Lecture 4

Game Theory and Strategy-Forming Considerations

• Game theory models strategic interactions between individuals within a species, not different species.
• The "hawk-dove" game analyzes aggressive versus passive strategies, where individuals may choose between competing aggressively or retreating passively or a mixed approach.
• Key factors in choosing strategies include food variability, resource availability, and the individual's current physiological state (energy reserves, etc.).

Competition Major Themes

• Competition occurs at various levels: resources, mates (intrasexual), and overlaps.
• Intraspecific competition: competition within a species, for example, between individuals of the same species for resources or mates.
• Interspecific competition: competition between different species.
• Intrasexual competition: competition between members of the same sex for mates.

Multiple Factors for Food Choices

• Two treatments were investigated: 1°C and 19°C
• When food is variable, a risk-prone strategy is preferred.
• When food is consistent, a risk-averse strategy is preferred.

Modelling Animal State

• Animals need a certain amount of energy to survive.
• Feeding options can be variable or fixed.
• Animal choices depend upon their energy reserves.

Food Strategy Preferences

• Variable food (0 or 6 seeds)
• Fixed food (3 seeds)

Modelling Organism's State

• Animals need 8 energy units to survive the night.
• Animals face choices at twilight: variable food sources (0 or 2 units with 50% probability) or a fixed food source (1 unit).

Conclusions

• Foragers react to variability in food rewards.
• Foragers make their choices based on their physiological state.

Observations

• Small birds in winter lose 10-15% body mass overnight.
• Usually, birds carry less fat than their maximum capacity in winter.
• On the harshest days, birds have nearly maximum possible fat.
• Weight gain is most rapid in the afternoon.

Hypothesis

• Fat storage offers benefits for surviving cold nights.
• Fat storage imposes costs due to greater weight, which affects foraging and vulnerability to predators.

Circumstantial Evidence

• Woods with Sparrow Hawks show birds lose 0.5 grams on average in ~20-gram birds during winter.
• This suggests that predation risk is related to body mass.

Experimental Evidence

• When birds were exposed to model hawks, a mass decline was observed, especially among high-status birds.
• High-status birds likely have priority access to resources.

Empirical Evidence: Food Storage

• Food storing chickadees exhibit high variance in seeds stored per day, whereas non-food storing chickadees exhibit variance relative to a constant environment.

Food Storage

• Risk from food theft must be balanced against the potential benefits of storing food.

Radioisotopes and Food Storage

• Radioisotopes are invested in food items to trace the storing and harvesting individuals.

Review: Decisions

• Environmental factors (1°C vs. 19°C).
• Physiological state (energy levels).
• Food variability and reliability.
• Presence of predators.
• Cost-benefit analysis.
• Time of day.
• Food storage option.

Competition Arrangements

• Consideration of individual actions depends on others.
• Evolutionarily Stable Strategy (ESS): A strategy that, if adopted by all members of a population, cannot be displaced by any alternative strategy.

Hawk-Dove Game Theory

• The game is a model of strategic interactions in ecology where the best option depends on the behavior of the competing individuals, who can choose from aggressive or passive options, including a mixture.

Game Theory (Clarity)

• A "hawk-dove" game is not about differences between species but differences in behavior options taken by an individual.
• Two options available: aggressive or passive.
• An individual might mix aggressive and passive behaviors throughout the day or in different encounters.

ESS May Not Translate to Individual Benefit

• Evolutionarily Stable Strategy (ESS) might not represent the best strategy for all individuals in a population within a given encounter, even when it provides a stable outcome for the whole group
• It's possible for self-interest to supersede the best overall strategy.

Generally (Competition and Parenting)

• Species with female-only parental care often exhibit lower productivity than those with biparental, male-only, or cooperative breeding.

Another Twist: Heterospecific Competition

• Competition for nesting sites may occur between different species.
• Competition for resources between different species is likely to cause conflicts, for example.
• This could favor certain behaviors, even if they are detrimental to a species' overall fitness

Red-head vs. Red-head and Black-head vs. Black-head

• Clutch size and offspring survival vary with different interbreeding scenarios.
• Genetic incompatibilities affect breeding success in mixed pairs.
• Assortative mating is commonly observed.

Postzygotic genetic Incompatibility

• Data show reduced mating success when parental phenotypes differ

One More Thing...

• Reduced or enlarged broods potentially relate to higher/lower red-head frequencies.

So... (Gouldian Finches)

• Two morphs (with red being hawk-like, black being dove-like) exist.
• Mate assortative mating is frequent—red-head with red-head, black-head with black-head.
• Lower reproductive success occurs with mixed pairings.
• Red-heads tend to outcompete for nest sites.

How Game Theory Applies

• Hawks are male Gouldian finches that are RR or Rr.
• Hawks have a competitive advantage in nest contests.
• Breeding success decreases as hawks become more common.
• Factors like mating strategies/patterns, competitive advantage of red males in nest site acquisition, frequency dependence, survival, and habitat all play roles affecting outcomes.

Population Stabilizes Quickly

• Population is relatively uniform in composition.
• Assortative mating will likely result in the red morph's extinction when removed.

Hawk-dove (Gouldian Finch)

• Sexual reproduction, sex-linked polymorphisms, and behavioral differences complicate this model considerably.

ESS Does Not Mean It's Best

• In zero-sum games, the best overall strategy might not be optimal for all individuals.
• Selecting traits for individual growth may favor a steady-state strategy, but this may not be optimal for a population. This is especially true when males compete for females.

Generally: Competition vs Parenting

• Species that mostly use just the female for care have lower levels of productivity than others.

Another Twist: Heterospecific Competition

• Nesting in cavities leads to competition against other species.
• This likely emphasizes the competition for nesting sites.

Males vs. Females

• Various studies indicated different levels of quality in males versus females.

Test your understanding of interspecific competition and foraging strategies in ecology. This quiz covers key concepts such as exploitation competition, risk strategies, and the implications of the Hawk-Dove game within ecological studies. Challenge your knowledge on how these strategies affect species interactions and population dynamics.