other hand, ecosystems show low levels of AET either because they receive

little precipitation, are very cold, or both. For example, both tundra and hot deserts display low

levels of AET (Michael Rosenzweig (1968)).

Figure 1 : Rosenzweig plot of the positive relationship between net primary production and

AET. (data from Rosenzweig 1968).

Rosenzweig case study illustrates that there is a positive relationship between the net primary

production and the AET. He tends to explain the variation in primary production across the

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whole spectrum of terrestrial ecosystem. As we can see that net primary production is an

independent variable and it affecting evapotranspiration. Increase in this cause an increase in

AET which in returns cause an increase in primary productivity.  Annual AET is positively

correlated with net primary production however, considerable variation in terrestrial primary

production occurs from differences in soil fertility as well.

EFFECT OF SOIL NUTRIENTS IN LIMITING TERESTERIAL PRIMARY

PRODUCTION:

Farmers know that adding fertilizer to the soil cause an increase in the agricultural production.

So the difference in the primary production of the terrestrial environment can be explained by the

difference in soil fertility. This effect is explained by many ecologists' case history, as in the case

of Gaius Shaver and Stuart Chapin (1988) study. They determine the effect of nitrogen,

phosphorous and the combination of both in different areas'.

They first observed the effect of these nutrients in limiting the production in arctic tundra. They

came up with the conclusion that addition of nutrients cause an increase in the net primary

production by 23%-300% when compared with the control plots.

Figure 2 : Effect of addition of nitrogen, phosphorus, and potassium on net aboveground

primary production in Arctic tundra (data from Sf haver and Chapin 1986).

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AQUATIC PRIMARY PRODUCTION:

Oceanographers and limnologists have calculated the rates of primary production and nutrients

availability in many oceans, lakes and at many coastal areas. The amount of phosphorous plays a

significant role in this case. As we can see in the figure 3:

This shows the effect of phosphorous in freshwater ecosystem while in the case of marine

ecosystem nitrogen limits the effect of marine primary production.

INFLUENCE OF OTHER ANIMALS ON PRIMARY PRODUCTIVITY:

Figure 3: Relationship between phosphorus concentration and algal

biomass in north temperate lakes (data from Dillon and Rigler

1974).

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Consumers can manipulate the rates of primary production in terrestrial and aquatic

ecosystems. Piscivorous fish can

indirectly reduce rates of primary

production in lakes by reducing the

density of plankton-feeding fish.

Reduced density of planktivorous fish

can lead to increased density of

herbivorous zooplankton, which can

reduce the densities of phytoplankton

and rates of primary production.

Intense grazing by large mammalian

herbivores on the Serengeti increases

annual net primary production by

inducing compensatory growth in grasses. Species diversity of plants or mycorrhizal fungi can

enhance primary productivity. These effects may also cascade up the food chain, increasing

herbivore biomass.

SECONDARY PRODUCTION

Productivity by heterotrophic organisms in the ecosystem is known as secondary productivity.

Secondary productivity is defined as “The rate of increase in the biomass of heterotrophs per unit

time and area is called secondary productivity.”

Figure 4: The trophic cascade

Page 8: Primary and secondary production, landscape ecology and ecological modeling

The large part of food material ingested by carnivores and herbivores is assimilated or absorbed

and a small part of it is egested. The assimilated food is then utilized for respiration, metabolism,

reproduction, growth and maintenance of body. Rest of the part is stored in somatic and

reproductive tissues. Secondary production is defined as “the net quantity of energy transferred

and stored in the somatic and reproductive tissues of heterotrophs over a certain period of time.”

This procedure is done by the heterotrophs which can't make their own sustenance however must

feed on producers or other living organisms. As it is derived from primary production so it is

called as secondary production. It can also be described as the rate of energy transferred or stored

at consumer levels for over a certain time frame.

ENERGY FLOW:

Energy flow is the stream of framework in a biological ecosystem through an external source

(solar energy) and progression of organism and back to the outer environment (outer space).

Organisms use carbon dioxide, water and daylight and return them back to the environment in

the form of byproducts of their metabolic processes. In an ecosystem energy flow is

unidirectional. For instance, lions eat deer to get vitality however deer cannot eat lions. Hence,

flow of energy is unidirectional in an ecosystem.

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The energy efficiency flow in an ecosystem is usually known as trophic level productivity or

efficiency which is the proportion of creation of one trophic level to the generation of next lower

trophic level. The flow of energy begins from green plants to next trophic level and so on. Green

plants have the capacity to change over 1 to 3% of the energy absorbed from the sun into plant

vitality. At that point the herbivores change over conceivably accessible plant energy into the

herbivorous energy which may be converted into carnivorous energy via carnivores. It is found

that the exchange of aggregate energy starting with one trophic level then onto the next is just

10% of the gross efficiency of producers. The energy flow in an ecosystem through a linked

pathway is known as food chain or food web.

LIMITATION OF PRIMARAY PRODUCTION BY ENERGY LOSS:

Ecosystem ecologists have arranged the trophic

level based upon the predominant source of

nutrition. Energy loss limits the primary production

of an ecosystem. Trophic level is determined by the

energy flow from the lower level to the higher Figure 5 Trophic level

Page 10: Primary and secondary production, landscape ecology and ecological modeling

level. sAs energy is transferred from one level to another the energy is lost due to respiration,

assimilation and heat production. This cause the decrease in energy as we go from lower to the

higher energy level and it obtain a pyramid shape. As a result of this energy loss there is not an

adequate amount of energy supporting the life.

FOOD CHAIN:

Food chain is a linkage of ‘who feed on whom’ through

which energy, chemical elements and different compounds

are exchanged or transferred from one organism to another

organism. A food chain includes a progression of life forms

and these gathered into trophic level. Trophic level

comprises of each one of those organisms in a food chain

that are away, the same number of encouraging levels, from the original source of energy. For

instance, green plants are one level far from the primary source (sun) so it is known as first

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trophic level. A single food chain must have at least three links to be completed. Food chain

exists in all types of habitats and communities, in terrestrial as well as in aquatic ecosystem.

FOOD WEB:

Some consumers feed on single source of energy but most consumers require more than one food

sources e.g. hawks feed on both mouse and snake. When individual food webs are interrelated

and inter connected, they form a food web. Food web is a complicated structure. The energy

flow in an ecosystem by means of food chain lost almost about 80 to 90% of potential energy in

the form of heat. Therefore the number of links in a sequence is limited usually 4 to 5. They

show the inverse relation. Shorter the food web greater is the energy available. Mostly terrestrial

food chains have shorter links whereas aquatic food chains show relatively longer links.

TERRESTRIAL FOOD CHAIN AND FOOD WEB:

Food chain in terrestrial ecosystem begins with green plants that produce sugar in the presence of

sunlight through the process of photosynthesis. These are the producers and placed in first

trophic level. Herbivores are those organisms that feed on plants and are members of second

trophic level.Carnivores are those that feed on other organisms such as herbivores. They are in

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third trophic level. Those carnivores that feed on third trophic level carnivores are grouped in

fourth trophic level and so on. Individual food chains are interconnected to form a food web.

Secondary production use the assimilation of organic material and building of tissues by

heterotrophs. Thus may involve animals eating

plants or other animals, or microorganisms

decomposing dead organisms to obtain energy

and nutrient resources required for producing

Biomass. Secondary production is also defined

as rate of biomass production. In a living

environment, living plant or animal tissue will

be accumulated over time. Biomass is the

amount of this accumulated material at a given time. In an aquatic ecosystem biomass may be

lost by export ( such as downstream transport of biomass) or gained by import from other

systems such as leaves falling into a stream.

THE FLOW OF ENERGY TO HIGHER TROPHIC LEVELS

Autotrophs provide the main source of energy available to

other organisms that are incapable of synthesizing their own

food and lack the capability of fixing light energy. Only a

limited amount of energy is available to higher trophic

levels because of continuous loss of energy due to metabolic

activity. This is explained by the second law of

thermodynamics.

Figure 6 SECONDARY PRODUCTION IN A SNAIL

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Trophic level is simply a feeding level represented in a food web or a food chain. Primary

producers comprise the bottom trophic level, followed by primary consumers (herbivores), then

secondary consumers (carnivores feeding on herbivores), and so on. When we talk of moving

"up" the food chain, we are speaking figuratively and mean that we move from plants to

herbivores to carnivores. This does not take into account decomposers and detritivores

(organisms that feed on dead organic matter), which make up their own, highly important trophic

pathways.

What happens to the NPP that is produced and then stored as plant biomass at the lowest

trophic level?

On average, it is consumed or decomposed. Theequation for aerobic respiration is;

C6H12O6 + 6 O2 -------- 6 CO2 + 6 H2O 

In this process energy in chemical bonds is converted into heat energy. If NPP is not consumed it

is accumulated somewhere in the body. Usually this does not happen but during early periods of

earth history such as Carboniferous and Pennsylvanian, large amount of NPP was accumulated in

swamps. It was buried and compressed to form coal and oil deposits that we mine today.

In a balanced ecosystem, the annual total respiration is equal to annual total GPP. Following

rules are applied as energy passes from one trophic level to another trophic level.

Only a limited fraction of available energy from one trophic level is transferred to the

next trophic level. This limited fraction constitutes only 10%.

The numbers and biomass of the organisms decrease as one ascends the food chain.

EXAMPLE

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In order to let us examine what happens to energy within a food chain. Suppose we have some

amount of plant matter consumed by hares and hares are in turn consumed by foxes. The

following diagram shows how it works in terms of energy loss at each level.

A hare ingests plant matter through the process of ingestion. A part of this material is processed

by the digestive system which is used to make new cells and tissues. This is called assimilation.

The part of this material which cannot be assimilated such plants stem and roots, are discarded

through the hare’s body by the process of excretion. Thus assimilation can be defined as;

Assimilation = Ingestion - Excretion

Efficiency of this process of assimilation varies in animals if the food is plant material ranging

from 15-50%, and from 60-90% if it is animal material.

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The hare uses only a significant fraction of this assimilated energy for maintaining high constant

body temperature, for hopping and synthesizing proteins. This loss of energy is associated to

cellular respiration. The remaining energy builds up more hare biomass by growth and

reproduction that is increasing overall biomass by producing off springs. The conversion of

assimilated energy into new tissue is known as secondary production in consumers. In this

example, secondary production of the hare is the energy available to the foxes who feed on hares.

As mentioned that all of the energy available to hares is consumed to carry out normal metabolic

activities, so the energy available to foxes is much less as compared to hares.

Similar to assimilation efficiency, net production efficiency for any organism can also be

calculated. This is equal to the ratio of NPP to the GPP for plants. Here production not only

refers to growth but also reproduction. Thus, net production efficiency is represented as;

Net Production Efficiency = Production / Assimilation

For Plants,

Net Production Efficiency = NPP / GPP

These ratios measure the efficiency with which an organism converts assimilated energy into

primary and secondary production. The amount of these efficiencies varies among different

organisms, mainly due to different metabolic requirements. For example, on average vertebrates

use about 98% of the assimilated energy for metabolism, and only the remaining 2% is used for

growth and reproduction. Invertebrates use only 80% of assimilated energy for metabolism, and

thus exhibit greater net production efficiency almost 20% as compared to vertebrates. Plants

show the greater net production efficiency that range from 30-85%. The reason that some

organisms have such high net production efficiency and some have low, is that they are

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poikilotherms, those organisms that do not regulate their temperatures internally so they require

less energy than homeotherms, those organisms that require large amount of energy to maintain a

constant body temperature.

So we conclude that

1. Net Secondary Production is less than Net Primary Production.

NSP <<NPP

2. Net Primary Production depends upon

Primary production, trophic status, and transfer efficiencies

3. Transfer Efficiency

Endotherms < Ectotherms

Herbivores < carnivores

LANDSCAPE ECOLOGY

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Landscape ecology as we can see from the name is the study of landscapes. Landscape ecology

particularly tells us about the structure, function as well as composition of the land. Despite the

fact that there are heap approaches to characterize "landscape" dependent upon the wonder under

thought, suffice it to say that a landscape is not inevitably characterized by its size; rather, it is

characterized by a connecting mosaic of components for example biological communities which

are important to some marvel under thought at any scale. Subsequently, a landscape is just a

region of area at any scale containing an intriguing example that influences and is influenced by

an environmental procedure of sideline.

Landscape ecology, then, includes the

investigation of these landscape patterns, the

relationship among the components of the pattern,

and how these examples and their relationship

change after some time. Moreover, includes the

application of these standards in the plan and

understanding of demonstrable issues.

Landscape ecology is basically focused on three things:

Spatial heterogeneity

Broader spatial extents than those traditionally studied in ecology.

The role of humans in creating and affecting landscape patterns and process.

SPATIAL HETEROGENEITY:

It may be characterized best by its emphasis on spatial heterogeneity and pattern: how to

portray it, where it originates from, how it changes through time, why it is important, and how

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people oversee it.

Spatial heterogeneity itself has five subject matters.

1. Distinguishing example and the scale at which it is communicated, and outlining it

quantitatively.

2. Recognizing and depicting the operators of design development, which incorporate the

physical abiotic layout, demographic reactions to this format, and unsettling influence

administrations overlaid on these.

3. Describing the adjustments and procedure over space and time; that is, the landscapes

progress, and outlining it quantitatively. An enthusiasm for scene flow essentially

summons models or something to that affect - on the grounds that scene are extensive and

they change after some time scales that are hard to grasp exactly.

4. Understanding the ecological consequence of pattern; that is, the reason it makes a

difference to populations, groups, and environments.

5. Overseeing land to accomplish human targets.

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BROAD SPATIAL EXTENTS:

It is recognized by its attention on more extensive spatial degrees than those customarily

concentrated on in biology. This stems from the human-centric starting points of the

order .Beginning catalyst for the order originated from the geographers flying perspective of the

earth. The emphasis on substantial geographic regions is steady with how people commonly see

the world–through a coarse lens. Nonetheless, present day scene biology does not characterize,

from the earlier, particular scales that may be all around applied; rather, the accentuation is to

recognize scales that best portray connections between spatial heterogeneity and the procedure of

interest.

HUMAN ROLE:

It is frequently characterized by it concentrate on the part of people in making what's more,

influencing scene designs and process. Without a doubt, landscape ecology is at times thought to

be an interdisciplinary science managing the interrelation between human culture and its living

surroundings. Consequently, an incredible arrangement of land nature manages "manufactured"

situations, where people are the overwhelming power and current land environment, with its

accentuation on the interaction between spatial heterogeneity and natural procedure, considers

people as one of numerous critical operators influencing scenes, and underscores regular, semi-

characteristic, and fabricated lands.

Emergence of Landscape Ecology:

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The development of landscape ecology was a noticeable sub discipline of ecology in the mid

1980's can be followed to various components.

Growing awareness of broad scale

environmental issues requiring a

landscape perspective,

Increasing recognition of the

importance of scale in studying and

managing pattern-process

relationships,

Emergence of the dynamic view of

ecosystems/landscapes, and

Technological advances in remote sensing, computer hardware and software.

ISSUES REGARDING LANDSCAPE:

Unwavering interest for more wares and administrations from worldwide ecological

communities has prompted various natural emergencies. Amazing misfortunes of topsoil every

year from a large portion of America's farmlands exhibit that these environments are being

abused. Disappointment of certain tropical damp timberlands to bounce back after clear slicing

drastically shows their powerlessness to radical unsettling influence. Equally compelling

evidence of ecosystem limits is seen in the altered flooding regimes, increased suspended loads,

chemical contamination, and community structure changes in virtually every temperate river in

the world. The degradation of Earth’s ecosystems is further signaled by the unprecedented

decline of thousands of species, many of which have become extinct. Many of these crises are

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the result of cumulative impacts of land use changes occurring over broad spatial scales (i.e.,

landscapes).

IMPORTANCE OF LANDSCAPE ECOLOGY:

Now a days, landscape ecology is very important specially for the businessmen because

land is different at different place and landscape ecology is founded on composition, structure

and function partially depend on the spatial context of the ecosystem. Therefore, there is a need

to observe ecology at every different location.

Following are the examples where it’s required.

METPOPULATIONS:

Metapopulations rely on upon the number and spatial course of action of natural

surroundings patches – where the likelihood of a living space patch being possessed whenever is

in any event in part subject to its vicinity to other habitat patches.

Centering administration on the individual site, for this situation, without thought of its land

context, can have lamentable results for the populations.

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Succession of Forest:

Neighborhood impacts can assume a critical part in deciding the succession reaction taking

after an aggravation. For instance, edge impacts that change the dispersion of vitality and water

and the plant species piece of the quick neighborhood which can impact the relative plenitude of

population can apply an in number impact on progression in woods holes and in bigger openings,

e.g., by means of wave-structure succession. Ignoring these impacts can prompt undesirable

results, incorporating an undesirable movement in species organization or a lacking recuperation

of vegetation through and through.

Habitat fragmentation:

Disturbance of living space availability is a noteworthy effect of human exercises on plant

and animal populations and one of the main sources of the biodiversity disaster. Anthropogenic

scene components for example streets, created area, dams can work as hindrances to the

development of life forms over the landscape, and the total effects of these obstructions over

wide spatial degrees can be pulverized.

ECOLOGICAL MODELING

INTRODUCTION:

Ecological modeling is the construction and analysis of mathematical models

of ecological processes, including both purely biological and combined

biophysical models. Models can be analytic or simulation-based and are used

to understand complex ecological processes and predict how real

ecosystems might change.

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Modeling has become an important tool in the study of ecological systems.

Models provide an opportunity to explore ideas regarding ecological

systemsthat may not be possible to field-test for logistical, political,or

financial reasons. Theprocess of formulating an ecological model is

extremelyhelpful for organizing one’s thinking, bringing hiddenassumptions

to light, and identifying data needs.

It isimportant to recognize the difference between models andthe modeling

process. A model is a representation of a particularthing, idea, or condition.

Models can be as simpleas a verbal statement about a subject or two boxes

connectedby an arrow to represent some relationship. Alternatively,models

can be extremely complex and detailed,such as a mathematical description

of the pathways ofnitrogen transformations within ecosystems. The modeling

process is the series of steps taken to convert an ideafirst into a conceptual

model and then into a quantitative model. Because part of what ecologists

do is revisehypotheses and collect new data, the model and the viewof

nature that it represents often undergo many changesfrom the initial

conception to what is deemed the finalproduct.

HISTORY:

Ecological modeling was introduced as a management tool around the year

1970. The field of ecological and environmental modeling has developed

rapidly during the last two decades due essentially to three factors:

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1. The development of computer technology, which has enabled us to handle

very complex mathematical systems.

2. A general understanding of pollution problems, including that a complete

elimination of pollution is not feasible ("zero discharge"), but that a proper

pollution control with the limited economical resources available requires

serious considerations of the influence of pollution impacts on ecosystems.

3. Our knowledge of environmental and ecological problems has increased

significantly. We have particularly gained more knowledge about

quantitative relations in ecosystems and between ecological properties and

environmental factors.Models are increasingly used in environmental

management, because they are the onlytool that is able to relate

quantitatively the impact on an ecosystem with theconsequences for the

state of the ecosystem.

The idea behind the use of ecological management models is demonstrated

in Figure 1. Urbanization and industrial development have had an increasing

impact on the environment. Energy and pollutants are released into

ecosystems, where they may cause more rapid growth of algae or bacteria,

extinguish species, or alter the entire ecological structure. Now, an

ecosystem is extremely complex, and so it is an overwhelming task to

predict the environmental effects that such an emission will have. It is here

that the model comes into the picture. With sound ecological knowledge, it is

possible to extract the features of the ecosystem that are involved in the

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pollution problem under consideration, to form the basis of the ecological

model. As indicated in Fig. 1, the model resulting can be used to select the

environmental technology best suited for the solution of specific

environmental problems.

Figure 1: The figure illustrates the idea behind using models to find the

relationshipbetween the impact on ecosystems and the consequences in the

ecosystems. The modelscan be used to select environmental technological

solutions.

ECOLOGICAL MODELS:

Ecological models can be classified in a number of ways. One of the

mostuseful is the distinction between single-level descriptive/empirical

modelsand hierarchical/multilevel explanatory (or mechanistic) models. An

example of a single-level descriptivemodel is a regression equation relating

annual net primary production, NPP, orcrop yield to annual precipitation

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and/or temperature. When used within therange of precipitation and

temperature included in the formulation of the regressionequation(s), such a

model may be rather accurate for interpolative prediction.It does not,

however, ‘explain’ the operation of the systems, and themodel may fail when

applied to conditions outside the environmental envelopeused for parameter

estimation, or when applied to a different ecosystem. Explanatorymodels

often include at least two levels of biological/ecological organization,using

knowledge at one level of organization (e.g., biological organs)to simulate

behavior at the next higher level of organization (e.g., organisms),although

other factors may come into play. Information at the lower levels maybe

empirical or descriptive information that helps explainbehavior at the level of

the organism. Of course, in explanatory ecologicalmodels, knowledge gaps

arise and simplifications are inevitable.Modeling terrestrial net primary

production provides a robust example of thespectrum of modeling possible in

ecology. Anew generation of NPP models uses satellite data for input, and

uses a simplelight conversion efficiency factor to compute NPP from

absorbed photosyntheticallyactive radiation. Use of satellite data for primary

input data has allowedbroad mapping of NPP from regional up to global

scales (Coops and Waring 2001, Running et al 2000).

THE CONCEPTUAL MODEL

The development of a conceptual model can be an integralpart of designing

and carrying out any research project.Conceptual models are generally

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written as diagrams withboxes and arrows, thereby providing a compact,

visualstatement of a research problem that helps determine thequestions to

ask and the part of the system to study. Theboxes represent state variables,

which describe the state or condition of the ecosystem components. The

arrows illustrate relationships among state variables, such as the movement

of materials and energy (calledflows) or ecological interactions (e.g.,

competition).

The model shouldstrike a balance between incorporating enough detail

tocapture the necessary ecological structure and processesand being simple

enough to be useful in generatinghypotheses and organizing one’s thoughts.

QUANTITATIVE MODELS

A quantitative model is a set of mathematical expressions for which

coefficients and data have been attached to the boxes and arrows of

conceptual models; with those coefficientsand data in place, predictions can

be made for thevalue of state variables under particular

circumstances.Ecologists use quantitative models for various

purposes,including explaining existing data, formulating predictions,and

guiding research.Constructing a quantitative model andrunning simulations

may help in the design of experiments forexample, to evaluate experimental

power for differenthypothesized effect sizes. Sensitivity analysis of a

quantitativemodel can reveal which processes and coefficientshave the most

influence on observed results and thereforesuggest how to prioritize

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sampling efforts. Quantitativemodels can even be used to generate

“surrogate” data onwhich to test potential environmental indicators or

evaluatepotential sampling schemes. Most important, quantitativemodels

translate ecological hypotheses into predictionsthat can be evaluated in light

of existing or new data.

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REFERENCES

http://www.tutorvista.com/content/biology/biology-iv/ecosystem/primary-secondary-

productivity.php

http://sky.scnu.edu.cn/life/class/ecology/chapter/Chapter18.htm

http://highered.mheducation.com/sites/007096341x/student_view0/chapter19/index.html

http://www.eolss.net/sample-chapters/c09/e4-20-03.pdf

http://izt.ciens.ucv.ve/ecologia/Archivos/Referencias/jkl/jackson-bioscience00.pdf

http://hahana.soest.hawaii.edu/agouroninstitutecourse/Thelimits.pdf

http://www.umass.edu/landeco/about/landeco.pdf

http://www.hydrol-earth-syst-sci.net/10/967/2006/hess-10-967-2006.pdf

http://www.montana.edu/hansenlab/documents/bio515_13/Wiens%202002.pdf

http://www2.ca.uky.edu/agc/pubs/for/for76/for76.pdf