Ch. 6 - Selective Predators and Responsive Prey Flashcards
Predator Preference
Defined as the difference between the proportion of that prey type in a predator’s diet
compared with the proportion of that prey type in the environment.
Can be positive (prey selected for) or negative (prey selected against)
What are the Three main factors that influence predator preference?
- The probability that a prey item will be encountered
- The probability that an encountered prey item will be attacked
- The probability that an attacked prey item will be successfully captured and
eaten
Principle elements and factors of the
predation process
references slide image
Optimal Diet Model (ODM)
Optimal foraging theory leads to a model
of predator diet choice - Derived by several ecologists in the early 1970’s
They were trying to determine what rules of prey choice would yield the greatest
energy gain per unit time spent foraging.
Two predictions of the ODM
- foragers should prefer the most profitable prey (those that yield the most energy per
unit handling time) - Efficient forager should broaden its diet to include more low-value prey as the
abundance of higher-value prey decreases.
Predictions about the nature of prey selection:
- Prey are always eaten upon encounter or never eaten upon the encounter
this is a binary relationship that is known as the zero one rule.
( never eaten zero always eaten - 1) - The inclusion of a prey type in the diet depends only on it profitability and the
characteristics of prey types of higher profitability.
In order to determine profitability value, ecologists will rank prey items from most
profitable to least profitable. One measure of ‘profitability’ is size of prey items
(assuming that larger prey have more energy contained).
Conclusions from Optimal Diet Model
feeding efficiency and maximization of energy gain play important roles in
determining predator diet choice.
This has contributed to our understanding of why some prey are selected, while others
ignored.
Optimal diet modle slide with daphnia and meal worms
A)high density prey preserves larger
low density broadens diet to medium and small size prey
B) predict low preyamount predator will eat large and small
result high density of prey - tended to choose the larger meal worms
what is the Optimal Foraging Theory
An explanation of data collected from numerous studies on foraging models
Moving forward it has potential for growth in the application to predict the potential feeding
links in size-based food webs.
By examining prey handling time as a function of the ratio of prey size to predator size, and assuming that prey energy value is a positive function of prey size we can attempt to predict
predator-prey links in real-world food webs.
All else being equal, predators should prefer to eat
the most profitable prey.
As the overall density of prey in the environment decreases, predator diets should
should broaden
to include more prey types.
as the overall density of prey in the environment
increases, predator diets should
narrow.
Nonconsumptive Predation Effects
?
Two predictions of the ODM
- foragers should prefer the most profitable prey (those that yield the most energy per
unit handling time) - Efficient forager should broaden its diet to include more low-value prey as the
abundance of higher-value prey decreases.
Natural Selection:
the process by which a
selective force (i.e. predator, parasite, abiotic
feature) causes some individuals in a population
to survive and reproduce to a greater degree than
others.
Fitness:
the level of ability to survive and
reproduce
natural selection to
cause the evolution of traits over time
- genetic variation
- selective force
- genotype frequency alterations
- differential reproduction
Natural Selection happens to
Individuals
Evolution happens to
Populations
Genetic variation
(mutation, sexual reproduction)
Selective Force
(alteration in background, parasite presence, etc.)
differential survival that leads to differential reproduction. That some
individuals are more successful at reproduction for a reason.
not sure how to make a question
examples of life history strategies
foraging strategies
territorial behaviors
signaling behaviors
reproductive behaviors
mating systems
Life history traits that have clear and direct bearing on fitness
reproductive lifespan and aging
age at first reproduction
number and size of offspring
Life History Theory
posits that the schedule and duration of key events in an organism’s lifetime are shaped
by natural selection to produce the largest possible number of surviving offspring.
Predators are a
selective force
(sometimes VERY strong selective force!)
Predation at particular life stages can
alter the life history (developmental timeline) of a
population or species.
Mayflies and trout: an example of
predation influence on life history traits
The may fly is a biological example of this cycle. Mayflies are one of the protein sources for trout. Thus as trout increase, may fly prey populations decrease because attack rate increases. Soon the population of mayflies will decrease to a point where the cycle changes direction and predators lose their nutrient source and begin to decrease in population, allowing the mayfly population to increase and the cycle begins again.
how do predators affect may flys
Shortened time to
sexual maturity =
smaller size at sexual
maturity =
smaller eggs/lower fecundity
the impacts of trout predation on mayfly populations test
Observed that mayflies that had streams with trout emerged earlier and at smaller adult
sizes than populations that lived in streams without trout.
BUT there is another potential
explanation: trout prefer to eat larger prey (remember from earlier… WHY would this
be?) and so the trout might be size-selecting the populations, so this might not be an
evolved response.
Predators can have generalist or specific preferences for prey type and those preferences
are influenced by
the probability that a prey item will be encountered
the probability that an encountered prey item will be attacked
the probability that an attacked prey item will be captured and eaten
Optimal foraging theory is
an approach to understanding predator diet choice by understanding how prey choice will influence predator energy gain.
The optimal diet model has data to support it, but
the fit of the data to the predictions of
the model are not 100%.
how does Predator behavior affect prey actions
why and what is the outcome
they directly and indirectly change the actions of prey.
This can happen due to consumption or nonconsumption behaviors
The outcome is the prey can alter habitat use, activity levels, evolution of morphology,
life history characteristics
