Individuals within species frequently show differences in traits. Yet, until relatively recently, researchers treated all conspecifics as ecologically equivalent. I investigated how environmental variation, temperature and sex may influence intraspecific variation in behavioural, morphological and physiological traits, and their covariance, in the ground beetle Carabus hortensis - a species that is currently undergoing range expansion.
By examining intraspecific variation in morphological traits across the C. hortensis expansion front, I showed that male, but not female, body size increased with proximity to the range edge. This may suggest that males evolved larger bodies and longer legs to increase mate searching efficiency where female density is low. Secondly, I found intraspecific variation in C. hortensis thermal biology, with males being active over a wider range of temperatures than females, and large females being more thermally sensitive than smaller females. Additionally, I showed that male and female movement in the wild is differentially influenced by temperature, and that laboratory measures of animal personality differences can be predictive of intraspecific variation in movement patterns in the wild.
I then tested the relationships between metabolic rate, exploratory behaviour and morphology, finding that the strength, direction, and temperature dependency of relationships differed between the sexes. Finally, I demonstrated that that relationships between metabolic rate and body mass are uninfluenced by temperature, and that individuals with high average metabolic rates and exploratory behaviour are more thermally sensitive.
My findings provide new insights into the roles of sex and thermal sensitivity in shaping intraspecific variation in traits, and their implications for individual fitness and population dynamics under continued climate change. Overall, my results suggest that increasing temperatures may select for smaller individuals and those with lower average metabolic rates and exploratory behaviour.

Dytiscid beetles are significant predators in freshwater aquatic ecosystems, playing a major role in structuring macro-invertebrate communities in some habitats (Cobbaert et al 2010). Great Diving Beetles (Dytiscus spp.) can be among the top predators, yet more than one species may be present in a particular physical location, prompting questions regarding how the Dytiscus species co-exist. This study investigated Dytiscus marginalis Linneaus 1758 and the much rarer Dytiscus dimidiatus Bergsträsser 1778 which occur together in drainage ditch ecosystems in the Somerset Levels and Moors in the United Kingdom. Estimates of niche breadths were made in relation to seasonal activity patterns, habitat usage and prey in order to gauge the degree of specialisation displayed by the two species. Findings broadly supported the view that D. marginalis is more of a generalist species than D. dimidiatus, however, a considerable degree of niche overlap was shown to exist. Evidence was found of a stronger preference in D. dimidiatus for shaded watercourses and for sections of ditch with less extensive coverage of duckweed (Lemna spp.) in the early part of the season. There were indications of both inter-specific and intra-specific predation of larvae by adults and larvae of Dytiscus spp. A major challenge overcome during the study concerned how to distinguish the larvae of the two species. Molecular ecological techniques (RAPD, PCRs and gene sequencing) were compared with morphological means to determine species identity. A relatively simple molecular method was found to distinguish the species based on species-specific sequences within a short fragment of the mitochondrial cytochrome oxidase 1 (CO1) gene. This technique successfully identified 90% of 108 individual larvae tested whereas morphology-based analysis failed to resolve them. The implications for conservation practice arising from these observations are discussed in relation to D. dimidiatus, which is considered at risk in the UK.