Cross-validation of δ15N and FishBase estimates of fish trophic position in a Mediterranean lagoon: The importance of the isotopic baseline

2013 ◽  
Vol 135 ◽  
pp. 77-85 ◽  
Author(s):  
Giorgio Mancinelli ◽  
Salvatrice Vizzini ◽  
Antonio Mazzola ◽  
Stefano Maci ◽  
Alberto Basset
Keyword(s):  
Cross Validation ◽  
Trophic Position ◽  
Mediterranean Lagoon ◽  
Isotopic Baseline ◽  
Fish Trophic Position

Ecophysiological determinants of the variation in 137Cs concentrations between and within lacustrine fish populations

2005 ◽  
Vol 62 (12) ◽  
pp. 2727-2739 ◽  
Author(s):  
Marcus Sundbom ◽  
Markus Meili
Keyword(s):  
Body Size ◽  
Trophic Position ◽  
Fish Populations ◽  
Chernobyl Fallout ◽  
Population Means ◽  
Activity Concentrations ◽  
Resource Specialization ◽  
Total Variability ◽  
Biomagnification Factors ◽  
Fish Trophic Position

One decade after the Chernobyl fallout, the variability of 137Cs activity concentrations among fish within a Swedish lake was >20-fold based on 1361 individuals from seven species collected continually during 1996–1999. Of the total variability, 64% was due to differences between species but only 7% due to temporal variation, which was 1.3-fold for the whole community and 1.3- to 2-fold for population means. Contamination increased with body size (0.6- to 6-fold) and decreased with body condition in most species (1.3-fold). Body size and time together accounted for about half of the total variation within populations. Fish 137Cs was related to differences in feeding ecology, both between and within populations. Biomagnification factors ranged from 2.4 to 5.8. Contamination was highest in piscivorous populations and individuals, intermediate in herbivores and zooplanktivores, and lowest in fish specialized in benthic invertebrates despite their association with contaminated sediments. The 137Cs variance within populations was not correlated with their niche width but moderately positively correlated with fish trophic position and strongly positively correlated with functional omnivory (diversity in prey 137Cs). We conclude that individual resource specialization is an important source of variation in 137Cs concentrations within fish populations.

Effects of Bythotrephes on the trophic position of native macroinvertebrates

2010 ◽  
Vol 67 (1) ◽  
pp. 58-69 ◽  
Author(s):  
Sophie E. Foster ◽  
W. Gary Sprules
Keyword(s):  
Stable Isotopes ◽  
Trophic Position ◽  
Nitrogen Isotope ◽  
Diet Overlap ◽  
Invertebrate Predators ◽  
Invasion Impacts ◽  
Isotopic Baseline ◽  
Zooplankton Communities

We measured the δ15N and δ13C stable isotopes of pelagic invertebrate predators in six central Ontario lakes, three invaded by Bythotrephes and three not invaded, to determine the effects of Bythotrephes invasion on diet overlap and trophic position of the predators. Seasonally averaged, lake-specific isotope signatures of bulk zooplankton were used as the isotopic baseline for determining nitrogen-based trophic position or carbon enrichment of the predators. Trophic positions of native Chaoborus , Leptodora , and Mysis in invaded lakes were not elevated compared with noninvaded lakes, suggesting that these predators do not feed directly on Bythotrephes. Nitrogen signatures of Mysis and Chaoborus were similar as were those of Leptodora and Bythotrephes, suggesting that invasion impacts will be greatest on Leptodora as has been observed. The trophic position of large Mysis was generally the highest and most variable of all predators, probably because it feeds on copepods that are more enriched in the heavier nitrogen isotope than bulk zooplankton and because Bythotrephes tends to decrease the ratio of cladocerans to copepods in invaded zooplankton communities.

Predicting mercury levels in yellow perch: use of water chemistry, trophic ecology, and spatial traits

2001 ◽  
Vol 58 (7) ◽  
pp. 1419-1429 ◽  
Author(s):  
Ben K Greenfield ◽  
Thomas R Hrabik ◽  
Chris J Harvey ◽  
Stephen R Carpenter
Keyword(s):  
Body Condition ◽  
Yellow Perch ◽  
Fish Community ◽  
Trophic Ecology ◽  
Trophic Position ◽  
Growth Patterns ◽  
Biological Traits ◽  
Lake Chemistry ◽  
Fish Samples ◽  
Fish Trophic Position

Recent research suggests that wetland abundance surrounding lakes, fish trophic position, and fish community composition may influence the bioavailability of mercury (Hg) to fish. To compare the importance of these spatial and biological factors to chemical factors known to influence bioavailability, we determined the relationship between 24 lake traits and Hg concentrations in yellow perch (Perca flavescens; whole fish samples) for 43 northern Wisconsin lakes. Independent variables included biological traits such as fish trophic position and body condition, spatial traits such as lake hydrologic position and surrounding wetland abundance, and chemical traits such as pH and water color. The strongest predictor of fish Hg levels was pH (R2 = 0.42; p < 0.002). Of the biological traits measured, yellow perch body condition explained significant additional variation (final R2 = 0.54; p = 0.024). Trophic position explained limited variability and population abundance of planktivores and piscivores were not correlated to perch Hg levels. Regression tree models indicated that small lakes with greater than 6% wetland in their watershed have moderately elevated fish Hg levels. Our results indicate that within-lake chemistry and fish growth patterns are stronger correlates of Hg levels in yellow perch than spatial traits, trophic position, or fish community attributes.

Within- and among-population variation in the trophic position of a pelagic predator, lake trout (Salvelinus namaycush)

2000 ◽  
Vol 57 (4) ◽  
pp. 725-731 ◽  
Author(s):  
M Jake Vander Zanden ◽  
Brian J Shuter ◽  
Nigel P Lester ◽  
Joseph B Rasmussen
Keyword(s):  
Body Size ◽  
Total Variation ◽  
Lake Trout ◽  
Prey Size ◽  
Trophic Position ◽  
Feeding Habits ◽  
Salvelinus Namaycush ◽  
Population Variation ◽  
Prey Fish ◽  
Fish Trophic Position

Many aquatic consumers have flexible feeding habits, and the diet and trophic position of a species can be expected to vary both within and among populations. In this study, we quantify the importance of both within- and among-population trophic variation for lake trout (Salvelinus namaycush) using stable isotope designations of trophic position from 13 Ontario and Quebec lakes. Lake-to-lake differences explained 78% of the total variation in lake trout trophic position. Analysis using both stable isotopes and published dietary data demonstrated that the trophic position of lake trout failed to increase appreciably as a function of animal body size. This finding was attributed to weak predator size - prey size relationships as well as to there being no relationship between prey fish trophic position and body size. The variance in trophic position of a population reflects the extent to which individuals forage as trophic specialists; however, we did not identify any one factor that was correlated with within-population trophic variation. Our finding that much of the total variation in trophic position represents among-population differences indicates that considering the average trophic position of a population does not mask substantial within-population trophic variation.

Item Bias Analysis of the Young Schema-Questionnaire for Psychopathology, Gender, and Educational Level

2011 ◽  
Vol 27 (1) ◽  
pp. 65-70 ◽  
Author(s):  
Marleen M. Rijkeboer ◽  
Huub van den Bergh ◽  
Jan van den Bout
Keyword(s):  
Educational Level ◽  
Cross Validation ◽  
Item Bias ◽  
Response Patterns ◽  
Dutch Population ◽  
Bias Analysis ◽  
Young Schema Questionnaire ◽  
Item Functioning ◽  
Item Level ◽  
Schema Questionnaire

This study examines the construct validity of the Young Schema-Questionnaire at the item level in a Dutch population. Possible bias of items in relation to the presence or absence of psychopathology, gender, and educational level was analyzed, using a cross-validation design. None of the items of the YSQ exhibited differential item functioning (DIF) for gender, and only one item showed DIF for educational level. Furthermore, item bias analysis did not identify DIF for the presence or absence of psychopathology in as much as 195 of the 205 items comprising the YSQ. Ten items, however, spread over the questionnaire, were found to yield relatively inconsistent response patterns for patients and nonclinical participants.

CROSS-VALIDATION IS NEEDED

1972 ◽  
Vol 17 (2) ◽  
pp. 85-86
Author(s):  
RICHARD F. Q. JOHNSON
Keyword(s):  
Cross Validation
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