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Population ecology > EE29 > Flashcards

EE29 Flashcards

1
Q

define true pradators

A

organisms that consume many entire prey their whole lives

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2
Q

define grazers

A

organisms that consume only part of their pre ybut attack many

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3
Q

define parasitoids

A

free living adult insects that lay eggs inside a living host

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4
Q

define parasites

A

consume part of the host but typically only 1 host per lifetime

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5
Q

define functional response

A

change in predator’s rate of prey consumption with change in prey density

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6
Q

what is numerical response associated with?

A

functional responses

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7
Q

what is numerical response?

A

change in predator density as a function of change of prey density

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8
Q

what is functional response type 1?

A

Response assumes a linear increase in intake rate with food density, either for all food densities, or only for food densities up to a maximum, beyond which the intake rate is constant. The linear increase assumes that the time needed by the consumer to process a food item is negligible, or that consuming food does not interfere with searching for food.

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9
Q

What functional response type is used in the Lotka-Volterra predator-prey midel?

A

functional response of type I is used in the Lotka–Volterra predator–prey model.

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10
Q

what does functional response type 1 imply?

A

that if you provide more prey, the predator will eat more, even if it is already satiated.CURVE SHOULD SATURATE

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11
Q

what does fr type 1 look like on a graph?

A

straight diagonal line

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12
Q

what is functional response type 2?

A

Type II functional response is characterized by a decelerating intake rate, which follows from the assumption that the consumer is limited by its capacity to process food. Type II functional response is often modeled by a rectangula hyperbola

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13
Q

what is type 2 functional response modelled by on a graph?

A

rectangular hyperbola

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14
Q

what is type 3 functional response?

A

similar to type II in that at high levels of prey density, saturation occurs. But now, at low prey density levels, the graphical relationship of number of prey consumed and the density of the prey population is a more than linearly increasing function of prey consumed by predators. This accelerating function is caused by learning time, prey switching, or a combination of both phenomena.

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15
Q

what is learning time? and in which response type is this?

A

In type 3. Learning time is defined as the natural improvement of a predator’s searching and attacking efficiency or the natural improvement in their handling efficiency as prey density increases.

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16
Q

who identified learning time and give an example:

A

Holling identified this mechanism in shrews and deer mice feeding on sawflies. At low numbers of sawfly cocoons per acre, deer mice especially experienced exponential growth in terms of the number of cocoons consumed per individual as the density of cocoons increased.

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17
Q

what is prey switching?

A

Prey switching involves two or more prey species and one predator species. When all prey species are at equal prey densities, the predator will indiscriminately select between prey species. However, if the density of one of the prey species decreases, then the predator will start selecting the other, more common prey species with a higher frequency

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18
Q

who identified prey switching and give an example.

A

Murdoch illustrated this effect with guppy preying on tubificids and fruit flies. As fruit fly numbers decreased guppies switched from feeding on the fruit flies on the water’s surface to feeding on the more abundant tubificids along the bed

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19
Q

In what case may it be true that the more prey are present the more the predators will eat?

A

passive predators such as spiders with webs

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20
Q

what type of responses can be seen in native and invasive fish?

A

Type 2 e.g inroach Rutilus rutilus, a visually foraging fish

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21
Q

what are 2 parameters are functional responses reliant on?

A

1)searching rate-volume searched for prey per unit time

2)handling time- time
taken to consume each prey item .

22
Q

In what way is it useful to think of functional responses?

A

Instead of thinking about the number of prey eaten, think about the percentage of prey eaten.

23
Q

If thinking of functional response curves in terms of percentage prey eaten what does the graph look like? what is this called?

A

look at flashcard (exponential decay)

Inverse density dependence

24
Q

what does stability require? what would this be in terms of proportion of prey eaten wrt to prey density? is this the case with functional responses?

A

density dependence - this would be a higher proportion of prey eaten at high density than at low–> HOWEVER- in reality a higher proportion of prey are eaten at lower prey availability

25
Q

Is the functional response stabilising?

A

No

26
Q

will predation stabilising a population be due to functional response?

A

No. it will be DESPITE the functional response

27
Q

what is stabilizing selection?

A

ype of natural selection in which genetic diversity decreases and the population mean stabilizes on a particular trait value.

28
Q

What are exceptions when functional responses can be stabilising? Due to what?

A

Type 3 functional responses. switching between prey species, or other behaviours that reduce the rate of predation once prey become scarce (e.g. loss of ‘search image’).

29
Q

what does the type 3 functional response graph of %prey eaten vs prey available look like?

A

a rough bell curve

30
Q

if functional responses are not usually those that stabilize populations what responses do?

A

Numerical responses

31
Q

what is a common mechanism of numerical response? explain it

A

spatial aggregation

  • Predators move into regions with higher-than-average prey numbers
  • Predators emigrate from patches once prey numbers become depleted
32
Q

What two mechanisms of numerical response are there?

A

demographic response

aggregational response

33
Q

what is the aggregation response? what was Turnbull’s experiment?
what did he prove?

A

change in predator population due to immigration into an area with increased prey population.

In an experiment conducted by Turnbull in 1964, he observed the consistent migration of spiders from boxes without prey to boxes with prey. He proved that hunger impacts predator movement.

34
Q

what is demographic response?

A

hanges in the rates of predator reproduction or survival due to a changes in prey density. The increase in prey availability translates into higher energy intake and reduced energy output. This is different from an increase in energy intake due to increased foraging efficiency, which is considered a functional response. This concept can be articulated in the Lotka-Volterra Predator-Prey Model.

dP/dt = acVP-mP

a = conversion efficiency: the fraction of prey energy assimilated by the predator and turned into new predators
P = predator density
V = prey density
m = predator mortality
35
Q

Is aggregation always stabilizing?

A

No. Data from Hassell showed Despite aggregation, % host parasitism may still be lower at high densities

Trichogamma pretiosum and Plodia interpunctella

36
Q

In the long term how do numerical responses act?

A

In the longer term, numerical responses act through changes in the predator’s birth and death rates

More prey means higher predator birth rate,lower predator death rate

37
Q

what can numerical responses drive?

A

population dynamics e.g lynx and snowshoe hare

38
Q

what two models are used to show how dynamics?

A

Nicholson Bailey models

Lotka Volterra models

39
Q

What is the nicholson bailey model for hosts and parasitoids?

A

Ht+1 = λHt e-aPt

Pt+1 = cHt[1 - e-aPt]

Where
Ht = density of host species in generation t
Pt = density of parasitoid in generation t
a = searching efficiency of parasitoids
λ = host reproductive rate
c = average number of viable eggs laid by a parasitoid on a single host.

40
Q

why is the Nicholson Bailey model very unstable?

A

tiny deviations from equilibrium mean population crash

41
Q

why use an unstable NB model?

A

you can suprisingly fit it to real data

1) prickly pear
2) parasitoid Encarsia formosa attacking the whitefly species Trialeurodes vaporiarorum

useful for biological control

42
Q

what is the cactus moth called?

A

cactoblastis cactorum

43
Q

what is the cactus latin name?

A

Opuntia stricta

44
Q

what is an example of successful biological control and how long did it take?

A

In 1930 prickly pear was pest for 150 miles.In 2 years by august 1932 90% of the prickly pear had collapsed

45
Q

define pseudointerference

A

Where consumers exhibit the aggregative response, the decline in their rate of consumption as their density on foraging patches increases. The effect resembles mutual interference, but in fact is a purely density-dependent consequence of high consumer density.

46
Q

what is mutual interference?

A

when access to resources is negatively affected by the presence of other individuals within a species. It is often modelled with a scaling exponent, m, on the number of predators.

47
Q

can aggregation increase most population size despite being stabilizing?

A

yes- you can stabilize interactions via enemy refugia and because of an INCREASED forging inefficiency as parasitoid density DECREASES -by pseudointerference.

48
Q

what does the nicholson bailey model assume wrt parasitoid distribution?

A

assumes they redistribute themselves each generation

49
Q

can heterogenity be stabilising?

A

yes (spatial heterogeneity=uneven destruction of various concentrations of each species within an area)`

50
Q

are theoretical results model dependent?

A

yes. only in continuous time models is density dependent aggregation stabilising and it always lowers host density

51
Q

what two aggregation types are there?

A

aggregation in patches of high or low host or prey density

aggregation independent of host prey density

(both can stabilize populations as contribute variation to risk of parasitism across host individuals

52
Q

what does the lotka volterra model show wrt aggregation and stability?

A
  • density independent aggregation=no stabilising effect
  • density dependent aggregation=stabilising

*but PAcala and hassel found evidence independent aggregation was more important

Population ecology (14 decks)

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