The impact of changes in snow cover on snowshoe hare camouflage

Climate change is regarded as a primary threat to global biodiversity. One avenue in which climate change is influencing survival is through the minimisation of the efficacy of anti-predator defences. Background matching camouflage is an anti-predator defence whereby an organism remains undetectable even when in plain sight. Within seasonal coat colour species, species which undergo a colour changing biannual moult thought to provide anti-predator colouration in their seasonally variable environment, the occurrence of camouflage mismatch is beginning to be recorded. The primary subject of this camouflage mismatch research has been the snowshoe hare (Lepus americanus). However, whilst this mismatch is being observed in nature and is impacting survival rate in snowshoe hares and other seasonal coat colour species, no research as of yet has examined whether these seasonal moults provide background-matching camouflage. In addition, no previous research has examined the impact of camouflage mismatch on detectability from an ecologically relevant visual system, such as the most common mammalian visual system: dichromatism. Within this thesis, both of these gaps in knowledge are explored through computer detection experiments and eye movement analysis in humans. In chapter two, I investigate the impact of predator visual system, camouflage efficacy, background complexity, coat colour, and seasonal background type on the detection rate of snowshoe hares. Participants were displayed 15 randomly generated images of snowshoe hares on a natural landscape and located the snowshoe hares as quickly as possible. Snowshoe hares were detected more rapidly when their camouflage was ineffective, both in colour and brightness. In addition, more complex backgrounds resulted in longer search times. Although visual systems did not differ in overall detection times, simulated dichromatic vision resulted in longer search times for brightness camouflaged snowshoe hares. Within chapter three, I build upon the findings of chapter two, utilising eye-tracking equipment to examine participant visual attention and search mechanisms whilst locating snowshoe hares. I found that simulated dichromatic and trichromatic visual systems differ dramatically in the mechanisms used within the detection and discrimination of a camouflaged target. I also found that camouflage efficacy and background complexity function primarily as a method to reduce detectability, but do not influence the discriminability of a snowshoe hare from its background. This thesis provides support to previous research indicating that climate change will have a significant negative impact on the efficacy of seasonal coat colour camouflage and thus survival. The effects of this are already being recorded in the wild, with mismatched snowshoe hares experiencing elevated predation rates. This thesis supports that the primary reason for the increased predation is ineffective background-matching camouflage. Many aspects of camouflage and prey detection are explored within this thesis which are yet to be tested in seasonal coat colour species in the wild. In particular, how background complexity influences detectability, and the importance of considering an ecologically relevant predator visual system when examining camouflage. Overall, this thesis indicates that as the camouflage efficacy of seasonal coat colour species further decreases due to climate change, detectability, and thus predation risk, will increase