Predator-Prey and Host-Parasite Interactions Flashcards
What are ‘natural enemies’ in ecology
Predators, parasites, parasitoids, and herbivores - organisms that harm or consume another
What are trophic or antagonistic interactions
Interactions where one species benefits at the expense of another, usually by gaining nutrition or other fitness advantages
What defines predation
An interaction where the prey is always killed, and the predator consumes many prey during its life
How do predators differ from parasites
Predators kill and consume multiple prey, parasites do not usually kill and infect only one or a few hosts
Give the 4 key features of parasitism
Host is harmed, but usually not killed
Parasite is smaller than host
Only part of the host is consumed
Usually one or few hosts in a parasite’s life
What are parasitoids
Organisms (often insects) that live in/on and eventually kill their host - unlike parasites, the host always dies
How many hosts does a parasitoid consume in its lifetime
Usually one
What is herbivory
A form of antagonistic interaction where a plant (primary producer) is damaged but not killed. Only part of the tissue is removed
How is herbivory different from predation
In herbivory, the resource (plant) often survives the attack, unlike predation where the prey is killed
What is the basic population growth equation
Nt+1 = Nt + Births - Deaths
When is a population at carrying capacity (K)
When births = deaths - the population size becomes stable
What factors influence births and deaths
Resource availability and intraspecific competition
Natural enemies (e.g., predators, parasites)
What is a trophic cascade
A top-down ecological process where predators indirectly affect lower trophic levels
What is biological control
The use of natural enemies to reduce the population of an invasive or pest species
What does the Lotka-Volterra model describe
The coupled dynamics of predator and prey populations
What is the prey equation
dN/dt = rN - aPN
Where:
r = prey growth rate
a = attack rate
P = number of predators
N = number of prey
What is the predator equation
dP/dt = faPN - qP
Where:
f = food conversion efficiency
a = attack rate
P = predators
N = prey
q = predator mortality rate
What are the zero isoclines
Prey zero isocline = predator-prey combos with no net prey change = r/a
Predator zero isocline = combos with no net predator change = q/fa
What is a functional response
The rate of prey intake by a predator as a function of prey density
What does the classic Lotka-Volterra model assume
A linear functional response, i.e. prey intake rate increases proportionally with prey density
What is a Type III functional response
A sigmoid curve - slow intake at low prey density, rapid increase at moderate density, and plateau at high density
How does prey density affect stability
Low density: predation is density-dependent (stabilising)
High density: predation becomes inversely density-dependent (destabilising)
How can parasites regulate host populations
Through density-dependent effects - more hosts lead to more parasites, increasing mortality or reducing reproduction
What does the Janzen-Connell hypothesis state
Pest pressure from specialised enemies (herbivores/pathogens) increases with density → seeds/seedlings survive better away from parents → promotes plant diversity
