Habitat

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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Jun

12

2008
 
 

Jets and sharks



Large predatory sharks are about to leave the Mediterranean

Do we still need a bigger boat?The Mediterranean sea is pretty much a big pond, so many European holiday makers would probably breathe a quiet sigh of relief to read in Conservation Biology that the number of big, fierce sharks swimming among them has plummeted in recent years. An international team, led by Dalhousie University’s Francesco Ferretti, fearlessly waded through public and private archives, searching for evidence of population trends among the twenty largest species known to prowl the Med. In the five species for which there were sufficient data – a paucity all too telling of our scientific neglect of these top oceanic predators – precipitous declines were clear. Hammerhead sharks Sphyrna spp. were worst hit: none have been seen in coastal waters since 1963, and no records of the sharks anywhere in the Mediterranean exist after 1995. Nervous bathers should note that only the thresher shark Alopias vulpinus has been recorded in coastal waters in recent years. If looks like it is safe to be in the water after all. Just as long as you’re not a shark. Source: Ferretti F, Myers RA, Serena F & Lotze HK (2008) Loss of large predatory sharks from the Mediterranean Sea. Cons. Biol. DOI: 10.1111/j.1523-1739.2008.00938.x

Image: © Bart Coenders

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Jun

11

2008
 
 

Tree of death



Evolutionary phylogeny of British birds flags up species at future risk

scary, isn't it?British bird species with declining populations are more closely related than expected, according to findings published today in the Proceedings of the Royal Society. The study’s author, Imperial College’s Gavin Thomas, suggests the link might help identify those species most at risk of extinction. The evolutionary tree, which Thomas constructed by comparing mitochondrial gene sequences of Britain’s resident birds, shows that red listed species are clustered together. The reason is simple: closely related species tend to share physical traits, so what’s bad for one is bad for another. However, the findings also suggest a way for conservationists to identify vulnerable species – by looking at those currently in decline it should be possible to work out which ones are next in line to fall off the perch. Source: Thomas G (2008) Phylogenetic distributions of British birds of conservation concern. Proc. Roy. Soc. Lond. B DOI: 10.1098/rspb.2008.0549

Image: © Graham McKenzie-Smith

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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

15

2008
 
 

Fly in flowers



Neotropical insect biodiversity greater than previously thought

Still think we're all just bugs?DNA barcoding has once again revealed a wealth of unknown species, this time in neotropical insects. Writing in this week’s Science, a team of researchers led by Cornell College’s Marty Condon tell of their study of a group of fruit flies – the Blepharoneura – whose larvae munch their way unseen through species of plants in the particularly tasty Curcurbitaceae family, a group that includes cucumbers, pumpkins and melons. From a Central and South American study area measuring some 5500 km by 3000 km, they caught and reared 2857 flies from 24 host plant species, then ground them up and extracted their DNA for analysis. What they found was a remarkable degree of species diversity: 52 species of flies, many of which looked pretty much identical. However, this abundance of biodiversity was linked to a high level of specialization, with many species feeding not only a single plant species, but often just one sex or structure. With many species found at a lone site, the findings are likely to complicate conservation work, although welcome light has been thrown on the interaction between geography and diversity in this evolutionary epicenter. Source: Condon MA, Scheffer SJ, Lewis ML & Swensen SM (2008) Hidden neotropical diversity: greater than the sum of its parts. Science DOI: 10.1126/science.1155832

Image © Marty Condon

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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 usThirty 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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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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May

5

2008
 
 

Prickly heat



Tropical biodiversity could be most vulnerable to small climate shifts, study warns

better start preying...It’s often touted that the greatest climate change effects will be at higher latitudes – hence all those pictures of stranded polar bears that we’re now worryingly familiar with. However, a study published today in PNAS argues that while the thermal shift at the tropics is likely to be relatively small, many species there are less tolerant to even the tiniest deviation from the more or less uniform temperatures they usually experience. Together with colleagues, Curtis Deutsch and Joshua Tewksbury – climate change scientists at UCLA and Washington universities respectively – assessed the impact of predicted climate change on land-based insects (a particularly speciose and temperature-sensitive group). In the steamy tropics, many bugs live life close to their thermal optimum, meaning increased average temperature could easily spell doom. At higher latitudes survival is a constant battle against the cold, so turning up the heat could be a good thing, at least for creepy crawlies. Unfortunately, the tropics are where it’s at for insect biodiversity… Source: Deutsch CA, Tewksbury JJ, Huey RB, Sheldon KS, Ghalambor CK, Haak DC & Martin PR (2008) Impacts of climate warming on terrestrial ectotherms across latitude. Proceedings of the National Academy of Sciences USA DOI: 10.1073/pnas.0709472105

Image © Chanyut Sribua-rawd

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