Formal modelling of predator preferences using molecular gut-content analysis

Roualdes, Edward A.; Bonner, Simon J.; Whitney, Thomas D.; Harwood, James D.

doi:10.1007/s10651-016-0341-3

Cited by 2 publications

(14 citation statements)

References 23 publications

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“…An additional laboratory experiment that allowed spiders to digest either prey group for varying times and at varying temperatures would be necessary to fully test our assumptions about how DNA detectability affected our study (Greenstone et al., ). Nonetheless, the inferences made about spider selectivity use an expectation‐maximization algorithm to compute maximum‐likelihood estimates, which is still a robust statistical procedure without priors of DNA detection time (Roualdes et al., ).…”

Section: Discussionmentioning

confidence: 99%

“…Population‐level prey selectivity was analysed with Roualdes’ c st using the R (Core Team R ) package spiders (Roualdes et al., ). First, the model uses the binary data from molecular gut‐content analysis of the predator population (presence or absence of prey DNA) and the count data from pitfall traps to create maximum‐likelihood estimates for the rate of prey capture.…”

Section: Methodsmentioning

confidence: 99%

“…The method of Roualdes et al. () allows counts to be modelled while observing only presence or absence of prey DNA. Roualdes et al.…”

Section: Methodsmentioning

confidence: 99%

“…To account for differing number of traps left out for variable lengths of time, Roualdes et al. () used trap–days as an index of time, which inherently accounts for any unbalanced sampling across the duration of the study.…”

Section: Methodsmentioning

confidence: 99%

“…These hypotheses are nested, so we used sequential likelihood ratio tests in order of most (selective foraging: c st = c st ) to least (frequency‐dependent foraging: c st = c) complex as in Roualdes et al. ().…”

Section: Methodsmentioning

confidence: 99%

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Selectivity underlies the dissociation between seasonal prey availability and prey consumption in a generalist predator

et al. 2018

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Generalist predators are capable of selective foraging, but are predicted to feed in close proportion to prey availability to maximize energetic intake especially when overall prey availability is low. By extension, they are also expected to feed in a more frequency-dependent manner during winter compared to the more favourable foraging conditions during spring, summer and fall seasons. For 18 months, we observed the foraging patterns of forest-dwelling wolf spiders from the genus Schizocosa (Araneae: Lycosidae) using PCR-based gut-content analysis and simultaneously monitored the activity densities of two common prey: springtails (Collembola) and flies (Diptera). Rates of prey detection within spider guts relative to rates of prey collected in traps were estimated using Roualdes' c model and compared using various linear contrasts to make inferences pertaining to seasonal prey selectivity. Results indicated spiders foraged selectively over the course of the study, contrary to predictions derived from optimal foraging theory. Even during winter, with overall low prey densities, the relative rates of predation compared to available prey differed significantly over time and by prey group. Moreover, these spiders appeared to diversify their diets; the least abundant prey group was consistently overrepresented in the diet within a given season. We suggest that foraging in generalist predators is not necessarily restricted to frequency dependency during winter. In fact, foraging motives other than energy maximization, such as a more nutrient-focused strategy, may also be optimal for generalist predators during prey-scarce winters.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…The method of Roualdes et al. () allows counts to be modelled while observing only presence or absence of prey DNA. Roualdes et al.…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Selectivity underlies the dissociation between seasonal prey availability and prey consumption in a generalist predator

et al. 2018

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A new electivity index for diet studies that use count data

Kimmerer

Slaughter

2021

Limnology & Ocean Methods

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Electivity indices summarize the results of field‐based feeding studies by comparing the relative abundance of a potential prey item with its relative prevalence in the diet of a predator. We developed a new electivity index based on odds ratios calculated from counts of individual prey taxa in ambient samples and in the gut of a predator. Many indices of electivity have been developed, though the literature lacks consensus on which is the best. Why use our index instead of one of these? Most of the extant indices lack the means for assessing uncertainty, treat proportions determined from count data as fixed rather than estimates, and ignore the skewness inherent in binomial data. The new index is calculated by Bayesian estimation from the binomial distributions of proportions in ambient samples and gut contents, providing full likelihoods of the index and its components. Indices from groups of predators can be aggregated without bias using the log odds ratio. Using simulated data, we show how the credible intervals of the index shrink with increasing numbers of total ambient and consumed prey and become increasingly asymmetrical as the index approaches its limits (0 and 1). Applying the method to diet data for an endangered planktivorous fish, we show how aggregating among fish and among samples was necessary to overcome the limitations imposed by low counts and high variability among individual fish. The indices for the smallest of five prey taxa varied inversely with total prey abundance, consistent with optimal foraging theory.

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Formal modelling of predator preferences using molecular gut-content analysis

Cited by 2 publications

References 23 publications

Selectivity underlies the dissociation between seasonal prey availability and prey consumption in a generalist predator

Selectivity underlies the dissociation between seasonal prey availability and prey consumption in a generalist predator

A new electivity index for diet studies that use count data

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