Psychology 351 – Animal Behavior

Alcock, Chapter 8 – Choosing Where To Live

Habitat Selection
- The rule that certain species live in particular places applies to all groups of animals.
- Habitat Management : another conservation tool based on the premise that particular species are matched to particular environments.
- Source Habitats : where the population grows.
- Sink Habitats : where the population declines.

Habitat Preferences of a Territorial Aphid
- Aggressive Competition for Habitat Selection : for territorial species, a truly free choice among habitats is not possible because some individuals can exclude others from superior sites.
  • Poplar Aphid : females of this species settle in poplar trees and try to find the biggest leaves to settle on. These females regularly encounter competitors, with whom they fight. Defeated females and small ones incapable of effective fighting are forced to accept inferior habitats.

The Cost and Benefits of Dispersal
- Dispersal : moving from one home base to another.
  • Example : when aphids find a place to live, they will spend the rest of their life there. For other species, such as the honey bee, dispersal from one home base o another is a regular occurrence.
- Costs of Dispersal : calories and materials that go into flight muscle development and maintenance for a cricket (fitness cost), energetic development & travel costs, & the threat of being exposed to predators.
- Inbreeding Depression : when two closely related individuals mate, the offspring they produce are more likely to carry damaging recessive alleles in double doses than are offspring produced by unrelated pairs.
- Benefits of Dispersal : avoidance of inbreeding, familiarity with hunting grounds, & safe breeding grounds.

- Migration : a form of dispersal that involves movement away from and subsequent return to the same location on an annual basis.
- Costs of Migration : for birds, the costs include the extra weight that the migrant has to gain in order to build up energy reserves for the trip, and also the risk of being exposed to predators along the way.

- Benefits of Migration : able to take advantage of seasonal food sources (songbirds fly to the Northern US & Canada in the summer, when long days fuel the growth of plants which herbivorous insects feed), able to take advantage of seasonal water sources (rainfall = water to drink & grass/plants to eat for herbivores), & also able to escape temperate climates (certain times of the year are too cold or too warm).

Migration as a Conditional Tactic
- Individuals in a population share a conditional strategy that enables them to choose between migrating and staying put, depending on the social conditions they encounter. Individuals will adopt whichever tactic yields higher fitness for them, given their social status.

- Territorial : defending the area in which one breeds.
- Costs of Territoriality : time cost of the behavior (injury & exhaustion), reduction of parental care & loss of immune function through hormonal changes.
- Benefits of Territoriality : able to monopolize more mates (more reproductive success).

Territorial Contests
- Studies show that winners in the competition for territories gain substantial indirect and direct reproductive benefits.
- Evolutionary Stable Strategy : an arbitrary rule for resolving conflicts between residents and intruders, and one that cannot be replaced by an alternative strategy.
- Resource Holding Power : a nonarbitrary advantage over others translates into this. Example : large body size, which would provide a physical edge for the territory holder.