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Blåmusslans populationsdynamik i en varierande miljö vid randen av artens utbredning
Full text linkSpatial and temporal variation in the abundance of species can often be ascribed to spatial and temporal variation in the surrounding environment. Knowledge of how biotic and abiotic factors operate over different spatial and temporal scales in determining distribution, abundance, and structure of populations lies at the heart of ecology. The major part of the current ecological theory stems from studies carried out in central parts of the distributional range of species, whereas knowledge of how marginal populations function is inadequate. Understanding how marginal populations, living at the edge of their range, function is however in a key position to advance ecology and evolutionary biology as scientific disciplines.
My thesis focuses on the factors affecting dynamics of marginal populations of blue mussels (Mytilus edulis) living close to their tolerance limits with regard to salinity. The thesis aims to highlight the dynamics at the edge of the range and contrast these with dynamics in more central parts of the range in order to understand the potential interplay between the central and the marginal part in the focal system. The objectives of the thesis are approached by studies on: (1) factors affecting regional patterns of the species, (2) long-term temporal dynamics of the focal species spaced along a regional salinity gradient, (3) selective predation by increasing populations of roach (Rutilus rutilus) when feeding on their main food item, the blue mussel, (4) the primary and secondary effects of local wave exposure gradients and (5) the role of small-scale habitat heterogeneity as determinants of large-scale pattern.
The thesis shows that populations of blue mussels are largely determined by large scale changes in sea water salinity, affecting mainly recruitment success and longevity of local populations. In opposite to the traditional view, the thesis strongly indicate that vertebrate predators strongly affect abundance and size structure of blue mussel populations, and that the role of these predators increases towards the margin where populations are increasingly top-down controlled. The thesis also indicates that the positive role of biogenic habitat modifiers increases towards the marginal areas, where populations of blue mussels are largely recruitment limited. Finally, the thesis shows that local blue mussel populations are strongly dependent on high water turbulence, and therefore, dense populations are constrained to offshore habitats. Finally, the thesis suggests that ongoing sedimentation of rocky shores is detrimental for the species, affecting recruitment success and post-recruit survival, pushing stable mussel beds towards offshore areas. Ongoing large scale changes in the Baltic Sea, especially dilution processes with attendant effects, are predicted to substantially contract the distributional range of the mussel, but also affect more central populations. The thesis shows that in order to understand the functioning of marginal populations, research should (1) strive for multi-scale approaches in order to link ecosystem patterns with ecosystem processes, and (2) challenge the prevailing tenets that origin from research carried out in central areas that may not be valid at the edge.Fluktuationer i populationsstorlek och struktur är ofta reflektioner av förändringar i miljön. En allmänt accepterad lära inom ekologin är den s.k. central-marginal teorin som förutspår att arter generellt förekommer rikligast i centrala delar av deras utbredning, för att minska i antal allt närmare periferin. Detta generella mönster har sitt ursprung i växelverkan mellan arten och dess miljö. Där de biotiska (levande) och abiotiska (icke-levande) processerna är gynnsamma, tenderar individantalet att vara högt medan individantalet minskar mot marginella områden där de fysiologiska och de ekologiska förhållandena närmar sig artens toleransgränser. Förändringar i miljön skapar kontinuerliga förskjutningar i arters utbredning och dessa förändringar är mest markanta vid randen av utbredningen. Eftersom olika processer verkar inom begränsade temporala och rumsliga skalor är det relevant att beskåda fenomenen ur flera perspektiv. Om vi förstår de faktorer som bestämmer dynamiken i randområden, har vi större förmåga att förstå de faktorer som är utslagsgivande i mer centrala populationer. Det har därför globalt förespråkats att studier i randområden är speciellt viktiga och borde erhålla mer vetenskaplig uppmärksamhet.
I mina doktorsstudier har jag studerat blåmusslans (Mytilus edulis) populationsdynamik vid randen av dess geografiska utbredning. Finska viken är speciellt intressant med hänsyn till blåmusslan eftersom de abiotiska miljöfaktorerna, huvudsakligen salthalten, förändras dramatiskt inom ett geografiskt litet område. Små abiotiska förändringar kan inom detta område ha drastiska effekter på blåmusslans förekomst och rekryteringsförmåga. Mina studier visar att småskaliga förändringar i salthalt kan ha dramatiska effekter på blåmusslans rekryteringsförmåga. Studierna visar att blåmusslorna på lokal nivå påverkas väsentligt av vågexponering, resulterande i ytterst täta populationer i det yttersta havsbandet för att minska markant mot fastlandet. Resultaten antyder att den ökade sedimenteringen av klippiga bottnar har menliga effekter på musslornas koloniseringsförmåga. Studien förutspår vidare att de ökade mörtbestånden (Rutilus rutilus) i de kustnära miljöerna har ofördelaktiga effekter på blåmusselpopulationerna och att predationstrycket från mört ökar väsentligt från centrala populationer mot randpopulationer. Slutligen antyder studien att biologiska habitatskapare befrämjar blåmusslans koloniseringsförmåga. Avhandlingen bidrar med ny information om Östersjöblåmusslans biologi och motsätter sig tidigare trossatser som antagit att predationstryck och biotisk växelverkan överlag endast har obetydliga effekter på norra Östersjöns blåmusselpopulationer. Trots att blåmusslan är kustekosystemets rikligaste makroskopiska art, och trots att arten innehar en nyckelposition för hela kustekosystemets välbefinnande, har blåmusslans populationsekologi inte studerats i Finland. Detta arbete kan därför ses som en pionjärstudie med såväl teoretisk som praktisk relevans.ei saavutettav
Populationsstruktur och tillväxthastighet hos sex blåmusselpopulationer i norra Östersjön : ett spatiellt och temporalt perspektiv
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Variation in Community Structure and Abundance of Fish in Simple Structured Shallow Sandy Habitats
Full text linkSandy beaches and their surf zones characterise many of the world's open coastlines. They are important breeding, nursery and feeding areas for many species of fish. Despite the commonness and importance of sandy beach surf zones, the dynamics, space occupancy and diversity patterns of residing fish is in many places poorly understood. The aim of this study was to (1) characterise the fish community structure in 11 simple structured sandy surf zones of the northern Baltic Sea and (2) relate variation in fish abundance and community structure to a set of chosen abiotic variables. Using beach seine, weekly or biweekly sampling was conducted at fixed sites at 10 occasions throughout a summer season. A total of 60,006 fish individuals belonging to 20 species were recorded. Changes in abundance and community structure were mainly driven by the variation of only five species reflecting species-specific recruitment patterns and different spatial responses to abiotic variables. Dominating groups were Gasterosteidae, Ammodytidae and Gobiidae that together formed 86% of the total adult fish catches. Larval numbers were completely dominated by Gobiidae. Multivariate analyses indicated species-specific responses to measured environmental variables, most important being a combination of wave exposure, beach slope, bottom roughness, and temperature. The present study shows that changes in fish abundance on simple structured sandy sublittoral beaches in the northern Baltic Sea are large over the course of a breeding season. It also reveals that variation in adult and juvenile fish are driven by a set of abiotic factors that influence on the fish assemblage structure through mainly species-specific, rather than through generic responses. Unravelling the degree to which the sandy shore fish community vary in the northern Baltic Sea will help in managing coastal environments that are increasingly being threatened by many anthropogenic stressors.202
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