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Biology 181 - Exam #4 Questions with Detailed
Verified Answers
(1) What proportion of all species are parasites or pathogens?
Ans: Most species on Earth! On average, every free-living species has at least one
(more likely several) host-specific parasite.
(1) What are some pathogen transmission strategies?
Ans: 1. Direct contact 2. Environmental (indirect) <-- density-dependent transmission.
SEEKING BEHAVIORS: 3. Vector-borne diseases (mosquitos seek host) 4. Sexually
transmitted diseases (host seeks another to copulate w/) <--frequency-dependent
transmission.
(1) What is the difficulty of the pathogen?
Ans: There is a trade-off between transmission rate (i.e. rate of host exploitation) and
host mortality
(1) What is the pathogen's R0?
Ans: Ro Pathogen = Number of new infections arising from each existing infection
(1) What does the popular MYTH of the "good" pathogen postulate?
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Ans: Pathogens should evolve to be benign or beneficial to hosts, or else they wouldn't
evolve. Harm caused by a pathogen is thought to be maladaptive.
(2) What is a vaccination's goal?
Ans: To lower the R0 to below 1 by reducing the number of S (susceptible individuals)
in the population
(2) What are 3 different factors contributing to disease cycles?
Ans: - External (environment forcing) - weather, season, humidity
- Entry of new individuals or migration
- Effects on populations
(2) What is the theory of how disease impacts biodiversity?
Ans: (Janzen-Connell hypothesis) By reducing the growth of host populations, diseases
result in opportunities for other species to establish in the community
(2) What is the biodiversity dilution effect?
Ans: Communities of high biodiversity have lower abundance (S) of any particular
species compared to where there is low biodiversity.
(3) What is mutualism?
Ans: An interaction between two species that is beneficial to both.
(3) Explain the three-party mutualism between leaf-cutter ants, fungi, and bacteria.
© Get it right 2025 Getaway - Stuvia US All rights reserved
Biology 181 - Exam #4 Questions with Detailed
Verified Answers
(1) What proportion of all species are parasites or pathogens?
Ans: Most species on Earth! On average, every free-living species has at least one
(more likely several) host-specific parasite.
(1) What are some pathogen transmission strategies?
Ans: 1. Direct contact 2. Environmental (indirect) <-- density-dependent transmission.
SEEKING BEHAVIORS: 3. Vector-borne diseases (mosquitos seek host) 4. Sexually
transmitted diseases (host seeks another to copulate w/) <--frequency-dependent
transmission.
(1) What is the difficulty of the pathogen?
Ans: There is a trade-off between transmission rate (i.e. rate of host exploitation) and
host mortality
(1) What is the pathogen's R0?
Ans: Ro Pathogen = Number of new infections arising from each existing infection
(1) What does the popular MYTH of the "good" pathogen postulate?
© Get it right 2025 Getaway - Stuvia US All rights reserved
, Click here for more: Scholars nexus
Ans: Pathogens should evolve to be benign or beneficial to hosts, or else they wouldn't
evolve. Harm caused by a pathogen is thought to be maladaptive.
(2) What is a vaccination's goal?
Ans: To lower the R0 to below 1 by reducing the number of S (susceptible individuals)
in the population
(2) What are 3 different factors contributing to disease cycles?
Ans: - External (environment forcing) - weather, season, humidity
- Entry of new individuals or migration
- Effects on populations
(2) What is the theory of how disease impacts biodiversity?
Ans: (Janzen-Connell hypothesis) By reducing the growth of host populations, diseases
result in opportunities for other species to establish in the community
(2) What is the biodiversity dilution effect?
Ans: Communities of high biodiversity have lower abundance (S) of any particular
species compared to where there is low biodiversity.
(3) What is mutualism?
Ans: An interaction between two species that is beneficial to both.
(3) Explain the three-party mutualism between leaf-cutter ants, fungi, and bacteria.
© Get it right 2025 Getaway - Stuvia US All rights reserved
