by Jennifer Fields
Recent research has demonstrated that exposure to elevated CO2 affects how fish observe their environment, affecting behavioral and cognitive processes leading to increased prey mortality. However, it is unknown if increased prey mortality is caused by changes in kinematics of predator-prey interactions or from just increasing prey activity levels. Allan et al. (2013) studied the effect of anticipated end of this century CO2 concentrations on the predatory-prey interaction of two tropical marine fish. Both a predator and prey fish was exposed to present day and elevated CO2 levels in a cross-factored design. The authors investigated the changes in locomotion performance, prey reaction distance, and capture success of the interaction. Authors found that predators had the lowest capture success when exposed to elevated CO2, but this was dependent on the presence of a CO2 exposed prey. Prey exposed to elevated CO2 had reduced escape distances and longer reaction times compared to control prey. The dynamics of predator-prey interactions under end of century CO2 concentrations will certainly be altered; however, the extent of the effect will depend on which species can or cannot adapt to elevated CO2.
Under ocean acidification conditions, fish have exhibited impaired olfactory and auditory responses, diminishment in predator escape abilities, and altered activity levels. These changes have been known to increase prey mortality. This increased mortality could be caused by changes in kinematics of the predator-prey interaction. Allan et al. (2013) examined these changes in two marine fish through a fully crossed experiment under current and the postulated end of this century CO2 conditions. A total of four combinations of CO2-treated and control predator and prey interactions were conducted: control predator vs. control prey; treated predator vs. treated prey; control predator vs. treated prey; treated predator vs. control prey. Both predator and prey fish were placed in an experimental arena for 10 minutes. During this time period, specific performance attributes of the predator and prey were measured. For the predator these included: capture success, attack rate, predator rate, predator attack distance, and maximum predator attack speed. For the prey, these included: prey reaction distance, prey avoidance responses, prey escape distance, maximum escape speed, and mean prey escape distance.
As predicted by the authors, there was an alteration in the kinematics of the predator-prey interaction with elevated CO2. When predators exposed to elevated CO2 were placed with control prey, capture success was 33% less than the treatment groups where both predator and prey were exposed to the same level of CO2. Capture success was also 14% less for predators exposed to present CO2 levels with elevated CO2 exposed prey compared to the other treatments. Six of the tested behavioral attributes were significant: attack rate, predation rate, predator attack distance, prey escape response, and prey escape distance. For the predator, there was no difference in attack rate when predators and prey were exposed to the same CO2 treatments. However, when elevated CO2 predators were paired with control prey, the attack rate was significantly decreased. This occurred again with present day CO2 predators paired with elevated CO2 exposed prey. Exposure to elevated CO2 also reduced the predation rate of the predator with control prey. Interestingly, predation rates increased with the CO2 predator was placed with a CO2 exposed prey. Elevated CO2 significantly affected predator attack distance, but the effect was depended on whether the prey had been exposed to elevated CO2 or not. For the prey, prey exposed to elevated CO2 allowed CO2 exposed predators to get closer to them before they elicited an escape response. Prey escape distance was also found significantly affected by elevated CO2. The maximum speed of both the predator and prey was not altered by elevated CO2.
Future CO2 levels that may occur by the end of the century may impact both the kinematics and timing of predator-prey interactions. Prey treated with elevated CO2 demonstrated changes in escape performance through shorter reaction distances and reduced escape distances. With these changes, prey could have increased vulnerability and ultimately increased mortality. The results of the predator are more complex to interpret because overall predation rate is result of both predator performances during the attack and its motivation to attack. Attack rates and attack distances were affected by elevated CO2, with the lowest attack rates occurring when predator and prey were from different CO2 treatments. This suggests that elevated CO2 has an effect on predator performance during a predator-prey interaction, but the extent of this effect is dependent on the changes in the prey affected by elevated CO2.
The results show that the behavior of both predator and prey in predator and prey interactions will be altered with increased CO2 concentrations. It is unknown whether CO2 will provide an advantage for the prey or predator or not. Many of these alterations are dependent on the ability of the individuals to adapt to the elevated CO2. The effects of elevated CO2 are not limited to only fish-fish interactions, but might expand to affect entire trophic connections and marine communities.
Allan, B.J.M., Domenici, P., McCormick, M.I., Watson, S.A., Munday, P.L. 2013. Elevated CO2 Affects Predator-prey Interactions Through Altered Performance. PLoS ONE published ahead of print March 6, 2013,doi:10.1371/journal.pone.0058520 Full paper: http://bit.ly/1qqANvx