Dome-shaped functional response induced by nutrient imbalance of the prey

Abstract

Nutritional ecological theory predicts that predators should adjust prey capture and consumption rates depending on the prey's nutritional composition. This would affect the predator's functional response, at least at high prey densities, i.e. near predator satiation. Using a simple fruitfly-wolf spider laboratory system in Petri dishes, we found that functional responses changed from day to day over a 7 day period. After 1 to 2 days of feeding, dome-shaped functional responses (i.e. reduced predation at highest prey densities) appeared in spiders fed nutritionally imbalanced prey, compared with steadily increasing or asymptotic functional responses with nutritionally near-optimal prey. Later again (days 5–7), the difference disappeared as the level of the functional response was reduced in both treatments. Experiments with adult females in spring and subadult spiders in autumn revealed opposite patterns: a dome-shaped response with high-lipid prey for reproductive females, for which protein-rich prey are optimal, and a dome-shaped (or simply reduced) response with high-protein prey for pre-winter subadults, for which high-lipid flies are the optimal prey. Our results have implications for predation theory and models of biological control that have, so far, neglected nutritional aspects; in particular, the dynamic nutritional state of the predators should be incorporated.

Optimal foraging for specific nutrients in predatory beetles

“…Conversely, if some prey species contain a higher concentration of lipid than is optimal, then predators should switch their focus towards more protein-rich prey species. A functional response matching this scenario was recently documented in wolf spiders (Pardosa amentata), which increased capture rate at increasing prey density when prey was protein-rich but reduced capture rate above a certain prey density when the prey was lipid-rich [51].…”

Individual Variability

“…When hunting individually, male weasels Mustela nivalis nivalis had higher predation rates than females (Sundell, 2003), while female wolf spiders Pardosa vancouveri had higher rates than males (Hardman and Turnbull, 1974). Both age and hunger level can then impact predation rates: starved damselflies Ischnura elegans had higher predation rates than satiated conspecifics (Akre and Johnson, 1979; see also Bressenford and Toft, 2011); sub-adult pumas have lower kill rates than adults, possibly because experience makes pumas more effective predators (Knopff et al, 2010). As with predation risk and prey selection, predation rate thus seems to vary between individuals and such variability can be structured according to phenotypic attributes.…”

“…variability may not be uncommon, especially among species that exhibit prey switching with size or age. For example, owing to changing nutritional needs during different life stages, adult wolf spiders Pardosa amentata have a Type II functional response for protein-rich fruit flies Drosophila melanogaster and a dome-shaped response for lipid-rich fruit flies, while sub-adult spiders display the opposite pattern (Bressenford and Toft, 2011). Putra and Yasuda (2006) examined larval hoverflies Eupeodes corolla preying on aphids Acyrthosiphon pisum and found that first instars had a unimodal response to prey density, second instars had a Type II curve, and third instars had a Type I (linear) response.…”

Cannibalism: Do risks of fighting and reprisal reduce predatory rates?

“…According to nutritional ecology theory, the type of a predator's functional response may vary because predators must adjust their prey capture and consumption rates to the nutritional composition of the prey and other factors (Bressendorff and Toff 2011).…”