Permanent Waters Research Articles

Economic valuation of changes in ecosystem services of 77 Ramsar wetlands in West Asia over 37 years (1984–2021)

SummaryIn the West Asia region, the vulnerability of Ramsar Convention wetlands due to unsustainable utilization driven by water scarcity continues to grow. Here, a global surface water product generated by the European Joint Research Centre was used to assess changes in surface water in 77 wetlands listed under the Ramsar Convention over a 37-year period (1984–2021). By combining this product with a quantitative valuation model, estimates were made of the economic value of the ecosystem services provided by these wetlands, enabling the determination of the economic losses resulting from any reduction in surface water. We show that 20% (7550 km2) of permanent surface waters in Ramsar sites have disappeared or are no longer classified as permanent. Based on this, USD 106 billion of the economic value of wetlands ecosystem services have been lost. Additionally, 33% (12 100 km2) of seasonal surface waters in these wetlands have experienced a decrease in area. Iran and Iraq account for 90% of water losses, primarily in 34 wetlands (30 in Iran and 4 in Iraq). These findings underscore the urgent need for water management policies and conservation strategies in the West Asia region.

Geospatial modelling of dry season habitats of the malaria vector, Anopheles funestus, in south-eastern Tanzania

BackgroundAnopheles funestus is a major malaria vector in Eastern and Southern Africa and is currently the dominant malaria-transmitting vector in many parts of Tanzania. Previous research has identified its preference for specific aquatic habitats, especially those that persist in dry months. This observation suggests the potential for targeted control through precise habitat mapping and characterization. In this study, we investigated the influence of habitat characteristics, land cover and human population densities on An. funestus distribution during dry seasons. Based on the results, we developed a habitat suitability model for this vector species in south-eastern Tanzania.MethodsEighteen villages in south-eastern Tanzania were surveyed during the dry season from September-December 2021. Water bodies were systematically inspected for mosquito larvae and characterized by their physico-chemical characteristics and surrounding environmental features. A generalized linear model was used to assess the presence of An. funestus larvae as a function of the physico-chemical characteristics, land use and human population densities. The results obtained from this model were used to generate spatially explicit predictions of habitat suitability in the study districts.ResultsOf the 1466 aquatic habitats surveyed, 440 were positive for An. funestus, with river streams having the highest positivity (74%; n = 322) followed by ground pools (15%; n = 67). The final model had an 83% accuracy in predicting positive An. funestus habitats, with the most important characteristics being permanent waters, clear waters with or without vegetation or movement and shading over the habitats. There was also a positive association of An. funestus presence with forested areas and a negative association with built-up areas. Human population densities had no influence on An. funestus distribution.ConclusionsThe results of this study underscore the crucial role of both the specific habitat characteristics and key environmental factors, notably land cover, in the distribution of An. funestus. In this study area, An. funestus predominantly inhabits river streams and ground pools, with a preference for clear, perennial waters with shading. The strong positive association with more pristine environments with tree covers and the negative association with built-up areas underscore the importance of ecological transitions in vector distribution and malaria transmission risk. Such spatially explicit predictions could enable more precise interventions, particularly larval source management, to accelerate malaria control.Graphical

Methane-carbon budget of a ferruginous meromictic lake and implications for marine methane dynamics on early Earth

Abstract The greenhouse gas methane (CH4) contributed to a warm climate that maintained liquid water and sustained Earth’s habitability in the Precambrian despite the faint young sun. The viability of methanogenesis (ME) in ferruginous environments, however, is debated, as iron reduction can potentially outcompete ME as a pathway of organic carbon remineralization (OCR). Here, we document that ME is a dominant OCR process in Brownie Lake, Minnesota (midwestern United States), which is a ferruginous (iron-rich, sulfate-poor) and meromictic (stratified with permanent anoxic bottom waters) system. We report ME accounting for ≥90% and >9% ± 7% of the anaerobic OCR in the water column and sediments, respectively, and an overall particulate organic carbon loading to CH4 conversion efficiency of ≥18% ± 7% in the anoxic zone of Brownie Lake. Our results, along with previous reports from ferruginous systems, suggest that even under low primary productivity in Precambrian oceans, the efficient conversion of organic carbon would have enabled marine CH4 to play a major role in early Earth’s biogeochemical evolution.

Urbanization affects plant species diversity of stormwater ponds in a large German city

Urban stormwater ponds (SPs) are important for flood protection strategies in areas with heavily sealed soils as they mitigate the negative effects of floods. SPs with temporary waters (TWs) are only flooded when water levels or surface runoffs are high, while SPs with permanent waters (PWs) contain a permanently flooded area. In urban areas, SPs are important secondary habitats for plants and animals as natural aquatic and semi-aquatic habitats are often destroyed during urbanization. In 2017, a large survey on vascular plant diversity of 80 SPs was conducted in the city of Hamburg (Germany). The aim of the study was to analyze plant diversity of TWs and PWs and to identify relationships between plant diversity and different urbanization parameters. In total, 30% of the plant species pool of Hamburg was found in the surveyed SPs representing 0.03% of the total area of Hamburg. We found significant differences in the number and proportion of aquatic, threatened and non-native species between the shoreline and bottom of TWs and PWs. The number and proportion of aquatic species was positively correlated with the proportion of urban green and negatively correlated with the degree of soil sealing in the direct surrounding of SPs. For the proportion of threatened species in the bottom of TWs, a positive relationship was found with the proportion of urban green in the surrounding of SPs. For the number and proportion of non-native species in the shoreline of SPs, negative relationships were found with the proportion of urban green and the number of different habitat types in the surrounding of SPs. Further, a positive relationship with the degree of soil sealing was identified. Our results highlight the nature conservation value of urban SPs for plants and showed the negative effects of urbanization on several plant species groups.

The Role of Old Relicts in Structuring the Boreal/Tropical Transitional Zone: The Case of East Asian Planktonic Cladocera (Crustacea)

Previous studies provided evidence of the mixing of boreal–tropical cladocerans (Crustacea) in the Far East of Eurasia, as well as the presence of numerous pre-Pleistocene relict endemics. In this study, we hypothesize that the colonization history is reflected in the proportions of endemic/boreal/tropical taxa among different habitat types within this region. We analyzed 442 qualitative samples collected from seven sub-regions of the Far East of Russia and South Korea along a latitudinal transect of approximately 2200 km, where we identified 101 Cladocera species. Our results showed a significantly higher proportion of endemic taxa in the plankton compared to the littoral and benthic zones. The proportions of endemic/boreal/tropical taxa in the permanent and temporary waters were similar. We observed a distinct shift in dominance in benthos and littoral zone across our transect: boreal taxa were prevalent in the northern sub-regions (1–4), while tropical taxa were prevalent in the southern sub-regions (5–7), with a pronounced boreal–tropical transition zone (sub-regions 4–5). Our findings suggest that this pattern arose due to the unhindered dispersion of the two faunas in a latitudinal direction until they met at the boundary during their arrival in the Late Pleistocene. In contrast, the proportions of the boreal and tropical taxa in plankton did not exceed 16% in any of the studied sub-regions, and the proportion of boreal taxa decreased from 16% to 10%, while that of the tropical taxa increased from 0% to 10% from north to south. We propose that the lower proportions and the absence of mixing of fauna in the plankton can be explained by the strong presence (sometimes dominance) of relics that occupy these water bodies before the arrival of colonizers from the north and south. Our findings highlight the significant role of biotic interactions in the formation of biogeographic boundaries, which was previously underestimated.

Paleoclimatic and paleoenvironmental reconstructions based on the small vertebrates from the Middle Paleolithic of Hohle Fels Cave, SW Germany

In this paper, we analyse the fish and small mammal assemblages from the Middle Paleolithic horizons of Hohle Fels Cave to reconstruct the paleoclimatic and paleoenvironmental conditions faced by the Neanderthal groups who occupied the site. The fish assemblage indicates that the freshwater ecosystem around this site was characterized by a pre-mountain river system with the presence of permanent, oxygen-rich, and cold running waters. The results of the Habitat Weighting Method and the Bioclimatic Model applied to the small mammal assemblage, coupled with the new dates obtained for the Archaeological Horizon (AH) IX, allow us to identify two different climatic phases. One phase (AH X-XII) is more temperate possibly corresponding to the end of Marine Isotope Stage (MIS) 5; the other (AH VI-IX) is colder and more arid corresponding to the end of MIS 4 through the beginning of MIS 3. Open environments with a relatively stable forest component dominated the landscape during this part of the Middle Paleolithic. These two climatic phases appear to correspond to different levels of occupational intensity by Neanderthals, with higher occupational intensity during mild climatic periods and lower intensity during cold, arid periods. Our climatic reconstruction and recent absolute dating, together with the recovery of a complete leaf point near the top of AH X, have important implications for the cultural stratigraphy and cultural chronology of the region. Archaeologist have traditionally viewed leaf points as key artefacts of the Blattspitzengruppe, a cultural complex attributed to the end of Middle Paleolithic; however, this stratigraphic, climatic, and chronological context indicates the need to revise this interpretation.

Seasonal flooding wetland expansion would strongly affect soil and sediment organic carbon storage and carbon-nutrient stoichiometry

In the past few decades, many non-flooding uplands (NF) and permanent flooding waters (PF) have been turned into seasonal flooding wetlands (SF) at the global scale. This trend could severely threaten global climate system by changing carbon cycling in terrestrial and aquatic ecosystems. However, the effects of SF expansion on soil and sediment organic carbon (SOC) storage and carbon-nutrient stoichiometry are far from clearly understood. Therefore, we explored SOC storage and carbon-nutrient stoichiometry among adjacent NF, SF and PF using 817 samples at 0–100 cm depth increment at Poyang Lake and Shengjin Lake in the middle-lower Yangtze River floodplain, China. The SFs of the two lakes were both Carex lakeshore wetlands. The NF of Shengjin Lake was a near-natural forest, while the NF of Poyang Lake was a disturbed grassland. The results showed that SOC storage at SFs of Poyang Lake and Shengjin Lake was 75.61 and 98.01 Mg C/ha at 0–100 cm depth increment. The difference in SOC storage among nearby NF, SF and PF depended on depth and disturbance. SOC storage at SF was equivalent to that at near-natural NF, but was much higher than that at disturbed NF. SOC storage at SF was 12.62%–24.50% higher than that at PF at 0–30 cm depth increment, but was 15.16%–25.87% lower than that at PF at 0–100 cm depth increment. Edaphic carbon and nutrients followed allometric relationships at most sites and C increased faster than N and P along the depth gradients. Carbon-nutrient stoichiometric relationships at SF and PF were similar, and were more coupled than those at near-natural NF. This research illustrates the strong effects of seasonal flooding on SOC sequestration in terrestrial and aquatic ecosystems, and expands our understanding of carbon cycling in these two ecosystems.

Non-marine ostracods of the Codó Formation (upper Aptian, Lower Cretaceous), Parnaíba Basin, NE Brazil: new biostratigraphic and paleoecological insights

The objectives of this work were to establish a biostratigraphic framework for the 1-UN-24-PI well, to suggest a new biostratigraphic approach to the study of the upper Aptian, Lower Cretaceous, and also to provide new paleoecological inferences based on ostracods for the Codó Formation in the Parnaíba Basin, NE Brazil. The described ostracod assemblages were recovered from 24 core samples, and are mainly represented by species of Harbinia. The identified species allowed recognition of the Harbinia spp. 201-218 Biozone. The last occurrences of Harbinia crepata and Harbinia micropapillosa are suggested as potential chronostratigraphic markers. A lagoon with brackish permanent waters and with permanent hydrologic connection (saline groundwaters) but intermittent direct connection to the sea is newly proposed as a paleoenvironmental model for the Codó Formation in the studied area.

Mid to late holocene dry events in Colombia’s super humid Western Cordillera reveal changes in regional atmospheric circulation

The Pacific coast of northern South America, from Panama to Ecuador, also known as the Chocó biogeographic region, is one of the wettest and more biodiverse places on Earth. These wet conditions are caused by the presence of a tropical low-level atmospheric current known as the Chocó low level Jet that transports moisture from the Pacific Ocean to the Andes of Colombia and is responsible for a large portion of moisture entering the continent, reaching as far as the Eastern Cordillera. In order to understand better the climate and ecosystem dynamics of such a wet region, we investigated the past hydroclimate and environmental conditions of a yet an unexplored area, the Medellincito wetland at 2020 m above sea level, located on the water divide of the Western Cordillera of Colombia, under the direct influence of the Chocó Jet. Our results indicate that between ∼6680 and 3710 cal yr BP the wetland had permanent waters and was surrounded by forest. This suggests wet conditions with a strong and persistent Chocó Jet. From ∼3710 to ∼1560 cal yr BP, the wetland dried out and open vegetation dominated by grasses replaced the forest. Later on, between ∼1200 and 750 cal yr BP the wetland formed again although with shallow waters, while open vegetation continued to expand. Humid conditions and the forest were re-established after 750 cal yr BP. We hypothesize that dry conditions in an otherwise very wet area were caused by the weakening of the Chocó Jet, possibly associated with ENSO-moderated changes in the temperature of the Pacific Ocean that coincided with changes in the position, relative to today’s, of the Intertropical Convergence Zone. This record highlights that the ecosystems’ dynamics in the Chocó biogeographic region are highly responsive to variations in moisture from the Chocó Jet, which in turn depends on temperatures in the Pacific Ocean. With current global change leading to the warming of the oceans, this highly biodiverse region can potentially be transformed into grass-rich ecosystems as it had occurred in the past.

Evaluating the Effects of Climate and Environmental Factors on Under-5 Children Malaria Spatial Distribution Using Generalized Additive Models (GAMs)

Although malaria burden has declined globally following scale up of intervention, the disease has remained a leading cause of hospitalization and deaths among children aged under-5 years in Nigeria. Malaria is known to be related to climate and environmental conditions. Previous research has usually studied the effects of these factors, neglecting possible correlation between them, high correlation among variables is a source of multicollinearity that induces overfitting in regression modelling. In this paper, a factor analysis was first introduced to circumvent the issue of multicollinearity and a Generalized Additive Model (GAM) was subsequently explored to identify the important risk factors that might influence the prevalence of childhood malaria in Nigeria. The GAM incorporated the complexity of the survey data, while simultaneously modelling the nonlinear and spatial random effects to allow a more precise identification of the major malaria risk factors that influence the geographical distribution of the disease. From our findings, the three latent factor components (constituted by humidity, precipitation, potential evapotranspiration, and wet days/maximum and minimum temperature/proximity to permanent waters, respectively) were significantly associated with malaria prevalence. Our analysis also detected statistically significant and nonlinear effect of altitude: the risk of malaria increased with lower values but declined sharply with higher values. A significant spatial variability in under-5 malaria prevalence across the survey clusters was also observed; malaria burden was higher in the northern part of Nigeria. Investigating the impact of important risk factors and geographical location on childhood malaria is of high relevance for the sustainable development goals (SDGs) 2015–2030 Agenda on malaria eradication, and we believe that the information obtained from this study and the generated risk maps can be useful to effectively target intervention efforts to high-risk areas based on climate and environmental context.

Effect of low temperatures on the reproduction of summer and perennial rotifers from temperate regions: ecological and life cycle implications

Summer and perennial planktonic rotifers from temperate regions can vary greatly in their ability to reproduce at low temperatures. The population growth rate (r day−1) of a Patagonian Keratella tropica was 0.025 at 3.9 °C and gradually increased to 0.083 at 9.3 °C. The ability of this rotifer to survive and reproduce at low winter temperatures suggests that populations in permanent waters with cold winters may have life cycles with little or no commitment to sexually produced diapausing eggs. In contrast, three Brachionus taxa from two localities in southeastern Australia reproduced poorly at low temperatures. At 3.9 °C, all females died before reproducing. At 6.1 °C, only a single amictic female of the Darling Brachionus (B. calyciflorus species complex) from Lake Littra survived to produce a few offspring. At 9.3 °C, amictic females of the Darling Brachionus from both Lake Littra and a billabong produced many more offspring (7–9 offspring female−1) than those of the Lake Littra B. calyciflorus and the billabong B. rubens (1–2 offspring female−1). At 14.9 °C, amictic females of the latter two taxa, and the Darling Brachionus from Lake Littra, produced many (14–17) offspring female−1. Seasonal changes in temperature occurring in natural populations of these Brachionus taxa should have important ecological and evolutionary implications. Low temperatures likely favor the occurrence and reproduction of the Darling taxon. The inability of active individuals to survive and reproduce at low winter temperatures may be a factor favoring selection for sexual reproduction and production of resting eggs in both permanent and temporary water bodies.

Global meta‐analysis reveals that invertebrate diversity is higher in permanent than in temporary lentic water bodies

Abstract One of the main constraints affecting invertebrate diversity in many freshwater lentic habitats is the presence of a dry phase which forces aquatic organisms to avoid this period through the migration to other water bodies or the production of resting stages. Field studies show contradictory results when comparing invertebrate diversity in permanent (PW) and temporary lentic waters (TW). Our objective was to test how diversity is influenced by the permanence of water in lentic habitats, and which factors affect the magnitude and direction of this difference, including sampling design. Through a systematic review, 66 publications were selected and classified according to the sampling design (spatial, temporal, and spatio‐temporal datasets). Meta‐analysis of the spatial dataset, which included 70% of the studies, revealed that diversity in PW was higher than in TW, and this difference was not influenced by annual precipitation, dispersal mode, habitat type or level of anthropogenic impact (proximity to urban or agricultural areas). We found a significantly higher effect size (PW greater than TW) when considering species richness rather than cumulative richness or Shannon diversity index, disconnected water bodies (hindering the exchange of individuals through water connection), organisms with passive dispersal (which cannot actively avoid the dry period), and study sites with high anthropogenic impact (where temporary habitats could undergo impacts; e.g. concentration of pollutants and eutrophication). We also found that the differences in diversity between PW and TW may decrease with increasing sampling effort. This result may be attributable to high species turnover due to the higher temporal environmental variation in TW relative to PW. Also, it indicates that sampling effort should be comparatively higher in TW to properly characterize the biodiversity in these environments in order to compare with PW. As global climate continues to change, our results suggest that loss in aquatic invertebrate diversity of TW will be likely to occur in regions where the frequency of drying events increases.

Surface Water Microwave Product Series Version 3: A Near-Real Time and 25-Year Historical Global Inundated Area Fraction Time Series From Active and Passive Microwave Remote Sensing

This letter summarizes substantial modifications made to the Surface Water Microwave Product Series (SWAMPS), a coarse-resolution (~25 km) global inundated area fraction data record derived from active and passive microwave remote sensing. SWAMPS is the most temporally dense, long-term record of global surface water dynamics publicly available today. This update improves upon the original release by: 1) incorporating a customized, consistent resampling and assembly of the Special Sensor Microwave Imager and Special Sensor Microwave Imager Sounder brightness temperature record; 2) eliminating signal contamination from ocean waters along coastlines; 3) inclusion of permanent surface waters as a component of the data record; and 4) reducing anomalous inundation retrievals over arid and semiarid regions. This update provides for the enhanced scientific utility of the full 25+ years of data records. Remaining uncertainties in the surface water fraction retrievals are principally in areas with bare, sandy surface cover and in areas with dense vegetation cover that diminishes radiometric sensitivity to surface water. This data record and associated documentation are freely available through the Alaska Satellite Facility, Fairbanks, AK, USA.

Allodiaptomus nongensis, a new diaptomid copepod (Copepoda: Calanoida) from a tributary of the Mekong River, with notes on its consumption by local people in Central Laos

A new calanoid copepod, Allodiaptomus nongensis n. sp., is herein described based on samples collected from the Xe Lanong River (a tributary of the Mekong River), and 13 other localities in Central Laos. This is the sixth species of the genus Allodiaptomus Kiefer, 1936. The other five members in the genus were recorded from India, South China, Cambodia, Thailand, and Vietnam. The features that stand out in the new species are in the male: the right caudal ramus has a large, biacuminate, conical process proximally, and the Exp-2 of the right P5 has a hook-shaped principal spine proximally. The new species is abundant in both temporary and permanent waters, but is restricted to Savannakhet Province. This Laotian endemic copepod is referred to by local people as “Pa Khayong”, which means tiny fish. Since high densities of this copepod can be found in the dry season (December until May), several man-made copepod traps are placed by local people along the river banks in Muang Nong District. Interestingly, large concentrations of individuals (body length: ~1 mm) belonging to the new species are harvested and consumed by these villagers. Additional information about this species and the copepod fisheries by local people in this area is provided herein. In this paper, the reassignment of Allodiaptomus rarus to the genus Mongolodiaptomus is proposed.

Inland surface waters in protected areas globally: Current coverage and 30-year trends.

Inland waters are unique ecosystems offering services and habitat resources upon which many species depend. Despite the importance of, and threats to, inland water, global assessments of protected area (PA) coverage and trends have focused on land habitats or have assessed land and inland waters together. We here provide the first assessment of the level of protection of inland open surface waters and their trends (1984–2015) within PAs for all countries, using a globally consistent, high-resolution (30 m) and validated dataset on permanent and seasonal surface waters based on Landsat images. Globally, 15% of inland surface waters are covered by PAs with mapped boundaries. Estimated inland water protection increases to 16.4% if PAs with reported area but delineated only as points are included as circular buffers. These coverage estimates slightly exceed the comparable figure for land but fall below the 17% goal of the Convention on Biological Diversity’s Aichi Target 11 for 2020. Protection levels are very uneven across countries, half of which do not yet meet the 17% target. The lowest coverage of surface water by PAs (<5%) was found in Africa and in parts of Asia. There was a global trend of permanent water losses and seasonal water gains within PAs, concomitant with an increase of both water types outside PAs. In 38% of countries, PAs lost over 5% of permanent water. Global protection targets for inland waters may well be met by 2020, but much stronger efforts are required to ensure their effective conservation, which will depend not only on sound PA governance and management but also on the sustainable use of water resources outside PAs. Given the pressures on water in a rapidly changing world, integrated management planning of water resources involving multiple sectors and entire basins is therefore necessary.

Comparison of visible and multi-satellite global inundation datasets at high-spatial resolution

Several new satellite-derived and long-term surface water datasets at high-spatial resolution have recently become available at the global scale, showing different characteristics and abilities. They are either based on visible imagery from Landsat – the Global 3-second Water Body Map (G3WBM) and the Global Surface Water Explorer (GSWE) – or on the merging of passive/active microwave and visible observations – Global Inundation Extent from Multi-Satellite (GIEMS-D3) – that has been downscaled from a native resolution of 25 km × 25 km to the 90 m × 90 m resolution. The objective of this paper is to perform a thorough comparison of the different water surface estimates in order to identify the advantages and disadvantages of the two approaches and propose a strategy for future developments of high-resolution surface water databases. Results show that due to their very high spatial resolution (30 m) the Landsat-based datasets are well suited to retrieve open water surfaces, even at very small size. GIEMS-D3 has a better ability to detect water under vegetation and during the cloudy season, and it shows larger seasonal dynamics. However, its current version overestimates surface water extent on water-saturated soils, and due to its low original (i.e. before downscaling) spatial resolution, it is under-performing at detecting small water bodies. The permanent waters for G3WBM, GSWE, GIEMS-D3 and GLWD represent respectively: 2.76, 2.05, 3.28, and 3.04 million km2. The transitory waters shows larger discrepancies: 0.48, 3.72, 10.39 and 8.81 million km2.Synthetic Aperture Radar (SAR) data (from ENVIronment SATellite (ENVISAT), Sentinel and soon the Surface Water Ocean Topography (SWOT)) would be a good complementary information because they have a high nominal spatial resolution and are less sensitive to clouds than visible measurements. However, global SAR datasets are still not available due to difficulties in developing a retrieval scheme adequate at the global scale. In order to improve our estimates of global wetland extents at high resolution and over long-term records, three interim lines of action are proposed: (1) extend the temporal record of GIEMS-D3 to exploit the full time series of microwave observations (from 1978 to present), (2) develop an approach to fuse the GSWE and GIEMS-D3 datasets leveraging the strengths of both, and (3) prepare for the release of SAR global datasets.

Squeezing out the last egg-annual fish increase reproductive efforts in response to a predation threat.

Both constitutive and inducible antipredator strategies are ubiquitous in nature and serve to maximize fitness under a predation threat. Inducible strategies may be favored over constitutive defenses depending on their relative cost and benefit and temporal variability in predator presence. In African temporary ponds, annual killifish of the genus Nothobranchius are variably exposed to predators, depending on whether larger fish invade their habitat from nearby rivers during floods. Nonetheless, potential plastic responses to predation risk are poorly known. Here, we studied whether Nothobranchius furzeri individuals adjust their life history in response to a predation threat. For this, we monitored key life history traits in response to cues that signal the presence of predatory pumpkinseed sunfish (Lepomis gibbosus). While growth rate, adult body size, age at maturation, and initial fecundity were not affected, peak and total fecundity were higher in the predation risk treatment. This contrasts with known life history strategies of killifish from permanent waters, which tend to reduce reproduction in the presence of predators. Although our results show that N. furzeri individuals are able to detect predators and respond to their presence by modulating their reproductive output, these responses only become evident after a few clutches have been deposited. Overall our findings suggest that, in the presence of a predation risk, it can be beneficial to increase the production of life stages that can persist until the predation risk has faded.

More invaders do not result in heavier impacts: The effects of non-native bullfrogs on native anurans are mitigated by high densities of non-native crayfish.

With accelerating species introductions in an era of globalization, co-occurring alien species have become increasingly common. Understanding the combined ecological impacts of multiple invaders is not only crucial for wildlife managers attempting to ameliorate biodiversity loss, but also provides key insights into invasion success and species coexistence mechanisms in natural ecosystems. Compared with much attentions given to single-invader impacts, little is known about the impacts of multiple co-occurring invaders. The American bullfrog (Lithobates catesbeianus=Rana catesbeiana) and the red swamp crayfish (Procambarus clarkii) are two aquatic invasive species in many different areas of the globe. They coexist with native anurans in a variety of permanent lentic waters, which provide an ideal model system to explore the combined effects of multiple invaders from different trophic levels on native species. Based on a global diet analysis covering 34 native and invasive bullfrog populations, and data from 10-year field surveys across 157 water bodies in the Zhoushan Archipelago, China, we observed a reduced impact of bullfrogs on native anurans at high crayfish densities when the two invaders co-occurred. The global diet analysis showed that crayfish occurrence reduced the number of native anuran prey consumed by bullfrogs in both native and invasive populations. After accounting for pseudoreplication of different observations among water bodies, islands, and survey time, model averaging analyses based on GLMMs showed a negative relationship between bullfrog density and native anuran densities for field observations of invasive bullfrogs alone and co-invaded observations with low crayfish density. However, this negative relationship disappeared when the two invaders co-occurred with high crayfish density. Structural equation modelling (SEM) analyses further validated that the impacts of bullfrogs on native frogs were mitigated by the negative interactions between crayfish and bullfrogs. Our results provide novel evidence of a density-dependent antagonistic effect of two sympatric invaders from different trophic levels on native species. This study highlights the importance of considering complex interactions among co-invaders and native species when prioritizing conservation and management actions and will facilitate the development of a more precise framework to predict invasion impacts.

Novel application of explicit dynamics occupancy models to ongoing aquatic invasions

Abstract Identification of suitable habitats, where invasive species can establish, is an important step towards controlling their spread. Accurate identification is difficult for new or slow invaders because unoccupied habitats may be suitable, given enough time for dispersal, while occupied habitats may prove to be unsuitable for establishment. To identify the suitable habitat of a recent invader, I used an explicit dynamics occupancy modelling framework to evaluate habitat covariates related to successful and failed establishments of American Bullfrogs (Lithobates catesbeianus) within the Yellowstone River floodplain of Montana, USA, from 2012 to 2016. During this 5‐year period, bullfrogs failed to establish at most sites they colonized. Bullfrog establishment was most likely to occur and least likely to fail at sites closest to human‐modified ponds and lakes and those with emergent vegetation. These habitat covariates were generally associated with the presence of permanent water. Suitable habitat for bullfrog establishment is abundant in the Yellowstone River floodplain, although many sites with suitable habitat remain uncolonized. Thus, the maximum distribution of bullfrogs is much greater than their current distribution. Synthesis and applications. Focused control efforts on habitats with or proximate to permanent waters are most likely to reduce the potential for invasive bullfrog establishment and spread in the Yellowstone River. The novel application of explicit dynamics occupancy models is a useful and widely applicable tool for guiding management efforts towards those habitats where new or slow invaders are most likely to establish and persist.

Fishpond dams affect leaf‐litter processing and associated detritivore communities along intermittent low‐order streams

Abstract Intermittent streams are common and widespread freshwater ecosystems globally. While dams greatly affect the ecology of permanent streams, the extent of their effects on intermittent streams remains largely unknown. The physical and chemical alterations induced by dams could have particularly strong impacts on the functioning of intermittent low‐order streams, especially due to the limitations they place on colonisation of aquatic biota from downstream permanent waters. Leaf‐litter breakdown (LLB) and associated communities (microbes and shredders) were studied to investigate the potential ecological continuum rupture caused by fishpond dams along the longitudinal gradient of intermittent streams. Three to four sites were investigated along three reference (no dam) and three impacted (with a fishpond dam) first‐order intermittent low‐order streams. LLB increased along the longitudinal gradient in all six streams regardless of the presence of dams (from 1.5 to 8.4 fold over &lt;1.5 km distance). This underscores the great variability of low‐order stream functioning even at fine scales. Such upstream to downstream gradients need to be taken into account before investigating the effect of any perturbation using LLB as a functional indicator. Fishponds dams tended to increase LLB downstream, and altered the downstream microbial communities (increase in fungal densities) and shredder assemblages (increase in Gammaridae). The effects of fishpond dams on intermittent stream functioning appeared to be most significant when they were associated with changes in hydrology, that is, when fishponds resulted in permanent flows downstream of dams. Our findings suggest that better management of fishpond dams in order to limit hydrological modifications downstream (for instance, by preventing leaks from the dam) could reduce their impact on ecosystem functioning in intermittent streams.