PhD Oral Exam - Kathleen Church, Biology
When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.
Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.
Structurally complex habitats support high species diversity and promote ecosystem health and stability, however anthropogenic activity is causing natural forms of complexity to rapidly diminish. At the population level, reductions in complexity negatively affect densities of territorial species, as increased visual distance increases the territory size of individuals. Individual behaviour, including aggression, activity and boldness, is also altered by complexity, due to plastic behavioural responses to complexity, habitat selection by particular personality types, or both processes occurring simultaneously. This thesis explores the behavioural effects of habitat complexity in four chapters. The first chapter, a laboratory experiment based on the ideal free distribution, observes how convict cichlids (Amatitlania nigrofasciata) trade-off the higher foraging success obtainable in open habitats with the greater safety provided in complex habitats. Dominants always preferred the complex habitat, forming ideal despotic distributions, while subordinates altered their habitat use in response to predation. The second chapter also employs the ideal free distribution to assess how convict cichlids within a dominance hierarchy trade-off between food monopolization and safety. Dominants again formed ideal despotic distributions in the complex habitat, while dominants with lower energetic states more strongly preferred the complex habitat. For both laboratory experiments, personality did not predict habitat preference. The third chapter, a field study with juvenile Atlantic salmon (Salmo salar), tested whether stream restorations that increase habitat complexity will also select for particular personality traits, and we again found that complexity did not favour any particular personality types. A broader range perspective regarding the effects of habitat complexity on behaviour was addressed in the fourth chapter via a meta-analysis on a wide range of territorial and non-territorial taxa. Territoriality modified the effects of complexity on behaviour, likely due to the strong reliance of territorial species on visual cues. Taken together, all four chapters demonstrate the high context dependency of the effects of complexity on behaviour. Nevertheless, whether or not an individual is territorial emerged as an important predictor of how habitat complexity is likely to affect its behaviour.