Abstract
Structural complexity is known to influence prey behaviour, mortality and population structure, but the effects on predators have received less attention. We tested whether contrasting structural complexity in two newly colonised lakes (low structural complexity lake—LSC; high structural complexity—HSC) was associated with contrasting behaviour in an aquatic apex predator, Northern pike (Esox lucius; hereafter pike) present in the lakes. Behaviour of pike was studied with whole-lake acoustic telemetry tracking, supplemented by stable isotope analysis of pike prey utilization and survey fishing data on the prey fish community. Pike displayed increased activity, space use, individual growth as well as behavioural differentiation and spent more time in open waters in the LSC lake. Despite observed differences between lakes, stable isotopes analyses indicated a high dependency on littoral food sources in both lakes. We concluded that pike in the HSC lake displayed a behaviour consistent with a prevalent ambush predation behaviour, whereas the higher activity and larger space use in the LSC lake indicated a transition to more active search behaviour. It could lead to increased prey encounter and cause better growth in the LSC lake. Our study demonstrated how differences in structural complexity mediated prominent changes in the foraging behaviour of an apex predator, which in turn may have effects on the prey community.
Highlights
Structural complexity is known to influence prey behaviour, mortality and population structure, but the effects on predators have received less attention
Oxygen concentration declined below the thermocline during the season in the HSC lake, to such an extent that the water was anoxic from 14 m depth and deeper in September (Fig. 2a), whereas oxygen concentrations were similar throughout the water column in the LSC lake at end of September (Fig. 2b)
Testing of Structural Complexity Index differences between lakes), but this difference became much less in September as the Structural Complexity Index was relatively unchanged in the HSC lake, but greatly increased in the LSC lake (P < 0.001 for the lake by macrophyte period interaction; Fig. 2c,d and areal distributions of SCI is given in SM Fig. S7)
Summary
Structural complexity is known to influence prey behaviour, mortality and population structure, but the effects on predators have received less attention. Some predators can alter their foraging behaviour and activity by switching between ambush and active pursuit[9,10,11,12] depending on the presence/absence of macrophytes. This ability is species-specific and it has been documented in various groups of invertebrates[6,12] and fish[9,11], where it has implications for hunting success. Besides the inherent ability of some species to modify foraging mode, recent research has revealed that there may be large individual variation in how these behavioural traits are e xpressed[13,14]. Many predators may be able to change foraging mode, many of these mechanisms suggest individual foraging specialization to a specific foraging m ode[15]
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