Lecture 12 Habitat Selection, Territoriality, and Migration

Habitat Selection Decision Making

• Choosing a habitat is often a complex process for animals, similar to human decision-making about homes.

• Factors influencing habitat choices include:

  • Location relative to resources such as food and mates

  • Presence of competitors

  • Risk of predation

  • Compromises must often be made to balance these needs.

Ideal Free Distribution Theory

• Originated from Fretwell & Lucas (1970).

• States that individuals will distribute themselves in habitats in proportion to the available resources.

• Limitations:

  • Assumes equal access among all individuals, ignoring competitive asymmetries.

  • In environments with patchy resources, preferred habitats might not always contain more individuals due to competition limits.

Ideal Despotic Distribution

• This concept highlights that territory establishment can limit habitat options:

  • Individuals might settle in lower-quality habitats due to established competitors.

  • Preferred areas may be under-utilized or not accessible due to competition.

  • Lower reproductive success in poor habitats compared to high-quality areas is common.

Examples of Competition and Territory

Red-winged Blackbirds

• Polygynous species with males attracting multiple females.

• Females may choose lower-quality territories if preferable ones are occupied by other females to gain better nesting sites and parental care.

Side-blotched Lizards (Uta stansburiana)

• Dominant males control high-quality territories; lower-quality males struggle with mating success even in larger areas.

• Enhanced territory quality leads to reduced area demands for dominant males.

Costs and Benefits of Territoriality

• Territorial behavior often incurs costs:

  • Increased activity and energy expenditure can lead to survival risks.

• Example: Yarrow's spiny lizard showed that testosterone-implanted males, more active, had lower survival without food supplementation.

When to Defend Territory

• Defining a territory includes controlling resources such as food, mates, and shelter.

• The benefit of defending a territory often includes increased reproductive success (RS).

Asymmetries in Competitor Interactions

1. Arbitrary Asymmetry: Residents often win disputes simply by being present first, regardless of strength.

   • Experiment with speckled wood butterflies showed residents win due to home advantage.

2. Non-arbitrary Asymmetry: Resource-holding potential, often linked to greater physical strength or advantage.

   • Example: Black-winged damselflies show fatter males win more contests.

3. Payoff Asymmetry: Older males or established residents defend territories vigorously due to higher investment and stakes.

   • Example: Older male egg fly butterflies fight harder to control territories regardless of physical strength.

Dynamics of Neighboring Territories

• Familiar neighbors tend to have reduced aggression compared to unfamiliar ones.

  • Little owls hoot less at known neighbors, demonstrating reduced conflict within known territories.

Dispersal and Migration

• Dispersal: One-time or seasonal movement from natal areas, increases risks and energy costs.

• Migration: Long-range movement for reproduction or survival; all migration must balance costs and benefits.

• Factors influencing migration include energy storage and physiological changes.

Cues Affecting Movement Decisions

• Body condition affects migratory routes, where birds with low fat reserves may opt for safer, longer paths over flying vast waters.

• Individuals can show migratory versus sedentary behaviors based on conditions, allowing strategy switching.

Final Thoughts on Animal Behavior

• Animals continually make decisions about habitat, resources, and competition based on availability and risk.

• Success often depends on balancing costs and potential advantages via various adaptive strategies.