Intro to Ecology Population Ecology Community Ecology Click to - - PDF document

Slide 1 / 131 Slide 2 / 131

AP BIOLOGY Ecology

www.njctl.org March 2013

Slide 3 / 131 Table of Contents

· Intro to Ecology · Population Ecology · Community Ecology

Click on the topic to go to that section

Slide 4 / 131

Intro to Ecology

Click to return to the Table of Contents

Slide 5 / 131 Ecology

Ecology is the study of how

• rganisms interact with each
• ther and their environments.

Clownfish interact with sea anemones in a manner that is positive to

• both. The sea anemone provides protection and nutrients to the
• clownfish. In return, clownfish fecal matter provides nutrients to the

sea anemone.

Slide 6 / 131 Biotic vs Abiotic

Factors that ecologists study can be either biotic or abiotic. Biotic factors of this coral reef include fish, corals, sea anemones, and plankton. Abiotic factors of this coral reef include water temperature, water salinity, nutrient availability and sunlight. Use this information to define the parameters of biotic and abiotic factors.

Slide 7 / 131 Biotic vs Abiotic

Biotic Factors Abiotic Factors Living factors in an environment. Nonliving factors in an environment. · Animals · Plants · Fungi · Bacteria · Sunlight · Water · Temperature · Nutrients · Soil

Slide 8 / 131

The salt marsh ecosystem is composed of land that is submerged by ocean water during high tide and is dry during low

• tide. Organisms that live in a salt marsh need to have the ability

to survive in both wet/dry conditions and in high/low salinity

• conditions. Plants are composed of grasses and shrubs.

Common animals include crabs, mussels and a variety of birds. Many fish use salt marshes as hatcheries.

Salt Marsh

Describe three biotic and three abiotic factors that affect the salt marsh.

Slide 9 / 131

Community

Levels of Biological Organization

Ecosystem SMALLEST LEVEL Population Organism

Slide 10 / 131 Levels of Biological Organization

Organism: Any individual that has all the characteristics of life.

Slide 11 / 131

Levels of Biological Organization

Population: A group of organisms of the same species that live in the same geographic area. Remember: What are the characteristics of a species?

Slide 12 / 131 Levels of Biological Organization

Community: All of the populations that live in the same geographic area.

Slide 13 / 131 Levels of Biological Organization

Ecosystem: All of the living organisms (communities) and the nonliving components of a geographic area.

Slide 14 / 131

1

Groups of different species living together and interacting in the same environment are referred to as a

A

Organism

B

Community

C

Ecosystem

D

Population

Slide 15 / 131

2

All of the following are abiotic factors EXCEPT:

A

Algae

B

pH

C

Temperature

D

Nutrients

Slide 16 / 131

3

Which of the following levels of biological organization includes both abiotic and biotic factors?

A

Species

B

Population

C

Community

D

Ecosystem

Slide 17 / 131 Habitat

The term habitat describes the specific area - including biotic and abiotic factors - where an organism lives within an ecosystem. A habitat is like an

• rganism's home

within an ecosystem.

Slide 18 / 131 Ecological Niches

An organism's niche is a description of the role it plays in its habitat. A niche includes all aspects of where and how an organism lives including: * the type of food it eats * how it obtains food * where it lives in its environment (tree, nest, hive, etc.) * when and how it reproduces

Slide 19 / 131

Komodo Dragon Niche Komodo dragons live in the Indonesian Islands. They hunt and ambush invertebrates, birds and mammals. They lay up to 20 eggs at a time in self-dug holes. The eggs incubate for eight months. Komodo dragons take nine years to mature and can live up to 30 years.

Ecological Niches Slide 20 / 131 Ecological Niches

A population's habitat answers the question "Where do you live?". A population's niche answers the question "How do you make a living?". Click this picture to watch a video about niches in the North African river plains.

Slide 21 / 131 Ecological Niches

No two species can occupy the same niche in the same environment at the same time. This is called niche overlap. When this occurs, competition for resources will displace one of the species. The figure below shows three different species of warblers that have established different niches in the same tree.

Slide 22 / 131 Ecological Niches

Niche overlap leads to a fundamental niche and a realized niche for a species. Fundamental niche - the

• ptimal niche of a species, in

the absence of limiting factors Realized niche - the actual niche of a species, as a result

• f competition

Slide 23 / 131

4 Traditionally, a polar bear's diet consists mainly of seals that it hunts from the edges of sea ice. As the sea ice melts and humans encroach on the existing habitat, polar bears are now known to hunt through human trash for nutrition. Describe the difference between the polar bear's fundamental niche and realized niche.

Students type their answers here

Slide 24 / 131

Population Ecology

Click to return to the Table of Contents

Slide 25 / 131 Populations

Factors that affect populations can be density dependent or density independent. Population ecology studies the interactions between populations and their environments.

Slide 26 / 131

Density dependent factors affect populations based on the density of that population. Examples include predation, competition and disease.

Density Dependent Factors

A low density population will suffer more from heavy predation than a high density population.

Slide 27 / 131 Density Independent Factors

Density independent factors affect a population, regardless

• f population density. Examples include weather and natural

disasters. Severe weather that causes flooding will destroy both high density and low density populations.

Slide 28 / 131

5 In 2005, hurricane Katrina deposited over 5 cm of sediment on the coastal wetland ecosystem of the Gulf of Mexico, destroying 100 km2 of wetland. Did hurricane Katrina have density dependent or density independent effects? A Density dependent B Density independent

Slide 29 / 131

6 In a field of wildflowers, population size is limited by available nutrients in the soil. When the density of flowers reaches a certain level, the death rate increases due to lack of nutrients. Is this population affected by density dependent or density independent factors? A Density dependent B Density independent

Slide 30 / 131

Leaving Entering

Population Size

Population size is positively correlated with birth rate and immigration and negatively correlated with death rate and emigration. Draw two graphs illustrating the relationship between population size and 1) birth rate/immigration and 2) death rate/emigration. Answer

Slide 31 / 131 Exponential Population Growth

When a population has access to unlimited resources, it experiences exponential growth. Exponential Population Growth dN dt = r N where r = growth rate and N = population size

Slide 32 / 131 Exponential Population Growth

After elephants in Kruger National Park, South Africa, were protected from hunting, the population grew exponentially for 60

• years. When population size threatened to destroy habitat and food

supply, park managers implemented elephant birth control and exportation.

Slide 33 / 131 Logistic Population Growth

Most populations do not have unlimited resources. When a population becomes too large, it exhausts food supply, water supply and shelter. At this point, intraspecific competition causes the population to decrease. Intraspecific competition - competition among members of the same

• species. These two lions

are competing for the same prey.

Slide 34 / 131

The population size that can be maintained with a given amount

• f resources is called the

carrying capacity. Populations that are limited in resources experience logistic growth. In logistic growth, the rate of increase approaches zero as the carrying capacity is reached.

Logistic Population Growth

Source: Nature.com

Slide 35 / 131 Case Study: Red Tail Hawk

Consider a new population of red tail hawks that have been released by conservationists into a woodland in upstate New York. Six years ago scientists released 50 hawks into a 900 acre woodland.

Slide 36 / 131

Consider a new population of red tail hawks that have been released by conservationists into a woodland in upstate New York. Since the hawks had no natural predators and plenty

• f prey in the

environment, they 
 
 
 
 
 
 
 showed exponential population growth.

Case Study: Red Tail Hawk

Slide 37 / 131

Consider a new population of red tail hawks that have been released by conservationists into a woodland in upstate New York. This year scientists believe the population has reached a peak population growth rate.

Case Study: Red Tail Hawk Slide 38 / 131

As an example, we will look at a new population of red tail hawks that have been released by conservationists into a woodland in upstate New York. Over the coming years growth will slow because the hawks have been consuming most of the prey. Their food source is becoming a limiting resource.

Case Study: Red Tail Hawk Slide 39 / 131

Consider a new population of red tail hawks that have been released by conservationists into a woodland in upstate New York. They estimate that after six additional years the population will reach the carrying capacity of the woodland. In other words, death and emigration rate will equal birth rate. What is the immigration rate of this population?

Case Study: Red Tail Hawk Slide 40 / 131 Human Population

The advent of new technologies has allowed human populations to grow exponentially. Food and energy have recently been made more abundant for the human species, leading to a surge in growth.

7,000,000,000 2011 world population

Slide 41 / 131 Human Population

The current population growth rate for humans is about 1.1% population increase per year. This rate has been decreasing which means that growth is slowing, but the population is still increasing.

Slide 42 / 131 Human Population

Many models predict that by 2040, the human population will exceed 10,000,000,000. This will effect the planet in a variety of negative ways.

Slide 43 / 131

Agriculture is a human technology that transforms natural ecosystems into areas devoted to the production of food and fuel. The current size of the human population was made possible by the advancements in this technology. Without the huge increase in edible biomass created by agricultural systems, there would simply not be enough to feed the 7,000,000,000 humans on Earth.

Human Population Slide 44 / 131

The land, water, and energy resources required to support this level of food production are vast. Agriculture represents a major way in which humans impact ecosystems.

Human Population Slide 45 / 131

Agriculture can be particularly damaging when chemicals are used to stop pests from eating crops. It may have unintended consequences. For example, DDT, a chemical used to control insects, nearly caused the extinction of the American Bald Eagle via biomagnification. Biomagnification is the process by which the concentration of a substance increases substantially as it moves up the food chain.

Source: US Fish & Wildlife

Human Population Slide 46 / 131

The lifestyle of an average citizen in a developed country requires enormous amounts of energy to power modern technology. As populations grow the environmental impact will grow exponentially.

Human Population

In what other ways will an increasing human population affect the planet?

Slide 47 / 131 7 When the collared dove first colonized Great Britain, the

population grew exponentially. Twenty years later, the population size was smaller than predicted by the exponential model. Which of the following is not a conclusion that can be made from this information?

A The rate of population growth had slowed. B The population had unlimited resources. C The population was approaching its carrying

capacity.

D Competition was decreasing population size. Slide 48 / 131

8 Which of the following is not a situation in which exponential growth could occur? A Bacteria growing in a petri dish. B Pine trees rebounding after a forest fire. C A population of snowshoe hares after the lynx population is decimated by disease. D A species of fish colonizing a new marine environment.

Slide 49 / 131

The red squirrel inhabits forests of Asia and Europe. When populations are high, competition for habitat results in some females obtaining low quality territory. This, in turn, results in low fecundity (reproductive success) for those females and the growth rate of the population decreases.

Case Study: Red Squirrels

Read the description of red squirrels and answer the questions that follow.

Slide 50 / 131

9 List one biotic and one abiotic factor that affects the red squirrel population.

Students type their answers here

Slide 51 / 131

10 What is the limiting factor for the red squirrel population? A Food B Predation C Habitat D Water

Slide 52 / 131

11 Is red squirrel population size being affected by density dependent or density independent factors? A Density dependent B Density independent

Slide 53 / 131

12 As the population growth rate slows in response to habitat availability, what is the population nearing? A Extinction B Speciation C Carrying Capacity D Exponential growth

Slide 54 / 131 Reproduction vs Survival

Survivorship is a population's expectation for average death rates at a given yearly age. Survivorship curves show how many individuals are alive after a certain period of time. There are three survivorship strategies.

Slide 55 / 131

Humans are an example of type I. Young humans are likely to survive well, but death rates increase exponentially as the years pass.

Reproduction vs Survival Slide 56 / 131

Birds are an example of type II. As the linear line shows, each year a bird is just as likely to die as they were the previous years. Young

• r old has no bearing on survivorship.

Reproduction vs Survival Slide 57 / 131

Frogs are an example of type III. They are very like to die at a young age but if they survive their youth, then they are likely to live a long time.

Reproduction vs Survival Slide 58 / 131

Type I Survivorship Characteristics:

• Stable environment
• Larger size
• Long life expectancy
• High level of parental care
• Few offspring

Reproduction vs Survival Slide 59 / 131

Type III Survivorship Characteristics:

• Unstable environment
• Early Maturity
• Little parental care
• High number of offspring
• Short lifetime

Reproduction vs Survival Slide 60 / 131 r/K Selection Theory

Survivorship strategies are a trade off between quantity and quality of

• ffspring. One strategy is not more successful than another.

Environmental conditions dictate which strategy will be favored. r and K selection theory relates parental investment with quantity and quality of offspring. vs

Slide 61 / 131

The theory gets its name from the algebraic expression of ecological population dynamics. r is the maximum growth rate of the population (N). K is the carrying capacity of its local environment.

r/K Selection Theory Slide 62 / 131 r/K Selection Theory

r-selection predominantes in unstable or unpredictable environments in which the ability to reproduce quickly is crucial. There is little advantage in adaptations that permit successful competition with other organisms, because the environment is likely to change again. Population size changes drastically. r-selection characteristics · high fecundity · small body size · early maturation · short lifespan

Slide 63 / 131

K-selection predominates in stable or predictable environments in which the ability to compete for limited resources is crucial. Populations sizes of K-selected organisms typically are constant and close to the maximum that the environment can accommodate. K-selection characteristics · low fecundity · large body size · late maturation · long lifespan · extensive parental care

r/K Selection Theory Slide 64 / 131

13 A turtle lays a large clutch of eggs on a beach. However, there is no parental support for the offspring and only a few will make it back to the ocean before being eaten by predators. A Type III survivorship B Type II survivorship

C Type III survivorship Slide 65 / 131

14 Elephants are large mammals that can live to be 80 years

• ld. Gestation lasts about two years with only one to two

babies being born at a time. Maturation does not occur until 9 years (females) and 15 years (males). A r-selection B K-selection

Slide 66 / 131

15 Which of the following is correctly paired? A r selection / Type I survivorship B K selection / Type I survivorship C r-K selection / Type II survivorship D K selection / Type III survivorship

Slide 67 / 131

16 Which graph shows a population using r-selection strategies?

A B Slide 68 / 131

Community Ecology

Click to return to the Table of Contents

Slide 69 / 131 Communities

Community ecology studies the interactions between different populations and their environments. Populations in a community interact with each other in a variety of ways.

Slide 70 / 131 Predation

Predation is an interaction in which one species (predator) kills and eats the other (prey). The whale shark is the largest extant (living) fish species, growing up to 14 meters in length. Despite this intimidating size, they are filter feeders, preying on algae, plankton and krill.

Slide 71 / 131 Predation

Predation leads to the evolution of adaptations that enable predators to capture prey and prey to elude predators. Predator adaptations Prey adaptations · claws · fangs · stingers · poison · cryptic coloration · herding · toxins · mechanical (spines)

Can you find the frog in this picture? This snake's hollow fangs secrete venom.

Source: livescience.com

Slide 72 / 131 Competition

Competition occurs when individuals vie for a limiting resource. Intraspecific competition

• ccurs when individuals of

the same species compete. Interspecific competition

• ccurs when individual of

different species compete.

Slide 73 / 131 Competitive Exclusion Slide 74 / 131 Slide 75 / 131 Symbiosis

Symbiosis is any long term interaction between species. In obligate symbiosis, species cannot survive without each other. In facultative symbiosis, species can survive without each other. A lichen is composed of a fungi and algae living as obligate symbiotes. The algae creates food via photosynthesis while the fungi offers protection and minerals.

Slide 76 / 131 Symbiosis

Commensalism is an interaction that benefits one species while the other species is neither benefited nor harmed. Remoras are fish that attach to larger marine animals, such as sharks. Remoras eat leftover food from the

• shark. The shark is not affected in the

process.

Slide 77 / 131 Symbiosis

Parasitism is an interaction that benefits one species while harming another species. Ticks are arachnids that attach to

• ther animals and ingest their blood.

The tick (parasite) gains nutrition from this relationship while the animal (host) experiences reduced health and possibly death.

Slide 78 / 131 Symbiosis

Mutualism is an interaction between species in which all species benefit. Pollination illustrates mutualism between flowering plants and their animal pollinators. Pollinators receive nutrition while the plants receive help with dispersal.

Slide 79 / 131

Interaction Species #1 Species #2 Predation Competition Commensalism Mutualism Parasitism

Interactions

In the table above, indicate whether each species in the interaction experiences a positive (+), negative (-) or neutral (0) effect. Answer

Slide 80 / 131

17 Oxpeckers are birds that perch on the backs of rhinos. They eat ticks and other parasitic bugs. A Predation B Competition C Commensalism D Mutualism E Parasitism

Slide 81 / 131

18 Parrot fish and yellow tang fish both eat algae on the same coral reef. A Predation B Competition C Commensalism D Mutualism E Parasitism

Slide 82 / 131

19 Some mites attach themselves to flies. The flies transport the mites to alternate locations while remaining unharmed in the process. A Predation B Competition C Commensalism D Mutualism E Parasitism

Slide 83 / 131

20 A fungus grows on the back of insects. Its tendrils penetrate the exoskeleton as it feeds on the inner soft tissue of the bug. It will eventually consume the host insect. A Predation B Competition C Commensalism D Mutualism E Parasitism

Slide 84 / 131

21 Describe how niche overlap can lead to competitive exclusion.

Students type their answers here

Slide 85 / 131

Nitrogen is the an essential nutrient required by all

• rganisms to make

proteins. Most nitrogen is found as a gas in the atmosphere; however,

• rganisms are unable

to use nitrogen in this form (N2).

Case Study: Nitrogen Cycle Slide 86 / 131

The cycling of nitrogen through the environment involves many organisms: · Bacteria in soil convert N2 into ammonia (NH3+) or ammonium (NH4) in a process called nitrogen fixation. · Other bacteria convert ammonia into nitrates (NO3-) and nitrates (NO2-). · Producers use ammonium, nitrates, and nitrites to make proteins. · Consumers eat producers and reuse the nitrogen to make their own proteins. · When organisms die, decomposers release the nitrogen back into the soil or convert the nitrates back into nitrogen gas in a process called denitrification.

Case Study: Nitrogen Cycle Slide 87 / 131 Case Study: Nitrogen Cycle

Rhizobia are soil bacteria that forms symbiotic relationships with

• legumes. The bacteria grow inside nodules in the plant roots

where they receive nutrients from the plant via photosynthesis. The plant, in turn, receives usable nitrogen from the bacteria via nitrogen fixation. The nodules of Rhizobia can be seen as bubble-like structures on these roots.

Slide 88 / 131

22 What type of interaction is diplayed between Rhizobia and legume roots? A Parasitism B Mutualism C Predation D Commensalism

Slide 89 / 131

23 Rhizobia cannot survive unless they have a host plant. What type of symbiotic relationship is this? A Obligate B Dominant C Facultative D Density dependent

Slide 90 / 131 Community Diversity

The diversity of a community is a description of the variety of species that make up the community. Community diversity has two components: · species richness · relative abundance Which community is more diverse?

Slide 91 / 131 Species Richness

Species richness is the number of species present in a community. In these hypothetical forest communities, each different tree species is represented by a different color. Which community is more diverse?

Slide 92 / 131 Relative Abundance

Relative abundance is the proportion that each species represents for the entire community. Relative abundance values: 2/8 = 25% 2/8 = 25% 2/8 = 25% 1/8 = 12.5% 1/8 = 12.5%

Slide 93 / 131 Community Diversity

Community diversity can be calculated using the following equation, called the Shannon diversity: H = - (pA ln pA + pB ln pB + pC ln pC + ...) H = - (3 (0.25 ln 0.25) + 2 (0.125 ln 0.125)) H = 1.57

Slide 94 / 131 Community Diversity

Communities that are more diverse: · have increased productivity · are more stable · are more resilient · are more resistant to invasive species

Slide 95 / 131

24 Which forest has a higher species richness?

Students type their answers here

Forest A Forest B

Slide 96 / 131

25 Which forest has a higher community diversity?

Students type their answers here

Forest A Forest B

Slide 97 / 131

26 An invasive fungal disease spreads through both forests. Which forest would be better able to recover from this event?

Students type their answers here

Forest A Forest B

Slide 98 / 131 Ecological Succession

Change is inevitable within communities - older members die, new organisms immigrate, sudden disturbances force change, etc. Ecological succession is the term used to describe the series of expected changes that occur within the community of an ecosystem

• ver time.

The first photo shows a forest one year after a forest fire. The second picture is the same forest two years after the fire.

Slide 99 / 131 Primary Succession

Primary succession refers to the founding of new communities in environments that initially had no living organisms, like rocks or new surfaces formed by volcanic eruptions or the movements of glaciers. The retreat of a glacier left behind this bare rock that can now undergo primary succession.

Slide 100 / 131 Pioneer Species

In primary ecological succession, the first organisms to populate an uninhabited environment are called the pioneer species. Lichen is the first organism to grow on the bare rock. It is the pioneer species.

Bare rock left after retreat of a glacier.

Time

Lichens, followed by moss, begin growing on the rock. As they die, the decaying matter is added to the rock, producing soil.

Pioneer Species

Slide 101 / 131 Primary Succession

Bare rock left after retreat of a glacier.

Time

Lichens, followed by moss, begin growing

• n the rock. As they

die, the decaying matter is added to the rock, producing soil.

Grasses and small plants start to grow. Nutrients supplied by decaying organic matter support the growth of grasses and small plants. These add more organic nutrients, which form deeper more fertile soil.

Slide 102 / 131 Primary Succession

Decaying organic matter create deeper soils that can hold

• water. This allows shrubs to grow.

Bare rock left after retreat of a glacier.

Time

Lichens, followed by moss, grow on the rock. As they die, the decaying matter is added to the rock, producing soil. Grasses and small plants start to grow.

Small shrubs colonize.

Slide 103 / 131 Climax Communities

Finally, larger trees can grow, and climax communities form. Climax communities are the organisms that remain stable in an ecosystem over time.

Time

Climax communities develop on mature soils.

Bare rock left after retreat of a glacier. Lichens, followed by moss, grow on the

• rock. As they die, the

decaying matter is added to the rock, producing soil. Grasses and small plants start to grow. Small shrubs colonize.

Slide 104 / 131

Secondary Succession

After ecosystems are dramatically altered by fires, floods, disease,

• r human activity, community interactions often restore

ecosystems to their original condition. The reestablishment of climax communities in an ecosystem is called secondary succession. Ground is cleared

• f existing

community to grow a single crop. Ground is abandoned and new species begin to grow. Small shrubs again colonize. New climax community forms.

Slide 105 / 131

27 How could high and low levels of disturbance reduce species diversity?

Students type their answers here

Slide 106 / 131

28 During ecological succession, describe one way in which early species can facilitate the presence of later species.

Students type their answers here

Slide 107 / 131 Community Ecology: Experimental Design

One way in which scientists study the interactions between populations in a community is to conduct exclusion experiments. In an exclusion experiment, one species is removed from an area. The area is then observed to see what occurs. What type of information can be gained from an exclusion experiment?

Source: Government of Bermuda, Dept of Conservation Services

This exclusion experiment attempted to determine the effect of sea turtles

• n sea grass populations. These

cages prevent sea turtles from grazing on these sea grasses.

Slide 108 / 131 Community Ecology: Experimental Design

In the 1950s, Joseph Connell studied the distribution in the intertidal zone of two different barnacles species: Chthamalus stellatus and Balanus balanoides. Upper Intertidal Zone Middle Intertidal Zone Lower Intertidal Zone Chthamalus Balanus How would you describe the distribution of Chthamalus and Balanus in the intertidal zone?

Slide 109 / 131 Community Ecology: Experimental Design

Connell wanted to determine why these barnacle species have these distribution patterns. He observed the species over a long period of time. In the spring of 1955, the area experienced very low tides. The portion of the intertidal zone that is normally occupied by both species did not receive any water. Results: Balanus showed high levels of mortality in the upper intertidal zone but not in the lower intertidal zones (which were covered in water). What could Connell conclude about the distribution pattern of Balanus in the upper intertidal zone?

Slide 110 / 131 Community Ecology: Experimental Design

The dessication information explained why Balanus was not present in the upper intertidal zone. However, it did not explain why Chthamalus was only found in the upper intertidal zone. Connell performed an exclusion experiment. · He established several study areas throughout the intertidal zone, in which he periodically mapped every single barnacle. · He removed Balanus from half of each study site. · He determined which half to exclude Balanus from by flipping a coin. Chthamalus Balanus

Slide 111 / 131 Community Ecology: Experimental Design

Results: · In the absence of Balanus, Chthamalus survived in the middle intertidal zone. · In the lower intertidal zone, Chthamalus experienced high mortality rates with or without Balanus. What conclusions can you make from these results?

Slide 112 / 131 Community Ecology: Experimental Design

Conclusions: · In the middle intertidal zone, competitive exlcusion of Balanus

• ver Chthamalus occurs.

· In the lower intertidal zone, predation excludes Chthamalus from growing.

Slide 113 / 131

29 Which barnacle species is better adapted to survive dessication? A Chthamalus B Balanus

Slide 114 / 131

30 "Competitive exclusion of Balanus over Chthamalus

• ccured in the middle intertidal zone." What does this

mean? A Chthamalus is able to compete for resources better than Balanus. B Balanus is better able to compete for resources than Chthamalus.

Slide 115 / 131

31 Why did Connell flip a coin to determine in which half of each study site he would remove Balanus?

Students type their answers here

Slide 116 / 131

32 In an exclusion experiment, what is an example of a control group? A The number of organisms present at the start of the experiment. B A study site in which nothing has been removed. C A study site in which the opposite organism has been removed. D A study site from a previous experiment in which no

• rganisms were removed.

Slide 117 / 131

Swedish Lake Food Chain

Energy Transfer

Feeding relationships in communities can be observed via food chains and food webs. These show the pathway of energy transfer in a community. What is the difference between a food chain and a food web?

Slide 118 / 131 Energy Transfer

Each organism in a food web/chain occupies a specific trophic level. Individuals feed on organisms at lower trophic levels. No matter what position is occupied in a food chain, eventually all

• rganisms become energy for decomposers.

Trophic Levels

Slide 119 / 131 Energy Transfer

Energy transfer between food chain trophic levels is not

• efficient. Only about 10% of the energy/biomass from one

trophic level is transferred to the next level. Because of this, food chains are limited in length.

Source: EPA

One of the food chains illustrated in this food web is: phytoplankton dragonfly salamander bald eagle If the biomass of phytoplankton in this community is 1000 kg, what biomass of bald eagle can survive?

Slide 120 / 131

33 In a forest community, shrubs and grasses are consumed by hares, who are, in turn, consumed by foxes. Insects also consume grasses and are, in turn, consumed by shrews and then foxes. This is an example of a A food chain. B food web.

Slide 121 / 131

34 Food chains will be longer in communities that have higher A numbers of tertiary consumers. B predation. C photosynthetic production. D competition.

Slide 122 / 131

35 Use this food web to determine the biomass of primary producers necessary to support an osprey biomass of 286 kg.

Slide 123 / 131 Dominant Species

A dominant species is one that has a large effect on a community due to high biomass. Tidal swamps are dominated by

• mangroves. (Mangroves have the

largest biomass in the community.) The mangrove root system traps sediments, dissipates wave energy and provides habitat for oysters. If a mangrove population were eliminated, the entire ecosystem would change drastically.

Slide 124 / 131 Keystone Species

In contrast to a dominant species, a keystone species has a low biomass but a large effect on community structure. Consider this simplified food web for Eel River, California: Algae

Predatory Insects

Roach fry Stickleback fry Large Roach Steelhead Larval insects

(fish) (fish) (fish) (fish)

Slide 125 / 131 Keystone Species

Mary Power conducted research in Eel River to determine the effect of fish on food web structure. Experimental Design: · She set up cages in Eel River that excluded movement of large fish but allowed movement of insects, stickleback and roach fry. · In 6 cages, she excluded large fish. · In 6 cages, she allowed steelhead and large roach. What is the control group in this experiment?

Slide 126 / 131 Keystone Species

Results: · In cages in which large fish were excluded, algal biomass grew exponentially. · In cages in which large fish were enclosed, algal biomass was reduced. Keeping in mind that large fish are at the top of the food chain, what can be concluded from these results?

Slide 127 / 131

36 In the cages where large fish were excluded, what would you predict would happen to the larval insect populations? A They would increase. B They would decrease.

Slide 128 / 131

37 If a virus eliminated steelhead and large roach from the Eel River, what would be a possible consequence? A The river would be overrun by algae. B Predatory insect populations would crash. C Algal populations would crash. D Nutrient levels in the river would increase.

Slide 129 / 131

38 What do dominant species and keystone species have in common? A They have large biomass. B They have minimal impact on community structure. C They have small biomass. D They have a large impact on community structure.

Slide 130 / 131

39 Dominant species are usually located where in a food chain? A tertiary consumer B decomposer C primary producer D primary consumer

Slide 131 / 131