Most invasion histories include an estimated arrival time, followed by range expansion. Yet, such linear progression may not tell the entire story. The European green crab (Carcinus maenas) was first ...recorded in the US in 1817, followed by an episodic expansion of range to the north. Its population has recently exploded in the Canadian Maritimes. Although it has been suggested that this northern expansion is the result of warming sea temperatures or cold-water adaptation, Canadian populations have higher genetic diversity than southern populations, indicating that multiple introductions have occurred in the Maritimes since the 1980s. These new genetic lineages, probably from the northern end of the green crab's native range in Europe, persist in areas that were once thought to be too cold for the original southern invasion front. It is well established that ballast water can contain a wide array of nonindigenous species. Ballast discharge can also deliver genetic variation on a level comparable to that of native populations. Such gene flow not only increases the likelihood of persistence of invasive species, but it can also rapidly expand the range of long-established nonindigenous species.
It is well known that microbes, zooplankton, and fish are important sources of recycled nitrogen in coastal waters, yet marine mammals have largely been ignored or dismissed in this cycle. Using ...field measurements and population data, we find that marine mammals can enhance primary productivity in their feeding areas by concentrating nitrogen near the surface through the release of flocculent fecal plumes. Whales and seals may be responsible for replenishing 2.3×10(4) metric tons of N per year in the Gulf of Maine's euphotic zone, more than the input of all rivers combined. This upward "whale pump" played a much larger role before commercial harvest, when marine mammal recycling of nitrogen was likely more than three times atmospheric N input. Even with reduced populations, marine mammals provide an important ecosystem service by sustaining productivity in regions where they occur in high densities.
Global nutrient transport in a world of giants Doughty, Christopher E.; Roman, Joe; Faurby, Søren ...
Proceedings of the National Academy of Sciences - PNAS,
01/2016, Letnik:
113, Številka:
4
Journal Article
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The past was a world of giants, with abundant whales in the sea and large animals roaming the land. However, that world came to an end following massive late-Quaternarymegafauna extinctions on land ...and widespread population reductions in great whale populations over the past few centuries. These losses are likely to have had important consequences for broad-scale nutrient cycling, because recent literature suggests that large animals disproportionately drive nutrient movement. We estimate that the capacity of animals to move nutrients away from concentration patches has decreased to about 8% of the preextinction value on land and about 5%of historic values in oceans. For phosphorus (P), a key nutrient, upward movement in the ocean by marine mammals is about 23% of its former capacity (previously about 340 million kg of P per year). Movements by seabirds and anadromous fish provide important transfer of nutrients from the sea to land, totalling ∼150 million kg of P per year globally in the past, a transfer that has declined to less than 4% of this value as a result of the decimation of seabird colonies and anadromous fish populations. We propose that in the past, marine mammals, seabirds, anadromous fish, and terrestrial animals likely formed an interlinked system recycling nutrients from the ocean depths to the continental interiors, with marine mammals moving nutrients from the deep sea to surface waters, seabirds and anadromous fish moving nutrients from the ocean to land, and large animals moving nutrients away from hotspots into the continental interior.
Whales as marine ecosystem engineers Roman, Joe; Estes, James A; Morissette, Lyne ...
Frontiers in ecology and the environment,
September 2014, Letnik:
12, Številka:
7
Journal Article
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Baleen and sperm whales, known collectively as the great whales, include the largest animals in the history of life on Earth. With high metabolic demands and large populations, whales probably had a ...strong influence on marine ecosystems before the advent of industrial whaling: as consumers of fish and invertebrates; as prey to other large-bodied predators; as reservoirs of and vertical and horizontal vectors for nutrients; and as detrital sources of energy and habitat in the deep sea. The decline in great whale numbers, estimated to be at least 66% and perhaps as high as 90%, has likely altered the structure and function of the oceans, but recovery is possible and in many cases is already underway. Future changes in the structure and function of the world's oceans can be expected with the restoration of great whale populations.
Marine mammals have recently been documented as important facilitators of rapid and efficient nutrient recycling in coastal and offshore waters. Whales enhance phytoplankton nutrition by releasing ...fecal plumes near the surface after feeding and by migrating from highly productive, high-latitude feeding areas to low-latitude nutrient-poor calving areas. In this study, we measured NH4+ and PO43- release rates from the feces of North Atlantic right whales (Eubalaena glacialis), a highly endangered baleen whale. Samples for this species were primarily collected by locating aggregations of whales in surface-active groups (SAGs), which typically consist of a central female surrounded by males competing for sexual activity. When freshly collected feces were incubated in seawater, high initial rates of N release were generally observed, which decreased to near zero within 24 hours of sampling, a pattern that is consistent with the active role of gut microflora on fecal particles. We estimate that at least 10% of particulate N in whale feces becomes available as NH4+ within 24 hours of defecation. Phosphorous was also abundant in fecal samples: initial release rates of PO43- were higher than for NH4+, yielding low N/P nutrient ratios over the course of our experiments. The rate of PO43- release was thus more than sufficient to preclude the possibility that nitrogenous nutrients supplied by whales would lead to phytoplankton production limited by P availability. Phytoplankton growth experiments indicated that NH4+ released from whale feces enhance productivity, as would be expected, with no evidence that fecal metabolites suppress growth. Although North Atlantic right whales are currently rare (approximately 450 individuals), they once numbered about 14,000 and likely played a substantial role in recycling nutrients in areas where they gathered to feed and mate. Even though the NH4+ released from fresh whale fecal material is a small fraction of total whale fecal nitrogen, and recognizing the fact that the additional nitrogen released in whale urine would be difficult to measure in a field study, the results of this study support the idea that the distinctive isotopic signature of the released NH4+ could be used to provide a conservative estimate of the contribution of the whale pump to primary productivity in coastal regions where whales congregate.
The European green crab, Carcinus maenas, has a native distribution that extends from Norway to Mauritania. It has attracted attention because of its recent invasions of Australia, Tasmania, South ...Africa, Japan and both coasts of North America. To examine the population structure of this global invader in its native range, we analysed a 502‐base‐pair fragment of the mitochondrial cytochrome c oxidase I (COI) gene from 217 crabs collected in the North Atlantic and 13 specimens from the Mediterranean. A clear genetic break (11% sequence divergence) occurs between the Mediterranean and Atlantic, supporting the species‐level status of these two forms. Populations in the Faeroe Islands and Iceland were genetically distinct from continental populations (FST = 0.264–0.678), with Iceland represented by a single lineage also found in the Faeroes. This break is consistent with a deep‐water barrier to dispersal in green crabs. Although there are relatively high levels of gene flow along the Atlantic coast of Europe, slight population structure was found between the central North Sea and populations to the south. Analysis of variance, multidimensional scaling, and the distribution of private haplotypes support this break, located between Bremerhaven, Germany, and Hoek van Holland. Similar biogeographical and genetic associations for other species, such as benthic algae and freshwater eels, suggest that the marine fauna of Europe may be generally subdivided into the areas of Mediterranean, western Europe and northern Europe.
Whales before Whaling in the North Atlantic Roman, Joe; Palumbi, Stephen R.
Science (American Association for the Advancement of Science),
07/2003, Letnik:
301, Številka:
5632
Journal Article
Recenzirano
It is well known that hunting dramatically reduced all baleen whale populations, yet reliable estimates of former whale abundances are elusive. Based on coalescent models for mitochondrial DNA ...sequence variation, the genetic diversity of North Atlantic whales suggests population sizes of approximately 240,000 humpback, 360,000 fin, and 265,000 minke whales. Estimates for fin and humpback whales are far greater than those previously calculated for prewhaling populations and 6 to 20 times higher than present-day population estimates. Such discrepancies suggest the need for a quantitative reevaluation of historical whale populations and a fundamental revision in our conception of the natural state of the oceans.
Changes in the type and prevalence of human diseases have occurred during shifts in human social organization, for example, from hunting and gathering to agriculture and with urbanization during the ...Industrial Revolution. The recent emergence and reemergence of infectious diseases appears to be driven by globalization and ecological disruption. We propose that habitat destruction and biodiversity loss associated with biotic homogenization can increase the incidence and distribution of infectious diseases affecting humans. The clearest connection between biotic homogenization and infectious disease is the spread of nonindigenous vectors and pathogens. The loss of predators and hosts that dilute pathogen transmission can also increase the incidence of vectorborne illnesses. Other mechanisms include enhanced abiotic conditions for pathogens and vectors and higher host-pathogen encounter rates. Improved understanding of these causal mechanisms can inform decisionmaking on biodiversity conservation as an effective way to protect human health.
In a single well-mixed population, equally abundant neutral alleles are equally likely to persist. However, in spatially complex populations structured by an asymmetric dispersal mechanism, such as a ...coastal population where larvae are predominantly moved downstream by currents, the eventual frequency of neutral haplotypes will depend on their initial spatial location. In our study of the progression of two spatially separate, genetically distinct introductions of the European green crab (Carcinus maenas) along the coast of eastern North America, we captured this process in action. We documented the shift of the genetic cline in this species over 8 y, and here we detail how the upstream haplotypes are beginning to dominate the system. This quantification of an evolving genetic boundary in a coastal system demonstrates that novel genetic alleles or haplotypes that arise or are introduced into upstream retention zones (regions whose export of larvae is not balanced by import from elsewhere) will increase in frequency in the entire system. This phenomenon should be widespread when there is asymmetrical dispersal, in the oceans or on land, suggesting that the upstream edge of a species’ range can influence genetic diversity throughout its distribution. Efforts to protect the upstream edge of an asymmetrically dispersing species’ range are vital to conserving genetic diversity in the species.
Ecological speciation in tropical reef fishes Rocha, Luiz A; Robertson, D. Ross; Roman, Joe ...
Proceedings of the Royal Society. B, Biological sciences,
03/2005, Letnik:
272, Številka:
1563
Journal Article
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The high biodiversity in tropical seas provides a long-standing challenge to allopatric speciation models. Physical barriers are few in the ocean and larval dispersal is often extensive, a ...combination that should reduce opportunities for speciation. Yet coral reefs are among the most species-rich habitats in the world, indicating evolutionary processes beyond conventional allopatry. In a survey of mtDNA sequences of five congeneric west Atlantic reef fishes (wrasses, genus Halichoeres) with similar dispersal potential, we observed phylogeographical patterns that contradict expectations of geographical isolation, and instead indicate a role for ecological speciation. In Halichoeres bivittatus and the species pair Halichoeres radiatus/brasiliensis, we observed strong partitions (3.4% and 2.3% divergence, respectively) between adjacent and ecologically distinct habitats, but high genetic connectivity between similar habitats separated by thousands of kilometres. This habitat partitioning is maintained even at a local scale where H. bivittatus lineages are segregated between cold- and warm-water habitats in both Bermuda and Florida. The concordance of evolutionary partitions with habitat types, rather than conventional biogeographical barriers, indicates parapatric ecological speciation, in which adaptation to alternative environmental conditions in adjacent locations overwhelms the homogenizing effect of dispersal. This mechanism can explain the long-standing enigma of high biodiversity in coral reef faunas.
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