Ecology Exam 2 Study Guide

Search image

A mental representation of what prey looks like that helps a predator recognize and locate that type of prey more efficiently with experience.

Assumptions of Diet Model

- Foragers maximize fitness by maximizing

energy intake rate

– Food items are encountered one at a time in

proportion to their abundance

– Food items can be ranked by their profitability

Assumptions of Optimal Patch Use Model/Marginal Value Theorem

• Foragers attempt to maximize

energy intake rate

• All patches are identical

• Travel time between patches is

constant

• The instantaneous harvest rate

declines as a forager depletes a

patch; the forager experiences

diminishing returns in each patch

How to calculate profitability

• Profitability = energy gained/ handling time

How to determine animal diets based on profitability and search time. Know how to calculate the optimal diet. (This is the diet model)

1. Given a list of food items, first calculate and then rank the profitability of them. Profitability is determined by energy/handling time

2. Calculate average energy intake rate which is (energy gained)/(Handling time + Search time)

3. Use profitability to determine which ones to add first, and then keep on going until diet becomes less profitable. Example:

• A: Energy = 10J, Handling time: 1s, Profitability = 10J/s

• B: Energy = 10J, Handling time: 3s, Profitability = 3.33J/s

• Search time for A only is 24, A+B is 12

If we then calculate average energy intake rate we can do for just A:

10/(24+1) = 0.4J/s

For A+B:

10/(12+2) = 0.71J/s

10 was numerator bc average of the two is (10+10)/2.

Therefore adding B makes the diet more optimal and you keep on going until the number you get for average energy intake rate decreases

Crow clam study: the researcher’s assumptions and results

– Drop clams on rocks until they can be pried

open

– Measured profitability of clams of different sizes

• Measured energy content

• Measured number of drops it took until clams could

be pried open with a fingernail

– Measured abundance of – and thus encounter

rate – for each clam size (estimate of search times)

Hypothesis: Crows attempt to maximize

energy intake rate according to the optimal

diet model

• Generated an OFT model to generate

predictions

• Prediction:

• Crows should eat all clams greater than 29

mm in size and reject all clams < 29 mm in

size.

Methods:

– Northwestern crows (Corvus caurinus)

– Recorded the size of clams that were eaten and

the size of clams picked up but not eaten

(rejected)

– Measured handling times of differently size

clams

– Measured energy content of differently size

clams

Results:

– Clams > 30 mm were almost

always eaten

– Clams < 28 mm were almost

always rejected

• Conclusion:

– Observed crow diets are

similar to the one predicted by

the diet model

– No zero-one rule, instead

exhibited partial preference,

probably because crows don’t

have perfect knowledge (important part to remember I think)

Assumptions (from the optimal diet model):

1. Crows attempt to maximize their energy intake rate (energy gained per unit of time).

2. Food items are encountered one at a time, with encounter rates depending on their abundance.

3. Clams can be ranked by profitability, calculated as energy obtained divided by handling time.

4. Zero-one rule: The model predicts that crows should always eat profitable clam types and always reject unprofitable types.

   1. The model also effectively assumes that crows can accurately assess which food items are worth eating.

The value of the use of multiple sensory cues

Study: Bees Use Multiple Senses to Enhance Foraging Efficiency (Kulahci et al., 2008)

Research Question: Is foraging more efficient when animals use multiple sensory cues?

Methods:

• Trained bumblebees to feed on artificial flowers containing sugar water.

• Flowers differed in shape (visual cues) and odor (chemical cues).

• Bees learned to locate food using either single or multiple sensory cues.

Results:

- Bees trained to use both visual and odor cues had the highest feeding performance.

Conclusion:

- Using multiple sensory cues improves foraging efficiency by helping animals locate food more effectively.

What to know for the exam

The value of multiple sensory cues: Animals can locate food more efficiently when they combine information from different senses, such as vision and smell, compared with relying on a single sense.

Key example: Bumblebees using both visual and odor cues demonstrated better feeding performance than bees using only one type of cue.

Zero-one rule

Each food item is either always eaten or always rejected

(derived from the profitability calculations that we did beforehand)

Ant salt study

How does the need for sodium affect diet choice? (Kaspari, Chang, & Weaver 2010)

Hypothesis: Sodium limitation affects the

feeding behavior of ants

• Prediction:

• Ants living in environments where sodium is

rare will have a strong preference for

sodium chloride (NaCl)

Methods:

– Examined recruitment to food vials by Tapinoma

sessile along four transects

– Half the vials contained sucrose, half contained

NaCl

– Transects (parallel) were 1, 10, 100, and 1000

m from a road that was salted with NaCl each

winter

– Recorded the number of sucrose and NaCl vials

that contained ants along each transect

Results: Ants showed a greater preference for salt relative to sugar as distance from the road increased. Near the road, ants visited approximately 1 salt bait for every 13 sugar baits, compared with 1 salt bait for every 5 sugar baits at 1,000 meters. Ants also preferred higher concentrations of both salt and sugar.

Conclusions: Ant foraging preferences depend on nutritional needs and environmental nutrient availability. Ants farther from salted roads were more attracted to sodium, suggesting that sodium becomes a limiting nutrient when environmental availability decreases.

Main takeaway for your exam: Animals do not always select food based solely on energy content. They also forage to obtain essential nutrients they lack, meaning nutrient availability can influence diet choice.

Brown’s Patch Use Model

A model predicting when animals should leave a food patch based on energy gains and three costs: energetic costs, predation risk, and missed opportunities.

GUDs

Giving-Up Density: the amount of food remaining in a patch when an animal stops foraging and leaves

• High GUD: Animal leaves more food behind, indicating it stopped foraging earlier.

• Low GUD: Animal consumes more food before leaving, indicating it foraged more extensively.

All the factors that affect GUDs under Brown’s Patch-Use Model

• Energetic costs: Energy expended while searching for and consuming food. Higher energetic costs generally lead to higher GUDs.

• Predation risk: Risk of being attacked while foraging. Higher predation risk increases GUDs because animals leave patches sooner.

• Missed opportunity costs: Other beneficial activities an animal gives up by continuing to forage in a patch. Higher opportunity costs increase GUDs

Opportunity costs: what are they and how do they affect foraging decisions

The benefits an animal gives up by spending time foraging instead of engaging in other potentially beneficial activities.

Bayesian estimation

a theoretical framework where animals make decisions or update their understanding of the environment by combiningprior beliefs (from past experience or evolutionary adaptation) withnew sensory or social sampling data

Crypsis

Crypsis is an antipredator adaptation that makes an animal difficult for predators to detect, often through camouflage or coloration that matches its environment.

evasive maneuvers

can often be taken by more slow moving prey that cannot get away from a predator by fleeing

tiger moths example (evasive maneuvers)

for example tiger moths stop flying just before a bat gets them to avoid capture

Vigilance

Vigilance is the behavior of scanning the environment to detect potential predators. Decrease with group size

predator harassment

rapid movement with loud noise

mobbing

harassment of predator by multiple individuals

Dilution effect

The dilution effect is the reduction in an individual's probability of being killed by a predator when it belongs to a larger group.

selfish herd

Animals in groups reduce their individual risk of predation by moving toward the center of the group, where they are less likely to be attacked.

flash disappearance

an anti-predator defense mechanism where a normally camouflaged (cryptic) animal suddenly reveals highly conspicuous color patches or sounds while fleeing, only to hide them completely upon settling back into a stationary position

alarm signal

prey advertise themselves to warn others of their species

move-on hypotheses

Prey animals harass predators to encourage them to leave an area, thereby reducing predation risk.

Trade-offs between predator avoidance and resource acquisition

Time spent avoiding predators is time that is not able to be spent foraging for food/acquiring resources. Opportunity cost missed in anti predator behavior.

Squirrel food carrying study

Hypothesis: Food-carrying behavior represents

a trade-off between feeding in safety and

obtaining high energy intake rates

• Predictions:

– Large items should be carried to safety more often

than small items

– As distance to safety increases, carrying behavior

should decline

Methods:

– Gray squirrels (Sciurus

carolinensis)

– Offered different sized food items

(1, 2, or 3 g) at varying distances

from the safety of trees (3, 6, 9,

or 12 m)

– Cost of carrying 1-3 g seed is

about same but handling time is

much greater for large seeds

– Recorded the proportion of items

carried to safe cover

Results:

• Squirrels were more likely to carry larger food items to safety than smaller ones.

• Squirrels were less likely to carry food to safety as the distance to the nearest tree increased.

Small food items were more frequently eaten immediately, while larger items were more frequently transported to trees.

Conclusions: Squirrels balance energy intake against predation risk. Carrying food to safety reduces exposure to predators but requires additional travel time and energy. Consequently, squirrels are more willing to transport larger food items and items found closer to protective cover.

Main takeaway for your exam: Antipredator behavior involves trade-offs between safety and feeding efficiency. Animals may sacrifice some feeding efficiency to reduce predation risk, but the decision depends on food size and the distance to safety

Types and drivers of dispersal and migration

Dispersal: Relatively short-distance, one-way movement away from an established location.

• natal dispersal

  • Breeding dispersal

Migration: Relatively long-distance, two-way movements, often occurring in response to environmental changes.

Natal dispersal

The movement of an animal from its birthplace (natal area) to a new location where it will live and potentially reproduce.

do it to avoid interbreeding, reduce competition, find better resources, find mating opportunities

Breeding Dispersal

The movement of an animal from one breeding location to another between reproductive attempts, after it has already bred.

Do it to find better mates, find better breeding habitats, avoid competition, respond to previous reproductive failure, avoid predators

Reasons for Migration

• Seasonal environmental changes: Animals migrate in response to changing environmental conditions.

• Resource availability: Animals move to locations with better food availability or quality.

• Competition: High population density and increased competition can encourage migration.

  • Individual condition: Animals in poorer condition may be more likely to migrate when remaining in place is disadvantageous

Types of Migratory Behavior

• Full migration: All individuals in a population migrate.

  • Partial migration: Some individuals migrate while others remain residents.

Reasons partial migration can persist

There are two possible explanations for why some animals migrate while others stay in the same area.

1. Migration is a fixed genetic trait (frequency-dependent selection).

• Whether an animal migrates is largely determined by its genes.

• Frequency-dependent selection means the advantage of migrating or staying depends on how many other animals are doing each.

  • For example, if most animals stay, migrating might be beneficial because there is less competition elsewhere.

• This helps maintain a polymorphism, meaning both migratory and nonmigratory individuals continue to exist in the population.

2. Migration depends on individual condition.

• Whether an animal migrates depends on its physical condition, such as health, body size, energy reserves, or nutritional status.

• For example, animals in better condition may be more capable of making long migrations, while those in poorer condition may stay.

Main difference: The first explanation says migration is genetically determined, while the second says migration depends on the animal's current condition.

Kittiwakes and Public Information — Boulinier et al. (2008) - Do kittiwakes use public information (the breeding success of neighboring birds) when deciding whether to return to the same breeding site?

Hypothesis: Kittiwakes use both their own breeding success and the breeding success of nearby birds to determine whether a breeding location is good.

Predictions: If kittiwakes only use personal information, birds whose nests fail should leave regardless of their neighbors' success. If they use public information, birds whose nests fail should be more likely to stay when their neighbors successfully reproduce.

Methods: Researchers studied black-legged kittiwakes nesting in colonies. They removed eggs from selected nests to cause breeding failure. In one group, all neighboring nests also failed because their eggs were removed. In the other group, only the focal birds' nests were made to fail, while surrounding birds could successfully reproduce. Researchers measured whether birds continued visiting their nests and whether they returned to the same breeding location the following year.

Results:

• Birds whose eggs were removed were more likely to continue visiting their nests when their neighbors were successful.

• Birds surrounded by unsuccessful neighbors were less likely to remain at their nests.

• Failed breeders were more likely to return to the same breeding location the following year if their neighbors had successfully reproduced.

• Areas with successful breeding also attracted more birds investigating potential nesting sites.

These differences occurred even though the focal birds had experienced breeding failure in both treatments.

Conclusion: Kittiwakes use public information when making breeding dispersal decisions. They judge the quality of a breeding location partly by observing whether neighboring birds successfully reproduce, rather than relying only on their own experience.

Main Takeaway: Even if a kittiwake's own nest fails, it may return to the same location if its neighbors successfully reproduce, because their success suggests the area is a good place to breed.

Competition and migratory

behavior of dippers - What maintains

resident and migratory behaviors within a

population? (Gillis et al. 2008)

Methods:

– American dippers

(Cinclus mexicanus)

– Uniquely banded

individuals

– Observed migration

behavior over seven

years

Results:

– 152 residents and 90 migrants

– Residents fledged 2.6 more

offspring than migrants

• Conclusion:

– The fitness of residents is

higher than that of migrants;

migratory behavior appears to

be condition-dependent, only

those in bad condition migrate. not genetic trait

– In fact, some individual birds

changed their migratory

behavior, indicating that it is

plastic and condition

dependent

Partial Migrant vs. Resident Population

Partial migratory population: A population in which some individuals migrate while others remain in the same area year-round.

Resident population: A population in which individuals generally remain in the same area rather than migrating seasonally.

Win-stay lose-shift strategy

Animals remain in a breeding location if they experience high reproductive success (win-stay), but move to a new breeding location if reproductive success is low (lose-shift).

Bicoordinate navigation

The ability of an animal to determine its geographic location using two environmental gradients, similar to how humans use latitude and longitude.

• Allows animals to determine where they are relative to their destination.

• Enables animals to navigate even when displaced into unfamiliar locations.

• Some animals use variations in Earth's magnetic field as geographic information.

Allows you to know where you are relative to your destination

Bicoordinate navigation in birds - Do birds display

bicoordinate navigation? (Chenetsov,

Kishkinev, & Mouritse 2008)?

Methods:

– Eurasian reed warblers

(Acrocephalus scirpaceus)

– Migrate between sub-

Saharan Africa and Eurasia

– Captured birds during

spring migration

– Displaced half 1000 km

east

Methods:

– Placed in Emlen

funnels to measure

orientation

Results:

– Displaced birds oriented

to northwest to

compensate for being

displaced

• Conclusion:

– Unlike Dung Beetles,

Eurasian reed warblers

display bicoordinate

navigation

Mechanisms and cues for homing covered in the slides

Look back at orientation/navigation/etc

How to calculate clock shifts

Animals that use a sun compass determine their direction by combining the sun's position with their internal biological clock.

Because the sun's position changes throughout the day, animals must know approximately what time it is to navigate correctly.

Clock shifting: Experimentally changing an animal's internal clock so that it misinterprets the sun's position and travels in an incorrect direction.

Earth rotates 360 degrees in 24 hours, so average of 15 degrees per hour

Angular shift is 15 degrees times hours shifted, so if we shifted 3 hours it would be 45 degrees shifted

Normally, monarch butterflies migrate south using the sun as a compass.

• At dawn, the sun is approximately east.

• A butterfly flying 90° to the right of the morning sun will travel south.

• Researchers manipulate the butterfly's internal clock so it interprets the noon sun as though it were the morning sun.

  • At noon, the sun is approximately south. Flying 90° to its right now sends the butterfly west.

• Delayed internal clock: Direction shifts clockwise (e.g., south to west).

  • Advanced internal clock: Direction shifts counterclockwise (e.g., south to east).

Dung Beetle Example

Purpose: Dung beetles use an orientation dance to establish and maintain a straight travel direction while rolling dung away from a dung pile.

This is important because dung piles attract many competing beetles. Moving away quickly in a straight line reduces the chance that another beetle will steal their dung ball.

Howdoestheorientationdancework?

1. Climb onto the dung ball: Before leaving, the beetle climbs on top of its ball.

2. Rotate its body: The beetle performs a brief dance, rotating while observing celestial cues.

3. Establish a direction: The beetle uses cues such as the sun, moon, polarized skylight, or Milky Way to establish a compass heading.

4. Roll in a straight line: The beetle climbs down and rolls its ball while maintaining its chosen direction.

5. Correct its direction if disturbed: If an obstacle disrupts its path, the beetle may climb onto the ball and dance again to reestablish its original heading.

Howdoesthebeetlerememberitsdirection?

Researchers believe the dance allows the beetle to take a kind of mental snapshot of the sky.

• The beetle records the arrangement of celestial cues relative to its chosen direction.

• While rolling, it uses those cues to maintain its heading.

• If disrupted, it can compare the current celestial information with its remembered direction and correct its movement.

They use orientation rather than true navigation

Isodar

Definition: An isodar is a line showing combinations of population densities in two habitats where individuals experience equal fitness.

Isodars are based on the Ideal Free Distribution (IFD) model, which predicts that animals distribute themselves among habitats until fitness is equal across habitats.

Howdoesanisodarwork?

• Different habitats have different resource quality.

• Higher-quality habitats can support more individuals before competition reduces fitness.

• At equilibrium, animals in both habitats experience equal fitness, even if their population densities differ.

• Plotting the density in habitat 1 against the density in habitat 2 produces an isodar.

Key prediction: The IFD model predicts a linear isodar.

Allee effect

An Allee effect occurs when individual fitness increases as population density increases, particularly when population density is low.

One of the justifications/explanations for conspecific attraction

Territory vs Home Range

Territory is area actively defended by an animal for exclusive access to resources

Home range is the area regularly used by an animal but doesn’t necessarily provide exclusive access

Factors affecting territory defense

Individual Body Condition

Animals need sufficient energy reserves to defend territories.

Resource Availability

The abundance of food affects how much territory an animal needs.

Competitor Density

The number of competitors can influence territory size and the costs of defense.

Resource value and fighting behavior in

penguins - Do animals adjust

fighting behavior based on the benefits?

(Renison et al. 2006)

Hypothesis: The value of a contested

resource like a nesting site affects fighting

behavior

• Prediction:

• Fights over high-value nesting sites should

be more intense than fights over low-value sites

Methods:

– Magellanic penguins

(Spheniscus magellanicus)

– Observed fights over nests

– A bill duel is a low-cost fighting

behavior

– Overt fights are more intense

and often lead to injuries (cuts)

– The value of a nest is high

before egg laying mid-October

and low after that time

Results:

– Overt fights were

common early in the

breeding season

– Bill duels were more

common after mid-

October

Results:

– More fights than duels occurred over

higher quality nests

– Males with higher quality nests fought

longer and received more cuts

– Duration of fights and length of skin cuts

was shorter early in the season,

because they were more intense?

• Conclusion:

– Fighting behavior (intensity) was

affected by the value a nest

Salamander Fights for Mates (Verrell, 1986) - Does female size affect how long male salamanders fight?

• Hypothesis: The reproductive value of a female affects male fighting behavior.

• Prediction: Males will fight longer over larger, more fertile females.

• Methods:

  • Researchers studied red-spotted newts.

  • They staged encounters between similarly sized males competing for a female.

  • They measured how long males wrestled.

• Results:

  • Males fought longer over larger females.

  • Wrestling duration increased with female body length.

• Conclusion: The value of a potential mate influences how long males fight.

Key takeaway: Males invest more effort in competition for higher-value mates.

Challenge Hypothesis

male-

male interactions stimulate

testosterone production and

sustain subsequent aggressive

behavior

Winner effect

winning an

aggressive encounter

enhances the likelihood of

winning subsequent

encounters

Assumptions and predictions of the ideal free distribution model

Animals distribute themselves among habitats based on resource availability and competition to maximize their access to resources.

Example: If one feeding area has twice as much food as another, approximately twice as many animals may gather there, balancing the food available per individual.

Assumptions:

• Individuals attempt to maximize fitness

  – Habitat locations differ in resources

  – Fitness is negatively density-dependent

  – Individuals are equal competitors

  – Individuals are free to move at no cost

Predictions:

• Individuals will settle in habitats based on the relative fitness payoffs: the number of individuals in each habitat will be proportional to habitat quality

• All individuals will have the same fitness no matter where they settle

Assumptions and predictions of the hawk-dove

Assumptions:

• Individuals compete for resources that have a benefit (B) and a potential fighting cost (C).

• Individuals have equal fighting abilities.

• Two possible strategies:

  • Hawk: Always fights aggressively until victory or injury.

  • Dove: Never escalates to a dangerous fight; uses low-cost displays and retreats if challenged by a hawk.

• The fitness payoff of each strategy depends on the opponent's strategy and the benefits and costs of fighting.

Predictions:

• When the benefit of winning exceeds the cost of fighting (B > C), the hawk strategy is favored.

• When fighting costs exceed resource benefits (C > B), both hawks and doves can coexist in a mixed evolutionarily stable strategy (ESS).

• At the mixed ESS, hawks and doves have equal average fitness, preventing either strategy from replacing the other.

• The predicted proportion of hawks at the mixed ESS is B/C.

Assumptions and predictions of the sequential assessment model

Assumptions:

• Individuals vary in fighting ability, unlike the equal-ability assumption of the hawk-dove model.

• Individuals assess their opponents' fighting abilities relative to their own.

• Individuals can use multiple fighting strategies, ranging from low-cost displays to dangerous physical combat.

• The costs and benefits of fighting depend on the opponent's ability and the value of the contested resource.

• Individuals can gather information about their opponent during a contest.

Predictions:

• Animals should initially use low-cost behaviors to assess their opponents before escalating to more dangerous fighting.

• Individuals should continue fighting only while the expected benefit of winning exceeds the cost of continuing.

• Evenly matched opponents will fight longer because determining the likely winner takes more time.

• Unequally matched opponents will have shorter fights because the weaker individual can recognize its disadvantage and withdraw.

  • Most contests should end without serious injury because individuals withdraw when they determine that their probability of winning is low.

Key difference between SAM and Hawk/dove

Key difference: The hawk-dove model assumes individuals have equal fighting abilities and use two fixed strategies, while the sequential assessment model allows individuals to evaluate their opponents and adjust their fighting behavior accordingly.