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The hydrologic regime is regarded as the primary driver of freshwater ecosystems, structuring the physical habitat template, providing connectivity, framing biotic interactions, and ultimately selecting for specific life histories of aquatic organisms. In the present study, we tested ecological theory predicting directional relationships between major dimensions of the flow regime and life history composition of fish assemblages in perennial free-flowing rivers throughout the continental United States. Using long-term discharge records and fish trait and survey data for 109 stream locations, we found that 11 out of 18 relationships (61%) tested between the three life history strategies (opportunistic, periodic, and equilibrium) and six hydrologic metrics (two each describing flow variability, predictability, and seasonality) were statistically significant (P < or = 0.05) according to quantile regression. Our results largely support a priori hypotheses of relationships between specific flow indices and relative prevalence of fish life history strategies, with 82% of all significant relationships observed supporting predictions from life history theory. Specifically, we found that (1) opportunistic strategists were positively related to measures of flow variability and negatively related to predictability and seasonality, (2) periodic strategists were positively related to high flow seasonality and negatively related to variability, and (3) the equilibrium strategists were negatively related to flow variability and positively related to predictability. Our study provides important empirical evidence illustrating the value of using life history theory to understand both the patterns and processes by which fish assemblage structure is shaped by adaptation to natural regimes of variability, predictability, and seasonality of critical flow events over broad biogeographic scales.
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... AA is a technique used to quantify the location of observations in multidimensional space from their distance to extreme points (Cutler & Breiman, 1994), yielding a proportional life history strategy score for each species in our analysis. This approach is conceptually appropriate because most fish species exhibit some combination of life history strategies rather than a single strategy King & McFarlane, 2003;Mims & Olden, 2012). ...
... We then summed life history strategy scores from species presence/absence data for each site and scaled the cumulative site scores from 0 to 1 (Mims & Olden, 2012;Olden & Kennard, 2010;Pecuchet et al., 2017). This provided an index of the relative importance of opportunistic, periodic, and equilibrium-based life history strategies at each sampling site for use in statistical models described below. ...
... results indicate the utility of life history theory for understanding the ecological importance of environmental stability and stochasticity. First, we identified trade-offs between fecundity, spawning season duration, and parental care that organized species along a trilateral continuum of opportunistic-, periodic-, and equilibrium-type life history strategies, consistent with prior researchMims & Olden, 2012;Winemiller & Rose, 1992). Second, we identified mechanistic effects of watershed hydrology: We showed that opportunistic life history strategies were more common where flashy runoff is expected and less common in karst terrain where groundwater inputs are expected to stabilize stream temperature and flow(Table 5).Prior research has demonstrated effects of flow regulation on life history diversity within riverine fish communities(Kominoski et al., 2018;Mims & Olden, 2013;Olden et al., 2006;Perkin et al., 2017), and our study extends this perspective from regulated rivers into headwater streams. ...
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Life history theory provides a framework to understand environmental change based on species strategies for survival and reproduction under stable, cyclical, or stochastic environmental conditions. We evaluated environmental predictors of fish life history strategies in 20 streams intersecting a national park within the Potomac River basin in eastern North America. We sampled stream sites during 2018–2019 and collected 3801 individuals representing 51 species within 10 taxonomic families. We quantified life history strategies for species from their coordinates in an ordination space defined by trade‐offs in spawning season duration, fecundity, and parental care characteristic of opportunistic, periodic, and equilibrium strategies. Our analysis revealed important environmental predictors: Abundance of opportunistic strategists increased with low‐permeability soils that produce flashy runoff dynamics and decreased with karst terrain (carbonate bedrock) where groundwater inputs stabilize stream flow and temperature. Conversely, abundance of equilibrium strategists increased in karst terrain indicating a response to more stable environmental conditions. Our study indicated that fish community responses to groundwater and runoff processes may be explained by species traits for survival and reproduction. Our findings also suggest the utility of life history theory for understanding ecological responses to destabilized environmental conditions under global climate change. We show that species traits for survival and reproduction explain fish community responses to groundwater and runoff processes in headwater streams. Our results also indicate the utility of life history theory for understanding ecological responses to destabilized environmental conditions under global climate change.
... We mapped fish biodiversity at the watershed level (i.e., Hydrologic Unit Code 8, or HUC8) across the CRB. We focused on three metrics: (a) the proportion of native species within each HUC8 (i.e., fish nativity); (b) the fish conservation value, calculated as the number of species of conservation concern present in that HUC8 (i.e., total number of Critically Endangered, Endangered, Vulnerable, and Near Threatened species); and (c) the seasonal dependency of each fish assemblage, calculated as the proportion of species adapted to seasonal flow regimes (Mims & Olden, 2012), that is, the aggregated share of opportunistic and periodic strategists. The list of species and origin (native vs. non-native) per HUC8 was obtained through NatureServe (Natureserve, 2018) and the U.S. Geological Survey's Non-indigenous Aquatic Species database (USGS, 2018), after excluding records from lentic systems and from non-self-established populations (e.g., eradicated or stocked populations, populations with failed establishment, vagrant species). ...
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Large dams are a leading cause of river ecosystem degradation. Although dams have cumulative effects as water flows downstream in a river network, most flow alteration research has focused on local impacts of single dams. Here we examined the highly regulated Colorado River Basin (CRB) to understand how flow alteration propagates in river networks, as influenced by the location and characteristics of dams as well as the structure of the river network—including the presence of tributaries. We used a spatial Markov network model informed by 117 upstream‐downstream pairs of monthly flow series (2003–2017) to estimate flow alteration from 84 intermediate‐to‐large dams representing >83% of the total storage in the CRB. Using Least Absolute Shrinkage and Selection Operator regression, we then investigated how flow alteration was influenced by local dam properties (e.g., purpose, storage capacity) and network‐level attributes (e.g., position, upstream cumulative storage). Flow alteration was highly variable across the network, but tended to accumulate downstream and remained high in the main stem. Dam impacts were explained by network‐level attributes (63%) more than by local dam properties (37%), underscoring the need to consider network context when assessing dam impacts. High‐impact dams were often located in sub‐watersheds with high levels of native fish biodiversity, fish imperilment, or species requiring seasonal flows that are no longer present. These three biodiversity dimensions, as well as the amount of dam‐free downstream habitat, indicate potential to restore river ecosystems via controlled flow releases. Our methods are transferrable and could guide screening for dam reoperation in other highly regulated basins.
... These analyses provide more information on ecosystem-level changes over time by grouping species based on feeding preference, habitat use, or reproductive mode (Dos Santos et al., 2017;Rogers, Bunnell, Madenjian, & Warner, 2014). Anthropogenic alteration of habitats can also greatly affect functional communities in ecosystems susceptible to frequent regime shifts (Melchiorre et al., 2013;Mims & Olden, 2012;Pool, Olden, Whittier, & Paukert, 2010). Changes to either functional composition or diversity in response to habitat alteration are more likely to affect ecosystem-level processes than species composition alone (Tilman et al., 1997). ...
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Large rivers are susceptible to anthropogenic alteration, which can result in drastic changes to their functional ecology. We evaluated spatial–temporal changes in the functional fish communities of the Upper Mississippi River System (UMRS) using data from six study reaches. Species were classified into one of 14 feeding guilds and mass per unit effort (MPUE) was then calculated for each feeding guild annually per gear type. MPUE was standardized using the multigear mean standardization method (MGMS) and log‐transformed. Both ANOSIM and Chi‐square tests were used to determine differences in MPUE among reaches. We then estimated functional diversity by calculating the number of functional groups (N), Margalef's d, Pielou's J′, Shannon's Diversity, and Simpson's Diversity Index. An AR(1) time series model was used to investigate proportional changes in each guild over 25 years. To evaluate the effect of invasive Carp species in invaded reaches, a Chow test was applied to observations between 2000 and 2005. Analyses revealed differences in the functional fish community among reaches. We found differences in functional diversity metrics among study reaches, but there was little evidence that this differed between invaded and non‐invaded reaches. Results determined that invertivore/detritivores have been consistently declining system‐wide, with few groups showing a net change. There was also little evidence that invasion altered the proportion of any functional guild. Evaluating the spatial–temporal patterns of functional communities is beneficial to understanding the resilience of a system and can provide further insight into its trophic needs when considering future restoration initiatives.
... Recent otolith microchemistry work with juvenile Chinook salmon, for example, demonstrated that individuals used a complex array of habitat types to achieve maximum growth prior to ocean migration [113]. The diversity of life histories found here suggests that Broad Whitefish populations experience frequent disturbance or high environmental variability [98,106,114]. ...
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Conservation of Arctic fish species is challenging partly due to our limited ability to track fish through time and space, which constrains our understanding of life history diversity and lifelong habitat use. Broad Whitefish (Coregonus nasus) is an important subsistence species for Alaska's Arctic Indigenous communities, yet little is known about life history diversity, migration patterns, and freshwater habitat use. Using laser ablation Sr isotope otolith micro-chemistry, we analyzed Colville River Broad Whitefish 87 Sr/ 86 Sr chronologies (n = 61) to reconstruct movements and habitat use across the lives of individual fish. We found evidence of at least six life history types, including three anadromous types, one semi-anadro-mous type, and two nonanadromous types. Anadromous life history types comprised a large proportion of individuals sampled (collectively, 59%) and most of these (59%) migrated to sea between ages 0-2 and spent varying durations at sea. The semi-anadromous life history type comprised 28% of samples and entered marine habitat as larvae. Nonanadromous life history types comprised the remainder (collectively, 13%). Otolith 87 Sr/ 86 Sr data from juvenile and adult freshwater stages suggest that habitat use changed in association with age, seasons, and life history strategies. This information on Broad Whitefish life histories and habitat use across time and space will help managers and conservation planners better understand the risks of anthropogenic impacts and help conserve this vital subsistence resource. PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone. Citation: Leppi JC, Rinella DJ, Wipfli MS, Brown RJ, Spaleta KJ, Whitman MS (2022) Strontium isotopes reveal diverse life history variations, migration patterns, and habitat use for Broad Whitefish (Coregonus nasus) in Arctic, Alaska. PLoS ONE 17(5): e0259921. https://doi.org/ 10.
... O aumento do nível da água, com consequente aumento da profundidade e largura dos riachos, contribui para o aumento do número de espécies. Diferenças hidrológicas ao longo do ano podem moldar a comunidade local de peixes (Mims & Olden 2012 No entanto, o PEC e áreas limítrofes têm registradas 60 espécies de anfíbios e 82 de répteis. Os dados incluíram métodos de armadilhas de interceptação e queda, procura visual e auditiva, encontros ocasionais, e trabalhos publicados sobre a herpetofauna da área de estudada. ...
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O Estado de Mato Grosso com seu extenso território, abriga atualmente 46 unidades de con- servação estaduais que ocupam uma área equivalente a 2,8 milhões de hectares, cujo território abriga grandes belezas naturais e uma rica biodiversidade, muitas vezes ainda desconhecida, sendo capaz de prestar serviços ambientais indispensáveis à sociedade. A Secretaria de Estado de Meio Ambiente (SEMA-MT) tem empenhado esforços juntamente com o Programa Áreas Protegidas da Amazônia (ARPA) e com pesquisadores da Universidade Federal de Mato Grosso (UFMT) no levantamento e catalogação do conhecimento sobre a flora e fauna existentes nas referidas áreas protegidas. Dentre os 18 parques, o Parque Estadual Cristalino é uma das unidades de conservação estaduais que possui grande potencial de uso público e uma excepcional biodiversidade, o que tem despertado interesse crescente por parte da comunidade científica. A grande riqueza das espécies vegetais deste parque está distribuída em diferentes fitofisionomias que variam desde Floresta Ombrófila Densa a manchas de Campinarana e Campo Rupestre. A significância desta unidade de conservação está relacionada, também, à proteção da riqueza e da composição das populações e comunidades faunísticas que vivem nesses variados ambientes, apresentando espécies ameaçadas de extinção, vulneráveis ou insuficientemente conhecidas. O Programa de Pesquisa em Biodiversidade - PPBio apoiou as atividades de campo e a implan- tação de um sistema de amostragem padronizada, um módulo com doze parcelas amostrais. No primeiro momento, 16 (dezesseis) grupos biológicos foram inventariados, os quais permiti- ram o conhecimento detalhado da biodiversidade do Parque Estadual Cristalino e a realização de estudos mais aprofundados de distribuição, dinâmica temporal e espacial, estudos de biopros- pecção e, bem como subsídios para o uso adequado de determinadas áreas do parque. Por meio da cooperação técnica entre a SEMA-MT, a UFMT e o ARPA, foi possível a publicação deste livro que contém a compilação dos estudos sistemáticos realizados no Parque Estadual Cristalino. O conhecimento científico gerado por este trabalho, possibilitará uma maior valorização da unidade de conservação por parte das comunidades acadêmicas e da sociedade em geral, princi- palmente para as populações locais, que poderão utilizar-se desta publicação como instrumen- to para o processo de conscientização em ações de educação ambiental, contribuindo, assim, para a conservação in situ da biodiversidade do Parque Estadual Cristalino e da Amazônia.
... Novel climates could trigger alterations at the watershed scale of rivers, and impact ecological and biological processes at downstream areas, signifying altered habitat conditions (Davies, 2010;Schneider et al., 2013). Such changes might pose threats to species that thrive in stable and predictable habitats, such as equilibrium (Mims and Olden, 2012). Our findings that equilibrium species are hosted in sub-basins with considerable climatic instability raise further concerns for their future, as even moderate modifications of climate would likely lead to major population fluctuations and reorganization of their communities. ...
Article
Understanding how climate change would affect biota inhabiting sensitive and highly valuable ecosystems, spanning broad regions, is essential to anticipate implications for biodiversity and humans, and to identify management and mitigation measures. Traditionally, assessments to evaluate climatic risks over broad regions and for many species, implement models that allow the projection of a climate driven redistribution of diversity. Still, the wealth and quality of the background information (e.g., species presence data) constrain the accuracy and representativeness of such frameworks. As an alternative, here, we developed a twofold approach to assess the vulnerability of 86 European freshwater fish. We accounted for shifts in a multidimensional climatic space of broader hydrological units that host freshwater bodies in Europe, and linked metrics of their climatic stability with groups of species, which were generated from six intrinsic traits that shape species adaptive capacity to climate change. Our results demonstrated that the climate of all (n = 538) river sub-basins hosted in the European Union territory would change by 2100, with more than 10% of them being projected to gain completely novel climates. Sub-basins predicted to lose more than 90% of their current climatic space were mainly identified in the area around the Baltic Sea, but also in Mediterranean regions (i.e., Iberian Peninsula). Important numbers of fish species with life history strategies that are considered susceptible to climate change were identified in sub-basins that were predicted to completely lose their current climatic conditions. Clearly, the climate of valuable freshwater ecosystems is changing, affecting species and their communities in varying ways. The risk is high, and is not limited to specific regions; thus, new effective strategies and measures are needed to conserve freshwater fish and their habitats across Europe.
... River flow discharge and water temperature are considered the main drivers of fish behaviour Mims and Olden, 2012). In this study, capture variability was significantly related to water temperature and river flow discharge in the case of L. sclateri. ...
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River connectivity is essential for the resilience of fish assemblages and populations and is a priority goal to reach good ecological status for river systems. Increasing knowledge on the functionality of restoration tools such as fishways is relevant for future management strategies. The present two-year assessment showed clear ecological contributions of different types of multispecies fishways in the fish assemblage of a strongly modified Mediterranean-type river. Just after their implementation, early and extended use by dominant river-resident fish of both naturelike and technical fishways were observed. All fishways were used in different seasons, especially during the migratory periods by potamodromous cyprinids, suggesting a possible use as migration corridors. Fishways also may provide compensatory habitats for small and juvenile individuals throughout the annual cycles, mostly for rheophilic fish inside nature-like bypasses and for limnophilics inside technical types. Fluvial habitat characteristics and lower flow variability inside the fishways could favour their role as a fish refuge, mainly to juveniles of cyprinids, in heavily regulated rivers where large flow fluctuations occurred. Nature-like fishways could be a better option to function as a compensatory habitat for rheophilic cyprinids in Mediterranean-type Rivers, even more because their use by large nonnative limnophilics seems to be very scarce. However, technical fishways could offer the opportunity to establish control traps of some nonnative fish, which could be of interest to reduce the risk of spreading invasive fish. Therefore, fish ecology and local hydrology should drive the decision between the types to implement. The obtained information on the ecological functionality of multispecies fishways should be considered for applying successful river restorations that are demanded by water and wildlife management schemes (e.g., the European Water Framework Directive).
... In addition, river flows play a role in the movement of geochemical and biological matter and energy in the environment and can become a habitat for river biota adapted to seasonally fluctuating flows. Rivers also provide spatial connectivity between habitats and allow for the spread of plants, animals, and fungi [90]. ...
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An extreme landscape is a spatially heterogeneous area with unusual topography that is prone to natural disasters but still exhibits interrelated structures and functions. One of the important functions of an extreme landscape is its ecological function. This study aimed to determine the structure and reveal the ecological functions of an extreme landscape in a tropical region of West Java, with special reference to Rongga Sub-district. The method used was a combination of remote sensing techniques and geographic information systems, which were required to process, analyze, and interpret Landsat 8 OLI/TIRS data. The landscape structure was quantified by landscape metrics, after which an analysis of ecological functions was carried out based on the constituent elements of the landscape. The results showed that the landscape structure of Rongga Sub-district consists of various elements of agroforestry land, open fields, settlements, shrubs, plantations, and rainfed and irrigated rice fields. Additionally, secondary forest land acted as a landscape matrix where rivers crossed as natural corridors. The amount of each element varied; agroforestry land had the highest value, indicating that this element showed a high degree of human intervention. Each patch was adjacent to other patch types, and the landscape diversity was quite high. The extreme topography of Rongga Sub-district supports the landscape connectivity and consequently the presence of wild animals in this area. Therefore, Rongga Sub-district has an essential ecological function as a refuge for protected animals living in non-conservation areas.
... | scielo.br/ni Although this model is widely used to classify the life histories of freshwater fishes (Mims, Olden, 2012;Logez et al., 2015), it has been applied predominantly to species that inhabit the floodplains of major rivers systems. In these environments, the flood pulse is the principal driver of the structure of aquatic communities and the life history strategies of resident fishes (Junk et al., 1989). ...
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The reproductive strategy of a species must be adjusted to variations in environmental conditions to guarantee population balance. Hydrological fluctuations in Amazonian streams of terra firme (non-flooded) are controlled primarily by local rainfall. Fish assemblages are composed predominantly of species of small size. We investigated the reproductive strategy of the cryptic catfish Helogenes marmoratus and assessed the influence of environmental variables (e.g., rainfall, conductivity, habitat descriptors) on its reproductive activity in a catchment of the Guamá River in the eastern Brazilian Amazon. Through monthly collections between March 2019 and March 2020, we identified an extended reproductive period between July 2019 and March 2020. Males mature at smaller sizes than females (♂ = 27.41 mm; ♀ = 31.36 mm). We confirmed batch spawning, low fecundity (59.55 ± 22.76 stage IV oocytes), and large oocytes (1.24 ± 0.15 mm). Our results indicated that H. marmoratus strategy occupies an intermediate place between opportunistic and equilibrium gradient. Multiple regressions showed that thalweg depth, electrical conductivity, leaf litter, and rainfall are important drivers of reproductive activity of females of H. marmoratus, explaining 32% of the variation of the GSI. Our study provides evidence of differentiated reproductive response between the sexes to environmental variables.
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Understanding the effects of hydrology on fish populations is essential to managing for native fish conservation. However, despite decades of research illustrating streamflow influences on fish habitat, reproduction, and survival, biologists remain challenged when tasked with predicting how fish populations will respond to changes in flow regimes. This uncertainty stems from insufficient understanding of the context‐dependent mechanisms underlying fish responses to, for example, periods of reduced flow or altered frequency of high‐flow events. We aim to address this gap by drawing on previous research to hypothesize mechanisms by which low and high flows influence fish populations and communities, identifying challenges that stem from data limitations and ecological complexity, and outlining research directions that can advance an empirical basis for prediction. Focusing flow ecology research on testing and refining mechanistic hypotheses can help narrow management uncertainties and better support species conservation in changing flow regimes.
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The National Water-Quality Assessment Program of the US Geological Survey is designed to assess the status of and trends in the quality of the Nation's ground- and surface-water resources and to link the status and trends with an understanding of the natural and human factors that affect the quality of water. The study design balances the unique assessment requirements of individual hydrologic systems with a nationally consistent design structure that incorporates a multiscale, interdisciplinary approach. The goal of the Occurrence and Distribution Assessment is to characterize, in a nationally consistent manner, the broad-scale geographic and seasonal distributions of water-quality conditions in relation to major contaminant sources and background conditions. from Authors
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The Flood Pulse Concept in River—Floodplain Systems Wolfgang J. Junk Max Planck Institut für Limnologie, August Thienemann Strasse 2, Post fach 165, D-2320 Pion, West Germany Peter B. Bayley and Richard E. Sparks Illinois Natural History Survey, 607 E. Peabody Dr., Champaign, IL 61820, USA Abstract JUNK, W. J., P. B. BAYLEY, AND R. E. SPARKS, 1989. The flood pulse concept in river-floodplain systems, p. 110-127. In D. P. Dodge [ed.] Proceedings of the International Large River Symposium. Can. Spec. Publ. Fish. Aquat. Sci. 106. The principal driving force responsible for the existence, productivity, and interactions of the major biota in river—floodplain systems is the flood pulse. A spectrum of geomorphological and hydrological conditions produces flood pulses, which range from unpredictable to predictable and from short to long duration. Short and generally unpredictable pulses occur in low-order streams or heavily modified systems with floodplains that have been leveed and drained by man. Because low-order stream pulses are brief and unpredictable, organisms have limited adaptations for directly utilizing the aquatic/terrestrial transition zone (ATTZ), although aquatic organisms benefit indirectly from transport of resources into the lotic environment. Conversely, a predictable pulse of long duration engenders organismic • adaptations and strategies that efficiently utilize attributes of the ATTZ. This pulse is coupled with a dynamic edge effect, which extends a "moving littoral" throughout the ATTZ. The moving littoral prevents prolonged stagnation and allows rapid recycling of organic matter and nutrients, thereby resulting in high productivity. Primary production associated with the ATTZ is much higher than that of permanent water bodies in unmodified systems. Fish yields and production are strongly related to the extent of accessible floodplain, whereas the main river is used as a migration route by most of the fishes. In temperate regions, light and/or temperature variations may modify the effects of the pulse, and anthropogenic influences on the flood pulse or floodplain frequently limit production. A local floodplain, however, can develop by sedimentation in a river stretch modified by a low head dam. Borders of slowly flowing rivers turn into floodplain habitats, becoming separated from the main channel by levées. The flood pulse is a "batch" process and is distinct from concepts that emphasize the continuous processes in flowing water environments, such as the river continuum concept. Flooclplains are distinct because they do not depend on upstream processing inefficiencies of organic matter, although their nutrient pool is influenced by periodic lateral exchange of water and sediments with the main channel. The pulse concept is distinct because the position of a floodplain within the river network is not a primary determinant of the processes that occur. The pulse concept requires an approach other than the traditional limnological paradigms used in lotic or lentic systems. Résumé JUNK, W. J., P. B. BAYLEY, AND R. E. SPARKS. 1989. The flood pulse concept in river-floodplain systems, p. 110-127. In D. P. Dodge [cd.] Proceedings of the International Large River Symposium. Can. Spec. Publ. Fish. Aquat. Sci . 106. Les inondations occasionnées par la crue des eaux dans les systèmes cours d'eau-plaines inondables constituent le principal facteur qui détermine la nature et la productivité du biote dominant de même que les interactions existant entre les organismes biotiques et entre ceux-ci et leur environnement. Ces crues passagères, dont la durée et la prévisibilité sont variables, sont produites par un ensemble de facteurs géomorphologiques et hydrologiques. Les crues de courte durée, généralement imprévisibles, surviennent dans les réseaux hydrographiques peu ramifiées ou dans les réseaux qui ont connu des transformations importantes suite à l'endiguement et au drainage des plaines inondables par l'homme. Comme les crues survenant dans les réseaux hydrographiques d'ordre inférieur sont brèves et imprévisibles, les adaptations des organismes vivants sont limitées en ce qui a trait à l'exploitation des ressources de la zone de transition existant entre le milieu aquatique et le milieu terrestre (ATTZ), bien que les organismes aquatiques profitent indirectement des éléments transportés dans le milieu lotique. Inversement, une crue prévisible de longue durée favorise le développement d'adaptations et de stratégies qui permettent aux organismes d'exploiter efficacement 1 'ATTZ. Une telle crue s'accompagne d'un effet de bordure dynamique qui fait en sorte que l'ATTZ devient un « littoral mobile'<. Dans ces circonstances, il n'y a pas de stagnation prolongée et le recyclage de la matière organique et des substances nutritives se fait rapidement, ce qui donne lieu à une productivité élevée. La production primaire dans l'ATTZ est beaucoup plus élevée que celle des masses d'eau permanentes dans les réseaux hydrographiques non modifiés. Le rendement et la production de poissons sont étroitement reliés à l'étendue de la plaine inondable, tandis que le cours normal de la rivière est utilisé comme voie de migration par la plupart des poissons. 110
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The paper reviews current concepts that relate particular life-history strategies to habitat characteristics. The strategy selection system is described: through effects on the fitness of individual organisms in ecological time certain combinations of adaptations for survival and reproduction are selected. These combinations arise through trade-offs between different tactics. The author's hypothesis that the habitat provides the templet on which evolution forges characteristic life-history strategies is further explored and related to similar concepts proposed by others. It is shown that in general these formulations define habitat along two axes: one being the frequency of disturbances and the other the general level adversity or harshness. When these axes and the orientation of the figures are made to correspond, the predictions from the different approaches have many similarities. Although the habitat may be defined in terms of two abiotic axes, the scaling of these in time and space must be appropriate to the temporal (e.g. generation time) and spatial (e.g. trivial range) scales of the organism being considered. It is pointed out that the pattern of trade-offs will be constrained by the available genetic variability (a reflection of the organism's phylogenetic history) and there may be more than one stable strategy for a particular environment. The templet constrains the range of life-history strategies, but it does not impose uniformity. The extent of variation may correspond to the dichotomy between high risk and low risk strategies recently explored by Ellner.
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The flood pulse concept of Junk, Bayley and Sparks is a major contribution to our understanding of river–floodplain interactions and has become an important paradigm in lotic ecology. The concept is based mainly on large tropical lowland rivers. Floodplains may, however, develop in all geographical areas and at different locations along a river corridor. We extend this concept to temperate areas by including information derived from near-natural proglacial, headwater and lowland floodplains. Specific attention is directed to the role of temperature as a major determinant of floodplain ecology. Further attention is directed to the importance of expansion–contraction cycles occurring well below bankfull (‘flow pulse’ versus ‘flood pulse’). Selected examples are presented that highlight the complexity of expansion–contraction events and their consequences on habitat heterogeneity and functional processes. Habitat heterogeneity is mainly a product of shifting water sources, different flow paths and the relative importance of autogenic processes. In different floodplain systems, expansion may enhance habitat heterogeneity (e.g. glacial floodplain) or create homogeneity (e.g. Danubian floodplain). Further, the ecological consequences of episodic flow and flood pulses are discussed. Finally, a landscape approach is suggested in order to document expansion and contraction processes and to elucidate how these processes influence landscape heterogeneity and biodiversity patterns. Such a landscape-based ecosystem model can be applied to rigorously assess the ecological integrity of river–floodplain systems. Copyright © 2000 John Wiley & Sons, Ltd.
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We illustrate the fundamental importance of fluctuations in natural water flows to the long-term sustainability and productivity of riverine ecosystems and their riparian areas. Natural flows are characterized by temporal and spatial heterogeneity in the magnitude, frequency, duration, timing, rate of change, and predictability of discharge. These characteristics, for a specific river or a collection of rivers within a defined region, shape species life histories over evolutionary (millennial) time scales as well as structure the ecological processes and productivity of aquatic and riparian communities. Extreme events – uncommon floods or droughts – are especially important in that they either reset or alter physical and chemical conditions underpinning the long-term development of biotic communities. We present the theoretical rationale for maintaining flow variability to sustain ecological communities and processes, and illustrate the importance of flow variability in two case studies – one from a semi-arid savanna river in South Africa and the other from a temperate rainforest river in North America. We then discuss the scientific challenges of determining the discharge patterns needed for environmental sustainability in a world where rivers, increasingly harnessed for human uses, are experiencing substantially altered flow characteristics relative to their natural states.