Dylanwad llifoedd isel ar bysgod y Salmo a’u hysglyfaeth, y macroinfertebratau.

O holl bysgod y Ddaear, anodd yw adnabod dwy rywogaeth sydd wedi eu hastudio cystal â’r brithyll brown (Salmo trutta L.) ac eog yr Iwerydd (Salmo salar L.). Cyflawna'r pysgod hyn swyddogaethau ecolegol ac economaidd sylweddol. Mae’n syndod, felly, nad oes dealltwriaeth fanylach o oblygiadau newid hinsawdd byd-eang ar y bysgodfa Salmo. Wrth i’r blaned gynhesu, a’r gylchred hydrolegol newid, disgwylir cynnydd yng ngerwinder ac amledd achosion o lif isel yn nentydd ac afonydd tiriogaeth gynhenid y pysgod hyn. Bwlch pendant ac amlwg yn y sail wybodaeth yw dealltwriaeth o ddylanwad llifoedd isel ar y brithyll a’r eog. Defnyddir dulliau gwreiddiol (astudiaethau mewn dyfroedd llifeiriol naturiol) a chyfleusterau arbrofol arloesol (mesocosmau rhaeadrol ucheldirol) i brofi dilysrwydd y ddamcaniaeth gyffredinol fod lleihad llif yn dylanwadu’n negyddol ar boblogaethau Salmo spp. ifanc, a’u hysglyfaeth, y macroinfertebratau. Ceir awgrym nad yw’r pysgod yn ceisio ffoi dylanwad llif isel cymedrol drwy symud i ddyfroedd dyfnach. Gwelwyd lleihad yn niferoedd pysgod o dan gyflyrau llif isel; roedd hyn yn gysylltiedig â chynhaliaeth maethol dlotach. Yn wahanol i leihad llif cymedrol, cyflwyna sychder eithafol gasgliad o heriau amgen i fiota dyfrol, gan gynnwys tymheredd uwch a chrynodiad ocsigen is; cyflyrau sy’n angheuol i bysgod y Salmonidae (Cuvier). Yn yr astudiaeth hon canfyddir fod sychder eithafol hefyd yn achosi crebachiad i gynhaliaeth maethol pysgodfa. O’r pysgod â lwydda i oroesi sychder, cofnodwyd cyfraddau twf is mewn arbrawf rhagarweiniol. Fel neges gyffredinol, arwain llifoedd is mewn nentydd ac afonydd at reolaeth lymach o boblogaethau Salmo ifanc, yn enwedig o safbwynt eu cynhaliaeth maethol. Ymresymir y bydd lleihad yn nifer yr aelodau a ffitrwydd y garfan hon o bysgod yn debygol o fod â goblygiadau pellach ar gyfer recriwtiad pysgod hŷn

Populations of high-value predators reflect the traits of their prey

The extent to which prey traits combine to influence the abundance of predators is still poorly understood, particularly for mixed predators in sympatry and in aquatic ecosystems. In this study, we characterise prey use and distribution in iconic bird (grey wagtails and Eurasian dippers) and fish species (brown trout and Atlantic salmon) to assess whether prey traits could predict populations of these four riverine predators. Specifically, we hypothesised that: 1) prey key traits would predict predator populations more effectively than 2) diversity of prey traits, 3) the taxonomic abundance or richness of prey (known as traditional or mass-effect types of biodiversity) or 4) the prevailing environmental conditions. Combined predator population sizes were predicted better by a few key traits – specifically those revealing prey habitat use, size and drifting behaviour – than by prey diversity or prey trait diversity or environmental conditions. Our findings demonstrate that the complex relationships between prey assemblages and multiple predator species can be represented mechanistically when the key prey traits that govern encounter and consumption rates are identified. Given their apparent potential to reveal trophic relationships, and to complement more traditional measures of prey abundance, we advocate further development of trait-based approaches in predator–prey research

Populations of high-value predators reflect the traits of their prey

The extent to which prey traits combine to influence the abundance of predators is still poorly understood, particularly for mixed predators in sympatry and in aquatic ecosystems. In this study, we characterise prey use and distribution in iconic bird (grey wagtails and Eurasian dippers) and fish species (brown trout and Atlantic salmon) to assess whether prey traits could predict populations of these four riverine predators. Specifically, we hypothesised that: 1) prey key traits would predict predator populations more effectively than 2) diversity of prey traits, 3) the taxonomic abundance or richness of prey (known as traditional or mass‐effect types of biodiversity) or 4) the prevailing environmental conditions. Combined predator population sizes were predicted better by a few key traits – specifically those revealing prey habitat use, size and drifting behaviour – than by prey diversity or prey trait diversity or environmental conditions. Our findings demonstrate that the complex relationships between prey assemblages and multiple predator species can be represented mechanistically when the key prey traits that govern encounter and consumption rates are identified. Given their apparent potential to reveal trophic relationships, and to complement more traditional measures of prey abundance, we advocate further development of trait‐based approaches in predator–prey research

An integrated spatio-temporal view of riverine biodiversity using environmental DNA metabarcoding 2

Anthropogenically forced changes in global freshwater biodiversity demands better monitoring approaches. Consequently, environmental DNA (eDNA) analysis is enabling ecosystem-scale biodiversity assessment, yet the accurate spatiotemporal resolution at which robust biodiversity information can be detected remains ambiguous. Here, using intensive, annual spatiotemporal eDNA sampling across space (five rivers in the USA and Europe, with an upper range of 20-35 km between samples), time (19 timepoints across 2017 to 2018) and environmental conditions (river flow, pH, conductivity, temperature and rainfall), we characterise the resolution at which information on diversity across the animal kingdom can be gathered from rivers. In space, beta diversity was mainly dictated by turnover, on a scale of tens of kilometres, highlighting that diversity measures are not confounded by eDNA from upstream. Fish communities showed nested assemblages along some rivers, coinciding with habitat use. Across time, seasonal life history events, including salmon and eel migration, were detected. Finally, effects of abiotic factors were taxon-specific, reflecting habitat filtering of communities rather than environmental effects on DNA molecules. We conclude that riverine eDNA metabarcoding can measure biodiversity at spatiotemporal scales relevant to species and community ecology, demonstrating its utility in delivering insights into river ecology during an epoch of environmental change

Challenges to implementing environmental-DNA monitoring in Namibia

By identifying fragments of DNA in the environment, eDNA approaches present a promising tool for monitoring biodiversity in a cost-effective way. This is particularly pertinent for countries where traditional morphological monitoring has been sparse. The first step to realising the potential of eDNA is to develop methodologies that are adapted to local conditions. Here, we test field and laboratory eDNA protocols (aqueous and sediment samples) in a range of semi-arid ecosystems in Namibia. We successfully gathered eDNA data on a broad suite of organisms at multiple trophic levels (including algae, invertebrates and bacteria) but identified two key challenges to the implementation of eDNA methods in the region: 1) high turbidity requires a tailored sampling technique and 2) identification of taxa by eDNA methods is currently constrained by a lack of reference data. We hope this work will guide the deployment of eDNA biomonitoring in the arid ecosystems of Namibia and neighbouring countries

An integrated spatio-temporal view of riverine biodiversity using environmental DNA metabarcoding

Anthropogenically forced changes in global freshwater biodiversity demand more efficient monitoring approaches. Consequently, environmental DNA (eDNA) analysis is enabling ecosystem-scale biodiversity assessment, yet the appropriate spatio-temporal resolution of robust biodiversity assessment remains ambiguous. Here, using intensive, spatio-temporal eDNA sampling across space (five rivers in Europe and North America, with an upper range of 20–35 km between samples), time (19 timepoints between 2017 and 2018) and environmental conditions (river flow, pH, conductivity, temperature and rainfall), we characterise the resolution at which information on diversity across the animal kingdom can be gathered from rivers using eDNA. In space, beta diversity was mainly dictated by turnover, on a scale of tens of kilometres, highlighting that diversity measures are not confounded by eDNA from upstream. Fish communities showed nested assemblages along some rivers, coinciding with habitat use. Across time, seasonal life history events, including salmon and eel migration, were detected. Finally, effects of environmental conditions were taxon-specific, reflecting habitat filtering of communities rather than effects on DNA molecules. We conclude that riverine eDNA metabarcoding can measure biodiversity at spatio-temporal scales relevant to species and community ecology, demonstrating its utility in delivering insights into river community ecology during a time of environmental change