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.
