The link between species invasions and the extinction of natives is widely accepted by scientists as well as conservationists, but available data supporting invasion as a cause of extinctions are, in many cases, anecdotal, speculative and based upon limited observation. We pose the question, are aliens generally responsible for widespread extinctions? Our goal is to prompt a more critical synthesis and evaluation of the available data, and to suggest ways to take a more scientific, evidence-based approach to understanding the impact of invasive species on extinctions. Greater clarity in our understanding of these patterns will help us to focus on the most effective ways to reduce or mitigate extinction threats from invasive species.

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Are invasive species a major cause of extinctions

Invertebrate species represent more than 99% of animal diversity; however, they receive much less publicity and attract disproportionately minor research effort relative to vertebrates. Nonmarine mollusks (i.e., terrestrial and freshwater) are one of the most diverse and imperiled groups of animals, although not many people other than a few specialists who study the group seem to be aware of their plight. Nonmarine mollusks include a number of phylogenetically disparate lineages and species-rich assemblages that represent two molluscan classes, Bivalvia (clams and mussels) and Gastropoda (snails, slugs, and limpets). In this article we provide an overview of global nonmarine molluscan biodiversity and conservation status, including several case studies documenting the diversity and global decline of nonmarine mollusks. We conclude with a discussion of the roles that mollusks and malacologists should play in conservation, including research, conservation management strategies, and education and ou...

https://www.jstor.org/stable/10.1641/0006-3568(2004)054%5B0321:TGDONM%5D2.0.CO;2

The Global Decline of Nonmarine Mollusks

Comparative, functional, and developmental studies of animal morphology require accurate visualization of three-dimensional structures, but few widely applicable methods exist for non-destructive whole-volume imaging of animal tissues. Quantitative studies in particular require accurately aligned and calibrated volume images of animal structures. X-ray microtomography (microCT) has the potential to produce quantitative 3D images of small biological samples, but its widespread use for non-mineralized tissues has been limited by the low x-ray contrast of soft tissues. Although osmium staining and a few other techniques have been used for contrast enhancement, generally useful methods for microCT imaging for comparative morphology are still lacking. Several very simple and versatile staining methods are presented for microCT imaging of animal soft tissues, along with advice on tissue fixation and sample preparation. The stains, based on inorganic iodine and phosphotungstic acid, are easier to handle and much less toxic than osmium, and they produce high-contrast x-ray images of a wide variety of soft tissues. The breadth of possible applications is illustrated with a few microCT images of model and non-model animals, including volume and section images of vertebrates, embryos, insects, and other invertebrates. Each image dataset contains x-ray absorbance values for every point in the imaged volume, and objects as small as individual muscle fibers and single blood cells can be resolved in their original locations and orientations within the sample. With very simple contrast staining, microCT imaging can produce quantitative, high-resolution, high-contrast volume images of animal soft tissues, without destroying the specimens and with possibilities of combining with other preparation and imaging methods. Such images are expected to be useful in comparative, developmental, functional, and quantitative studies of morphology.

/pdf/microct-for-comparative-morphology-simple-staining-methods-31kkpwlfyt.pdf

MicroCT for comparative morphology: simple staining methods allow high-contrast 3D imaging of diverse non-mineralized animal tissues

Wildlife in a Changing World presents an analysis of the 2008 IUCN Red List of Threatened Species. Beginning with an explanation of the IUCN Red List as a key conservation tool, it goes on to discuss the state of the worlds species and provides the latest information on the patterns of species facing extinction in some of the most important ecosystems in the world, highlighting the reasons behind their declining status. Areas of focus in the report include: freshwater biodiversity, the status of the worlds marine species, species susceptibility to climate change impacts, the Mediterranean biodiversity hotspot, and broadening the coverage of biodiversity assessments.

Wildlife in a changing world : an analysis of the 2008 IUCN red list of threatened species

The integration of phylogenetics, phylogeography and palaeoenvironmental studies is providing major insights into the historical forces that have shaped the Earth's biomes. Yet our present view is biased towards arctic and temperate/tropical forest regions, with very little focus on the extensive arid regions of the planet. The Australian arid zone is one of the largest desert landform systems in the world, with a unique, diverse and relatively well-studied biota. With foci on palaeoenvironmental and molecular data, we here review what is known about the assembly and maintenance of this biome in the context of its physical history, and in comparison with other mesic biomes. Aridification of Australia began in the Mid-Miocene, around 15 million years, but fully arid landforms in central Australia appeared much later, around 1-4 million years. Dated molecular phylogenies of diverse taxa show the deepest divergences of arid-adapted taxa from the Mid-Miocene, consistent with the onset of desiccation. There is evidence of arid-adapted taxa evolving from mesic-adapted ancestors, and also of speciation within the arid zone. There is no evidence for an increase in speciation rate during the Pleistocene, and most arid-zone species lineages date to the Pliocene or earlier. The last 0.8 million years have seen major fluctuations of the arid zone, with large areas covered by mobile sand dunes during glacial maxima. Some large, vagile taxa show patterns of recent expansion and migration throughout the arid zone, in parallel with the ice sheet-imposed range shifts in Northern Hemisphere taxa. Yet other taxa show high lineage diversity and strong phylogeographical structure, indicating persistence in multiple localised refugia over several glacial maxima. Similar to the Northern Hemisphere, Pleistocene range shifts have produced suture zones, creating the opportunity for diversification and speciation through hybridisation, polyploidy and parthenogenesis. This review highlights the opportunities that development of arid conditions provides for rapid and diverse evolutionary radiations, and re-enforces the emerging view that Pleistocene environmental change can have diverse impacts on genetic structure and diversity in different biomes. There is a clear need for more detailed and targeted phylogeographical studies of Australia's arid biota and we suggest a framework and a set of a priori hypotheses by which to proceed.

/pdf/birth-of-a-biome-insights-into-the-assembly-and-maintenance-1kbja6w5q6.pdf

Birth of a biome: insights into the assembly and maintenance of the Australian arid zone biota.

The world’s gastropod fauna from continental waters comprises ∼4,000 valid described species and a minimum of 33–38 independent lineages of Recent Neritimorpha, Caenogastropoda and Heterobranchia (including the Pulmonata). The caenogastropod component dominates in terms of species richness and diversity of morphology, physiology, life and reproductive modes and has produced several highly speciose endemic radiations. Ancient oligotrophic lakes (e.g., Baikal, Ohrid, Tanganyika) are key hotspots of gastropod diversity; also noteworthy are a number of lower river basins (e.g., Congo, Mekong, Mobile Bay). But unlike many other invertebrates, small streams, springs and groundwater systems have produced the most speciose associations of freshwater gastropods. Despite their ecological importance in many aquatic ecosystems, understanding of even their systematics is discouragingly incomplete. The world’s freshwater gastropod fauna faces unprecedented threats from habitat loss and degradation and introduced fishes and other pests. Unsustainable use of ground water, landscape modification and stock damage are destroying many streams and springs in rural/pastoral areas, and pose the most significant threats to the large diversity of narrow range endemics in springs and ground water. Despite comprising only ∼5% of the world’s gastropod fauna, freshwater gastropods account for ∼20% of recorded mollusc extinctions. However, the status of the great majority of taxa is unknown, a situation that is exacerbated by a lack of experts and critical baseline data relating to distribution, abundance, basic life history, physiology, morphology and diet. Thus, the already considerable magnitude of extinction and high levels of threat indicated by the IUCN Red List of Threatened Species is certainly a significant underestimate.

Global diversity of gastropods (Gastropoda; Mollusca) in freshwater

Sequence data for two segments of 28S and Histone H3 from 36 gastropod taxa, a chiton, two bivalves and Nautilus are used to test recently published morphology-based phylogenetic hypotheses of gastropod relationships. Statistical results suggest that the accuracy of the available hypotheses could be improved. The data support the monophyly of the Patellogastropoda (true limpets), Euthyneura and the ‘higher’ vetigastropods and the polyphyly of the ‘Cocculiniformia’. The division of the gastropods into two major clades (Eogastropoda and Orthogastropoda) as has been proposed on morphological grounds is not supported, and neither the Caenogastropoda nor Heterobranchia is well supported. Within the Euthyneura, opisthobranchs are paraphyletic with respect to the pulmonates. The hot vent taxon, Depressigyra, groups with the lower vetigastropod Pleurotomaria in some analyses. Much of the variability in the 28S rDNA segments lies in discrete areas of the sequence. Forone of the segments, corresponding to positions 691–942 of the mosquito Aedes albopictus 28S sequence, the variable regions represent known expansion regions (D4 and D5). For the other segment, corresponding to positions 2259–2538 of the A. albopictus sequence, the variable area, which is found in the patellogastropods, vetigastropods and Nautilus, represents an unreported expansion region. The data show marked variability in the rate of evolution in both segments of the 28S rDNA, whether or not the expansion regions are included. The variability is largely clade specific. Rates are high in the patellogastropods, vetigastropods, the lower heterobranch ‘Heterostropha’ (Cornirostra and Philippea), Depressigyra and the deep sea cocculinid limpet Coccopigya and substantially lower in other taxa. Rate variation in the histone H3 data is less extreme. The correlation between evolutionary rates in the two 28S rDNA segments is very high, andis also significant for the the pairing of each of the 28S rDNA segments with H3. The rate variability may be due to differential selection but no causative factor has been identified. The histone H3 data have high codon usage bias. For all amino acids encoded by multiple codons, at least some triplets occur at a frequency of less than a quarter of their expected usage. For all three-, four-and sixfold degenerate amino acids, the most abundant triplet occurs at least twice as frequently as expected. Despite the usage bias, there is a large amount of apparent homoplasy in synonymous alternatives at both the first and third codon positions.

Gastropod evolutionary rates and phylogenetic relationships assessed using partial 28S rDNA and histone H3 sequences

Potamopyrgus antipodarum ― a molluscan coloniser of Europe and Australia

http://www.bio-nica.info/biblioteca/Colgan2006Caenogastropoda.pdf

Winston F. Ponder

Papers

The Global Decline of Nonmarine Mollusks

Global diversity of gastropods (Gastropoda; Mollusca) in freshwater

Gastropod evolutionary rates and phylogenetic relationships assessed using partial 28S rDNA and histone H3 sequences

Potamopyrgus antipodarum ― a molluscan coloniser of Europe and Australia

Molecular phylogenetics of Caenogastropoda (Gastropoda: Mollusca)