Topic 19 -Predation Flashcards
Fitness depends on an individuals ability to grow, survive and reproduce it requires…
suitable environmental conditions (abiotic factors)
sufficient resources to acquire appropriate quantities of energy and acquire energy efficiently (gain>loss)
Predation
an individual of one species (predator) consumes all or part of a living individual of another species (prey)
Predation does not include
but includes
scavengers or decomposers
blood feeders
What are the 3 predation categories
Herbivory
Carnivory
Parasitism
herbivory
prey is plant or algae
carnivory
prey is an animal, predator is typically also an animal
parasitism
for those parasites that feed on host tissues
Specialist
an individual takes one or a few prey items
Generalist
an individual takes many prey items
preference
proportion of a prey type in the diet is higher than in the environment
what does preference depend on
Energy content of prey
Nutritional content of prey (vitamins and minerals)
switching of preference depends on
the abundance of different prey types
“Prey switching”
may not occur right away if….
switching to increased consumption rates of a more abundant prey type
may not occur right away if predator still operates on search image of the prey type that used to be abundant
Profitability
net energy gained after energy is spent capturing and consuming the prey
Search time
search efficiency for prey
Handling time
time to pursue, subdue and ingest prey
Increased search and handling time both operate to
reduce consumption rate of predators
Increased size of prey population decreases
search time and in some cases can decrease handling time
Passive and filter feeders functionally have a handling time of
zero (spider web)
in general consumption rates and prey population size have a
linear relationship until saturation
at very low population sizes consumption rates will decrease disproportionately which means
need to learn new capture strategies
prey switching has not occurred yet
Refuges exist -hiding spots for prey
what is the goal of Optimal foraging theory
What is it based on
What does it offer
predict the optimal foraging strategy under certain conditions
based on mathematical models derived from economics
offers a powerful way to understand foraging decisions of predators
Assumptions for optimal foraging theory
foraging behaviour enhances fitness (i.e. foraging strategy= a behavioural trait favours by natural selection in the past)
animals maximize net energy gain ensures high fitness
predators must expend energy to obtain prey
energy loss:
energy gain:
searching and handling time
consumption
Diet model
if the predator knows how profitable each prey type is
specialist-
generalist-
energy lost searching ~ consume more profitable prey
consume less profitable prey~ low energy searching
In terms of the environment if search time is > handling time
A generalist strategy would be best ex raccoon
In terms of the environment if handling time is > search time
A specialist strategy would be best ex lion
Optimal foraging theory Model assumptions
Predators know everything about foraging environment
predators perform complex mathematics to determine the profitabilities of prey types
Optimal foraging model predicts
individuals that approach the optimal strategy will have higher fitness
predators may use general rules
ex take the less profitable prey type after searching for a fixed amount of time
predators may not maximize net energy gain
ex take less profitable prey type with a specific dietary requirement -nutrient, vitamin
predators may minimize their own risk of predation
ex take a less profitable prey type to avoid foraging near a predator
Optimal foraging theory assumes prey is limited and not highly mobile, it…
works off the habitat patch concept
a foraging animal should leave a patch when consumption rates
drop below the average for the range
giving up time
the point at which consumption rates become average and to maximize energy gain the animal should leave the patch
OFT also is heavily influenced by the distance between patches, the individual will
stay longer if the next patch is far away
