Lecture G2 (2025-11-06): Competition and Cooperation Among Foragers

In this lecture, we pivot from thinking about optimal group size when animals have positive externalities to using the same logic to better understand how animals distribute themselves within a habitat. We introduce interference and scramble competition as mechanisms that couple animal decision making, and then we introduce the Ideal Free Distribution (IFD) as a concept that can predict the likely location of animals under these competitive pressures. The IFD is a natural extension of the matching law from psychology. There can be variations of the IFD due to differences in competitive ability (which are modeled by the ideal despotic distribution, IDD) as well as due to non-foraging-related conspecific attraction (which can lead to colony life). The IFD does give us an opportunity to introduce the Nash equilibrium, which we then use to discuss another important model in social foraging, the stag hunt game. Closing with the stag hunt game lets us introduce concepts such as social efficiency, payoff and risk dominance, and coordination and assurance games.

Topic highlights:

• habitat selection
• interference and scramble competition
• the ideal free distribution (IFD) and the matching law
• conspecific attraction and colony life
• game theory and the Nash equilibrium
• the stag hunt game as an assurance/coordination game

Important terms: habitat choice/selection, interference competition, scramble competition, ideal free distribution (IFD), matching law (from psychology), ideal despotic distribution (IDD), conspecific attraction, colony, Nash equilibrium, Pareto/socially efficient/optimal, stag hunt game, payoff dominant, risk dominant, coordination game, assurance game

Lecture G1 (2025-11-04): Exploitation in Group Foraging

In this lecture, we introduce social foraging as an opportunity for exploitation by conspecifics to either: (a) exploit positive externalities from the foraging behaviors of others, or (b) make foraging choices that reduce the benefit to others around them (imposing negative externalities). We discuss how these pressures complicate understanding the foraging group sizes observed in nature – such as densities of socially foraging bats and sizes of wolf packs. In particular, we introduce the tragedy of the commons (and open-access/common-pool resources) as a conceptual framework for understanding group sizes. We then pivot to focusing on within a group, how do individuals decide whether they should search for food or pay attention to others who are searching for food (and then parasitize the discovered food locations). This gives us an opportunity to use basic game theory to make predictions about behaviorally stable strategies (i.e., strategies that can change dynamically but will have consistent outputs in consistent contexts).

Topic highlights:

• positive and negative externalities in social foraging
• open-access/common-pool resources and the tragedy of the commons
• optimal group size and equilibrium group size
• producer–scrounger game
  • Stable Equilibrium Frequency (SEF) and Behaviorally Stable Strategy (BSS)

Important terms: positive externality, negative externality, open-access resource/common-pool resource, tragedy of the commons, G* (“G star”; intake-maximizing group size), G^ (“G hat”; open-access equilibrium group size), producer–scrounger game, finder’s advantage, Stable Equilibrium Frequency (SEF), Behaviorally Stable Strategy (BSS)

Lecture F3 (2025-10-30): To Eat or Not to Eat? Optimal Prey Choice

In this lecture, we continue using an opportunity cost perspective to predict optimal foraging behavior of predators. We pivot from a review of the marginal value theorem (and the patch model for patch residence times) from the last lecture to an introduction of the prey model of optimal diet choice. This allows us to introduce the profitability-ranking solution of the prey model. After exploring experimental evidence for the validity of this solution, we turn attention to how physiological constraints and shift animals to other diet portfolios. We give examples from sodium limitation in moose, water limitation in spiders, and ballast constraints in shorebirds. Overall, we come to the conclusion that there are many drivers of foraging behavior, and behavioral ecologists choose different model organisms specially to allow for focusing on the effect of each one.

Topic highlights:

• Review of the patch model, optimal patch residence times, and the marginal value theorem
• Introduction of the prey model of predator diet choice
• Solution of the prey model with profitability ranking and opportunity cost thresholding
• Experimental validation of the prey model
• Effect of physiological constraints on optimal foraging behavior
  • Sodium-limited moose example
  • Water-limited spider example
  • Ballast-constrained molluscivore example

Important terms: patch, patch residence time, diet choice/prey choice, marginal returns/gain, diminishing marginal returns, opportunity cost, optimal foraging theory, rate maximization, Marginal Value Theorem (MVT), The Prey Model, diet choice, zero–one rule, profitability, profitability ranking, risk-sensitive foraging, risk/variance prone/seeking/averse, stretch goal, bet hedging, gizzard, partial preferences

Lecture F2 (2025-10-28): The Role of Time in Foraging and Predation

In this lecture, we focus on adaptations to foraging that are shaped by opportunity cost and risk of starvation. Before getting to that, we open with a short discussion of different trophic strategies and the time pressures on each of them. After discussing the ways in which sit-and-wait/ambush predators can use lures and special placement to alter the rate at which they encounter prey, we then switch our focus to mobile predators that make decisions about how long to stay in patches of prey items that they encounter in a heterogeneous, clumpy environment (i.e., how to balance instantaneous rewards of local exploitation with the costs of lost opportunity from continuing to search more broadly). This discussion lets us introduce the Marginal Value Theorem (MVT) of optimal foraging theory and interpret it as a biological version of the equimarginal principles used in economic analysis of consumer behavior. We then shift to thinking not about opportunity cost so much as the risk of starvation for foragers that must reach a minimum threshold for energetic gain by a certain time in order to survive. This lets us introduce risk-sensitive foragers (including risk-prone and risk-averse foragers), the notion of a "stretch goal," and the notion of "bet hedging."

Topic highlights:

• Holling's disc equation
• handling time and its role in the predator saturation/swamping/starvation reproductive strategy of potential prey
• trophic strategies and how they relate
• sit-and-wait/ambush predation and luring
• central-place foragers
• the "patch model" from optimal foraging theory and the problem of choosing the best patch residence time
• diminishing marginal returns and opportunity cost
• marginal value theorem (MVT) and the equimarginal principle
• other applications of the MVT, including:
  • optimal diving models
  • parasitoid oviposition
  • electric vehicle charging (speculative)
• risk-sensitive foraging
  • stretch goals and bet hedging

Important terms: predator saturation/swamping/starvation, trophic strategies, carnivory, hematophagy, herbivory, frugivory, folivory, omnivory, scavenging, carrion, predation, sit-and-wait/ambush predators, pursuit predation, parasitism, parasitoid, parasitoid oviposition, micro-predator, kleptoparasitism, active hunter/predator, foraging, central-place forager, handling time, opportunity cost, optimal foraging theory (OFT), patch, marginal returns, patch residence time, marginal value theorem (MVT), equimarginal principle, optimal diving models, risk-sensitive foraging, risk prone/risk averse, stretch goal, bet hedging

Lecture F1 (2025-10-23): Foraging Foundations

In this lecture, we introduce the foundations and key motivations behind the study of foraging behavior, including some of the foundations of (optimal) foraging theory. We start by highlighting how the key difference between plants and animals comes down to energy acquisition and movement and thereby establish foraging (the search for food) as a key driver of movement behavior in "animated" animals (as opposed to "planted" plants that do not have to search for their source of energy but do have to compete for access to it). We note that movement is also needed for other contributors to reproductive success, such as fighting, fleeing, and reproduction, and so foraging strategies must balance the direct gains of those strategies against the opportunity costs of other things that could be done with that time. Toward that end, we introduce fitness proxies and give a rationale for why energetic rate of gain is a common proxy used that encapsulates the opportunity cost of other activities. We then discuss motivational examples from the study of quail foraging behavior and nutrient-constrained foraging in sloths.

Topic highlights:

• movement and its role in energy acquisition as the key discriminator between plants and animals
• foraging as one of the major drivers of movement behavior
• opportunity costs while foraging, both in terms of non-foraging activities and alternative foraging activities
• fitness proxies and the rationale for the use of energetic rate maximization (as opposed to absolute energetic maximization)
• functional response curves and Holling's disc equation
• motivational examples:
  • simultaneous choice of diet and prey search speed in quail
  • sloth–moth–fungus–algae mutualism and its role in shaping nutrient-constrained sloth behavior

Important terms: autotroph (primary producer), heterotroph (consumer), foraging, opportunity cost, fitness proxy/fitness surrogate/currency, functional response (type-I, type-II, type-III), Holling’s disc equation, handling time, instantaneous rate of discovery of each prey

Lecture E2 (2025-10-21): Homing, Migration, and Dispersal

In this lecture, we continue to discuss navigation in the context of homing and migration and then move on to discuss dispersal movement. We use examples from a few key model organisms (such as Cataglyphis ants, homing pigeons, wolf spiders, and monarch butterflies) to highlight different ways that odometry can be used to update idiothetic information used in navigation as well as different external cues that can serve as allothetic information for navigation. We transition from a detailed discussion of homing to an overview of key topics in migration (and navigational tools used there). We then close with a discussion of the function and mechanisms of dispersal.

Topic highlights:

• navigational tools involved in homing and migration
• a few key model organisms for studying navigation (e.g., Cataglyphis ants, homing pigeons, wolf spiders, monarch butterflies)
• idiothetic information and odometry (step counting, optical flow)
• allothetic information (landmarks, snapshots, magnetic maps/compass, celestial cues)
• cognitive maps
• migration versus homing
• dispersal
  • functions of dispersal in terms of benefits and costs to the individual/genes (competition, outbreeding), not the species
  • mechanisms of dispersal (who disperses and who stays behind)

Important terms: navigation, homing, Cataglyphis ants, homing pigeons, path integration, home vector, idiothetic information, odometer (and odometry), step counting, visual odometry (optical flow), allothetic information, landmarks, displacement experiments, snapshot orientation, magnetic maps, magnetic compass, celestial cues (and the sun compass), cognitive map, migration, stopover, dispersal

Lecture E1 (2025-10-16): Fundamentals of Movement and Navigation

In this lecture, we introduce key concepts in the study of animal movement related to movement during search and navigation. We start with a motivating examples from fiddler crabs -- homing and path integration as well as search (both for food and for displaced burrows). Ending those examples with search allowed us to discuss other more general search-related topics, such as kinesis, taxis, and triangulation. We then close coming back to path integration, but this time in Cataglyphis desert ants and their step-counting odometer. 

Before starting into movement and navigation in this lecture, we discuss the expectations for the final team project. 

Topic highlights:

• path integration, homing behavior, and odometry
• search movement strategies
  • random movement
  • directional movement
  • Lévy flights/walks
• kinesis (stimulus triggered movement) and taxis (oriented movement)
• triangulation

Important terms: navigation, homing, path integration, search, Lévy flight/walk, orientation, directional movements, random movements. odor-plume tracking, kinesis (plural kineses), klinokinesis, orthokinesis, taxis (plural taxes), klinotaxis, tropotaxis, telotaxis, anemo-, chemo-, geo-, magneto-, photo-, skoto-, triangulation, sequential triangulation, simultaneous triangulation, stereopsis, allothetic information, idiothetic information, odometer (and odometry)