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DISEASE E&E Final Exam > 14. Host Population Ecology and Infectious Disease > Flashcards

14. Host Population Ecology and Infectious Disease Flashcards

1
Q

Biological population:

A

-group of individuals of one species that live and interbreed in same place at same time

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2
Q

Population ecology:

A

-study of processes that affect the distribution and abundance of animal (and plant) populations

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3
Q

4 factors that influence population size (N):

A

-births
-deaths
-immigration
-emigration

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4
Q

Births:

A

-production of newborns increases the size of the focal population

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5
Q

Deaths:

A

-individuals dying decreases the size of the focal population

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6
Q

Immigration:

A

-individuals coming from neighbouring populations increase the size of the focal population

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7
Q

Emigration:

A

-individuals leaving the focal population decrease the size of focal population

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8
Q

Exponential population growth models:

A

-assume that change in N depends only on birth and death rates
-assume there is unlimited resources
>birth and death rates are constant
-assume growth is approximately continuous (growing smoothly)
*use continuous differential equations to describe population growth

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9
Q

Continuous population growth (smooth growth):

A

-realistic assumption for many long-lived organisms (ex. humans) with overlapping generations

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10
Q

Population growth depends on: (population growth models)

A

-birth rate (b)
-death rate (d)
-population size (N)
=(b-d)N
>change in N over a small interval of time

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11
Q

Population growth and r:

A

-let (b-d) = r
-r=instantaneous rate of increase
individuals/(individualstime)

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12
Q

Instantaneous rate of increase (r):

A

-determines the fate of a population
-can change units by simple division
*r for host populations is like R0 for pathogens

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13
Q

r>0:

A

-population grows exponentially
-b>d

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14
Q

r=0:

A

-population remains constant in size
-b=d

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15
Q

r<0:

A

-population declines to extinction
-b<d

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16
Q

Ring-necked pheasants on Protection Island:

A

-introduced in 1937 (off the coast of Washington State)
-“closed”: poor fliers and the island is far enough offshore (no immigration or emmigration)
-essentially predator free
-started with 8 adults, then 6 years later (1943) there was 2000
*example of exponential growth

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17
Q

b and d:

A

-NOT constant
-depend on N (population density)
>death rate increases with N
>birth rate decreases with N

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18
Q

Definition of carry capacity for a biological population:

A

-maximum population size of the species that the environment can SUSTAIN INDEFINITELY
>given the food, habitat, water and other necessities available in the environment

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19
Q

Carry capacity (K)

A

-maximum N that can be supported
-includes all limited resources
-measured in units of individuals
-b=d
-r=0

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20
Q

Logistic population growth:

A

-simple way to ensure the population does NOT exceed carrying capacity
=equation for exponential growth (rN) x (1-N/K)

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21
Q

(1-N/K):

A

-represents the unused portion of the carrying capacity

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22
Q

Uncrowded population:

A

-7% of K
-(1-N/K)=0.93
>population is growing at 93% of the growth rape of an exponentially increasing population

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23
Q

Crowded population:

A

-98% of K
-(1-N/K)=0.02
>population is only growing 2% of exponential growth

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24
Q

If N>K:

A

-(1-N/K) becomes negative
>population growth is negative
*population (N) will decline until it reaches K

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25
Q

Logistic population growth graph:

A

-N vs. time: S-shaped curve
-when population small=increases rapidly, at a rate slightly less than that predicted by exponential model

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26
Q

Population growth is fastest when:

A

-N=K/2 (MSY)
-growth decreases as population approaches K
-if population begins above K, growth is negative and N will decline toward K

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27
Q

MSY:

A

-maximum sustained yield
-often used in fisheries management
*maximize number of fish harvest and maximize population growth

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28
Q

Northern fur seal population, St. Paul Island, AK:

A

-driven to extinction by hunting in late 1800s
>banned in 1911 and they made a comeback
-today: oscillates around 10,000 individuals (carry capacity)
*shows that animal populations have density-dependent population growth

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29
Q

Factors that divide the factors that affect the size of populations:

A

-density-dependent factors
-density-independent factors

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30
Q

Density-independent factors (DIFs):

A

-influence N regardless of population density
*limiting factors
Ex. weather, climate

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31
Q

Density-dependent factors (DDFs):

A

-effects intensify as N increase
*regulating factors (what ecologists are interested in)
>their potential for maintaining population density within a narrow range of values

32
Q

Examples of DDFs:

A

-predation
-competition over limited resources (food, space)
-infectious disease

33
Q

Dynamics of animal populations:

A

-influenced by DDF and DIF
-relative effects of the factors vary among populations

34
Q

Density-dependant population growth:

A

-growth depends on size of population
-shrink when they are too large (N>K)
-grow when they are too small (N<K)

35
Q

Traditionally wildlife ecologists ignored pathogens:

A

-focused on predation and competition as important DDF
>epidemics that caused mass mortality were viewed as ‘natural disasters’ where ecosystem was out of balance
-pathogens and parasites weren’t seen as important DDF
>if diseased animal was eaten, it’s death was due to predation and not infectious disease

36
Q

Technical reasons why ecologist ignored pathogens and infectious diseases:

A

-determine role of infectious disease in wildlife is difficult
>don’t usually find the dead and diseased individuals
-requires tools that many wildlife ecologists do not have (PCR, immunology)

37
Q

Rabies:

A

-widely distributed across the world
-55,000 deaths per year
-95% of deaths in Africa and Asia
-most human deaths from dogs
-30-60% are children under 15
*vaccination of dogs and wildlife can eliminate rabies

38
Q

Rabies in Europe 1850-1950:

A

-free of rabies

39
Q

Rabies epizootic in foxes in Europe:

A

-1948-1988
-dog-rabies non-existent due to mandatory vaccination
-rabies spread from Poland to Central and Western Europe
-front of epizootic moved 20-60km per year

40
Q

Control measures for rabies epizootic in Europe:

A

-shooting
-trapping
-poisoning
-gassing

41
Q

Why use rabies to study whether pathogens can exert DD control on their host population:

A

-rabies causes death (high virulence)

42
Q

Rabies as a model:

A

-latent period
-add category of exposed (E) hosts
-infected individuals all die
-no recovered host category

43
Q

Rabies latency period in foxes:

A

-1/(latency parameter)
-30 days

44
Q

Latency parameter:

A

-determines the conversion of exposed to infectious individuals

45
Q

Rabies duration of infectious period in foxes:

A

-1/(alpha, virulence)
-5 days

46
Q

Virulence parameter:

A

-determines conversion of infectious individuals to dead individuals
*disease-induced additive mortality in infectious individuals

47
Q

SEI model with DD mortality (DDM):

A

*latency period where exposed are not yet infectious
-only infectious individuals experience disease induced morality (virulence)
-all experience DDM
>in absence of pathogen, fox population does NOT grow exponentially
-only susceptible foxes produce offspring

48
Q

Susceptible foxes (S):

A

-become E when they are bitten by rabies-infected foxes
*only ones producing offspring
>all are susceptible
*experience only DDM

49
Q

Exposed foxes (E):

A

-individuals that have acquired the pathogen but they are NOT infectious (cannot transmit the disease by biting other individuals)
*not reproducing
*experience only DDM

50
Q

Infected individuals (I):

A

-have developed full-blown rabies
-only individuals that can transmit the disease by biting other individuals
*experience disease induced mortality (virulence) and DDM

51
Q

Production of E:

A

-depends on product of density of S, density of I and transmission rate
-DD transmission (DDT) = (beta)(S)(I)

52
Q

Production of I:

A

*all E become I
-latency rate describes conversion

53
Q

Birth rate of foxes SEI rabies:

A

-constant
>no effect of fox density on fox birth rate

54
Q

Condition for pathogen in SEI model of rabies

A

-R0 gives the condition under which rabies can invade the fox population
>R0 increases with transmission rate, carry capacity and latency rate
>R0 decreases with virulence and birth rate
*if N drops below KT, rabies will go extinct
>rabies will go extinct BEFORE the fox population!

55
Q

SEI rabies equilibrium:

A

-when DDM rate (d+cN) is equal to birth rate

56
Q

To increase R0 and probability that rabies will invade the fox population:

A

-transmission rate must be high
-disease-free K of habitat must be high (high population of susceptible)
-latency rate must be high
-latency period must be short
-virulence must be low
-DDM must be low
-birth rate must also be low

57
Q

High transmission rate and high S:

A

-good for disease invasion

58
Q

Low virulence:

A

-causes long duration
>good for disease invasion

59
Q

High latency rate:

A

-good
>infectious individuals that transmit the disease not exposed
Ex. if long, foxes would die before they could become infectious

60
Q

High population turn over:

A

-high birth and death rates
*bad for disease invasion
>infectious individuals rapidly replaces with uninfected S individuals

61
Q

Is rabies more likely in high-quality or low-quality habitat for foxes?

A

-high quality
>high carrying capacity=more likely to see an epidemic due to high densities

62
Q

Major insights from rabies model:

A

-R0 of rabies, depends on S foxes and hence K of the environment
-can only invade in populations were K>KT
-endemic rabies is more likely in high quality habitats with high K
-at equilibrium N*(rabies infected fox population size)<K’ rabies controls fox population in model
>predicts constant prevalence or cycles with 3-, 4-, or 5-year period

63
Q

KT for rabies and foxes:

A

-1 fox per km^2

64
Q

Prevalence of rabies cycles in wildlife:

A

-rabies outbreaks every 3-4 years
-rabid foxes and rabid skunk
*consistent with SEI model

65
Q

Does the graph (rabies wildlife cycles) show that rabies makes the fox population cycle as well?

A

-NO
-population may just be holding steady and only rabies is going up and down
>easy to find a dead fox and figure out it died from rabies

66
Q

Rabies and cycles in FOX population:

A

-foxes shot by hunters and foxes dead from rabies
-fox population had 3 waves of rabies
-fox population decreased following the rabies outbreaks
>gradual recovery
*rabies controls fox population

67
Q

If rabies goes extinct, how does it come back?

A

-local extirpation
>it is introduced from another area where it was not extinct

68
Q

Spatiotemporal distribution of rabies:

A

-shows how rabies moves through an area

69
Q

Theoretical model predicts cycles:

A

-3, 4 or 5 year oscillations
-produced by:
>DD transmission
>high virulence
>DD growth of fox population

70
Q

Rabies invades fox population if:

A

-carry capacity of fox population (K) is greater than threshold carrying capacity for rabies (KT)

71
Q

As prevalence of rabies builds in fox population:

A

-rabies-infected foxes die and fox population decreases
-once fox population drops below KT=rabies goes extinct
>rabies-free fox population now increases towards K
*once fox population size surpasses KT, rabies virus can invade again!

72
Q

Oral rabies vaccination (ORV) in Europe:

A

-red fox was main reservoir
-culling did not work
-introduced in 1978
*reduced incidence of rabies in Europe
-2014: 10 European countries are rabies-free

73
Q

10 rabies free countries in 2014:

A

-Austria
-Belgium
-Czech Republic
-Finland
-France
-Germany
-Italy
-Luxemburg
-Netherlands
-Switzerland

74
Q

Fox populations bounced back after ORV:

A

-ORV started in 1978
-rabies free in 1998
*fox population increased dramatically from 1985-1995

75
Q

Key messages:

A

-rabies uses SEI, no recovered class
-include DDT, DDM and high virulence
-rabies depresses N* below K
-rabies causes cycles in fox populations
-ORV eliminated rabies from European fox populations
-fox population in Switzerland increased following rabies elimination

76
Q

Evidence for regulation of virus on fox population:

A

-rabies depresses N* below K
-rabies causes cycles in fox populations

DISEASE E&E Final Exam (11 decks)

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