Estimates Of Diet Composition Research Articles

Evaluation of long-chain alcohols as diet composition markers in goats grazing heathland areas

An experiment was conducted to assess the potential of long-chain alcohols (LCOH), in alternative or combined with alkanes and long-chain fatty acids (LCFA), as faecal markers to estimate the diet composition of goats grazing heathland vegetation with associated improved pastures. A total of seven diets were offered across the grazing season. The diets were composed of mixtures of herb species (Lolium perenne and Trifolium repens) and woody species (Erica spp., Calluna vulgaris and Ulex gallii) in an attempt to simulate diet selection of goats on these complex vegetation areas. The diet composition was estimated using LCOH markers alone or combined with alkanes, LCFA and alkanes+LCFA, by least square optimization procedures. The data showed large differences between plant species in their LCOH profile. Generally, plant species showed higher LCOH concentrations than those of alkanes and lower than LCFA markers. Faecal recovery of LCOH was incomplete and increased in a linear manner (P < 0.001) with the carbon-chain length, and was influenced by diet composition and its digestibility. The diet composition estimates based on LCOH alone were more accurate (P < 0.05) than those using alkanes or LCFA alone. Results showed that the combination of LCOH with alkanes, LCFA and alkanes+LCFA resulted in more accurate (P < 0.05) estimates of diet composition, indicating that LCOH provided different discriminatory information to that of alkanes and LCFA, helping in the discrimination of the plant species used in this experiment. Results indicate that correction of faecal LCOH concentrations to incomplete faecal recovery is necessary to obtain more accurate estimates of diet composition. Nevertheless, it seemed that the use of a less accurate recovery correction on LCOH markers had a lower impact on the accuracy of estimates than that of alkanes and LCFA.

Integrating Stomach Content and Stable Isotope Analyses to Quantify the Diets of Pygoscelid Penguins

Stomach content analysis (SCA) and more recently stable isotope analysis (SIA) integrated with isotopic mixing models have become common methods for dietary studies and provide insight into the foraging ecology of seabirds. However, both methods have drawbacks and biases that may result in difficulties in quantifying inter-annual and species-specific differences in diets. We used these two methods to simultaneously quantify the chick-rearing diet of Chinstrap (Pygoscelis antarctica) and Gentoo (P. papua) penguins and highlight methods of integrating SCA data to increase accuracy of diet composition estimates using SIA. SCA biomass estimates were highly variable and underestimated the importance of soft-bodied prey such as fish. Two-source, isotopic mixing model predictions were less variable and identified inter-annual and species-specific differences in the relative amounts of fish and krill in penguin diets not readily apparent using SCA. In contrast, multi-source isotopic mixing models had difficulty estimating the dietary contribution of fish species occupying similar trophic levels without refinement using SCA-derived otolith data. Overall, our ability to track inter-annual and species-specific differences in penguin diets using SIA was enhanced by integrating SCA data to isotopic mixing modes in three ways: 1) selecting appropriate prey sources, 2) weighting combinations of isotopically similar prey in two-source mixing models and 3) refining predicted contributions of isotopically similar prey in multi-source models.

Effects of human disturbance on the diet composition of wild red deer (Cervus elaphus)

Disturbance from human recreational activities may affect the nutrition of free-ranging herbivores due to trade-offs between feeding in preferred habitats and perceived predation risk. To test this hypothesis, we estimated diet composition for red deer in the Scottish highlands in spring, when recreational activity tends to be high, and in winter when it is lower. We analysed faecal samples from three habitat types (grassland, heather moorland and woodland) collected at sites close to a busy track (disturbed) and at a distance from it (less disturbed). The diet consisted of 39% grasses, sedges, herbs and rushes (GSHR) and 58% Calluna vulgaris and Erica spp. (heather) in spring, compared with 14% grasses and 77% heather in winter, with small quantities of Vaccinium spp. (berry) and Pinus sylvestris (tree) in both seasons. In spring, faeces from disturbed grass and woodland sites indicated a diet with less GSHR and more heather and tree than faeces from less-disturbed sites, which could be due to an increased need for vigilance in exposed grassland and the need to seek cover. In contrast, faeces from all disturbed sites in winter indicated a diet with more GSHR and less heather than faeces from less-disturbed sites. This could be due to a seasonal decline in recreation and increase in hunting activity reversing the disturbance levels at the different sites, since hunting is not normally carried out in areas used by the public for recreation. We conclude that there may be nutritional benefits to deer of reducing disturbance near open grassland.

The utilization of long‐chain fatty acids as markers for diet composition estimates in ruminants: effects of animal species, diet composition and marker combination

AbstractUtilization of long‐chain fatty acids (LCFA) as diet composition markers, combined or not with alkanes, was evaluated in a study performed with sheep, goats and cattle fed on two different diets composed of herbaceous species and heather. Proportions of plant species were estimated from LCFA concentrations in plant species and faeces, using least‐square procedures, and were compared with those obtained using alkanes or LCFA + alkane. The impact of grouping plant species with similar LCFA + alkane profiles and the application of different levels of feeding selectivity within the dietary group on the accuracy of estimates were also assessed. Results showed that LCFA faecal recoveries were incomplete and tended to increase with carbon‐chain length in a curvilinear fashion in both diets and all animal species. Furthermore, differences between ruminant species and diets in the LCFA faecal recovery were observed. Combination of alkanes and LCFA provided the most accurate estimates of diet composition, while estimates based on LCFA alone were better than those using alkanes alone. Accuracy of these estimates differed among animal species but was not influenced by diet composition. Grouping plant species with similar LCFA + alkane profiles reduced the accuracy of estimates with a clear underestimation of the dietary group.

Evaluation of n-alkanes and their carbon isotope enrichments (δ13C) as diet composition markers

Plant cuticular n-alkanes have been successfully used as markers to estimate diet composition and intake of grazing herbivores. However, additional markers may be required under grazing conditions in botanically diverse vegetation. This study was conducted to describe the n-alkane profiles and the carbon isotope enrichment of n-alkanes of common plant species from the Mid Rift Valley rangelands of Ethiopia, and evaluate their potential use as nutritional markers. A total of 23 plant species were collected and analysed for long-chain n-alkanes ranging from heptacosane to hexatriacontane (C27 to C36), as well as their carbon isotopic ratio (13C/12C). The analysis was conducted by gas chromatography/combustion isotope ratio mass spectrometry following saponification, extraction and purification. The isotopic composition of the n-alkanes is reported in the delta notation (δ13C) relative to the Vienna Pee Dee Belemnite standard. The dominant n-alkanes in the species were C31 (mean ± s.d., 283 ± 246 mg/kg dry matter) and C33 (149 ± 98 mg/kg dry matter). The carbon isotopic enrichment of the n-alkanes ranged from −19.37‰ to −37.40‰. Principal component analysis was used to examine interspecies differences based on n-alkane profiles and the carbon isotopic enrichments of individual n-alkanes. Large variability among the pasture species was observed. The first three principal components explained most of the interspecies variances. Comparison of the principal component scores using orthogonal procrustes rotation indicated that about 0.84 of the interspecies variances explained by the two types of data sets were independent of each other, suggesting that the use of a combination of the two markers can improve diet composition estimations. It was concluded that, while the n-alkane profile of the pasture species remains a useful marker for use in the study region, the δ13C values of n-alkanes can provide additional information in discriminating diet components of grazing animals.

Carbon-based balanced trophic structure and flows in the offshore Lake Ontario food web before (1987–1991) and after (2001–2005) invasion-induced ecosystem change

Replicate mass-balanced solutions to Ecopath models describing carbon-based trophic structures and flows were developed for the Lake Ontario offshore food web before and after invasion-induced disruption. The food webs link two pathways of energy and matter flow: the grazing chain (phytoplankton–zooplankton-fish) and the microbial loop (bacteria–protozoans) and include 19 species-groups and three detrital groups. Mass-balance was achieved by using constrained optimization techniques to randomly vary initial estimates of biomass and diet composition. After the invasion, production declined for all trophic levels and species-groups except Chinook salmon. The trophic level (TL) increased for smelt, adult sculpin, adult alewife and Chinook salmon. Changes to ecotrophic efficiencies indicate a reduction in phytoplankton grazing, increased predation pressure on Mysis, adult smelt and alewife and decreased predation pressure on protozoans. Specific resource to consumer TTE changed; increasing for protozoans (8.0–11.5%), Mysis (0.6–1.0%), and Chinook salmon (1.0–2.3%) and other salmonines (0.4–0.5%) and decreasing for zooplankton (20.2–15.1%), prey-fish (9.7–8.8%), and benthos (1.7–0.6%). Direct trophic influences of recent invasive species were low. The synchrony of the decline in PP and species-group production indicates strong bottom-up influence. Mass balance required an increase of two to threefold in lower trophic level biomass and production, confirming a previously observed paradoxical deficit in lower trophic level production. Analysis of food web changes suggest hypotheses that may apply to other similar large pelagic systems including, (1) as pelagic primary productivity declines, overgrazing of zooplankton results in an increase in protozoan production and a loss of trophic transfer efficiency, (2) habitat and food web changes increased Mysis predation on Diporeia and contributed to their recent decline, and (3) production of Chinook salmon, the primary piscivore, was uncoupled from pelagic production processes. This study demonstrates the value of food web models to better understand the impact of invasive species and to develop novel hypotheses concerning trophic influences.

Sensitivity of stable isotope mixing models to variation in isotopic ratios: evaluating consequences of lipid extraction

Summary 1. Stable isotopes of carbon and nitrogen are increasingly used in studies of animal diet reconstruction via mixing models. However, isotope ratios of both consumer and source tissues can be altered by various amounts of lipids, potentially leading to biased estimates of diet composition when they are not taken into account. 2. We investigated the consequences of lipid correction on the estimation of diet composition with mixing models. Using empirical data from three northern terrestrial trophic systems, we illustrated the direct effects of lipid extraction (LE) on the δ13C and δ15N of source and consumer tissues and its ultimate effects on the reconstruction of the consumer’s diet. 3. In parallel, we developed a simulation tool in R, called fatsim, to assess sensitivity of mixing models to variation in isotopic ratios of samples from source or consumer tissues. This tool can be used to assess the effect of shifts in isotopic ratios caused by LE, or other sources of variation, in any trophic system and thus aid in decision making regarding lipid removal. 4. Using fatsim, we showed that the potential effects of LE on estimates of diet composition cannot be predicted without simulations, even in relatively simple systems. The sensitivity of a mixing model isotopic shift depends on the complexity of the system (number of sources) and on the relative positions of sources and consumers within the isotopic mixing space. 5. Our study confirms that the presence of lipids in tissues can bias the interpretation of diet reconstruction results. In a given trophic system, testing the sensitivity of a mixing model to LE can help decide whether lipid removal is required in order to avoid this bias.

Comparison of long-chain fatty acids and alkanes as markers to estimate diet composition of equines and cattle consuming heathland vegetation species

This study aimed to evaluate the application of long-chain fatty acids (LCFA) as an alternative or as a complement to alkanes to estimate diet composition in equines and cattle. Twelve mature crossbreed mares (385 ± 47 kg live weight – LW) and 6 adult non-lactating cows (499 ± 36 kg LW) of Asturiana de los Valles breed were divided in groups of 3 animals and housed in individual stalls. Animals received a daily total amount of 1.0 kg DM/100 kg LW of different diets composed of herbaceous ( Lolium perenne) and woody species ( Ulex gallii and heather). Diet composition was estimated from LCFA (i.e., C 22–C 34) and alkane (i.e., C 25–C 31 and C 33) concentrations in diet and faeces by least-squares procedures, using marker faecal concentrations uncorrected for incomplete faecal recovery (FC0), corrected using mean recovery rate of the dietary treatment that the animal belonged to (FC1), or corrected using mean recovery rate across all experimental diets (FC2). For all diet components, LCFA concentrations were higher than the alkane ones, with even-chain LCFA accounting for more than 0.80 of total LCFA. In general, faecal recovery (FR) of the markers was incomplete and related to their carbon-chain length. In equines, the FR of both markers tended to decrease with carbon-chain length in a curvilinear fashion ( P < 0.001), whereas in cattle LCFA and alkane FR tended to increase with carbon-chain length in a curvilinear ( P < 0.001) and linear ( P < 0.001) fashion, respectively. Diet composition had an effect ( P < 0.001) on the LCFA and alkane FR in both animal species, and, in equines, seemed to be related with diet digestibility, i.e., decrease of marker disappearance from the digestive tract with a decrease of diet digestibility. In general, diet composition estimates based on LCFA alone were more accurate than those obtained using alkanes alone. Combination of LCFA and alkane markers resulted in an increase ( P < 0.05) in the accuracy of diet estimates in both animal species, indicating a higher discriminatory power among plant species. The use of FC0 and FC2 resulted in the worst ( P < 0.05) estimates of diet composition, while high levels of accuracy were observed when using more accurate faecal corrections (FC1). Results showed that LCFA can be useful markers for studying diet selection of equines and cattle grazing on heathland vegetation communities, if a proper adjustment of their faecal concentrations prior to their application is applied. It is also concluded that use of LCFA in combination with alkanes can increase the accuracy of diet composition estimates.

Balancing nutrient supply and nutrient requirements in grazing sheep

Attempting to achieve a balance between the supply of and requirements for the major nutrients implies that demands for major nutrients can be adequately quantified, that the nutritive value of the consumed diet can be described in similar terms and that the diet actually consumed by the grazing sheep can be estimated, or at least predicted, from pasture and animal conditions. Several systems exist for defining the nutrient requirements of sheep and, whilst there are real differences between them, all are sufficiently accurate to allow their use in ration formulation and in grazing animal management. Similarly, nutritive value of feed components can be defined accurately. In grazing sheep, the major difficulty in balancing the supply of consumed nutrients against nutrient requirements is the estimation of diet composition and intake. Computer-based decision support tools are a useful aid to overcoming this problem. It is suggested that since profit derives from animal production per hectare and not per animal, the balancing of nutrient supply and requirements should not be attempted on an individual-animal basis.

Using fatty acids as dietary tracers in seabird trophic ecology: theory, application and limitations

Analysis of fatty acids (FAs) is an increasingly utilized tool in studies of trophic ecology in marine ecosystems. This powerful technique has proved useful in delineating spatial and temporal variability in diets, identifying the consumption of key species, and providing quantitative estimates of diet composition. Although consumer FA signatures are undeniably influenced by diet, they can also be affected by other factors including life-history stage, diet quality, and physiological state. Here, we review how FAs are assimilated, deposited, and metabolized in birds, and the implications of these processes on the various tissues commonly sampled for FA analyses. We then examine the assumptions underlying FA signature analysis when used in studies of seabird trophic ecology and propose a direction for future laboratory experiments that are needed to refine the approach. The correct interpretation of FA data relies on accounting for factors that alter predator FA metabolism and controlling for variability in the lipid content and FA composition of prey. Efforts should also be made to incorporate uncertainty associated with predator metabolism into models designed for quantitative diet estimation.

Evaluation of very long-chain fatty acids and n-alkane epicuticular compounds as markers for estimating diet composition of sheep fed heathland vegetation species

Application of very long-chain fatty acids (VLCFA) as an alternative or a complement to the alkane markers to estimate diet composition of sheep offered six different diets was evaluated. Twenty-four adult crossbred sheep were housed in metabolic crates and fed with diets composed of different proportions of herbaceous ( Lolium perenne and Trifolium repens) and woody species ( Erica spp., Calluna vulgaris and Ulex gallii). Diet composition was estimated from VLCFA (i.e., C 22–C 34) and alkane (i.e., C 25–C 33) concentrations in diet and faeces, by least-squares procedures, considering the plant species effectively offered to the animals (C1) or these plant species plus feeds that were not part of the diets but were available in the field at each experimental period (C2). Prior to this, faecal VLCFA and alkane concentrations were uncorrected for incomplete faecal recovery (FC0), corrected using recovery data for each individual ewe (FC1), corrected using mean recovery rate of the dietary treatment that the animal belonged to (FC2), or corrected using mean recovery rate across all experimental diets (FC3). For all diet components, total VLCFA concentrations were higher ( P<0.01) than those observed for alkanes, with a predomination of even-chain ( P<0.001) over odd-chain. Faecal recovery was incomplete and tended to increase with carbon-chain length in a curvilinear ( P<0.001) fashion for the even-chain VLCFA, and a linear ( P<0.001) one for odd-chain VLCFA and alkanes. Diet composition had an effect ( P<0.001) on faecal recovery of both markers. Estimates of diet composition obtained using alkanes alone were more accurate ( P<0.05) than those obtained with VLCFA alone while their combination resulted in an improvement ( P<0.05) of the accuracy. Estimates obtained when considering plant species offered effectively to the animals were more accurate ( P<0.001) than those obtained when considering more plant species as possible diet components. In general, use of faecal marker concentrations corrected with FC2 and FC3 provided equally accurate estimates of diet composition, indicating that an overall recovery data can be applied to these markers in grazing studies without losing accuracy in the estimation. Although the use of alkanes resulted in more accurate estimates of diet composition, results obtained in this study showed that VLCFA can be useful markers for studying diet selection of sheep grazing on shrubland vegetation communities. However, a suitable adjustment of their faecal concentrations prior to their application is recommended. It is also concluded that use of VLCFA in combination with alkanes could result in more accurate estimates of diet composition.

Botanical composition of diets grazed by beef cows in the Kansas Flint Hills during winter

Analysis of microscopic plant fragments recovered from the gut of wild herbivores (i.e., microhistological analysis) has been used to estimate diet composition, but there is debate as to whether microhistological analysis of fecal samples is an appropriate method for characterizing diets of grazing beef cattle. Therefore, our goal was to determine whether this approach could effectively quantify the botanical composition of diets grazed by mature beef cows in the Kansas Flint Hills during winter.

Grazing behaviour of domestic ruminants according to flock type and subsequent vegetation changes on partially improved heathlands

The management of different livestock species may promote different vegetation dynamics that will affect subsequent animal performance and the sustainability of extensive grazing systems. The grazing behaviour of two livestock species (domestic cattle and sheep) under two different managements (monospecific or mixed with goats), and the subsequent vegetation changes were studied on mechanically cleared heathlands (Ulex gallii Planchon-Erica spp.), with one third of the total area improved with perennial ryegrass-white clover pasture (Lolium perenne L.-Trifolium repens L.). Results showed that animals in mixed herds spent more time grazing than in monospecific groups. Goats spent more proportional time grazing on shrubland (68%) compared to sheep (35%) and cattle (19%), which spent most of the time on the improved pasture. The diet composition estimates also confirmed that these two animal species basically selected herbaceous species (89-95%) whilst gorse was an important element of goats" diets (28%). Throughout the experiment, an increment of gorse cover, height and phytomass was observed, especially under single grazing; whereas dead matter and herbaceous covers decreased more under single than under mixed grazing. Besides, heather percentage and gorse height underwent a higher increase under cattle than under sheep grazing. On the improved areas the sward height was significantly higher with cattle, and the gorse sprouting was more controlled under sheep grazing treatments. It is concluded that the complementary grazing of goats can enhance the utilization of these heterogeneous plant resources, providing a more efficient way for both productive and environmental goals than single cattle or sheep grazing.

Assessment of very long-chain fatty acids as complementary or alternative natural fecal markers to n-alkanes for estimating diet composition of goats feeding on mixed diets1

This study aimed to assess the use of very long-chain fatty acids (VLCFA) as an alternative or a complement to n-alkane markers for estimation of diet composition of goats fed 7 different diets, composed of different proportions of herbaceous (Lolium perenne and Trifolium repens) and heathland woody species (Erica umbellata, Erica cinerea, Calluna vulgaris, Erica arborea, and Ulex gallii), in a metabolism study. Diet composition was estimated from VLCFA (i.e., C(22) to C(34)) and alkane (i.e., C(25) to C(33)) concentrations in diet and feces, by least squares procedures. For all plant species VLCFA concentrations were greater than their alkane concentrations, especially for the herbaceous species and U. gallii. In general, fecal recovery of both markers was incomplete and increased in a curvilinear (P < 0.001) fashion with carbon-chain length. The plants comprising the diets had a significant effect (P < 0.001) on fecal recovery of VLCFA and alkanes. Diet composition estimates based on VLCFA alone were less accurate (P = 0.013) than those obtained using alkanes alone. Combination of VLCFA and alkane data resulted in the most accurate (P < 0.05) estimates, indicating an increase on the discriminatory power among plant species. Use of uncorrected fecal marker concentrations provided the poorest estimates of diet composition, and use of individual recovery data and mean fecal recovery data of the dietary treatment yielded the most accurate ones. Results obtained in this study show that VLCFA have potential to be used as diet composition markers along with alkanes.

Tissue-specific isotopic discrimination factors in gentoo penguin ( Pygoscelis papua) egg components: Implications for dietary reconstruction using stable isotopes

Stable isotope analysis ( δ 13C and δ 15N) is a useful tool when examining animal diets due to a general enrichment in heavier isotopes from prey tissues to the tissues of the predators consuming them. However, the amount of this enrichment, or discrimination, can vary among taxa and tissue type, limiting the use of stable isotope analysis when estimating diet composition. In this study we calculate the dietary isotopic discrimination factors of specific Pygoscelis penguin egg tissues, including eggshell, shell membrane, albumen and yolk, using a captive population of gentoo penguins fed known diets. We found that discrimination factors varied by isotope, tissue, and whether factors were calculated from whole fish or fish muscle. The observed variation in discrimination factors across tissues likely reflects differences in biochemical and metabolic processes during tissue synthesis. We validated the use of tissue discrimination factors derived in this study by independently reconstructing the diet composition of wild gentoo penguins at Cape Sherriff, Livingston Island, Antarctica using the δ 15N values of eggshell organics and shell membrane. While eggshell organics and shell membrane from the same egg differed in raw δ 15N values, modeling confirmed that these differences were due to tissue-specific isotopic discrimination. Furthermore, our results suggest that in 2006, female gentoo penguins at Cape Sherriff consumed a higher percentage of krill than fish during the egg-laying period.

The potential use of long-chain alcohols and fatty acids as diet composition markers: factors influencing faecal recovery rates and diet composition estimates in sheep

The limitations of the alkane technique in estimating the diet components of herbivores call for the introduction of new diet composition markers. Recently, long-chain alcohols (alcohols) and long-chain fatty acids (acids) have received the most attention and show great potential, when combined with alkanes, to estimate composition of complex diets. In the current study, faecal recoveries of alcohols and acids were determined in sheep in four different live weight groups fed three herbage species, either Leymus chinensis, L. dasystachys or Elymus sibiricum. Analysis of variance (ANOVA) was used to examine the effects of herbage species and live weight of sheep on faecal recoveries of individual alcohols and acids. Further, an indoor experiment with six sheep fed a diet of equal proportions, on dry matter (DM) basis, of three herbages was performed, allowing to assess the accuracy of alcohols and/or acids in combination with alkanes, to estimate diet composition. A one-sample t-test was carried out to test the accuracy of these estimates. Results of the first experiment indicated that the faecal recoveries of alcohols and acids were significantly affected by herbage species (P < 0.05). While the effects were significant or near significant for the faecal recoveries of some alcohols (C24-ol, C30-ol and C26-ol) (P ⩽ 0.05), no effect of live weight on faecal recoveries of acids was observed (P > 0.05). Therefore, adjustments based on diet-specific faecal recoveries might improve diet composition estimates. This was illustrated by the results of the second experiment. The diet composition estimated from alcohols or all combinations of alcohols with other marker types, after diet-specific correction of faecal recoveries, did not significantly differ from the actual composition (P > 0.05). However, using acids as additional markers resulted in poorer diet composition estimates. This study confirmed the utility of alcohols, combined with alkanes, as markers to estimate composition of complex diets. Although corrections based on mean faecal recoveries, average over animals and diets, resulted in some accuracy loss, results were still satisfactory and better than without recovery correction.

Differences between domestic herbivores species in alkane faecal recoveries and the accuracy of subsequent estimates of diet composition

This study aimed to evaluate effects of animal species on faecal recovery of n-alkane markers. In addition, impacts of using different sets of alkane faecal recoveries on diet composition estimates was assessed. Six mature crossbred mares (383 ± 59 kg live weight (LW)), six adult cows (500 ± 72 kg LW) of Asturiana de los Valles breed, eight Cashmere does (29 ± 5 kg LW) and eight crossbreed ewes (30 ± 5 kg LW) were used. Animals were housed in individual stalls and randomly assigned to one of two diets composed of herbage (D1) or herbage plus heather (D2) (3 animals per diet in the equine and cattle groups and 4 animals per diet in the goat and sheep groups). Diet composition was estimated from alkane concentrations ( i.e., C 25–C 33) in diets and faeces by least-squares procedures. Alkane faecal recovery (AFR) was incomplete and increased ( P<0.001) linearly with carbon chain length in all animal species. Animal species had an effect on faecal recovery of all alkanes, with equines having the highest recovery and goats the lowest. Differences in AFR between equines and ruminant species were higher for the shorter chain alkanes and tended to decrease with increased of carbon chain length. Within ruminant species, cattle had, in general, the highest faecal recovery for all alkanes indicating a lower level of disappearance of these markers in the digestive tract of cattle. The AFR set used in diet composition calculations affected ( P<0.05) the estimated proportions of all plant species in both diets. Utilization of uncorrected faecal alkane concentrations (AFR0) provided the poorest estimates of diet composition, and use of mean faecal recovery data of the dietary treatment (AFR1) yielded the most accurate. Results show that application of a general set of alkane faecal recoveries (AFR2) results in estimates of diet composition which distinguish less well between diet components with similar alkane profiles.

Use of faecal genotyping to determine individual diet

Abstract Faecal genotyping has been proposed as a method to examine the diets of individuals, but this application has been virtually unexplored by wildlife biologists. We used faecal genotyping and conventional scat analysis to determine the diets of 42 coyotes Canis latrans belonging to nine social groups in Alaska. We use rarefaction to examine the effect of scat sample size on the accuracy and precision of individual diets, and we simulate diets from scats to determine how diet richness and evenness affect sample size requirements. We then demonstrate the utility of this technique by examining variation in diet among individual coyotes and social groups in relation to prey availability. Estimates of diet diversity and composition were highly variable when <10 scats were used to construct the diet. Diets simulated with a uniform (i.e. even) distribution of prey items required generally smaller sample sizes to estimate diet diversity and richness than diets with exponentially distributed items; however,...

Validation of the n-alkane and NIRS techniques to estimate intake, digestibility and diet composition in sheep fed mixed lucerne: ryegrass diets

An experiment was carried out with sixteen non-pregnant, non-lactating adult Rasa Aragonesa ewes fed different proportions of lucerne and ryegrass hays to validate the use of n-alkanes and NIRS methods to estimate diet composition, intake and digestibility. The effect of two different faecal sampling procedures (daily pool (S1) or rectal spot samples (S2)) was also tested. The faecal concentration of n-alkanes was affected by the sampling procedure, although differences were lower than 12%. Faecal recoveries were not affected by diet, except in the case of C 23 ( P < 0.0001), C 28 ( P = 0.0264) and C 33 ( P = 0.0241), and followed a curvilinear pattern with alkane chain length. Recovery was complete in the case of C 29, C 31 and C 33, which countersigns the usefulness of these internal markers for digestibility and digestive flow studies (especially C 31, given its high concentration in most plants). The faecal recoveries of C 31 and C 32 were not similar, the assumption of identity affecting in an important way the reliability of intake estimates. The NIRS methodology appeared as a promising alternative for predicting diet composition ( R 2 of the cross-validation = 0.98) and faecal concentration of most natural alkanes, although that was not the case for dosed alkanes. In all cases, the prediction equations obtained from the spectra of the faecal spot samples were better than those obtained from daily pool samples.

Convergence of diet estimates derived from fatty acids and stable isotopes within individual grey seals

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 354:267-276 (2008) - DOI: https://doi.org/10.3354/meps07263 Convergence of diet estimates derived from fatty acids and stable isotopes within individual grey seals Strahan Tucker1,*, W. Don Bowen2, Sara J. Iverson1 1Department of Biology, Dalhousie University, 355 Oxford Street, Halifax, Nova Scotia B3H 4J1, Canada 2Population Ecology Division, Bedford Institute of Oceanography, Department of Fisheries and Oceans, 1 Challenger Drive, Dartmouth, Nova Scotia B2Y 4A2, Canada *Email: stucker2@dal.ca ABSTRACT: What animals consume is perhaps one of the most fundamental questions in ecology. Limitations of stomach content and faecal analyses have led to the development of alternative biochemical methods, namely fatty acid (FA) signature analysis and stable isotope (SI) analysis. Proportional estimates of diet composition can be made at the level of the individual by statistically matching a consumer’s FA signature to an inclusive prey database, after accounting for predator metabolism effects in a mixing model. Both of these approaches provide inferences about or quantitative estimates of diet that are time-integrated and readily applied to most taxa of interest, thereby alleviating many problems associated with conventional analysis. Moreover, analysis is done at the level of individual predators, thereby increasing our ability to detect differences amongst various demographic groups. However, it is difficult to validate diet estimates from either of these methods in the field, particularly for wide-ranging aquatic predators such as seals or seabirds consuming complex diets. Concurrent sampling of individual predators for both stable isotopes and fatty acids provide 1 such independent test. To that effect, we analyzed SI and FA for grey seals Halichoerus grypus (n = 75) and potential fish and invertebrate prey (n = 45). We show 2 lines of evidence for the convergence of stable isotope and fatty acid estimates of diet. First, in fish, invertebrates and grey seals, principal components derived from fatty acid signatures are correlated to the stable-carbon isotope (δ13C) signature of the same species. Second, both the estimated portion of pelagic prey and the trophic level of the diet derived from the quantitative analysis of fatty acid signatures of individual seals are positively correlated with the stable-carbon (δ13C) and stable-nitrogen (δ15N) signatures in those same individuals. The corroboration of independent measures of diet provides further validation of these biochemical methods to understand the foraging ecology of consumers. KEY WORDS: Fatty acids · Stable isotopes · Diet estimation · Corroboration · Grey seals Full text in pdf format PreviousNextCite this article as: Tucker S, Bowen WD, Iverson SJ (2008) Convergence of diet estimates derived from fatty acids and stable isotopes within individual grey seals. Mar Ecol Prog Ser 354:267-276. https://doi.org/10.3354/meps07263 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 354. Online publication date: February 07, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.