1,721,010 research outputs found
Variable orientation within a natural population of the sandhopper Talitrus saltator (Crustacea: Amphipoda) as a response to a variable environment: The case-study of Berkoukesh beach, Tunisia
No full textSandy beaches are harsh environments, driving resident arthropod populations to various typical adaptations, particularly behavioural ones. Here we evaluated the effects of seasonal meteorological variability on the behaviour of Talitrus saltator on Berkoukesh beach (N-W Tunisia). The site is characterised by a Mediterranean climate, but is particularly exposed to seasonal winds and storms. The shoreline is in morphodynamic equilibrium. We tested sandhopper Talitrus saltator orientation in April, when sudden rainfall and storms are common, and in June, when as a rule the weather is warm and dry. The results were analysed with circular statistics and multiple regression models adapted to angular distributions, in order to highlight differences in orientation under the various conditions. Depending on the environmental conditions, amphipods from the same population appeared to utilise various orientation strategies as a response to different environmental constraints. The use of a range of behavioural mechanisms (sun-orientation seaward, sun-orientation landward, and phototaxis) resulted in links to the local landscape and to the animals' life cycle. As a general conclusion, we can infer that the behavioural variability found within the same population represents a response to seasonal environmental fluctuation. Such an increase in variability is likely to develop on a beach in dynamic equilibrium, where landscape references are stable, and a variable behaviour represents a strategy for dealing with environmental fluctuations. © 2007 Elsevier Ltd. All rights reserved
Deconstructing responses of sandy beach arthropodofauna to shoreline erosion: looking for the proper spatial scale to monitor biodiversity
No full textThe suitability of the small spatial scale of sandy beaches was tested as unit for monitoring biodiversity. The study targeted a coastal stretch in central Mediterranean, characterised by a patchy landscape and erosion trend. Beach arthropod communities (abundance, biodiversity and behavioural adaptation) were considered in the context of ongoing changes and threats to beach habitats. Nine beach units were selected as part of three main coast sectors, each with a different exposure. Beach units were sampled for arthropod diversity, which was assessed at different levels of organisation: taxa abundance, diversity indices and behavioural adaptation. These features were used as response variables in models considering beach physical factors. Sand grain size, swash extent and beach slope resulted the driving forces for abundance and diversity. Behavioural tests indicated a local adaptation to the shoreline direction, with mean angles of orientation seawards. Data related to biodiversity assessment were applied to the estimate of Conservation and Recreation Indices (CI and RI). Coast sectors subject to different erosion rates scored differently, pointing to a potential conflict in management of beaches subject to physical erosion. Overall, data depicted beach sectors, each one including one or more beach units, as the most suitable dimension for deconstruction to the small-spatial scale. The selection of the scale for deconstruction, applicable to geomorphological, biological and managerial contexts, would be of paramount importance to guide decision-making and compare coastal stretches also in other geographic contexts
Exploratory analysis of talitrid population genetics as an indicator of the quality of sandy beaches
No full textAllozymic variation was studied at 23 loci in 10 populations of Talitrus saltator, two populations of Talorchestia deshayesii and two populations of Talorchestia brito from the Mediterranean and Baltic Seas. Levels of genetic differentiation among the three species showed a close relationship between T. saltator and T. deshayesii, whereas T. brito was more genetically differentiated. Within T. saltator, it was possible to recognise two main clusters, the first grouping consisting of Baltic, Tyrrhenian and North African populations, the second comprising Adriatic and East Mediterranean populations. Talitrus saltator populations were generally characterised by low levels of gene flow (Nm < 1). The relationship between Nm and geographic distances was analysed to test for an isolation by distance pattern in the spatial genetic variation. Isolation by distance was detected at the scale of the whole Mediterranean, with geographic distance explaining about 50% of the variance in gene flow. The North African populations showed an island model of genetic structuring; this result is mainly due to the anomalous genetic pattern of a population from a Tunisian beach (Tabarka) highly exploited for tourism. Human activities, which may influence T. saltator population dynamics, are believed to be responsible for the observed pattern of genetic variation in North Africa
Abundance and orientation responses of the sandhopper Talitrus saltator to beach nourishment and groynes building at San Rossore natural park, Tuscany, Italy
No full textBeach nourishment and groynes building were implemented to counteract erosion in sandy beaches located at San Rossore natural park (Tuscany, Italy), near the mouth of Arno river. From 2000 to 2003, nine groynes were built along 3.6 km of coastline at intervals of ca. 400 m, and two of the eight beach segments were filled with marble gravel. Here, we analysed the effects of these beach changes on the abundance and behaviour of the amphipod Talitrus saltator, using field and laboratory observations. Sampling with pitfall traps in order to use the capture frequency as a proxy of abundance was performed bimonthly from September 2004 to January 2006, and orientation experiments were carried out in autumn (2004 and 2005), and spring and summer 2005. Physical variables (beach width, swash width, beach slope, sand penetrability, mean grain size and salinity) were also recorded. The abundance of T. saltator increased with the distance from the river mouth, towards sites with: negligible amounts of marble locally used for nourishment; higher beach width and salinity; lower slope and penetrability values; medium grain sizes, and during the spring/summer seasons. A Generalized Linear Model with a predictive power of 64.5% considered three main descriptors in the model as significant: distance from the river mouth, sand penetrability and a seasonal factor. Orientation experiments showed a highly variable behaviour among sites, depending on coastal stability: at the site stabilized by the concurrent actions of nourishment and groynes protection measures, sandhoppers were oriented to the shoreline direction by using a sun compass; alternatively, at a site situated only 2 km from the nourished sites, they showed scattered orientation. These between-site differences in orientation, described through Spherically Projected Linear Models, were consistent throughout the study period. Different responses obtained at the individual (orientation) and population (captures) levels stress the need to account for several bioindicators to characterize biotic responses to both natural and anthropogenic changes in sandy beaches. © 2007 Springer-Verlag
Orientation of sandhoppers at different points along a dynamic shoreline in southern Tuscany
No full textOrientation experiments were carried out on Talitrus saltator (Crustacea Amphipoda) at four points along 3 km on a dynamic sandy beach inside the Maremma Regional Park (Grosseto, Italy) to highlight behavioural variation related to distance from a river mouth, to erosion or accretion of shoreline, and to human trampling on the beach. Tests were performed using circular transparent Plexiglas arenas, contemporaneously at the four points. Replicates were made in 2 different months (September 2002 and May 2003), on 2-3 successive days, in the morning and afternoon. The distributions of the angles of orientation were compared for the different points and seasons, and multiple regression analysis was performed to test the effects of environmental and intrinsic variables on orientation. Sandhoppers showed the highest scatter at the eroded shoreline, intermediate scatter at the accreting beach most distant from the river mouth, and consistent orientation seaward at the least disturbed point. Orientation of sandhoppers was significantly affected by season, global radiation, time of day, distance from the river mouth, and human trampling. Sex and air humidity were of minor significance in the multiple regression model. The results, on the one hand, confirm plasticity in orientation of sandhoppers living on a dynamic shoreline, and on the other hand, show that variation in orientation could potentially be used as a bioindicator of shoreline changes. © Springer-Verlag 2005
Effects of beach nourishment and groynes building on population and community descriptors of mobile arthropodofauna
No full textFor decades beach nourishment and groyne building have been used to combat sandy beach erosion, but their effects on sandy beach macrofauna are often neglected. Here, we analysed the effects of beach nourishment and groyne building on a sandy beach within the San Rossore-Migliarino-Massaciuccoli Regional Park (a natural park in Tuscany, Italy) on two different levels of organization: the abundance of the crustacean amphipod Talitrus saltator (population level) and community descriptors of the sandy beach arthropod fauna (community level), with emphasis on supralittoral species. Samples were taken bimonthly from September 2004 to January 2006 using pitfall traps. T. saltator abundance was described by generalized linear models (GLMs) and arthropodofauna community descriptors were estimated by species number, diversity indexes and ordered with multivariate ordination methods. The abundance of T. saltator in different seasons was influenced by the month of sampling during the autumn-winter season and by beach width, substrate penetrability and the "species number" biotic factor during the spring-summer season. The abundance models revealed no direct effects of beach nourishment. T. saltator was shown to be both a typifying and discriminating species, confirming its key role in the community of sandy beaches. The arthropodofauna community showed sensitivity to the substrate grain size and quality changes generated by beach nourishment, as the community composition changed at the nourished sites in line with seasonal dynamics. Human actions to stabilise the shoreline therefore emerged as a driving environmental feature, altering the beach's physical characteristics and consequently its fauna on different organizational levels: it was shown to have a direct effect on the arthropodofauna community structure and on sandhopper population abundance by determining habitat availability. © 2008 Elsevier Ltd. All rights reserved
Monitoring changes in sandy beaches in temperate areas through sandhoppers' adaptations
No full textSandhoppers (Amphipoda, Talitridae) are keystone species of sandy beach ecosystems in temperate areas. Several traits have been studied and proposed as bioindicators of impacts on sandy beaches, at individual (physiology and behaviour), population (life cycle, abundance, population dynamics and structure, morphometry and fluctuating asymmetry) and species (genetic structure and variation) levels. Sandy beaches, where these species spend their whole life cycle, are dynamic environments, subject to periodic changes (night-day, tides and seasons), as well as to impacts that may cause erosion or accretion of the littoral zone. The first response of an animal to potentially injuring factors is shown by its avoidance behaviour regarding the potential stress. This behaviour may be a rapid escape reaction, shown by single individuals, the whole or part of the population. Activity rhythms, changes in zonation, burrowing, escape reactions, orientation towards the optimal zone on the beach, are all adaptations to environmental changes, increasing the survival chances of the individuals and populations that express such behaviours. In this paper we present case studies of the talitrid species' behavioural adaptations related to natural and human impacts on sandy beaches in the Mediterranean: (1) erosion/accretion dynamics of a Tyrrhenian beach in central Italy (Maremma Regional Park), and (2) increasing urbanisation on a beach in north-western Morocco (Oued Laou river mouth). The best behavioural adaptation was shown by the populations from more stable coastlines. For the survival value of rapid and possibly anticipatory responses to stressful factors, behavioural variation may be proposed as an early-warning indicator of environmental changes. The adaptation at higher levels (population and species) may reflect, on the one hand, the evolvability of the species and, on the other hand, the changeability of the environment. Adaptations at population level may be used as bioindicators of past changes over generations and evolutionary times. © Koninklijke Brill NV, Leiden, 2013
ORIENTATION BEHAVIOR AND HETEROZYGOSITY OF SANDHOPPER POPULATIONS IN RELATION TO STABILITY OF BEACH ENVIRONMENTS
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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
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