Variable Functional Responses of a Marine Predator in Dissimilar Homogeneous Microhabitats

Abstract

Adult soft—shelled clams (Mya arenaria) persist at low densities in Chesapeake Bay sandy habitats despite intense predation by blue crabs (Callinectes sapidus). Clam persistence may be a consequence of variation in blue crab foraging rates as a function of clam density and sediment composition. In laboratory aquaria, we measured the functional responses (prey consumption per predator as a function of prey density) of large blue crabs to six densities of adult soft shelled clams buried at natural depths in two sediment types (mud and sand). Functional responses in sand and mud were differentiated statistically by analyses of (1) residuals and residual sums of squares of discrete and continuous—time models, and (2) the exponent b of a general functional response model. Crab predation rates were significantly higher in mud than sand, and functional responses differed significantly between these two substrates. Blue crabs displayed type III (sigmoid) density—dependent functional responses in sand, and type II (decelerating rise to an upper asymptote) inversely density—dependent responses in mud. Risk of mortality for clams decreased sharply in sand at low densities similar to those observed in the field near the end of the annual period of active predation. These observations (1) suggest that variable blue crab functional responses result in microhabitat—specific mortality rates of benthic prey, and (2) indicate that functional responses can differ significantly according to the physical properties of topographically simple habitats.

Temperature-dependent functional response of Aenasius bambawalei (Hymenoptera: Encyrtidae) to different population densities of the cotton mealybug Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

“…Although reviews indicate that the type II functional response is more frequently recorded for parasitoids and type III is not prevalent in parasitic insects, the form of the functional response on its own does not determine the success or failure of parasitoids in biological control (Fernandez-Arhex & Corely, 2003). Other factors like numerical response, intrinsic growth rates, host patchiness, and competition (Pervez, 2005), as well as abiotic and biotic environmental factors such as habitat heterogeneity (Lipcius & Hines, 1986), temperature (Mahdian et al, 2006;Jalali et al, 2010), host plant (Salehi et al, 2016) and light (Koshi & Johnson, 2002) also affect the effi cacy of natural enemies in pest management.…”

Advancing impact prediction and hypothesis testing in invasion ecology using a comparative functional response approach

“…Further, counter to the traditional view, functional responses are not fixed for predator-prey species pairs, and functional responses can change from Type II to Type III or vice versa under different circumstances. For example, it is well established that functional responses may change under the influence of a number of environmental variables, such as temperature, light levels and habitat structure (Lipcius and Hines 1986;Eggleston 1990;Koski and Johnson 2002;Jeschke et al 2004;Alexander et al 2012, in press). Also, predators may have different functional response types with different prey species (e.g.…”

Foraging and agonistic activity co-occur in free-ranging blue crabs (Callinectes sapidus): observation of animals by ultrasonic telemetry

“…In this ecosystem, crabs are the sole predators on whole clams, and may take them as 50% of their diets . Thus, factors affecting crab foraging success on clam patches have explained much about patterns of clam survivorship in the field (Lipcius and Hines, 1986;Eggleston et al, 1992). The other major predators on clams in the system are fishes (spot, Leiostomus xanthurus; croaker, Micropogonius undulatus; and hogchoker, Trinectes maculatus) that only graze clam siphons .…”