Lecture 20

Question 1

interactions in which one organism consumes all or part of another

Answer 1

1. predation/carnivory:
   - prey is killed
   - predator generally larger than prey
   - multiple prey individuals per predator
2. grazing/herbivory:
   - plant survives, usually
3. parasitism/disease:
   - host may or may not survive
   - host generally larger than parasite
   - multiple parasites per host

Question 2

Brood parasites

Answer 2

• some birds lay eggs in the nests of other bird species, avoiding the costs of parental care
• often involves brood mimicry, in which parasite eggs evolve to resemble host eggs

Question 3

Lotka-Volterra models for predator-prey interaction tend to..

Answer 3

cycle
- similar to competition models: two differential equations
- predict couples, lagged population cycles
draw diagram

Question 4

most common lab result for cycles in predator-prey interactions

Answer 4

predator and prey do not coexist, interaction is unstable.
For Huffaker to achieve 3 cycles was a triumph of persistence

Question 5

most famous predator-prey cycles outside the lab

Answer 5

Lynx and Hare

Question 6

why are Lynx-hare cycles not simple Lotka-Volterra predator-prey cycles?

Answer 6

additional factors probably include:
- heavy browsing degrades quality of plant food available to hares - hares may also be cycling with food plants
- social stresses in overcrowded hare populations

Question 7

give an example of a disease cycle

Answer 7

measles before vaccination
- number of measles cases between 1944 and 1966 cycled
- in outbreak years, where there are many infections, most people would recover from the infection and become immune
- after an outbreak year, the measles couldn’t infect many new hosts
- once enough babies were born, the measles would spread again
- cycles driven by no of susceptible and immune humans in the population

Question 8

describe how COVID cycles in humans

Answer 8

• waves of COVID cases were thought to be caused by human behaviour changes

Question 9

antagonistic co-evolution

Answer 9

• coevolution = reciprocal adaptation
• prey evolve defences; predators evolve counter-adaptations to overcome defences
• frequently described as an ‘arms race’
• key to the ‘red queen hypothesis’

Question 10

red queen hypothesis

Answer 10

species must constantly adapt, evolve, and proliferate in order to survive while pitted against ever-evolving opposing species

Question 11

Garter snake and rough-skinned newt

Answer 11

• Pacific newts (Taricha) make a poison called tetrodotoxin (TTX) that is extremely toxic to many predators
• garter snakes (Thamnophis) have evolved resistance to TTX

in populations where newts are more toxic, snakes are more resistant to TTX

Question 12

Life-dinner principle

Answer 12

• predator–prey interactions are characterised by unequal selection pressures operating on the participants.
• one party is ‘running for their life’ and the other merely for their dinner

Question 13

give examples of victim defences

Answer 13

• prey morphology, chemistry, behaviour
• plant secondary chemicals
• human immune system
• Daphnia ‘helmets’

Question 14

inducible defenses

Answer 14

defences turned on in response to threats or attacks

Question 15

Impact of competition on biodiversity

Answer 15

Competition tends to decrease biodiversity;
superior competitors exclude inferior
competitors

Question 16

How does predation affect
species diversity in a
community?

Answer 16

Classic example is Paine’s
Pisaster (sea star) experiment in the rocky
intertidal
- Pisaster predation prevents mussels from competitively excluding other species in rocky intertidal communities, maintaining biodiversity

Question 17

How do predators and parasites influence biological invasions?

Answer 17

• invasive species achieve high population sizes and have negative effects on the communities they invade
• enemy release hypothesis: invaders’ impacts result from having fewer natural enemies (predators, parasites, or pathogens) in their new range, compared to their native range

Question 18

example of how predators and parasites influence biological invasions

Answer 18

fungal and viral pathogens of 473 plant species that have been introduced from Europe to North America is much lower in naturalised environment than native environment

Question 19

describe the life cycles of parasites

Answer 19

• some parasites have a single host species - direct life cycle
• many parasites require two or more host species to complete their life cycle = complex life cycle
• the parasite that causes malaria passes through two hosts, a mosquito and a human

Question 20

vectors

Answer 20

hosts that transport parasites to their next shot

Question 21

zoonotic diseases

Answer 21

diseases transferred between animals and humans

Question 22

host species of zoonotic diseases

Answer 22

reservoirs

Question 23

what affects parasite abundance and transmission?

Answer 23

distribution, life history traits, and behaviours of hosts

Question 24

How is disease risk to humans, livestock, or wildlife affected by the broader ecological community?

Answer 24

Competing ideas:
- Dilution effect: for diseases that infect many hosts, host diversity can “dilute” disease risk to humans or animals
- Amplification effect: more host or vector species can support larger populations of disease-causing organisms, increasing risk to humans or animals§

Question 25

Amplification effect: malaria

Answer 25

• The malaria-causing parasite Plasmodium falciparum is vectored by many species of Anopheles mosquitoes
• study region in Kenya examined four mosquito species: A. arabiensis, A. funestus, A. gambiae, and A. merus
• positive relationship between mosquito species richness and prevalence of malaria in Kenya schoolchildren

Question 26

Latitudinal gradient in species richness

Answer 26

Species richness, or biodiversity, increases from the poles to the tropics for a wide variety of terrestrial and marine organisms

Question 27

Latitudinal gradient in human pathogen species richness

Answer 27

On average, tropical areas harbor higher pathogen species diversities compared to more temperate areas.