Lecture 15. Foraging Behavior and Optimality

Foraging Behavior and Strategies

Overview of Foraging

• Foraging refers to the behavior of searching for and exploiting food resources.

• Different species exhibit unique strategies based on environmental factors and food availability.

Case Study: Oystercatchers and Mussels

• Optimal Mussel Selection:

  • Oystercatchers maximize caloric intake by choosing the most profitable mussels, not necessarily the largest.

  • Study by Meire and Ervynck observed that larger mussels provided more calories per minute despite taking longer to open.

• Key Prediction:

  • Researchers predicted oystercatchers would select larger mussels based on caloric content. However, this prediction was proven incorrect.

  • Initial model (Model A) was rejected due to prolonged opening times for large, barnacle-encrusted mussels.

• Model Revision:

  • Revised Model B presented a more accurate depiction of mussel selection by oystercatchers.

  • It emphasized efficiency in foraging strategies over mere caloric value.

Factors Influencing Foraging Behavior

• Foraging behavior can be influenced by various non-food factors:

  • Predation Risk: Garden skinks decrease movement in the presence of snake odors.

  • Dietary Preferences:

  • Howler monkeys select leaves low in toxins and high in protein.

  • Red grouse choose heather leaves rich in nutrient content (nitrogen, phosphorous).

• Fitness and Dietary Oddities:

  • Some species (e.g., macaws) consume clay possibly due to zinc deficiency or to alleviate diarrhea.

  • Spice consumption (e.g., garlic, oregano) is tied to reducing bacterial contamination in diets.

Locating Food: Search Image Theory

• Search Image Concept:

  • Developed by Luuk Tinbergen; refers to a predator's ability to form mental images of specific prey types to enhance foraging success.

  • Observations showed parent birds returning with prey in greater proportions than expected.

• Impact of Prey Crypticity:

  • Studies by Gendron, Goss-Custard, and Smith indicated that a predator's search speed decreases when searching for cryptic (camouflaged) prey.

• Improvement of Search Images:

  • Blue Jays improved their search images after repeated exposure to a specific prey type, enhancing foraging efficiency.

Group Foraging Behavior

• Communication in Bees:

  • Bees communicate food locations through round and waggle dances, where they gauge distance traveled using optic flow.

  • Optic flow is the perception of the movement of nearby objects relative to distant ones, influencing how bees find resources.

• Ravens as Information Centers:

  • Ravens (Corvus corax) utilize communal roosts to share information about food locations.

  • Experimental studies with sheep carcasses showed that spatial distribution of food information was influenced by roost dynamics.

Locating Prey by Deceit

• Some predators (e.g., certain spiders) mimic non-prey species to lure in unsuspecting victims, showcasing a complex foraging strategy.

• Visual deceptions enhance predator success rates.

Conclusion: Optimizing Foraging Behavior

• Not Always Optimal:

  • It's important to recognize that not all foraging behavior results in optimal outcomes, particularly in environments impacted by human activity or climate change.

  • Adaptation and flexibility in foraging strategies are critical for survival in changing habitats.

Introduction to Animal Behavior and Foraging Theory

• Overview of how observing animal behaviors enhances understanding of biological processes.

Case Study: Reto Sack's Experiments on Crows

• Objective: Investigate how crows utilize tools to access food.

• Observation: Crows drop whelks (a type of seafood) from a height to break the shells and access the food inside.

• Experiment Details: Reto measured the size of whelks and the height needed for effective shell opening.

• Findings:

  • Data Table: Relationship between whelk size, drop height, and number of drops required.

  • Larger whelks require higher drop heights and multiple drops to crack open.

  • Smaller whelks can be cracked with lower heights and fewer drops.

  • Indicates that energy expenditure in flying high affects foraging strategies.

Optimal Foraging Decisions

• Crows and their choice of food based on size and energy efficiency.

• Not all animals prefer the largest prey; efficiency in foraging is crucial.

• Comparative Studies: Mary and Ebernik researched oyster catchers, birds that also open mussels and varied their selections.

• Key Finding: Animals adapt foraging behavior based on food availability; middle-sized prey often preferred due to abundance.

The Balance of Energy Expenditure and Food Acquisition

• Foraging Theory: Models suggest animals aim for profit maximization in food gathering.

• The availability of food types (medium vs._large) affects the foraging choices and strategies employed by animals.

Factors Influencing Foraging Behavior

• Energy Needs and Habitat Structure: The physical environment impacts how and where animals forage.

• Predator Presence: Predation risk alters foraging behavior.

• Learned Behaviors: Individuals adapt foraging tactics based on experiences and environmental cues.

• Food Location: Search images are formed—mental representations that help identify prey.

Search Images and Learning in Foraging

• Animals develop a search image based on food preferences, which enhances hunting efficiency.

• Examples from bird behaviors illustrating the concept of search images and learning outcomes in foraging success.

Communication in Foraging: Altruism and Cooperation

• Waggle Dance in Bees: Method of communication that informs hive members about food source direction and distance.

  • Demonstrates social dynamics in foraging behavior.

• Group Foraging: Animals might share information on food sources post-roosting, leading to collective foraging success.

Conclusions on Behavioral Adaptation in Animals

• Animals exhibit behavioral plasticity in response to predation, food availability, and habitat structures.

• Learning from experience shapes their foraging behaviors.

• The intersection of instinct and experience plays a critical role in survival and optimizing food acquisition strategies.

Unique Foraging Strategies

• Clay Eating in Animals: Consuming clay for nutritional benefits like obtaining zinc.

• Use of Spices by Humans: Reflects on the historical significance of spices in food preservation and safety from microbial growth.

Final Thoughts on Animal Behavior and Foraging

• Foraging behavior is complex and influenced by ecological factors, energy needs, and interspecies interactions.

• Optimal foraging involves trade-offs between energy expenditure and food availability, evolving strategies based on environmental conditions.