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Potential drivers of seasonal shifts in fish omnivory in a subtropical stream

Authors:
  • Centro Universitario Litoral Norte Universidad de la República
  • Universidad de la República de Uruguay- CURE-Maldonado

Abstract and Figures

The trophic structure of fish assemblages often varies seasonally, following the changes in food availability and supposedly water temperature. To unveil potential drivers of trophic shifts, we studied changes in fish trophic structure at both whole-assemblage and species levels at contrasting food availability and water temperatures in a subtropical stream. We analysed the diet of the most abundant omnivorous species (Bryconamericus iheringii) monthly along the year, searching for relationships with environmental variables changing seasonally (i.e. temperature and water level) and with fish reproductive stage. We ran a single-species food choice field experiment with fixed animal and vegetal food availability in contrasting seasons to test food availability as driver of diet shifts. At the assemblage level, we found a higher consumption of vegetal during summer, reflecting the increased proportion of vegetal in the diet of omnivores, which dominated the assemblage. At the species level, the enhanced vegetal consumption was related to increases in temperature and reduction in water level. Moreover, fish selected for vegetal during summer and for animal food in winter under experimental conditions. Our findings support the role of temperature driving food web dynamics by increasing fish herbivory towards warmer scenarios, with potential strong implications for whole-assemblage trophic structure.
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... Indeed, several studies support this hypothesis. Caterpillars increased their preference for carbohydrates at higher temperatures (Lee et al. 2015), whereas omnivorous fish consume proportionally more plant material with increasing temperatures (Prejs 1984, Behrens and Lafferty 2007, Gonzá lez-Bergonzoni et al. 2016. Similarly, the herbivorous amphipod Ampithoe longimana Smith, 1873, collected in a cold-temperate environment, consumed more low organic and protein content seaweeds at higher temperatures (Sotka and Giddens 2009). ...
... Studies which support that rising temperature increased herbivory of aquatic omnivo res covered five taxa, including zooplankton , tadpoles (Carreira et al. 2016), crayfish (Carreira et al. 2017), aquatic snail (Zhang et al. this study) and fishes (Prejs 1984, Behrens and Lafferty 2007, Guinan Jr et al. 2015, Emde et al. 2016, Gonzá lez-Bergonzoni et al. 2016, Vejříková et al. 2016). Therefore, it seems a common phenomenon for aquatic ectothermic omnivores to increase herbivory as temperature increases. ...
... , Gonzá le z-Bergonzoni et al. 2016, Vejříková et al. 2016, Carreira et al. 2017. Therefore, I conclude that it might be a common phenomenon for aquatic omnivores to increase herbivory with rising temperature. ...
... González-Bergonzoni et al., 2015), and rivers(López-Rodríguez et al., 2019). ...
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... At the community level, a decrease in carnivory (i.e., with omnivorous and herbivorous species becoming more abundant and even dominant) within fish communities occurs at lower latitudes and in warmer climates(González-Bergonzoni et al. 2012). A change in diet towards more herbivory with increasing water temperature has been observed at individual, population, and community levels(González-Bergonzoni et al. 2016), following intra-annual variations. Food webs in tropical and subtropical lakes are thus more truncated than food webs in similar temperate shallow lakes, as found in comparative studies(Iglesias et al. 2017). ...
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... González-Bergonzoni et al. 2016), following intra-annual variations. Food webs in tropical and subtropical lakes are thus more truncated than food webs in similar temperate shallow lakes, as found in comparative studies(Iglesias et al. 2017). ...
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Chapter
If a fish is to be represented genetically in the next generation, at some time in its life it must begin to allocate resources to reproduction. Its reproductive success will depend on where and when it reproduces and on the resources it allocates to reproduction. Consequently, a study of the ecology of reproduction will include analyses of these problems in relation to the effects of environmental factors: where and when does spawning take place and what resources are allocated to reproduction as opposed to maintenance and growth? The problem of timing raises two sets of questions. The first set asks at what age does a fish becomes sexually mature and what factors determine this age? The second set asks what factors determine when in the year reproduction takes place? The problem of allocation also has two basic components: what portion of available resources is allocated to each reproductive attempt; and of the material resources that are allocated to reproduction, what portion is allocated to each individual offspring? This chapter explores each of these questions, where possible in relation to the effect that environmental factors have on their resolution.
Chapter
Competition is an interaction between individuals in which one or more of the participants suffers a net loss of fitness and none show a net gain compared with values in the absence of the competitive interaction. In terms of Table 8.1, competition is defined as - 0 or - -. The competition is asymmetrical if the loss in fitness suffered by some participants is much greater than that suffered by others. Mutualism is classified as + 0 or + + in Table 8.1. Some or all of the participants in the interaction show a net gain in fitness and none shows a net loss.
Chapter
The energy in the food ingested has one of two fates. Some is dissipated in the form of waste products or heat and some is incorporated as new tissue. The heat losses are generated by the metabolic processes through which the energy in the food is released to do useful work. This includes the work done in tissue function and repair, synthesizing new tissue and swimming. The processes which result in the dissipation of energy can be grouped together as maintenance. New tissue may take two forms: growth or gametes (Fig. 1.2). The income of energy (and nutrients) will be limited by time, the availability of food and the capacity of the gut to process food. How should this limited income be allocated among maintenance, growth and reproduction? What pattern of allocation will maximize the lifetime production of offspring? This chapter starts the discussion of these questions by first introducing the concept of an energy budget and then describing the effects of abiotic environmental factors on the maintenance item in the energy budget using a classification originally developed by Fry (1971). The succeeding three chapters examine the allocation of time and energy in relation to patterns of movement (Chapter 5), growth (Chapter 6) and reproduction (Chapter 7).
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