PREY DNA DETECTABILITY HALF-LIVES: TURNING PCR POSITIVES INTO QUANTITATIVE PREDATION RATES

PREY DNA DETECTABILITY HALF-LIVES: TURNING PCR POSITIVES INTO QUANTITATIVE PREDATION RATES

Bastian Egeter (CIBIO-InBIO, Portugal) | September 15, 2017 | 3rd Symposium on Ecological Networks and 3rd Symposium on Molecular Analysis of Trophic Interactions, Uppsala, Sweden

Predation affects every facet of species ecology, either in the context of being a predator or being prey, including distribution, resource partitioning, population fluxes, circadian rhythms and evolution. Furthermore, predation influences important conservation and resource management issues such as the impact of introduced fauna on native prey or the impact of pest predators on commercially valued prey (e.g. pollinators, game or fish). Diet analysis remains one of the most important tools in predation studies and PCR has largely surpassed traditional morphological diet analysis as a means of detecting prey items in animal gastrointestinal and faecal samples. Usually, DNA-based diet analysis results in qualitative (or semi-quantitative) Frequency of Occurrence data. Depending on the objective, these data alone can be useful, but where the objective is to measure the impact of one species on another, quantitative predation rates are necessary. Here we present a case study that combined DNA-based diet analysis, prey detectability half-lives, predator density and prey availability to estimate the impact of introduced ship rats (Rattus rattus) on New Zealand´s Archey´s frog (Leiopelma archeyi), which is currently ranked as the world´s most endangered amphibian (ZSL Amphibian EDGE list). Predation rates were estimated in a unit of frogs consumed per rat per night, information that was utilised by the Department of Conservation in the decision making process on providing rodent control. The study represents the first to measure prey DNA detectability half-lives in mammal stomachs, the first to compare half-lives of stomach and faecal contents for any vertebrate, and the first to report a quantitative predation rate from PCR diet analysis.