Ch. 6 - Selective Predators and Responsive Prey

Question 1

Predator Preference

Answer 1

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)

Question 2

What are the Three main factors that influence predator preference?

Answer 2

1. The probability that a prey item will be encountered
2. The probability that an encountered prey item will be attacked
3. The probability that an attacked prey item will be successfully captured and
   eaten

Question 2

Principle elements and factors of the
predation process

Answer 2

references slide image

Question 3

Optimal Diet Model (ODM)

Answer 3

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.

Question 4

Two predictions of the ODM

Answer 4

1. foragers should prefer the most profitable prey (those that yield the most energy per
   unit handling time)
2. Efficient forager should broaden its diet to include more low-value prey as the
   abundance of higher-value prey decreases.

Question 5

Predictions about the nature of prey selection:

Answer 5

1. 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)
2. 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).

Question 6

Conclusions from Optimal Diet Model

Answer 6

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.

Question 7

Optimal diet modle slide with daphnia and meal worms

Answer 7

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

Question 8

what is the Optimal Foraging Theory

Answer 8

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.

Question 9

All else being equal, predators should prefer to eat

Answer 9

the most profitable prey.

Question 10

As the overall density of prey in the environment decreases, predator diets should

Answer 10

should broaden
to include more prey types.

Question 11

as the overall density of prey in the environment
increases, predator diets should

Answer 11

narrow.

Question 12

Nonconsumptive Predation Effects

Answer 12

?

Question 13

Two predictions of the ODM

Answer 13

1. foragers should prefer the most profitable prey (those that yield the most energy per
   unit handling time)
2. Efficient forager should broaden its diet to include more low-value prey as the
   abundance of higher-value prey decreases.

Question 14

Natural Selection:

Answer 14

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.

Question 15

Fitness:

Answer 15

the level of ability to survive and
reproduce

Question 16

natural selection to
cause the evolution of traits over time

Answer 16

• genetic variation
• selective force
• genotype frequency alterations
• differential reproduction

Question 17

Natural Selection happens to

Answer 17

Individuals

Question 18

Evolution happens to

Answer 18

Populations

Question 19

Genetic variation

Answer 19

(mutation, sexual reproduction)

Question 20

Selective Force

Answer 20

(alteration in background, parasite presence, etc.)

Question 21

differential survival that leads to differential reproduction. That some
individuals are more successful at reproduction for a reason.

Answer 21

not sure how to make a question

Question 22

examples of life history strategies

Answer 22

foraging strategies

territorial behaviors

signaling behaviors

reproductive behaviors

mating systems

Question 23

Life history traits that have clear and direct bearing on fitness

Answer 23

reproductive lifespan and aging

age at first reproduction

number and size of offspring

Question 24

Life History Theory

Answer 24

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.

Question 25

Predators are a

Answer 25

selective force (sometimes VERY strong selective force!)

Question 26

Predation at particular life stages can

Answer 26

alter the life history (developmental timeline) of a population or species.

Question 27

Mayflies and trout: an example of predation influence on life history traits

Answer 27

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.

Question 28

how do predators affect may flys

Answer 28

Shortened time to sexual maturity = smaller size at sexual maturity = smaller eggs/lower fecundity

Question 29

the impacts of trout predation on mayfly populations test

Answer 29

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.

Question 30

Predators can have generalist or specific preferences for prey type and those preferences are influenced by

Answer 30

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

Question 31

Optimal foraging theory is

Answer 31

an approach to understanding predator diet choice by understanding how prey choice will influence predator energy gain.

Question 32

The optimal diet model has data to support it, but

Answer 32

the fit of the data to the predictions of the model are not 100%.

Question 33

how does Predator behavior affect prey actions why and what is the outcome

Answer 33

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