1,721,008 research outputs found
Barnacle larval supply to sheltered rocky shores: a limiting factor?
No full textIn northwest Europe, sheltered rocky shores are dominated by fucoid canopy algae and barnacles are rare, although the latter are extremely abundant on exposed shores. The supply of the intertidal barnacle Semibalanus balanoides (L.) to sheltered, fucoid dominated rocky shores was investigated to determine the importance of larval supply in limiting the abundance of adults in shelter. Larval supply was measured at two spatial scales, at the scale of shore (100s of metres), by comparing larval concentrations at exposed and sheltered sites, and at a smaller spatial scale (m), by examining the role of fucoid canopies in limiting supply to the substratum. Replicate plankton trawls were carried out above the intertidal zone at high water at two sheltered sites and nearby exposed headlands. The concentration of S. balanoides cyprid larvae was significantly higher at the sheltered sites on two out of three sampling occasions with up to 14 times greater larvae on one occasion than the nearby exposed site. The effect of the macroalgal canopy on supply to the substratum was assessed in two ways: directly, by pumping water from the substratum in areas with and without Ascophyllum nodosum (L.) Le Jolis, and indirectly by measuring cyprid settlement in a canopy-manipulation experiment. Pumped plankton samples from mid tide level showed that the A. nodosum canopy did not form a barrier to larval supply and may have had a positive effect on larval concentrations at the substratum. Cyprid settlement was assessed in the mid shore A. nodosum and low shore Fucus serratus L. zones to areas with canopy algae (but protected from the sweeping effects of macroalgal fronds) and without canopy. Settlement over three consecutive 24-h periods showed a consistent pattern; settlement was consistently lower beneath the F. serratus canopy than in cleared areas, suggesting that this algal species forms a barrier, limiting supply of cyprid larvae to the substratum
Long term effects of Ascophyllum nodosum canopy removal on mid shore community structure
No full textThe long term effects of macroalgal canopy removal on community composition were investigated over a 12 year period. Experimental removal of the dominant Ascophyllum nodosum canopy led to short term changes in community composition, the major features of which were still apparent 12 years later. Ascophyllum was slow to recover despite high recruitment, and experimental plots were dominated by Fucus species. After 12 years a mixed assemblage of Fucus serratus, Fucus vesiculosus and Ascophyllum had developed. Canopy removal resulted in a change in the balance between grazing limpets and the cover of red algal turf in the understorey community. The cover of turfing algae declined significantly allowing the area grazed by limpets to extend. This led to a 3–6 fold increase in the limpet population 12 years after canopy removal
Performance of a warm-water limpet species towards its poleward range edge compared to a colder-water congener
No full textThe demography and individual performance of species at their range edges provide important insight into how climate warming is impacting species distributions. The boreal limpet Patella vulgata and the Lusitanian limpet P. depressa have overlapping geographic ranges and local distributions in Britain. We measured individual performance at the 2 leading edges of P. depressa distribution (North Wales and South/South-east England) and in non-range edge populations in South-west England. Individuals of P. depressa towards both leading edges were expected to have reduced growth rates and higher mortality rates when compared with non-range edge populations. Conversely, P. vulgata was expected to have equivalent performance across regions, coinciding with the centre of its range. Tagged individuals did not show between-species differences in growth and mortality over a 12 mo period. Nonetheless, individual growth rates and population mortality rates of both Patella species were higher towards the range edge of P. depressa in South/South-east England, when compared with populations at its poleward edge and those in South-west England. Further analysis showed that growth and mortality rates were higher in denser populations for both P. depressa and P. vulgata, with equivalent site-specific performance patterns for both species in all regions. Thus, performance patterns of P. depressa reflected local factors in the same way as P. vulgata, overriding patterns of declining performance expected towards species borders. Comparisons between key congeneric species and their unexpected patterns of performance across their ranges provide insights into processes setting species boundaries and thereby their responses to climate change
Physical and biological control of fucoid recruitment in range edge and range centre populations
No full textThe structure of rocky shore assemblages is determined to a large extent by the interaction between abiotic and biotic processes. Understanding of the strength and interactive nature of these processes over different spatial and temporal scales provides insight into key structuring mechanisms and clarifies what sets species’ distributions. Here we examine the potential interactive effect of physical environment (insolation stress) and grazing pressure on recruitment success of fucoid species (Fucus spp.) in North Wales and Portugal, in order to understand patterns of distribution at the centre and equatorward edge of their range. Contrary to expectations, amelioration of the physical environment through reduction of insolation stress did not improve recruitment in either geographical region. Grazing activity of patellid limpets was found to be an important process regulating fucoid recruitment only on northern European shores. The top-down control of fucoid recruitment at the northern latitude was apparent, even at half the normal densities of patellid limpets. The use of reduced light levels and reduced grazing pressure in southern regions was expected to improve fucoid recruitment, but results indicate amelioration of physical and biological pressures cannot compensate for an inherently low supply of propagules. Our study confirms that strong top-down control by grazers (Patella spp.) can directly determine the distribution and abundance of fucoid algae in core areas of its range, but toward the range edge factors other than those examined are responsible for low recruitment and, ultimately, the observed decline in fucoid abundance in southern European regions
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
Rocky intertidal community structure in oceanic islands: scales of spatial variability
Full text linkThere is a clear bias in the literature on island ecology towards terrestrial rather thanmarine systems, which have remained comparatively poorly studied. Marine populations are typicallyopen, and local production may have little impact on local recruitment, such that long-distancedispersal is an important determinant of population ecology. Since oceanic islands form discretepatches of habitat surrounded by a structurally different environment, we tested the general hypothesisthat processes operating at the scale of islands have a greater influence on these populationsthan the processes operating at smaller, intra-island scales. A hierarchical design examined the patternsof abundance and distribution of conspicuous taxa at 3 tidal heights at a range of spatial scales,ranging from a few meters to hundreds of kilometres apart in the rocky intertidal of the Azores. Bothuni- and multivariate analyses showed that at the largest scale (islands), significant variation wasdetected in the lower and mid-shore communities, but not on the upper shore. Along the verticalgradient of immersion there was a trend for increasing small-scale patchiness towards the top of theshore. The potential role of local environmental stress gradients and broad-scale oceanographicpatterns of recruitment in structuring these assemblages is discussed. This study corroborates thesuitability of the analytical tools used here to examine patterns of distribution over a range of spatialscales and its applicability in the field of island marine ecology
Exploitation of rocky intertidal grazers: population status and potential impacts on community structure and functioning
Full text linkA wide range of anthropogenic activities are impacting the ecology of coastal areas. Exploitation of marine resources is one such activity, which, through cascading trophic effects, can have influences well beyond that of the target species. We investigated the mid-rocky-shore community structure of the Azores archipelago, a seldom-studied habitat, where there is a local tradition of exploiting limpets, the main intertidal grazers. The limpet population structure differed among islands, and there was an inverse relationship between the abundance of larger limpets and the human population per coastal perimeter, but not the associated catch data. At small scales of resolution (quadrats), there was a negative relationship between the cover of algae and limpets and a positive relationship between barnacles and limpets. These relationships were also apparent at the larger scale of islands as a function of the gradient of exploitation. Our results show how natural habitat fragmentation may be useful where the experimental testing of a hypothesis is not possible, and provide evidence for the trophic cascading effects of limpet exploitation at landscape scales
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
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