Date on Master's Thesis/Doctoral Dissertation

12-2013

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Biology

Committee Chair

Eason, Perri K.

Author's Keywords

Territoriality; Landmarks; Defensive costs; Sex differences; Cichlid; Territory boundary

Subject

Territoriality (Zoology); Cichlids--Territoriality; Fishes--Territoriality

Abstract

Behavioral adjustments in response to the presence of landmarks can exert strong effects on population dynamics of territorial species as well as the evolution of behavior and social systems. Hence, an understanding of the role of landmarks in animal contests provides a link between behavioral decision-making and population dynamics, which has been viewed as a major goal in ecology. This dissertation investigates the effects of landmarks on territory defense, focusing on how landmarks affect differences in sex roles, the landscape of aggression and fundamental territory properties. To investigate these ideas, I used three different cichlid fish species as model systems. My results clearly demonstrate that landmarks have strong effects on territoriality of cichlid fish, and thus are likely to have been significant influences on the population dynamics and the evolution of the behavior. The laboratory experiments revealed that the resource-free space between territories can function as a visual landmark to reduce aggression between territorial neighbors. I found that male and female Neolamprologus multifasciatus, an African shell-brooding cichlid fish, respond differently to changes in defensive costs that arose as a result of the presence/absence of a buffer zone. Males were more sensitive to the effect of increased defensive costs, compared to females as males increased both the time spent in defense and the use of highly aggressive acts. This increased responsiveness of males could be partly due to males having stronger tendency to intrude when a buffer zone is absent. This study also suggests that, at least in some species, females’ contribution to territory defense may vary relatively little regardless of overall costs. Visual landmarks also influenced the landscape of aggression in Hypsophrys nicaraguensis, a Central American cichlid fish. Findings of this field study revealed that in the absence of landmarks fish left larger areas between each other, and these spaces may act as buffer zones. In addition, this work found that landmarks are useful in both precisely defining territory borders and allowing fish to interact at landmarks when such landmarks are available. These factors may have contributed to lower the overall defensive costs in several ways, by decreasing accidental intrusions, reducing risk of escalation, easily identifying when an intrusion is occurring, and spending less time in boundary patrolling. Landmarks also affected the fundamental territory properties such as territory size, shape and the location of boundaries in Amatitlania siquia territories. In this field study, I observed that territories were significantly smaller when landmarks were present. The reduced size was mainly driven by relocating the boundary closer to the landmark, with pairs giving up an area lacking a clearly defined boundary. This behavior suggests that it is beneficial to defend a smaller territory with well-defined boundaries compared to a larger territory with undefined territory borders. The willingness of fish to move the boundary closer to the nest also suggests that landmarked boundaries provide benefits substantial enough to overcome the cost of high predation on fry when the boundary is closer to the nest. In addition, with the presence of a linear landmark, territories were elongated. However, the presence of a point landmark did not alter territories’ optimal round shape. Findings of my dissertation will provide a means by which researchers will be able to manipulate territories and address fundamental questions about territory structure, territory function as well as the evolution of territoriality and its role in population dynamics. In addition to contributing to the knowledge base of territoriality, these results have important implications for wildlife managers and captive breeders as it suggests that providing landmarks maximizes space use and reduces aggression in territorial species.

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