xvii, 141 p. : ill. / Territoriality, defined as an animal or group of animals defending an area, is thought to have evolved as a means to acquire limited resources such as food, nest sites, or mates. Most studies of territoriality have focused on vertebrates, which have large territories and even larger home ranges. While there are many models used to examine territories and territorial interactions, testing the models is limited by the logistics of working with the typical model organisms, vertebrates, and their large territories. An ideal organism for the experimental examination of territoriality would exhibit clear territorial behavior in the field and laboratory, would be easy to maintain in the laboratory, defend a small territory, and have movements and social interactions that were easily followed. Lottia gigantea , the owl limpet, is just such a model animal. With a small territory (< 900 cm 2 ) and slow movements (3 mm/min), the interactions of several L. gigantea can be continuously and simultaneously monitored. Using time-lapse photography, experiments were conducted to observe behaviors of L. gigantea , ranging from how L. gigantea form home ranges to how territorial L. gigantea interact. Lottia gigantea formed home ranges within four weeks, returning to a home scar after each foraging cycle. To determine whether L. gigantea returned to areas with greater food resources, three different algal density treatments were used, and individuals were monitored to see which tiles they frequented the most. Lottia gigantea actually avoided areas with a thick algal covering, potentially due to the loss of suction they experienced while moving across algae. When L. gigantea established territories, home ranges overlapped considerably. Two individuals were placed in one arena, under the assumption that a dominance hierarchy would be established. Dominant status was predetermined, and in four of the seven dyads both individuals were evasive. When subjected to territorial encounters for two weeks, L. gigantea avoided areas where they experienced agonistic losses. Mucus may serve as an olfactory cue to define territorial boundaries. Individuals avoided tiles with conspecific's mucus more often than tiles with self-mucus or no mucus. / Committee in charge: Barbara (“Bitty”) Roy, Chairperson; Alan Shanks, Advisor; Craig Young, Member; Mark Hixon, Member; Frances White, Outside Member