Lec 18- disease ecology

Question 1

3 ways to look at simple dynamics of population?

Answer 1

1. time series
2. population of change
3. per capita rate of change

Question 2

what is time series?

Answer 2

number of individuals (N) at each time t

Question 3

what is population rate of change?

Answer 3

added individuals per time step vs. population size (N); population grows with increase N

Question 4

does per capita rate change with N?

Answer 4

no

Question 5

when would slope decrease linearly (dN/dt/N vs. Population size size)

Answer 5

resources become limiting
with increasing N, so per capita
growth inevitably declines

Question 6

Carrying capacity K:

Answer 6

the number of individuals of a particular
species that the local environment can support

Question 7

why talk about disease?

Answer 7

Disease can alter individual fitness
and impact population dynamics.

Question 8

disease

Answer 8

An “atypical” condition in a living
organism that causes some sort of
physiological impairment.
Can be caused by a variety of factors:
genetic abnormalities, exposure to
toxins, and interactions with organisms

• all disease-causing organisms are exploitative/selfish (donor + fitness)

Question 9

infectious diseases:

Answer 9

caused by
organisms (e.g., viruses, bacteria,
fungi, etc.)

Question 10

disease-causing parasite is restricted to?

Answer 10

protozoans*, helminths (parasitic worms)**, and
ectoparasites

Question 11

covid-19 causes what health issues

Answer 11

severe acute respiratory syndrome (sARS coronavirus 2)

Question 12

disease transmission

Answer 12

• direct: by physically touching an infected individual
• indirect: by touching a surface that physically touched an infected individual (inanimate contaminated object), animal vectors (ticks, fleas)

Question 13

horizontal transmission

Answer 13

• among individuals of the same generation
• ex. influenza
• can be direct or indirect, usually no genetic basis

Question 14

vertical transmission

Answer 14

from parent to offspring

Question 15

is influenza horizontal or vertical transmission?

Answer 15

horizonal

Question 16

3 steps to how viruses replicate in living cells

Answer 16

1.Virus bindsto and enters cells,then
2.deliversits genome to a site where it can
produce new copies of viral proteins and RNA
3.Viral proteins and RNA assemble into
new viral particles, and exit the host cell;
via the cell wall bursting (or‘lysing’)

Question 17

both vertical and horizontally transmitted diseases

Answer 17

HIV, chicken pox, microcephaly and ZIKA

Question 18

is covid horizontal or vertical?

Answer 18

Mostly horizontally transmitted (respiratory droplets, aerosols), vertical
transmission is rare

Question 19

endemic

Answer 19

constant presence but
relatively low spread;
e.g., malaria in African
regions, possibly HIV

Question 20

epidemic

Answer 20

sudden increase (high spread)
in certain regions;
e.g., Lyme disease,
early COVID spread

Question 21

pandemic

Answer 21

global epidemic;
e.g., swine flu (2009),
COVID-19

Question 22

disease fitness eq

Answer 22

𝑅0 =𝛽 𝑁 / (𝜈 + 𝑑 + 𝑟)

Question 23

𝑅0

Answer 23

Basic reproduction number

average # of susceptible people that will be infected by a person with a disease in a native population w/o transmission interventions

Question 24

𝛽

Answer 24

transmission rate (probability of infection)

Question 25

N

Answer 25

number of hosts available for infection

Question 26

v

Answer 26

virulence (disease induced death rate of host)

Question 27

d

Answer 27

mortality (natural death rate of host)

Question 28

r

Answer 28

recovered hosts

Question 29

is 𝑅0 a contants?

Answer 29

no, influenced by the enviro behaviour

Question 30

what is 𝑅0 replaced with when a disease spreads?

Answer 30

replaced by Re
(Rt) (effective reproduction number)

Question 31

what does 𝑅0 inform us about?

Answer 31

how easily a disease spreads and how difficult it is to contain a disease

it doesn’t reveal virulence (pathogens ability to damage a host)

Question 32

basic reproduction number (𝑅0, Re, Rt) can vary how

Answer 32

since they aren’t constants they can very
1. spatially (from region to region)
2. temporally (over time)
3. based on model used

Question 33

compartment models

Answer 33

• rate of spread to new hosts limits spread of the disease
• birth, susceptible, infected, immune, death

Question 34

how to slow a disease

Answer 34

behaviour change and herd immunity (vaccinations)

Question 35

herd immunity

Answer 35

• occurs when vaccination rates are high enough that the population growth rate (r) of pathogen is negative, and may go extinct

Question 36

geometric population growth

Answer 36

• each successive generation differs in size by a constant ratio

Question 37

exponential population growth

Answer 37

• each successive generation differs in size based on a constant ratio times population size at that moment in time

Question 38

geometric

Answer 38

• models population growth in organisms with discrete generations caused by pulsed reproduction

Question 39

exponential

Answer 39

models continuous population growth that have overlapping generations

Question 40

logistic population growth

Answer 40

• if resources become limited, population growth rate will slow and eventually stop

Question 41

why do carrying capacities exist?

Answer 41

• all resources, whether its water, light, food, space are limited
• a given environment can only support so many individuals of a given species

Question 42

msy

Answer 42

maximum sustainable harvest
that can occur w/o decreasing
the population growth rate