DOI: 10.5061/dryad.2rh22
title: Data from: Environmental stability increases relative individual specialisation across populations of an aquatic top predator

description: The concept of the niche has long been a central pillar in ecological
 theory, with a traditional focus on quantifying niches at the species or
 population level. However, the importance of individual-level niche
 variation is increasingly being recognised, with a strong focus on
 individual specialisation. While examples illustrating the contribution of
 the individual niche to whole population niche structure are accumulating
 rapidly, surprisingly little is known about the conditions that shape the
 differences between these two potentially divergent components. Though
 theory predicts that stability should influence the extent of such
 intra-specific specialisation, we know of no previous study that has
 investigated its role in individual specialisation, and the
 differentiation between individual- and population niches. Here, we
 studied the diet of individuals from multiple populations of an aquatic
 top-predator, Salmo trutta, inhabiting contrasting stable, groundwater fed
 and unstable, surface water fed pre-alpine streams. Based on stomach
 content analysis, we found that individuals living in stable environments
 displayed a higher degree of specialisation than those in unstable
 environments, with the between-individual component of niche width being
 approximately twice as high in the former. We subsequently validated these
 results by evidence gained from stable isotope analysis of muscle tissue.
 As such, we reveal that environmental stability can significantly
 influence individual niches within populations, leading to increased
 specialisation.
description: All trout
 sampledFile including the
 length, weight, and river sampled from for each fish in the study, as well
 as the unique identifier of each individual. Individuals can be traced
 through all other files through this identifier.Kicksampled
 invertebratesNumber of invertebrates
 from each taxonomic group found in kicksamples taken in each stream. The
 number of invertebrates was estimated by counting a large subsample, then
 multiplying up to reach the number of inverts in the whole
 sample.Quantitative
 FishingsQuantitative fishing
 effort for all streams used in the study to calculate average density of
 fish in both groundwater and surface water fed streams. The file shows raw
 data for counts in each run, number of runs fished, and length and average
 width of the stream in the sampled section. Densities are calculated using
 a removal sampling formula to calculate "true" number of fish in
 the section, then dividing by the area.Stomach
 contentsRaw stomach content
 count data. For every fish, with its given unique identifier number, the
 number of prey items of each taxonomic group found in the stomach is
 given. These are total counts of all stomach contents, not estimates based
 on a subsample.Raw Isotope
 DataRaw isotopic values for
 each fish, along with length, weight and unique identifier for these fish.
 In addition, baseline values for each stream are also contained in the
 file.Habitat
 DataFlow regime and
 substrate type data, recorded in percent of each river. PCA of stability
 is based on these variables.