Exam 7

Question 1

Community

Answer 1

Group of interacting species

All species interact in some way with other species

Question 2

Examples of community interactions (4)

Answer 2

Interspecific competition
Predation
Coevolution
Symbiosis

Question 3

Interspecific competition

Answer 3

Competition between individuals of different species

Question 4

Niche

Answer 4

An organism’s role in an ecosystem (profession)

What it eats, where it lives, who eats it, what it needs to survive, who competes with it

Question 5

Competition coefficient

Answer 5

Indicates strength of effect on the other species

If a=1, the species have no net effect on each other

When a12 is < 1 the effect of species 2 on species 1 is less than the effect of species 1 on its own members.

Conversely, when a12is > 1 the effect of species 2 on species 1 is greater than the effect of species 1 on its own members.

Question 6

Ex: alpha1,2

Answer 6

Effect of species 2 on species 1

Question 7

Stable equilibrium

Answer 7

K1 and K2 are lower than K1/a12 and K2/a21
When INTRAspecific competition is stronger than interspecific competition
2 species can coexist because there is little overlap between needs of the 2 species

Question 8

Unstable equilibrium

Answer 8

INTERspecific competition greater than intraspecific competition
One of the 2 species is likely to drive the other out, but it is random who wins

Question 9

Which population fluctuates in size as a result of changes in carrying capacity?

Answer 9

Predator, because prey is a resources for the predators

Question 10

Coevolution of predator and prey leads to

Answer 10

Adaptations to capture prey

Adaptations to avoid being detected/eaten

Question 11

3 types of adaptations to capture prey

Answer 11

Mechanical adaptations
Chemical adaptations (venom)
Camouflage of predator

Question 12

5 types of adaptations to avoid being eaten/detected

Answer 12

Mechanical defenses
Chemical defenses (toxins)
Camouflage
Mimicry
Synchronized reproduction

Question 13

Mimicry

Answer 13

Harmless animal resembles danger

Question 14

Synchronized reproduction

Answer 14

Satiates predators before all offspring are consumed

Ex: cicada

Question 15

Symbiosis

Answer 15

2 species live in close association with each other

Question 16

3 forms of symbiosis

Answer 16

Parasitism
Commensalism
Mutualism

Question 17

Parasitism

Answer 17

One species benefits to detriment of the other
Host species evolve mechanisms to minimize effects of parasites (cysts/galls, immune response)
Parasites have greatest impact on host population when newly introduced (no prior coevolution)
Parasites evolve to manipulate host for improved transmission

Question 18

Commensalism

Answer 18

One species benefits and other is unaffected

Ex: barnacles on whales

Question 19

Mutualism

Answer 19

Both species benefit
Cooperation or reciprocal exploitation?
Ex: microrrhizae: fungus-plant mutualism
Ex: Plant-insect mutualisms (defense-ants and acacia trees; pollination by bees)

Question 20

Why aren’t all species engaged in mutualistic relationships?

Answer 20

Costs may be prohibitive (small benefits don’t outweigh costs)
Conflict of interest between participants generates selective advantage to “cheaters”

Question 21

Community structure

Answer 21

Interactions within community are often diffuse, involving many species (competition/predation between any 2 species may be weak, even if it has a strong effect overall on the community)
Interactions are often indirect, propagating throughout the community (keystone species)

Question 22

Keystone species

Answer 22

Have significant influence on community structure

Ex: removing a predator species can reduce diversity by increasing competition among prey

Question 23

2 types of community structure control

Answer 23

Top-down control
Bottom-up control
Hard to test if populations are more under top-down or bottom-up control

Question 24

Top-down control

Answer 24

Through the effects of predators

Question 25

Bottom-up control

Answer 25

Through availability of resources to higher levels

Question 26

‘No difference in rates of multiplication can be so slight as to negate the exclusion principle.’ What does this mean?

Answer 26

No 2 processes in the real world are exactly equal. There is always going to be some difference, even if small, in reproduction rates between species. But even if the difference is very small, eventually one species will overtake the other given enough time, according to the exclusion principle. There is no small enough difference to make the principle false.

No matter how small the difference between the two rates (so long as there is a difference) such will be the outcome.

Question 27

According to the paper, why is it difficult to test the competitive exclusion principle? In what way do the interpretations become circular?

Answer 27

Suppose you believe the principle is true and set out to prove it empirically. First you find two noninterbreeding species that seem to have the same ecological characteristics. You bring them together in the same geographic location and await developments. What happens? -Either one species extinguishes the other or they coexist. If the formerS you say, “The principle is proved.v But if the species continue to coexist indefinitely, do you conclude the principle is false? Not at all. You decide there must have been some subtle difference in the ecology of the species that escaped you at firstS so you look at the species again to try to see how they differ ecologically, all the while retaining your belief in the exclusion principle. There is a danger of a circular process here

Question 28

David Lack wrote a ‘little classic’ called ‘Darwin’s Finches.’ How did ‘Gause’s contention’ change the way Lack interpreted the differences in beak shape among these birds?

Answer 28

Two species with similar ecology cannot live in the same region (Gause, 1934). This is a simple consequence of natural selection. If two species of birds occur together in the same habitat in the same region, eat the same types of food and have the same other ecological requirements, then they should compete with each other, and since the chance of their being equally well adapted is negligible, one of them should eliminate the other completely. Nevertheless, three species of ground finch live together in the same habitat on the same Galapagos islands, and this also applies to two species of insectivorous tree-finch. There must be some factor which prevents these species from effectively competing.

Question 29

The paragraph that begins ‘Economics’ on page 1296 explains the application of the competitive exclusion principle to aspects of human economic behavior. How is the example described in this paragraph analogous to that of Darwin’s finches?

Answer 29

??

Question 30

Under what circumstances do the equations predict that two species can co-exist?

Answer 30

When both species’ carrying capacities are lower than the other’s carrying capacity divided by the competition coefficient

Question 31

What do the ants gain from their relationship with the fungus?

Answer 31

The fungus breaks down the toxins in the leaves and swells with proteins and sugars that the ants eat

Question 32

Does the fungus gain anything from its relationship with the ants?

Answer 32

The ants bring the leaves/food to the fungus.

Question 33

Would you describe the relationship between ants and fungus as parasitic, commensalistic, or mutualistic? Why?

Answer 33

Mutualistic because both species rely on each other for survival.

Question 34

What is the role of the bacteria?

Answer 34

The bacteria cover the ants and produce antibiotics that keep mold from killing the fungus.

Question 35

According to the paper, why are arboreal herbivores rare among mammals?

Answer 35

Species that forage on plant matter in trees possess a highly constrained lifestyle. On one hand, they must be small and light to be supported in the canopy; on the other hand, small body size limits digestive capacity, especially for processing plant matter, which is rich in fibre but low in digestible nutrients.

Question 36

How do sloths benefit (directly) from the presence of algae, and (indirectly) from the presence of moths in their fur?

Answer 36

Sloths consume algae from their fur, which is highly digestible and lipid-rich to supplement diet.

Moths are portals for nutrients, increasing nitrogen levels in sloth fur, which fuels algal growth.

Question 37

What behavior performed by sloths is argued to benefit the moths? How does it benefit the moths?

Answer 37

When a sloth descends a tree and defecates, gravid female moths leave the sloth and oviposit in the fresh excrement. Larvae are copraphagous, developing entirely within the dung, and adults emerge and fly to the canopy to seek their mating grounds in sloth fur to continue their life cycle.

Question 38

What physical adaptation in the sloths appears to benefit the algae?

Answer 38

Individual hairs of three-toed sloths possess unique transverse cracks, which allow the hair shaft to become saturated with rainwater, and which algae then colonize and grow hydroponically.