Synthesizing drivers of fish functional responses across species

Abstract

Fishes are subject to numerous stressors, including climate change, fishing and impacts by alien species. One of the challenges in understanding species and community responses to these stressors is identifying how they modify predator-prey interactions, a key process shaping aquatic food webs. Here, we aim to synthesize how species traits, such as size, activity level and alien status, and environmental factors, such as water temperature, shape the functional response: the change in predator consumption rate in relation to changes in prey density. We compiled over 300 fish functional responses and examined sources of variation in two key parameters dictating its shape: handling times and space clearance rates. We found that compared to cold waters, warmer waters were characterized by decreased handling times and increased space clearance rates for smaller predators, but had an opposite effect for bigger predators, suggesting that, across species, altered predation rates may underlie the decrease in size at higher temperatures (the temperature-size rule).We also found that the negative effect of increased temperature on the functional response of larger predators is more pronounced in active species. Finally, we found that known alien species do not exhibit different functional response parameters when examined on their native prey, suggesting that alien species are not primed for invasion via their high functional response. Together, these asymmetric changes imply that, across species, warmer waters may alter predator-prey relationships differentially according to predator size, prey size and activity levels.

Functional Response of Harmonia axyridis to the Larvae of Spodoptera litura: The Combined Effect of Temperatures and Prey Instars

“…However, variation in prey size owing to ontogeny and individual variation is ubiquitous, and predation rates typically depend on the size of the predator, the prey, or both (Cogni et al, 2002;Mccoy et al, 2011). This variation stems from the effect of predator and prey body size on the functional response parameters (i.e., handling time and space clearance rate) (DeLong, 2014; Uiterwaal and DeLong, 2020;Buba et al, 2021). Generally, handling time increases as prey size increases and decreases as predator body size increases.…”

“…Generally, handling time increases as prey size increases and decreases as predator body size increases. Space clearance rate may increase with predator body size, while the effect of prey body size on space clearance rate is more variable (Uiterwaal and DeLong, 2020;Buba et al, 2021). Similarly, functional responses often are estimated at only one temperature, despite the widespread effect of temperature on functional response parameters.…”

“…Across many systems and in several focused studies, the temperature has a unimodal effect on both space clearance rate and handling time (Uszko et al, 2017;Uiterwaal and DeLong, 2020). In smaller comparative studies, however, the temperature may have a monotonic effect on functional responses (Buba et al, 2021;. It is imperative to consider the temperature in biological control strategies, especially for biological control with non-indigenous natural enemies (Islam et al, 2020(Islam et al, , 2021.…”

Predator feeding rates may often be unsaturated under typical prey densities

“…For the predator taxa, only fish showed a positive partial effect on the degree of saturation at the median prey abundance. This may reflect the generally higher space clearance rates of fish relative to the other predator taxa, which has been attributed to their relatively higher velocities in moving through their environment after accounting for body size (Wootton et al, 2021;Buba et al, 2022;Pawar et al, 2012). This conclusion is partially supported by generally positive partial effect for mammals and birds which also are likely to have higher velocities in their environments for their body sizes in an analysis including these predator taxa but not accounting for arena size (Supplementary Information S5).…”

Predator feeding rates may often be unsaturated under typical prey densities

“…For the predator taxa, only fish showed a positive partial effect on the degree of saturation. This likely reflects the generally higher space clearance rates of fish relative to the other predator taxa, which has been attributed to their relatively higher velocities in moving through their environment after accounting for body size (Pawar et al 2012;Buba et al 2022;Wootton et al n.d.).…”