Degree Name

Master of Science (MS)

Semester of Degree Completion


Thesis Director

Paul V. Switzer


Territoriality can reduce competition for resources, but territorial defense can be costly. Therefore any behavior that reduces territorial costs may increase the net benefit of territoriality. Some species will align their territory boundaries with conspicuous landmarks that may serve to reduce defense costs. Dragonflies, including black saddlebags (Tramea lacerata), defend territories at breeding sites, keeping rival males away to allow themselves access to females. We used three treatments to investigate whether T. lacerata used landmarks: constraining landmarks (an object that provided a physical barrier to flight), non-constraining landmarks (an object of the same dimensions and construction that did not impede flight), and a control without landmarks. We observed patrolling male black saddlebags and recorded the locations of turns at their territory boundary and interactions with other dragonflies. When either type of landmark was present, individuals placed their boundary at the landmark far more often than any other location. In addition, individuals that used landmarks had a significantly narrower range of tum locations than those that did not. Unlike other studies the use of a landmark did not seem to reduce defense costs, and interestingly not all individuals used landmarks when they were provided. The lack of an observed reduction in defensive costs could be due to the collection of data during territory maintenance rather than territory establishment, when the costs may have been higher, or landmarks may be important as part of a spatial reference system that aids male dragonflies in efficiently searching for females.

Included in

Entomology Commons