NAME ____________________
Mrs. K. Coffey
Biology I – Period ____
Date ____________________
CHAPTER 37 - Communities and Ecosystems
Opening Thought
How humans benefit from healthy ecosystems?



Therefore, understanding what makes an ecosystem healthy is essential.
Guided Notes
Community Structure and Dynamics
37.1 A community includes _________________________________________________________
 In the hierarchy of life, a __________________ is a group of interacting individuals of a particular species.
 The next step up is a biological ________________, an assemblage of all the populations of organisms living
close enough together for potential interaction.
 Community ecology is concerned with factors that influence the___________________________ of
communities and with factors that affect ____________________________.
What is the relationship between a community and a population?
___________________________________________________________________________________________
37.2 Interspecific interactions are __________________________________________
 Interspecific interactions
 are ______________________________________________________________
 greatly affect _____________________________________________.
 In Table 37.2, interspecific interactions are classified according to ________________________________.
 ______________________________ occurs when populations of two different species ________________
___________________________________.
 In mutualism, _______________________________. Symbol for this is (____/____)
 In predation, ______________ (the predator) __________________ (the prey). (_____/_____)
 In herbivory, an _____________________________________.
 In parasitism, the host plants or animals are _________________________________________.
Populations of Eastern Bluebirds declined after the introduction of non-native house sparrows and
European starlings. All three species nest in tree cavities. Suggest how an interspecific interaction could
explain the bluebird’s decline. ____________________________________________________________
_____________________________________________________________________________________
37.3 Competition may occur when ___________________________________
 An ecological niche is the __________________________________________________________________.
 Interspecific competition occurs when the ______________________________________ and both populations
_____________________________________________.
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383
 In general, competition _____________________________________ for competing populations because the
resources used by one population are _______________________________________.
Which do you think has more severe effects, intraspecific competition, or interspecific competition? Explain
why. ____________________________________________________________________________________
________________________________________________________________________________________
37.4 Mutualism ____________ both partners
 Reef-building corals and photosynthetic dinoflagellates provide a good example of how mutualists benefit from
their relationship.
 Photosynthetic dinoflagellates
 _________________________________________________
 _______________________________________________________________________________
 _________________________________________, including carbon dioxide (CO2) and ammonia (NH3), a
valuable source of nitrogen for making proteins.
When corals are stressed by environmental conditions, they expel their dinoflagellates in a process called
bleaching. How is widespread bleaching likely to affect coral reefs? _______________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
37.5 EVOLUTION CONNECTION: Predation leads to diverse adaptations in prey species
 Predation benefits the _______________ but kills the _____________.
 Numerous adaptations for predator avoidance have evolved in prey populations through natural selection,
including
 _____________________________________________________________________________________
 _____________________________________________________________________________________
 _____________________________________________________________________________________
Explain why predation is a powerful factor in the adaptive evolution of prey species? _______________
______________________________________________________________________________________
______________________________________________________________________________________
37.6 EVOLUTION CONNECTION: Herbivory leads to diverse adaptations in plants
 A plant whose body parts have been eaten by an animal must expend energy to replace the loss.
 Consequently, numerous defenses against herbivores have evolved in plants.
 Plant defenses against herbivores include
 ______________________________________________________________________________________
 ______________________________________________________________________________________
 Some herbivore-plant interactions illustrate ______________________, a series of reciprocal evolutionary
adaptations in two species.
People find most bitter tasting foods objectionable. In evolutionary terms, why do you suppose we have taste
receptors for bitter-tasting chemicals? __________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
Homework: Mastering HW 37-01 (M) Sections 37.1-37.7
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37.7 Parasites and pathogens can affect community composition
 A parasite lives on or in a host from which it obtains nourishment.
 Internal parasites include nematodes and tapeworms.
 External parasites include mosquitoes, ticks, and aphids.
 Plants are attacked by parasites, including nematodes and aphids, that tap into the phloem and suck plant sap.
 Pathogens are disease-causing microscopic parasites that include bacteria, viruses, fungi, or protists.
 Non-native pathogens can have rapid and dramatic impacts.
 The American chestnut was devastated by the chestnut blight protist.
 A fungus-like pathogen is currently causing sudden oak death on the West Coast.
37.8 Trophic structure is a key factor in community dynamics
 Every community has a trophic structure, a pattern of feeding relationships consisting of several different
levels.
 The sequence of food transfer up the trophic levels is known as a food chain.
 This transfer of food moves chemical nutrients and energy from producers up through the trophic levels in a
community.
 Producers are autotrophs that support all other trophic levels.
 Consumers are heterotrophs.
 Herbivores are primary consumers.
 Secondary consumers typically eat herbivores.
 Tertiary consumers typically eat secondary consumers.
 Quaternary consumers typically eat tertiary consumers.
 Detritivores derive their energy from detritus, the dead material produced at all the trophic levels.
 Decomposers
 are mainly prokaryotes and fungi and
 secrete enzymes that digest molecules in organic materials and convert them into inorganic forms in the
process called decomposition.
37.9 VISUALIZING THE CONCEPT: Food chains interconnect, forming food webs
 A more realistic view of the trophic structure of a community is a food web, a network of interconnecting food
chains.
 A consumer may eat more than one type of producer, and several species of primary consumers may feed on
the same species of producer.
 Some consumers weave into the food web at more than one trophic level.
37.10 Species diversity includes species richness and relative abundance
 Species diversity is defined by two components:
1. species richness, the number of different species in a community, and
2. relative abundance, the proportional representation of a species in a community.
 Low species diversity is characteristic of most modern agricultural ecosystems.
37.11 SCIENTIFIC THINKING: Some species have a disproportionate impact on diversity
 Ecologist Robert Paine hypothesized that the species diversity of a community is directly related to the ability of
predators to prevent any one species from monopolizing local resources.
 Paine’s experiment with sea stars and others like it gave rise to the concept of a keystone species, one whose
impact on its community is larger than its biomass or abundance indicates and that occupies a niche that holds
the rest of its community in place.
 The word “keystone” comes from the wedge-shaped stone at the top of an arch that locks the other pieces in
place.
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CHAPTER 37 Communities and Ecosystems 385
 Although a keystone species has low biomass or relative abundance, its removal from a community results in
lower species diversity.
37.12 Disturbance is a prominent feature of most communities
 Disturbances are events such as storms, fires, floods, droughts, or human activities that change biological
communities by removing organisms from it or altering the availability of resources.
 The types of disturbances, their frequency, and their severity vary from community to community.
 Small-scale disturbances often have positive effects. However, communities change drastically following a
severe disturbance that strips away vegetation and removes significant amounts of soil.
 Ecological succession is a transition in species composition of a community.
 Primary succession is the gradual colonization of barren rocks.
 Secondary succession occurs after a disturbance has destroyed a community but left the soil intact.
37.13 CONNECTION: Invasive species can devastate communities
 Invasive species
 are organisms that have been introduced into non-native habitats by human actions and
 have established themselves at the expense of native communities.
Ecosystem Structure and Dynamics
37.14 Ecosystem ecology emphasizes energy flow and chemical cycling
 An ecosystem consists of
 all the organisms in a community and
 the abiotic environment with which the organisms interact.
 In an ecosystem,
 energy flow moves through the components of an ecosystem and
 chemical cycling is the transfer of materials within the ecosystem.
37.15 Primary production sets the energy budget for ecosystems
 Primary production is the conversion of solar energy to chemical energy by photosynthesis.
 The total amount of primary production during a given time period is gross primary production.
 Producers use some of this organic material to fuel their own cellular respiration.
 The remainder, or net primary production, is the amount of new organic material added to an ecosystem in
a given period.
37.16 Energy supply limits the length of food chains
 A pyramid of production shows the flow of energy from producers to primary consumers and to higher trophic
levels.
 Only about 10% of the energy stored at each trophic level is available to the next level.
37.17 CONNECTION: An energy pyramid explains the ecological cost of meat
 As omnivores, people eat plant material and meat.
 When humans eat
 grain or fruit, we are primary consumers,
 beef or other meat from herbivores, we are secondary consumers, and
 fish like trout or salmon, we are tertiary or quaternary consumers.
 A field of corn can support many more human vegetarians than meat-eaters.
37.18 Chemicals are cycled between organic matter and abiotic reservoirs
 Ecosystems are supplied with a continual influx of energy from the sun and Earth’s interior.
 Except for meteorites, there are no extraterrestrial sources of chemical elements.
 Thus, life depends on the recycling of chemicals.
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 Biogeochemical cycles include
 biotic components,
 abiotic components, and
 abiotic reservoirs, where chemicals accumulate or are stockpiled outside of living organisms.
 Biogeochemical cycles can be
 local or
 global.
37.19 The carbon cycle depends on photosynthesis and respiration
 Carbon
 is the major ingredient of all organic molecules,
 has an atmospheric reservoir,
 cycles globally, and
 resides in plant and animal biomass, fossil fuels, soils, sedimentary rocks, and as dissolved carbon.
37.20 The phosphorus cycle depends on the weathering of rock
 Organisms require phosphorus, usually in the form of the phosphate ion (PO43−), as an ingredient of nucleic
acids, phospholipids, and ATP, and as a mineral component of bones and teeth.
 In contrast to the carbon cycle and the other major biogeochemical cycles, the phosphorus cycle does not have
an atmospheric component.
 Because phosphates are transferred from terrestrial to aquatic ecosystems more rapidly than they are replaced,
the amount in terrestrial ecosystems gradually diminishes over time.
37.21 The nitrogen cycle depends on bacteria
 Nitrogen is
 an ingredient of proteins and nucleic acids,
 essential to the structure and functioning of all organisms, and
 a crucial and often limiting plant nutrient.
 Nitrogen has two abiotic reservoirs:
1. the atmosphere, of which about 80% is nitrogen gas, and
2. soil.
 Nitrogen fixation converts N2 to compounds of nitrogen that can be used by plants.
 Various bacteria in soil (and root nodules of some plants) convert gaseous N2 to compounds that plants can use,
such as ammonium (NH4+) and nitrate (NO3−).
37.22 CONNECTION: A rapid inflow of nutrients degrades aquatic ecosystems
 In aquatic ecosystems, primary production is limited by low nutrient levels of phosphorus and nitrogen.
 Nutrient input from fertilizer and other sources causes rapid eutrophication, resulting in decreased species
diversity and oxygen depletion of lakes, rivers, and coastal waters.
 Humans rely upon natural ecosystems to
 supply fresh water and some foods,
 recycle nutrients,
 decompose wastes, and
 regulate climate and air quality.
37.23 CONNECTION: Ecosystem services are essential to human well-being
 Wetlands
 buffer coastal populations against tidal waves and hurricanes,
 reduce the impact of flooding rivers, and
 filter pollutants.
 Natural vegetation helps to
 retain fertile soil and
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CHAPTER 37 Communities and Ecosystems 387
 prevent landslides and mudslides.
 Ecosystems that we create are also essential to our well-being. But agricultural methods introduced over the past
decades have pushed croplands beyond their natural capacity to produce food.
 Sustainability is the goal of developing, managing, and conserving Earth’s resources in ways that meet the
needs of people today without compromising the ability of future generations to meet theirs.
Chapter Guide to Teaching Resources
Community Structure and Dynamics (37.1–37.13)
Student Misconceptions and Concerns
 For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye,
some background is required to understand the method of composition, the significance of components, and the
nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar
systems. (37.1–37.13)
 The concept of an ecological niche can be confusing. Ecologist Eugene Odum has suggested that an ecological
niche is like an organism’s habitat (address) and its occupation combined. (37.3)
 The student expectation that ecosystems are relatively stable is common. Natural disturbances of any sort (fires,
earthquakes, floods, or strong storms) are often seen as tragic and damaging to ecosystems. Before beginning the
topic of ecological disturbances, consider asking your students to briefly respond to news reports that a state or
federal park has (a) been burned, (b) been struck by high winds and/or lightning, or (c) been temporarily flooded.
In addition, consider asking what, if anything, should be done to prevent or repair this damage. (37.12)
Teaching Tips
 Many students have been exposed to diverse ecosystems only through electronic media, which have likely
focused on a few species. Before discussing this chapter, consider showing the class a good program (it need not
be long) about an ecosystem. The program can then serve as a shared recent experience to which you can relate
the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional
example with which most students are familiar. There may even be a distinct community on your campus, such as
a pond, wooded area, and so on, that students could visit and return from with new insights. (37.1–37.13)
 In human society, a community might be roughly equivalent to a local population, perhaps all the people living in
a town or city. The definition of a biological community is more inclusive, comprising all of the populations of
organisms living close enough together for potential interaction. (37.1)
 Examples of interspecific competition are as close as the nearest lawn. Although students may be more likely to
think of animal examples, the various grasses and weeds in a lawn reveal different strategies in their competition
for sunlight, moisture, and soil. (37.2)
 If your class includes students with business interests, they may enjoy the following analogy. To better understand
competition, students might think about fast-food restaurants in your region. Challenge your students to identify
the strategies employed by these restaurants to compete with each other. As each restaurant makes changes, does
the other restaurant respond? Restaurants changing strategies in response to each other is analogous to
coevolution. (37.2–37.3, 37.6)
 Students who are business-oriented may enjoy this analogy. Many corporate leaders describe the best business
deals as mutualistic, fostering a win-win relationship. For example, perhaps a new company creates a marketable
product from another company’s wastes. (37.4)
 Rattlesnakes are a good example of a highly specialized predator. Because they are unable to move fast enough to
catch their prey, rattlesnakes typically ambush them, a process facilitated by their camouflaged bodies.
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Rattlesnakes often feed during the cooler parts of the day, using heat-detecting facial pits to identify prey before
injecting them with fast-acting venom. The prey is immediately released (perhaps to avoid damage to the snake
from struggling prey) but is disabled by the venom within seconds. The rattlesnake then uses a variety of senses to
track the prey the short distance to where it has collapsed. (37.5)
 Coevolution is illustrated by organisms that exhibit reciprocal evolutionary adaptations. Challenge students to
explain how rewarding a pollinator with nectar has benefited some plants. Why would plants that have
adaptations for only certain pollinators have an advantage? In many cases, pollinators that are restricted to certain
species are more likely to transport pollen between members of that species instead of wasting pollen by taking it
to other species. (37.6)
 Pathogens are probably what most people refer to as germs. Students might believe that this general term refers to
some specific type of organism. (37.7)
 Diversity within a species has some of the same advantages as diversity within a community. In both situations,
diversity limits the damage from a pathogen or predator specialized to attack only one variation within a species
or one species in a community. (37.10)
 Many keystone species have been identified in ecosystems, including sea otters, elephants, freshwater bass, and
Pisaster, a sea star noted in Figure 37.11C. Challenge your class to explain how the concept of a keystone species
affects the efforts of conservation biologists. Why might some species be more important to conserve? (37.11)
 Ecologist Robert Paine, who helped introduce experimental manipulations into the field of ecology, died in June
2016. (37.11)
 News reports of rare disturbances such as flood or earthquakes may note that they are one in a 1,000-year events.
Even if they are, it is important to note that in 1 million years, such events happened 1,000 times. Thus, if such
rare events have been happening over such long periods, we can expect that the species in the impacted
communities are adapted in ways that have promoted historical recoveries. Such a situation appears to exist in the
communities surrounding Mt. St. Helens and its history of eruptions in Washington State. (37.12)
 Before and after images of the impact and recovery of an ecosystem from a natural disaster can be more powerful
than any verbal explanation of the process. Consider locating before and after images of ecosystems damaged by
hurricanes, fire, or the 1980 eruption of Mt. St. Helens, to show recovery. (37.12)
 Depending on your location and its circumstances, consider a short field trip on or near your campus to show
disturbed regions and signs of recovery. (37.12)
 Numerous U.S. government agencies have websites devoted to invasive species. These include:
a. The United States Department of Agriculture at https://www.invasivespeciesinfo.gov
b. The National Invasive Species Council at https://www.doi.gov/invasivespecies/
c. The California Department of Fish and Wildlife at https://www.fws.gov/invasives/. (37.13)
 Students who are interested in wildlife may collect an animal to keep as a pet or to admire for a few days. This
might be a good time to remind them that if they hope to return a wild animal to its natural environment, they
should do so quickly and return it to within a few feet of the spot of its collection. Reintroducing an organism to a
nearby environment may spread disease and potentially extend the organism’s natural range. Further, the
introduction of commercial specimens from fish tanks, such as the marine algae Caulerpa or lionfish dumped into
the ocean, have had devastating consequences. The following website examines this issue:
www.invasivespeciesinfo.gov/aquatics/caulerpa.shtml. (37.13)
 The accidental introduction of the Brown Tree Snake into Guam during World War II has had a devastating
impact on the ecology and economy of Guam. Details of this ongoing crisis can be found at the North America
Brown Tree Snake Control site at www.nabtsct.net. (37.13)
Active Lecture Tips
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CHAPTER 37 Communities and Ecosystems 389
 See the Activity “Students as Parasites of Their Parents” on the Instructor Exchange. Visit the Instructor
Exchange in the Mastering Biology instructor resource area for a description of this activity. (37.2)
 See the Activity “A Chance Discovery of Endosymbiosis? A Case Study” on the Instructor Exchange. Visit the
Instructor Exchange in the Mastering Biology instructor resource area for a description of this activity. (37.2)
 Students have often had prior exposure to the concepts of food webs and food chains. Present a food web (perhaps
Figure 37.9) to your class and challenge them to work in small groups to predict the consequences of a decrease
or increase in the population of one of the organisms. This activity can help students understand how difficult it is
to make precise predictions about these complex systems. (37.8–37.9)
Ecosystem Structure and Dynamics (37.14–37.23)
Student Misconceptions and Concerns
 Without an understanding of basic physics and the inefficiency of aerobic metabolism, students might not
understand how chemical energy in food is lost as heat. Consider expanding upon the explanations given in the
book. (37.14)
 The environmental impact of eating farm animals may not be appreciated by most students who otherwise may be
concerned about global climate change and the conservation of natural ecosystems. This chapter section helps
explain the basis of the increased costs associated with a diet that includes meat. (37.17)
 Students are unlikely to have any prior knowledge of biogeochemical cycles. Although some transfers between
the biotic and abiotic components of ecosystems, such as the use of fertilizer on plants, may be known to them,
the broader fact that the biosphere is a self-cycling system is not appreciated by most students. Before you lecture,
consider asking your students to explain how carbon, phosphorus, and nitrogen cycle through the atmosphere.
Pretesting your students on their knowledge can confirm both what they understand and what they may need
explained to them in more detail. (37.18–37.21)
Teaching Tips
 The heat generated as a by-product of metabolism, which is quite evident during strenuous exercise, is much like
the heat produced by a running automobile engine. In both circumstances, heat is a by-product of the fuel-burning
process. (37.14)
 Energy flow through an ecosystem is analogous to the flow of fuel through a car or electricity through a vacuum
cleaner. These systems will not work without a steady input. NASA, however, must rely on some closed systems
for its spacecrafts. Students might enjoy investigating the recycling of gases and fluids in these systems. (37.14)
 Some students might be interested in eating more proteins and fewer carbohydrates because of popular diet plans.
However, do high-protein diets always require the consumption of more meat? The many sources of plant
proteins might be surprising to students. Some high-protein vegetarian options are described by the Vegetarian
Society on its website, www.vegsoc.org. (37.17)
 As you discuss the importance of the biogeochemical cycles, consider explaining the basic label information
provided on a container of plant fertilizer. Consider an example that might be used on houseplants and, therefore,
more likely to be familiar to students. Typically, plant fertilizers contain various forms of nitrogen and
phosphorus, which are essential chemicals for growth. (37.18–37.20)
 As rising atmospheric carbon dioxide levels affect global climate, carbon cycling has become an increasingly
important issue. If your course will not cover Module 38.5 on global climate change, consider including a brief
discussion of the topic here. (37.19)
 Discussing the movements of water through your local community can help students better understand the
concept of biogeochemical cycling. You may want to ask students to consider all of the possible inputs of water
into your community as well as the possible routes of exit. (37.20)
 As noted in Module 37.20, phosphate contamination of aquatic systems typically leads to increased algal growth
and potentially disastrous fish kills. (37.20)
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 The nitrogen-fixing bacteria living in the roots of soybeans add nitrogen to the soil. Corn does not have this
relationship with bacteria. However, by annually rotating corn and soybean crops, farmers can allow corn crops to
use some of the nitrogen fixed by the soybean crop in the previous year. Such rotation has other benefits. Because
corn is a monocot and soybeans are eudicots, few pests attack both corn and soybeans. Thus, crop rotation also
helps to control the pest populations that target each type of plant, reducing the need for other pest-fighting
strategies. (37.21)
 The studies of the Hubbard Brook Experimental Forest (described well at www.hubbardbrook.org/) provide an
opportunity to explain how basic principles of scientific investigation are applied to ecological studies. Consider
discussing the difficulties of conducting these broad experiments in other locations, where water cycling may not
be so restricted and other biogeochemical cycles not as well defined. (37.22)
 Most human communities include at least one golf course where heavy chemical applications of fertilizers occur.
Discuss with your students the environmental impact of replacing a natural prairie or forested ecosystem with a
golf course, noting the change in species diversity and broader ecological impacts of applications of fertilizers and
pesticides and the related increase in fossil fuel consumption. Immediate examples from your local community
help students immediately relate to the topics of this chapter. (37.23)
Active Lecture Tips
 Challenge students to work in pairs or small groups to explain why the areas of greatest primary production are
near the equator. (Answer: Primary production is a consequence of photosynthesis. Regions near the equator
receive the highest levels of solar input.) (37.15)
 Ask your students to work in pairs or small groups to explain why food chains and food webs typically have only
three to five levels. This question, which is seldom considered by students, is addressed directly in this section of
the chapter. It can spark a good opening discussion before a lecture on food chains and food webs. (37.16)
Key Terms
abiotic reservoir
biogeochemical cycle
biomass
chemical cycling
coevolution
community
decomposer
decomposition
detritivore
detritus
disturbance
ecological niche
ecological succession
ecosystem
energy flow
food chain
food web
gross primary production
herbivory
interspecific competition
interspecific interactions
invasive species
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CHAPTER 37 Communities and Ecosystems 391
keystone species
mutualism
net primary production
nitrogen fixation
predation
primary consumer
primary production
primary succession
producer
quaternary consumer
scavenger
secondary consumer
secondary succession
species diversity
sustainability
tertiary consumers
trophic structure
Word Roots
a- = without; bio- = life (abiotic reservoir: a part of an ecosystem where a chemical, such as carbon or nitrogen,
accumulates or is stockpiled outside of living organisms)
de- = from, down, out (decomposer: prokaryotes and fungi that secrete enzymes that digest organic material and break it
down into inorganic forms)
detrit- = wear off (detritus: dead organic matter); -vora = eat (detritivore: an organism that consumes organic wastes and
dead organisms)
geo- = Earth (biogeochemical cycle: any of the various chemical circuits that involve both biotic and abiotic components
of an ecosystem)
herb- = grass; -vora = eat (herbivory: the consumption of plant material by an animal)
inter- = between (interspecific interactions: interactions between organisms of different species)
mutu- = reciprocal (mutualism: an interspecific relationship in which both partners benefit)
quatr- = four (quaternary consumer: an organism that eats tertiary consumers; the fourth step on the food chain)
terti- = three (tertiary consumer: an organism that eats secondary consumers; the third step on the food chain)
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