Use of chi-square tests to analyze scat-derived diet composition data

Wright, Bryan E.

doi:10.1111/j.1748-7692.2009.00308.x

Cited by 20 publications

(18 citation statements)

References 13 publications

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“…The %RFO method has been criticised, for example by Wright (2010), as it violates the assumption of independence when carrying out chi-squared t ests, t hus leading t o pseudoreplication. However, alternative methods, such as the absolute frequency of occurrence (%AFO) are not without problems.…”

Section: Discussionmentioning

confidence: 99%

“…There are inherent difficulties associated with spraint analyses, with quantification of prey remains found in spraints, and statistical analysis of the results, all of which have been discussed thoroughly elsewhere (see Reynolds and Aebischer 1991;Carss and Parkinson 1996;Miranda and Escala 2007;Wright 2010). One particular form of bias occurs because each prey item is counted only once in each spraint, with the result that the number of small fish (such as common bullheads) actually consumed may be underestimated.…”

Section: Limitations To This Studymentioning

confidence: 99%

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Fish selection by riverine Eurasian otters in lowland England

Grant

Harrington

2015

Mamm Res

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Eurasian otters (Lutra lutra) may conflict with humans using fish stocks for food, income or recreation. Understanding fish selection by otters is important for predicting and managing potential conflicts. We used spraint analysis to describe the diet of Eurasian otters on rivers in the Upper Thames Valley, lowland England, in summer and winter, focusing specifically on the species and size of fish consumed. We assessed the proportion of fish consumed that were of potential commercial or sporting value (the 'Potential Value' category). Within this group, we assessed relative selection for family and length by comparing fish found in otter diet with their local availability. Local availability was estimated from UK Environment Agency electrofishing survey data. Fish represented 46 % (relative frequency of occurrence, RFO) of total otter diet, with fish of Potential Value representing 19 % (RFO). In the Potential Value category, cyprinids were relatively avoided; percids and esocids were relatively preferred. Most (∼80 %) fish prey items originated from fish 4-13 cm in length, 3 % from fish>20 cm. Smaller (0-10 cm) percids and cyprinids, and larger (16-20 cm) esocids, were preferred. In summer, diet was broad, comprising 31 % (RFO) fish, 24 % birds and 14 % crayfish. In winter, diet was predominantly fish (68 % RFO) with crayfish and birds accounting for ∼5 % each. In summer, most fish consumed (70 % RFO) were the relatively slow-swimming common bullhead (Cottus gobio). Significantly more of the fasterswimming cyprinids were consumed in winter, presumably because they are easier to catch when the water is colder.

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Section: Discussionmentioning

confidence: 99%

Section: Limitations To This Studymentioning

confidence: 99%

Fish selection by riverine Eurasian otters in lowland England

Grant

Harrington

2015

Mamm Res

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“…To account for differences in sample sizes among seasons, here we calculated the absolute FO for each prey species by simply dividing the number of occurrences for each species by the number of scats collected in the respective seasons (Wright 2010). Top prey species were identified as those with FO ≥ 25% during one of the 2 seasons (Luxa 2008).…”

Section: Harbor Seal Dietmentioning

confidence: 99%

“…Top prey species were identified as those with FO ≥ 25% during one of the 2 seasons (Luxa 2008). For statistical comparisons of prey occurrence in harbor seal diet between seasons, Pearson's chi-square tests were used to compare the occurrence of the top prey species and the occurrence of adult and juvenile herring between seasons (Womble & Sigler 2006, Wright 2010.…”

Section: Harbor Seal Dietmentioning

confidence: 99%

“…In the early 1980s, the Discovery Bay spawning population of Pacific herring was exceptionally large, but it has since undergone a sustained decline (Stick 2005, Gustafson et al 2006, Stick & Lindquist 2009). Despite the fact that herring still spawn in those areas in appreciable numbers, it is possible that the magnitude of the prey pulse in Discovery Bay may no longer be sufficient to elicit a response from harbor seals (Ostfeld & Keesing 2000, Nowlin et al 2008, Yang et al 2008, 2010. However, if harbor seals only respond to exceptionally large magnitude spawning herring aggregations, then one would expect Protection Island harbor seals to have consumed a large proportion of herring during the spawn season when Strait of Juan de Fuca herring were historically abundant.…”

Section: Harbor Seal Dietmentioning

confidence: 99%

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Harbor seal foraging response to a seasonal resource pulse, spawning Pacific herring

Thomas

Lance²,

Jeffries³

et al. 2011

Mar. Ecol. Prog. Ser.

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Evidence suggests that Pacific harbor seals Phoca vitulina are likely to alter their foraging behavior in response to seasonal prey pulses. We hypothesized that spawning herring Clupea pallasii aggregations are seasonally important prey for harbor seals, predicting that (1) harbor seal consumption of adult herring would peak during the spawning season, (2) harbor seals would seasonally change their foraging areas to take advantage of spawning herring aggregations, and (3) seal diving behavior would reflect the vertical distribution of herring during the spawning season. The predictions were tested using an analysis of harbor seal prey remains, GPS telemetry, and satellite-linked time/depth recorder data. Contrary to predictions, herring in harbor seal diet was comprised of 74% juveniles and 26% adults in the spawn season, versus 37% juveniles and 63% adults in the post-spawn season. Harbor seal use of documented herring areas was highest during the season when herring did not spawn, and seal diving behavior did not reflect the vertical distribution of herring. The lack of response by harbor seals to spawning herring pulses is likely explained by the low energy density of adult herring during the spawn season, and the availability of profitable alternative prey such as juvenile herring. This study highlights the influence of relative prey profitability on the foraging behavior of harbor seals, and may help to explain why predators do not always respond as predicted to resource pulses. KEY WORDS: Phoca vitulina · Resource pulse · Utilization distribution · Diet · Diving · Marine predatorsResale or republication not permitted without written consent of the publisher

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Regional differences in winter diets of bobcats in their northern range

Newbury

Hodges

2018

Ecology and Evolution

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When generalist predators have wide geographic ranges, diets may differ dramatically, largely as a result of differing prey communities. Bobcats (Lynx rufus) are widely distributed across southern North America, with their northern range edge occurring in southern Canada and in the northern US states. Within this northern range, bobcats are exposed to cold and snowy winters and a limited number of prey species, conditions that are atypical for most of the range of bobcats. We examined winter diets of bobcats in high elevation and very snowy forests in northwest Montana to determine how these generalist predators managed in these harsh conditions in comparison with elsewhere in the northern range. Bobcats consumed five major prey types: Red squirrels (Tamiasciurus hudsonicus) and Cricetid rodents comprised >78% of the dietary biomass, whereas the larger snowshoe hares (Lepus americanus), deer (Odocoileus spp.), and grouse were consumed much less often. The standardized niche breadth of bobcat diets was 0.29; bobcats from across the northern range also routinely ate multiple prey species, although Eastern bobcats appear to consume more lagomorphs than do Western bobcats. These results indicate that bobcats remain generalists in difficult winter conditions while preying primarily on small‐bodied prey, although bobcats have highly variable diets across their northern range.

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Use of chi-square tests to analyze scat-derived diet composition data

Cited by 20 publications

References 13 publications

Fish selection by riverine Eurasian otters in lowland England

Fish selection by riverine Eurasian otters in lowland England

Harbor seal foraging response to a seasonal resource pulse, spawning Pacific herring

Regional differences in winter diets of bobcats in their northern range

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