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

1
Q

Describe the broad classification of interactions

A

antagonism, competition and mutualism

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2
Q

Describe competition

A

negative effect on both species

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3
Q

Describe antagonism

A
  • one species gaining nutrition from another across trophic levels
  • involves a negative effect on only one
  • e.g. predation, parasitism and parasitoidy
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4
Q

Describe mutualism

A
  • confers a positive effect on both species
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5
Q

Describe predation

A
  • 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
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6
Q

Describe parasitism

A
  • 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
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7
Q

Describe parasitoidy

A
  • (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.
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8
Q

Describe herbivory

A
  • primary producer has tissue removed by a herbivorous consume
  • temporary parasitism, where only part of the tissue is consumed, and therefore the cost lesser
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9
Q

Describe a primary producer

A

the resource individual

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10
Q

Population size is determined by the

A

relative rates of natality and mortality.

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11
Q

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

A

Nt+1 = Nt + Births – Deaths

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12
Q

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

A

natality is equal to mortality

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13
Q

The factors influencing natality and mortality are:

A
  • intra- and inter-specific competition for resources
  • natural enemies
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14
Q

natural enemies aka

A

antagonists

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15
Q

Predator-prey dyanmics can be analysed using the

A

inter-trophic Lotka-Volterra predator-prey model

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16
Q

Describe the Lotka-Volterra predator-prey model

A
  • 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).
17
Q

Give the Lotka-Volterra predator-prey model equations

A

dN/dt = rN – aPN
dP/dt = faPN – qP

18
Q

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

A
  • increases exponentially under starvation pressure
  • q
19
Q

Describe zero isoclines

A

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

20
Q

Describe a prey zero isocline

A

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

21
Q

Describe a predator zero isocline

A

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

22
Q

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

A

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

23
Q

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

A

population cycles

24
Q

Population cycles

A
  • 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
25
Describe the assumptions of the Lotka-Volterra model
- fragmenting the populations in space: ignoring other interactions between them - Type I response between prey density and number of prey consumed by a predator
26
Type I
linear
27
Type III
- sigmoidal - density-independent
28
Describe the functional response between prey intake rate of the consumers and prey density (how attack rates scale with prey density)
non-linear
29
Describe what determies whether predation is density-dependent or density-intendent
- the shape of the predator response curve - the range of prey densities
30
Describe what happens when prey population levels are very high (>D)
- predation is likely to become inversely density-dependent - destabilisng upon the prey population - role in prey density limitation becomes weaker and weaker
31
Average prey population
labelled D
32
Describe what happens when prey population levels are low (
- predation will become density-dependent - stabilising upon the prey population, since prey are hard to find, and predators are dispersed relative to their population
33
Describe density-dependent population limitation through host parasitism
- cliff swallow population Hirundo pyrrhonota - nest colonially - number of ectoparasites per nestling increases with the size of the colony
34
Describe the Janzen-Connell hypothesis
‘pest pressure’ from specialised herbivores, or pathogens, cause density-dependent survival of seeds or seedlings, promoting diversity.