Nutrient-Specific Compensation Following Diapause in a Predator: Implications for Intraguild Predation

Abstract

In recent years it has become clear that intraguild predation (where predators feed on other predators) has important consequences for food webs, and yet very little is known about its nutritional or functional bases. In the most detailed study of the nutritional basis of foraging by a predator to date, we used geometrical analysis to test the ability of the generalist invertebrate predatory beetle, Agonum dorsale (Carabidae), to forage selectively for lipid and protein over a 10-day period following emergence from winter diapause, and we measured associated changes in body lipid and nitrogen content. Over the first 48 hours, beetles that were offered two nutritionally imbalanced but complementary foods self-selected a diet high in lipids, and thereafter the proportion of protein in the selected diet increased. Beetles confined to a single food with excess lipid (higher lipid:protein ratio than the self-selected diet) regulated intake to meet lipid requirements, while suffering a shortfall of protein. Those given diets with a lower lipid:protein ratio than the self-selected diet showed a progressive tendency across the 10-day experiment to over-ingest protein, thereby reducing the lipid deficit in their diet. Body composition changed markedly during the experiment, with the lipid content of the self-selecting insects increasing over the first 48 hours from 14% to 46% by dry mass, and thereafter remaining stable. We discuss some implications of our results for the understanding of intraguild predation.

Macronutrient ratios in pollen shape bumble bee ( Bombus impatiens ) foraging strategies and floral preferences

“…Furthermore, our studies demonstrate that B. impatiens does not simply avoid pollen (or diets) with high lipid content: One of their most preferred plant species, T. ohiensis, had relatively high lipid concentrations (Table 1), and they preferentially consumed modified diets with moderate lipid concentrations. Thus, similar to other insects [caterpillars and predators (37,38,44)], B. impatiens appears to regulate the intake of dietary P:L ratios, which may, at least partially, drive feeding behavior in bees.…”

“…These results suggest that bees may consistently navigate through a variety of environmental influences to find optimal pollen resources. Furthermore, optimizing the P:L intake may improve the fitness of B. impatiens, as is the case in other insect species (6,(37)(38)(39), although additional research must examine effects on individual, larval, and colony health and productivity. The species-specific nutritional needs and preferences of bees should be considered when designing protocols and policies for conservation and management of bee populations.…”

“…Additional studies are needed to determine if these ratios are optimal to support bumble bee fitness (6,42,43). Indeed, in studies using the geometric framework for nutrition approach (6,60,61), bees can regulate their protein and carbohydrate intake (42,43), and other arthropod species can regulate their protein and lipid intake to support fitness (37)(38)(39).…”

“…Furthermore, given the nutritional importance of lipids, bees may assess the ratios of proteins and lipids when they are foraging for pollen. Indeed, other arthropod species (e.g., beetles and spiders) can regulate their dietary intake and forage selectively to meet specific ratios of lipids and proteins (37)(38)(39).…”

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

“…Increased, unchanged or lowered predation rates may result when the prey deviate from the optimal nutrient composition, depending on which rule is followed. The predators analysed so far all show asymmetric responses, depending on whether the imbalance is towards the protein or the lipid side of the optimal composition [14,15]. Predators tend to exaggerate intake of protein-rich foods but maintain or even lower the intake of lipid-rich foods compared with balanced food.…”