Disentangling the effects of ecology and life history on ectothermic temperature-size responses

Abstract

Body size is considered to be one of the most important traits of an organism due to its strong links to many ecological and life history traits, and adult body size is often an important indicator of fitness. Recent research suggests that a decrease in body size is a common response to climate warming, particularly in ectotherms. However, my research shows that this is not the case for all species, with some showing the reverse response and others showing no response to temperature at all. My thesis shows that ecological and life history factors are important to consider when assessing the direction and strength of temperature-size responses across ectotherms. The overall aim of this study was to determine which ecological and life history factors may be important for determining ectotherm temperature-size responses using two representative taxa, marine gastropods and butterflies. This was achieved by using a combination of historical museum specimens (covering a temporal range of over 100 years) and modern field data. The results from the study show that factors such as taxon, developmental stage, sex and trophic level and habitat type are important for predicting temperature-size responses in ectotherms. Many species of terrestrial ectotherms, particularly insects, have been shown to increase in size with increasing temperatures. Yet, this study shows that when size is studied in relation to temperatures during each immature stage, that temperature-size responses can vary between life stages. Thus, overall changes in size will rely upon during which stage the individuals are experiencing warm or cool temperatures. Conversely, most aquatic species are expected to decrease in size as temperatures continue to rise. The results presented here, however, show that not all aquatic species respond in this way. None of the species studied decreased in size overtime, but size and shape vary spatially suggesting that the results may be a product of local conditions and not climate warming. Additionally, the work in this thesis highlights the importance of using museum collections in ecological research and the potential future applications given the technological advances such as digital collections and computer vision software.

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Identifiers

ORCID for Rebecca, Jayne Wilson: orcid.org/0000-0002-5705-6078

ORCID for Phillip Fenberg: orcid.org/0000-0003-4474-176X

ORCID for Jasmin Godbold: orcid.org/0000-0001-5558-8188

ORCID for Judith Lock: orcid.org/0000-0002-1673-4207

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