Ecology Unit 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