Final Exam - Community Ecology - Lecture 13 - Fill in the Blanks

Question 1

What are indirect effects?

Answer 1

When one species affects a second species through a change in an intermediate 3rd species.

Question 2

What are examples of indirect effects?

Answer 2

Indirect mutualism, apparent competition, habitat facilitation, trophic cascades, etc.

Question 3

What are keystone species?

Answer 3

Species whose effects on the ecosystem are disproportionately large for their biomass.

Question 4

Exploitative competition is an example of what?

Answer 4

Indirect effects

Question 5

Interference competition is an example of what?

Answer 5

Direct effect

Question 6

What is exploitative competition?

Answer 6

Also called resource competition.

Occurs when species share a limited resource, making the resource less available for the other species.

Question 7

What is interference competition?

Answer 7

Occurs when one species limits access of another species to a limiting resource.

Question 8

What is apparent competition?

Answer 8

Non-competing species that share a predator may have negative indirect effects on each other by increasing predation on each other.

Question 9

What is facilitation?

Answer 9

An interaction where presence of one species alters the environment to enhance growth, survival and reproduction of another species.

Question 10

What is habitat facilitation?

Answer 10

Foundation species modify habitat to provide structure habitat for other species.

Question 11

Size-selective predation affects the _______ of ______ as well as ______ species. (in freshwater planktonic communities)

Answer 11

1) diversity
2) predator
3) prey

Question 12

Dodson’s hypothesis was: complementary feeding niches by size selective predation.
In his study he found that:
Larval salamander creates a feeding niche for a second predator via _____ ______ _______ on _____ zooplankton.

Answer 12

1) size selective feeding

2) large

Question 13

Giguere:

Tested Dodson’s hypothesis by ______ _______ ____ from 1 arctic pond and compared to a control pond.

Answer 13

Removing salamander eggs

Question 14

The interaction between the salamander and the small zooplankton is what?

Answer 14

commensalism

Question 15

Removal of ______ shifts zooplankton to _____ sized species and this corresponds to a decline in Chaoborus, the _____ sized species.

Answer 15

1) Salamander
2) Large
3) Small

Question 16

Trophic cascades:

• Effect of one species is:
• _______ to the trophic level below it
• _______ to the next lowest level
• ________ to the next lowest level after that
• continuing in an ________ _______ depending on the number of trophic levels in the food web

Answer 16

1) Negative
2) positive
3) Negative
4) Alternating effect

Question 17

Trophic cascades are referred to as ___-___ processes.

Answer 17

top-down

Question 18

There are six reasons to why the world is green, the first three are:
1 - Not all that is green is ______
2 - Nutrients critical for animals are often in _____ _____ in ______ matter so ________ can’t obtain sufficient nutrients to grow and reproduce
3 - ______ factors limit herbivores

Answer 18

1 - edible
2 - short supply in plant matter so herbivores
3 - abiotic factors

Question 19

There are six reasons to why the world is green, the last three reasons are:
4 - _______ and ________ __________ reduce availability of _______….so herbivores can’t always locate plants efficiently
5 - Herbivores limit their own numbers via __________ and ___________ _________
6 - ________ limit herbivores

Answer 19

4 - spatial and temporal heterogeneity reduce the availability of plants
5 - intraspecific and interference competition
6 - predators

Question 20

Which of the six reasons why the world is green is the hallmark of the World is Green hypothesis?

Answer 20

Number six: predators limit herbivores.

Question 21

The HSS (or the World is Green) model has a couple different key notions:

• ________ reduce the abundance of ________ which increase ________
• 3 trophic levels
• herbivores are _______ limited
• terrestrial food chains

Answer 21

1) Predators reduce the abundance of herbivores which increase producers
2) herbivores are predator limited

Question 22

Another insight from the HSS model is that:

- one process, either _______ ________ or _______ ________, should dominate at any given trophic level.

Answer 22

Resource limitation or predator limitation

Question 23

There are also criticisms to the HSS model:
1 - Plants have _________, reducing the effects of _________ on plants
2 - _________ may be limited by territories/nesting sites (factors from the previous six reasons)
3 - Applicable to food chains but, most communities have _____ _____

Answer 23

1) defenses; herbivores
2) Herbivores
3) food webs

Question 24

The HSS paper initiated what was to become the _______ ________.

Answer 24

trophic cascade

Question 25

How did Okanen (or Oksanen) test HSS?

Answer 25

Treated each trophic level as a single homogeneous population.

Question 26

What is potential primary productivity (G)?

Answer 26

the maximum primary productivity allowed by the environment in the absence of consumers.

Question 27

What was Oksanen’s hypothesis?

Answer 27

Ecosystems with low G support fewer trophic levels (smaller chain)

Question 28

Oksanen found that herbivore population (consumer density) is limited by what?

Answer 28

Both resource limitation and predators

Question 29

Craig Osenberg and Gary Mittelbach - data from an oligotrophic lake

• Each trophic level showed a greater change in ________ in response to resource addition than predator removal.
• so, ________ ________ was more severe than _________ _________ for each trophic level

Answer 29

1) biomass

2) resource limitation; predator limitation

Question 30

There are three predictions of the consumer-resource theory applied to trophic levels:
1 - In food chains of a given length, an increase in G will increase abundances of populations at ___ trophic levels and _________ trophic levels, but not _________ trophic levels
2 - Reduction in abundances of populations at top trophic levels will alternatively increase and decrease abundances in lower trophic levels - a ______ ______
3 - Increase in G should increase ________ of ________ _________ in an ecosystem (increase food chain ______)

Answer 30

1) top; alternating; intervening
2) trophic cascade
3) number of trophic levels; food chain

Question 31

Other studies of natural studies have demonstrated abundances of ____ trophic levels increased with __.
This means that ______ _______ within the food web matters.

Answer 31

1) all
2) G
3) species composition

Question 32

Wooton and Power;
Manipulated ________ levels primary productivity in a California river: replicates of various _______ (_______ = photosynthesis) treatments over _________

Answer 32

1 - light
2- shade
3 - light
4 - channels

Question 33

In the example of a food web where herbivores represent 2 prey types that share a common resource and predator;
Herbivore 1 (N1) is a better \_\_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_\_\_\_ but is more vulnerable to \_\_\_\_\_\_\_\_; N2 on the other hand is more \_\_\_\_\_\_\_\_\_\_ resistant

Answer 33

1 - resource competitor
2 - predation
3 - predator

Question 34

Heterogeneity in species composition with trophic level, together with trade-off between competitive ability and vulnerability to predation leads to:

1) ________ ___________ along productivity gradients
2) _________ in _________ of all trophic levels with increase in G

Answer 34

1) Species replacements

2) Increases in abundance

Question 35

A species replacement along a productivity gradient represents a shift from a good _______ _______ to good ________ __________.

Answer 35

Resource competitor to predator resistor

Question 36

What are three examples of potential mechanisms by which resources are less available to higher trophic levels?

Answer 36

• Adaptive foraging behaviours
• Inducible defences
• Omnivory
• ratio-dependent predation
• complex life histories (invulnerable life stages)
• etc.

Question 37

Resource limitation and predator limitation should often act in concert to limit __________.
But, not simply a dichotomy of top-down vs. bottom up.
_______ ________ may differ.

Answer 37

1) abundance

2) Relative strengths

Question 38

Predation limiting herbivores would be an example of ___-___ control whilst resource limitation would be an example of ___-___ control.

Answer 38

• Top-down

- Bottom-up

Question 39

There are many reasons for why trophic cascades are more prevalent in aquatic ecosystem rather than terrestrial ones. These include:
1 - Terrestrial producers are _____(sentence)
2 - Terrestrial food webs have more _______ (sentence)
3 - Relative sizes of producers and consumers and nutritional quality of plants compared to algae

Answer 39

1 - Terrrestrial producers are longer lived and better defended against herbivory
2 - Terrestrial food webs have more generalists feeder, more omnivores and so more diverse pathways and weaker interaction strengths due to multiple food web links

Question 40

Trophic cascades provide strong evidence for importance of ___-___ processes; yet, says little about the relative importance of _______ vs. _________ limitation.

Answer 40

1 - Top-down

2 - resource vs. predator limitation