Camouflage in Aotearoa | New Zealand stick insects: an investigation of their ecology and behaviour

Abstract

One of the most important agents of selection, shaping the traits of animals is predation. Understanding how various camouflage strategies allow animals to minimize predation helps us to elucidate predator-prey relationships. Camouflage can be divided into multiple strategies, including background matching and masquerade. Stick insects represent an ideal model system to study camouflage. Although it is intuitive to assume that the appearance of stick insects function as a camouflage defence, the study of camouflage in stick insects is significantly lacking. This thesis presents an integrative examination of how the appearance of rō | stick insects in Aotearoa | New Zealand benefits them through camouflage. I use multiple approaches including literature review, observations, behavioural laboratory experiments, image analysis and field experiments to investigate the functional significance of the appearance of various species of New Zealand stick insects. This research is the first to use artificial clay models of stick insects, image analysis and animal vision modelling to determine the effectiveness of stick insect camouflage. I investigate for the first time how behaviour interacts with camouflage through the use of posture and orientation in stick insects. I also provide a review of known predators of stick insects in New Zealand, and an observation of a previously undocumented oviposition strategy in one of our native stick insect species. My findings show that birds are likely to be able to detect stick insects on their substrate, but the effectiveness of their camouflage is still demonstrated by low predation in the field. Stick insects in New Zealand may therefore employ masquerade as a camouflage strategy but likely benefit from background matching in certain contexts. Their appearance suggests they can blend into their background or be mistaken for a stick depending on the cognitive and processing abilities of their receiver. Overall, this thesis is the first to provide insights into the adaptive significance of the appearance of stick insects in New Zealand and the world.