Invasive species

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

18

2008
 
 

There’s a catch, after all



Offsetting marine bycatch could do more harm than good, study finds

Trawling for solutionsCan fisheries bycatch impacts be offset by making efforts to protect afflicted species elsewhere? Not according to a study published today in PLoS ONE, which claims that the “compensatory mitigation for marine bycatch” approach is a non-starter. A baker’s dozen of international scientists, led by University of California Santa Cruz researcher Myra Finkelstein, found that diverting attention to other conservation measures – such as removing non-native predators from breeding grounds – could potentially spell disaster. The problem is that such an approach requires action for each individual bycatch species, thereby spreading conservation resources too thinly. The focus should remain on finding ways to reduce bycatch, Finkelstein’s team concludes. Source: Finkelstein M, Bakker V, Doak DF, Sullivan B, Lewison R, Satterthwaite WH, McIntyre PB, Wolf S, Priddel D, Arnold JM, Henry RW, Sievert P & Croxall J (2008) Evaluating the potential effectiveness of compensatory mitigation strategies for marine bycatch. PLoS ONE DOI: 10.1371/journal.pone.0002480

Image: © Thomas Shortell

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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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Jun

4

2008
 
 

Flight from an evolutionary trap



Island birds adjust nesting behaviour in response to alien predators

bellbird... not at the nest!Island life for many species was easy until we showed up with our various commensal hangers-on in tow. The arrival of rats, mice, cats, hedgehogs, stoats and even brush tail possums was a disaster for New Zealand’s birds, but a study published today in PLoS ONE shows it’s not all doom and gloom. University of Canterbury researcher Melanie Massaro and colleagues found that the endemic bellbird Anthornis melanura copes with perceived predator threat by altering its nesting behavior, making fewer, more lengthy incubating visits. Massaro interprets this as an adaptation to reduce activity around the nest in an effort to avoid being spotted by hungry predators. The behavioral shift has probably evolved within the last 700 or so years, because that’s when the first boatload of horrible mammals arrived. And the rats, mice, cats, hedgehogs, stoats and brush tail possums… Source: Massaro M, Starling-Windhof A, Briskie JV & Martin TE (2008) Introduced mammalian predators induce behavioural changes in parental care in an endemic New Zealand bird. PLoS ONE DOI: 10.1371/journal.pone.0002331

Image: © Dave Ozanne

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May

30

2008
 
 

Wise owls in germ warfare



Rare bird of prey threatened by malaria as competing species moves in

spotted owlSpotted owls Strix occidentalis are fighting a turf war with the increasingly invasive barred owl S varia; the two species competing for both food and limited nesting sites in old-growth forest. San Francisco State University researchers Heather Ishak, Ravinder Sehgal and colleagues now report in PLoS ONE how the spread of barred owls could also be increasing spotted owls’ risk of malaria and other blood-borne parasites. West coast barred owls were found to have significantly lower rates of infection than spotted owls inhabiting the same region. One possible explanation is that barred owls have better defenses – the Northern spotted owl population shows evidence of a recent genetic bottleneck, which could adversely affect their ability to mount an immune response. If true, barred owls could be acting as vectors for the parasites, passing them on to the increasingly threatened spotted owls, who promptly pass away. Source: Ishak HD, Dumbacher JP, Anderson NL, Keane JJ, Valkiūnas G, Haig SM, Tell LA & Sehgal RNM (2008) Blood parasites in owls with conservation implications for the spotted owl (Strix occidentalis). PLoS ONE DOI: 10.1371/journal.pone.0002304

Image: © Travis Manley

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May

29

2008
 
 

The need for weeds



Turkish flora threatened by intensive agriculture, almost unnoticed

weeds“Weeds” provide valuable food for many species, yet their conservation status has been largely overlooked. A study by Cengiz Türe and Harun Böcük at Anadolu University, Turkey, now illustrates the extent of the oversight. Writing in Weed Research, they report on a worryingly high number of species – some 112 all told – listed on the wrong end of the IUCN’s Red List scale of endangerment. The intensification of arable farming in Europe has coincided with a dramatic decline in native plant species, hampering subsequent efforts to restore lost biodiversity. Turkey is particularly rich in endemic plant taxa, but modern agricultural practices are designed to eliminate non-crop species. Türe and Böcük make the bizarre, yet perfectly logical, suggestion that farmers should nurture weeds. Quite how farmers will react is another story… Source: Türe C & Böcük H (2008) Investigation of threatened arable weeds and their conservation status in Turkey. Weed Research DOI: 10.1111/j.1365-3180.2008.00630.x

Image: © Lane Erickson

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May

24

2008
 
 

From cradle to grave



Tree pathogen brought to the US by keen gardeners, genetic study shows

dead treesSudden Oak Death, a straightforwardly named disease caused by the fungus Phytopthora ramorum, is gaining a worrying foothold in Pacific coastal forests. A study published recently in Molecular Ecology has traced the genetic origins of the pathogen in samples from dying trees at 14 Californian forests, together with samples taken from infected nursery plants in 12 states across the US. Leading an international team, Matteo Garbellotto, a University of California, Berkeley forestry pathlogist, has uncovered genetic evidence suggesting the fungus escaped into nearby forests from plant nurseries, where it affects many common species. If that’s not SOD’s law, nothing is. Source: Mascheretti S, Croucher PJP, Vettraino A, Prospero S & Garbelotto M (2008) Reconstruction of the Sudden Oak Death epidemic in California through microsatellite analysis of the pathogen Phytophthora ramorum. Molecular Ecology DOI: 10.1111/j.1365-294X.2008.03773.x

Image: © Ilbusca

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May

8

2008
 
 

The ghost at the feast



Loss of seed dispersers has far-reaching ecosystem impacts

one hungry tortoise

Rewilding is a controversial topic: when important native species have gone, is it OK to bring in exotic alternatives to perform an essential ecosystem role? This week in PLoS ONE Stanford University researcher Dennis Hansen and colleagues report on their experiments to help save the critically endangered tree Syzygium mamillatum, which grows only on the famously dodo-devoid oceanic island of Mauritius. Plants often depend on large herbivores to disperse their seeds: Hansen’s experiments addressed the Janzen-Connell effect, whereby seedling survivorship increases dramatically with dispersal distance by virtue of escaping the specialist herbivores that plague its poor mother. Using Aldabra tortoises Aldabrachelys gigantea as willing stand-ins for the two extinct Mauritanian giant tortoise species Cylindraspis triserrata and C. inepta, Hansen’s team recorded seedling survival in relation to distance from a mature tree and whether it had passed through the gut of one of those lucky tortoises. Despite relatively few gut-passed seeds surviving the ordeal, and coupled with a lower germination rate, the fact that they are likely to be deposited many meters from their parent tree could mean an overall benefit to tortoise seed predation. So, should tortoises be brought in to help save S. mamillatum? After all, they’re not exactly the most difficult animals to keep track of… Source: Hansen DM, Kaiser CN & Müller CB (2008) Seed dispersal and establishment of endangered plants on oceanic islands: the Janzen-Connell model, and the use of ecological analogues. PloS ONE DOI: 10.1371/journal.pone.0002111

Image © Dennis Hansen

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Apr

21

2008
 
 

Heavy metal rock(cress)



Pollution-gobbling weed gives up its genetic secret to success

heavy metal fanMost plants don’t like heavy metals such as zinc or cadmium, but Arabidopsis halleri will happily put down roots in the most contaminated soils. Reporting in Nature this week, a team of scientists led by Max Planck Institute biologist Ute Krämer – now at the University of Heidelberg – has unraveled the genetic basis underlying the little weed’s hardiness. Extra copies of the HMA4 (HEAVY METAL ATPASE 4) gene – are responsible: splicing it into the much more famous A. thaliana confers the same pollution-tolerating ability. Toxins are stored in the plant’s leaf cells, raising the possibility of developing plants that, when harvested, could drain contaminated soil of its poisonous elements. Even weeds have their strengths. Source: Hanikenne M, Talke IN, Haydon MJ, Lanz C, Nolte A, Motte P, Kroymann J, Weigel D & Krämer U (2008) Evolution of metal hyperaccumulation required cis-regulatory changes and triplication of HMA4. Nature DOI: 10.1038/nature06877

Image © Vasiliy Koval

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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-souperPond 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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