Parasitism, Predation and Grazing

Question 1

How does the prey population grow in the absence of predation?

Answer 1

The population grows exponentially.

Question 2

What factors affect how predators influence the prey population?

Answer 2

Prey density, predator density and predator hunting efficiency.

Question 3

What is Holling Type I predator handling efficiency?

Answer 3

A linear increase in feeding with prey density until a maximum is reached i.e. cannot feed any faster.

Question 4

What is Holling Type II predator handling efficiency?

Answer 4

Consumption increases as density increases but prey handling time becomes the limiting factor.

Question 5

What is Holling Type III predator handling efficiency?

Answer 5

Sigmoidal relationship between host/prey density and consumption rate. Low prey density results in increased search effort.

Question 6

What is the SIR model?

Answer 6

Susceptible, infected and recovered. The simplest parasite/pathogen model.

Question 7

What impacts the proportion in each group of the SIR model?

Answer 7

Infection rate and recovery rate.

Question 8

What are some of the assumptions in the SIR model?

Answer 8

Closed population with no population growth.
No death in infected population.
Recovered population is either immune, dead or quarantined.

Question 9

What is R0?

Answer 9

The number of primary infections arising from 1 infected individual in a wholly susceptible population. It is very hard to estimate

Question 10

What does an R0 value of over 1 mean?

Answer 10

An epidemic can take off - the infected population is going to increase.

Question 11

What does an R0 value of less than 1 mean?

Answer 11

An epidemic cannot take off - the infected population is going to decrease.

Question 12

How are parasites distributed in a host population?

Answer 12

In an aggregated distribution; most hosts have just a few parasites, a few hosts have many.

Question 13

Why are parasites distributed in a certain way?

Answer 13

Host survivorship/fecundity depends on parasite number.

Question 14

What impacts immune responses to parasites?

Answer 14

Parasite type, parasite location, parasite behaviour and the damage the parasite causes.

Question 15

How does the immune system and parasite interact?

Answer 15

The parasite can suppress the immune system or promote the immune system - sometimes this is advantageous.

Question 16

Define predation.

Answer 16

Any interaction between organisms in which an organism (predator) consumes all or part of another organism (prey).

Question 17

What are some prey adaptations in response to predation?

Answer 17

Toxins, cryptic colouration, mimicry, weaponry and herding behaviour.

Question 18

What causes the cyclic oscillations of predator-prey populations?

Answer 18

Predators eat the prey so prey numbers drop.
Predators starve and decline in number.
With fewer predators, prey population increases.
With more prey, predator population increases.

Question 19

What is a keystone species?

Answer 19

A strongly interacting species that has a large impact on species diversity and competition in its ecosystem. Often predators.

Question 20

What is the escape mechanism for reducing herbivory?

Answer 20

Developing traits that reduce the likelihood of discovery by a herbivore eg size or dispersal.

Question 21

What is the tolerance mechanism for reducing herbivory?

Answer 21

Developing traits that reduce the negative impacts of herbivory eg compensatory growth and resource allocation.

Question 22

What is the defence/resistance mechanism for reducing herbivory?

Answer 22

Developing traits that affect herbivore behaviour and reduce herbivore performance.

Question 23

What are constitutive defences?

Answer 23

Defences produced and present in the plant irrespective of attack.

Question 24

What are induced defences?

Answer 24

Defences produced by and present in the plant in response to attack. A form of phenotypic plasticity.

Question 25

What are some examples of structural defences?

Answer 25

Thorns, spines, prickles, trichomes and sclerophylly.

Question 26

What are secondary metabolites?

Answer 26

Compounds produced that appear to have no direct function in photosynthesis, growth or respiration.

Question 27

What are some functions of secondary metabolites in plants?

Answer 27

Providing protection to the primary metabolism from herbivores.
Attracting pollinators.
Provide advantages in plant-plant competition.

Question 28

What are some examples of chemical defences?

Answer 28

Alkaloids, terpenoids, steroids, phenolic compounds, cyanogenic compounds and glucosinolates.

Question 29

What can lead to induced defence reactions?

Answer 29

Abiotic stress conditions (eg drought), grazing or volatile compounds from neighbouring damaged plants (inter + intraspecific).

Question 30

What is the Pest Pressure Hypothesis?

Answer 30

High species abundance leads to increased vulnerability to predators. Where a plant species is common, you get a build-up of its specific herbivores.

Question 31

What is the Competition Pressure Hypothesis?

Answer 31

Intense competition leads to exclusion of less competitive species. Reduced competition results in greater species diversity. Suppression of competitive species increases diversity.