School of BioSciences - Theses
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ItemImpacts of streetlights on sleep in urban birds( 2019)Over the past century, artificial light has dramatically transformed our environment. Light at night is increasing globally, to the extent that in many places, true darkness no longer exists. As the timing of light can influence almost all aspects of biology, the alteration of natural light cycles could pose a severe threat to wildlife. One particularly harmful impact could be the disruption of sleep. In this dissertation, I investigate the impacts of artificial light at night on sleep. Despite the importance and prevalence of sleep across the animal kingdom, sleep is arguably underappreciated in studies of ecology and conservation. After providing a general introduction (Chapter 1), I begin by giving a broad perspective of sleep research, including current methods, opportunities, and the significance of sleep for issues such as artificial light at night (Chapter 2). I then provide a review of the evidence for impacts of artificial light at night, in both humans and wildlife (Chapter 3). Finally, I explore the effects of artificial light at night on two diurnal bird species: pigeons (Columba livia) and black swans (Cygnus atratus). I focus on the effects of one of the most common sources of outdoor lighting: streetlights. Light at night from LED streetlights caused pigeons to have less rapid eye movement (REM) sleep and non-REM sleep, have more fragmented sleep, and sleep less intensely than during darkness (Chapter 4). Some of these effects persisted for more than a day after exposure to light at night. In black swans, light at night in a naturalistic environment reduced night-time rest, which we demonstrate reflects reduced sleep (Chapter 5). This research provides the first direct evidence that exposure to environmentally-realistic artificial light at night can disrupt sleep in birds. One possible strategy for reducing disruption of sleep could be to alter the colour of lighting. To test this idea, I compare the effects of two different lighting colours: white (blue-rich) and amber (blue-reduced) light. Previous research has shown that blue wavelengths of light have the greatest effect on melatonin, a hormone important for sleep regulation. However, contrary to my predictions, amber and white light had very similar effects on sleep in both pigeons (Chapter 4) and swans (Chapter 5). Together, these findings will help councils and other land managers to make more informed decisions about lighting, particularly for areas that might offer important refuges for wildlife.
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ItemPredicting ectotherm life cycles under a variable climate: physiological diversity of matchstick grasshopper eggs and their ecological and evolutionary implications( 2019)Understanding the processes underlying the phenology and distribution of species is a key problem in ecology. These relationships are important for predicting the responses to species to environmental change. Phenology and distribution are closely linked to climate and weather through the thermal dependence of life cycles. However, for many biodiverse taxa, like insects, we have a poor understanding of the mechanistic links between adaptive traits and how life cycles are adapted to seasonal and variable temperature patterns. Insect life cycles are synchronised with suitable climatic conditions at critical life stages, such as the egg stage. Variation in thermal sensitivity of development and dormancy are two mechanisms by which insects can generate adaptive life cycle phenotypes. Eggs, therefore, present a unique opportunity to link adaptive variation in traits with corresponding variation in life cycles and thermal environments to examine how life cycles are adapted to variable climates. To understand the adaptation of insect life cycles to variable climates, we require a mechanistic understanding of the interactions between adaptive developmental traits of eggs and variation in the thermal environment on adaptations. Our ability to test thermal adaptation in ectotherms is also limited by our ability to efficiently characterise thermal responses. In this thesis, I described how thermocyclers are an efficient means of characterising the thermal response of small ectotherms with enough precision and sample size. I then used the widely distributed, endemic and flightless Australian matchstick grasshopper genera Warramaba (Orthoptera: Morabidae) as a model system to examine the significance of variation in thermal responses at the egg stage for life cycles under a variable climate. I used a mechanistic modelling framework to tease apart developmental and environmental sources of variation in life cycles at the egg stage and simulate their consequences for phenology and distribution in the field. Matchstick grasshoppers showed remarkable diversity in developmental responses to temperature at the egg stage, primarily in the expression of dormancy. I found that diverse Warramaba life cycles are shaped by the interactions between such developmental variation and local environmental temperatures. I demonstrated that we can achieve a mechanistic understanding of life cycle adaptation by considering the evolution of temperature-dependent traits and the evolution of life history within the context of seasonal temperature cycles. Mechanistic models are powerful tools to investigate the sources of life cycle variation and their consequences for insect distribution and phenology. Such frameworks are directly transferrable to other socio-economically important or threatened species to understand how insects are adapted to local climatic conditions and predict responses to a changing climate.