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East Kilbride, United Kingdom

Votier S.C.,University of Plymouth | Bearhop S.,University of Exeter | Witt M.J.,University of Exeter | Inger R.,University of Exeter | And 2 more authors.
Journal of Applied Ecology | Year: 2010

The large amount of discards produced by commercial fisheries can have major impacts on marine predator populations: this abundant food may increase populations of some scavengers or decrease others via accidental bycatch. Yet, despite the conservation implications of discard practices, the ecology of individual scavengers is poorly understood. Here, we assess the influence of commercial fisheries' activity on the foraging behaviour of individual breeding northern gannets Morus bassanus. Using recent developments in stable isotope mixing models (Stable Isotope Analysis in R or SIAR) we estimate individual discard consumption. Using GPS tracking and the Vessel Monitoring System (VMS), we investigate behavioural responses to trawlers. Analysis of conventional diet samples, as well as stable isotope ratios of carbon and nitrogen in blood (plasma and cells), highlight marked individual differences in the proportion of fishery discards in the diet. Individual differences in foraging behaviour revealed by stable isotopes show evidence of both short-term consistency and behavioural flexibility. At-sea path tortuosity of 25 gannets (tracked using GPS loggers) revealed scale-dependent adjustments in response to VMS-derived fishing vessel locations, as well as to sea surface temperature, chlorophyll a concentration and copepod abundance. The results also indicate individual variability in behavioural response to trawlers. Individual differences in the amount of discards estimated from SIAR were negatively correlated with differences in foraging trip length and body condition, indicating potential fitness consequences. Synthesis and applications. The management of commercial fisheries and apex predators is a daunting task. Ultimately, reducing bycatch and removing dependency on discards remain key conservation priorities, but managers should also ensure that scavenging species have sufficient alternative food to meet their energetic needs, to ameliorate potential unforeseen knock-on consequences. The results of Stable Isotope Analysis (SIAR) reveal intra-population differences in discard consumption by gannets; differences that have impacts on foraging effort and body condition. The use of GPS tracking and Vessel Monitoring Systems (VMS) reveal that gannet at-sea behaviour is influenced by fishing vessels, although this also varies among individuals. A combination of SIAR, GPS tracking and VMS can be used to study fishery/scavenger interactions in detail at the individual level, to answer fundamental questions about scavenging behaviour. © 2010 The Authors. Journal compilation © 2010 British Ecological Society. Source

Siwertsson A.,University of Tromso | Knudsen R.,University of Tromso | Praebel K.,University of Tromso | Adams C.E.,University of Glasgow | And 2 more authors.
Evolutionary Ecology | Year: 2013

Natural populations often vary in their degree of ecological, morphological and genetic divergence. This variation can be arranged along an ecological speciation continuum of increasingly discrete variation, with high inter-individual variation at one end and well defined species in the other. In postglacial fishes, evolutionary divergence has commonly resulted in the co-occurrence of a pelagic and a benthic specialist. We studied three replicate lakes supporting sympatric pelagic and benthic European whitefish (Coregonus lavaretus (L.)) morphs in search for early signs of possible further divergence into more specialized niches. Using stomach content data (recent diet) and stable isotope analyses (time-integrated measure of trophic niche use), we observed a split in the trophic niche within the benthic whitefish morph, with individuals specializing on either littoral or profundal resources. This divergence in resource use was accompanied by small but significant differences in an adaptive morphological trait (gill raker number) and significant genetic differences between fish exploiting littoral and profundal habitats and foraging resources. The same pattern of parallel divergence was found in all three lakes, suggesting similar natural selection pressures driving and/or maintaining the divergence. The two levels of divergence (a clear and robust benthic - pelagic and a more subtle littoral - profundal divergence) observed in this study apparently represent different stages in the process of ecological speciation. © 2012 The Author(s). Source

Evans K.L.,University of Sheffield | Newton J.,NERC Life science Mass Spectrometry Facility | Gaston K.J.,University of Sheffield | Gaston K.J.,University of Exeter | And 5 more authors.
Oikos | Year: 2012

How individuals colonising novel environments overcome the diverse suite of new selection pressures is a fundamental question in ecology and evolution. Urban environments differ markedly from the rural ones that they replace and successful colonisation of urban areas may therefore require local adaptation and phenotypic/genetic divergence from ancestral populations. Such a process would be facilitated by limited dispersal to and from the novel habitat. Here we assess divergence in migratory behaviour between seven pairs of urban and rural European blackbird Turdus merula populations along a 2800 km transect across Europe. This former forest specialist is now amongst the most abundant urban birds across most of its range. We use a stable isotope approach due to the lack of sufficient ringing data from multiple urban populations, and compare hydrogen isotopic ratios of tissues grown in the breeding (feathers) and wintering areas (claws) to derive an index of long distance migratory behaviour. We find a tendency for urban blackbirds to be more sedentary than rural ones at all sites and this divergence is particularly strong at the north-eastern limit of our transect, i.e. in Estonia and Latvia. These urban populations are those that have been established most recently (from the late 1930s to 1950s) implying that urbanisation can promote rapid ecological divergence. The increased sedentary behaviour of urban birds could promote further ecological divergence between rural and urban populations, such as the earlier breeding of urban blackbirds, and in some cases may contribute to their previously documented genetic divergence. © 2011 The Authors. Oikos © 2012 Nordic Society Oikos. Source

Hooker O.E.,University of Glasgow | Barry J.,University of Glasgow | van Leeuwen T.E.,University of Glasgow | Lyle A.,University of Glasgow | And 3 more authors.
Hydrobiologia | Year: 2016

Phenotypic variation in populations of fishes that inhabit postglacial lakes is often associated with trophic specialisations. A common sympatric foraging divergence seen in Arctic charr is into either plankton or littoral-zoobenthos feeding specialisms. In this study, we report a sympatric polymorphic Arctic charr population which is not centred on this divergence but instead manifests as a plankton (pelagic)—profundal zoobenthos foraging specialisms. The head shape of profundal fish was round and robust, the body thick set and pectoral fins long and wide. In contrast, the head of pelagic fish was pointed and slender, the body fusiform in shape and with short, narrow pectoral fins. There was no difference between profundal and pelagic fish in gill raker number. Body lipid content was significantly higher in pelagic fish as were the number or Diphyllobothrium cysts. The carbon isotope ratio was more heavily depleted in profundal fish. There was no dietary overlap in the prey items recovered from stomach contents of profundal and pelagic fish. We suggest the proximate driver behind the sympatric divergence was the successful exploitation of the profundal zone. The consequences of this have led to the development of adaptations in morphology and behaviour to support and maintain this divergence. © 2016 The Author(s) Source

Knudsen R.,University of Tromso | Siwertsson A.,University of Tromso | Adams C.E.,University of Tromso | Adams C.E.,University of Glasgow | And 2 more authors.
Ecology of Freshwater Fish | Year: 2014

Two unconnected time-integrated tracers of niche use provided similar conclusions about individual foraging behaviour and niche adaptations (functional traits in head shape) within a subarctic lake population of Arctic charr (Salvelinus alpinus). Zooplanktivorous individuals mainly from the pelagic zone were characterised by having low δ13C values, high infections of the parasites transmitted by pelagic copepods (especially Diphyllobothrium spp.) and slender heads with long snouts. In contrast, fish individuals that had consumed benthic prey in the littoral zone were enriched in δ13C and had high abundances of parasites transmitted by Gammarus lacustris (Cyathocephalus truncatus and Cystidicola farionis) and a robust head shape. There were strong positive correlations between individual δ13C values and the abundance of the two parasite species transmitted by Gammarus, but a negative correlation between δ13C and the infection of copepod-borne parasites. The close relationships between diet variation (foraging behaviour), the time-integrated ecological tracers (SI and parasites) and functional trophic morphology (niche adaptations) evidently reflect long-term temporally stable niche use of each individual predator. The two independent time-integrated tracers both gave valuable information of specialised trophic behaviour at the individual level, which is an important basis for studies related to ecological (e.g., resource partitioning) and evolutionary (e.g., polymorphism) topics within a population. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd. Source

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