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Title: The detectability half-life in predator-prey research: what it is, why we need it, how to measure it, and what it’s good for

Author
item Greenstone, Matthew
item PEYTON, MARK - Oklahoma State University
item Weber, Donald
item Hu, Jing - Hu
item Simmons, Alvin

Submitted to: Molecular Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2013
Publication Date: 11/8/2013
Citation: Greenstone, M.H., Peyton, M.E., Weber, D.C., Hu, J.S., Simmons, A.M. 2013. The detectability half-life in predator-prey research: what it is, why we need it, how to measure it, and what it’s good for. Molecular Ecology. DOI:10.1111/mec.12552.

Interpretive Summary: Predatory arthropods, such as spiders, lacewings, and ladybeetles, are important natural enemies of agricultural pests. These animals are small and often hidden, making it difficult to study the predator-prey process directly, so we have come to rely on sophisticated molecular tools to detect the remains of insect prey in the bodies of predators. These tools are very powerful but the results derived from using them are difficult to interpret because different kinds of predators digest the remains of their prey at different rates. The so-called detectability half-life was invented to eliminate the effect of different digestive rates on interpretation of these results. However, our review of research over the past fifteen years reveals that measurement and interpretation of the half-life has not been properly standardized. Here we have laid down rules for their proper measurement and interpretation, and also shown how they can be used to study fundamental aspects of predator physiology and life history. This work is of interest to insect ecologists and evolutionists, and to insect pest managers.

Technical Abstract: Molecular gut-content analysis enables detection of arthropod predation with minimal disruption of ecosystem processes. However, gut-content assays produce qualitative results, necessitating care in using them to infer the impact of predators on prey populations. In order for gut-content assays to be made useful for ecological research and pest management decisions, the detectability half-life for molecular prey remains must be determined for each predator-prey combination. If this is not done, interpretations of predator impact will be biased toward those with the longest half-lives. Here we present the challenges in determining detectability half-lives, including unstated assumptions that have sometimes been ignored when feeding trials are performed. We also show how detectability half-lives should be used to properly weight assay data to rank predators in importance in prey population suppression, and how sets of half-lives can reveal testable hypotheses concerning predator physiology and life history evolution and ecology. We also use a previously published data set to generate hypotheses on taxonomic differences in the half-life, and test it with two previously unstudied predators.