An individual based model (IBM) of the female brown crab Cancer pagurus population exploited off South Devon, UK is described. Size dependent movement rules are ascribed to individuals based on previous observations of predominantly westward migration down the English Channel. Two additional versions of the movement rules explored whether the empirically derived rule was necessary to model the temporal and spatial distribution of crabs. Local crab movement was dependent on substrate type and water depth. Females prefer a soft substrate in which they can bury when temperatures are low or they have eggs to incubate. Crabs have size dependent depth preferences with larger crabs preferring greater depths. Two recruitment functions are used which relate the number of incoming crabs to the sea surface temperature five years earlier. Model outputs were tested against 10 years of logbook data from three crab fishers and against data from a year-long sampling programme on eight of the vessels exploiting the area. The model reproduces the long-term pattern which is mostly temperature driven. Spatial variation in catch is captured effectively by the model with more crabs being caught in the east of the area than the west and more caught offshore than inshore. The significance of the results is discussed in relation to the crab life cycle, management of the fishery and the potential effects of increasing temperatures.

Typical examples of cultural phenomena all exhibit a degree of similarity across time and space at the level of the population. As such, a fundamental question for any science of culture is, what ensures this stability in the first place? Here we focus on the evolutionary and stabilising role of ‘convergent transformation’, in which one item causes the production of another item whose form tends to deviate from the original in a directed, non-random way. We present a series of stochastic models of cultural evolution investigating its effects. The results show that cultural stability can emerge and be maintained by virtue of convergent transformation alone, in the absence of any form of copying or selection process. We show how high-fidelity copying and convergent transformation need not be opposing forces, and can jointly contribute to cultural stability. We finally analyse how non-random transformation and high-fidelity copying can have different evolutionary signatures at population level, and hence how their distinct effects can be distinguished in empirical records. Collectively, these results supplement existing approaches to cultural evolution based on the Darwinian analogy, while also providing formal support for other frameworks – such as Cultural Attraction Theory – that entail its further loosening.

A model is used to explore whether local density-dependent recruitment relationships can be observed when considering a larger scale. A virtual population of spawners is tracked within an artificial environment composed of cells. Spawners can move from one cell to another on a spatial grid defined as a square lattice (lattice scale) made of 20 × 20 jointed hexagonal cells (local scale). Five spawner's behaviours are experimented successively: i) spawners stay in the same cell to spawn; ii) they move randomly towards one of the neighbouring cells; iii) they move towards the least populated neighbouring cell; iv) they move towards the most populated neighbouring cell; and v) they move randomly towards a neighbouring cell and then move towards the most populated neighbouring cell. When the migration of spawners is achieved, spawners reproduce only once, recruitment takes place and then they disappear. The recruitment is an event which occurs at a local scale: at the scale of the cell. Using Ricker's stock-recruitment relationship, in each cell the number of recruits is a function of the spawners. Random migrations and migrations towards the less populated cell allow a homogeneous distribution of the spawners throughout the lattice. Whereas in the three other cases, this distribution is not homogenised. The homogenisation of the lattice allows synchrony between local populations and then a stock-recruitment relationship is observable at the lattice scale. Simulations show that local density-dependence is not always detectable when considering large spatial scale. This result strengthens the idea that the choice of spatial scale is essential when studying stock-recruitment relationship.