Browsing by Autor "Dean Jacobsen"

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Aquatic biota responses to temperature in a high Andean geothermal stream
(Wiley, 2021) Estefania Quenta; Antonio Daza; Xavier Lazzaro; Dean Jacobsen; Olivier Dangles; Sophie Cauvy‐Fraunié
Abstract The impact of global warming on mountain ecosystems is predicted to be high, and particularly in the tropical region. Geothermal streams have provided comprehensive evidence about how aquatic biodiversity changes across natural thermal gradients, but current knowledge is restricted to arctic and temperate zones. Thermal tolerances are different in tropical biological communities, resulting in high thermal sensitivity and low capacity to endure change in their thermal environments. This feature can change the response of aquatic organisms to warming, yet there is little empirical evidence to support this assumption. In this study, we address this issue by evaluating how water temperature affects biodiversity, and the structure of primary and secondary producers of a high‐elevation geothermal stream system (4,500 m above sea level) in the Bolivian Andes. We analysed multi‐taxa responses to increased water temperature using benthic macroinvertebrate families, benthic algae and cyanobacteria, fishes, and macrophytes as study organisms. Different models were run to assess the response of aquatic biota to temperature. In addition, threshold indicator taxa analysis (TITAN) was used to identify changes in macroinvertebrate taxa distributions along the thermal gradient. We found that macroinvertebrate richness decreased at 24–25°C due to the different taxon‐specific responses to temperature. Threshold indicator taxa analysis identified 17 temperature thresholds for each family of macroinvertebrates. Changes in macroinvertebrate community composition were significantly associated with changes in water temperature. Similarly, changes in macrophytes were associated with temperature differences, and high macrophyte richness was found at 19–20°C. Chlorophyll ‐a concentration of green algae and diatoms was higher at intermediate temperatures 20–22°C, macroinvertebrates density peaked at 27°C, and fish body size reduced linearly with temperature. Temperature increase in the geothermal stream resulted in a reduction of aquatic diversity and primary and secondary producers by simplifying the community structure to a few warm‐adapted taxa and reduced body size. These patterns differed from those obtained in temperate/arctic geothermal streams, but are similar to other studies at high‐elevation. In a context of increasing warming, the ecological structure of high‐elevation streams might lose cold‐adapted taxa, and change to smaller populations. Additional studies based on ecosystem functioning of geothermal streams could lead to a better understanding on how warming affects high‐elevation streams.
Biodiversity Patterns and Continental Insularity in the Tropical High Andes
(Institute of Arctic and Alpine Research, 2014) Fabien Anthelme; Dean Jacobsen; Petr Macek; Rosa Isela Meneses; Pierre Moret; Stephan Beck; Olivier Dangles
Alpine areas of the tropical Andes constitute the largest of all tropical alpine regions worldwide. They experience a particularly harsh climate, and they are fragmented into tropical alpine islands at various spatial scales. These factors generate unique patterns of continental insularity, whose impacts on biodiversity remain to be examined precisely. By reviewing existing literature and by presenting unpublished data on beta-diversity and endemism for a wide array of taxonomic groups, we aimed at providing a clear, overall picture of the isolation-biodiversity relationship in the tropical alpine environments of the Andes. Our analyses showed that (1) taxa with better dispersal capacities and wider distributions (e.g., grasses and birds) were less restricted to alpine areas at local scale; (2) similarity among communities decreased with spatial distance between isolated alpine areas; and (3) endemism reached a peak in small alpine areas strongly isolated from main alpine islands. These results pinpoint continental insularity as a powerful driver of biodiversity in the tropical High Andes. A combination of human activities and warming is expected to increase the effects of continental insularity in the next decades, especially by amplifying the resistance of the lowland matrix that surrounds tropical alpine islands.
Bolivian Altiplano streams with low richness of macroinvertebrates and large diel fluctuations in temperature and dissolved oxygen
(Springer Science+Business Media, 2007) Dean Jacobsen; Rubén Marín
Direct and indirect effects of glaciers on aquatic biodiversity in high Andean peatlands
(Wiley, 2016) Estefania Quenta; Jorge Molina‐Rodriguez; Karina Gonzales; François Rebaudo; Jérôme Casas; Dean Jacobsen; Olivier Dangles
The rapid melting of glacier cover is one of the most obvious impacts of climate change on alpine ecosystems and biodiversity. Our understanding of the impact of a decrease in glacier runoff on aquatic biodiversity is currently based on the 'glacier-heterogeneity-diversity' paradigm, according to which there is high α-diversity at intermediate levels of glacial influence due to the high degree of environmental heterogeneity caused by glacier water. This α-diversity pattern generates high levels of between-site aquatic community variation (high β diversity) and increases regional diversity (γ-diversity). There is a rich conceptual background in favor of this paradigm, but empirical data supporting it are scarce. We investigated this paradigm by analyzing the different diversity patterns (α, β and γ-diversity) of four aquatic groups (zooplankton, macroinvertebrates, algae and macrophytes) living in high-elevation peatlands (>4500 m above sea level). We sampled 200 pools from 20 peatlands along a glacier gradient in the Cordillera Real of Bolivia. We performed structural equation modeling (SEM) to analyze the potential mechanisms underlying the observed diversity patterns. Intermediate levels of glacial influence (15-20% cover) resulted in high heterogeneity, but α-diversity responded to glacial influence only for the zooplankton group (Cladocera). Our SEM analysis did not identify environmental heterogeneity as a significant variable explaining the relationship between glacier and α-diversity. Peatland area had a strong positive effect on heterogeneity and diversity. β-diversity was significantly associated with glacier gradient, and 12.9% of the total regional diversity (γ-diversity) was restricted to peatlands with a high degree of glacial influence. These species might be lost in a context of glacial retreat. These findings provide new insight into the potential effects of glacial retreat on the aquatic environment and biodiversity in the peatlands of the tropical Andes.
Ecosystem sentinels for climate change? Evidence of wetland cover changes over the last 30 years in the tropical Andes
(Public Library of Science, 2017) Olivier Dangles; Antoine Rabatel; Martin J. Kraemer; Gabriel Zeballos; Álvaro Soruco; Dean Jacobsen; Fabien Anthelme
While the impacts of climate change on individual species and communities have been well documented there is little evidence on climate-mediated changes for entire ecosystems. Pristine alpine environments can provide unique insights into natural, physical and ecological response to climate change yet broad scale and long-term studies on these potential 'ecosystem sentinels' are scarce. We addressed this issue by examining cover changes of 1689 high-elevation wetlands (temporarily or perennial water-saturated grounds) in the Bolivian Cordillera Real, a region that has experienced significant warming and glacier melting over the last 30 years. We combined high spatial resolution satellite images from PLEIADES with the long-term images archive from LANDSAT to 1) examine environmental factors (e.g., glacier cover, wetland and watershed size) that affected wetland cover changes, and 2) identify wetlands' features that affect their vulnerability (using habitat drying as a proxy) in the face of climate change. Over the (1984-2011) period, our data showed an increasing trend in the mean wetland total area and number, mainly related to the appearance of wet grassland patches during the wetter years. Wetland cover also showed high inter-annual variability and their area for a given year was positively correlated to precipitation intensities in the three months prior to the image date. Also, round wetlands located in highly glacierized catchments were less prone to drying, while relatively small wetlands with irregularly shaped contours suffered the highest rates of drying over the last three decades. High Andean wetlands can therefore be considered as ecosystem sentinels for climate change, as they seem sensitive to glacier melting. Beyond the specific focus of this study, our work illustrates how satellite-based monitoring of ecosystem sentinels can help filling the lack of information on the ecological consequences of current and changing climate conditions, a common and crucial issue especially in less-developed countries.
Environmental and spatial filters of zooplankton metacommunities in shallow pools in high‐elevation peatlands in the tropical Andes
(Wiley, 2018) Estefania Quenta; Dean Jacobsen; Jérôme Casas; Olivier Dangles
Abstract Understanding metacommunity organisation in freshwater ecosystems is particularly important at high elevation in the tropical Andes, as this region is considered an important biodiversity hotspot with many endemic species threatened by climate change. High levels of dispersal at the regional scale and strong environmental filters at the local scale are thought to structure aquatic communities in these systems. However, metacommunity organisation patterns at the limit of aquatic life (>4,500 m a.s.l.) remain largely unknown. Given the extreme environmental conditions experienced by organisms at high elevation, environment filters would be expected to play a greater role than spatial filters in community assemblages. We assessed the effects of environmental and spatial filters on zooplankton (Cladocera), to gain insight into metacommunity organisation in the shallow high‐elevation pools of the tropical Andes. We sampled zooplankton communities and assessed nine environmental variables, for 200 pools from 20 peatlands in the Cordillera Real of Bolivia. We performed redundancy and variation partitioning analyses on both abundance and presence/absence data, to evaluate the contribution of environmental and spatial processes (geographic and elevation distances) to cladoceran metacommunity assembly at different spatial scales. We identified 18 cladoceran species, eight of which were endemic to the Andes. We found that both environment and spatial filters made a significant contribution to the structuring of cladoceran communities at higher spatial scales (i.e. intervalleys and within valleys), whereas only the environmental filter operated at small spatial scales (i.e. within peatlands). Elevation had a significant effect on cladoceran community variation (e.g. 6.9% within valleys, for abundance data), but not on species diversity. Similar patterns were obtained with presence/absence data. Macrophyte cover, pool area and pH were the most important variables explaining community variation and the species diversity of cladocerans at pool level. These results suggest that species sorting is probably the main process generating variation in cladoceran communities at all spatial scales. At larger spatial scales (intervalleys and within valleys), limited dispersal may also filter species composition. We identified factors significantly contributing to the variation observed, but their overall explanatory power was low. This finding highlights the difficulties involved in evaluating the response of aquatic organisms to their environment and suggests that other environmental variables should be considered. Moreover, frequent and unpredictable disturbances and high stochasticity probably operate simultaneously with environmental filters to structure zooplankton organisation in these unique and harsh aquatic systems.
Invertebrate Metacommunity Structure and Dynamics in an Andean Glacial Stream Network Facing Climate Change
(Public Library of Science, 2015) Sophie Cauvy‐Fraunié; Rodrigo Espinosa; Patricio Andino; Dean Jacobsen; Olivier Dangles
Under the ongoing climate change, understanding the mechanisms structuring the spatial distribution of aquatic species in glacial stream networks is of critical importance to predict the response of aquatic biodiversity in the face of glacier melting. In this study, we propose to use metacommunity theory as a conceptual framework to better understand how river network structure influences the spatial organization of aquatic communities in glacierized catchments. At 51 stream sites in an Andean glacierized catchment (Ecuador), we sampled benthic macroinvertebrates, measured physico-chemical and food resource conditions, and calculated geographical, altitudinal and glaciality distances among all sites. Using partial redundancy analysis, we partitioned community variation to evaluate the relative strength of environmental conditions (e.g., glaciality, food resource) vs. spatial processes (e.g., overland, watercourse, and downstream directional dispersal) in organizing the aquatic metacommunity. Results revealed that both environmental and spatial variables significantly explained community variation among sites. Among all environmental variables, the glacial influence component best explained community variation. Overland spatial variables based on geographical and altitudinal distances significantly affected community variation. Watercourse spatial variables based on glaciality distances had a unique significant effect on community variation. Within alpine catchment, glacial meltwater affects macroinvertebrate metacommunity structure in many ways. Indeed, the harsh environmental conditions characterizing glacial influence not only constitute the primary environmental filter but also, limit water-borne macroinvertebrate dispersal. Therefore, glacier runoff acts as an aquatic dispersal barrier, isolating species in headwater streams, and preventing non-adapted species to colonize throughout the entire stream network. Under a scenario of glacier runoff decrease, we expect a reduction in both environmental filtering and dispersal limitation, inducing a taxonomic homogenization of the aquatic fauna in glacierized catchments as well as the extinction of specialized species in headwater groundwater and glacier-fed streams, and consequently an irreversible reduction in regional diversity.
Rapid decline of snow and ice in the tropical Andes – Impacts, uncertainties and challenges ahead
(Elsevier BV, 2017) Mathias Vuille; Mark Carey; Christian Huggel; Wouter Buytaert; Antoine Rabatel; Dean Jacobsen; Álvaro Soruco; Marcos Villacís; Christian Yarlequé; O. Elison Timm
Relationships between stream macroinvertebrate communities and new flood‐based indices of glacial influence
(Wiley, 2014) Sophie Cauvy‐Fraunié; Rodrigo Espinosa; Patricio Andino; Olivier Dangles; Dean Jacobsen
Summary As glacier shrinkage is accelerating due to climate change, it is important to understand the effect of changes in glacier runoff on downstream aquatic communities. The overall goal of this study was to test the relevance of recently developed wavelet‐based metrics of flow variations caused by glacial melting cycles to deepen our knowledge about the relationship between glacial influence and aquatic biodiversity. In an equatorial glacierised catchment, we selected 15 stream sites covering a gradient of direct contribution from glacial runoff. At each site, we recorded water level time series for 10 months and sampled benthic macroinvertebrates. Wavelet analyses on the water level time series were used to calculate three indices: glacial flood intensity, frequency and temporal clustering. We then examined how these three indices were related to macroinvertebrate community composition using generalised additive models. While macroinvertebrate density decreased significantly with glacial flood intensity, we found a significant hump‐shaped relationship between local taxon richness and glacial flood intensity, a pattern that was not produced simply by overlapping broad taxon distributions from either end of the environmental gradient. These results suggest that glacial meltwater contribution creates local peaks in macroinvertebrate richness and enhances regional diversity in the catchment. The significant relationships between faunal metrics and the new glacial influence indices suggest the latter are valuable for assessing the effects of altered meltwater contributions on aquatic communities of glacier‐fed rivers. Relationships differed depending on the feature of the glacial disturbance considered (glacial flood intensity, frequency, temporal clustering). We anticipate that these distinctions may help disentangle the mechanisms driving aquatic biodiversity in glacierised catchments, especially in terms of identifying resistance and/or resilience as key processes in glacial macroinvertebrate communities.
Technical Note: Glacial influence in tropical mountain hydrosystems evidenced by the diurnal cycle in water levels
(Copernicus Publications, 2013) Sophie Cauvy‐Fraunié; Thomas Condom; Antoine Rabatel; Marcos Villacís; Dean Jacobsen; Olivier Dangles
Abstract. Worldwide, the rapid shrinking of glaciers in response to ongoing climate change is modifying the glacial meltwater contribution to hydrosystems in glacierized catchments. Determining the influence of glacial runoff to streams is therefore of critical importance to evaluate potential impact of glacier retreat on water quality and aquatic biota. This task has challenged both glacier hydrologists and ecologists over the last 20 yr due to both structural and functional complexity of the glacier–stream system interface. Here we propose quantifying the diurnal cycle amplitude of the streamflow to determine the glacial influence in glacierized catchments. We performed water-level measurements using water pressure loggers over 10 months at 30 min time steps in 15 stream sites in 2 glacier-fed catchments in the Ecuadorian Andes (> 4000 m a.s.l.) where no perennial snow cover is observed outside the glaciers. For each stream site, we performed wavelet analyses on water-level time series, determined the scale-averaged wavelet power spectrum at 24 h scale and defined three metrics, namely the power, frequency and temporal clustering of the diurnal flow variation. The three metrics were then compared to the percentage of the glacier cover in the catchments, a metric of glacial influence widely used in the literature. As expected, we found that the diurnal variation power of glacier-fed streams decreased downstream with the addition of non-glacial tributaries. We also found that the diurnal variation power and the percentage of the glacier cover in the catchment were significantly positively correlated. Furthermore, we found that our method permits the detection of glacial signal in supposedly non-glacial sites, thereby revealing glacial meltwater resurgence. While we specifically focused on the tropical Andes in this paper, our approach to determine glacial influence may have potential applications in temperate and arctic glacierized catchments. The measure of diurnal water amplitude therefore appears as a powerful and cost-effective tool to understand the hydrological links between glaciers and hydrosystems better and assess the consequences of rapid glacier shrinking.
Temporal scaling of high flow effects on benthic fauna: Insights from equatorial glacier‐fed streams
(Wiley, 2015) Sophie Cauvy‐Fraunié; Patricio Andino; Rodrigo Espinosa; Dean Jacobsen; Olivier Dangles
Abstract We used equatorial glacier‐fed streams as a model system to investigate the relationships between flow fluctuation and benthic fauna at different temporal scales. Water level was measured at 30 min intervals over 29 months (942 d) and benthic macroinvertebrates were sampled 14 times over the study period. We performed wavelet analyses on water‐level time series to identify temporal scales at which significant flow variation occurs, and calculated three indices: intensity, frequency and temporal clustering of the diurnal flow variation for periods from 2 d to 50 d. We determined the effect of temporal scaling (length of the periods considered) on relationships between benthic community dissimilarity (using Sørensen index) and differences in flow indices among the 14 sampling dates. Temporal scaling affected flow‐variation frequency and temporal clustering and their subsequent relationships with benthic community dissimilarity. A time scale of 15 d before benthic sampling was relevant to the assessment of flow‐biota relationships. Community dissimilarity significantly increased with increasing difference in flow‐fluctuation intensity. This dissimilarity was associated with a decrease in the density of dominant taxa and a taxa turnover along the temporal gradient in flow‐fluctuation intensity. Although flow fluctuations are frequent and highly predictable in equatorial glacier‐fed streams, macroinvertebrate communities exhibited a temporal variability in taxon assemblage, which was linked to the intensity of flow fluctuation. We explain these patterns by downstream displacement during high flow events and upstream displacement during low flow periods, thereby highlighting the need of considering temporal scaling effects on benthic fauna to understand the ecological dynamics of lotic systems.