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The Ecosystem and how it relates to Sustainability

"I bequeathe myself to the dirt, to grow from the grass I love;
If you want me again, look for me under your boot-soles."
- Walt Whitman

In this lesson, we will learn answers to the following questions:

• What is an ecosystem, and how tin we study one?
• Is the Globe an open up or closed organisation with respect to energy and elements?
• How practise we define "biogeochemical cycles," and how are they of import to ecosystems?
• What are the major controls on ecosystem function?
• What are the major factors responsible for the differences betwixt ecosystems around the world?

Introduction

In the previous lectures we accept learned about the Earth and its environment, and we have learned well-nigh the diversity of life on the planet and well-nigh ecological interactions between species. At present we volition combine these ii basic components and consider how the environs and life collaborate in "ecosystems". But before that we should return to a topic introduced at the very start of class, which is that of sustainability and how we view it in terms of system science.

Sustainability and System Scientific discipline - The case of sustainability used at the showtime of class was to consider that I give everyone a dollar each time y'all come to class. The question was: Is that sustainable? In lecture we agreed that more than information was needed to reply that question. For example, nosotros needed to know how much money exercise I have, or the "stock" of money (e.g., if there were 100 students in form and I had a stock of $100, this would work once...). What if I spend coin on other stuff like food? What is the "input" or renewal rate or "turnover fourth dimension" of money in my bank account, compared to how fast I consume money? What if the class size grows because form popularity increases? Correct abroad nosotros come across that this is a "system" that has a residual betoken in information technology that depends on many other parts of the "system".  Solving this problem is an example of"systems thinking", and we need to learn how to apply that to science and to issues of sustainability.

Scientific Concepts, applied to ecosystems and to sustainability.

Working through this simple example illustrates how complex the event of sustainability can become.  However, what we also detect is that in all such problems there is a mutual gear up of central scientific concepts and principles that we volition learn to understand in this course – these concepts include the following (there will be more specific examples given after on):

Standing Stock = the corporeality of material in a "pool", such as the amount of oil in the basis or greenhouse gases in the atmosphere. "Continuing" refers to the amount at the electric current fourth dimension (like what is the stock of trees standing in the forest correct now).

Mass Balance = asking the question of "do the numbers add upwards?" If I demand $100 each class to give to students, but I only have $1, then the mass residuum is off. We can besides use a mass residue equation to decide how a system is changing over time (we will practice this in a later lecture for heat-trapping gases in the atmosphere).

Fabric Flux Rate = the input or output of material from a system, such as the amount of oil nosotros pump out of the ground each year, or the corporeality of greenhouse gas nosotros pump into the atmosphere each year by burning fossil fuels.

Residence Time = the standing stock divided past the flux rate, which provides the average time that materials spent circulating in a pool - for example, the residence time of methyl hydride in the atmosphere is nearly 10 years.

Negative and Positive Feedbacks = negative feedbacks tend to dull a process, while positive feedbacks tend to accelerate a process. For case, in a warming world the ice caps will cook, which reduces the World'due south albedo, nosotros retain more of the lord's day's heat free energy, and that accelerates warming which in turn melts more ice cap -- this is a positive feedback.

What is an Ecosystem?

An ecosystem consists of the biological community that occurs in some locale, and the physical and chemical factors that make upwards its non-living or abiotic environment. At that place are many examples of ecosystems -- a swimming, a woods, an estuary, a grassland. The boundaries are not fixed in any objective way, although sometimes they seem obvious, every bit with the shoreline of a minor swimming. Usually the boundaries of an ecosystem are chosen for practical reasons having to do with the goals of the item report.

The study of ecosystems mainly consists of the report of sure processes that link the living, or biotic, components to the not-living, or abiotic, components. The 2 master processes that ecosystem scientists report are Energy transformations and biogeochemical cycling . Every bit we learned before, environmental generally is defined as the interactions of organisms with 1 another and with the environment in which they occur. Nosotros tin written report ecology at the level of the individual, the population, the customs, and the ecosystem.

Studies of individuals are concerned by and large about physiology, reproduction, development or behavior, and studies of populations usually focus on the habitat and resource needs of item species, their grouping behaviors, population growth, and what limits their affluence or causes extinction. Studies of communities examine how populations of many species interact with ane some other, such as predators and their prey, or competitors that share mutual needs or resource.

In ecosystem ecology nosotros put all of this together and, insofar as we can, we attempt to sympathize how the organisation operates as a whole. This means that, rather than worrying mainly about particular species, we endeavor to focus on major functional aspects of the system. These functional aspects include such things as the amount of energy that is produced past photosynthesis, how energy or materials flow along the many steps in a nutrient chain, or what controls the rate of decomposition of materials or the charge per unit at which nutrients (required for the product of new organic matter) are recycled in the arrangement.

Components of an Ecosystem Y'all are already familiar with the parts of an ecosystem. From this grade and from general cognition, you too take a basic understanding of the variety of plants and animals, and how plants and animals and microbes obtain water, nutrients, and food. Nosotros tin clarify the parts of an ecosystem past listing them nether the headings "abiotic" and "biotic".

ABIOTIC COMPONENTS	BIOTIC COMPONENTS
Sunlight	Primary producers
Temperature	Herbivores
Precipitation	Carnivores
Water or moisture	Omnivores
Soil or water chemistry (e.m., P, NO3 , NH4)	Detritivores
etc.	etc.
All of these vary over space/time

Past and large, this set of components and environmental factors is of import almost everywhere, in all ecosystems.

Usually, biological communities include the "functional groupings" shown above. A functional grouping is a biological category composed of organisms that perform more often than not the aforementioned kind of function in the system; for example, all the photosynthetic plants or primary producers class a functional grouping. Membership in the functional group does not depend very much on who the actual players (species) happen to be, simply on what function they perform in the ecosystem.

Processes of Ecosystems

This figure with the plants, zebra, lion, and then forth, illustrates the two main ideas well-nigh how ecosystems function: ecosystems take energy flows and ecosystems cycle materials . These two processes are linked, but they are non quite the same (come across Figure one).

Figure one. Free energy flows and material cycles.

Free energy enters the biological system equally light energy, or photons, is transformed into chemic energy in organic molecules past cellular processes including photosynthesis and respiration, and ultimately is converted to heat free energy. This energy is dissipated, meaning it is lost to the system as heat; once it is lost information technology cannot exist recycled.  Without the continued input of solar energy, biological systems would speedily shut down. Thus the Earth is an open system with respect to free energy.

Elements such as carbon, nitrogen, or phosphorus enter living organisms in a variety of means. Plants obtain elements from the surrounding temper, water, or soils. Animals may also obtain elements directly from the physical environment, only usually they obtain these mainly every bit a consequence of consuming other organisms. These materials are transformed biochemically within the bodies of organisms, but sooner or after, due to excretion or decomposition, they are returned to an inorganic land (that is, inorganic fabric such equally carbon, nitrogen, and phosphorus, instead of those elements being bound up in organic matter). Often bacteria complete this process, through the process chosen decomposition or mineralization (run across adjacent lecture on microbes).

During decomposition these materials are not destroyed or lost, and so the World is a closed system with respect to elements (with the exception of a meteorite entering the system now and and then...). The elements are cycled endlessly between their biotic and abiotic states inside ecosystems. Those elements whose supply tends to limit biological activity are called nutrients .

The Transformation of Energy

The transformations of energy in an ecosystem begin first with the input of free energy from the lord's day. Energy from the sun is captured by the process of photosynthesis. Carbon dioxide is combined with hydrogen (derived from the splitting of water molecules) to produce carbohydrates (the autograph notation is "CHO"). Energy is stored in the loftier energy bonds of adenosine triphosphate, or ATP (see lecture on photosynthesis).

The prophet Isaah said "all flesh is grass", earning him the title of first ecologist, considering nearly all energy available to organisms originates in plants. Because information technology is the first step in the production of energy for living things, it is called master product (click hither for a primer on photosynthesis). Herbivores obtain their energy by consuming plants or plant products, carnivores eat herbivores, and detritivores consume the droppings and carcasses of united states of america all.

Figure two portrays a uncomplicated nutrient chain, in which energy from the sun, captured by plant photosynthesis, flows from trophic level to trophic level via the nutrient chain . A trophic level is composed of organisms that brand a living in the aforementioned mode, that is they are all chief producers (plants), principal consumers (herbivores) or secondary consumers (carnivores). Dead tissue and waste matter products are produced at all levels. Scavengers, detritivores, and decomposers collectively account for the employ of all such "waste product" -- consumers of carcasses and fallen leaves may be other animals, such as crows and beetles, just ultimately it is the microbes that finish the job of decomposition. Non surprisingly, the amount of primary production varies a great deal from place to place, due to differences in the amount of solar radiation and the availability of nutrients and water.

For reasons that we will explore more fully in subsequent lectures, free energy transfer through the food chain is inefficient. This means that less energy is available at the herbivore level than at the principal producer level, less nevertheless at the carnivore level, and so on. The issue is a pyramid of energy, with of import implications for understanding the quantity of life that tin be supported.

Normally when we think of food chains we visualize green plants, herbivores, and then on. These are referred to as grazer food chains , because living plants are directly consumed. In many circumstances the principal energy input is not green plants simply dead organic matter. These are called detritus food chains . Examples include the woods floor or a woodland stream in a forested area, a salt marsh, and most obviously, the ocean floor in very deep areas where all sunlight is extinguished 1000'south of meters higher up. In subsequent lectures nosotros shall render to these important issues concerning energy menstruation.

 Finally, although we have been talking about food chains, in reality the organization of biological systems is much more complicated than can be represented by a simple "chain". There are many food links and chains in an ecosystem, and we refer to all of these linkages as a food web . Food webs can be very complicated, where it appears that "everything is connected to everything else" (this is a major take-home bespeak of this lecture) , and information technology is important to sympathise what are the most important linkages in whatsoever particular food spider web. The next question is how practise we determine what the of import processes or linkages are in food webs or ecosystems? Ecosystem scientists use several different tools, which can be described generally under the term "biogeochemistry".

Biogeochemistry

How tin can we study which of these linkages in a food web are most of import? One obvious way is to report the menstruation of free energy or the cycling of elements. For example, the cycling of elements is controlled in office by organisms, which store or transform elements, and in part by the chemistry and geology of the natural globe. The term Biogeochemistry is defined every bit the study of how living systems (biology) influence, and are controlled by, the geology and chemistry of the earth. Thus biogeochemistry encompasses many aspects of the abiotic and biotic earth that we live in.

There are several main principles and tools that biogeochemists use to study globe systems. About of the major environmental problems that we face in our globe today can be analyzed using biogeochemical principles and tools. These problems include global warming, acid rain, environmental pollution, and increasing greenhouse gases. The principles and tools that we utilize can be broken downwards into iii major components: element ratios, mass balance, and element cycling .

ane. Element ratios

In biological systems, we refer to important elements as "conservative" . These elements are often nutrients. By "conservative" nosotros mean that an organism can change but slightly the amount of these elements in their tissues if they are to remain in skilful wellness. It is easiest to remember of these conservative elements in relation to other important elements in the organism. For example, in salubrious algae the elements C, Northward, P, and Fe have the following ratio, chosen the Redfield ratio after the oceanographer who discovered it. The ratio of number of atoms of these elements (referenced to one P atom) is as follows:

C : N : P : Atomic number 26 = 106 : sixteen : 1 : 0.01

Once we know these ratios, we can compare them to the ratios that we measure in a sample of algae to determine if the algae are lacking in one of these limiting nutrients.

ii. Mass Balance

Some other important tool that biogeochemists utilise is a simple mass residual equation to draw the land of a arrangement. The system could be a snake, a tree, a lake, or the entire globe. Using a mass rest approach we tin can make up one's mind whether the organisation is irresolute and how fast information technology is changing. The equation is:

NET CHANGE = INPUT + OUTPUT + INTERNAL Alter

In this equation the net change in the organisation from one fourth dimension catamenia to some other is adamant by what the inputs are, what the outputs are, and what the internal modify in the organisation was. The example given in class is of the acidification of a lake, because the inputs and outputs and internal modify of acid in the lake.

3. Element Cycling

Element cycling describes where and how fast elements move in a arrangement. In that location are 2 full general classes of systems that nosotros can analyze, as mentioned above: closed and open systems.

A closed arrangement refers to a organization where the inputs and outputs are negligible compared to the internal changes. Examples of such systems would include a canteen, or our entire globe. There are two ways we can depict the cycling of materials inside this closed system, either past looking at the charge per unit of motility or at the pathways of movement.

1. Charge per unit = number of cycles / time . As the rate increases, productivity increases
2. Pathways - important because of dissimilar reactions that may occur along different pathways

In an open arrangement in that location are inputs and outputs also as the internal cycling. Thus we tin can describe the rates of movement and the pathways, but equally nosotros did for the airtight system, but we can also define a new concept chosen the residence time (one of our scientific concepts mentioned at the beginning of lecture). The residence fourth dimension indicates how long on average an element remains within the organization before leaving the system.

1. Rate
2. Pathways
3. Residence fourth dimension, Rt

Rt = total amount of matter / output rate of matter

(Notation that the "units" in this adding must cancel properly)

Controls on Ecosystem Function

Now that we have learned something about how ecosystems are put together and how materials and free energy menstruum through ecosystems, we can ameliorate address the question of "what controls ecosystem function"? In that location are 2 dominant theories of the control of ecosystems. The first, chosen bottom-upwards control, states that it is the nutrient supply to the main producers that ultimately controls how ecosystems part. If the nutrient supply is increased, the resulting increase in production of autotrophs is propagated through the food web and all of the other trophic levels volition respond to the increased availability of food (energy and materials volition wheel faster).

The second theory, called acme-down control, states that predation and grazing by higher trophic levels on lower trophic levels ultimately controls ecosystem part. For case, if you have an increase in predators, that increase will result in fewer grazers, and that decrease in grazers will result in turn in more principal producers because fewer of them are being eaten by the grazers. Thus the control of population numbers and overall productivity "cascades" from the superlative levels of the nutrient chain downwards to the bottom trophic levels. In before lectures this idea was also introduced and explained as a "trophic cascade".

So, which theory is correct? Well, as is often the case when there is a clear dichotomy to choose from, the answer lies somewhere in the middle. There is testify from many ecosystem studies that BOTH controls are operating to some caste, but that NEITHER control is complete. For case, the "elevation-downwards" event is often very stiff at trophic levels near to the top predators, only the command weakens equally you move further downward the nutrient chain toward the primary producers. Similarly, the "bottom-up" effect of adding nutrients usually stimulates primary product, merely the stimulation of secondary production further up the nutrient chain is less stiff or is absent.

Thus we find that both of these controls are operating in any arrangement at any time, and nosotros must understand the relative importance of each control in social club to assist u.s. to predict how an ecosystem will behave or change nether different circumstances, such as in the confront of a changing climate.

The Geography of Ecosystems

There are many different ecosystems: rain forests and tundra, coral reefs and ponds, grasslands and deserts. Climate differences from place to place largely make up one's mind the types of ecosystems we see. How terrestrial ecosystems appear to us is influenced mainly by the dominant vegetation.

The discussion "biome" is used to describe a major vegetation type such as tropical rain forest, grassland, tundra, etc., extending over a big geographic area (Figure 3). It is never used for aquatic systems, such as ponds or coral reefs. It always refers to a vegetation category that is ascendant over a very large geographic scale, and thus is somewhat broader geographically than an ecosystem.

Figure 3: The distribution of biomes.

Nosotros can depict upon previous lectures to remember that temperature and rainfall patterns for a region are distinctive. Every place on Globe gets the aforementioned total number of hours of sunlight each year, but not the same amount of oestrus. The sun'south rays strike low latitudes straight but loftier latitudes obliquely. This uneven distribution of oestrus sets upward not only temperature differences, but global wind and ocean currents that in turn have a keen deal to do with where rainfall occurs. Add together in the cooling effects of elevation and the effects of state masses on temperature and rainfall, and we get a complicated global pattern of climate.

A schematic view of the earth shows that, complicated though climate may be, many aspects are predictable (Figure 4). Loftier solar energy striking near the equator ensures nearly constant high temperatures and high rates of evaporation and plant transpiration. Warm air rises, cools, and sheds its moisture, creating just the conditions for a tropical rain forest. Contrast the stable temperature merely varying rainfall of a site in Panama with the relatively constant precipitation only seasonally changing temperature of a site in New York State. Every location has a rainfall- temperature graph that is typical of a broader region.

Effigy 4. Climate patterns affect biome distributions.

We can draw upon plant physiology to know that certain plants are distinctive of sure climates, creating the vegetation appearance that we call biomes. Annotation how well the distribution of biomes plots on the distribution of climates (Effigy 5). Notation as well that some climates are impossible, at least on our planet. High precipitation is not possible at low temperatures -- there is not enough solar energy to ability the water bike, and most water is frozen and thus biologically unavailable throughout the year. The loftier tundra is every bit much a desert as is the Sahara.

Figure 5. The distribution of biomes related to temperature and precipitation.

Summary

• Ecosystems are made up of abiotic (non-living, environmental) and biotic components, and these bones components are important to well-nigh all types of ecosystems.  Ecosystem Ecology looks at free energy transformations and biogeochemical cycling within ecosystems.
• Energy is continually input into an ecosystem in the class of calorie-free free energy, and some free energy is lost with each transfer to a higher trophic level. Nutrients, on the other hand, are recycled within an ecosystem, and their supply normally limits biological activity.  So, "energy flows, elements bike".
• Energy is moved through an ecosystem via a food web, which is made up of interlocking nutrient bondage. Energy is first captured past photosynthesis (chief production). The amount of main production determines the corporeality of energy bachelor to higher trophic levels.
• The written report of how chemical elements cycle through an ecosystem is termed biogeochemistry. A biogeochemical cycle tin can exist expressed as a set of stores (pools) and transfers, and can exist studied using the concepts of "stoichiometry", "mass remainder", and "residence time".
• Ecosystem role is controlled mainly by two processes, "superlative-down" and "bottom-upwardly" controls.
• A biome is a major vegetation blazon extending over a large expanse. Biome distributions are determined largely by temperature and precipitation patterns on the Earth's surface.

Review and Self Examination

• Review of principal terms and concepts in this lecture.

Suggested Readings:

• Borman, F.H. and K.East. Likens. 1970. "The nutrient cycles of an ecosystem." Scientific American, October 1970, pp 92-101.
  
• Wessells, N.1000. and J.Fifty. Hopson. 1988. Biological science. New York: Random Business firm. Ch. 44.
  

All materials � the Regents of the Academy of Michigan unless noted otherwise.

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Source: https://globalchange.umich.edu/globalchange1/current/lectures/kling/ecosystem/ecosystem.html

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