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Fresh water

Jun

24

2008

Shed a tear for a croc

Scientists discover widespread crocodile die-off at cane toad invasion front

crocodile tears... You wouldn’t think a frog could kill a crocodile, but that’s exactly what’s happening in Australia’s Northern Territory. The invasion by cane toads Bufo marinus – a highly toxic South American species – has given scientists a unique set of lessons on the destructive power evolution can unleash upon a non-adapted ecosystem. In the latest installment, Mike Letnic and colleagues at the University of Sydney report a mass die-off of freshwater crocodiles Crocodylus johnstoni at the invasion front. Ironically, the arid conditions that make a cane toad’s life difficult leads them to seek refuge in the few available water bodies, which also tend to be home to the hungry crocs. The decimation – populations were reduced by as much as 73 percent – could have widespread ecological consequences, writes Letnic in Biological Conservation. However, selection weaves its magic in many ways, and crocs will probably either learn not to eat cane toads or develop tolerance to their poison. Either way, the problem should be over in a snap! Source: Letnic M, Webb JK & Shine R (2008) Invasive cane toads (Bufo marinus) cause mass mortality of freshwater crocodiles (Crocodylus johnstoni) in tropical Australia. Biol. Conserv. DOI: 10.1016/j.biocon.2008.04.031

Image: © Stanko Mravljak

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Jun

17

2008

Woe be-toad them

Global analysis could help identify frog species at risk in time to act

going, going, gone A number-crunching study has thrown light on the mysterious global declines in hundreds of amphibian species. Imperial College London researcher Jon Bielby and colleagues collected data on habitat types, species ranges, disease prevalence and a host of other factors to produce a broad scale picture of the health of the world’s frog populations. Of particular note was the finding that aquatic, slowly reproducing species were most susceptible to the fatal Batrachochytrium dendrobatidis fungus. The results, published in Conservation Letters confirm earlier, more restricted findings and should help conservationists decide how to set priorities by enabling them to identify species at risk before it’s too late. Source: Bielby J, Cooper N, Cunningham AA, Garner TWJ & Purvis A (2008) Predicting susceptibility to future declines in the world’s frogs. Conservation Letters DOI: 10.1111/j.1755-263x.2008.00015.x

Image: © Sergey Korotkov

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May

14

2008

Our fault? Sure is

Comprehensive analysis links global ecological changes to human activity

melting glaciers are down to us Thirty five years’ worth of data covering hundreds of independent studies put beyond reasonable doubt the impact of human activity on the planet, according to a paper published today in Nature. NASA scientist Cynthia Rosenzweig and colleagues collated a diverse array of findings, allowing them to pin down the causes of physical (glacier shrinkage, warmer oceans and so on) and biological (early leaf burst, breeding seasons and algal blooms) changes that have been documented in recent decades. More than 95 percent of some 829 physical, and 90 percent of the nearly 29,000 biological changes they examined were in a direction consistent with a warming climate. If there’s any comfort to be drawn from the findings, it’s that climate warming is overwhelmingly the most important factor influencing changes in the natural world: habitat destruction, overfishing and pollution are mere trifles by comparison, so at least we know which problem to tackle first! Source: Rosenzweig C, Karoly D, Vicarelli M, Neofotis P, Wu Q, Casassa G, Menzel A, Root TL, Estrella N, Seguin B, Tryjanowski P, Liu C, Rawlins S& Imeson A (2008) Attributing physical and biological impacts to anthropogenic climate change. Nature DOI: 10.1038/nature06937

Image © Sburel

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Apr

9

2008

Something else in the water

Ghosts of residents past and present show up in pond water, DNA analysis reveals

pee-souper Pond water is a veritable soup of DNA, the ingredients of which are the shattered fragments of mucus, urine, faeces and remains of its past and present inhabitants. To Université Joseph Fourier researcher Gentile Ficetola and colleagues, that soup tells tales. The group carried out lab and field tests on samples of water that were known to have contained – or not – American bullfrogs Rana catesbeiana, an invasive species that causes declines in many native amphibian populations. Using molecular techniques designed to extract tiny stretches of DNA, the Grenoble-based team showed that it is possible to detect the presence or absence of a given species – great news for those wishing to track the progress of an invasion front. Writing in Biology Letters, they also suggest the ability to detect secretive, low-density populations should help other conservation projects too. Source: Ficetola GF, Miaud C, Pampanon F & Taberlet P (2008) Species detection using environmental DNA from water samples. Biology Letters DOI: 10.1098/rsbl.2008.0118

Image © Michael Mill

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Mar

25

2008

Waving goodbye to frogs

New study finds no evidence that climate change causes amphibian decline

A not so colorful future ahead? The alarming decline in global amphibian populations has been blamed on several factors including disease, climate change and habitat loss – not to mention various combinations of them. The precise causes are difficult to pin down, as often little is known about individual species, living as they do in inaccessible habitats. However, a study published this week in PLoS Biology makes a stab at analyzing what data we do have and rules out climate change as the driving force behind die-offs of harlequin frogs. Species in the Atelopus genus are a pretty endangered lot, but their scarcity owes more to the classical spread of the fungal infection chytridiomycosis than anything else. Southern Illinois University researcher Karen Lips and colleagues performed statistical tests on existing data to show that the most likely cause for amphibian declines in southern Central and northern South America is the repeated introduction of the causative pathogen Batrachochytrium dendrobatidis, most likely aboard a non-native species. The findings are good news in the sense that conservation workers in regions where the disease has yet to emerge can concentrate their efforts on preventing the import of animals that could carry it. Source: Lips KR, Diffendorfer J, Mendelson JR III & Sears MW (2008) Riding the wave: reconciling the roles of disease and climate change in amphibian declines. PLoS Biology DOI: 10.1371/journal.pbio.0060072

Image © Darren Green

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Mar

20

2008

Fish in a pickle

Overexploitation destabilizes population sizes, meta-analysis finds

Ooooh, but they look so tasty! The trouble with rare things – like many of the fish species we’ve driven to near extinction – is that their numbers become prone to extreme swings, rendering them vulnerable to hitting that final zero. That’s the message from a paper published this week in Nature. Dalhousie University biologist Coilín Minto and colleagues analyzed fisheries data from 147 wild populations of fish, comprising a total of 39 species. Historically overexploited species, such as North Sea herring, showed the highest levels of year-on-year variation in numbers. Understanding how variability is affected by population size could help conservationists estimate more accurately the time needed for overfished stocks to recover. Source: Minto C, Myers RA & Blanchard W (2008) Survival variability and population density in fish populations. Nature DOI: 10.1038/nature06605

Image © esemelwe

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Feb

5

2008

A pile of carp

Fish invasions around the world are linked to GDP, study finds

These hungry carp are in a moat, but others are invading rivers near you Human activities are the best predictor of the extent to which a freshwater ecosystem has been invaded by non-native fish, according to a study published today in PLoS Biology. Fabien Leprieur and colleagues studied data on 9968 fish species from 1055 river basis around the world, their aim being to unravel the mysteries of what makes some areas more prone to non-native invasions than others. Gross domestic product — which serves as a useful proxy for how much we’ve degraded our environment (the relationship being positive, of course) — closely mirrors the pattern of fish invasions, with six global hotspots identified: the Pacific coast of North And Central America, southern South America, western and southern Europe, Central Eurasia, South Africa and Madagascar, and southern Australia and New Zealand. Leprieur’s findings are actually good news, because they hint at ways to predict which areas might be most vulnerable to invasions in the future. As the CNRS-Université Paul Sabatier, Toulouse, researcher points out, developing countries with booming economies are the most likely to suffer the same ecological fate as the old empires. At least we can plan for it this time. Source: Leprieur F, Beauchard O, Blanchet S, Oberdorff T & Brosse S (2008) Fish invasions in the world’s river systems: when natural processes are blurred by human activities. PLoS Biology DOI: 10.1371/journal.pbio.0060028

Related story in Conservation magazine: Snakes On Planes

Image © Nick Atkinson

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Jan

30

2008

Time to wake up

Is the writing on the wall for Lake Victoria’s papyrus?

Going fishing... but for how long? “Darwin’s nightmare” continues at Lake Victoria, according to a report published in Wetlands Ecology and Management. Tanzania National Parks ecologist Yustina Andrew Kiwango and collaborator Eric Wolanski studied the effects the lake’s twin hydroelectric dams – Nalubaale and Kiira – are having on its ecosystem, and as you’d expect things don’t look good. The lack of coordination between the two dams mean that together they draw off too much water, exposing the vulnerable peat wetlands that fringe the lake. These wetlands are swathed in papyrus, which plays two vital ecological roles. It provides juvenile tilapia with safe refuge — until they’re big enough to be caught by the artisan fishermen whose livelihoods depend on them — and draws nutrients out of the severely eutrophicated water. Losing the papyrus would be disastrous for the lake’s inhabitants, including the million or so humans cramped around its shores. Sustainably harvesting it, however, could prove a neat way to clean its polluted waters, Kiwango and Wolanski suggest. Source: Kiwango YA & Wolanski E (2008) Papyrus wetlands, nutrients balance, fisheries collapse, food security, and Lake Victoria level decline in 2000–2006. Wetlands Ecology and Management DOI: 10.1007/s11273-007-9072-4

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Dec

16

2007

How frogs do the splits

Habitat fragmentation is more painful when larvae and adults have different needs

red eyed from doing the splits Having different habitat requirements at different life stages solves all sorts of life’s problems – such as avoiding predators and competition with one’s own species – but it can also create them, especially when humans are taken into the equation. Writing in Science this week, Brazilian scientists — led by Carlos Roberto Fonseca — illustrate the effects of what they call “habitat split”. Terrestrial amphibians whose larvae require aquatic habitat are now often forced to leave forest fragments to find suitable water bodies in which to reproduce, whereas in the past the two habitats graded into one another. The same goes for the metamorphosed juveniles, who face a dangerous trek back to the forest. The separation of habitat types, primarily due to anthropogenic disturbance, could be why those species with aquatic larvae are suffering worse population declines than those whose entire life cycle is completed in the same place. Source: Becker CG, Fonseca CR, Haddad CFB, Batista RF & Prado PI (2007) Habitat split and the global decline of amphibians. Science DOI: 10.1126/science.1149374

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Dec

13

2007

Out of the frying pan

Salmon farms pose a greater threat to wild stocks than the fisheries they replace

Doing more farm than good Long-held suspicions that fish farms act as disease reservoirs for wild populations are well founded, according to findings published this week in Science. University of Alberta mathematical biologist Marty Krkošek and colleagues show that outbreaks of salmon lice Lepeophtheirus salmonis among wild pink salmon Oncorhynchus gorbuscha populations — the direct result of infestations within the open-net aquaculture pens the juveniles must swim past on their migration to the sea — can bring virtual extinction in just four generations. The pressure wild stocks are placed under by the disease risk from fish farms is much greater than that caused by over-exploitative harvesting: the very factor that prompted aquaculture in the first place. It’s surely time for a re-think on fish farming. Source: Krkošek M, Ford JS, Morton A, Lele S, Myers RA & Lewis MA (2007) Declining wild salmon populations in relation to parasites from farm salmon. Science DOI: 10.1126/science.1148744

Related stories in Conservation magazine: Salmon Farms Create Deadly Clouds of Sea Lice | 10 Solutions to Save the Ocean

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