The majority of species are under predatory risk in their natural habitat and targeted by
predators as part of the food web. During the evolution of ecosystems, manifold mechanisms
have emerged to avoid predation. So called secondary defences, which are used after a
predator has initiated prey-catching behaviour, commonly involve the expression of toxins
or deterrent substances which are not observable by the predator. Hence, the possession of
such secondary defence in many prey species comes with a specific signal of that defence
(aposematism). This paper builds on the ideas of existing models of such signalling
behaviour, using a model of co-evolution and generalisation of aversive information and
introduces a new methodology of numerical analysis for finite populations. This new
methodology significantly improves the accessibility of previous models.
In finite populations, investigating the co-evolution of defence and signalling requires
an understanding of natural selection as well as an assessment of the effects of drift as
an additional force acting on stability. The new methodology is able to reproduce the
predicted solutions of preceding models and finds additional solutions involving negative
correlation between signal strength and the extent of secondary defence. In addition,
genetic drift extends the range of stable aposematic solutions through the introduction of
a new pseudo-stability and gives new insights into the diversification of aposematic
displays.