TOPIC 2.2: COMMUNITIES AND ECOSYSTEMS
An ecosystem has diverse living organisms. In the study of Ecology, these living organisms are categorized on the basis of the level of organization. So at the basic numbers level we have the population, then we identify the species and community to which that organism belongs, how it interacts with the ecosystem and other organisms in the ecosystem. Scientists have also studied the interaction between different organisms and classified their interactions into different types.
This unit will take a minimum of 5.5 hours.
The interactions of species with their environment result in energy and nutrient flows.
Photosynthesis and respiration play a significant role in the flow of energy in communities..
The feeding relationships of species in a system can be modelled using food chains, food webs and ecological pyramids.
What strengths and weaknesses of the systems approach and the use of models have been revealed through this topic?
What are the strengths and weaknesses of models of food chains, food webs, and ecological pyramids?
How can pyramids of productivity be used to predict the effect of human activities on ecosystems?
How can systems diagrams be used to show energy flow through ecosystems? What are the strengths and weaknesses of such diagrams?
Knowledge and Understanding
2.2.U1 A community is a group of populations living and interacting with each other in a common habitat
Define community with reference to a named example
Community refers to all the populations in a specific area or region at a certain time. Its structure involves many types of interactions among species. Some of these involve the acquisition and use of food, space, or other environmental resources. Others involve nutrient cycling through all members of the community and mutual regulation of population sizes. In all of these cases, the structured interactions of populations lead to situations in which individuals are thrown into life or death struggles.
In general, ecologists believe that a community that has a high diversity is more complex and stable than a community that has a low diversity. This theory is founded on the observation that the food webs of communities of high diversity are more interconnected. Greater interconnectivity causes these systems to be more resilient to disturbance. If a species is removed, those species that relied on it for food have the option to switch to many other species that occupy a similar role in that ecosystem. In a low diversity ecosystem, possible substitutes for food may be non-existent or limited in abundance.
2.2.U2 An ecosystem is a community and the physical environment with which it interacts
Define ecosystem with reference to a named example
Everything in the natural world is connected. An ecosystem is a community of living and non-living things that work together. Ecosystems have no particular size. An ecosystem can be as large as a desert or a lake or as small as a tree or a puddle. If you have a terrarium, that is an artificial ecosystem. The water, water temperature, plants, animals, air, light and soil all work together. If there isn't enough light or water or if the soil doesn't have the right nutrients, the plants will die. If the plants die, animals that depend on them will die. If the animals that depend on the plants die, any animals that depend on those animals will die. Ecosystems in nature work the same way. All the parts work together to make a balanced system!
Some ecosystems can cross several countries and so their conservation and ecology has an international dimension.
2.2.U3 Respiration and photosynthesis as processes with inputs, outputs and transformations of energy and matter.
[The details of chloroplasts, light-dependent and light-independent reactions, mitochondria, carrier systems, adenosine triphosphate (ATP) and specific intermediate biochemicals are not expected]
Describe photosynthesis and respiration in terms of inputs, outputs and energy transformations.
Photosynthesis should be understood as requiring carbon dioxide, water, chlorophyll and certain visible wavelengths of light to produce organic matter and oxygen. The transformation of light energy into the chemical energy of organic matter should be appreciated.
Respiration should be recognized as requiring organic matter and oxygen to produce carbon dioxide and water. Without oxygen, carbon dioxide and other waste products are formed. Energy is released in a form available for use by living organisms, but is ultimately lost as heat.
sunlight as energy resource, carbon dioxide and water
chlorophyll traps sunlight; energy is used to split water molecules; hydrogen from water is combined with carbon dioxide to produce glucose.
glucose used as an energy source for the plant and as a building block for other organic molecules; oxygen is released to the atmosphere through stomata.
light energy is transformed to store chemical energy.
glucose and oxygen
oxidation processes inside cells
release of energy for work and heat
stored chemical energy to kinetic energy and heat
2.2.U4 Respiration is the conversion of organic matter into carbon dioxide and water in all living organisms, releasing energy.
[The details of mitochondria, carrier systems, adenosine triphosphate (ATP) and specific intermediate biochemicals are not expected]
Describe the process of respiration
Summarize the equation for respiration
Respiration releases energy for cells from glucose. This can be aerobic respiration, which needs oxygen, or anaerobic respiration, which does not.
Respiration is a series of reactions in which energy is released from glucose. Aerobic respiration is the form of respiration which uses oxygen. It can be summarized by this equation:
glucose + oxygen → carbon dioxide + water (+ energy)
Energy is shown in brackets because it is not a substance. Notice that:
Glucose and oxygen are used up
Carbon dioxide and water are produced as waste products
Aerobic respiration happens all the time in the cells of animals and plants. Most of the reactions involved happen inside mitochondria, tiny objects inside the cytoplasm of the cell. The reactions are controlled by enzymes.
2.2.U5 During respiration, large amounts of energy are dissipated as heat, increasing the entropy in the ecosystem while enabling organisms to maintain relatively low entropy and so high organization.
State how energy in an organism can be lost
Respiration is a chemical reaction where food, water and oxygen is turned into energy for us to use (also allowing us to breathe etc.)
In every reaction there are 2 types of energy; useful and wasted. the useful energy is the stuff we want and wasted is the stuff that's just converted accidentally while making the useful energy. it's wasted because energy can't be destroyed or created, just changed. one type of wasted energy that's created in most reactions is thermal, or heat energy.
As respiration is a chemical reaction, there are useful energy transfers taking place, however as a byproduct of these reactions heat energy is produced.
2.2.U6 Primary producers in most ecosystems convert light energy into chemical energy in the process of photosynthesis.
[The details of chloroplasts, light-dependent and light-independent reactions and specific intermediate biochemicals are not expected]
Describe the process of photosynthesis
Explain why photosynthesis is so important
Describe how plants use some of the end products of photosynthesis
Primary producers, also called autotrophs, are organisms that can produce their own food. Most autotrophs lie at the bottom of the food chain, serving as food sources for animals farther up the line. Primary producers are self-sufficient when it comes to meals: they produce their own food using light, carbon dioxide, water and sometimes other chemicals too.
Producers (autotrophs) are typically plants or algae that produce their own food using photosynthesis and form the first trophic level in a food chain. Exceptions include chemosynthetic organisms that produce food without sunlight.
2.2.U7 The photosynthesis reaction is can be represented by the following word equation. carbon dioxide + water yields glucose + oxygen
Summarize the equation for photosynthesis
Photosynthesis is the process of converting light energy to chemical energy and storing it in the bonds of sugar. This process occurs in plants and some algae. Plants need only light energy, CO2, and H2O to make sugar. The process of photosynthesis takes place in the chloroplasts, specifically using chlorophyll, the green pigment involved in photosynthesis.
The photosynthesis reaction is can be represented by the following word equation.
2.2.U8 Photosynthesis produces the raw material for producing biomass
[Biomass, measured in unite of mass (for example, g m-2) should be distinguished from productivity, measured in units of flow (for example, g m-2 hr-1 or J m-2 hr-1)]
Define compensation point
Biomass is organic, meaning it is made of material that comes from living organisms, such as plants and animals. The most common biomass materials used for energy are plants, wood, and waste. These are called biomass feed stocks. Biomass energy can also be a non-renewable energy source.
Biomass contains energy first derived from the sun: Plants absorb the sun’s energy through photosynthesis, and convert carbon dioxide and water into nutrients (carbohydrates).
2.2.U9 The trophic level is the position that an organism occupies in a food chain, or the position of a group of organisms in a community that occupy the same position in food chains
Define the term trophic level.
Identify and explain trophic levels in food chains and food webs selected from the local environment.
In ecology, the trophic level is the position that an organism occupies in a food chain, or a group of organisms in a community that occupy the same position in food chains - what it eats, and what eats it.
Ecologists look at a natural "economy of energy" that ultimately rests upon solar energy. When they look at an ecosystem there is almost always some foundation species that directly harvests energy from the sun, for example, grass (however in deep sea hydrothermal vents chemosynthetic archaea form the base of the food chain)
2.2.U10 Producers (autotrophs) are typically plants or algae that produce their own food using photosynthesis and form the first trophic level in a food chain. Exceptions include chemosynthetic organisms that produce food without sunlight.
Distinguish between autotroph and chemosynthetic organisms.
All life depends ultimately on primary producers, the organisms which capture the energy in sunlight by photosynthesis. On land, they are easily recognized as plants. Although marine primary production by coral reefs, mangroves and seagrasses is relatively better-known, the vast majority of primary production in the sea is by microscopic single-celled plants called phytoplankton. Phytoplankton account for 50% of the oxygen produced
An example is photosynthetic plants that make their own food from sunlight (using a process called photosynthesis) and chemosynthetic bacteria that make their food energy from chemicals in hydrothermal vents. These are called autotrophs orprimary producers.
2.2.U11 Feeding relationships involve producers, consumers and decomposers. These can be modelled using food chains, food webs and ecological pyramids
[The distinction between storage of energy illustrated by boxes i energy-flow diagrams (representing the various trophic levels), and the flows of energy or productivity often sown as arrows (sometimes of varying widths) needs to be emphasized.]
Distinguish between autotroph and heterotroph
Define producer with reference to a named example
Define consumer with reference to a named example
Define decomposer with reference to a named example
Define top carnivore with reference to a named example
Distinguish between herbivore, carnivore and omnivore
All living things need to feed to get energy to grow, move and reproduce. But what do these living things feed on? Smaller insects feed on green plants, and bigger animals feed on smaller ones and so on. This feeding relationship in an ecosystem is called a food chain. Food chains are usually in a sequence, with an arrow used to show the flow of energy. Below are some living things that can fit into a food chain
Producer: can make their own food, as they use sunlight to make food and are called the basis of every ecosystem which helps the rest of the species through input of energy and new biomass. This all happens through photosynthesis which is the process when the producer uses the sun for energy.
Consumer: feed on other organisms, they do not contain photosynthesis pigments so they cannot make their own food. They have to get energy, minerals and nutrients by eating other organisms. This makes the heterotrophs. Herbivores feed on autotrophs, carnivores on other heterotrophs and omnivores on both.
Decomposer: get their food from the breakdown of a dead organism matter. They break down tissue and release nutrients for absorption by other producers. Decomposers also improve the nutrient capacity in the soil by breaking down the organic material.
2.2.U12 Ecological pyramids include pyramids of numbers, biomass and productivity and are quantitative models that are usually measured for a given area and time
Explain the principles of pyramids of numbers, pyramids of biomass, and pyramids of productivity, and construct such pyramids from given data.
An ecological pyramid is an illustration of the reduction in energy as you move through each feeding (trophic) level in an ecosystem. The base of the pyramid is large since the ecosystem's energy factories (the producers) are converting solar energy into chemical energy via photosynthesis. A food chain can also depict a reduction in energy at each feeding level if the arrows, drawn between the different levels, continue to be reduced in size.
Pyramids are graphical models of the quantitative differences that exist between the trophic levels of a single ecosystem. A pyramid of biomass represents the standing stock of each trophic level measured in units such as grams of biomass per square metre (g m–2). Biomass may also be measured in units of energy, such as J m –2.
2.2.U13 In accordance with the second law of thermodynamics, there is a tendency for numbers and quantities of biomass and energy to decrease along food chains; therefore, the pyramids become narrower towards the apex
[This topic should be actively linked with sub-topic 1.3 as questions will arise requiring students to use their knowledge of thermodynamics with energy flow in ecosystems]
Discuss how entropy affects the structure of an ecological pyramid
Energy is lost as it is transferred between trophic levels; the efficiency of this energy transfer is measured by net production efficiency and trophic level transfer efficiency. Only 10% of the energy is transferred to the next, so the trophic efficiency=10%.
Endotherms have a low NPE and use more energy for heat and respiration than ectotherms, so most endotherms have to eat more often than ectotherms to get the energy they need for survival.
Energy transfers within food webs are determined by the first and second laws of thermodynamics..
The second law relates to the quality of energy. This law states that whenever energy is transformed, some of the energy will lost to a less useful form. In ecosystems, the biggest losses occur as respiration. The second law explains why energy transfers are never 100% efficient. In fact, ecological efficiency, which is the amount of energy transferred from one trophic level to the next, ranges from 5-30%. On average, ecological efficiency is only about 10%.
Because ecological efficiency is so low, each trophic level has a successively smaller energy pool from which it can withdraw energy. This is why food webs have no more than four to five trophic levels. Beyond that, there is not enough energy to sustain higher-order predators
2.2.U14 Bioaccumulation is the build-up of persistent or non-biodegradable pollutants within an organism or trophic level because they cannot be broken down
Define bioaccumulation with reference to a named example
Include concentration of non‑biodegradable toxins in food chains, limited length of food chains, and vulnerability of top carnivores. Consider the terms biomagnification, bioaccumulation and bioconcentration.
Bioaccumulation refers to how pollutants enter a food chain. It is an increase in concentration of a pollutant from the environment to the first organism in a food chain
If a pollutant is short-lived, it will be broken down before it can become dangerous. If it is not mobile, it will stay in one place and is unlikely to be taken up by organisms. If the pollutant is soluble in water it will be excreted by the organism. Pollutants that dissolve in fats, however, may be retained for a long time.
Toxins such as DDT and mercury accumulate along food chains due to the decrease of biomass and energy
2.2.U15 Biomagnification is the increase in concentration of persistent or non-biodegradable pollutants along a food chain
Explain why top consumers are most at risk of toxic effects of biomagnification
Biomagnification refers to the tendency of pollutants to concentrate as they move from one trophic level to the next. It is an increase in concentration of a pollutant from one link in a food chain to another.
We are concerned about these phenomena because together they mean that even small concentrations of chemicals in the environment can find their way into organisms in high enough dosages to cause problems. In order for biomagnification to occur, the pollutant must be:
soluble in fats
2.2.U16 Toxins such as DDT and mercury accumulate along food chains due to the decrease of biomass and energy
Explain how DDT and mercury accumulate in a food chain
In the environment, insects would encounter DDT and absorb some of it into their bodies. Often, they would receive a sub-lethal dose, enough to impair them but perhaps not kill them. In any event, it stands to reason that insects either dying or merely slowed down by pesticide intake would become easy targets for birds. Upon ingestion, the DDT in the insect bodies is released and makes its way into the tissues of the bird's body, particularly the fat deposits. Because an individual bird eats many insects, and because the DDT does not leave the bird's body, and because DDT resists breaking down (either in the environment or the body), it accumulates to higher levels in the bird's tissues. In other words, the DDT that was spread out over, say 1,000 crickets will be concentrated in one bird.
2.2.U17 Pyramids of numbers can sometimes display different patterns; for example, when individuals at lower trophic levels are relatively large (inverted pyramids)]
Identify the function of the pyramid of numbers
List the strengths and weakness of the pyramid of numbers
Pyramid of numbers:
shows the number of organisms at each trophic level in a food chain. Pyramids of numbers can sometimes display different patterns; for example, when individuals at lower trophic levels are relatively large (inverted pyramids).
easy method of giving an overview
good for comparing changes in population numbers over different times
all organisms included regardless of their size
numbers can be too great to represent accurately
2.2.U18 A pyramid of biomass represents the standing stock or storage of each trophic level, measured in units such as grams of biomass per square metre (g m-2) or Joules per square metre (J m-2)(units of biomass or energy)
[Although there is variation in the literature, for this syllabus pyramids of biomass refers to a standing crop (a fixed point in time) and pyramids of productivity refer to the rate of flow of biomass or energy]
Identify the function of the pyramid of biomass
List the strengths and weakness of the pyramid of biomass
Pyramid of biomass:
Contains the biomass at each trophic level. A pyramid of biomass represents the standing stock or storage of each trophic level, measured in units such as grams of biomass per square metre (g m–2). Pyramids of biomass can show greater quantities at higher trophic levels because they represent the biomass present at a fixed point in time, although seasonal variations may be marked.
overcomes the problems of pyramids of numbers
only uses samples from populations, so it’s impossible to measure biomass exactly
organisms must be killed to measure dry mass
2.2.U19 Pyramids of biomass can show greater quantities at higher trophic levels because they represent the biomass present at a fixed point in time, although seasonal variations may be marked.
[Although there is variation in the literature, for this syllabus pyramids of biomass refers to a standing crop (a fixed point in time) and pyramids of productivity refer to the rate of flow of biomass or energy]
Pyramid of biomass is a diagram representing the amount of biomass measured in grams of dry mass per square metre (g m−2), found in a particular habitat at ascending trophic levels of a food chain. Biomass decreases at each ascending level of the food chain. A pyramid of biomass is a more accurate representation of the flow of energy through a food chain than a pyramid of numbers, but seasonal variations in the rate of turnover of the organisms at a particular level may result in higher or lower values for the amount of biomass sampled at a particular time than the average amount over the whole year.
2.2.U20 Pyramids of productivity refer to the flow of energy through a trophic level, indicating the rate at which that stock/storage is being generated
Identify the function of the pyramid of productivity
List the strengths and weakness of the pyramid of productivity
Pyramid of productivity:
Pyramids of productivity refer to the flow of energy through a trophic level,
indicating the rate at which that stock/storage is being generated. It contains the flow of energy through each trophic level; shows the energy being generated and available as food to the next trophic level during a fixed period of time, measured in units such as flow of biomass or energy per square metre (g m-2 yr-1) or Joules per square metre (J m-2 yr) (units of biomass or energy).
shows the actual energy transferred and allows for rate of production
very difficult and complex to collect energy data as the rate of biomass production over time is required
2.2.U21 Pyramids of productivity for entire ecosystems over a year always show a decrease along the food chain.
Energy flows through the food chain in a predictable way, entering at the base of the food chain, by photosynthesis in primary producers, and then moving up the food chain to higher trophic levels. Because the transfer of energy from one trophic level to the next is inefficient, there is less energy entering higher trophic levels. Thus, diagrams showing how much energy enters each trophic level will have a distinct pyramid shape.
In accordance with the second law of thermodynamics, there is a tendency for numbers and quantities of biomass and energy to decrease along food chains; therefore the pyramids become narrower as one ascends.
Application and Skill
2.2.A1 Explain the transfer and transformation of energy as it flows through an ecosystem.
Almost all energy enters Earth's ecosystems as solar insolation. That energy is then transformed and used by the diverse variety of organisms that make up food webs. Through photosynthesis, producers transform sunlight into glucose, which they then use for respiration. Chloroplasts in plant cells use sunlight to convert CO2 and water to glucose and oxygen gas. The plants' mitochondria then use the sugars for energy to drive respiration, their cellular processes required to stay alive.
Explain pathways of incoming solar radiation incident on the ecosystem including:
•loss of radiation through reflection and absorption
•conversion of light to chemical energy
•loss of chemical energy from one trophic level to another
•efficiencies of transfer
•overall conversion of light to heat energy by an ecosystem
•re-radiation of heat energy to the atmosphere.
2.2.A2 Analyse the efficiency of energy transfers through a system.
Gross primary production is a measure of the energy that a plants transform from the sun. The fraction of that energy that is converted into glucose reflects the gross productivity of the plant. The energy remaining after respiration is considered the net primary production. In general, gross production refers to the energy contained within an organism before respiration and net production the energy after respiration. The terms can be used to describe energy transfer in both autotrophs and heterotrophs.
Energy will decrease with each increase in trophic level- second law of thermodynamics states that during any transfer of energy, some is lost due to the tendency toward an increase in disorder (entropy). Energy for higher trophic levels is also constrained by loss due to metabolic respiration, as well as defensive strategies in some organisms that lowers the quality of food Energy transfer between trophic levels is generally inefficient, such that net production at one trophic level is generally only 10% of the net production at the preceding trophic level
2.2.A3 Explain the relevance of the laws of thermodynamics to the flow of energy through ecosystems
Two laws of physics are important in the study of energy flow through ecosystems. The first law of thermodynamics states that energy cannot be created or destroyed; it can only be changed from one form to another. Energy for the functioning of an ecosystem comes from the Sun. Solar energy is absorbed by plants where in it is converted to stored chemical energy.
The second law of thermodynamics states that whenever energy is transformed, there is a loss energy through the release of heat. This occurs when energy is transferred between trophic levels as illustrated in a food web. When one animal feeds off another, there is a loss of heat (energy) in the process. Additional loss of energy occurs during respiration and movement. Hence, more and more energy is lost as one moves up through trophic levels.
2.2.A4 Explain the impact of a persistent or non-biodegradable pollutant in an ecosystem.
This refers to how long a pesticide remains active in the environment. Some chemicals are broken down by decomposers in the soil (they’re biodegradable) and so are not persistent, while others cannot be broken down by microbes (they’re non biodegradable) and so continue to act for many years, and are classed as persistent pesticides. The early pesticides (such DTT) were persistent and did a great deal of damage to the environment, and these have now largely been replaced with biodegradable insecticides such as carbamates and pyrethroid
2.2.S1 Construct models of feeding relationships such as food chains, food webs and ecological pyramids from given data
Systems diagrams can be used to show the flow of energy through ecosystems. Stores of energy are usually shown as boxes which represent the various trophic levels Flows of energy are usually shown as arrows (with the amount of energy in joules or biomass per unit are represented by the thickness of the arrow).
2.2.S2 Construct system diagrams representing photosynthesis and respiration.
Chloroplasts and Mitochondria worksheet
Photosynthesis Cellular Respiration poster
Constructing Ecological Pyramids worksheet
Eating at a Lower Trophic Level worksheet
Ecological Pyramids Problems
Impact on Food Chains and Food Webs
Effects of Fishing on Food Web Structure
How Whaling Effects the Food Chain
Nitche Science - 2.2 Communities and Ecosystems: Respiration and Photosynthesis
Rates of Photosynthesis and Ecosystem Respiration - Internet Chemistry
Ecosystem Animation - Wardsworth Media
Ecosystem Model - Annenburger Learner
Ecological Pyramid Quizlet
Build a Food Web - Gould League
Build a Food Chain - Parenting The Next Generation
Food Chains - BrainPop
Build a Food Web - Teacher Scholastic
Food Chains and Food Webs from BBC Bitesize
Assignment Discover Food Webs - How Stuff Works
Food Chains - USGS
Biomagnification Animation - Living Envrionment
Bioaccumulation Animation - McGraw-Hill
Trade Secret - PBS
Mercury in Fish from Utah State
Minimata Disease - Wikipedia
Binomial Nomenclature- Science Pro Online
In the News
Minamata Bay Japan - ProQuest Feb 2007
Study finds trace levels of Fukushima radiation in albacore - KVAL.com Apr 28, 2014
Feeding relationships can be represented by different models—how can we decide when one model is better than another?
Ecosystems such as lakes and forests can exist across political boundaries
Ecosystems, Organisms and Their Environment
In which Hank does some push ups for science and describes the "economy" of cellular respiration and the various processes whereby our bodies create energy in the form of ATP. However, get hte basic idea. You won't need to know the specific details
Hank explains the extremely complex series of reactions whereby plants feed themselves on sunlight, carbon dioxide and water, and also create some by products we're pretty fond of as well. However, get the basic idea. You won't need to know the specific details
The grassland ecosystem and the food chain.
Hank brings us to the next level of ecological study with ecosystem ecology, which looks at how energy, nutrients, and materials are getting shuffled around within an ecosystem (a collection of living and nonliving things interacting in a specific place), and which basically comes down to who is eating who
Interactions between species are what define ecological communities, and community ecology studies these interactions anywhere they take place. Although interspecies interactions are mostly competitive, competition is pretty dangerous, so a lot of interactions are actually about side-stepping direct competition and instead finding ways to divvy up resources to let species get along. Feel the love?
Feeling a little hungry? Then grab a snack and watch Bill Nye the Science Guy's episode on the Food Web
New York State routinely produces health advisories for fish caught in local waters. These advisories are based on the potential for harmful substances- that is, pollutants- to be present in the flesh of the fish, which can be transferred to humans through consumption.
A short clip about industrial mercury poisoning at Minamata Bay, Japan
Communities and Ecosystems (2.2)