Lecture 20 Flashcards
interactions in which one organism consumes all or part of another
- predation/carnivory:
- prey is killed
- predator generally larger than prey
- multiple prey individuals per predator - grazing/herbivory:
- plant survives, usually - parasitism/disease:
- host may or may not survive
- host generally larger than parasite
- multiple parasites per host
Brood parasites
- 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
Lotka-Volterra models for predator-prey interaction tend to..
cycle
- similar to competition models: two differential equations
- predict couples, lagged population cycles
draw diagram
most common lab result for cycles in predator-prey interactions
predator and prey do not coexist, interaction is unstable.
For Huffaker to achieve 3 cycles was a triumph of persistence
most famous predator-prey cycles outside the lab
Lynx and Hare
why are Lynx-hare cycles not simple Lotka-Volterra predator-prey cycles?
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
give an example of a disease cycle
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
describe how COVID cycles in humans
- waves of COVID cases were thought to be caused by human behaviour changes
antagonistic co-evolution
- 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’
red queen hypothesis
species must constantly adapt, evolve, and proliferate in order to survive while pitted against ever-evolving opposing species
Garter snake and rough-skinned newt
- 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
Life-dinner principle
- 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
give examples of victim defences
- prey morphology, chemistry, behaviour
- plant secondary chemicals
- human immune system
- Daphnia ‘helmets’
inducible defenses
defences turned on in response to threats or attacks
Impact of competition on biodiversity
Competition tends to decrease biodiversity;
superior competitors exclude inferior
competitors
How does predation affect
species diversity in a
community?
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
How do predators and parasites influence biological invasions?
- 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
example of how predators and parasites influence biological invasions
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
describe the life cycles of parasites
- 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
vectors
hosts that transport parasites to their next shot
zoonotic diseases
diseases transferred between animals and humans
host species of zoonotic diseases
reservoirs
what affects parasite abundance and transmission?
distribution, life history traits, and behaviours of hosts
How is disease risk to humans, livestock, or wildlife affected by the broader ecological community?
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§
Amplification effect: malaria
- 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
Latitudinal gradient in species richness
Species richness, or biodiversity, increases from the poles to the tropics for a wide variety of terrestrial and marine organisms
Latitudinal gradient in human pathogen species richness
On average, tropical areas harbor higher pathogen species diversities compared to more temperate areas.
