Midterm 1 - Sociality and Inbreeding Depression, Foraging

Question 1

What are social spiders?

Answer 1

Spiders that live in colonies. These spiders cooperate in brood care, maintenance of the nest, feeding and cooperate in capturing prey.

Question 2

Are social spiders common?

Answer 2

No, they are exceedingly rare. Most spiders are solitary

Question 3

We know of about _____ species of social spiders, _____ of them having evolved sociality independently. All of these spiders are distributed around the ____

Answer 3

20 social spider species
18 evolved sociality independently
All of them are distributed around the tropics

Question 4

Is there mixing between individuals from different colonies even if they are the same type of social spider species?

Answer 4

No mixing between colonies. Mating happens only within colonies.

Question 5

Within spider genera, there’s a range of social behaviour. It goes from being solitary (no social behaviour), to subsocial, to social.

What are subsocial spider species? Are they inbred or outbred?

Answer 5

These are species in which the young are taken care of by the mother, until they are adults and then when they reach adulthood, they disperse and find unrelated mates.

Because they disperse to mate with non-relatives, they are considered outbred.

Question 6

Define “Inbreeding Depression.”

Answer 6

A reduction in fitness in a population as a result of inbreeding.

Question 7

Why is inbreeding depression bad?

Answer 7

All spiders, including the outbred ones, carry recessive deleterious alleles. Those that are outbred don’t have it expressed because they have high genetic variation (from mating with non-relatives).

Inbred spiders are likely to carry the same type of deleterious recessive allele. Such that the bad phenotype is more likely to be expressed in their offspring if they mate.

Question 8

Studies show that social spider species have originated from what kind of spider ancestors?

Answer 8

subsocial spider ancestors

Question 9

What is the formula for inbreeding depression?

Answer 9

IB = 1 - (Winbred/Woutbred)

Question 10

True or false. To find fitness, you usually have to look at traits that are correlated with fitness.

Answer 10

True

Question 11

What is one reason we discussed in class that could explain why the transition from outbred subsocial species to inbred social species has happened?

Answer 11

An experiment by Leticia concluded that:

Inbreeding depression is evident in solitary, but not social phases of the lifecycle of a subsocial spider species (that has been manipulatively inbred)

Maternal care probably buffers the negative fitness effects of inbreeding on the social phases (i.e. the baby phases) of the lifecycle.

Question 12

One of the things an animal must do in order to pass their genes is to find food. Behavioural ecologists use the word ___________ to describe finding food

Answer 12

foraging.

Question 13

What characteristics of food items are relevant for a forager when choosing what food items to include in their diet? (8 things)

Answer 13

1. The abundance
2. The distribution
3. Seasonality
4. The size of the food item
5. How accessible it is/how difficult to acquire it is
6. Escape ability
7. Nutritional value
8. Palatability/Toxicity of food item

Question 14

What is the Optimal Foraging Theory?

Answer 14

A theory that explains that animals will choose a foraging strategy that maximizes the benefits and minimizes the cost, to create an optimum foraging strategy.

Question 15

What is an optimality model? Did we look at an example of this in class?

Answer 15

A graphic tool used to portray costs and benefits of animal behaviours. In class we had an example of optimality models using “food choice” as the behaviour, with oystercatchers and mussels.

Question 16

Oystercatchers have been seen to prefer intermediate-sized mussels in the wild. What does this say about the NET energy gain curve? Please don’t mistake this curve as the benefit curve.

Answer 16

The net energy gain curve is the benefit curve minus the cost curve.

If oystercatchers prefer intermediate mussels, that means the NET ENERGY CURVE is maximized there i.e. the peak of the curve coincides to intermediate sizes on the x-axis.

Question 17

What is the benefit we’re talking about when considering the benefit curve for oystercatcher mussel size choice?Does the benefit curve increase linearly for mussel size in oystercatchers?

Answer 17

The benefit is the amount of energy. Mussels that are bigger are greater sources of energy than smaller ones.

No, it will increase but then plateau. This is because there is only so much energy the oystercatchers can gain from one mussel, the animal gets satiated at the same point regardless of how big the mussel is.

Question 18

How does the cost curve change in the oystercatcher mussel size case? Does this curve plateau?

Answer 18

The cost goes up exponentially with size. This is because bigger mussels have a longer handling time. The curve does not plateau

Question 19

The distance between the cost curve and the benefit curve would be __________(lowest/greatest) at intermediate mussel size

Answer 19

greatest

Question 20

True or false. In an optimality model, the distance between the cost curve and the benefit curve should always be greatest at the most optimum food item size.

Answer 20

true

Question 21

Are the oystercatchers making a conscious choice when they go for the intermediate mussels, i.e. are they weighing the benefits and costs in their heads like an economic transaction?

Answer 21

No.

Natural selection has simple evolved to favour individuals that go for intermediate mussels, since those individuals receive the maximum benefit, and are thus more fit.

Question 22

One mathematical statistic that is used in the Optimal Foraging Theory is __________

Answer 22

profitability

Question 23

What is profitability? What is the equation for it and what do the variables stand for?

Answer 23

A mathematical statistic that measures the NET gain in ENERGY one obtains from eating a certain food item.

The equation is..

profitability = Ei / hi

where Ei is the energy gained from eating the food item “i” and hi is the handling time spent on the food item “i”

Question 24

Can eating small items ever be preferred over large ones i.e. profitability is higher for smaller food items than larger ones?

Answer 24

In the profitability equation, profitability = Ei / hi, we can increase profitability if the handling time is really short/fast. So if small food items have very small handling times, it might be more profitable to eat smaller food items.

Question 25

What is an example of an animal that chooses small food items because of a greater profitability?

Answer 25

Star-nosed moles have a much greater profitability with smaller prey than larger prey, because the smaller prey have very low/fast handling times.

Question 26

what are the units for profitability?

Answer 26

J/s

Question 27

Define the Optimal Foraging Theory (OFT).

Answer 27

This is a theory that determines the kind of diet an animal will have (i.e. whether they will be a generalist or specialist) by outweighing the benefits and costs.

According to this theory, an animal will be a generalist in unproductive environments (i.e. search time for a specific type of food is too high, so by adding more food items, you can obtain enough food).
Also, an animal will be a specialist in productive environments (search time is low enough that there is no need to add a new food item).

Question 28

What are the two equations that the optimal foraging theory utilizes?

Answer 28

The “profitability” equation and the “average rate of energy intake” equation. Both in units of J/s

Question 29

What is the “average rate of energy intake” equation, i.e. describe the variables?

Answer 29

Average rate of energy intake = Eave/(Save+have)

Every variable in this equation is supposed to be an average. Take note of that!

Eave = average energy obtained from all the food items in the diet of interest.

Save = the average searching time for all the food items in the diet of interest.

have = the average handling time for all the food items in the diet of interest

Question 30

Pretend that these coloured circles represent different types of food item:

Diet 1:
🌑

Diet 2:

🌑 🔴

Diet 3:

🌑 🔴 🔵

An animal has a choice between being a specialist (diet 1) or a generalist (diet 2 or diet 3).

Diet 1 has an average search time for that food item that is 24 seconds. What is the average search time for diet 2 and 3?

Answer 30

The time would be divided by how many items you have in the diet, compared to the most specialist diet (diet 1).

Diet 1: we were told Save = 24 seconds

Diet 2: would be half of diet 1 because a new food item is added –> 24/2 = 12 seconds

Diet 3: would be one-third of diet 1 –> 24/3 = 8 seconds

Question 31

Diet 1:
🌑

Diet 2:

🌑 🔴

Diet 3:

🌑 🔴 🔵

The handling time for the grey food item is 1 secs
The handling time for the red food item is 3 secs
The handling time for the blue food item is 8 secs

Calculate the average handling time for the three diets

Answer 31

diet 1:

have = 1/1 = 1 secs

diet 2:

(1 + 3)/2 items = 2 secs

diet 3:

(1+3+8)/3 items = 4 secs

Question 32

Diet 1:
🌑

Diet 2:

🌑 🔴

Diet 3:

🌑 🔴 🔵

All the food items give 10 J of energy. Calculate the average energy obtained in each diet.

Answer 32

Diet 1:

Eave = 10/1 = 10 J

Diet 2:

Eave = (10+10)/2 = 10 J

Diet 3:

Eave = (10+10+10)/3 = 10 J

Question 33

Diet 3:

🌑 🔴 🔵

You calculated in the previous questions that for this diet…

Save = 8 secs
Eave = 10 J
have = 4 secs

Calculate the average rate of energy intake (J/s)?

Answer 33

Average rate of energy intake = Eave/(Save+have)

= 10 / (8+4) = 10/12 = 0.83 J/s

Question 34

Here are the average rate of energy intakes in the following four diets:

Diet A: 0.4 J/s
Diet B: 0.71 J/s
Diet C: 0.83 J/s
Diet D: 0.67 J/s

Which diet is the optimal diet for the animal?

Answer 34

Diet C, because it has the highest value for the average rate of energy intake.

Question 35

You have two food items.

Food item A

Profitability = 10 J/s
Average rate of energy intake = 0.91

Food item B

Profitability = 5 J/s
Average rate of energy intake for including B with A = 0.5 J/s

What equation would you use to figure out whether you should add item B to the diet?

Answer 35

profitability of item B > Average rate of energy intake of item A + B

5 > 0.5

This is true, so add food item B

Question 36

What are the four assumptions of the Optimal Foraging Theory?

Answer 36

1. The animal is a predator (i.e. not an herbivore, not a parasite)
2. The food items are not clumped (they are randomly distributed)
3. Assumes only energy content of the food (not other nutritional value parameters, not the toxicity)
4. Assumes search time and handling time does NOT improve with experience.

Question 37

What kind of graph represents a resource that is clumped? (“Number of resources” on y-axis, and “time” on the x-axis)

Answer 37

A curve of diminishing returns.

Question 38

What factors might determine how long you should stay at a patch before moving on to another one?

Answer 38

1. abundance
2. how far away the next patch is
3. competition in the patch
4. ripeness

Question 39

what is residence time?

Answer 39

The amount of time spent in a patch

Question 40

what is travel time?

Answer 40

The amount of time it takes to find a new patch

Question 41

On a curve of diminishing returns, how do you find the residence time?

Answer 41

Draw a tangent line from the travel time to the highest point (the hump) of the curve of diminishing returns.

Question 42

What does the Marginal Value Theorem tell us?

Answer 42

The marginal value theorem is used to describe how long an animal will stay in a patch of resources, if the resources they use tend to be clumped.

According to this theorem…

• If travel time is high, i.e. it takes a long time to find a new patch, the residence time (time spent in a patch) tends to be high
• If a patch has more resources (number of resources on y-axis), then residence time is higher.

Question 43

Describe risk-sensitive foraging. Make sure to define what “risk-prone” , “risk-averse” and “average expected reward” mean.

Answer 43

Animals when they are foraging need to meet energy requirements.

In this theory, resources that are “variable” are called “risk-prone” because these resources can be sometimes abundant, and sometimes scarce.

Inversely, resources that are “less variable” are called “risk-averse,” because these resources are often reliable in their abundance.

When we say “average expected reward,” what we mean is the amount of resource the animal expects from the source.

According to this theory…

An animal will choose to be risk-aversive (choose the more reliable option) if the average expected reward from the resource is greater than the usual energy requirements of the animal.

In contrast, an animal will choose to be risk-prone, going for more ballsy resources, if the average expected reward from the reliable option (risk-averse option) is not enough to cover the requirements of the animal.