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Behavioral ecology and evolution
Lecture 4
9 August 2012
Sucking the planet dry
Gleeson et al 2012 Nature…
in YESTERDAY’S issue!
Grey=magnification representing amount of water that people are currently pumping out of that aquifer, compared to the rate of natural replenishment.
www.npr.org/blogs/thesalt/2012/08/08/158417396/heres‐where‐farms‐are‐sucking‐the‐
planet‐dry
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http://www.nature.com/nature/journal/v488/n7410/full/nature11295.html#/access
Sucking the planet dry
• Water in most aquifers flows slowly underground feeding rivers and lakes
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Outline: Behavioral ecology and evolution
• Response to environmental variation
• Theory of Evolution by Natural Selection
– Variation within species
– Balancing Selection
– Behavioral changes via natural selection
– Speciation
– Patterns of Evolution
• Adaptive behavior
– All behaviors have costs and benefits
– Territorial defense
– Optimal foraging and diet width
– Group living (costs, benefits, examples)
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Response to Environmental Variation
Each species has a range of environmental
tolerances that determines its potential
geographic distribution.
• A fundamental principle in ecology and biogeography is that geographic ranges of species are related to constraints imposed by the environment.
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Coping with the environment
• Organisms have two options for coping with environmental variation: Tolerance and avoidance.
• Spruce trees in the boreal forest cannot avoid temperature extremes so must be able to tolerate air temps that drop below –50°C in winter, and up to 30°C in summer.
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Figure 4.1 A Frozen Frog
An extreme example of tolerance
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Figure 4.4 Climate and Aspen Distribution (Part 1)
Climate envelope
• A species’ climate envelope is the range of condition over which it occurs.
• It is a useful tool for predicting a species’ response to climate change.
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Response to Environmental Variation
• Physiological processes have a set of optimal conditions for functioning.
• Deviations from the optimum reduce the rate of the process.
• Stress—environmental change results in decreased rates of important physiological processes, lowering the potential for survival, growth, or reproduction.
• Stress can limit the range of species
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Options vary over time
• Many organisms can adjust to stress through behavior or physiology—called acclimatization.
• Over time, natural selection can result in adaptation to environmental stress (next section)
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Variation in Temperature
• Ectotherms: Primarily regulate body temperature through energy exchange with the external environment.
• Endotherms: Rely primarily on internal heat generation, mostly birds and mammals.
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Figure 4.7 Temperature Ranges for Life on Earth
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Outline: Behavioral ecology and evolution
• Response to environmental variation
• Theory of Evolution by Natural Selection
– Variation within species
– Balancing Selection
– Behavioral changes via natural selection
– Speciation
– Patterns of Evolution
• Adaptive behavior
– All behaviors have costs and benefits
– Territorial defense
– Optimal foraging and diet width
– Group living (costs, benefits, examples)
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Hypotheses and Theories
• Scientific Hypothesis: an explanation of events or observations
• Scientific Theory: the highest level of scientific understanding, based on numerous hypotheses and years of study by many scientists.
Evolution is a scientific theory
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Theory of Evolution by Natural Selection
• Natural selection is the mechanism that explains evolution
• Natural Selection: scale = individual
• Evolution: scale = many generations
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Adaptation through natural selection “descent with modification”
Evolution by natural selection: Over time, traits will be selected to match well with a particular species’ environment 1. Genetic variation (morphological, physiological, behavioral traits)
•
There is variation among individuals (we are each unique)
•
Some of this variation has a genetic basis and thus is inheritable (we can see which traits are truly genetic with common garden experiment)
2.
Competition (“survival of the fittest”)
•
Organisms produce more young than can survive.
3. Differential reproduction (the “fittest” reproduce to pass genes on to the next generation)
•
Individuals with traits most suited to environment (i.e., with the greatest “fitness”) most likely to survive and reproduce.
•
Because they reproduce, these individuals have the greatest influence on the heritable characteristics of subsequent generations
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Variation within species
• Sexual dimorphism: secondary sex characteristic distinction
• Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism
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Variation within the peppered moth (Biston betularia)
• Industrial Melanism
– dark color morphs dominate populations in industrial areas
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http://porpax.bio.miami.edu/~cmallery/150/evol/melanism2.gif
% Dark moths
Variation Within Species
1811 dark moths were
an uncommon morph
1848 1st dark moth found
1864 most common morph
1895 98% frequency!
Smoke pollution control
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Variation Within Species
• Poecilia reticulata (a guppy) inhabits freshwater systems in northeastern South America
• In Trinidad, downstream flow isolates populations in mountainous areas
• In the absence of predation males are brightly decorated
– AND, there is variation in the # and size of colored spots
• Females prefer to mate with decorated males
• Predators are absent in upper reaches
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Variation Within Species
Experiment
1. Three experimental populations, each with high natural variation in # spots/fish
2. Introduced different predatory pressures to different populations
Weak Predators
No Predators
Dangerous Predators
Endler 1980
• Balancing Selection
– Two well‐adapted phenotypes, but in different environments
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Balancing Selection
• Heterozygote Advantage
– When an individual who is heterozygous at a particular gene locus (e.g., they have both type A and B genes) has a fitness advantage over a homozygous individual
– When heterozygotes are fitter than the homozygotes (AA or BB), natural selection will maintain a polymorphism
hemoglobin gene
HgbA HgbA
HgbA HgbS
HUMAN CASE STUDY: sickle cell anemia and malaria resistance
HgbS HgbS
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Genotype
Life Expectancy
Malaria Resistance
Normal
Hemoglobin Gene (HgbA)
Normal
No
HgbA + HgbS
Some Problems
Yes
Variant
Hemoglobin Gene (HgbS)
Short
Yes
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Malaria resistance
Frequency of HgbS
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Figure 4
Balancing Selection
Source: Current Biology , Volume 21, Issue 18, Pages R718‐R725
(DOI:10.1016/j.cub.2011.08.022)
Copyright © 2011 Elsevier Ltd Terms and Conditions
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Outline: Behavioral ecology and evolution
• Response to environmental variation
• Theory of Evolution by Natural Selection
– Variation within species
– Balancing Selection
– Behavioral changes via natural selection
– Speciation
– Patterns of Evolution
• Adaptive behavior
– All behaviors have costs and benefits
– Territorial defense
– Optimal foraging and diet width
– Group living (costs, benefits, examples)
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Behavioral changes via natural selection
• Animal behavior=interactions with food, resources, mates, & other members of species group
– Ex: Changes in feeding behavior lead to changes in bill shape and other specialized feeding traits
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Darwin’s finches
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Figure 6.11 Rapid Adaptive Evolution in Soapberry Bugs
Speciation
• So, that was variation within species.
• We know that speciation also occurs.
• When do we have speciation vs. just variation within species?
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Speciation
•
What’s a species?
–
–
•
A group of living organisms capable of interbreeding to produce viable offspring
Organisms belonging to two separate species cannot produce viable offspring.
How do species form?
–
Usually (with many exceptions), populations of the same species
1. Becomes geographically isolated
2. Natural selection drives adaptation to the local environment
3. Reproductive isolation happens (e.g., Different courtship rituals)
4. If the two populations meet again:
a)
b)
Cannot produce viable offspring: Speciation has happened!
Can produce viable offspring, but their offspring are less fit then either of the “purebred” types, then natural selection will favor further reproductive isolation. Speciation has NOT occurred, but may happen in the future
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Speciation
• Darwin’s finches
• Probably evolved from a single ancestor which was geographically separated from the mainland
• At the Galapagos, ancestor evolved to exploit different resources on the islands: seeds, leaves, flowers, beetles, soft insects
– Competition among the finches led to specialization, which led to speciation.
• This richness of endemic species is typical for island chains. Because they are isolated
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Mechanisms for isolating populations (leading to speciation): Allopatric and Sympatric
• Allopatric speciation (a.k.a. geographic speciation)
– Allopatry = Occurring in separate, nonoverlapping geographic areas.
– Allopatric speciation can occur when biological populations of the same species become isolated
– No secondary contact after initial isolation (at least for a long time)
– Especially likely for island species
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The grand canyon formed 5‐17 million years ago
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South Rim: dry desert
North Rim: ponderosa and pinyon pine forests
Two squirrel populations diverged in characteristics over the last ~10,000 years
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What would happen if we removed the Grand Canyon?
(i.e., made the two populations sympatric?)
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1. The squirrels breed with each other, and their gene pools mix freely. Still one species.
2. Speciation has occurred, making breeding impossible
3. The squirrels breed with each other, but gene flow only occurs in a small region where populations overlap (hybrid zone)
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1. The squirrels breed with each other, and their gene pools mix freely. Still one species.
2. Speciation has occurred, making breeding impossible
3. The squirrels breed with each other, but gene flow only occurs in a small region where populations overlap (hybrid zone)
In this case, are they two species or one?? ANSWER: One. But, speciation may occur in the future
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Because two species are still able to breed with each other, should we consider them the same species?
Or, since the gene pools don’t completely mix, should we consider them different species?
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ALLOPATRIC SPECIATION
In the process of allopatric speciation
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Mechanisms for isolating populations (leading to speciation): Allopatric and Sympatric
• Sympatric speciation
– Sympatric = occurring in the same area
– Sympatric speciation happens when genetic divergence occurs among groups of individuals living in the same place
– Physical isolation is not necessary. Instead there is some form of ecological isolation between the groups.
– Not many examples. Sympatric speciation is a debated subject.
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Sympatric Speciation?
• Apple maggot flies Rhagoletis lay eggs in:
• (1) hawthorns (Crataegus)
– Native to NE U.S.
• (2) apples (Pyrus)
– Apples introduced c. 300 ya
• The flies belong to the same species; there is phenotypic plasticity in use of hosts. Individuals are simply responding differently to different environmental conditions
• But, this specialization in host‐use may be the beginning steps towards sympatric speciation.
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Speciation despite globally overlapping distributions in Penicillium spp: the population genetics of Alexander Fleming’s lucky fungus (various sps from a single ancestor)
SYMPATRIC SPECIATION
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Speciation despite globally overlapping distributions in Penicillium spp: the population genetics of Alexander Fleming’s lucky fungus (various sps from a single ancestor)
“this apparently ubiquitous fungus is actually composed of at least two genetically distinct species”
SYMPATRIC SPECIATION
“little geographic population subdivision”
“However, no hybridization was detected between the species”
“competition [for resources] may facilitate species maintenance despite globally overlapping distributions”
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Outline: Behavioral ecology and evolution
• Response to environmental variation
• Theory of Evolution by Natural Selection
– Variation within species
– Balancing Selection
– Behavioral changes via natural selection
– Speciation
– Patterns of Evolution
• Adaptive behavior
– All behaviors have costs and benefits
– Territorial defense
– Optimal foraging and diet width
– Group living (costs, benefits, examples)
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Speciation may occur gradually, or in bursts
(this continues to be debated)
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Marine zooplankton
Geological periods
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Patterns of Evolution
Divergent
Convergent
Parallel 49
Divergent evolution
• Similar species become more and more distinct
• Adaptation to different environmental conditions
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Divergent evolution
• Adaptive radiation is an example of divergent evolution
– Ancestral species evolve into different species that occupy different niches (food habits) or habitats
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Convergent Evolution
• Acquisition of the same biological trait in unrelated lineages
• Adaptation by different species to similar
environmental conditions
• Many examples
– E.g., wings for flying in birds (Class Aves) and bats (Class Mammalia)
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Parallel Evolution
• Evolution of similar niches following isolation
• Marsupials arrived on what would become Australia ~90 million years ago
• The only other mammals present were monotremes
(e.g., Echidna)
• Adaptive radiation of Australian marsupials closely mimicked radiation of placental mammals on other continents 53
What leads to endemism?
(species found nowhere else)
• Small genetic input (the founder effect). Entire populations have the genetic make‐up of the founding couple.
• Isolation ‐ no connection with mainland gene pool to dilute changes. • Unusual selection pressures. NOT no selection pressures, but very different to mainland life with diseases and predators.
‐ Given these conditions, evolution can act rapidly. ‐ Wallabies released on Hawaii in 1910 already have very different color, size and enzyme polymorphisms to Tasmanian populations. Possibly a new species (in only 100 years!).
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Islands and Speciation
• Isolation promotes endemism
– Isolation can be due to geography and/or the dispersal ability of the organism
– The evolution of endemic species on islands is strongly associated with species’ dispersal ability
long‐horned beetles
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Islands and Speciation
• Endemism: A species found no where else
– Common among island archipelagos, because they are isolated.
• The island scrub jay, Aphelecoma
insularis, found only on Santa Cruz Island, differs from the western scrub jay, Aphelecoma californica, by its larger size and stouter bill. – A result primarily of its diet incorporating the thick‐shelled acorns of island live oak, Quesrcus
tomentella, another endemic species 56
Continental Drift and Evolution (isolation on
a LARGE scale)
• Patterns of speciation occurring on
islands also occur on a much larger
scale across continents
– They all share a common ancestor
(150 myr)
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Evolutionary Perfection? • Evolutionary processes work with the genetic variation that is available
– Survival of the fittest available, or fittest yet
• Past events have profound repercussions on the present
– Features acquired from ancestors influence fitness at present – Geography (continental drift, ice ages, etc.)
• Environmental conditions can guide and limit evolution
– Physical properties of air and water guide development of wings , flippers and fins
– Gravity typically limits development of whale‐sized land animals
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Fundamentals of Evolutionary Ecology
• Individuals within a species are not identical
• Some variation among individuals is heritable
– Variation has a genetic basis
• Most individuals die before reproduction
– Among the reproducing minority, most reproduce at less than their maximal rate
– i.e., not all young produced survive (to reproduce themselves)
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Fundamentals of Evolutionary Ecology
• Selective forces for and/or against particular traits
• Selection affects survival and/or reproductive capacity of the individual
• Selective forces:
– Environmental: climate, physics
– Ecological: species interaction (co‐evolution)
– Both: Biophysical habitat conditions
• Individuals with traits most suited to the environment are most likely to survive and reproduce
– Because they reproduce, these individuals have the greatest influence on the heritable characteristics of subsequent generations
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Adaptive Evolution
• Rapid adaptive evolution can happen on a continental scale.
• Clines are gradual changes in a characteristic over a geographic region.
• Populations with adaptations to unique environments are called ecotypes.
• Ecotypes can eventually become separate species as populations diverge and eventually become reproductively isolated.
Littorina saxatilis,
6 ecotypes
Littorina
subrotundata,
as found on
barnacles
Littorina
subrotundata
as found in
marsh area
Outline: Behavioral ecology and evolution
• Response to environmental variation
• Theory of Evolution by Natural Selection
– Variation within species
– Balancing Selection
– Behavioral changes via natural selection
– Speciation
– Patterns of Evolution
• Adaptive behavior
– All behaviors have costs and benefits
– Territorial defense
– Optimal foraging and diet width
– Group living (costs, benefits, examples)
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Adaptive behavior
• Trade‐offs= compromises between two activities – ex: foraging versus hiding from predators
– ex: parental care versus reproduction and other activities
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All behaviors have costs and benefits
• Costs
– energy consumed – probability of injury – risk to predation
• Benefits
– Survival rate
– Reproductive success (# young / time)
– Feeding efficiency (energy gained/ time)
– Mating success (# matings/ time)
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Territorial defense
• Garibaldi adults defend a shelter hole, grazing area and sometimes nest site (red algae cultured by males)
• Females allowed into site only to spawn, then males guard eggs until they hatch into plankton
• intraspecific and interspecific defense (including humans!)
• territorial defense may have evolved to increase reproductive success
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Size of feeding territory and costs
Optimal size is when benefits‐costs = greatest
• Relationship varies across species, habitat, age, mating status, resource availability, etc
• Optimal may not be actual due to additional factors absent from model
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Consumer Behavior: Optimal Foraging
a. Where is foraging concentrated?
• Long‐term gain high but risk higher?
• Intake lower but risk low?
b. Does the location chosen just reflect the expected energy intake?
• Or, balance with risk of predation?
c. How long do consumers remain in one location before moving on?
• Stay to avoid costly excursions?
• Leave before local resource is depleted?
d. What are the effects of competition?
• Go where resource is abundant?
• Go where competitors are few?
e. Optimal diet width?
• Specialist: Focus on one/few resources
• Generalist: Expand diet to include many types of resources
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Optimal Foraging Behavior
• How have particular patterns of foraging behavior (e.g., specialist versus generalist) been favored?
– Goal of any individual: Net intake of energy from a resource consumed > energy expended finding and handling (consuming) that resource
• To obtain food, any predator must expend time and energy
– Searching/finding the resource (s)
– Handling the resource (h)
• Pursuing
• Subduing • Consuming
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Optimal Foraging Behavior
• While searching, a consumer will encounter numerous food items
– Predator behavior characterizes it as a…
Generalists
OR
Specialists
–
Consumes many types of resources
Focuses on one/few resources
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Optimal Diet Width
Generalists
Include low‐profitability items in their diet (because eats a variety of foods)
Rate of energy intake is low, but steady (because access to many foods)
Specialists
Only include high‐profitability items (those most ‘worth’ the energy needed to get them)
Rate of energy intake is mostly negative (because lots of time spent handing the food), but sometimes very positive (when resource is finally consumed!)
How do consumers maximize the overall net rate of energy intake?
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Optimal Diet Width
•
A predator’s perspective of a resource: – E = energy content of the resource
– s = search time (time required to find the resource)
– h = handling time (time required to capture, subdue and consume the resource)
– E/(s+h) = net rate of intake = profitability of the resource to the predator 
•
Assumption: Of all the resources in the predator’s diet, the predator will always choose to consume the most profitable one
– If E/(s+h) is the highest possible for the predator, then definitely eats that resource
•
While searching for its most profitable resource, the predator encounters a resource of another type
– s = 0, because already found the resource
Enew
Profitability of the new resource 
hnew
Ebest
sbest  hbest
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Optimal Diet Width
“To eat it, or not to eat it?” That is the question
E = energy content of resource
s = search time h = handling time E/(s+h) = net rate of intake • When a consumer comes across a new resource it will:
1.
Eat the new resource if:
Enew
Ebest

hnew sbest  hbest
2.
Move on if:
Enew
Ebest

hnew sbest  hbest
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Optimal Diet Width
E = energy content of resource
s = search time h = handling time E/(s+h) = net rate of intake • when the consumer comes across a THIRD new resource:
1.
Eat the new resource if:
Eaverage ( best  2 nd )
Ethird

hthird saverage ( best  2 nd )  haverage ( best  2 nd )
2.
Move on (go look for the foods already in its diet) if:
Eaverage ( best  2 nd )
Ethird

hthird saverage ( best  2 nd )  haverage ( best  2 nd )
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Optimal Diet Width
E = energy content of resource
s = search time h = handling time E/(s+h) = net rate of intake • More generally: When a consumer comes across a new
resource it can:
1.
Eat the new resource if:
Eaverage
Enew

hnew saverage  haverage
1.
Move on if:
Eaverage
Enew

hnew saverage  haverage
Consumer will keep adding new resources to its diet if it can easily handle them compared with the time it takes to search for and handle existing resources in its diet
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Optimal Diet Width: Some Insights
• Specialists
– Long handling times, relative to search times
– Lions
• Short search time, because live in sight of their prey
• Long and energy-intensive handling time (includes stalking, chasing,
consuming)
• Thus, optimal strategy is to ‘handle’ only the most profitable prey: the old
and weak
Eaverage
Enew

hnew saverage  haverage
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Optimal Diet Width: Some Insights
• Specialists
– Long handling times, relative to search times
– Owls: mainly nocturnal predators with exceptional hearing
• Short search time, because can hear everything!
• Long handling time, because takes energy to capture and digest prey
• Thus, optimal strategy is to ‘handle’ only the most profitable prey
– Small rodents
Eaverage
Enew

hnew saverage  haverage
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Optimal Diet Width: Some Insights
• Generalists
– Short handling times, relative to search times
– Insectivorous birds
• Searching for insects takes time (not tons, but some)
• Handling (consuming) an insect takes very little time
• Thus, optimal strategy is to consume nearly every insect they encounter
Eaverage
Enew

hnew saverage  haverage
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Optimal Diet Width: Some Insights
• Generalists
– Short handling times, relative to search times
– Raccoons: will eat almost anything (including your trash)
• Searching for food takes time (not tons, but some)
• Handling (consuming) food takes very little time
– Well adapted paws for capturing a variety of prey
– Have strong gut for digesting lots of food types
• Thus, optimal strategy is to consume nearly everything they encounter
– berries, insects, eggs and small animals.
Eaverage
Enew

hnew saverage  haverage
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Specialists and Generalist Predators
Advantages to being a
specialist
1. Avoid interspecific
competition
2. Allows evolution to
overcome chemical defense
3. Allows evolution of cryptic
coloration that matches prey
- mostly for insects on
plants
4. Increases chance of mate
encounter
Advantages of being a
generalist
1. Flexibility in face of
environmental uncertainty
2. Broad diet needed to get all
necessary nutrients and
vitamins
3. Avoid overdosing on any
one toxin - mostly for
animals grazing on
chemically defended plants
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Outline: Behavioral ecology and evolution
• Response to environmental variation
• Theory of Evolution by Natural Selection
– Variation within species
– Balancing Selection
– Behavioral changes via natural selection
– Speciation
– Patterns of Evolution
• Adaptive behavior
– All behaviors have costs and benefits
– Territorial defense
– Optimal foraging and diet width
– Group living (costs, benefits, examples)
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Group living
Potential Benefits Potential Costs Increased foraging efficiency Intraspecific competition for food
Reduced predation
Increased risk of disease,
parasites, and attraction of predators
Increased access to mates
Loss of paternity, brood parasitism
Help from kin, indirect
evolutionary success
Loss of individual reproduction
Evolution of traits that increase survival and reproductive success of kin=kin selection
(Krebs Table 4.1)
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Group living
• Herbivorous herds (e.g.,caribou), schooling fish, carnivores, birds (e.g. starlings), 82
Group living in ospreys
do not school
 school
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(Krebs Figure 4.9)
Group behavior in western gray kangaroos
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(Krebs Figure 4.11)
Group behavior: Starlings
• Near Oxford ‐ England. This was filmed at an Royal Society for the Protection of Birds (RSPB) reserve called Otmoor. • http://www.youtube.com/watch?v
=XH‐groCeKbE
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