Page 87 - University of Pretoria RESEARCH REVIEW 2016

successful in many other branches of science and engineering in modelling processes with a saturation effect.
Despite its successes in describing the mitigating effect of the size of the population on its growth, the Verhulst model does not capture the perils facing small populations. In 1931, Warder Clyde Allee observed that many populations have a window of sizes within which they can survive – they cannot grow too large lest they overexploit the resources, and they perish if they decrease below a certain survival threshold. The latter can happen due to insufficient capacity to collect food or to organise
a defence against predators or, on an evolutionary time scale, due to too small a pool of mutations allowing for adaptation to changing environments.
SOCIAL PARASITISM IN HONEYBEES
Studying the behaviour and chemical communication of social insects (ants, wasps, bees and termites) leads to insights into social cohesion, hierarchies and reproductive dominance in colonies of these insects. Researchers at UP have shown how bee colonies rapidly decline and die when infested by capensis parasitic workers.
The work of Dr Abdullahi Yusuf (right) includes studies of the
pheromones of sub-species of African honeybees, their conservation,
population genetics as well as pathogens that affect them. As
one of the principal investigators within the M3B2 SARChI Chair,
together with colleagues, Dr Yusuf is using mathematical models
to understand the population dynamics of honeybee colonies under normal conditions, and also when they are challenged by diseases and parasites.
There have been substantial colony losses as a result of infestation by social parasitic bees that are endemic to the Cape region of southern Africa. Dr Yusuf’s modelling has explored the dynamics of the changing composition of the workers in an infected colony with the decline of host workers and the increasing numbers of social parasites, which result in significant losses of colonies in apiaries, a phenomenon called the Capensis Calamity.
UP Research Review 2016 | 85
Christian Pirk