The use of territorial gardening versus kleptoparasitism by a subtropical reef fish (Kyphosus cornelii) is influenced by territory defendability

Many territorial herbivorous animals increase the productivity or quality of the prey community on their territory. However, this gardening tactic may be vulnerable to kleptoparasitism unless gardeners can exclude others from the patch. We investigated the influence of territory defendability on the decision of western buffalo bream (Kyphosus cornelii) to defend an algal garden or to leave their territories and invade those of conspecifics. Fish monitored while away from their territories did kleptoparasitize the gardens of conspecifics. We manipulated the structural complexity of territories through the addition of short or tall simulated vegetation. Increasing the height of simulated vegetation on the territory decreased the defendability of territories but increased their safety for fish; territories with tall vegetation were more easily invaded by conspecifics, but fish returned more rapidly to these territories after being disturbed. In a paired experiment, fish spent more time away from their territories (roving) when tall vegetation was added than when short vegetation was added. However, this effect was influenced by depth, with a greater difference between treatments on deeper territories, and by body size, with a greater difference for larger fish. These results support the prediction that territory-holding individuals faced with a trade-off between defending their own garden or kleptoparasitizing from others adjust their use of these tactics based on the defendability of resources.