ABSTRACT Chemical recovery of anthropogenic acidified streams is being observed in North Hemisphe... more ABSTRACT Chemical recovery of anthropogenic acidified streams is being observed in North Hemisphere countries, while biological recovery processes are delayed and appear to be complex. Here, we conducted a one year survey on several Baetis species, a known acid-sensitive genus, highlighting how developmental strategies could influence the presence and abundance of their populations in streams of varying acid levels. We found contrasting sensitivity of Baetis species to acidification, ranging from "very" acid-sensitive (B. melanonyx) and "slightly" acid-sensitive (B. alpinus and B. rhodani) to "acid-benefiting" (B. vernus). The study highlighted that both B. alpinus and B. rhodani showed similar patterns under acidic conditions. Occurrence and abundance appeared unequivocally related to the high level of plasticity of their bivoltine cycle. On the contrary, the univoltine B. vernus and B. melanonyx demonstrated opposite responses to acidification revealing strong differences in their sensitivity at early stages. Our findings underline the importance of life cycle knowledge in considering species specific responses to freshwater acidification and its implication on the understanding and monitoring of biological recovery processes.
ABSTRACT Species in complex ecosystems, such as streams, are influenced by multiple top-down and ... more ABSTRACT Species in complex ecosystems, such as streams, are influenced by multiple top-down and bottom-up control factors. Food-resource and competition/predation mechanisms are among the most influential factors controlling population ecology. Balancing the effects of bottom-up control by food resources and top-down control by competition/predation can trigger compensatory responses leading to changes in species ecology within the limit of their plasticity. These effects have been well studied in simple controlled conditions, but predicting their outcome is difficult for natural populations in genuine ecosystems because of the heterogeneity of environmental conditions and the complexity of biotic interactions. We investigated the ecological response in terms of feeding habits and population parameters of the stream-dwelling predator, Siphonoperla torrentium, to modifications of its prey abundance and of competition/predation mechanisms induced by a gradient of acidification. We conducted a 1-y survey in a set of 3 streams showing very similar abiotic conditions except for their acidification status. Despite significantly lower potential prey availability and higher potential intraspecific competition in the most acidic stream compared to neutral streams, the proportion of prey in the diet of S. torrentium did not differ across streams. However, S. torrentium was less aggregated, and had higher secondary production, longer larval development, and smaller adult size in the most acidic stream than in the less acidic streams, results suggesting compensatory mechanisms. Our study design did not permit us to differentiate the importance of the biotic factors involved, but the study contributes to our understanding of the importance of conjugated biotic effects on population ecology.
Numerous papers associate the rate of leaf litter decomposition with the presence/abundance of ga... more Numerous papers associate the rate of leaf litter decomposition with the presence/abundance of gammarids. However, recent studies showed that Gammarus sp. may have high diet diversity (as animals, moss, algae). In this context, we quantify the diet of Gammarus fossarum to highlight and statistically consider what many authors affirmed rather by observation. To this end, we used a recently described multivariate analysis, called %PCA, which allows investigating data dealing with diet composition. Body size and microhabitat type were revealed highly significant variables governing several parameters of the diet. In particular, our results show that food item size and predatory behaviour increased with body size, whilst the type and abundance of food consumed was related to microhabitat type. Furthermore, body-size had a significant effect on specialisation whatever the microhabitat type. Niche overlap also decreased as pairwise differences in body-size increased, allowing the aggregation of individuals from different instars. We conclude that G. fossarum exhibit an opportunistic behaviour, which makes necessary to reconsider the importance of gammarid "shredding" activity to accurately assess stream functioning and flux/ redistribution of energy and matter (leaf litter breakdown). We discuss the functional feeding group membership of G. fossarum at the individual and population level.
ABSTRACT SynonymsAcid stress; Freshwater acidification; Surface water acidificationGlossaryAcidos... more ABSTRACT SynonymsAcid stress; Freshwater acidification; Surface water acidificationGlossaryAcidosis: Increase of blood or hemolymph acidity.ANC (acid-neutralizing capacity): ANC or buffering capacity, expressed as μeq.L−1, describes the ability of a solution to resist changes in pH by neutralizing the acidic input. ANC is defined as the difference between strong base cations and strong acid anions. Low freshwater ANC (−1) suggests that aquatic organisms can be submitted to acid stress associated with the runoff of acidic waters (during rainfall or snowmelt events) into streams or lakes.Biomarker: “A biochemical, cellular, physiological or behavioural variation that can be measured in tissue or body fluid samples or at the level of whole organisms that provides evidence of exposure to and/or effects of, one or more chemical pollutants (and/or radiations)” (Depledge 1994).Collectors (active collectors, filterers): Collect fine particulate organic matter (FPOM, 0.45 μm t ...
Implemented for decades as part of the ‘best management practices (BMPs)’ for controlling urban r... more Implemented for decades as part of the ‘best management practices (BMPs)’ for controlling urban runoff impacts on receiving waters, stormwater management ponds (SMPs) have been increasingly viewed as potential habitats for urban wildlife. However, since SMPs are subject to a lot of environmental constraints, research toward assessing their ecological quality and their actual benefits as habitats for biota is needed. In this study, the sediment toxicity of eight SMPs located in Southern Ontario, Canada was assessed using the sediment quality triad (SQT) approach. Sediment samples were collected for chemical, ecotoxicological and biological analyses. An oligochaete-based index approach (Oligochaete Index of Lake Bioindication and percentage of pollution-sensitive species) was used as the biological endpoint and integrated into a weight-of-evidence approach to assessing the general sediment quality of the ponds. Our results showed that (i) heavy metals in the sediment and (ii) chloride...
ABSTRACT Chemical recovery of anthropogenic acidified streams is being observed in North Hemisphe... more ABSTRACT Chemical recovery of anthropogenic acidified streams is being observed in North Hemisphere countries, while biological recovery processes are delayed and appear to be complex. Here, we conducted a one year survey on several Baetis species, a known acid-sensitive genus, highlighting how developmental strategies could influence the presence and abundance of their populations in streams of varying acid levels. We found contrasting sensitivity of Baetis species to acidification, ranging from "very" acid-sensitive (B. melanonyx) and "slightly" acid-sensitive (B. alpinus and B. rhodani) to "acid-benefiting" (B. vernus). The study highlighted that both B. alpinus and B. rhodani showed similar patterns under acidic conditions. Occurrence and abundance appeared unequivocally related to the high level of plasticity of their bivoltine cycle. On the contrary, the univoltine B. vernus and B. melanonyx demonstrated opposite responses to acidification revealing strong differences in their sensitivity at early stages. Our findings underline the importance of life cycle knowledge in considering species specific responses to freshwater acidification and its implication on the understanding and monitoring of biological recovery processes.
ABSTRACT Species in complex ecosystems, such as streams, are influenced by multiple top-down and ... more ABSTRACT Species in complex ecosystems, such as streams, are influenced by multiple top-down and bottom-up control factors. Food-resource and competition/predation mechanisms are among the most influential factors controlling population ecology. Balancing the effects of bottom-up control by food resources and top-down control by competition/predation can trigger compensatory responses leading to changes in species ecology within the limit of their plasticity. These effects have been well studied in simple controlled conditions, but predicting their outcome is difficult for natural populations in genuine ecosystems because of the heterogeneity of environmental conditions and the complexity of biotic interactions. We investigated the ecological response in terms of feeding habits and population parameters of the stream-dwelling predator, Siphonoperla torrentium, to modifications of its prey abundance and of competition/predation mechanisms induced by a gradient of acidification. We conducted a 1-y survey in a set of 3 streams showing very similar abiotic conditions except for their acidification status. Despite significantly lower potential prey availability and higher potential intraspecific competition in the most acidic stream compared to neutral streams, the proportion of prey in the diet of S. torrentium did not differ across streams. However, S. torrentium was less aggregated, and had higher secondary production, longer larval development, and smaller adult size in the most acidic stream than in the less acidic streams, results suggesting compensatory mechanisms. Our study design did not permit us to differentiate the importance of the biotic factors involved, but the study contributes to our understanding of the importance of conjugated biotic effects on population ecology.
Numerous papers associate the rate of leaf litter decomposition with the presence/abundance of ga... more Numerous papers associate the rate of leaf litter decomposition with the presence/abundance of gammarids. However, recent studies showed that Gammarus sp. may have high diet diversity (as animals, moss, algae). In this context, we quantify the diet of Gammarus fossarum to highlight and statistically consider what many authors affirmed rather by observation. To this end, we used a recently described multivariate analysis, called %PCA, which allows investigating data dealing with diet composition. Body size and microhabitat type were revealed highly significant variables governing several parameters of the diet. In particular, our results show that food item size and predatory behaviour increased with body size, whilst the type and abundance of food consumed was related to microhabitat type. Furthermore, body-size had a significant effect on specialisation whatever the microhabitat type. Niche overlap also decreased as pairwise differences in body-size increased, allowing the aggregation of individuals from different instars. We conclude that G. fossarum exhibit an opportunistic behaviour, which makes necessary to reconsider the importance of gammarid "shredding" activity to accurately assess stream functioning and flux/ redistribution of energy and matter (leaf litter breakdown). We discuss the functional feeding group membership of G. fossarum at the individual and population level.
ABSTRACT SynonymsAcid stress; Freshwater acidification; Surface water acidificationGlossaryAcidos... more ABSTRACT SynonymsAcid stress; Freshwater acidification; Surface water acidificationGlossaryAcidosis: Increase of blood or hemolymph acidity.ANC (acid-neutralizing capacity): ANC or buffering capacity, expressed as μeq.L−1, describes the ability of a solution to resist changes in pH by neutralizing the acidic input. ANC is defined as the difference between strong base cations and strong acid anions. Low freshwater ANC (−1) suggests that aquatic organisms can be submitted to acid stress associated with the runoff of acidic waters (during rainfall or snowmelt events) into streams or lakes.Biomarker: “A biochemical, cellular, physiological or behavioural variation that can be measured in tissue or body fluid samples or at the level of whole organisms that provides evidence of exposure to and/or effects of, one or more chemical pollutants (and/or radiations)” (Depledge 1994).Collectors (active collectors, filterers): Collect fine particulate organic matter (FPOM, 0.45 μm t ...
Implemented for decades as part of the ‘best management practices (BMPs)’ for controlling urban r... more Implemented for decades as part of the ‘best management practices (BMPs)’ for controlling urban runoff impacts on receiving waters, stormwater management ponds (SMPs) have been increasingly viewed as potential habitats for urban wildlife. However, since SMPs are subject to a lot of environmental constraints, research toward assessing their ecological quality and their actual benefits as habitats for biota is needed. In this study, the sediment toxicity of eight SMPs located in Southern Ontario, Canada was assessed using the sediment quality triad (SQT) approach. Sediment samples were collected for chemical, ecotoxicological and biological analyses. An oligochaete-based index approach (Oligochaete Index of Lake Bioindication and percentage of pollution-sensitive species) was used as the biological endpoint and integrated into a weight-of-evidence approach to assessing the general sediment quality of the ponds. Our results showed that (i) heavy metals in the sediment and (ii) chloride...
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