Lecture 20- Food Webs IV

Question 1

How is energy flow and community structure controlled?

Answer 1

• Species involved in it
• How is energy flowing up it
• Are there limitations to energy flow
• What species are most affected

Question 2

What is a bottom up model?

Answer 2

Primary production controls the number of herbivores

Question 3

How does plant availability control populations?

Answer 3

By limiting or providing abundance for the herbivores in the system. Then the number of herbivores in the system will affect the number of predators in the system

Question 4

What is a top down model?

Answer 4

Herbivores are controlled by predation pressure of carnivores

Question 5

How do carnivores control populations?

Answer 5

How fluctuations in their population can apply pressure or release pressure on herbivores. Then this puts or released pressure on plants

Question 6

What is a reciprocal model?

Answer 6

All working together (each member has an effect on each other)

Question 7

Food chain length ____ with system productivity

Answer 7

Increases

Question 8

What is the exploitation ecosystem hypothesis?

Answer 8

Food chain length increases with system productivity

Question 9

The exploitation ecosystem hypothesis is based on what?

Answer 9

Bottom up model

Question 10

What is the difference between low productivity, medium productivity and high productivity?

Answer 10

1. Low productivity = cant support herbivores
2. Medium productivity = can support herbivores but not predators
3. High productivity = can support both herbivores and predators

Question 11

If primary productivity is low, the system ______

Answer 11

Cannot support herbivores

Question 12

If a system cannot support herbivores, plants are _____

Answer 12

Not regulated by grazing

Question 13

Low productivity = ____ of primary producers

Answer 13

Low abundance

Question 14

In a low productivity system, plant biomass becomes limited by what?

Answer 14

Limited by nutrient availability

Question 15

In a moderate productivity system, what limits the plants?

Answer 15

Herbivores exert strong control on plants

Question 16

A high productivity system is dominated by a ?

Answer 16

System is dominated by a predator-herbivore interactions

Question 17

A medium productivity system is dominated by a?

Answer 17

Plant-herbivore system dominates

Question 18

How do high productivity systems work?

Answer 18

• Predators exert pressure on herbivores
• Releases control on plants = plants increase
• More control from higher trophic levels
• Three way interaction

Question 19

What is secondary production?

Answer 19

Productivity of the herbivore (high plant production = high herbivore abundance)

Question 20

Describe the exploitation ecosystem hypothesis based on the concept of thresholds

Answer 20

• Once threshold for primary productivity is met, herbivores can establish
• Keep plants in check until they reach a threshold to support predators
• This releases control on plants

Question 21

What type of model is used to describe Snowy owls and Lemmings?

Answer 21

Bottom up model

Question 22

Describe the relationship between Snowy owls and Lemmings

Answer 22

• Fluctuations in lemming populations are driven by vegetation and snow depth
• When you get a crash in lemming populations, you dont see any predators at all
• Lower trophic levels controling the higher trophic levels
• More prey available = more predators

Question 23

What type of model do you have for Caribou and Woody vegetation?

Answer 23

Top down model

Question 24

Describe the system between caribou and woody vegetation

Answer 24

• Higher caribou herbivory pressure linked with lower cover of tall woody plants
• Stomping down on shrubs controls their plant growth
• Counteracts warming response of vegetation

Question 25

What are the four hypothesis for Lynx and Snowshoe Hare population interactions?

Answer 25

1. Bottom up = Hare cycle caused by winter food shortage and delayed recovery of winter browse damaged by excessive browsing
2. Bottom up = Hare cycles caused by changes in food quality as a result of heavy browsing by peak hare densities which triggered an increase in secondary compound production by the plants
3. Top down = Hare cycles caused by heavy predation and the time lag of predator rates of population growth relative to hares
4. Top down = Hare cycle caused by both food and predator, with food shortage at the peak followed by heavy predation in the decline

Question 26

What were some predictions of the Lynx and Snowshoe hare experiment?

Answer 26

• Food addition will increase hare density
• Plant defense compounds will be high during hare peaks
• Predator exclusion will increase hare density
• Food addition and predator exclusion will interact to increase hare density

Question 27

What were the results of the Lynx and Snowshoe hare experiment?

Answer 27

• When predators excluded, hare increased over control
• When food is supplemented, hare increased over control
• When predators are excluded and food is supplemented, hare populatioin exploded

Question 28

How does predation pressure of hares from lynx reduce reproduciton?

Answer 28

• Ecountering predators whrn predator densities are high = causes chronic stress on the mother
• Stress releases hormones that can be passed to offspring
• Can reduce their survivorship
• Mother has lower reproductive success
• Likely to cause lower reproductive success in their offspring
• Can cause a delay in the population recovery

Question 29

What are the conclusions to the lynx and snowshoe hare experiment?

Answer 29

• Hares are regulated by BOTH food and predators
• Lynx are only regulated by prey
• Stress associated with food quality and predators leads to reduced birth rates in hare
• Lower reproduction is inherited