ArticlePDF Available

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.
This content is subject to copyright. Terms and conditions apply.
A preview of the PDF is not available
... The response of zooplankton density and biomass to temperature variation has been previously observed at Lake Mangueira (Rosa et al., 2017(Rosa et al., , 2021. Seasonal processes affecting zooplankton, directly through the metabolism of organisms, mortality rates, reproductive events or competition, or indirectly through changes in resource availability, are induced by changes in temperature (Sartori et al., 2009;González-Bergonzoni et al., 2016). Responses of MTZ to WT related to ORP could indicate an indirect relationship with nutrient availability and system production, since biologically important elements, such as nitrogen, undergo redox changes. ...
... Under these circumstances, resources are available to benthic organisms and other generalist species that could drive the omnivorous fishes to benthivory (Bezerra et al., 2018). Such alternative state increases energy dissipation in the upper trophic levels (D'Alelio et al., 2016), which is also linked to omnivory (González-Bergonzoni et al., 2016) and the consumption of benthos (Bezerra et al., 2018). This phenomenon can be described as "benthification" in oligotrophic waters (Mayer et al., 2014), representing a sudden change from turbidity to clarity caused by invertebrate filter feeders consuming phytoplankton, a change which benefits generalist fish (Karatayev et al., 2007). ...
Article
Full-text available
We analyzed the seasonal variation in the diet, trophic niche breadth (Levins index), the partitioning of food resources (Pianka’s symmetric index) and trophic level (weighed average of trophic level of each prey determined in FishBase and SeaLifeBase platform) of Plagioscion squamosissimus (Heckel, 1840) and Hydrolycus scomberoides (Cuvier, 1819) in the Machado River, Rondônia, Brazil. Fish samplings were conducted bimonthly from June 2013 to May 2015 in five sites, using eight sets of gillnets. The occurrence frequency and volumetric frequency were used to quantify the food items. We analyzed the stomach contents of 283 individuals, 134 of H. scomberoides and 149 of P. squamosissimus. Fish were the most consumed food item by both piscivorous species. However, H. scomberoides mostly ingested pelagic fish (e.g. Characiformes fishes and Prochilodus nigricas Spix & Agassiz, 1829), while P. squamosissimus mostly consumed benthic fish [e.g. Pimelodus blochii Valenciennes, 1840 and Tenellus trimaculatus (Boulenger, 1898)]. Hydrolycus scomberoides presented the trophic level 3.55 for both periods analyzed, while P. squamosissimus 4.01 in the flood period and 3.82 in the drought period. Seasonal variations in the diet of H. scomberoides and P. squamosissimus were observed (PERMANOVA). Specifically, P. squamosissimus consumed mainly “Siluriformes” fishes and P. blochii in the drought period. The trophic niche breadth of P. squamosissimus was greater than that of H. scomberoides in the flood period. The species P. squamosissimus and H. scomberoides had low (0.35) food niche overlap in both seasons analysed. The data indicated that P. squamosissimus has a generalist feeding habit, while H. scomberoides is specialized in prey selection. The overlap of food niche between the species in both periods of the hydrological cycle was low, indicating that niche partitioning was probably the main mechanism of coexistence of these species, with little relationship with variations of the hydrological cycle. KEYWORDS Diet; trophic niche; Machado River; seasonal variation
... González-Bergonzoni et al., 2015), and rivers(López-Rodríguez et al., 2019). ...
Article
With 6 main basins, and being the second smallest country in South America, Uruguay has a high freshwater ecosystem diversity. The study of zooplankton communities dates back to 1949, but remained marginal until the end of the 20th century when the number of publications increased notably. Here, we revise the history and accumulated knowledge on the zooplankton community in Uruguayan continental ecosystems, highlighting the main approaches and milestones. So far, ca. 100 academic papers with 219 authors have been published in international, regional, and local journals, accumulating more than 2150 citations. Most of the published studies come from shallow lakes, followed by reservoirs and estuaries, and were concentrated in the southern part of Uruguay. Most taxonomic records correspond to the Río de la Plata basin, followed by the Atlantic Ocean basin, and the Río Uruguay basin. The number of records in the rest of the country is comparatively low, with minima occurring in the basins of the rivers Negro and Santa Lucía. A total of 170 species belonging to 117 genera have been recorded, mainly for Copepoda, Cladocera and Rotifera. Limnological studies in Uruguay have historically followed an ecosystemic approach, thus, most of the literature referring to zooplankton has such a perspective. The most relevant ecological aspects analyzed so far include trophic interactions, species survival and dispersion, biological invasions, the relationship with eutrophication and climatic variability, and have applied traditional as well as functional and trait-based approaches. Our analysis allowed us to detect important knowledge gaps, that warrant attention for future studies which can help elucidate local and regional processes in freshwater zooplankton in Uruguay.
... 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). ...
Preprint
Full-text available
NON FORMATED PUBLISHED VERSION Feedbacks between climate change and eutrophication: revisiting the allied attack concept and how to strike back Despite its well-established negative impacts on society and biodiversity, eutrophication continues to be one of the most pervasive anthropogenic influence along the freshwater to marine continuum. The interaction between eutrophication and climate change, particularly climate warming, was explicitly focused upon a decade ago in the paper by Moss et al. (2011), which called for an integrated response to both problems, given their apparent synergy. In this review, we summarise advances in the theoretical framework and empirical research on this issue and analyse the current understanding of the major drivers and mechanisms by which climate change can enhance eutophication, and vice versa, with a particular focus on shallow lakes. Climate change can affect nutrient loading, through changes at the catchment and landscape levels by affecting hydrological patterns and fire frequency, and through temperature effects on nutrient cycling. Biotic communities and their interactions can also be directly and indirectly affected by climate change, leading to an overall weakening of resilience to eutrophication impacts. Increasing empirical evidence now indicates several mechanisms by which eutrophying aquatic systems can increasingly act as important sources of greenhouse gases to the atmosphere, particularly methane. We also highlight potential feedbacks between eutrophication, cyanobacterial blooms, and climate change. Facing both challenges at the same time is more pressing than ever. Meaningful and strong measures at the landscape and water body levels are therefore required if we are to ensure ecosystem resilience and safe water supply, conserving biodiversity, and decreasing the carbon footprint of freshwaters.
... 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). ...
Article
Full-text available
Despite its well-established negative impacts on society and biodiversity, eutrophication continues to be one of the most pervasive anthropogenic influence along the freshwater to marine continuum. The interaction between eutrophication and climate change, particularly climate warming, was explicitly focused upon a decade ago in the paper by Moss et al. (2011), which called for an integrated response to both problems, given their apparent synergy. In this review, we summarise advances in the theoretical framework and empirical research on this issue and analyse the current understanding of the major drivers and mechanisms by which climate change can enhance eutophication, and vice versa, with a particular focus on shallow lakes. Climate change can affect nutrient loading, through changes at the catchment and landscape levels by affecting hydrological patterns and fire frequency, and through temperature effects on nutrient cycling. Biotic communities and their interactions can also be directly and indirectly affected by climate change, leading to an overall weakening of resilience to eutrophication impacts. Increasing empirical evidence now indicates several mechanisms by which eutrophying aquatic systems can increasingly act as important sources of greenhouse gases to the atmosphere, particularly methane. We also highlight potential feedbacks between eutrophication, cyanobacterial blooms, and climate change. Facing both challenges at the same time is more pressing than ever. Meaningful and strong measures at the landscape and water body levels are therefore required if we are to ensure ecosystem resilience and safe water supply, conserving biodiversity, and decreasing the carbon footprint of freshwaters.
Article
Full-text available
In South America, the knowledge of trematode diversity parasitizing freshwater fishes is still scarce, as less than 5% of the freshwater fish fauna has been examined for parasites. A similar situation applies to studies on digenean life cycles, which have become increasingly rare. Among the digenean families parasitizing freshwater fishes in the region, Haploporidae is considered the richest in species diversity. However, information about the developmental stages of haploporid life cycles remains fragmentary. Particularly, in Argentina, nine cercariae attributed to the family Haploporidae have been described using morphological analysis, and only two life cycles of this family have been completely elucidated. In this study a new type of cercaria, morphologically assigned to the family Haploporidae and collected from the snail Heleobia parchappii (Cochliopidae) in Los Padres shallow lake, Buenos Aires province, was identified using morphological and molecular techniques. The molecular analysis, based on 28S and ITS2 sequences, revealed that the cercariae were 100% identical to adult specimens of Saccocoelioides nanii (Haploporidae) parasitizing the fish Prochilodus lineatus (Prochilodontidae) from Los Talas, Buenos Aires province. Our results not only provide information about the life cycle of S. nanii but also show that a molecular and morphological approach can be extremely useful in identifying the developmental stages of digeneans and elucidating their life cycles.
Article
Full-text available
Human activities are one of the main causes of biodiversity loss and the reduction of ecosystem services. These activities, together with seasonality and the associated ecological and physicochemical changes, are the main modulators of fish communities in subtropical streams. Using data from 62 streams from Uruguay, we analyzed the effect of environmental variables on several attributes of fish community structure. First, we evaluated the effect of climatic seasonality on fish biomass, density, mean body length and weight using a paired t-test. Secondly, we analyzed the relationship between seasonality, environmental variables (environmental degradation, watershed area, and habitat diversity), and species richness with fish biomass using a linear mixed model. Fish biomass and density were higher in summer meanwhile, mean length was higher in winter. We found a humped relationship between biomass and environmental degradation in winter and summer, with low biomass in sites with high and low quality. Our model shows that species richness increase generates an increase in biomass, with the magnitude of this increase being greater during winter. In view of this results, we highlight that the humped pattern founded in our work should have special management attention to avoid misinterpretation of biomass increases caused by environmental degradation.
Article
Nature's variability plays a major role in maintenance of biodiversity. As global change is altering variability, understanding how key food web structures maintain stability in the face of variation becomes critical. Surprisingly, little research has been undertaken to mechanistically understand how key food web structures are expected to operate in a noisy world and what this means for stability. Omnivory, for example, has been historically well studied but largely from a static perspective. Recent empirical evidence suggests that the strength of omnivory varies in response to changing conditions in ways that may be fundamental to stability. In the present article, we extend existing omnivory theory to predict how omnivory responds to variation and to show that dynamic omnivory responses are indeed a potent stabilizing structure in the face of variation. We end by synthesizing empirical examples within this framework, demonstrating the ubiquity of the theoretical mechanisms proposed across ecosystem types, spatial scales, and taxa.
Article
Full-text available
To investigate the potential long-term consequences of environmental warming in subtropical systems, we compare the trophic structure of shallow lakes in tropical and subtropical regions. In total, 25 meso-eutrophic lakes with piscivorous fish were sampled during summer along a latitudinal gradient in South America. The fish catch per unit of effort and the omnivorous fish to zooplankton biomass ratios were significantly lower in the tropical lakes. Despite the lower fish biomass, no significant difference was found in zooplankton or phytoplankton communities or in the zooplankton to phytoplankton biomass ratio between the two sets of lakes. Nevertheless, regression models based on the combined dataset show higher cyanobacteria and total phytoplankton biomass at lower zooplankton to phytoplankton biomass ratio and higher omnivorous fish to zooplankton biomass ratio. Cyanobacteria biomass was dominated by non bloom-forming taxa and was inversely related to the biomass of calanoid copepods suggesting that these herbivores may play an important role in controlling edible cyanobacteria in warm shallow lakes. Overall, our results, however, suggest that warming will have relatively minor impacts on the pelagic trophic structure of shallow subtropical lakes supporting the idea of weaker trophic cascades in warm (sub)tropical lakes in comparison to temperate ones.
Article
Full-text available
Body size is usually considered a good indicator of trophic position in fish communities. Indeed, the proverbial wisdom that “Big Fish Eat Little Fish” is consistent with observations from marine systems where systematic removal of the largest individuals has occurred, with cascading effect in the ecosystems. Trophic cascades are also well documented in temperate lakes but may not be as pronounced in (sub)tropical lakes due to higher degree of fish omnivory. We analysed fish communities along a climatic gradient and showed the classical correlation between body size and relative trophic position disappears in warmer climates where large fish appear to be feeding systematically on the lowest trophic levels. This concurs with experimental findings demonstrating that omnivorous fish tend to include more plant and less animal matter in their diet at higher temperatures. Accordingly, the community-wide trophic web indicators, calculated based on stable isotopes (δ¹³C and δ¹⁵N), showed that the average degree of trophic diversity declined from cold to warm lakes and that the trophic webs become more truncated towards warmer climates. This has implications for lake restoration approaches in warmer climates and in temperate lakes within the context of global warming.
Article
Full-text available
Climate and hydrology are relevant control factors determining the timing and amount of nutrient losses from land to downstream aquatic systems, in particular of phosphorus (P) from agricultural lands. The main objective of the study was to evaluate the differences in P export patterns and the performance of alternative monitoring strategies in streams under contrasting climate-driven flow regimes. We compared a set of paired streams draining lowland micro-catchments under temperate climate and stable discharge conditions (Denmark) and under sub-tropical climate and flashy conditions (Uruguay). We applied two alternative nutrient sampling programs (high-frequency composite sampling and low-frequency instantaneous-grab sampling) and estimated the contribution derived from point and diffuse sources fitting a source apportionment model. We expected to detect a pattern of higher total and particulate phosphorus export from diffuse sources in streams in Uruguay streams, mostly as a consequence of higher variability in flow regime (higher flashiness). Contrarily, we found a higher contribution of dissolved P in flashy streams. We did not find a notably poorer performance of the low-frequency sampling program to estimate P exports in flashy streams compared to the less variable streams. We also found signs of interaction between climate/hydrology and land use intensity, in particular in the presence of point sources of P, leading to a bias towards underestimation of P in hydrologically stable streams and overestimation of P in flashy streams. Based on our findings, we suggest that the evaluation and use of more accurate monitoring methods, such as automatized flow-proportional water samplers and automatized bankside analyzers, should be prioritized whenever logistically possible. However, it seems particularly relevant in currently flashy systems and also in systems where climate change predictions suggest an increase in stream flashiness.
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).
Article
(1) The effects of a reduction in food supply during the breeding season of female Gasterosteus aculeatus L. were examined. (2) The number of spawnings and total egg production were a function of ration level. Although the normal maintenance ration of a non-spawning female was estimated to be about 100 J day-1, a ration more than five times greater was required for the females to spawn regularly without showing a net loss in weight. At lower rations the females subsidized egg production from body tissue. (3) Females that were spawning had relatively high levels of tissue hydration and relatively low liver weights, and in these features showed some similarities to starved females. (4) Starved females spawned only once at the most after the onset of food deprivation. (5) Egg production per spawning was not a function of ration level but was positively related to the weight of the female, but the interval between successive spawnings (inter-spawning interval) was negatively related to ration level. (6) Estimates of the gross efficiency of the conversion of food into eggs indicated that this efficiency was positively related to the weight of the female, but decreased with increasing inter-spawning interval.