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Marine Realm (marine + realm)
Selected AbstractsTaxonomic diversity gradients through geological timeDIVERSITY AND DISTRIBUTIONS, Issue 4 2001J. Alistair Crame Abstract., There is evidence from the fossil record to suggest that latitudinal gradients in taxonomic diversity may be time-invariant features, although almost certainly not on the same scale as that seen at the present day. It is now apparent that both latitudinal and longitudinal gradients increased dramatically in strength through the Cenozoic era (i.e. the last 65 my) to become more pronounced today than at any time in the geological past. Present-day taxonomic diversity gradients, in both the marine and terrestrial realms, are underpinned by the tropical radiations of a comparatively small number of species-rich clades. Quite why these particular taxa proliferated through the Cenozoic is uncertain, but it could be that at least part of the explanation involves the phenomenon of evolutionary escalation. This is, in essence, a theory of biological diversification through evolutionary feedback mechanisms between predators and prey; first one develops an adaptive advantage, and then the other. However, there may also have been some form of extrinsic control on the process of tropical diversification, and this was most likely centred on the phenomenon of global climate change. This is especially so over the last 15 my Various Late Cenozoic (Neogene) vicariant events effectively partitioned the tropics into a series of high diversity centres, or foci. It has been suggested that, in the largest of these in the marine realm (the Indo-West Pacific or IWP centre), a critical patterns of islands acted as a template for rapid speciation during glacioeustatic sea level cycles. The same process occurred in the Atlantic, Caribbean and East Pacific (ACEP) centre, though on a lesser scale. Tropical terrestrial diversity may also have been promoted by rapid range expansions and contractions in concert with glacial cycles (a modified refugium hypothesis). We are beginning to appreciate that an integrated sequence of Neogene tectonic and climatic events greatly influenced the formation of contemporary taxonomic diversity patterns. [source] Facilitation research in marine systems: state of the art, emerging patterns and insights for future developmentsJOURNAL OF ECOLOGY, Issue 6 2009Fabio Bulleri Summary 1. Positive species interactions are increasingly recognized as important drivers of community structure and ecosystem functioning. Although the literature on facilitative interactions in terrestrial environments has been reviewed and emerging patterns have been synthesized, comparable attempts are lacking for the marine realm. 2. By means of a quantitative survey of the literature, I provide a critical summary of current knowledge on positive species interactions in marine environments. In particular, I (i) assess how marine facilitation research compares to that carried out in terrestrial environments in terms of focus and philosophical approach; (ii) illustrate the mechanisms by which facilitation takes place in different habitats; (iii) assess whether benefactor and beneficiary species are more likely to belong to the same or to a different trophic level; and (iv) provide examples of how including facilitation into ecological theory might advance our understanding of the mechanisms that regulate ecosystem functioning. 3. Except for some studies in intertidal habitats, few studies in marine environments have been framed within mainstream facilitation theory (e.g. the Stress Gradient Hypothesis) and research does not seem to be organized in a self-contained theme. Amelioration of physical conditions appears to be the most common mechanism of facilitation in intertidal habitats, whilst associational defence predominates in the subtidal. 4. In contrast to the terrestrial literature, dominated by plant,plant interactions, marine benefactors and beneficiary species often belong to different trophic levels. This might imply little overlapping of resource niches or a differential response to environmental conditions or consumer pressure, with implications for the persistence of facilitative effects at the extreme ends of stress gradients. 5. Recent research shows that facilitation can enhance temporal variability and invasibility of marine communities and emphasizes the central role of positive species interactions in regulating the functioning of natural ecosystems. 6.Synthesis. Studies encompassing a wide variety of life histories and environmental conditions are central to achieving a unified facilitation theory. Research in marine environments can provide new insights into the mechanisms underlying variations in the strength and direction of species interactions, but this will require greater awareness and consideration of facilitation. [source] Defining reproductively isolated units in a cryptic and syntopic species complex using mitochondrial and nuclear markers: the brooding brittle star, Amphipholis squamata (Ophiuroidea)MOLECULAR ECOLOGY, Issue 7 2008E. BOISSIN Abstract At a time when biodiversity is threatened, we are still discovering new species, and particularly in the marine realm. Delimiting species boundaries is the first step to get a precise idea of diversity. For sympatric species which are morphologically undistinguishable, using a combination of independent molecular markers is a necessary step to define separate species. Amphipholis squamata, a cosmopolitan brittle star, includes several very divergent mitochondrial lineages. These lineages appear totally intermixed in the field and studies on morphology and colour polymorphism failed to find any diagnostic character. Therefore, these mitochondrial lineages may be totally interbreeding presently. To test this hypothesis, we characterized the genetic structure of the complex in the French Mediterranean coast using sequences of mitochondrial DNA (16S) and for the first time, several nuclear DNA markers (introns and microsatellites). The data revealed six phylogenetic lineages corresponding to at least four biological species. These sibling species seem to live in syntopy. However, they seem to display contrasted levels of genetic diversity, suggesting they have distinct demographic histories and/or life-history traits. Genetic differentiation and isolation-by-distance within the French Mediterranean coasts are revealed in three lineages, as expected for a species without a free larval phase. Finally, although recombinant nuclear genotypes are common within mitochondrial lineages, the data set displays a total lack of heterozygotes, suggesting a very high selfing rate, a feature likely to have favoured the formation of the species complex. [source] Progress and challenges in freshwater conservation planningAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2009Jeanne L. Nel Abstract 1.Freshwater ecosystems and their associated biota are among the most endangered in the world. This, combined with escalating human pressure on water resources, demands that urgent measures be taken to conserve freshwater ecosystems and the services they provide. Systematic conservation planning provides a strategic and scientifically defensible framework for doing this. 2.Pioneered in the terrestrial realm, there has been some scepticism associated with the applicability of systematic approaches to freshwater conservation planning. Recent studies, however, indicate that it is possible to apply overarching systematic conservation planning goals to the freshwater realm although the specific methods for achieving these will differ, particularly in relation to the strong connectivity inherent to most freshwater systems. 3.Progress has been made in establishing surrogates that depict freshwater biodiversity and ecological integrity, developing complementarity-based algorithms that incorporate directional connectivity, and designing freshwater conservation area networks that take cognizance of both connectivity and implementation practicalities. 4.Key research priorities include increased impetus on planning for non-riverine freshwater systems; evaluating the effectiveness of freshwater biodiversity surrogates; establishing scientifically defensible conservation targets; developing complementarity-based algorithms that simultaneously consider connectivity issues for both lentic and lotic water bodies; developing integrated conservation plans across freshwater, terrestrial and marine realms; incorporating uncertainty and dynamic threats into freshwater conservation planning; collection and collation of scale-appropriate primary data; and building an evidence-base to support improved implementation of freshwater conservation plans. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||