Ecological marginality and recruitment loss in the globally endangered freshwater pearl mussel

Aim Ecological marginality is the existence of species/populations in the margins of their ecological niche, where conditions are harsher, and the risk of extinction is more pronounced. In threatened long-lived species, the disparity between distribution and population demography may provide understanding of how environmental heterogeneity shapes ecological marginality, potential extinction patterns and range shifts. We set out to evaluate this by combining a species distribution model (SDM) with population-specific demography data. Location Sweden, 450,000 km(2). Major Taxa Studied Freshwater pearl mussel (FPM, Margaritifera margaritifera) and two salmonid fish species. Methods A SDM for the mussel was constructed with MaxEnt using salmonid host fish (Salmo trutta plus S. salar) density, extreme low and high temperatures, precipitation, altitude, and clay content as explanatory variables. The output was used to test the ecological marginality hypothesis by evaluating whether lowly predicted populations had higher loss of recruitment. Logistic regression was used to explicitly test the factors involved in recruitment loss. Results Host fish density contributed the most (50.3%) to the mussel distribution, followed by lowest temperature the coldest month (34.3%) and altitude (10.3%), while the remaining explanatory variables contributed minimally (<3.3%). Populations with lower SDM scores lacked recruitment to a significantly higher degree. Populations inhabiting areas at low altitude, with lower densities of host fish, and warmer winter temperatures have lost recruitment to a higher degree. Main Conclusions We found support for the ecological marginality hypothesis. The patterns indicate that FPM habitat niche may shift northwards over time. Salmonid host fish density seems to be a driving factor for both historical distribution and recent demographic performance. Finally, we emphasize the value of combining SDMs with independent data on population demography as it both lends rigidity to model validation and understanding of how ecological marginality affects species distribution and viability

Thiamin dynamics during the adult life cycle of Atlantic salmon (Salmo salar)

Thiamin is an essential water-soluble B vitamin known for its wide range of metabolic functions and antioxidant properties. Over the past decades, reproductive failures induced by thiamin deficiency have been observed in several salmonid species worldwide, but it is unclear why this micronutrient deficiency arises. Few studies have compared thiamin concentrations in systems of salmonid populations with or without documented thiamin deficiency. Moreover, it is not well known whether and how thiamin concentration changes during the marine feeding phase and the spawning migration. Therefore, samples of Atlantic salmon (Salmo salar) were collected when actively feeding in the open Baltic Sea, after the sea migration to natal rivers, after river migration, and during the spawning period. To compare populations of Baltic salmon with systems without documented thiamin deficiency, a population of landlocked salmon located in Lake Vänern (Sweden) was sampled as well as salmon from Norwegian rivers draining into the North Atlantic Ocean. Results showed the highest mean thiamin concentrations in Lake Vänern salmon, followed by North Atlantic, and the lowest in Baltic populations. Therefore, salmon in the Baltic Sea seem to be consistently more constrained by thiamin than those in other systems. Condition factor and body length had little to no effect on thiamin concentrations in all systems, suggesting that there is no relation between the body condition of salmon and thiamin deficiency. In our large spatiotemporal comparison of salmon populations, thiamin concentrations declined toward spawning in all studied systems, suggesting that the reduction in thiamin concentration arises as a natural consequence of starvation rather than to be related to thiamin deficiency in the system. These results suggest that factors affecting accumulation during the marine feeding phase are key for understanding the thiamin deficiency in salmonids. Atlantic salmon, Baltic Sea, M74 syndrome, Salmon life cycle, Thiamin, Thiamin deficiencypublishedVersio

Våtmarker som fiskevårdsåtgärd vid kusten: Utvärdering av restaurerade våtmarkers effekt på fiskreproduktion och ekosystemet längs Östersjökusten

Många av Östersjöns kustfiskar är av sötvattenursprung och fortplantar sig i grunda vikar och kustnära våtmarker. Historiska utdikningar, kustexploatering och övergödning har lett till förluster av fiskens lek- och uppväxtområden, vilket tillsammans med fiske bidragit till minskande bestånd av exempelvis gädda och abborre. För att motverka nedgången har flera förvaltningsåtgärder initierats. Ungefär 100 våtmarker har restaurerats längs svenska ostkusten för att gynna reproduktionen av gädda och abborre. I samma syfte har fiskvandringshinder i kustmynnande vattendrag tagits bort på cirka 40 platser. Det fåtal uppföljningar som genomförts visar att sådana åtgärder har en god potential att bidra till stärkta kustbestånd av gädda och abborre. Mängden gäddyngel i kustvattnen utanför våtmarkerna tenderar att öka kraftigt efter åtgärderna, medan ingen tydlig förändring kan ses för mängden abborryngel. Det är dock stor variation i utfallet. En studie indikerar även en tydlig lokal ökning av gäddbestånden i kustvattnen utanför våtmarkerna. Sammanställningen visar även att borttagning av vandringshinder i kustmynnande vattendrag förbundna med olika sjösystem kan vara en effektivare metod än att restaurera våtmarker för attgynna abborre, vilket bör undersökas vidare. Det finns få studier som specifikt undersökt om åtgärderna kan ge så stark effekt på rovfiskbestånden att det indirekt påverkar resten av födoväven och ekosystemet. Det finns en potential för sådan påverkan. Men ökningen av rovfisk till följd av de åtgärdade våtmarkerna har i dagsläget inte varit tillräckligt kraftig för att leda till tydliga ekosystemeffekter, så som mindre mängd bytesfisk och påväxtalger. Även om våtmarker kan ge en lokal ökning av mängden fisk måste fler och kompletterande åtgärder till för att stärka kustens rovfiskbestånd. Åtgärderna bör utformas som en del av en tydligt samordnad och långsiktig förvaltning av kust och hav. Förutom en starkare reglering av kustfisket behövs exempelvis bättre skydd mot exploatering av fiskens lek- och uppväxtområden. Även lokal reduktion av mängden gråsäl och storskarv kan vara en möjlig åtgärd i områden där dessa rovdjur medför hög dödlighet på gädda och abborre. Utformningen av fiskeriförförvaltningen i öppet hav måste ha en mer rigid tillämpning av ekosystemansatsen och beakta konsekvenser för kustens ekosystem. Exempelvis tyder mycket på att förändringar i utsjöns fiskbestånd är en viktig bidragande orsak till att storspigg har ökat kraftigt de senaste decennierna. Storspiggen migrerar mellan utsjö och kust. Eftersom den äter gädd- och abborryngel minskar möjligheten att med lokala åtgärder stärka rovfiskbestånden vid kusten. Sammanställningen visar på en bristfällig koordinering och uppföljningav det senaste decenniets fiskevårdsåtgärder. För att skapa en bättre kunskapsbas för framtida förvaltningsbeslut finns därför ett behov av fler och samordnade mångåriga uppföljningar av åtgärder på såväl yngelproduktionoch lokala fiskbestånd som på kustekosystemet

Lokala anpassningar hos migrerande gädda i Östersjön

Population divergence shaped by natural selection is central to evolutionary ecology research and has been in focus since Darwin formulated “The origin of species”. Still, the process of adaptive divergence among sympatric populations is poorly understood. In this thesis I studied patterns of adaptive divergence among subpopulations of pike (Esox lucius) that are sympatric in the Baltic Sea but become short-term allopatric during spawning and initial juvenile growth in freshwater streams. I also examined causes and consequences of phenotypic variation among individuals within subpopulations to evaluate the contribution of natural selection to population divergence.   I first investigated homing behaviour and population structures of pike to assess the potential for adaptive divergence among sympatric pike that migrate to spawn in different streams. Mark-recapture data suggested that migrating pike displayed homing behaviour and repeatedly returned to the same stream. Analyses of microsatellite data revealed partial reproductive isolation among subpopulations spawning in different streams. These subpopulations, however, were truly sympatric during the life-stage spent in the Baltic Sea.   To address whether short-term allopatry has resulted in adaptive divergence among sympatric subpopulations I combined observational, experimental and molecular approaches. Observational data showed that subpopulations differed in morphological and life-history traits and common-garden experiments suggested that differences were, at least in part, genetically based. Moreover, QST-FST comparisons indicated that genetically based phenotypic differences has been driven by divergent selection, and a reciprocal translocation experiment showed that phenotypic variation represented local adaptations to spawning habitats. Finally, longitudinal and cross-sectional comparisons among individuals revealed associations between phenotypes, performance and fitness components.   In conclusion, my thesis illustrates how short-term allopatry due to migratory behaviour can result in adaptive divergence among sympatric subpopulations. These findings advance the understanding of evolutionary processes at the finest spatiotemporal scale and illustrate that local adaptations can arise in environments with high connectivity.  The results also emphasise that fine spatial scale population structures must be taken into consideration in management and conservation of biodiversity in the Baltic Sea.EcoChang

Data from: Predator-prey role reversal may impair the recovery of declining pike populations

Many fish populations have experienced declines in recent decades due to anthropogenic disturbances, such as overfishing and habitat exploitation. Despite management actions many populations show a limited capacity to recover. This may be attributed to reversal of predatory‐prey roles, yet empirical evidence to that effect remains scarce. Here we combine field and laboratory studies to investigate the interaction between pike (Esox lucius), a large keystone top predatory fish, and the small‐bodied mesopredatory threespine stickleback (Gasterosteus aculeatus) in the Baltic Sea where pike populations have declined. Our data suggest that stickleback predation on pike larvae depletes a large proportion of the recruitment and influences the size distribution through size‐selective predation, which is corroborated by a gape‐limitation experiment and diet analysis of wild captured sticklebacks. The effects of stickleback predation are present across several populations and years, and our data suggests that early arrival of sticklebacks has stronger effects on juvenile pike survival. Finally, we use data on pike gape‐limitation and the size distribution of sticklebacks to illustrate the process of role reversal. These findings suggest that mesopredator behaviour can reduce recruitment of a top predator species and impair the capacity of populations to recover. This emphasizes predator‐prey role reversal as an important ecological and evolutionary driver that influences the outcome of restoration and management actions

Temporal variation in abundances

Data on the number of captured pike juveniles with (predation site) and without (no predation site) sticklebacks present. Data sampled in one popualtion (pop O) across 5 years (2007-2009, 2013-2014

Ecological marginality and recruitment loss in the globally endangered freshwater pearl mussel

Aim: Ecological marginality is the existence of species/populations in the margins of their ecological niche, where conditions are harsher, and the risk of extinction is more pronounced. In threatened long-lived species, the disparity between distribution and population demography may provide understanding of how environmental heterogeneity shapes ecological marginality, potential extinction patterns and range shifts. We set out to evaluate this by combining a species distribution model (SDM) with population-specific demography data. Location: Sweden, 450,000?km2. Major Taxa Studied: Freshwater pearl mussel (FPM, Margaritifera margaritifera) and two salmonid fish species. Methods: A SDM for the mussel was constructed with MaxEnt using salmonid host fish (Salmo trutta plus S. salar) density, extreme low and high temperatures, precipitation, altitude, and clay content as explanatory variables. The output was used to test the ecological marginality hypothesis by evaluating whether lowly predicted populations had higher loss of recruitment. Logistic regression was used to explicitly test the factors involved in recruitment loss. Results: Host fish density contributed the most (50.3%) to the mussel distribution, followed by lowest temperature the coldest month (34.3%) and altitude (10.3%), while the remaining explanatory variables contributed minimally (&lt;3.3%). Populations with lower SDM scores lacked recruitment to a significantly higher degree. Populations inhabiting areas at low altitude, with lower densities of host fish, and warmer winter temperatures have lost recruitment to a higher degree. Main Conclusions: We found support for the ecological marginality hypothesis. The patterns indicate that FPM habitat niche may shift northwards over time. Salmonid host fish density seems to be a driving factor for both historical distribution and recent demographic performance. Finally, we emphasize the value of combining SDMs with independent data on population demography as it both lends rigidity to model validation and understanding of how ecological marginality affects species distribution and viability

Size, connectivity and edge effects of stream habitats explain spatio-temporal variation in brown trout (Salmo trutta) density

Ecological theory postulates that the size and isolation of habitat patches impact the colonization/extinction dynamics that determine community species richness and population persistence. Given the key role of lotic habitats for life-history completion in rheophilic fish, evaluating how the distribution of swift-flowing habitats affects the abundance and dynamics of subpopulations is essential. Using extensive electrofishing data, we show that merging island biogeography with meta-population theory, where lotic habitats are considered as islands in a lentic matrix, can explain spatio-temporal variation in occurrence and density of brown trout (Salmo trutta). Subpopulations in larger and less isolated lotic habitat patches had higher average densities and smaller between-year density fluctuations. Larger lotic habitat patches also had a lower predicted risk of excessive zero-catches, indicative of lower extinction risk. Trout density further increased with distance from the edge of adjacent lentic habitats with predator (Esox lucius) presence, suggesting that edge- and matrix-related mortality contributes to the observed patterns. These results can inform the prioritization of sites for habitat restoration, dam removal and reintroduction by highlighting the role of suitable habitat size and connectivity in population abundance and stability for riverine fish populations

Gape-limitation

Data on relationships between total length (mm)/body depth (mm) and total length (mm)/gape size (mm) for both juvenile pike and adult sticklebacks

Spatial variation in abundances

Data on the number of captured pike juveniles with (predation site) and without (no predation site) sticklebacks present. Data were sampled in 2014 and represent four populations of anadromous pike