Skip to main content

Mathematical & Theoretical Physical Biosciences

This group is funded through the NRF South African Research Chair in Mathematical and Theoretical Physical Biosciences held by Prof Cang Hui, working on the interface between mathematics and biology. 

Research overview

Biological processes and structures are highly complex and adaptive. Using the current mathematical instrument of Newtonian mechanics tends to be a cumbersome way to describe the biological complexity. In order to quantify emergent biological patterns and to investigate their hidden mechanisms, we need to rely on the simplicity of mathematical language. 

We have focused on developing novel and applying available methods in mathematics, statistics and theoretical physics for unlocking the mechanisms behind realistic biological patterns, especially on how patterns related to the heterogeneity of species distributions and their genetic structures, the hierarchy of biological networks and the size of adaptive traits. 

We have collaborated with biologists on an international level on various theoretical and applied models of living systems. Through ongoing research, it has become clear that there is currently a drive in the biosciences to develop new mathematical and statistical approaches that are suitable for analysing and forecasting complex living systems. 

A number of postdoctoral fellows and postgraduate students are part of this group, actively working on a variety of projects that are designed for developing novel methods in mathematics, statistics and theoretical physics for unlocking the processes and mechanisms behind real emergent patterns in biology. 

Research focus areas

Biomathematics is a multidisciplinary research field at the interface of mathematics and biology/life sciences. It aims to provide meaningful theoretical insights into understanding and predicting biological phenomena. According to the scope for the Journal of Theoretical Biology, the research areas of biomathematics are extremely wide, including brain and neuroscience; cancer growth and treatment; cell biology; developmental biology; ecology; evolution; immunology; infectious and non-infectious diseases; mathematical, computational, biophysical and statistical modelling; microbiology, molecular biology, and biochemistry; networks and complex systems; physiology; pharmacodynamics; animal behaviour and game theory.

Prof Cang Hui

Prof Cang Hui
Image by: Stellenbosch University
SARCHI Chair in Mathematical and Theoretical Physical Biosciences
(021) 808-3853
Mathematical Sciences Building
Hanlie Swart
Personal assistant to Prof Cang Hui
(021) 808-4907, 3853
(021) 808-3853
Mathematical Sciences Building

Ecological patterns are emerging structures observed in populations, communities and ecosystems. Elucidating drivers behind ecological patterns can greatly improve our knowledge on how ecosystems assemble, function and respond to change and perturbation. Due to the non-random nature, most, if not all, ecological patterns change with measurement and organization scales and exhibit distinct scaling properties. Models in this section are dealing with inferring patterns across scales that are in close proximity. 

As such, these models are often developed to ensure the consistency of measurements across different scales. To ensure the consistency, patterns across scales are normally bridged using probability theory. Specifically, this section presents models that investigate how aggregated structures of organisms and biodiversity change with measurement scales, which biological patterns resonate with underlying processes at the same characteristic scales, and why.

Species distributions are not uniform across space, reflecting the interplay between habitat heterogeneity and the underlying nonlinear biotic regulation. When ecologists examine such non-random, aggregated patterns across scales, the Modifiable Areal Unit Problem presents itself. The problem can be described as the change in species distribution characteristics as the grain and extent of sampling change. 

The aim here is to depict how species occupancy and its aggregation level change when scaling up and down and therefore provide a universal basis for ensuring cross-scale consistency. Under certain conditions, these models further allow extrapolating fine-scale occupancy and population densities from coarse-scale observations. Great potential exists to apply such predictive models in various cross-scale pattern analyses.

Species diversity patterns, such as the species-area curve, endemics-area relationship, distance decay of similarity and occupancy frequency distribution, reflect the scale-dependence of species turnover. Measures of spatial turnover in the compositional similarity or difference between assemblages are commonly based on beta diversity which was originally derived for pairwise comparisons of individual assemblages. However, none of the metrics of species turnover are able to fully reduce all diversity partitions in multiple-assemblage cases, i.e. the diversity components of three or more assemblages cannot be completely expressed using pairwise species turnover. That is, pairwise metrics are not entirely adequate for depicting compositional similarity across multiple assemblages. 

To exploit resources while mitigating conflicts, species often partition available habitats, forming co-distribution patterns of association or dissociation. Null models based on permutation or neutral/niche processes have been widely applied for detecting signals of bio-interactions from co-occurrence patterns. However, co-occurrence is scale dependent and should be used with caution for inferring biotic interactions or processes.

The spatial and temporal scales of ecological processes are intertwined. Processes that account for the spatial distribution of species also underpin its temporal dynamics. This means that we can potentially forecast the future or rebuild the history based solely on current spatial distribution, without resorting to long-term time series. Specifically, the scaling pattern of occupancy has been found to be related to population trends. As the ability to forecast the temporal trend of a focal species provides crucial information on its performance and viability, the methodology of space-for-time substitution is extremely appealing, especially since our ability to obtain spatial records has been drastically improved in recent years.

Just as two tuning forks of the same characteristic frequency resonate, so do ecological patterns and processes working at the same scale. Species distributions are regulated by a variety of abiotic and biotic processes working in concert but at different characteristic scales, whereas identified key processes, e.g. using multivariate statistics, are those resonate with the measurement scale of the study. That is, information being picked up is diluted by the measurement scale, rather than the intrinsic cross-scale mechanism. This finding brings into question many regional management planning practices that are based on the upscale extrapolation of local-scale studies.

The two dominant theories on the development and structure of communities are niche and neutral theory. Niche theory explains the structure of communities using the relationship between species traits and habitat characteristics. Meanwhile, neutral theory assumes a fixed species pool in the absence of speciation and invasion, and considers all species to be ecologically equivalent, with stochastic dispersal and ecological drift being the only processes determining community structure. Despite contrasting opinions on the value of neutral theory, it is now generally accepted that neutral and niche processes interact in natural communities and both contribute towards the structure of species assemblages. The relative roles of neutral and niche processes have been shown to differ across spatio-temporal scales and modelling these processes in combination better represents biological patterns than neutral or niche models alone.

Postdoctoral fellows

Dr Sandra MacFadyen

Spatiotemporal ecosystem dynamics

Dr Gabi Kietzka

Freshwater bioindicators and surrogates

Dr Damien Gergonne

Invasive Vespula population genetics

Dr Jack Jansma

Microbial system dynamics

PhD candidates

Lorenzo Ruaro

Spatial modelling of African rhinoceros

Richard Gibbs

Perceptions and games of adaptive foragers

Mukhtar Yahaya

Ecosystem informatics and modelling

Maarten Trekels

Trait-based community assembly

PhD candidates (co-supervised)

Claudia Justus

Biodiversity matrix partitioning

Alison Govaerts

Population modelling of lions and wild dogs

Alyssa Little

Parasite geneflow in rodents

Jessica Kipling

Ectoparasites of Ottomys unisulcatus

Core collaborators

Dr Pietro Landi

Senior lecturer, Applied Mathematics Division