9 research outputs found

    Structuring factors for macroinvertebrate communities and the importance for ecosystem processing

    No full text
    Aquatic macroinvertebrates play important roles in our ecosystems and are essential for the ecosystem processing. An improved knowledge of structuring factors, such as competition and predation, and the way in which they operates in the macroinvertebrate community is crucial for our understanding of not only the macroinvertebrates but also the ecosystem in general. Furthermore, today our ecosystems are also faced with a new range of threats including brownification and invasive species. The objective of my thesis is therefore to enhance the knowledge of the structuring factors and how it affects the ecosystem processes. In this theses I have studied (both in field and in the laboratory), both the general and interactive effects of predation risk, competition, brownification and invasive species, on macroinvertebrate ( Radix balthica, Cloeon dipterum, Gammarus pulex, Asellus aquaticus and Potamopyrgus antipodarum ) fitness factors (growth and mortality) as well as ecosystem processing (grazing and decomposition). I found that indirect effects of predation affected ecosystem processing; decomposition increased whereas grazing decreased in treatments with predator cues. Furthermore, predator cues had a positive effect on R. balthica growth, most likely due to high quality leaf biofilm. Competition, both intraspecific and interspecific, had a negative effect on both ecosystem processing as well as fitness factors. However, I also found facilitation between species, cascading further to affect ecosystem processing. Furthermore, water colour had a significant effect on predation. In clear water fish predated selectively on R. balthica , whereas there was no difference in prey preference in brown water. An increase in water colour had a negative effect on both decomposition and grazing, most likely due to changes in species composition of periphyton and leaf biofilm. Increased water colour also had a negative effect on R. balthica growth. In contrast, the invasive species P. antipodarum was more tolerant, both to predation as well as the effect of water colour, explaining their success as an invasive species. P. antipodarum also had higher grazing rates than the native species, which may have implications for the invaded ecosystems. My results illustrate the importance of competition, indirect effects of predation, water colour as well as the introduction of invasive species, not only for the individual fitness of macroinvertebrates but also for ecosystem possessing. Furthermore, it also shows the complexity of macroinvertebrate population dynamics and how the outcome of interactions is greatly dependent on which species are involved and in what combinations

    Åtgärdsprogram för temporära sötvatten : med fokus på organismer i naturbetesmarker, hällkar och alvarmiljöer

    No full text
    Det här åtgärdsprogrammet fokuserar på temporära sötvatten och de organismer som lever i sådana miljöer. Med temporära vatten menas små stillastående sötvattensamlingar som utmärker sig genom att periodvis torka ut. Dessa saknar tillflöde i form av rinnande vatten och är således helt grundvatten- eller nederbördsförsörjda. Temporära vatten bildas i sänkor i landskapet eller i fördjupningar i berghällar. Det är en heterogen grupp av naturtyper, dit allt från små regnpölar till större vattensamlingar i betesmarker räknas in. Den främsta anledningen till att temporära vatten, och många av deras organismer drabbats negativt, är att de har försvunnit vid de omfattande utdikningar som gjorts under många år till fördel för åkermark.This Action plan focuses on the preservation of temporary freshwaters occurring in pastures, rock pools and on Nordic alvar, as well as the organisms dependent on these habitats. Temporary waters are small, stagnant areas of freshwater which have a high probability of drying out on a yearly basis. It includes a wide range of habitats, ranging from small rain puddles to larger wetlands. These temporary habitats are either entirely groundwater fed or created by water from precipitation. Temporary waters are typically formed in depressions in the landscape or in the bedrock.   Today temporary waters with high biological values have become rare, primarily due to the historical draining of the landscape in favour of more arable land. Furthermore, some temporary habitats located in rock-pools were subjected to acid rain in the 1970s and 1980s, having had negative effects on the fauna and flora.  This action plan pays special attention to four target species that all are dependent on temporary waters for their survival; the diving beetle Hydaticus continentalis, the tadpole shrimps Triops cancriformis and Lepidurus apus and the clam shrimp Limnadia lenticularis. They all have in common being listed on the Swedish Red list in 2015, but also that their ecology, distribution and habitat requirements in Sweden are poorly known.    The guidelines in this Action plan are effective from 2019 to 2023 and include several measures that should lead to improved knowledge and improved conditions for the temporary freshwaters and their organisms. The long-term goal of the action plan is to improve the general knowledge and distribution of temporary freshwaters in the landscape, in particular of those harbouring any of the target species. In addition to this, an important challenge is to increase the awareness of authorities and the public about temporary habitats and their unique fauna. To succeed in this, their existence in the landscape as important habitats for biodiversity must be generally accepted, and guidelines to preserve these habitats must be given.   The short-term goal of the action plan is to identify and characterise existing and potential temporary freshwaters for the target species, with traditional mapping methods as well as with supplementary environmental DNA (eDNA) monitoring.  The Action plan proposes for instance the following actions: Create or restore at least 20 habitats for each habitat type.  Inventory of known and historic localities of the target species    Inventory of target species by means of eDNA in temporary waters Educate unexperienced inventors, as well as personnel working with advice and management at local and regional authorities Present strategies to reduce conflicts between creation of permanent waters and the conservation of temporary waters Write a literature review that result in guidelines for monitoring and conservation of temporary habitats and their organisms. Re-introduce target species where there may be requisites for a longterm conservation.  Form at least four protected areas (e.g. nature reserves) to benefit the target species  The expected costs for the conservation measures, to be funded from the Swedish Agency for Water and Marine management allocation for action plans is estimated at € 184 000 during the actions plans' validity period 2019-2023. 

    Kalkningens betydelse för flodkräftan

    No full text
    Sammanställningar av kalkningseffekter på flodkräftbestånd gjordes under 1980- och början av 1990-talet. Resultaten visade i flera fall att beståndsminskningar upphört efter kalkning, men i andra fall kunde ingen effekt observeras trots förbättrad vattenkvalitet. En slutsats var att en längre tids kalkning krävs för att se effekter på bestånden. Data avseende kräftförekomster finns samlade i den Nationella Kräftdatabasen som innehåller cirka 24 000 förekomster av flod- och signalkräfta. Genom att kombinera med GIS-skikt över åtgärds- och målområden för kalkning och koppla provfiskedatum till kalkstart analyserades förändringar i fångster och individstorlek i förhållande till hur länge kalkningen pågått. Även en jämförelse av fångster i kalkade respektive okalkade vatten genomfördes. Via länsstyrelserna inhämtades information om utvecklingen i kalkade målområden: vilka som fortfarande hyser flodkräfta, vilka som förlorat bestånden samt de där signalkräfta konstaterats. Efterhand som data utvärderades uppkom behov av att förklara de stora variationerna i fångstresultat. Därför genomfördes fördjupade analyser av ett urval kvantitativa provfisken från sjöar där uppgifter om substrattyp och förekomst av signalkräfta fanns tillgängliga. Resultaten visar följande: Antalet kalkade målområden med flodkräfta har minskat dramatiskt till följd av ökad utbredning av pestspridande signalkräftor. Enligt länsstyrelserna förekommer flodkräfta som motiv för kalkning i 390 sjöar och 246 vattendrag. Av dessa finns flodkräfta med säkerhet kvar i 30 % av sjöarna och 22 % av vattendragen, medan signalkräfta förekommer i 16 % av sjöarna och 28 % av vattendragen. I 20 % av sjöarna och 33 % av vattendragen är flodkräftan med säkerhet försvunnen och i 50 % av sjöarna och 46 % av vattendragen är det inte känt om den finns kvar. Särskilt i de sydöstra delarna av landet uppges flodkräftan vara försvunnen, eller ha osäker förekomst, i många av de kalkade vatten där bestånd tidigare förekom. En försiktig tolkning av resultaten är att kalkningen haft positiv effekt då de flesta analyser visar att fångsterna av flodkräfta i kalkade och okalkade vatten inte skiljde sig nämnvärt. Analysen av det största provfiskematerialet (141 kalkade sjöar och 143 okalkade sjöar) visade emellertid att det i genomsnitt fångades något fler flodkräftor i sjöar som inte kalkats. Detta kan tolkas som att kalkningen inte fullt ut återskapat samma beståndstätheter som innan försurningen etablerades. Det är emellertid också sannolikt att de okalkade sjöarna, som aldrig försurats, naturligt har högre kalciumhalter och sannolikt även högre näringsstatus än de kalkade. Resonemanget antyder att kräftbestånden i de kalkade sjöarna, till följd av naturgivna förutsättningar, inte fullt ut kan förväntas nå samma tätheter som i de okalkade sjöarna. Nästan alla kalkade vatten som provfiskades inom 10 år efter kalkstart uppvisade låga fångster. Det indikerar att bestånden var påtagligt påverkade av försurning och att eventuella effekter av kalkningen ännu inte visat sig i provfiskena. Efter kalkning i 15–25 år förekom ganska många bestånd med höga tätheter, men också många där fångsten var liten. Det antyder att responsen påkalkningen var mycket varierande. I viss utsträckning skulle detta kunna tillskrivas etablering av signalkräfta. I ännu högre grad kan effekten av signalkräftan förklara de, nästan genomgående, svaga fångsterna i vatten som kalkats i mer än 25 år. Andra orsaker än signalkräfta till den stora variationen i fångst av flodkräfta i kalkade sjöar var andel hårdbotten, tätheter av fisk, höjd över havet och vattenfärg. Fångsten av flodkräfta var större i lågt belägna sjöar, med mindre färgat vatten och en större mängd fisk. I sjöar utan signalkräftförekomst tenderade fångsten av flodkräftor att öka med andelen hårdbotten oavsett omsjöarna var kalkade eller ej. Där signalkräfta förekom var fångsterna av flodkräfta alltid låga, oavsett bottensubstrat. Sammantaget visar utvärderingen att eventuella effekter av kalkning på flodkräftbestånd till stor del överskuggas av den ökade spridningen av signalkräfta och därav följande förlust av flodkräftbestånd. Historiskt har försurningen påverkat många flodkräftbestånd och i de få vatten som har tidsseriedata visar provfiskena på ökade fångster efter kalkning.Kalkningsinsatser bör prioriteras i försurade vatten där flodkräftan har en rimlig chans att överleva på sikt, det vill säga i de områden där signalkräfta saknas

    Predicting harvest of non-native signal crayfish in lakes —a role for changing climate?

    No full text
    The signal crayfish (Pacifastacus leniusculus) was introduced to Sweden in 1960, and it has a high commercial and recreational value, but it may also have negative effects on native ecosystems. To better predict how climate warming will affect population dynamics of this cool-water crayfish, we explored the role of temperature and density dependence as explanatory factors of the subsequent years’ catch rates of commercially sized signal crayfish in four Swedish lakes. We found air temperatures to be good proxies for water temperatures in all lakes, except during winter. We could only obtain water temperature data for Lake Vättern, and winter temperature data were therefore only included in the analysis of catch-per-unit-effort patterns in this lake. Our results indicate that increasing mean air temperatures will potentially affect the population dynamics of coolwater freshwater crayfish species such as the signal crayfish. Based on data from four lakes, it seems that the population dynamics of signal crayfish are lake-specific and could be affected by either recruitment during the juvenile stage, the survival and growth of adults, or both. Increased fluctuations in water temperature during winter may potentially influence adult survival. To better predict the effects of global warming on the dynamics of cool-water crayfish populations, we suggest that future studies should investigate recruitment in crayfish along temperature gradients and the influence of variations in water temperature on winter mortality

    Facilitation and interference among three predators affect their consumption of a stream-dwelling mayfly

    No full text
    1. We experimentally tested if a multiplicative risk model accurately predicted the consumption of a common mayfly at risk of predation from three predator species in New Zealand streams. Deviations between model predictions and experimental observations were interpreted as indicators of ecologically important interactions between predators. 2. The predators included a drift-feeding fish [brown trout (T), Salmo trutta], a benthivorous fish [galaxiid (G), koaro, Galaxias brevipennis] and a benthic predatory stonefly (S; Stenoperla sp.) with Deleatidium sp. mayflies as prey. Eight treatments with all predator species combinations and a predator-free control were used. Experiments were performed in aquaria with cobbles as predator refuges for mayflies and we measured the proportion of prey consumed after 6 h for both day and night trials. 3. Trout consumed a higher proportion of prey than other predators. For the two predator treatments we found less than expected prey consumption in the galaxiid + trout treatment (G + T) for both day and night trials, whereas a higher than expected proportion of prey was consumed during night time in the stonefly + trout (S + T) treatment. 4. The results indicate interference (G + T) and facilitation (S + T) between predators depending on predator identity and time of day. Thus, to make accurate predictions of interspecific interactions, it is necessary to consider the ecology of individual species and how differences influence the direction and magnitude of interactions

    Population collapses in introduced non-indigenous crayfish

    No full text
    Invasive species often have instable population dynamics and are known to collapse or oscillate heavily after passing through the initial lag/growth phases. Long-term data-series documenting these fluctuations are however rare. We use long-term (starting in the early 1960s), semi-quantitative data on the invasive signal crayfish (Pacifastacus leniusculus), capturing its population development after introduction in 44 Swedish lakes. In total 18 (41 %) of these populations had experienced a collapse. A stepwise discriminant function analysis including 20 different ecological or physicochemical characteristics identified three variables explaining collapses in the following order: stocking year, population age and mean air temperature. Populations stocked in the 1980s were more likely to collapse than populations stocked in the 1970s. Lakes with collapses were located in areas with 0.4 A degrees C higher yearly mean air temperatures than the still viable populations. Collapses also depended on the time phase of the population and started to occur 12 years after stocking and were most frequent in the interval 16-20 years after stocking and after 11-15 years duration of the established phase with harvestable densities. An analysis of prevalence and pathogen load of Aphanomyces astaci was conducted in eight of the studied populations. A. astaci was present in all populations but neither the level of prevalence nor the pathogen load in infested specimens differed significantly between lakes with collapses and lakes without. Our results highlight the potential sensitivity and instability of introduced crayfish. The importance of density-dependence and temperature suggest that both climate variability and/or fisheries can influence these processes

    Competition and facilitation within and between a snail and a mayfly larva and the effect on the grazing process

    No full text
    We studied the competitive effects within and between two taxonomically distant freshwater herbivores, a snail and a mayfly, common in Swedish lakes, Lymnaea peregra and Cloeon dipterum, respectively, and their effect on grazing in a laboratory experiment. The experimental set-up consisted of 2-l aquaria, each containing a periphyton covered tile. Intra- and interspecific effects were tested by increasing the density of one species at a time in four different treatments, (1) snails (intraspecific treatment), (2) mayflies (intraspecific treatment), (3) mixed-snails (interspecific treatments, snails kept constant) and (4) mixed-mayflies (interspecific treatments, mayflies kept constant). Intraspecific competition affected both snails and mayflies negatively, i.e. increasing mortality with increasing con-specific density. Furthermore, there was a decrease in snail growth with increasing snail density. In the mixed-species treatments both species changed their microhabitat use indicating interspecific competition. Despite this, we also found a positive effect of mayfly density on snail growth, most likely due to indirect commensalism. No density-dependent effect of grazing on periphyton was found, probably due to interference competition between grazers. However, there was a significant difference in periphyton biomass, due to species composition of grazers. Irrespective of their densities, if they co-existed, the two grazer species decreased the periphyton biomass significantly compared with both single-species treatments. We considered this as a joint action of facilitation and interaction. Our results suggest that competition can be an important structuring factor in macroinvertebrate communities and that species composition can be significant for ecosystem processes within lentic environments
    corecore