© 2011 Pearson Education, Inc. CHAPTER 4 Interrelationships

© 2011 Pearson Education, Inc.

CHAPTER 4

Interrelationships


Two Secrets of Survival: Energy Flow and Matter Recycle

• An ecosystem survives by a combination of energy flow and matter recycling.

Figure 3-14Figure 3-14


Interrelationships…

• How various populations interact with each other…

• Because there are only so many resources (food, water, space, etc) and each population wants to be “on top” some populations rely on each other, or try to snuff each other out!


Size – number of individuals

Density – number of individuals in a certain space

Distribution – spatial pattern – clumping,uniform dispersion,random dispersion

Age distribution structure - percentage of individuals in each age group

Population DynamicsPopulation Dynamics


Community interactions• Relationships between species may be positive (helpful),

negative (harmful), or neutral for each species• Predation: one member benefits, the other is harmed (+−)

• Includes parasitism, herbivory

• Competition: both species are harmed (−−) because they’re competing for the same niche.• Interspecific competition: between different species• Intraspecific competition: between the same species

• Mutualism: both species benefit (++)• Commensalism: One species benefits, the other is not

affected (+0)


The niche as a two-dimensional shape

Niche represented by a 2-dimensional area

Species A

© 2008 Paul Billiet ODWS


Separate niches

No overlap of niches. So coexistence is possible

Species A Species B



Overlapping niches

Interspecific competition occurs where the niches overlap

Species CSpecies B



Species C

Specialisation avoids competition

Evolution by natural selection towards separate niches

Species B’ Species C’

Specialisation into two separate niches

Species B



This niche is not big enough for the both of us!

Species A Species D

Very heavy competition leads to competitive exclusionOne species must go



Total exclusion

Species A has a bigger niche it is more generalist

Species E has a smaller niche it is more specialistSpecialists, however, do tend to avoid competitionHere it is total swamped by Species A



Major types of interactions between species


Predation• Predator: the organism that does the feeding• Prey: the organism that is fed upon• Predator-prey interaction: carnivores (meat eaters)

eat herbivores (plant eaters)• Herbivores feed on plants• Parasites feed on hosts

• Parasite: an organism (plant or animal) that feeds on its “prey,” usually without killing it

• Host: the organism that is being fed upon


Parasitic organisms• Include tapeworms, disease-causing bacteria,

viruses, fungi• Parasites affect host populations in a density-

dependent way• Increased population density makes it easier for

parasites and their vectors (carriers of the parasite) to find new hosts

• Pathogens: bacteria and viruses that cause disease• No real ecological difference from other parasites• Highly specialized parasites


Several types of parasites


Mutualism• An arrangement between two species where both

benefit• Examples of mutualism

• Pollinators (e.g., bees) receive nutrition while plants receive pollination

• Fungi on roots: the fungus gets nutrition; the plant gets easier intake of soil nutrients

• Lichens are made of a fungus and an alga• The anemone fish protects the anemone from

predation by the butterfly fish, and the anemone protects the fish


Mutualistic relationships


Mutualism – Ant and Aphid

http://www.richsoil.com/antsandaphids/ants_aphids_sugar.jpg


The Aphid and the Ant

• Aphids feed on the sap of the plant they are on. • Ants use their antennae to stimulate the aphids and cause

them to excrete from their abdomen a substance called honeydew which is rich in the nutrients ants require.

• Each worker ant goes from aphid to aphid collecting honeydew which she stores in her abdomen until it's full; then, she returns to the nest and regurgitates to feed other members of the colony.

• Ants, in return for the honeydew, protect the aphids from predators such as flies, wasps, and beetles.

• The ants, like human ranchers, sometimes move their aphids to richer grazing grounds.

• YUMMY!


A Little Aphid Ant Humor

http://images.google.com/imgres?imgurl=http://www.ibiblio.org/Dave/Dr-Fun/inline/thumbs/tn20001013.jpg&imgrefurl=http://www.ibiblio.org/Dave/ar00295.htm&h=190&w=258&sz=20&hl=en&start=9&tbnid=5x78fixpPQkJAM:&tbnh=82&tbnw=112&prev=/images%3Fq%3Daphid%2Bant%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DN


Commensalism and amensalism• Commensalism: one species benefits; the other is

unaffected• More rare• Buffalo stir up insects that cattle egrets eat• Orchids live on trees but do not harm or feed off of them

• Amensalism: one species is harmed; the other is unaffected• Usually accomplished by natural chemical compounds• Black walnut trees produce a chemical that kills other plants

• Symbiosis: two species live close to each other• Can be beneficial (mutualism) or harmful (parasitism)


Commensalism


Keystone species• Removal of one species can create a cascade of

effects• Impacting far more than just the other species they

interact with

• Sea stars eat mussels in rocky intertidal zones• Removing sea stars allows mussels to crowd out all

other species, reducing diversity

• Keystone species: play a crucial role in maintaining ecosystem biotic structure• Moderate other species that would take over• Allow other, less-competitive species to flourish


Sea stars: a keystone species


Keystone species


Indicator Species

• Plants or animals that show something about the environment by their presence or absence

• Warning signs that something may have changed—very sensitive to change


Competition• Interactions where both species are harmed

• They compete for a scarce resource

• Species that compete have overlapping niches• Over time, there is pressure to reduce the overlap


CHAPTER 4

Populations and Communities

Active Lecture Questions


(Births plus ________) minus (________ plus Emigration) = Change in population number

a. Emigration; Birthsb. Immigration; Deathsc. Immigration; Birthsd. Emigration; Deaths

Review Question-1


(Births plus ________) minus (________ plus Emigration) = Change in population number

a. Emigration; Birthsb. Immigration; Deathsc. Immigration; Birthsd. Emigration; Deaths

Review Question-1 Answer


True or False: Natural selection results in a modification of the gene pool toward traits that enhance survival and reproduction of a population.

a. Trueb. False

Review Question-2


True or False: Natural selection results in a modification of the gene pool toward traits that enhance survival and reproduction of a population.

a. Trueb. False



The rate at which members of a species reproduce if there are no limiting factors is referred to as

a. K-strategy.b. r-strategy.c. environmental resistance.d. biotic potential.

Review Question-3


The rate at which members of a species reproduce if there are no limiting factors is referred to as

a. K-strategy.b. r-strategy.c. environmental resistance.d. biotic potential.



A species that has a critical role in maintaining an ecosystem’s biotic structure is a

a. J-curve species.b. K-strategist.c. keystone species.d. biotic potential.

Review Question-4


A species that has a critical role in maintaining an ecosystem’s biotic structure is a

a. J-curve species.b. K-strategist.c. keystone species.d. biotic potential.



The theory that has helped us understand earthquakes, volcanic activity, and the geographic distribution of present-day biota is

a. the law of limiting factors.b. the Laws of Thermodynamics.c. the theory of evolution.d. plate tectonics.

Review Question-5


The theory that has helped us understand earthquakes, volcanic activity, and the geographic distribution of present-day biota is

a. the law of limiting factors.b. the Laws of Thermodynamics.c. the theory of evolution.d. plate tectonics.



According to Fig. 4-2, the population growth curve that represents logistic growth is

a. the J-curve.b. the S-curve.

Interpreting Graphs and Data-1


According to Fig. 4-2, the population growth curve that represents logistic growth is

a. the J-curve.b. the S-curve.

Interpreting Graphs and Data-1 Answer


According to Fig. 4-8, the approximate date that this population reached its greatest level of environmental resistance was

a. 1944.b. 1955.c. 1963.d. 1991.

Interpreting Graphs and Data-2


According to Fig. 4-8, the approximate date that this population reached its greatest level of environmental resistance was

a. 1944.b. 1955.c. 1963.d. 1991.

Interpreting Graphs and Data-2 Answer


A K-strategist’s population size typically fluctuates around

a. the midpoint of the J-curve.b. carrying capacity.c. density-dependent factors.d. density-independent factors.

Thinking Environmentally-1


A K-strategist’s population size typically fluctuates around

a. the midpoint of the J-curve.b. carrying capacity.c. density-dependent factors.d. density-independent factors.

Thinking Environmentally-1 Answer


A sudden hard freeze that kills members of an ecosystem is an example of

a. a critical number.b. a density-dependent factor.c. a density-independent factor.d. density-driven resistance.

Thinking Environmentally-2


A sudden hard freeze that kills members of an ecosystem is an example of

a. a critical number.b. a density-dependent factor.c. a density-independent factor.d. density-driven resistance.

Thinking Environmentally-2 Answer

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© 2011 Pearson Education, Inc. CHAPTER 4 Interrelationships