Primary production landscape ecology ecological modelling

1. 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.

2. 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,

3. 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:

4. 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
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).

5. 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
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'.
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).

6. 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.
 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).

7. 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.”
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,
Figure 4: The trophic cascade

8. 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.

9. 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

10. 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

11. 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

12. 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

13. 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.

14.  EXAMPLE
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

15. 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.
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

16. 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
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

17. LANDSCAPE ECOLOGY
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:

18. 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
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.

19. 5. Overseeing land to accomplish human targets.
 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:

20. 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

21. 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.

22. 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.

23. 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:
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

24. 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 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.

25. 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 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

26. 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 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

27. 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 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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