Predation Flashcards
Symbiosis
Unlike organisms living together, independent of the outcome
Close association between 2 different organisms living together (prolonged physical intimacy)
Commensalism
One species benefits, the other is unaffected
Amensalism
One species suffers, the other is unaffected
Competition
Both species suffer
Usually due to resources being limited (or perceived to be limited)
Predation, parasitism
One species benefits, the other suffers
Neutralism
Neither species benefits or suffers from the interaction
Mutualism
Interaction between 2 species that benefits both of them
Key to origin of eukaryotic cells (mitochondria and chloroplasts)
Key to land colonisation by plants (symbiotic fungi)
Reciprocal exploitation
Each partner is a net beneficiary
Predation
The consumption of one organism, in whole or in part, by another, where the consumed organism is alive when the consumer first attacks it
‘True’ predators
Kill and eat their prey
Grazers
Often eat part of the organism they are consuming
Usually herbivores
Parasites
Obtain nutrients from one or a few individuals and are harmful but may not be deadly - often symbiotic
Parasitoids
Insects in which the larva develops inside a single host which is ultimately killed
Effects of predation on prey populations
Suppress populations of prey
Can have little influence on numbers of prey even though they eat a large proportion of the population- other factors may control the prey population
Can actually increase prey population through indirect interactions
Tools to investigate predation
Observations of natural phenomena
Natural experiments
Carefully manipulated experiments in lab and field
Detritovores
Organisms that eat dead organisms
What is the classic study of predator -prey interactions
Snowshoe hare cycle
Predator prey cycle hypotheses
Prey run out of food – predators follow
Predators run out of food by eating too many prey
Prey numbers build up and they get diseased at high densities
Something else is responsible for both predator and prey abundance (e.g. weather)
Some combination of above
Predator mediated coexistence
Predators can maintain diversity by feeding on the competitively dominant species in the community
Forcing variable for snowshoe hares
Number of sunspots seems to affect numbers
How do predators respond to prey populations
Numerical response
Functional response
Numerical response
Change in the population in response to the density of prey
Consists of reproduction and aggregation
Functional response
Relationship between rate of consumption by a predator and the density of prey
Types I, II, III
Type I functional response
linear – the more food the more is eaten (no processing or searching time)
Type II functional response
decelerating – there is processing time (handling, eating) leading to a maximum intake rate
Type III functional response
accelerating up to a maximum – (possibly due to learning or switching to the most abundant prey)
How do numbers of predators and prey determine each other
dN/ dt = rN - a’CN
dN/dt = rate of change in population size
dN = rate in change of numbers
dt = rate of change in time
N = population size
r = per capita rate of growth
a’ represents searching efficiency or attack rate of predator
C is the number of predators
How does the predator population change
dC/dt = fa’CN - qC
C is the number of predators
q is predator mortality rate
a’CN is the rate at which food is consumed
f is the predator’s efficiency at turning food into baby predators
If there is no food predators die and fail to reproduce….
Behavioural impacts
Predators change the behaviours of their prey (not just numbers)
‘Landscapes of fear’ – prey avoid areas perceived as risky
One US study quantified significant financial benefit of reduced collisions between deer and vehicles when wolves were present
Lotka - Volterra equations for prey and predators
prey = dN/dt = rN = a’CN
Predators dC/dt = fa’CN = qc
Holling’s functional responses of predators to prey density
Type I/II/III
X axis = density of prey population
Y axis = number of prey consumed
