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On the importance of body size in the colonization of ephemeral resource patches by vagile consumers
No full textA study on the colonisation of leaf detritus patches by vagile macroinvertebrates in a brackish lagoon is presented in the framework of a conceptual model where a body size-related constraint on patch use behaviour is explicitly considered. Abundance patterns of dominant macroinvertebrate taxa were characterised by short-term, non-random fluctuations, showing significant site-dependent variations. Yet, a site-independent covariation was observed between patterns' fractal dimension and the average body mass of each taxon, indicating that, while the temporal scales characterising the colonisation patterns may be highly species-specific, cross-species generalisations are possible based on body size. The generality of these results was supported by literature data on temporal patterns of carcass colonisation by bathyal fish. The importance of size-related mechanisms in regulating the aggregation of vagile consumers on resource patches and, ultimately, their coexistence at both an inter- and intra-specific level, is discussed
Colonization of ephemeral resource patches by vagile consumers: the importance of body size
Full text linkThe potential of ephemeral resource patches (ERPs) to contribute to central ecological issues has been recently acknowledged, in particular for the diversity-function debate. Due to their intrinsic spatial-temporal heterogeneity and dissipative ontogeny influenced by consumers from different trophic levels, ERPs can be used for further testing hypotheses on mechanisms driving the assembly of animal communities. Here, the results of a study on the colonization of decaying leaf detritus patches by vagile macrobenthic invertebrates are presented in the framework of a conceptual model where body size-related constraints on patch use behaviour are explicitly considered. Invertebrate abundance patterns were characterised by short-term, nonrandom fluctuations, showing significant site-dependent variations. Yet, a site-independent covariation was observed between the fractal dimension of abundance patterns and the average body mass of each taxon, indicating that, while the temporal scales characterising ERPs colonization patterns may be highly speciesspecific, cross-species generalizations are possible based on body size. The generality of these results was supported by literature data on i) temporal patterns of carcass colonization by bathyal fish and ii) spatial patterns of detrital patches colonization by terrestrial invertebrates. The importance of size-related mechanisms in regulating the aggregation on ERPs of vagile consumers and, ultimately, their coexistence at both an inter- and intra-specific level, is discussed
Quantitative assessment of animal-induced leaf damage: a test with three brackish crustaceans feeding on leaf detritus
No full text1 - A computerized image analysis technique was implemented to quantify small-scale leaf damage due to different feeding strategies of macrobenthic invertebrates. Additionally, a foraging strategy index (FSI) was developed to provide a quantitative estimation of inter-specific changes in feeding strategies. 2 - Laboratory feeding trials were run with the three brackish crustaceans Idotea baltica and Lekanesphaera hookeri (Isopoda) and Gammarus aequicauda (Amphipoda); the effect of their feeding activities were tested on decaying leaves of Cymodocea nodosa and Phragmites australis. 3 - Opposite foraging strategies characterised the isopods: Idotea baltica shredded the leaf blade heavily, whereas Lekanesphaera hookeri scraped the leaf surface removing the waxy cuticle and associated heterotrophic microflora. Qualitative observations corresponded to consistent variations in FSI values, with I. Baltica showing the lowest and S. hookeri the highest FSI values, respectively. Leaves consumed by Gammarus aequicauda, on the other hand, showed both shredding and scraping damages, with FSI values intermediate between those observed for I. Baltica and L. hookeri, respectively. 4 - The aforementioned differences in trophic strategy were independent from the trophic resource exploited inter-specific. 5 - The methodology and the index herein presented were effective in providing a quantitative assessment of species-specific differences in the feeding strategy of three ubiquitous components of Mediterranean macrobenthic communities, for which only qualitative, phenomenological descriptions of feeding effects on trophic resources have been to date provide
To bite, or not to bite? A quantitative comparison of foraging strategies among three brackish crustaceans feeding on leaf litters
No full textA computerized image analysis technique was implemented to evaluate the damage done to leaf litters by macrophagous crustaceans characterized by different feeding strategies. In addition, a foraging strategy index (FSI) was tested to provide a quantitative estimation of both inter- and intra-specific, density-dependent changes in feeding strategies. Laboratory trials were run with the isopods Idotea baltica and Lekanesphaera hookeri and the amphipod Gammarus aequicauda. The effect of their feeding activities was tested on decaying leaves of Cymodocea nodosa and Phragmites australis. In addition, tests were run using three different abundances of each species to assess the occurrence of density-dependent shifts in feeding strategies. Independently from the leaf litter type, opposite foraging strategies characterized the isopods. Idotea baltica shredded the leaf blade heavily, whereas L. hookeri scraped the leaf surface removing the epidermis. Qualitative observations corresponded to consistent variations in FSI values, with Idotea showing the lowest and Lekanesphaera the highest FSI values. Leaves consumed by G. aequicauda, conversely, were characterized by both shredding and scraping damages, corresponding to intermediate FSI values compared to those measured for the isopods. Furthermore, negligible density-dependent changes in FSI values occurred for both isopods; Gammarus, in contrast, showed a significant shift in trophic strategies, with FSI values close to that observed for Lekanesphaera at high densities and to Idotea at low densities of conspecifics, respectively. The methodology and the FSI index herein presented provided an effective, quantitative assessment of species-specific differences in the feeding strategy of three ubiquitous components of Mediterranean detritivorous epifauna, for which only qualitative, phenomenological descriptions have been to date provide
ON THE ATLANTIC BLUE CRAB (Callinectes sapidus RATHBUN 1896) IN SOUTHERN EUROPEAN COASTAL WATERS: TIME TO TURN A THREAT INTO A RESOURCE?
No full textThe native distribution of the Atlantic blue crab Callinectes sapidus extends in the Western Atlantic from Nova Scotia to Uruguay, and along the US coasts the blue crab supports an important fishery. It has been introduced to Europe at the beginning of the 20th century and to date the species is recorded almost ubiquitously in the Mediterranean and Black Sea, where it is starting to penetrate the southern European shellfish market. The present review carries out a pragmatic evaluation of the management scenarios for the Atlantic blue crab in southern European waters, including the Mediterranean and Black Sea and the eastern Atlantics coasts of the Iberian Peninsula. The double-fold nature of C. sapidus as both an invasive species and a fishery resource was considered with the following objectives: 1) to provide an updated assessment of the occurrence and abundance of population stocks in view of future commercial exploitation; 2) to identify different management scenarios and examine the potential of the blue crab as a shellfish product in European markets for alimentary and non-alimentary purposes. The review is concluded by a thorough appraisal of the current trends in global and European crustacean fisheries. The opportunity of using the on-going expansion of C. sapidus and other alien portunids of Indo-Pacific origin as management case studies is emphasized, harmonizing the need to control invasive species and mitigate their ecological impacts, and the opportunity to value them as new fishery resource
On the trophic ecology of Gammaridea (Crustacea: Amphipoda) in coastal waters: a European-scale analysis of stable isotopes data
No full textGammaridean amphipods are found throughout a diverse range of coastal and brackish environments and are generally considered macrophagous herbivores/detritivores. While predation and cannibalism have been shown to be common in freshwater species, motivating a revision of the group functional role, only qualitative information is available on marine Gammaridea. In this study, a survey was conducted of the available literature on stable C and N isotopic signatures of macrophagous, fully aquatic Gammaridea and their potential basal resources in European brackish and coastal environments. The contribution of intra- and inter-specific predation to the signatures of gammarideans was verified by a mixing model procedure where the diet-tissue enrichment constant was not set a priori. Specifically, for each study included in the survey the minimum and maximum diet-tissue nitrogen enrichment factors (D15Nmin and D15Nmax) providing a non-zero solution were calculated for a range of carbon enrichment factors, assuming that both metrics would increasingly differ from the values expected for a single trophic level as predation and/or cannibalism increased in the diet of the consumer. The minimum enrichment factors D15Nmin estimated for a D13C of _2.6& and þ0.5& were found to be independent from resource-related artefacts and provided the highest number of successful model runs. D15Nmin values were consistent with a diet based on living or decaying primary producers and not compatible with cannibalism or intra-guild predation. However, they showed a bimodal distribution and were on average far below the range found in the literature, matching the enrichment factors of gammarideans measured under laboratory conditions. These results are discussed considering the interaction of the distinctive isotopic features of basal resources in coastal habitats and the biology and ecology of gammaridean amphipods. Particular emphasis is placed on the high variability of nitrogen enrichment factors, and on their crucial role in attaining reliable results from isotopic models used for food web studie
Intraspecific, size-dependent variation in the movement behaviour of a brackish-water isopod: a resource-free laboratory experiment
No full textIntraspecific variability represents an important, yet inadequately investigated factor affecting the movement behaviour and ecology of mobile organisms. Here, the influence of sex, seasonality and body size on the movement behaviour of the brackish isopod Lekanesphaera hookeri were examined under resource-free laboratory conditions. The mean step length, total path length and average speed were determined twice during the year for adult and juvenile isopods encompassing a 10-fold range in body length. The scale-independent fractal dimension D was used to quantify the tortuosity of the movement paths. No relationships were observed between sex or season and all the movement metrics. In contrast, isopods' body size scaled negatively with the fractal dimension D of movement paths with a breakpoint at 2.6 mm, roughly corresponding to the size of morphometric maturation. No other relationships were observed between the body length of isopods and mean step length, total path length and average speed. The results indicate a sex- and season-independent ontogenetic shift in movement behaviour in L. hookeri. This suggests that in sphaeromatid isopods post-embryonic development determines not only continuous variations in size and proportions, but also a discontinuous change in the movement strategy adopted to interact with the surrounding space. Overall, these findings underscore the need to account explicitly for such changes in models predicting the spatial distribution of organisms characterised by wide intra-population size variatio
The influence of allochthonous leaf detritus on the occurrence of crustacean detritivores in the soft-bottom macrobenthos of the Po River delta area (northwestern Adriatic Sea)
No full textCore samples were examined quarterly at two coastal sites (S1 and S2) and at an offshore station (S3) located in the Po River delta area (northwestern Adriatic Sea). Analyses focused on (i) occurrence of coarse detritus of allochthonous origin in the sedimentary matrix and (ii) the relative influence of macrodetritus enrichment and other environmental factors on the vagile macrofauna. Plant debris occurred in site S1 sediments only in summer and autumn; in contrast, fragments of the phanerogams Cymodocea nodosa and Zostera spp. were found in site S2 sediment throughout the sampling period. Sediments from the offshore site S3 were characterized by negligible plant material, even though in summer and autumn samples debris of continental origin was observed. Even though leaf detritus occurrence at site S2 was ∼5-fold higher compared to the other coastal site S1, it did not influence the total organic matter and its distribution among grain-size classes. Conversely, the specific organic content of dimensional fractions provided an effective assessment of detritus enrichment processes occurring at the two coastal sites. A group of brackish-originated crustaceans (i.e. the amphipods Gammarus insensibilis and G. aequicauda and the isopod Idotea baltica) was the main determinant of among-site multivariate differences in the vagile macrofauna; depositivorous ophiuroids accounted for the residual differences observed during the study period. The analysis of taxa abundance and individual body size indicated that in both site S1 and S3 macrodetritus advection to the benthic system corresponded with passive dispersal of brackish crustaceans, that provided a negligible contribution to the macrobenthic production. In contrast, in site S2 allochthonous inputs from marginal environments could have represented the key factor for the persistence of an authochthonous population of Gammarus insensibilis. The amphipod provided a considerable (19.4%) contribution to the total macrobenthic production of the site, dominated by filter-feeding bivalves and tubicolous deposit feeders. The potential effects of detritivorous crustaceans on soft-bottom macrobenthic assemblages of the northern Adriatic Sea are discusse
Decontextualizing big data for a better perception of macroecology
Full text linkFish species are charismatic subjects widely used for ecological assessment and modelling. We investigated the influence of electrofishing in an attempt to illuminate the extent to which datasets might be merged together. Three American Midwestern regions in Ohio were chosen as study area and the changes in the size-biomass spectra of more than 2000 fish assemblages were analysed. These communities behaved differently according to the sampling method in conjunction to the morphology of the investigated streams and rivers, as shown by decreasing predatory species and lowering of allometric slopes. There are here several lines of evidence indicating that the chosen sampling method, as determined by different habitats, acts as a pitfall and strongly influences the allometry of fish spectra. In the ongoing data-rich era, our results highlight that macroecological investigations, often performed by machine-learning systems without considering the different procedures adopted to collect original data, can easily produce artefactual allometric scalings
Body size-related constraints on the movement behaviour of the arctic notostracan Lepidurus arcticus (Pallas, 1973) under laboratory conditions
Full text linkThe movement behaviour of individuals has long been acknowledged as a key determinant of species distribution in space and time. Information on benthic macroinvertebrates from aquatic habitats are still scant, however, and for polar species are virtually nonexistent. Here, the influence of body size on the movement behaviour of the arctic notostracan Lepidurus arcticus (Pallas) was examined under resource-free laboratory conditions. The mean step length, total path length and average speed were determined for specimens varying in body dry mass by six orders of magnitude. The scale-independent fractal dimension D was used to quantify movement path tortuosity. Among the different movement metrics considered, the body size of specimens scaled significantly only with path tortuosity; specifically, a negative relationship with a breakpoint was observed between individual body masses and the D values of the respective movement paths. The results are discussed considering similar results obtained for benthic crustaceans from temperate habitats. Additionally, their implications for future investigations explicitly considering temperature effects on movement behaviour are briefly considere
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