Functional Response of an Ambush Predator: Chaoborus americanus Predation on Daphnia pulex

Abstract

Estimations of invertebrate predation parameters usually rely on behavioral observations and on feeding rates in single, arbitrary prey densities. In this study, predation parameters were estimated directly from functional response data. This type of analysis relies on many prey densities and therefore should lead to more widely applicable parameter values.Functional response curves of third-and fourth-instar Chaoborus americanus preying on five sizeclasses of Daphnia pulex in the laboratory were examined. Data for each size-class were fitted to Rogers' random predator equation, a modification of Holling's type II functional response equation. The data fit the model well.The parameters a' (instantaneous attack rate) and T. (handling time) were calculated for each prey size from these curves. Attack rate reached a maximum, indicating highest vulnerability, at an intermediate size. Deduced handling times were greater than simple observation would suggest and were highly correlated with prey dry mass, suggesting digestion as the primary component.Results of mixed-size-class experiments were compared to predictions based on the parameters from single-size-class experiments. The ratio of predation-caused mortality rates for prey size-classes was consistent with the predictions, suggesting that no active behavioral selection was occurring. Feeding rates in mixed-size-class experiments were underestimated when experiments were run a month later than the single-size-class experiments during the 1st yr of this study. However, when single-and mixed-size-class experiments were run simultaneously during the 2nd yr, predictions were very close to observed feeding rates. This indicates the possibility that predator age and seasonal physiological changes affect functional response parameters.Attack rate increased with temperature, probably due to increased encounter rates as Daphnia swimming speed increased. Handling time decreased with increased temperature, probably due to increased digestive rate.The biological significance of Holling's parameters and those of other more behaviorally based models is discussed.

Density‐dependent predation of early instar Chaoborus feeding on multispecies prey assemblages1

“…This study and several others (Murtaugh 1984;Spitze 1985;Stemberger 1986) emphasize the role of digestion times for invertebrate predator-prey interactions.…”

“…For example, secondinstar Chaoborus can consume S. pectinata in 1.9 s (Moore and Gilbert 1987), yet total gut passage for this prey species can take up to 1 h (Fig. 4 and Spitze (1985), using Holling's method, reported handling times of -l-10 h at 15°C by third-and fourth-instar C.…”

“…Although 256 it has not been used to estimate predation rates for Chaoborus, it has been applied to a diverse array of aquatic predators: chaetognaths (Feigenbaum and Maris 1984), mysids (Rybock 1978), and larval predatory insects including stonefly (Allan 1982) and caddisfly (Hildrew and Townsend 1982) larvae. Still another method for estimating predation rates includes laboratory feeding experiments conducted at various prey densities (Pastorok 1980b; Vinyard and Menger 1980;Spitze 1985). Such functional response experiments yield not only estimates of predation rate but, when modeled (i.e.…”

Long-term changes in invertebrate size structure and composition in a boreal headwater lake with a known minnow introduction

“…In thermally stratified lakes, zooplankton that show DVM behaviour are likely to experience at least some periods of cooler water temperatures, compared to zooplankton within nearby isothermal lakes. Cooler water temperatures decrease rates of digestion, metabolism, and respiration (Swift, 1976;Giguère, 1981;Spitze, 1985), all of which often increase prey-handling time, and consequently reduce predation rate and success (MacPhee et al, 2011). Hence, predation intensity as inferred by Bosmina size attributes may be sensitive to climate-induced shifts in lake water properties.…”

“…Chaoborus are gape-limited ambush predators (Spitze, 1985) that are efficient at consuming small zooplankton prey (Mumm, 1997). Chaoborid community composition is a significant determinant of zooplankton community structure, although predation has been found to play less of a role than environmental factors in structuring zooplankton communities in relatively small and shallow Boreal Shield lakes (Kurek et al, 2011).…”