Diet choice of a predator in the wild: overabundance of prey and missed opportunities along the prey capture sequence

Abstract

Citation: Brechbü hl, R., J. Casas, and S. Bacher. 2011. Diet choice of a predator in the wild: overabundance of prey and missed opportunities along the prey capture sequence. Ecosphere 2(12):133. doi:10.1890/ES11-00323.1Abstract. Optimal diet theory (ODT) postulates that predators adjust their foraging decisions by calculating a prey value from the potential biomass gain, handling time, prey vulnerability and encounter rate. Tests of ODT have however so far mainly been restricted to laboratory settings. By video surveillance, we gathered a large data set of more than 2000 field observations of crab spider (Misumena vatia) encounters with potential prey. We then tested whether the complex ODT or two simpler models (prey identity and prey traits) best explain foraging decisions. Insect prey were killed with an average chance of 3.5% when alighting on an inflorescence harboring a spider. Spiders refused to attack suitable prey in 46-79% of encounters when prey was in attack range, indicating an over-abundance of prey relative to the needs of the spiders. Reduction of opportunities to capture prey along the prey capture sequence differed among pollinator groups, with syrphids and solitary bees showing strong avoidance of spiders early in the sequence and bumblebees resisting the final strike. Simple prey traits explained foraging decisions better than ODT, which was not supported. In the absence of food limitation, optimality decisions may be less stringent. The over-abundance of prey indicates that, in contrast to current theory, prey encounter rates are not the most important factor driving predator foraging decisions. Our results are highly coherent with those obtained in earlier field studies on patch leaving strategies and predator-prey encounters. Prey overabundance and non-optimal predator behavior are apparently not uncommon in nature, and we highlight some of the implications for predator-prey theory.

Macronutrient intake affects reproduction of a predatory insect

“…Our results, along with several other recent studies (Mayntz et al 2009, Jensen et al 2011, 2012), contribute to the growing evidence that studies of predator diets need to consider more than just energy alone (e.g. optimal diet theory; Schoener 1971, Sih and Christensen 2001, Brechbühl et al 2011), and that macronutrient composition of prey can have large effects on the growth and reproduction of predatory arthropods.…”

“…Studies of the foraging ecology of predators have historically focused only on the energy content of prey items (Sih and Christensen 2001, Stephens et al 2007, Brechbühl et al 2011). However, our results contribute to the growing evidence that particular nutrients in prey, such as protein, can have large effects on the fitness of predators (Mayntz et al 2005, Jensen et al 2011, 2012).…”

“…Much of what is known of the nutritional ecology of animals is based on studies of herbivores and omnivores (Sterner and Elser 2002, Raubenheimer et al 2009, Simpson and Raubenheimer 2012). Fewer studies have examined the nutritional ecology of predators, in part because classic theories of diet regulation by predators, such as optimal diet theory, have suggested that predators primarily regulate the energy content of their diet with little consideration of prey nutrient content (Schoener 1971, Pyke et al 1977, Sih and Christensen 2001, Brechbühl et al 2011). Yet it has long been recognized that the species of prey fed upon can affect growth and reproduction of predators and that prey can vary widely in their nutrient composition (Slansky and Scribner 1985, Fagan et al 2002, Wilder et al 2010, Lease and Wolf 2011, Wilder 2011).…”

A demographic approach to evaluating the impact of stressors on bumble bee colonies

“…Consequently, the probability of surviving each day is [1 − (1.8 × 10 −5 )] 527 = 0.991 (0.998, 0.971) and the expected daily mortality rate is therefore 1% (0.2%, 3%). The voraciousness of the crab spiders in Lincoln County is probably representative because similar capture rates were observed in Bern, Switzerland [Doakland: 0.37% vs. Bern: 0.24%, or two captures in 821 encounters (Brechbühl et al ., )].…”

Triple interaction network among flowers, flower visitors and crab spiders in a grassland ecosystem

“…Brechbühl, Casas, et al (2010) found that prey capture success was lower than 10% of total visits for most of the flower visitors, except for non-syrphid flies (less specialized flies) whose success was higher than 20%. Brechbühl et al (2011) measured the vulnerability of all flower visitors, and indeed flies were the most vulnerable ones, together with some solitary bees. These were also two groups that were strongly avoiding flowers with spiders (see also Brechbühl, Casas, et al 2010;Brechbühl, Kropf, et al 2010).…”