Interference competition in a planktivorous fish (Rutilus rutilus) at different prey densities and temperatures

Abstract

The effect of interference competition can be assessed by comparing the capture rate of a predator foraging alone with that of the predator within a group. Since such an effect could be prey density dependent, a constant density of prey must be maintained while assessing this effect, irrespective of the elimination of prey by predation. However, when studying a predator-harvester, such as a planktivorous fish, which collects zooplankton at a rate of up to 1 prey s -1 , instantaneous replacement of each consumed prey item is not feasible. This problem was solved in short-lasting mesocosm experiments by minute-byminute supplementation to replace eliminated Daphnia and maintain a constant average prey density. Such experiments were performed with different numbers of foraging roach (Rutilus rutilus) at three prey densities and in two ranges of ambient temperature. The number of Daphnia required at the start of each experiment to establish the initial prey density and the number that it was necessary to add per minute were determined in experiments conducted without prey supplementation and in preliminary experiments with prey supplementation. The results of this study revealed that fish foraging in a group eat less, due to both exploitation and non-aggressive competition for space. Moreover, the effect of interference competition was stronger at higher temperatures, irrespective of the prey density, indicating that natural populations of roach foraging in shoals may suffer more from competitive interactions in warmer waters.

Heterogeneity in prey distribution allows for higher food intake in planktivorous fish, particularly when hot

“…This notion is supported by the high number of fish leaving the high-prey-density tank after the first minutes of each feeding session, despite the prey density still being much higher than in the neighbouring region. Neither the earlier observations of rudd behaviour (Maszczyk et al 2014 ), nor the video recording from the two experimental sections have ever suggested that the permanent appearance of fish in the other low-prey-density locations was due to interference competition resulting from either passive competition or aggressive behaviour in the high-prey-density tank that would further increase with the arrival of new individuals into the patch of prey. This is why the cause may instead stem from perceptual constraints such as weak memory, insufficient knowledge of the pattern of prey distribution, and an insufficient ability to accurately assess resource distribution (Abrahams 1986 ).…”

“…The results of this study also show that the optimal exploitation of patches of zooplankton prey leads to their rapid annihilation. This occurs as a result of the combined effects of the predator’s functional response [an increase in the capture rate up to the highest values ever observed in planktivorous fish in laboratory and field studies of 0.8 prey s −1 (Bartosiewicz and Gliwicz 2011 )] and the predator’s rapid numerical response in space, when the decline in prey concentration and interference within the overexploited patch of prey may encourage fish to swim faster to compensate for the reduced encounter rate, thus increasing the probability of mechanical interference with one another (Persson 1986 ; Maszczyk et al 2014 ). As a consequence, the role of aggregating in zooplankton as an antipredation defence against fish predation (Pijanowska and Kowalczewski 1997 ) becomes questionable, and this is the point where the results of this study meet the theoretical approach focused on the stabilizing role of predators in their top–down regulation of prey density and distribution in space and time (Morozov et al 2011 ).…”

“…Immediately before the end of a feeding session, the visible light was switched off and staff equipped with infrared goggles entered the experimental room through an illumination lock/chamber to shut all inter-tank windows, count the fish accumulated in the high-prey-density tank of the section with patchy prey distribution (e.g., tank 7) while transferring them to the neighbouring tank (tank 8) which had been first sampled for the remaining prey, transfer all fish of the section to this tank (tank 8), do exactly the same in the respective tanks (e.g., tanks 7 and 8) in the section with homogeneous prey distribution, and—after switching the lights on—sample all nine remaining tanks of each of the two sections. The brief, high density of fish (up to 0.5 fish L −1 ) in one of the tanks (tank 8) was assumed to be below the critical density that might have caused interference competition in roach of a similar size tested in a similar experimental system (Maszczyk et al 2014 ).…”

An integrated experimental and mathematical approach to inferring the role of food exploitation and interference interactions in shaping life history

“…However, such an experimental design has been conducted only in a few systems due to its strong experimental limitations. Two studies, one using a crab‐bivalve system and the other using a roach‐daphnia system, excluded food exploitation (Maszczyk et al., 2014; Smallegange et al., 2006). Specifically, they prevented food depletion by replenishing instantaneously any consumed food items.…”

Video playback versus live stimuli to assess quantity discrimination in angelfish (Pterophyllum scalare)

“…The benefits include more efficient foraging (Day et al, 2001 ; Hintz & Lonzarich, 2018 ) and swimming (Marras et al, 2015 ; Miller & Gerlai, 2011 ), as well as better protection from predators (e.g., see Ioannou, 2017 ). The disadvantages include enhanced conspicuousness to predators (Botham et al, 2005 ), elevated parasitism (Poulin, 1999 ) and resource competition within the group (Maszczyk et al, 2014 ). These costs and benefits may vary with group size.…”