The significance of facultative scavenging in generalist predator nutrition: detecting decayed prey in the guts of predators using PCR

Abstract

Gut-content analyses using molecular techniques are an effective approach to quantifying predator-prey interactions. Predation is often assumed but scavenging is an equally likely route by which animal DNA enters the gut of a predator/scavenger. We used PCR (polymerase chain reaction) to detect scavenged material in predator gut homogenates. The rates at which DNA in decaying slugs (Mollusca: Pulmonata) and aphids (Homoptera: Aphididae) became undetectable were estimated. The detectability of DNA from both carrion types in the guts of the generalist predator Pterostichus melanarius (Coleoptera: Carabidae) was then determined. The effects of carrion age and weight, as well as beetle sex, on detection periods, were quantified. Laboratory trials measured prey preference of beetles between live and decaying prey. Further experiments measured, for the first time, feeding by P. melanarius on dead slugs and aphids directly in the field. In both field and laboratory, P. melanarius preferentially fed on dead prey if available, but preference changed as the prey became increasingly decayed. Disappearance rates for slug carrion in wheat fields and grasslands were estimated and P. melanarius was identified as the main scavenger. Comparison of the retention time for dead slugs in the field, with the detection period for decaying slug material in the guts of the predators, showed that PCR-based techniques are not able to distinguish between predated and scavenged food items. This could potentially lead to overestimation of the impact of predation on slugs (and other prey) by carabids. Possible implications of facultative scavenging by invertebrate predators for biocontrol and food-web research are discussed.

Comparison of the bacterial community structure within the equine hindgut and faeces using Automated Ribosomal Intergenic Spacer Analysis (ARISA)

“…According to McOrist et al (2002), use of the QIAamp kit in the extraction of bacterial DNA from faeces gave superior downstream performance in PCR. Other studies found that this kit was effective for overcoming problems of coextracted PCR inhibitors from faecal samples (Foltan et al, 2005;Nechvatal et al, 2008). In the present study, even though the DNA extraction methods have no impact on bacterial community profiles obtained using ARISA, we chose to extract equine gut content microbial DNA using the Yu and Morrison (2004) method as it provided a better yield and purity of DNA allowing a superior downstream performance in PCR.…”

Detecting arthropod intraguild predation in the field

“…Positive detection of a prey species in a predator does not necessarily indicate that the predator has directly eaten or killed and eaten the prey species. The detected prey species could have been eaten by another predator which in turn was consumed by the predator under investigation or the detected prey could be dead when consumed by the predator (Harwood et al 2001;Foltan et al 2005;. Using an aphid-spider-beetle model system, showed secondary predation by the beetle Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) of the grain aphid Sitobion avenae (F.) (Hemiptera: Aphididae) which had been eaten by the spider Tenuiphantes tenuis (Blackwall) (Araneae: Linyphiidae).…”

Predation or scavenging? Thoracic muscle pH and rates of water loss reveal cause of death in arthropods

“…Facultative scavenging is one of the most common foraging strategies of both vertebrates (DeVault et al, 2003;Hunter et al, 2007) and invertebrates (Sunderland and Sutton, 1980;Foltan et al, 2005). Considering that invertebrates comprise much of the global terrestrial animal biomass (Williams, 1960;May, 2000), the importance of invertebrate carrion as a resource for scavenging predators has received surprisingly little attention.…”

“…Considering that invertebrates comprise much of the global terrestrial animal biomass (Williams, 1960;May, 2000), the importance of invertebrate carrion as a resource for scavenging predators has received surprisingly little attention. Many predatory invertebrates can engage in facultative scavenging, including Amphipoda (Ide et al, 2006), Coleoptera (Sunderland and Sutton, 1980;Juen and Traugott, 2005), Decapoda (Wolcott, 1978), Dermaptera (Sunderland and Sutton, 1980), Diptera (Foltan et al, 2005), Hemiptera (Velasco and Millan, 1998), Hymenoptera ), Isopoda (Barradas-Ortiz et al, 2003, Litobiomorpha (Sunderland and Sutton, 1980), Neuroptera (Foltan et al, 2005) and Opiliones (Sunderland and Sutton, 1980). Several studies have identified ants as key scavengers of small invertebrate carrion (Fellers and Fellers, 1982;Fellers, 1987;Retana et al, 1991).…”

“…Furthermore, the effort required to detect even a few direct instances of predation, which typically involve multiple species of predators (Heimpel et al, 1997;Rosenheim et al, 1999), makes it difficult to obtain sample sizes large enough for meaningful statistical inference. For these reasons, ecologists rely heavily on PCR-based methods (Symondson, 2002;Sheppard et al, 2004;Foltan et al, 2005;King et al, 2008) and stable isotope analyses (Kelly, 2000;Fiedler et al, 2007;Hood-Nowotny and Knols, 2007) to characterize species interactions and to infer trophic level. A major shortcoming of such methods, however, is their inability to differentiate killed prey from scavenged carrion for consumers that engage in both behaviors (Morris et al, 1999;Foltan et al, 2005;Juen and Traugott, 2005;Tillberg et al, 2007;King et al, 2008).…”