Movement patterns in dung beetles and in the dung fly

Movements in coprophagous beetles between cow pats are discussed in relation to two hypotheses: (i) that the movement patterns are results of selection to maximize the net rate of energy intake; (ii) that the rates of immigration to and emigration from droppings are governed by simple stochastic rules of behaviour. Observations support the latter hypothesis, and contrast with predictions from the simplest optimization model. Reasons for this discrepancy are discussed. Spatio-temporal occurrence of the dung fly, Scatophaga stercoraria, around cow pats is re-analysed from Parker's data. A simple Markov chain model predicts the observations well, but it does not solve the question of the type of selection responsible for the values of the behavioural parameters. It is argued that difficulties in coping with a stochastic environment, and the consequences of movements being manifested on many spatial and temporal levels, favour evolution consisting of few key behavioural parameters being singled out and subsequently adjusted by selection.