Animal Behavior and Behavioral Ecology

Behavioral Ecology

What is Behavioral Ecology?

Behavioral ecology is a subfield of ecology that examines the evolutionary and ecological underpinnings of animal behaviors. It treats behaviors as traits shaped by natural and sexual selection pressures. These pressures, whether social or environmental, can mold the behaviors observed in various animals, including reptiles, amphibians, arthropods (like insects), birds, and mammals.

Tinbergen's Four Questions

The Dutch behavioral biologist Nico Tinbergen proposed a framework of four questions to understand animal behavior comprehensively:

  1. Causation (Mechanism): How is the behavior caused through neural, muscular, or other physiological processes?
  2. Development (Ontogeny): How does the behavior develop over an individual's lifetime?
  3. Adaptive Function (Survival Value): How does the behavior enhance the survival and/or reproduction of individuals?
  4. Evolution (Phylogeny): Where and how did the behavior arise in the past?

These questions can be categorized into proximate (short-term processes within an individual's lifetime) and ultimate (long-term evolutionary processes) explanations.

Proximate Explanations
  • Developmental: Enquires how a behavior is acquired during an individual's lifetime.
  • Mechanistic: Concerns the physiological processes (neural, muscular, etc.) that cause the behavior.
Ultimate Explanations
  • Evolutionary (Phylogenetic): Investigates the historical origins and evolution of the behavior.
  • Adaptive Function: Focuses on how the behavior increases an individual's chances of survival and reproduction.

Case Study: Bird Song

Let's apply Tinbergen's framework to understand why a bird sings:

  • Mechanistic Causation: Hormone levels change due to variations in day length. Air moving through the syrinx (a specialized singing organ) causes membranes to vibrate rhythmically.
  • Development: A male bird learns the song from its father.
  • Adaptive Function: A male bird sings to attract a mate for reproduction.
  • Evolutionary History: Complex bird songs may have evolved from simpler vocalizations that became standardized over time.

It's important to note that a behavior's current function may differ from its original function. For example, a song that initially evolved for territory defense might now be used to attract mates.

Hormones and Behavior: Anolis Lizards

Hormones play a significant role in influencing behavior. For example, testosterone influences courtship displays in male Anolis lizards, which in turn affects sexual activity in females.

Experiment on Anolis Lizards:

Three groups of lizards were studied during the breeding season:

  1. Five females, no males: 80% of females were prepared for reproduction with egg follicles in their ovaries.
  2. One male, five females: The male displayed courtship behavior, and 100% of the females became reproductively active due to the male's courtship stimulating hormone production in females.
  3. Multiple males, five females: Only about 40% of females underwent ovarian development because males were focused on fighting each other rather than courting females.

Nature vs. Nurture

The interplay between genes and the environment is vital in shaping behavior. Innate behaviors are instinctive and carried out regardless of prior experience.

Example: Silkworm Moth

A male silkworm moth (genus Bombix) flies towards a female-produced pheromone (an airborne chemical signal) to attract a mate. The pheromone triggers action potentials in antennal sensory hairs. When approximately 200 hairs are activated per second, the male flies upwind, tracking the increasing pheromone concentration, even over distances of a kilometer or more. This behavior is innate and doesn't require learning.

However, behaviors can also be learned through experience, such as tool use, foraging techniques, and complex social interactions. Even simple organisms can exhibit learning behaviors. Nature (genetics) and nurture (environment) are intertwined, and most behaviors are shaped by both.

Complex behaviors are influenced by genetic and environmental factors, having both innate and learned components. Scientists often study simple behaviors to isolate these components.

Displays and Fixed Action Patterns

Displays are species-specific, repeatable patterns of behavior. Natural selection favors displays that are unmistakable signals.

Example: Courtship Displays

Male blue-footed boobies showing off their blue feet. Birds raised in isolation still perform courtship displays with precision, indicating a strong genetic component.

Fixed action patterns are sequences of behaviors that, once triggered, are followed through to completion, regardless of interruption.

Example: Goose Egg Retrieval

Niko Tinbergen studied the response of a goose to an egg that has fallen from its nest. The key stimulus is the sight of the misplaced egg. This provokes the egg retrieval fixed action pattern where the goose rolls the egg back to the nest using its beak. The response is performed to completion regardless of interruption. If the egg is removed, the goose will persist in its rolling motion. Birds respond most strongly to the largest round object, even a soccer ball, which is considered a supernormal stimulus because it is larger than a normal egg and elicits an exaggerated response.

Stimulus Recognition and Feature Detectors

The nervous system processes stimuli to recognize important signals. Feature detectors are specialized sensory receptors that respond to species-specific signals. Frogs distinguish their own species-specific calls using feature detectors.

Example: Frog Calls

By recording and altering frog calls (pitch, duration, pulse frequency), researchers can identify the components that trigger recognition of a specific call. Correct identification of the sound leads to the appropriate behavior.

Single-Gene Effects on Behavior

Some complex behaviors are strongly influenced by a single gene.

Example: Fruit Fly Foraging

The foraging gene in fruit flies influences the feeding behavior of larvae. Two alleles are common:

  • Sitters: Barely move in the presence of food, feeding on the immediate patch.
  • Rovers: Move extensively within and between food patches.

About 70% are rovers, and 30% are sitters. Rovers are selected in crowded environments, while sitters are selected when there are less crowded environments.

Genetic Influence on Mating Behavior in Voles

Studies of North American voles (genus Microtus) show that closely related species can have different mating behaviors. Prairie voles are monogamous, while montane voles are promiscuous.

Role of ADH Receptors

Antidiuretic hormone (ADH) controls urine concentration, but its receptor also affects behavior in the brain. Prairie voles and montane voles produce ADH, but their hormone receptors differ.

Experiment with Lab Mice

Insulin Young inserted the prairie vole ADH receptor gene (with its regulatory region) into a lab mouse (a promiscuous species). The transgenic male mouse pair-bonded with the female, indicating that a single gene can affect complex behaviors like pair bonding.