Ecology Final Notes

• Competitive Exclusion
  • Two species that use a limiting resource in the same way cannot coexist for long periods of generational time
  • But how similar do two niches have to be before competitive exclusion applies
  • Look at two values
    • D = distance between two niches
    • W = width of a niche
  • Exclusion is likely if d is small or w is large (or both). Lots of overlap leads to lots of potential for competition
  • Changes in environmental conditions or variations in habitats occupied by a single community, can results in a competitive reversal - the
• Disturbance
  • An event that upends a stable habitat, usually making more resources available
  • Intermediate disturbance hypothesis
    • The frequency of disturbance in a habitat explains variation in how likely one (rest in slides)
    • Number of species is highest at intermediate frequencies of disturbance
    • Yards have different levels of flowers
  • When there are very few disturbances, competitive exclusion drives to extinction species that are inferior competitors in those conditions. Only species good in “undisturbed” conditions persist
  • When there are very frequent disturbances, competitive exclusion drives to extinction species that are inferior competitors in those conditions. Only species good in “disturbed” conditions persist
• Ecological and evolutionary consequences
  • Competitive exclusion drives one population to exclusion
  • Natural Selection doesn’t favor quitters
  • Natural selection may favor traits (evolution and/or expression) in both plates that limit niche overlap because this allows competitive coexistence
    • Resource partitioning
    • Maybe via Character displacement
    • Robert MacArthur
      • Similar bird species even in the same habitat (tree) don’t necessarily use the habitat in the same way.
  • Maybe via character displacement (evolutionary change resulting in resource partitioning)
  • Character Displacement
    • Resource partitioning can result in evolutionary changes to organismal traits and life history
    • The phenotypes (including behavior) of competing species become more different over time, educing the competition between species
    • Character displacement- species traits in sympathetic relationships diverge in response to competition.
  • Galapagos Finches
    • Seeds are a limiting resource for the different finch species
    • Beak size determines which seeds can be most efficiently processed
    • To test for character displacement
      • Examine 2 species when in sympatric or allopatric
      • Predict more differences
    • Competition for seeds
    • Selection for divergence
    • Character displacement and likely decreased interspecific competition
  • Competition Exclusion drives one population to extinction
  • Natural Selection doesn’t favor specialization when there are no competitors
  • Ecological Release
    • Release from competition results in niche expansion
  • Predation
    • Introduced predators often decimate native prey
      • Prey are native (inexperienced)
      • Lack a coevolutionary history (no defense)
      • Snakehead fish and brown tree snakes
  • Effects of Introduced Predators
    • Schoener and Spiller studied Anolis lizard predators and the spider prey in the bahamas
    • 12 islands: 4 had lizards naturally, 4 had lizards introduce for the study, and 4 had no lizards
    • On Islands with introduced lizards, 13 times more spider species went extinct than on control islands
    • Density of spiders was roughly 6 times higher on islands without lizards
  • Understanding the effects of predation/parasitism/herbivory on communities
    • Understanding predator-prey dynamics key to conservation efforts, population management, and biological control
• Population Cycles
  • A variety of factors can prevent predators from driving prey to extinction
    • Habitat complexity
    • Prey switching in predators
      • Diet Breadth (diet is a component of the niche)
        • Most predators eat a broad range of prey species, without showing preference
        • Herbivores tend to eat a more narrow range of “prey” species
    • Spatial refuges (where predators can hunt effectively)
      • Sort of intuitive, and a lot like habitat complexity but there may be a refuge (in space or time) where the population can grow free from predation
    • Evolutionary changes in prey population
      • Example: Hariston’s rotifers
        • Algae changes in response to predation
        • Algal genotypes most resistant to predators were poor competitors (Trade offs)
        • At high predator density, resistant genotypes increase, then predators decease
        • At low predator density, the resistant genotype is outcompeted by other genotypes and they increase, Then the predator population increases
  • Habitat complexity
    • Predators and their prey can persist due to habitat heterogeneity
• Ecosystem
  • Community + biotic environment
  • Differences in the abiotic environment lets us understand
  • What are the key characteristics of ecosystems that help determine these differences?
    • What is the simplest way to explain these differences?
      • Energy
      • Temperature
      • Water
      • Nutrients
• The greenhouse effect
  • Earth absorbs solar energy (⅔) and warming up
  • Earth radiates heat
  • Heat radiated from Earth’s surface is absorbed by GHG molecules
  • Atmosphere warms, it radiates heat
  • Some heat escapes to space, some warms Earth surface

-------------------------------------------------------------------------------------------------------------------------------

Exam 1

Hierarchy in Ecology

• Individual
  • Singular organisms
  • Evolution
    • Selection acts on individuals (some increase or decrease in the population)
    • Occurs in Populations
• Populations
  • Set of individual species that interact with (influence) one another
• Community
  • Sets of populations of different species that interact with (influence) one another.
• Ecosystem
  • Communities and the abiotic environment they are in

Evolution

• Evolution - Change in the allele frequency in a population over time
• Mechanisms of Evolutions
  • Non Adaptive mechanisms
    • Mutation
    • Genetic Drift
    • Migration/Gene Flow
  • Mechanisms
    • Natural Selection
    • Sexual Selection
• Color is genetic (a trait evolved)
• Populations interbreed fine (all one species)
• Conspicuous color may protect against predators, and used for female choice and male-male contests

How and Why did Color Evolve?

• What conditions must be met for each possibility to be true?
  • Allele frequency does not change and is still random even if pressured by the environment to evolve.

Asking Questions in Science

• Important and/or Interesting, Testable, Drawing Conclusions
• Important
  • Answering this question is critical to a party of interest
• Very important
  • Answer this question matters to lots and lots of parties of interest
• Interesting
  • Answering this question matters to solving some mystery, learning something unknown
• Very Interesting
  • Answering this question will solve many mysteries, learning many unknown things

Asking a Testable Question

• A testable question - Can be resolved with data that can be accessed objectively
• You want the question to be something original
• Descriptive Natural History - worthwhile, valuable, and important (can be used to document change and compiled to test big ideas)
• Hypothesis Driven Work
  • There is something observable about the world
  • We start with the proposition, “Nobody knows why….” this observable phenomenon occurs/is true.

How to Test an Idea

• 1) Formulate a hypothesis
• 2) Draw testable predictions from the hypothesis
• Identify: Hypothesis or Prediction
  • Usage of these terms is often slightly different among fields
  • This distinction is often lost on even seasoned biologists
  • Many “statements” might be neither a good hypothesis nor a good prediction
• Identify: Hypothesis
  • Proposed explanation for an observed phenomenon
  • The most common challenge
    • Start with an observable phenomenon
      • This is a statement of fact that can be readily agreed upon
  • Can be used to generate any number of predictions
• Identify: Prediction
  • A prediction is simply a statement of expected results
  • Tells us what will happen (Using Numbers)
    • So if we showed your prediction to many people, we should have one description of what will happen in your work.
  • The most common challenge
    • Your prediction is not/cannot be the same as your observable phenomenon

Make a box: Proximate vs Ultimate

• Proximate mechanisms - How a trait works, what detectable changes in the animal precede a behavior or trait expression
  • Neurobiology, endocrinology, genetics, development
• Ultimate mechanisms - Why a trait has evolved, How is it adaptive? Generally, how does variation in a trait influence fitness
• Questions
  • Why do some animals hibernate?
    • Proximate: changes in light trigger hormonal shifts, hormonal shifts reduce heart and breathing rates
    • Ultimate: food is limited in the winter and migration is impractical so hibernation allows survival through the winter
  • Why do plants exhibit phototropism (Bend towards light)
    • Proximate: pigments in plant tissue absorb light change the qualities of cell membranes
    • Ultimate:
  • Why do animals like sweet food?
    • Proximate: stimulates the brain and releases dopamine
    • Ultimate: associated with sugar which is rare and a good source of energy

Evolution

• Evolution - Change in allele frequency in a population over time
• Individuals do not evolve, populations evolve
• Selection acts at the level of the individual
• Populations evolve because things are happening to individuals (they are born, and die, have more or few babies)
• Non Adaptive Mechanisms
  • Mutation
    • Change in the nucleotide sequence of an organism's DNA
    • Ultimate source of all variation
    • Mutation is RANDOM
      • With respect to the selective pressures imposed on the phenotypes they produce
    • Why is it important?
      • Ultimate source of all genetic variation
      • Relatively weak evolutionary force on its own
    • Common Misconception
      • Mutations are not goal oriented, do not arise because they are adaptive
      • Antibiotic resistance seems to exist only where i t is needed most
  • Genetic Drift
    • Change in allele frequency as a result of random sampling
    • Why is it important
      • Limits variation available in a population
      • Washes out selection
    • Differential success via drift is RANDOM with respect to alleles
    • Founder effect - small group of individuals start new population
    • Differential survival and reproduction that might be unrelated to a particular phenotype
      • Natural disasters
      • “Just happens”
    • More important in small population
      • More likely to change in meaningful way
    • Probability of alleles going extinct just by chance declines with the more individuals breeding
    • A small subset of a population is unlikely to exactly match the population as a whole.
    • Founder effect - a random subset starts a new population
      • But……if some alleles are overrepresented because they are associated with migration probability
    • Bottleneck: a random tiny subset survives a catastrophe
      • But….doesn’t count if the alleles were designed to survive the catastrophe
    • By definition Genetic Drift is unpredictable
    • Important because it limits variation available in a population
    • Counters selection
  • Migration
    • What’s migration/gene flow
      • Changes in allele frequency because individuals join or leave the population
    • Why is migration/gene flow important?
      • Can prevent divergence of populations
      • Homogenizes allele frequency among populations
    • Migration can limit differentiation (and adaption)
      • Example: Water snake with and without bands
        • Near Islands

Unbanded is more cryptic (rocks)

Both occur at equal frequency

• • • • • Near Land

Banded is more cryptic (vegetation)

Banded more common

• • • • • With random movement more individuals are coming to the islands while a fewer number are moving to the land.
  • Mutation, Drift, Migration can all influence allele frequency in a population (drive evolution).
  • Drift is unpredictable.
  • Drift and Migration can counter selection.
  • Important to testing adaptive hypotheses
• Adaptive Mechanisms
  • Natural Selection
    • Conditions under which evolution will take place via Natural Selection
      • 1. There must be variation among individuals of a species
      • 2. The variation must be heritable (parents resemble the offspring)
      • 3. Each generation, some individuals are more successful than others.
      • 4. This differential reproduction is due to the variation among individuals
      • Example: didn’t have children because of having hairy knuckles (so no natural selection)
    • Natural Selection is predictable
  • Sexual Selection
    • Evidence for naturally selected traits
      • Individual with the trait (brown) survives to reproduce more often than individuals without the trait
    • Sexually selected traits
      • Individuals without the trait (Huge Tail) survive more often than individuals with the trait
        • But they mate more often
    • Sexual selection explains traits not explained by natural selection
    • Sexually selected traits
      • Attract a mate
      • Wins a mate
    • Selection does not equal perfect populations
      • Imperfectly adapted populations do not provide evidence against natural selection.
      • Selection responds to average payoffs, multiple functions can’t be optimized simultaneously (Fish has larger organ which is better for mating and bad for swimming)
• Mechanisms of Evolutions
  • Mutation - source of new alleles, minor evolutionary force alone
  • Selection - result of differential allele success due to alleles (non random, predictable pattern) Results in adaptation
  • Drift - differential allele success due to chance, decreases variation and unlikely to be adaptive
  • Migration/Gene Flow - change in frequency due to immigration/emigration. Homogenizes populations (often limits adaptation)

Evolutionary Ecology of Virulence

• Virulence - how harmful a pathogen is to its host (the organism that is infected)
  • Applies to any disease or parasite
• Pathogens/parasite populations evolve
• Mechanisms of evolution can explain diversity of parasite traits (virulence)
• What is virulence?
  • Capacity of a parasite to reduce host fitness
  • Fitness - the number of grand offspring an individual produces
• Observed Phenomenon
  • Rhinovirus - mild
  • Dengue - more severe
• For natural selection to act, must be variation within population
• How do we explain variation in virulence?
  • Three Main Hypotheses
    • 1. Non-Adaptive Virulence Hypothesis
      • In the “true” host (i.e the host exerting the most selection on the parasite) virulence is low
      • High virulence comes when this pathogen jumps into a novel host. Presumably many jumps also result in a failed infection, but these are not commonly detected.
      • Variation is result of “accidents”
      • Virulence is due to traits evolved in natural host
      • “Accidental” Infections with no/limited further transmission
    • 2. Based on Natural Selection for the level of virulence
      • 2A. Avirulence hypothesis
        • All pathogens will evolve towards 0 virulence because virulence comes at the cost of transmission
        • Variation is virulence is the result of pathogens just not having hit avirulence yet (getting sick is the result of temporal bad luck
        • Eventually a pathogen will have no effect
        • Virulence comes at a cost to transmission

(Deadly disease vs a Cold) deadly disease spreads less than cold because it kills quickly

• • • • • Virulence reduces parasites own R_0 by decreasing contact with susceptible host individuals
        • Selection favors pathogens with low virulence because they are transmitted more often
        • Interest of host and parasites converge
        • (Recent) harmful parasites in a transitory state of maladaptation
        • Testing the prediction that pathogens evolve to avirulence

Mutualists and commensals may have originally been parasites

Organelles may have originally been parasites

10% of human genome incorporated past viruses

Novel jumps….high virulence (but what are we missing)

Virulence often high after host shift

• • • • • Natural selection and virulence

Typically aggressive strains (faster replication) is more virulent (takes more resources from the host

Within hosts, aggressive strains will outcompete more benign strains

• • • • • New Idea: Virulence might not always come at the cost of transmission

In some cases virulence effects will have a direct benefit for transmission

• • • • 2B. Adaptive trade-off hypothesis
        • Prevailing view incorporating evolution and ecology
        • Virulence has fitness costs and benefits for the pathogen
        • Variation in virulence comes from differences in the trade-off between virulence and transmission
        • Chart

Y = Cost or Benefit

X = Virulence increasing

(Benefit line) The more coughs and sneezing causes more people to get sick

Causes a positive curve which begins to stop increasing in Y direction due to everyone being infected

(Cost line) When you are sick the less likely you are to come to class and people will sit farther away if you show up

Causes positive curve which begins to stop increasing in X direction due to less interactions with people

Cost curve can lower in Y values overall and increase X values

• • • • Questions
        • Some drugs relieve the symptoms of an infection but do not remove the infection itself
        • How might the widespread use of such drugs shape the evolution of pathogens?
        • Masks wearing lowes the probability than an infected individual will infect new hosts (i.e at the same level of virulence transmission is lower)
• Fitness of Parasites
  • Depends on the spread: transmission
  • Basic reproductive number
    • R_0 = number of new hosts infected per original infection
    • Parasites are predicted to evolve such that R_0 is maximized

----------------------------------------------------------------------

Exam 2

• Ewald 1993 (Exam) and Slagsvold and Wiebe 2007
  • Pathogens spread the best when their spread outnumbers their virulence
  • To avoid being destroyed, pathogens will hide in cells without effects
    • STDS

Evolutionary Ecology of Virulence

• Virulence - how harmful a pathogen is to its host (the organism that is infected)
  • Applies to any disease or parasite
• Pathogens/parasite populations evolve
• Mechanisms of evolution can explain diversity of parasite traits (virulence)
• What is virulence?
  • Capacity of a parasite to reduce host fitness
  • Fitness - the number of grand offspring an individual produces
• Observed Phenomenon
  • Rhinovirus - mild
  • Dengue - more severe
• For natural selection to act, must be variation within population
• How do we explain variation in virulence?
  • Three Main Hypotheses
    • 1. Non-Adaptive Virulence Hypothesis
      • In the “true” host (i.e the host exerting the most selection on the parasite) virulence is low
      • High virulence comes when this pathogen jumps into a novel host. Presumably many jumps also result in a failed infection, but these are not commonly detected.
      • Variation is result of “accidents”
      • Virulence is due to traits evolved in natural host
      • “Accidental” Infections with no/limited further transmission
    • 2. Based on Natural Selection for the level of virulence
      • 2A. Avirulence hypothesis
        • All pathogens will evolve towards 0 virulence because virulence comes at the cost of transmission
        • Variation is virulence is the result of pathogens just not having hit avirulence yet (getting sick is the result of temporal bad luck
        • Eventually a pathogen will have no effect
        • Virulence comes at a cost to transmission

(Deadly disease vs a Cold) deadly disease spreads less than cold because it kills quickly

• • • • • Virulence reduces parasites own R_0 by decreasing contact with susceptible host individuals
        • Selection favors pathogens with low virulence because they are transmitted more often
        • Interest of host and parasites converge
        • (Recent) harmful parasites in a transitory state of maladaptation
        • Testing the prediction that pathogens evolve to avirulence

Mutualists and commensals may have originally been parasites

Organelles may have originally been parasites

10% of human genome incorporated past viruses

Novel jumps….high virulence (but what are we missing)

Virulence often high after host shift

• • • • • Natural selection and virulence

Typically aggressive strains (faster replication) is more virulent (takes more resources from the host

Within hosts, aggressive strains will outcompete more benign strains

• • • • • New Idea: Virulence might not always come at the cost of transmission

In some cases virulence effects will have a direct benefit for transmission

• Costs and Benefits
  • Thinking of a trait as having COSTS and BENEFITS, not “net benefits” is a key to understanding how traits/strategies evolve in different habitats
  • The animal at the most optimal benefits and costs will leave the most offspring
  • When in doubt think “kill you quickly” for costs
• 2B) Adaptive Virulence
  • Virulence will evolve to optimal level based on cost-benefit trade off
  • Current level of virulence has been shaped by selection
  • Optimal level of virulence can change, even for the same pathogen
• Vectored Parasites
  • Relatively low cost for immobilizing host
    • Something that bites you (flea, mosquito)
  • Immobilization may even increase transmission (no fly swatting)
  • Lower cost for immobilizing host, so lower cost to transmission at any level of virulence
    • 
• Waterborne Parasites
  • Water system can act as a vector
  • High parasite replication has clear benefits, low costs
  • Adaptations (e.g. Cholera toxins increase dissemination)
  • 
• Where should costs of virulence be high
  • Sexually Transmitted Diseases
    • 
    • Promiscuity rate is predicted to influence virulence evolution
    • Monogamy and low mating rates should select for less virulent pathogens due to reduced transmission potential
    • 
• Broader message
  • Any trait has costs and benefits
  • Costs and Benefits depend on trait value
  • The shape of these relationships determine variation in the optimum

Foraging

• If behaviors evolve, they must have a genetic basis (dog breeds act differently)
• Nature vs Nurture
  • Why do you care whether behaviors have some sort of genetic basis? As an evolutionary biologist or ecologist
    • Lead making people assholes/mentally worse
  • Why is the answer to the nature/nurture “debate” important to the general public
  • What are the potential implications of your answer
  • To evolve, traits must have a genetic basis
    • There’s almost never a gene “for” a trait
    • We can, experimentally, demonstrate genetic effects, including on behavior
  • Common Garden Experiment
    • Two populations that are different in a trait (different color or food habits, etc)
    • Grow them up in the same environment and then question if they are different or not
    • If the trait is different then there is evidence for the trait to be genetic
• The Four F’s of Behavior
  • Feeding
    • Key Assumption: Selection favors individuals that maximize benefits and and minimize costs
    • Costs:
      • Energy usage
      • Exposure to predation.
      • Parasite Ingestion
      • Toxins (not food!)
    • Benefits
      • Calories
      • Nutrients
      • Mates (directly)
    • Why Study Foraging?
      • Costs and Benefits are measurable
      • Animals eat often (lots of chances to test theory)
      • Body of theory is broadly applicable
    • Other optimality problems
      • Fighting/Fleeing
        • Is this mate/territory worth fighting over
        • Should I fight or flee?
      • Life History
        • Should I reproduce now or wait until I’m older
        • How many mates (polygamy or monogamy)
        • How many offspring (a few big ones or many small ones)?
  • Fighting
  • Fleeing
  • Fucking
• Study of Foraging
  • Key Assumption: Natural selection favors individuals that maximize energy intake and minimize costs
    • Those that maximize intake and minimize costs will have greater reproductive success, on average than less efficient individuals
  • Cutting out the middleman
    • Ultimately, the utility of food is reproduction but sometimes this is more direct
      • Tidbitting - male uses food to lure over a female
      • Nuptial gifts - the bigger the food given the longer they can mate
      • Courtship feeding - food directly influences reproductive performance of female
    • Do males mimic food?
      • Female guppies benefit by consuming fruits rich in, among other things carotenoids
      • Female sensory system is tuned to detect orange (males grow orange spots to mimic food)
  • Foraging Behavior steps
    • 1. Locating Food
      • Develop a Search Image
        • Blue jay focuses on the majority (blue butterflies) and ignores minority (red butterflies)
        • Switching the two means the bird will focus on red butterflies and ignore blue butterflies
      • Get Help from others
        • Birds find the combs and Humans rip honeycombs out of trees and birds eat the larvae in combs

(lowers costs of searching for combs and lowers costs of honey being contaminated)

• • • 2. Capture Food OR
      • Get the prey to come to you (cuts predation risk)
        • Spider web
        • Angler fish lure
      • Get Help
        • Lions hunting in a pack
    • 2. Selecting food then Capture Food
      • Fox could eat grasshoppers or rabbits
    • 3. Consuming Food
      • Having strong jaws are costly because they are so powerful
      • Vultures evolved to have featherless heads so blood and guts don't stick (like rolling up sleeves so things don’t stick on to gross stuff)
      • If two tadpoles are in a pond and one eats shrimp, it will develop a beak, big jaw muscles, and shorter stomach, the one that doesn’t eat the shrimp it will not develop these features
        • Short Gut: Benefits - food processes quickly
        • Big Gut: Benefits - allows food to be processed longer
        • NOT TWO SPECIES
        • 

Bigger line is benefits outweighing costs

• • • Anything that increases the efficiency of any step can increase fitness
    • Traits can lower costs or increase benefits at ANY step of this process
• Theorems of Foraging
  • Optimal prey choice
    • “What do you eat?”
    • “Natural selection favors individuals that maximize energy intake while minimizing costs (energetic costs, predators, toxic meals, etc)”
      • An animal should forage, when ON AVERAGE, Benefits - Costs are largest
    • Two potential food items
      • Energy (nutrient) content (benefit)
      • Handling time (cost)
    • Energy (nutrient) content
      • Typically, and most simply, quantified in terms of calories or energy
      • Hereafter E1, and E2
        • Calories aren't all that’s important
        • Easier to talk about this
        • Can be modified (fitness value of a meal)
    • Handling Time
      • Time needed to capture and consume prey
      • Hereafter h1, and h2
    • Profitability (Math on Exam)
      • (Energy (nutrient) content)/(handling time)
      • OR
        • E grasshopper/ h grasshopper and E rabbit / h rabbit

E1/h1 and E2/h2

• • • • • One with higher number is better
      • Comparing two items is straight forward
      • Oystercatcher
        • Bigger muscles contain more calories but require more energy to open
        • Shell size (x axis) is correlated to Energy (y-axis)
    • Build a model
      • Model A - foragers just care about calorie intake
        • Handling time increases with shell size
        • Optimum is when benefits are greater than costs
      • Model B - Foragers prefer medium sized shells
        • Results support this model
  • Ideal free distribution
    • Predicting how a group will be distributed in a habitat
    • Predicting the number of individuals per patches
      • Looking for an equilibrium
    • Popular stuff has long line
    • Unpopular stuff has no line
    • Trees Examples:
      • One tree has 10 fruits per sq ft
      • Another tree has 5 fruits per sq ft
      • The fruit would end up sq ft away
      • Individuals will try both trees and go from tree to tree
        • The happier they are the less likely they are to go to other tree
        • Equilibrium will be when more individuals move from 10 to the 5.

“Line is too long, I’m going to other one”

• • • Assumptions
      • Foragers have perfect information about patch quality
        • “Know how much fruit is where”
      • Have perfection information on number of individuals per patch
        • Happiness will rise and fall in linearity with number of individuals waiting
      • Unconstrained movement
        • Not a lot of limits and doesn’t take energy
    • Everyone acts in their own interests and if assumptions are met then everyone is getting equal return.
  • Central place foraging
    • Most animals have a home. So they leave from and return to a central place
      • Different from marginal value theorem because animals have a return to
        • Travel time is a factor both share
    • This drives costs and benefits, and thus optimal choice
    • Key Predictions:
      • Load size increases as distance away from central place increases
      • Food preparation (lowers the cost of travel with the food) increases when the patch is far away
      • More likely to prepare food when the patch is far away
        • Bulking up and packing food that’s not available from home (Kyle and kitchen cooked chips)
        • NOT EATING WHEN FAR AWAY, animals will bring the food back to share or store, (bird brings mouse back to nest to feed to babies)
    • Maximizing Benefits
      • Food will be depleted close to “home base”
      • Travel time might not be worth it sometimes and animals may look for scraps close by and when those are depleted they might spent more travel time to find food
    • Travel Costs
      • Include time, energy, and opportunity costs (0 at home)
      • As you move farther away
  • Marginal value theorem
    • Doesn’t cover a single patch but an average patch
    • 
    • 
      • Marginal gain rate (EXAM, WHERE IS MARGINAL GAIN RATE THE HIGHEST AND LOWEST)
      • The highest is the tangential line at the beginning and the lowest is at the end
    • Slope is the difference of the time spent and not spending time
    • Optimal choice of how long to STAY in a given patch depends on costs to reach next patch
      • Solution: the optimal (best) duration for STAYING is defined by the tangent to the gain function from Tt (travel time)
    • Consumer quits early if time spent in patch is less than tangential line of travel time.
    • Consumer quits too late if time spent in patch is greater than the tangential line of travel time
    • Graphically you can see there is no real world solution (one that touches the cumulative gain curve) that produces a steer slope: all other slopes are shallower.
    • Marginal Value Theorem: 3 components
      • 1. Travel time to next patch
      • 2. Richness of the average patch (shape of cumulative gain curve)
      • 3. Optimal time in patch
      • 
    • What happens when we increase travel time
      • Stay longer to reach optimality
    • What happens when we vary patch richness
      • Spend more time in longer patch (easier to get more)
      • Not poor patch because 0 is reached much quicker
    • Marginal Value Theorem Assumptions
      • Foragers know shape of cumulative gain curve (average richness)
      • Foragers know distance between patches
      • Unit cost of travel = unit cost of harvesting
    • A lot harder to do in lab
    • How long foragers stay in a patch (amount of time)
    • Example: Apple trees
      • Time spent is less in an orchard than compared to a tree in a field
        • 

-------------------------------------------------------------------------------------------------------------------------------

Exam 3

• EXAM QUESTIONS
  • Beetle larvae grow in the lawn, what do I need to know for why are they big when they are not beetles?
    • What are the costs of transitioning now vs later
  • Why do some things not reproduce until later
    • Trade off of reproduction time and larger offspring
  • Female fruit flies don’t live as long as virgin female flies, what fundamental life assumption explains this
    • Reproduction is costly
  • If breeding in a small size is more costly than a larger size what should that select for
    • Reproduce at an older age.
  • True or False, Natural selection favors individuals that total with current reproduction
    • False
  • Natural selection favors survival of the species (ALWAYS FALSE)
    • False

Multi-layer application of foraging theory

• Marsh tits carefully hide individual seeds
  • Husks were covered with radioactive coating, these tagged seeds were put on a feeding tray, these were then tracked and were on average, 7m apart
  • Hypothesis: distance has evolved to maximizes the value of hidden caches
  • Prediction: spacing <7m increases theft rate, OR 7m is the optimal distance
    • If they are spaced less than 7m, they get eaten and higher than 7m they lose the value (x and y chart)

Extrinsic Constraints (about the environment)

• Fewer lizards are active and more are hiding in wooden blocks when predators are present

Intrinsic Constraints

• Constraints on optimal foraging (cognitive)
  • Foraging theory gives animal brains a lot of credit
  • The Rescorla Wagner Model
    • Predicts the strength of an association comes not from the value of the stimulus (Food) but the difference between previous state and state after food
    • Implications for optimal foraging?
    • Sterlings received food after short delays (10s) when well fed and longer delays (10-17s) when hungry
      • Delay duration associated with color
      • Sterlings preferred colors associated with longer delays and therefore with food reward in hungry state
    • Pigeon trained on operant task
      • In one set of tasks, had to work harder (20 pecks vs 1 peck) to obtain the same amount of food
      • Each set of tasks associated with a different stimulus
      • Preferred stimulus is associated with harder work (longer handling time
• Discounting
  • “I’ll give you $1 today or $1.01 tomorrow or “I’ll give you $1 today or $10 tomorrow
  • Spatial and temporal discounting functions in tamarins and marmosets
    • Cotton-top tamarin
      • Ranges over large distances feeding on insects
    • Common marmoset
      • Feeds on tree sap
    • Who has a steeper discounting function for travel distance?
      • Cotton-top tamarin
    • Who has a steeper discount for time delays?
      • Marmoset
    • Tamarin will travel for larger reward, marmosets wont
    • Marmosets are twice as patient

Constraints on optimal foraging

• Brains (the strategies they employ) evolve to maximize energy intake
• “Rules of thumb” are subject to trade-offs like anything else

-------------------------------------------------------------------------------------------------------------------------------

Life History

• Life History
  • How does an individual allocate these resources to maximize fitness
  • Key Assumption
    • By definition, natural selection favors individuals that produce the most grand offspring
    • Selection on life history favors individuals that produce offspring that survive to reproduce at the lowest cost (in terms of other offspring)
    • Maximizing
      • Reproductive value - current output + future output
  • Life History theory
    • An organism’s “life history”
      • Set of age or stage-specific traits…
    • Observed phenomenon
      • Variation in life history traits: time to maturity
        • Mouse, 2 months vs Gorilla, 2 years
    • Relevant questions for formulating hypotheses
      • Components of life history (not exhaustive)
      • Are there patterns to this variation?
    • Reproductive value = current output + future output
      • Residual reproductive value (RRV)
      • Breed ASAP
        • Current output = low
        • Future output = low
      • Hold off:
        • Current output = 0
        • Future output = high (if survive)
  • When to reproduce
    • Juvenile (no reproduction)
    • Adult (reproduction)
    • Senescence (no more reproduction)
  • Life stages (VERY generally)
    • 1) Not really doing anything (no growth)
    • 2) Growing, but not free living (animal in womb or egg)
    • 3) Free living, not reproductive (juvenile)
    • 4) Reproductive
    • 5) Not reproductive (maybe)
    • 6) Dead
  • When to transition
    • Optimality
      • Given my current phenotype/circumstances, should I continue to grow or switch stages
    • Trade offs
      • I can’t be in both stages at the same time
    • How does timing of hatching influence survival and (eventual) reproduction
      • Potential habitats
        • Frog staying in egg or moving to pond
        • Egg might be safe but fewer resources
        • Pond might be risky but has many resources
        • (more in slides)
  • Life-history decisions
    • A proximate story
    • Tree Frog laying eggs
    • How does timing of hatching influence survival and (eventual) reproduction?
    • Fitness prospect is at 0 until frog has ability to leave egg
    • Two things can be true at the same time
      • When you detect a predator, the cost of staying in the egg has changed
      • Populations and habitats may have a different average
    • Probability of success in water has not changed when snake is present
    • Probability of success in the egg has changed when a snake is present, changing the optimal decision
      • (Best of a Bad Lot) - making the best of a bad situation
    • When to leave the water (Benefits)
      • More you eat, the bigger you are
      • The bigger you are the more likely you are to survive on land
    • Probability of success (at a particular size) out of water hasn’t changed
    • Probability of death (costs)
• Ephemeral Habitat
  • Habitats that exist for a short time (a small pond)
  • Benefits
    • Lower predation risk
  • Costs
    • Doesn’t last long (dries up quick and kills tadpoles, etc)
  • How should declines in aquatic food abundance predict the timing of metamorphosis?
    • “Get out of there”
  • Spadefoot toads
    • Breed in ephemeral habitats
    • Variation in how likely ponds are to dry
  • The species from the most ephemeral habitats vary in size, but not age at metamorphosis
    • Everything dries up at the same time and food is abundant
  • Species from less ephemeral habitats vary in both
    • Habitat may dry or cause tadpoles to emerge quicker than others
• Plasticity
  • Expression of a trait (morphology, physiology, behavior) in response to environmental variation
  • The same individual could express a range of different phenotypes
    • Hot peppers grow to become hotter as a protection by removing leaves
  • The same individual could express a range of different phenotypes
    • This range can evolve
  • Plastic trait expression
    • An interaction between genes and the environment
      • Example: Body size - genes determine range and response to nutrition, but nutrition is necessary
        • Teacup pig is a staved piglet
  • Plasticity: why is it good?
    • No plasticity in skeleton growth
      • Puppy given little food will become starved
      • Puppy given a lot of food will become obese
    • Plasticity in skeleton growth
      • Small food leads to smaller dog, normal sized, or starved dog
      • Large food leads to bigger dog or obese dog
  • Life history strategies on two levels
    • 1) Evolutionary…..(in slides)
    • 2) Ecological time (Individual) responses to average payoffs of the current conditions
      • Ponds sometimes dry up so being able to to speeded up when those cues are sound is a winning approach
• When to transition
  • Life stages
    • Depends on the relative costs and benefits of your current phenotype in each potential life stage
    • Plasticity allows you take advantage of (maximize the benefits of) unknown (or unknowable) variation
• When to reproduce
  • A very loose analogy
    • You would like to buy a house
    • You start saving money
    • Once you buy, no more saving
    • Longer you wait from a certain age you can buy a better house
      • Child buys tent, elderly person buys mansion
    • House is analogy for body
    • Longer you wait the less time you’ll be able to use it
  • Fish
    • Eggs produced
      • Smaller you are the less eggs will be produced
      • However the smaller you are the less likely you are to get eaten
    • Events per Lifetime
      • Decreases with the larger size you are/longer you wait
  • Trade-offs
    • How big do you get before shifting to reproduction
    • Breed ASAP
      • Will never have large outputs
    • Hold off
      • May never breed, won’t live forever
    • IMPOSSIBLE to maximize both parameters at the same time
      • Can’t be maximum size and breed immediately
      • Resources are finite
      • Resources spent on one thing cannot also be spent on another
      • Another way to think about this is that the two parameters are negatively correlated
      • Big House, Fast Car Theory
        • Resources are larger for rich person (owning big house and fast car) even though resources are finite for most
      • Another kind of trade-off that is central to life history evolution
        • Quantity vs Quality
• Quantity vs Quality
  • Often measured as the number vs size of offspring
  • Sunfish
    • 200 million tiny eggs
  • Dolphin
    • 1 calf (35-65 lbs)
  • Egg size- Egg number trade offs in fence lizards
  • Things to Know
    • Larger eggs - fewer offspring
    • Larger egg- larger young - better escaping predators, but takes longer time to hatch
      • (more likely when more predators)
    • Trade-off between egg size and time to hatch
    • QUESTIONS FROM PAPER ON TEST
    • Lizard Questions
      • How many offspring are being compared? Which has the highest and lowest predation pressure? (EXAM)
    • Quantity and Quality in Plants
      • Think about how many seeds and largest seeds and which has the most per unit biomass
      • 
  • Lack Clutch Size
    • Hypothesis: Avian clutch size has evolved to match the maximum number of offspring parents, can, on average, rear independence
    • Prediction: The clutch size birds lay is the clutch size that maximizes surviving offspring on average.
    • Experimentally enlarged bird clutches
      • 1) More current offspring
      • 2) Fewer offspring next year
      • 3) Lower survivorship until next year
• How long to live: Trade-offs
  • Impossible to maximize both parameters at the same time
  • Reproduction is costly
    • So given this, you cannot maximize reproductive value and longevity simultaneously
    • The lower a bird mates per year the higher the likelihood they survive
    • Hypothesis: Reproduction is costly in brown anoles
    • Predictions: Surgically removing eggs will increase performance and survivorship
      • Females with eggs removed can run faster and increase stamina
        • It also increases survivorship
  • Current vs Future Reproduction
    • The shape of the relationship (Trade-off) between current and future reproduction matters
      • Having an offspring now costs you lots later, so you should wait
      • Slope = -1: 1 offspring now costs 1 later. Should spread out reproduction evenly
      • Breeding some now is ok, breeding lots might be bad (in middle)
      • 
    • Parity: Current vs future reproduction (How many times reproduce per lifetime?)
    • Organisms that reproduce once and then die: semelparous (monocarpic in plants)
      • (salmons, mayflies, etc)
    • Organisms that reproduce repeatedly: Iteroparous (polycarpic in plants)
      • Bluegills, mosquitos, etc
• Thought Experiment
  • NOT REAL
  • Darwinian Demon (Reproduce with no trade offs)
    • Any age, reproduce all the time and immediately
    • Have lots of offsprings
    • Live forever
  • Tie in to competition/population growth
    • Exotic species are free from trade-offs imposed by the environments
      • (predators, parasites, competitors)
      • Animal introduced into new environment (most likely to die but some end up in very good situation) (Asian Carp)
    • Tie in to sexual selection
      • Trade-offs might come from other things in your environment
        • Testosterone makes you vulnerable to parasites
      • When parasites are present, being “sexy” puts you at risk for parasites and costs (eventually) exceed benefits
      • If there are no parasites, there are not as many costs to be “sexy” and a new mean value is favored
• Life-History Diversity
  • Life History Evolution
    • All else being equal: Reproduce early, reproduce many (high fecundity)
    • However there is a diversity of complex life cycles on fast-slow continuum, Proximately, this comes from the simple fact that it typically takes longer for larger organisms to develop and mature
  • K vs r strategies
    • K-strategies
      • Slow development with delayed maturity
      • Large adult size
      • Reproduce rarely
      • High parental investment/offspring
      • Long Lifespan
    • R-strategies
      • Fast development with early maturity
      • Small adult size
      • Reproduce often
      • Low parental investment/offspring
      • Short lifespan
  • The ultimate (evolutionary) cause of r vs K strategies is
    • R vs K selection
      • Natural selection can vary across space and time and favor one strategy or the other
    • K selection
      • Population is near carrying capacity (k)
      • Competitive ability of offspring explains fitness differences among individuals
      • Generally, persistent, stable habitats (or those in which resources are limited and subject to competition)
    • R-selection
      • Population is growing rapidly, resources not limiting
      • Quantity (not quality) of offspring (children, grandchildren, great grandchildren) explains fitness differences among individuals
      • Often, disturbed or temporary habitats (those in which nobody is already using the resources)
    • R vs K strategies: consequences
      • Population growth
        • Species shaped by r-selection have rapid population growth
      • Example:
        • We colonized a new planet with no life forms and plant wheat
        • Can we predict what will happen to populations?
        • Population of mice increases quicker than humans
        • Once we hit max wheat, mice population decreases while humans keep increasing due to us killing mice for wheat
• Natural selection
  • Group Selection
    • Why are many animal species strongly territorial?
      • Group selection answer
        • Helps over taxing the habitat (incorrect)
      • Individual selection answer
        • Because self promoting individuals are hogging land (attracting more mates, breeding more successfully
  • Why is aggression so frequently ritualized (like roaring and dueling red deer)? That is, why is it so stylized that rivals tend to not injure one another?
    • Group selection answer
      • To avoid injuring fellow group members
    • Individuals selection answer
      • Because rivals punch back
  • Why do animals live in flocks, schools, and herds?
    • Group selection answer
      • To facilitate censuring of local population density (followed by reproductive restraint)
    • Individual selection answer
      • For many selfish reasons such as less predation risk
  • Why do females spend so much energy choosing mates
    • Group selection answer
      • To ensure survival of the species
    • Individual selection answer
      • To ensure the survival of their offspring
  • Altruistic behavior: one that reduces an individual’s fitness and raises the fitness of another individual (or other individuals)
    • Populations (or species) with high levels of altruism will have less conflict and thus outcompete selfish populations
      • Is this true?
        • Yes, literally communism
  • When everyone cooperates, the overall productivity might be higher
  • Think about all the energy that is spent in competition
    • On advertisement?
  • The problem with group selection
    • Populations (or species) with high levels of altruism will have less conflict and thus out compete selfish populations BUT in every generation individuals producing more offsprings will leave more (look for rest in slides)
    • All mutation arise first in the individual
    • What happens if the gene helps the group survive, but harms the individual
    • Selection acts most powerful (rest in slide)
    • Altruistic Behavior
      • One that reduces a gene’s fitness and raises the fitness of another gene
        • Kim selection
    • Other major mistake of group selection
      • Never testing the assumption of “reduces a gene’s fitness
  • Kin selection
    • Phenotypic vs genetic altruism
      • Ground squirrel
        • If it sees a predator it can either issue an alarm call
        • Unique prediction of kin selection

Individuals should call more relatives then around non relatives

• • So in summary genes that make individuals more likely to behave altruistically will decrease in frequency
    • Unless…those altruistic behaviors are directed at other copies of the same gene
  • Mutation is always RANDOM
• Relatedness
  • Coefficient of relatedness
    • Probability that two individuals share an allele because of common descent
• Population Ecology
  • Population - group of individuals of a single species in one area
  • Population Ecology - study of characteristics, growth, and dynamics of populations
    • Properties beyond individuals
      • Number at a time
      • Density
      • Sex Ratio
      • Age Distribution
      • Population inputs and outputs
      • Dynamics - change over time
    • Emergent properties of a group of individuals
      • What determines the rate of increase in populations
      • What limits population sizes
  • Population growth and regulation
    • Ecological Maxim - no populations can increase in size forever
    • Resources are finite
    • Energy is finite
    • Organisms are physiologically constrained
  • What determines population sizes
    • Nt = N0 + Immigrants - Deaths - Emigrants
    • Nt = number at a later time
    • N0 = originated number
  • Births and Deaths
    • Growth rate [R] = (Births + Immigrants) - (Deaths + Emigrants)
    • Mean number of offspring produced
    • Probability of death (proportion that die)
    • Changes with age
  • Life table
    • Provides a summary of how survival and reproductive rates
  • Cohort life tables
    • Follow all individuals birth to death
  • Static life table
    • Counts current individuals (must be known age) in a population, assumes birth.death rates have been constant throughout time
  • Survivorship curves
    • Tracks mortality
    • Type 1 - high survival rate the whole life
    • Type 2 - Constant survival rate the whole life
    • Type 3 - high mortality rate at young age, high survival rate later in life
    • Can Vary
      • Between males and females
      • Among populations of a species
      • Among cohorts that experience different environmental conditions
  • Real survivorship curves
    • Often combinations of the idealized survivorship curves
    • Typically high mortality rate in life and accelerating mortality rate later in life
    • Mid life spikes in mortality often result from sexual maturity and competition for males
    • Possible to build for extinct species and makes inferences about populations
      • Albertosaurus
• Age Structure
  • We can graphically represent age structure shape
  • 
    • Top is Post-reproductive
    • Middle is Reproductive
    • Bottom is Pre-reproductive
  • Shapes
    • Triangle
      • There are more individuals in pre-reproductive ages than reproductive age classes, If more individuals will be reproducing in the future than are currently reproducing, will the population in the future be larger, smaller, or the same? (SAME)
    • Arrowhead
    • Inverted Arrowhead
      • There are more individuals in post-reproductive ages than reproductive age classes than in pre-reproductive age classes. If fewer individuals will be reproducing in the future.
  • How is this predictive capacity used?
    • Conservation Biology (one example)
      • Understand individuals species
      • Compare species
      • Etc
    • Insurance having different rates based on age
• What observed phenomenon does the feeding constraint hypothesis explain
  • Young nestlings in an asynchronous will starve and die
• What is the Feeding Contrast Hypothesis in your own words and phrased as a hypothesis
  • Young Nestlings starve because parents bring back larger food which nestlings cant eat
• Why are large prey less profitable than small prey for small nestlings
  • They require more energy to eat
• How would you expect patterns to be different if parent birds were not central place foragers? For example, if they carried nestlings with them?
  • Profitability of large food would be larger than it normally was

-------------------------------------------------------------------------------------------------------------------------------

Exam 4

• Population Growth
  • Central Question
    • How big will a population of a given size be in some point in the future
    • Estimate: N_t+x
    • Using: N_t, growth rate
  • Two general families of population growth
    • Exponential Growth
      • No limits on population growth
        • Makes sense when exotic species finds success in new habitat (Asian Carp)
      • Population size changes by a constant ratio over time (no per capita increases in growth rate)
      • Population is “picking up steam” because new reproductive individuals are entering the population (not because each is having more offspring)
      • Abundant resources (also lack of competition)
      • Buffalo curve would be steeper if life history was different
      • Per Individual birth (b) and deaths (d)
        • Instantaneous birth rate “b”

All births in population (B) - birth per individual (b) * number of individuals (N) or b=B/N

• • • • • Instantaneous death rate “d”

D=dN or d= D/N

• • • • Per capita rate of increase ( r ): the contribution each individual (on average) makes to the growth of the population at each instant in time
        • (r = instantaneous birth rate - instantaneous death rate
        • (r = b-d
        • If r = 0, no growth; if r>0 growth if r<0, shrinking
        • Exponential growth equation

(N_t)(N_0) (rest in slides)

• • • • (r - selection
        • Resources not limiting (doesn’t mean infinite, just means they are limiting for this population at this time
        • Quantity (not quality) of offspring (children, grandchildren, great grandchildren) explains fitness differences among individuals
        • So selection on individuals acts in a way that maximizes r in a population
      • (r just has to be in units of t (if you want to look at t in years then growth needs to be in years)
      • Two Kinds of Exponential Growth
        • Continuous
        • Discrete (aka Geometric)

Population changes via discrete pulses of new individuals

Constant ratio of increase at each time step

Finite rate of increase = λ

• • • • Unlimited exponential growth unrealistic
        • Growth without limits is physically impossible
        • For short periods populations may follow exponential growth
    • Logistic Growth
      • Goes flat at carrying capacity
• Mechanisms that regulation population growth
  • Natural populations do not routinely explode. Why?
  • Hypotheses
    • Density Independent population growth
      • Growth rate varies over time and/or space, and overall averages
    • Density dependent population growth
      • Growth rate declines as N increases
      • If population size grows, r goes down, then if N goes down, death rate must increase or Births must go down
  • Categories of the things that influence survival and population growth
    • Density independent
      • Factors that shape births and deaths of individuals but are not related to the number of individuals in the population
    • Density Dependent
      • Factors that shape births and deaths of individuals that are directly related to the number of individuals in the population
• Density Dependant Mechanisms
  • Resource Depletion
    • Resource - something necessary for survival and reproduction
    • As N increases resources per capita availability decreases
    • May reduce b
    • May increase d
  • Interference
    • Interference - direct harm of one individual by another
    • As N increases, encounters and aggression increases (more people in a bar)
    • May reduce harm/waste of time.
    • May increase d: harm/cannibalism/waste time
  • Predation/Parasitism
    • As N increases attacks or pathogen transmission may increase
    • Predators attack more numerous prey
    • May increase d
    • May reduce b (time spent hiding time invested in defense
  • Emigration
    • Leave when it gets crowded
    • As N increases proportion of population leaving increases
• Logistic population growth
  • Shaped limits to growth, population may stabilize at a maximum size, the carrying capacity, K
  • Often, population increases rapidly (exponential growth) then stabilizes at the carrying capacity, K, (maximum population size)
  • Things are in exponential growth until a freak accident (natural disaster) and are then in logistic growth
  • Even if food is 4 times the size it doesn’t mean carrying capacity is 4 times the size due to other factors such as interference
  • Equilibrium - a relatively stable population sizes that changes little over time
• Carrying Capacity
  • Carrying capacity is a feature of the environment and can change
• Community Ecology
  • Community - a group of actually or potentially interacting populations in the same location
  • Grouped by
    • Shared Environment and
    • Network of influence each population (species) has on others (interactions)
  • Way we determine how species interact with each other is how they affect the populations growth rate of each other
  • Questions in community ecology
    • Why do some species contain more species than others?
    • Does species A influence the abundance of species B? How?
  • Real communities are dynamic and interconnected
  • Borders of a community often set by the research question
  • Definity the community: common subdivisions
    • Taxonomic affinity - all closely related species in a community
      • (Example: all birds)
    • Guild - group of species that use the same resources
      • (Example: all animals that rely on floral resources for food)
    • Functional group - species that function in similar ways, but do not necessarily use the same resources
      • (Example: wasps, birds, and bats catching stuff in the air)
    • Trophic level: groups of species that obtain energy in similar ways in the community
      • Green (living) Food Webs
        • Primary Producers
        • Primary Consumes
        • Secondary Consumers
        • Tertiary Consumers
      • Brown (Dead) Food Webs
        • Detritus
        • Primary consumers
        • Secondary Consumers
        • (Another one in slides + definitions)
  • Richness, Evenness
    • Species richness - number of species (S)
    • Species evenness - relative abundance (E)
      • Maximal when all species are equal
    • Species Diversity - includes number, but also abundances of species (E + S) many different metrics used
  • Measuring Diversity
    • Issues for a budding biologist
      • Numerous different measures
      • Single attribute (richness diversity evenness) describes complex community structure
      • Valuable information thrown away
  • Dominance diversity plots
    • Geometric model - species sequentially take a set fraction of available resources, abundance proportional. Rare.
    • Broken Stick model - high evenness rare.
    • Log Normal Distribution - few species very commonly, few extremely rare, most intermediate, common pattern
    • Log series distribution - a few species dominate but most species have low abundance
  • Biodiversity at multiple scales
    • Alpha Diversity - with a local habitat unit
      • No set definition of local
    • Beta Diversity - between local habitat units
      • Number of species represented in only one of two habitats you are comparing (beta diversity is calculated between two habitats)
      • Can only be calculated between two total units
      • Calculated by what they don’t have in common
    • Gamma Diversity - total diversity of all habitat units in a landscape
• What Determines whether a species will occur in a community and whether a population of that species can persist
  • 1. It can't get there
  • 2. Once it's there, it might not be able to persist
• Getting There: Dispersal links populations
  • Dispersal - movement of an organism from birth place to another location
    • Immigration - movement into a new area
    • Emmigration - movement out of an area
  • Why does an individual disperse?
    • What are the costs and benefits?
  • What kinds of selective pressures favor dispersal?
    • What are the costs and benefits?
  • Organisms vary in their ability to disperse
• What determines where a species is found
  • Dispersal limitation - the inability of an organism to reach a suitable habitat.
    • Example: Hawaii only has 1 native mammal, the hawaiian hoary bat.
  • Abiotic factors
    • Moisture, temperature
  • Biotic factors
    • Species distributions are affected by herbivores, predators, competitors, parasites, and pathogens
  • Interaction of abiotic and biotic variables
    • Abiotic factors for example, can make individuals (and thus the population) more sensitive to biotic factors
    • Biotic factors could also make it easier for individuals (and thus populations) to exist in challenging abiotic environments
  • Some species can tolerate broad ranges of physical conditions, others have narrow ranges
• What determines where a species will occur in a community and whether a population of that species can persist?
  • Something might be able to get there, but once it’s there, can’t live (so there's no population)
• ALLEE effect - if something is rare it struggles heavily to find a mate making the population hard to exist
• Source-sink
  • More deaths than births however the species does not go extinct
  • Place is good and population is growing in that place
  • Bloomington - Normal is a small place, trees grow in the middle of a sea of corn
    • Where’s the source?
    • Where’s the sink?
    • Does it depend on the organism?
• The Niche
  • A set of factors or conditions (abiotic and biotic) that define the space in which an organism can survive and reproduce
  • Defined for a species, and can be used to predict abundance, survival, growth, reproduction
  • A niche axis is one gradient
  • Niches explain relative abundance across gradients
• Fundamental Niche
  • Full range of environmental conditions in which a species COULD exist (multi-dimensional)
• Realized Niche
  • (usually) narrower set of conditions where species ACTUALLY found
  • Picture of graph in slide show
• Fundamental vs Realized Niche
  • Can the organism tolerate the conditions? (physiological filter)
    • Fundamental Niche
  • Why is the realized niche different from the fundamental niche?
• Species Interaction
  • Something that can explain species distribution
  • The way we know how species A interacts with species B is how their populations are affected
• Competition
  • Both species A and B are harmed
• Amensalism
  • The interaction harms one species (individual) and does not affect the other species (individual)
    • Example: Clydesdale horses stomps rabbits and grass
  • How is the population growth rate (births - deaths) affected by the interaction with the other species
  • How does the species interaction shape the distribution (and population viability) of each participant
• Symbiosis
  • Living in an intimate association
  • Symbioses may be
    • Exploitative (parasite)
    • Commensal (example: skin bacteria)
    • Mutualistic, but mutualisms are not always be symbiotic
• Commensalism
  • The interaction helps one species (individual) and does not affect the other species (individual)
    • Digging in a garden exposes worms which robins then come down to eat
  • How is the population growth rate (births - deaths) affected by the interaction with the other species
  • How does the species interaction shape the distribution (and population viability) of each participant
  • Commensalism: substrate for growth
    • Common form of commensalism
      • Example: lichens that grow on trees or bacteria on your skin
      • Example: Barnacles on whales
  • Cattle egrets
    • Moved to north america from south america due to the introduction of cattle and other large hoofed animals which south america lacked
• Mutualism
  • Can be facultative or obligate
  • Obligate - the interaction is required for survival and/or reproduction (of a partner)
  • Facilitative - interaction, though beneficial, is not absolutely required
  • A pair of mutualists may compromise of any combination of obligate and/or facultative mutualists
  • May be specialists (only right partner species will do) or generalists (“any” partner species will do)
• Coevolution
  • When two populations interact, traits may evolve in response the the characteristics of the other population if it impacts an organism reproduction (e.g reciprocal evolutionary processes)
  • Over time reciprocal evolutionary processes can lead to specialization: the interaction of a species with a limited number of other species
    • This does not always result in mutualism (e.g. herbivore and plant defense interactions; parasite and host interactions)
    • Example:
      • Trait Species 1 (Plant)
        • Toxicity of chemical defense
      • Trait Species 2 (Herbivore)
        • Resistance to toxicity
      • This is a cycle that repeats
• Types of mutualisms
  • Trophic mutualism - partners trade food/resources for food/resources
    • Trophic mutualism plants and mycorrhizal fungi
      • The fungi increases the surface area for the plant to take up water and soil nutrients
      • Plant gets: water, soil nutrients
      • Fungus gets: carbohydrates
    • Does not have to be equal
      • Example: Humans and cows
    • Leaf cutter ants
      • Ants cut leaf -> fungus decomposes cellulose -> grows -> ant eats fungus
      • 1:1 specialization ant species and fungus species
  • Habitat mutualism - one partner gets a place to live, often trading i) defense or ii) food
    • Ants and Acacia
      • Ants live in hollow thorns of the tree
      • Tree produces high protein body which the ants gather to feed on the larvae
      • In exchange ant workers protect the tree from other insects and herbivores
  • Service mutualism - (Slides
    • Cleaner and client
      • Crocodile and bird
    • Pollination and seed dispersal
      • Bird gets fruit and disperses seeds
      • Bees transfer pollen to fertilize plants
      • Rarely in close living arrangement
  • For mutualism to Persist
    • The partners in a mutualism are not altruistic
    • Both partners action promote their own interests
• A mutualism evolves and is maintained because the net effect is advantageous to both partners
• Mycorrhizal fungi and plants
  • Roots deplete phosphorus in sol
  • Presence of fungal hyphae increase accessible range of P
  • Benefit: plants get more P
• Depends on P availability
  • Low P soil
    • Plant needs fungi to get enough P
    • Fungi plants grow more than non plants (slides for the rest)
  • Cheaters
    • Good behavior is rewarded and bad behavior is penalized
    • Rewards: found that plants supply more sugar to mycorrhizal fungi that provide more P
• Competition
  • Both participants are harmed by their share use of resources
    • Example: Lions and Hyenas fighting over food
  • You are looking at changes in population size across time of two different species existing in the same habitat
    • Once food reaches maximum, population begins to decrease as both species fight each other for food.
    • Species that use resources differently can coexist
    • Species that use a limiting resource the same way can not coexist
    • Gause’s Competitive Exclusion Principle: two species can use a limiting resource in the same way cannot coexist indefinitely
  • Competitive Exclusion
    • Two species that use a limiting resource in the same way cannot coexist for long periods of generation time (into infinity)
• Predation, parasitism, herbivory
  • The interaction harms one species (individual) and helps the other (individual)
  • Masting - plants produce large number of seeds in some years and hardley in any other years, hiding from seed eating herbivores in time
• Species richness - number of species