Whole-organism responses and environmental change
This research area includes measuring traits such as metabolism, water balance, temperature and desiccation tolerance, locomotion performance under a range of temperatures or environmental conditions (salinity, oxygen availability, etc). The emphasis on the organism provides a link with broader ecological and evolutionary themes. Aims include measuring basal physiological traits, magnitude of developmental and reversible plasticity, and responses to biotic and abiotic variation, including interactive effects. These questions are tackled using both controlled (laboratory) and field conditions and a variety of methodological techniques are applied.
Environmental adaptation: testing theoretical models
As we face an increasing number of challenges (global warming, biological invasions, habitat alteration, human population growth), we have little predictive power in terms of organisms’ responses to environmental change, more so if theoretical models are not supported by empirical data. My aims are to test some proposed theories and hypotheses (e.g. performance optimality models; hotter is better hypothesis; cost benefit trade-off of thermoregulation) and aim at improving or proposing new ones. This research area integrates experimental, modeling and field approaches, and includes single-species and multi-species comparative studies.
Macro-climate, micro-climate and organismal climate space
The aims are to use modern technology, biophysics and available databases to improve the knowledge of the environment in which an organism functions, the ‘operative environment’. Further limits can be incorporated with physiological thresholds, life-history and behavioural constraints. Questions asked include: are the ‘macro-micro-space’ relationships for a particular species consistent across habitat types, or in modified versus native landscapes? Practical applications of this research are, for example, improving mechanistic understanding of species responses to climate change.
Physiological and functional diversity
This area of research investigates intra- and inter-specific variation of physiological and morphological traits at various scales: from regional to global scales and from individuals to species assemblages. Examples include patterns of skin reflectance variation of ectotherms across latitudes as well as relationships between physiological traits such as thermal tolerance, preference or performance and climate variables at small and large geographical scales (see Publications). A current research project examines key performance traits of dung beetles with the aim to test potential mechanisms that structure dung beetle assemblages in two distinct habitat types in Tembe Elephant Park (KZN, South Africa).
Mechanisms structuring species assemblages in changing landscapes: dung beetles as model organisms
Collaborative project: S Clusella-Trullas (C•I•B, Stellenbosch University) and B. Van Rensburg (University of Pretoria)
Major threats to global biodiversity and ecosystem function include habitat alteration and fragmentation, climate change and invasive species. South Africa is also facing such challenges with many pressing issues for land use, water availability and natural energy resources likely to make significant impacts on rates of biodiversity loss and species conservation. The effects of climate change only exacerbate these issues and the need to understand how species respond to rapidly changing climate is essential for the future conservation and management of biodiversity.
During times of environmental change species may respond broadly in three ways: (i) adapt, (ii) migrate/disperse or (iii) face extinction. The mobility of many insects enables them to readily alter their distribution as climate changes. However, much of the land space available today has been dramatically altered. Therefore, it is essential to investigate “how” and “why” insect assemblages vary across habitat types and identify species that act as indicators of climate change impacts. While many studies have focused on identifying species composition (abundance and richness) within and across habitat types, much fewer studies have explored the mechanisms underlying distinct species assemblages. Understanding these mechanisms is essential to accurately predict the effects of anthropogenic climate change on biodiversity.
Ectotherms strongly depend on their surrounding environment to maintain tolerable body temperatures. A departure from optimal levels can impair physiological performance of an individual, which in turn may affect its fitness. According to the spatial and temporal scale of the environmental change, impacts on whole populations and species can take place, especially if populations are small in size or have limited distributions. Because of the strong link between functional capacity of ectotherms and environmental conditions, and their considerable global diversity and abundance, it is particularly useful to target this group. As such, dung beetles (Coleoptera: Scarabaeidae) have been studied extensively and represent an ideal model organism. They are globally distributed, have an important role in ecosystem function by recycling nutrients, and are generally highly sensitive to human and habitat disturbance.
Dung beetle assemblages have been shown to differ substantially between two dominant habitat types (sand forest and mixed woodland) of the Maputaland Centre of Endemism, KZN, South Africa. In addition, habitat disturbance caused by elephants has also affected dung beetle assemblages at various degrees, providing a gradient of disturbance across the sand forest-mixed woodland matrix. The main goal of this project is to explore the mechanisms that may explain variation in dung beetle assemblages among habitat types and across disturbance gradients.
The study focuses on two major hypotheses. The first one proposes that habitat alteration affects the structure of the vegetation which may directly impact the locomotion performance of individuals. For example, a heavily vegetated, structurally complex habitat will increase the amount of physical barriers to flight compared to an open habitat. The second hypothesis proposes that habitat alteration will modify microclimates available to dung beetles, and therefore will influence their thermal budget by constraining optimal body temperatures. If behaviour, such as changes in thermoregulatory activity patterns, is not sufficient to compensate for temperature changes, species may be displaced, respond to the changes via phenotypic plasticity and/or adaptation, or possibly even go extinct, ultimately influencing the composition of these assemblages. This project tests these mechanisms by exploring morphological (e.g. wing size, body size) and physiological (e.g. performance, metabolic rate) traits characterizing sand forest and mixed woodland assemblages. In addition, confounding factors such as phylogenetic relatedness, soil and vegetation types and nutrient (dung) availability are taken into account. The results of this project are critical to the effective mitigation and management of climate change impacts on South African biodiversity.