Diurnal Refuge Competition in the Freshwater Prawn, Macrobrachium Australiense

Abstract

This study examined important stimuli influencing agonistic conspecific pairs of Macrobrachium australiense and how these affected diurnal refuge usage. The results demonstrated key behaviours underlying refuge competition, and have ramifications for how we view the link between conspecific competition and exposure to predation. Different levels of vegetation stalk density were employed to examine the effects of increased refuge quality on the hierarchical interaction. The data analysis demonstrated that the prawns were responding to nearby stimuli which altered detectability, e.g., vegetation density, conspecific size, conspecific movement. Dominants and subordinates both responded to the same stimuli, however, the behavioural response was different. Increasing subordinate size lead to increased dominant activity in all refuges, irrespective of vegetation density. Increasing dominant size caused an increase in subordinate activity in high density refugia but a reduction in low density refugia. The increased activity lead to an overall increase in time spent outside of the refuge for all individuals. Subordinates spent substantially more time outside of the refuge than the dominant individuals. As such refuge competition biases the exposure of individuals to risk, localised changes to this bias, i.e., the size of neighbouring conspecifics, can influence this risk and determine the vulnerability of specific demographics, i.e., smaller individuals, to predation.