Community Ecology

Question 1

What is a community in an ecological context?

Answer 1

Groups of organisms living close enough together for interactions to occur.

Question 2

What is biodiversity?

Answer 2

The variety of organisms that make up a community.

Question 3

What two components make up biodiversity?

Answer 3

1) Species richness: how many different species are there? 2) Relative abundance: how many individuals of each species are there.

Question 4

What is the Shannon-Wiener diversity index?

Answer 4

It is a measure of diversity, represented by the formula H=−∑i=1n​(pi​ln(pi​)). You don’t need to know how to use it, but should be aware of what it does. Pi is the proportion of each species. Estimates diversity of species within a community.

Question 5

What does a higher value in the Shannon-Wiener diversity index indicate?

Answer 5

A higher value indicates: 1) More species and 2) Species are more equally represented.

Question 6

What is competition in ecology?

Answer 6

Organisms competing for the same resources.

Question 7

What are the two types of competition?

Answer 7

Interspecific (between different species) and Intraspecific (within the same species).

Question 8

Explain interspecific competition using the barnacle example.

Answer 8

Two species of barnacle live in intertidal areas. One lives higher on rocks (better at surviving drying out) and the other lives lower. If the lower species is removed, the upper species moves down and takes over. If the lower species is allowed back, it outcompetes the upper species lower down. The opposite is also true.

Question 9

What is the principle of competitive exclusion?

Answer 9

Two species in the same place cannot coexist if they are competing for the same resources; one will do better than the other.

Question 10

What is intraspecific competition?

Answer 10

Competition within the same species.

Question 11

Why is intraspecific competition important in agriculture?

Answer 11

If plants like corn are planted too densely, too many individuals in an area compete for water and nutrients from the soil, causing them to be stunted and not grow well.

Question 12

What is an organism’s niche?

Answer 12

All the biotic and abiotic factors that an organism needs to survive.

Question 13

Differentiate between biotic and abiotic factors in the context of a niche.

Answer 13

Biotic factors are biological factors like food availability. Abiotic factors are non-biological factors such as temperature or rainfall.

Question 14

What is resource partitioning?

Answer 14

Different organisms use different resources in a particular habitat, which minimizes competition and leads to the evolution of different characteristics to help divide up resources.

Question 15

How does predation affect a community?

Answer 15

Predation can actually increase species diversity within a community.

Question 16

Explain how predation can be a ‘good’ thing, using the sea otter-kelp example.

Answer 16

Kelp forests support diverse communities. Sea otters feed on sea urchins, which feed on kelp. When sea otters were endangered, sea urchins ate most of the kelp, causing kelp forests to disappear. As otter populations recovered, kelp forests returned. However, killer whales eating sea otters in some areas are causing kelp forests to disappear again.

Question 17

What effects has predation had on evolution?

Answer 17

Predation leads to the evolution of characteristics that help animals catch prey, or help animals avoid becoming prey.

Question 18

Give an example of an evolutionary adaptation related to predation for both prey and predators.

Answer 18

Camouflage (blending into surroundings). This applies to prey to avoid being seen, and to predators to ambush prey.

Question 19

What is mimicry?

Answer 19

Looking like something deadly or unpalatable to avoid being bothered.

Question 20

What is Batesian mimicry?

Answer 20

One species is dangerous, and another harmless species imitates it, providing an advantage to the imitator. However, there cannot be too many imitators, or the protection would fail. (e.g., King snakes looking like coral snakes or Monarch butterflies looking like Viceroy butterflies).

Question 21

What is Mullerian mimicry?

Answer 21

Both species are dangerous and look like each other. This is an advantage for both because predators learn to avoid them more quickly.

Question 22

How is herbivory similar to predation?

Answer 22

It is similar in that plants are ‘fighting back’ against herbivores.

Question 23

What are some defense mechanisms plants use against herbivory?

Answer 23

Many plants are toxic, have spines, or other defense mechanisms. An example is silica granules in leaves, which grind down the teeth of herbivores.

Question 24

Does herbivory typically kill the plant?

Answer 24

No, herbivory often doesn’t kill the plant.

Question 25

How does disease affect a community?

Answer 25

Disease can have wide-ranging and unexpected effects.

Question 26

Give examples of how disease has impacted populations.

Answer 26

The vicuñas case study discussed previously. Rinderpest killed enormous numbers of animals in East Africa, changing the structure of the Serengeti. Plague killed between 1/4 and 1/3 of humans globally. Smallpox may have killed 90% of people in the New World.

Question 27

What is parasitism?

Answer 27

One species is hurt, and the other comes out ahead.

Question 28

Give examples of parasites.

Answer 28

Tapeworms, ticks, roundworms, pinworms, etc.

Question 29

Do parasites typically kill their host?

Answer 29

Parasites often don't kill their host, because if the host dies, the parasite may also die.

Question 30

What are exceptions to parasites not killing their host?

Answer 30

Sometimes a parasite needs to kill the host to get into the next host.

Question 31

Explain the example of Toxoplasmosis.

Answer 31

The parasite causes mice to lose their fear of cats. Cats are the primary host, releasing eggs in feces, which mice pick up from contaminated grasses/seeds.

Question 32

Explain the example of Trichinosis.

Answer 32

The parasite lodges in the muscles of the host, weakening it. The host is then eaten, and the cycle repeats.

Question 33

What is commensalism?

Answer 33

One species gets a benefit, and the other is unhurt.

Question 34

Give an example of commensalism.

Answer 34

Cattle egrets follow large ungulates (like cows) and eat insects scared up by the cows as they move around. The cows are unaffected, and the egrets get food.

Question 35

What is mutualism?

Answer 35

Both species come out ahead.

Question 36

Give three examples of mutualism.

Answer 36

Honey bees and flowers, sea anemones and clownfish, and acacias and ants, turtles and algae

Question 37

Explain the mutualistic relationship between sea anemones and clownfish.

Answer 37

The sea anemone gets food from the fish, and the fish gets protection from the anemone's stingers.

Question 38

Explain the mutualistic relationship between Acacias and ants.

Answer 38

Ants get shelter and food from the acacia tree, and in return, fiercely protect the tree from predators and competitors. If the ants are removed, the tree often dies, and ants are not found without the tree.

Question 39

What was the purpose of the KLEE project related to Acacia and ants?

Answer 39

It is a long-term study, set up in 1995, to evaluate the effects of grazing by herbivores, cattle, and other animals.

Question 40

What happens to Acacias when grazing stops, depending on the ant species present?

Answer 40

If the most common mutualistic ant species is present, Acacias start making less food and homes for ants. A second ant species may then increase, which doesn't nest in the 'homes' and encourages stem-boring beetles that damage the tree.

Question 41

What is disturbance in ecology?

Answer 41

Things like fire, hurricanes, overgrazing, human activities, etc., that disrupt a community.

Question 42

Are all disturbances bad?

Answer 42

No, not all disturbances are bad, and some communities rely on them to perpetuate themselves.

Question 43

Give an example of a community that relies on disturbance.

Answer 43

Some pine trees (e.g., Monterey pine) only release their seeds after fire has caused their cones to open.

Question 44

What happens as a result of disturbance?

Answer 44

A community goes through what is called succession.

Question 45

What is succession?

Answer 45

Starting with an essentially lifeless area and 'succeeding' through various stages until the original community is restored.

Question 46

What are the stages of succession in the local area (as an example)?

Answer 46

Grasses → shrubs → pine trees → deciduous trees.

Question 47

What is the end stage of succession called?

Answer 47

The climax community.

Question 48

What is primary succession?

Answer 48

Succession that takes place when all living things in an area have been removed. Examples include after new rocks have formed from volcanism or reclaiming a parking lot.

Question 49

What is secondary succession?

Answer 49

Succession where not all living things have been removed. Examples include clearcutting a forest for lumber, fire, or hurricanes.

Question 50

Can we rely on succession to deal with environmental damage?

Answer 50

No, we are damaging the environment quicker than it can recover.

Question 51

What are trophic levels?

Answer 51

A description of the energy that is available to organisms.

Question 52

Why are there more herbivores than carnivores?

Answer 52

There is more overall energy available to herbivores because energy is lost each time it moves up the food chain.

Question 53

What supports all life, and what are they?

Answer 53

All life is essentially supported by autotrophs, which are mostly plants and algae. They provide energy for other organisms.

Question 54

Define the terminology for consumers in a food chain.

Answer 54

Herbivores are primary consumers. Carnivores that eat herbivores are secondary consumers. Carnivores that eat secondary consumers are tertiary consumers, and so on.

Question 55

What are detritivores?

Answer 55

Organisms that eat dead stuff, such as vultures, many fungi, and dung beetles.

Question 56

What is a food web, and why do we typically see them instead of food chains?

Answer 56

Animals usually don't eat at just one trophic level, so we get complex food webs instead of simple food chains.

Question 57

Why can't there be too many 'top' carnivores?

Answer 57

Energy is limited, and only about 10% (on average) of the energy at one trophic level makes it to the next. This makes it difficult to support many trophic levels, so you won't find many quaternary consumers.

Question 58

Why is it more efficient to eat vegetables/fruits/grains rather than meat to feed humans?

Answer 58

Cows only provide 10% of the energy to humans that plants can, due to energy loss at each trophic level.