Interactions between populations I: Predator-prey and host-parasite interactions

Question 1

Describe the broad classification of interactions

Answer 1

antagonism, competition and mutualism

Question 2

Describe competition

Answer 2

negative effect on both species

Question 3

Describe antagonism

Answer 3

• one species gaining nutrition from another across trophic levels
• involves a negative effect on only one
• e.g. predation, parasitism and parasitoidy

Question 4

Describe mutualism

Answer 4

• confers a positive effect on both species

Question 5

Describe predation

Answer 5

• prey is killed by the predator
• confers a benefit to the predator and a cost to the prey
• many times in a predator’s lifetime, but only once in a prey’s

Question 6

Describe parasitism

Answer 6

• host is harmed by a parasite which lives on (an ectoparasite) or in (an endoparasite)
• confers a benefit to the parasite, and a cost to the host
• cost to a parasite host is less than the cost of a predator’s prey; only part of the host is consumed
• rarely a fatal antagonism
• at a species level, only one, or very few, hosts are consumed during a parasite’s life history

Question 7

Describe parasitoidy

Answer 7

• (likely arthropod) host is killed by a parasitoid which lives on (ectoparasitoid) or in (endoparasitoid) it
• parasitoid will consume only one host in its lifetime.

Question 8

Describe herbivory

Answer 8

• primary producer has tissue removed by a herbivorous consume
• temporary parasitism, where only part of the tissue is consumed, and therefore the cost lesser

Question 9

Describe a primary producer

Answer 9

the resource individual

Question 10

Population size is determined by the

Answer 10

relative rates of natality and mortality.

Question 11

The equation for population change over time can be written thus:

Answer 11

Nt+1 = Nt + Births – Deaths

Question 12

A population is said to have reached its carrying capacity (K), when …

Answer 12

natality is equal to mortality

Question 13

The factors influencing natality and mortality are:

Answer 13

• intra- and inter-specific competition for resources
• natural enemies

Question 14

natural enemies aka

Answer 14

antagonists

Question 15

Predator-prey dyanmics can be analysed using the

Answer 15

inter-trophic Lotka-Volterra predator-prey model

Question 16

Describe the Lotka-Volterra predator-prey model

Answer 16

• prey undergo exponential increase
• but their removal rate from the population is dependent upon the product of predator-prey encounters (P x N) and on the attack rate of the predator (a).

Question 17

Give the Lotka-Volterra predator-prey model equations

Answer 17

dN/dt = rN – aPN
dP/dt = faPN – qP

Question 18

Describe predator mortality rate under the Lotka-Volterra predator-prey model

Answer 18

• increases exponentially under starvation pressure
• q

Question 19

Describe zero isoclines

Answer 19

solving for dN/dt = 0 in the Lotka-Volterra predator-prey model

Question 20

Describe a prey zero isocline

Answer 20

when the combinations of predator and prey lead to an unchaning prey population (r/a)

Question 21

Describe a predator zero isocline

Answer 21

when combinations of predator and prey lead to an unchanging predator population (q/fa).

Question 22

How do we explore the dynamics of both predator and prey species acting in concert?

Answer 22

Superimposing dP/dt on top of dN/dt graphically under the Lotka-Volterra predator-prey model

Question 23

What does the Lotka-Volterra predator-prey model reveal?

Answer 23

population cycles

Question 24

Population cycles

Answer 24

• aka coupled oscillations
• display linkage between the rises and falls of predator and prey abundances
• intimate linkages are rare in nature: regular cycles are the exception rather than the rule

Question 25

Describe the assumptions of the Lotka-Volterra model

Answer 25

• fragmenting the populations in space: ignoring other interactions between them
• Type I response between prey density and number of prey consumed by a predator

Question 26

Type I

Answer 26

linear

Question 27

Type III

Answer 27

• sigmoidal
• density-independent

Question 28

Describe the functional response between prey intake rate of the consumers and prey density (how attack rates scale with prey density)

Answer 28

non-linear

Question 29

Describe what determies whether predation is density-dependent or density-intendent

Answer 29

• the shape of the predator response curve
• the range of prey densities

Question 30

Describe what happens when prey population levels are very high (>D)

Answer 30

• predation is likely to become inversely density-dependent
• destabilisng upon the prey population
• role in prey density limitation becomes weaker and weaker

Question 31

Average prey population

Answer 31

labelled D

Question 32

Describe what happens when prey population levels are low (<D)

Answer 32

• predation will become density-dependent
• stabilising upon the prey population, since prey are hard to find, and predators are dispersed relative to their population

Question 33

Describe density-dependent population limitation through host parasitism

Answer 33

• cliff swallow population Hirundo pyrrhonota
• nest colonially
• number of ectoparasites per nestling increases with the size of the colony

Question 34

Describe the Janzen-Connell hypothesis

Answer 34

‘pest pressure’ from specialised herbivores, or pathogens, cause density-dependent survival of seeds or seedlings, promoting diversity.