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Attack Predation

Not-returning

Fig. 11.1. The daily probabilities of attack and predation by crab spiders on a worker bumble bee and a worker honeybee (data from Morse 1986), and two values each for bumble bees and honeybees of overall daily disappearance rates of workers observed at the hive. (Data from Rodd et al. 1980; Goldblatt & Fell 1987; Wolf & Schmid-Hempel 1989; Dukas & Visscher 1994.)

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July. Other studies found up to 20% parasitism by conopids in Switzerland (Shykoff & Schmid-Hempel 1991) and in the northeastern United States (Heinrich et al. 1977).

Indirect effects of predation

Documented low rates of predation may inform us little about the importance of predation. First, even relatively low rates of predator attack are significant because of the severe consequences: injury or death. Second, observed predation rates already represent an equilibrium under which animals typically have taken various measures to decrease probabilities of attack and capture by predators (Lima 1990; Lima & Dill 1990; Ydenberg 1998).

Although experiments with pollinators are lacking, ants have been experimentally shown to modify their foraging to avoid patches with higher densities of predatory ants (Fig. 11.2) (Nonacs & Dill 1990, 1991), or to forage less at times when phorid parasitoids are more active (Folgarait & Gilbert 1999; see also Feener 1988). Hymenopteran flower visitors presumably have similar capabilities.

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