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Archive for October, 2010

This fortnight’s photo is of a plated millipede found in the Amazon rainforest by Alexander Torrenegra – I never even knew such things existed! According to David Attenborough’s Life in the Undergrowth, despite ‘milli’ meaning thousand, no millipede actually has 1,000 legs (more like 100-400 depending on species) and though they look ferocious in actual fact all millipedes are vegetarians, while centipedes are all carnivorous (i.e. eat meat). To tell the difference: centipedes have just one pair of legs per segment, and their legs are long and stick out from their body, while millipedes have two pairs per segment and their legs are shorter and more tucked underneath their body.

plated millepede (by Alex Torrenegra)

Further info on millipedes and centipedes:

Introduction to the Myriapoda

Orders of Millipedes

Millipedes, centipedes and pill bugs

Centipedes and millipedes -how to tell them apart

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The IUCN (International Union for Conservation of Nature) compiles a ‘Red List’ where each species is described and their status classified – from Critically Endangered (50%+ probability of extinction within 10 years or 3 generations (whichever is longer)) through Endangered (20% probability of extinction within 20yrs or 5 generations) and Vulnerable (probability of extinction of 10% within 100yrs) to Near Threatened and Least Concern (Fig 1).  A paper by Hoffmann et al (2010) published in Science today has analysed this data on 25,780 species of the world’s vertebrates (all mammals, birds, amphibians, and cartilaginous fish (sharks and rays), and most reptiles and bony fish) and found that one-fifth of Earth’s vertebrates are Threatened and that this figure is increasing yearly.

Figure 1. Red List categories (from IUCN website)

This is sad, but not wholly unexpected news – after all, although extinctions have always happened in our planet’s history, the current levels are 100-1000 times above pre-human rates (Pimm et al 1995) and it’s well known that a vast number of species are in trouble. Fortunately it’s not all bad news as Hoffman’s study also demonstrates that conservation does work and, although current levels of conservation are not enough to overcome the significant threats to animals, there have been successes with species being downgraded in recent time due to the efforts to conserve them. Hoffmann mentions that the Humpback Whale Megaptera novaeangliae has moved from Vulnerable to Least Concern since the commercial whaling ban in 1955, and Butchart et al (2006) calculated that between 1994 and 2004 at least 16 bird species were saved from extinction by the conservation programmes implemented for them; so a turn-around of the extinction trend is possible with concerted effort, political will, and public support.

With Hoffmann concluding that, on average, 52 species move one category closer to extinction each year, the time for us all to take action is now.

References and Further Info

Butchart SHM et al 2006. How many bird extinctions have we prevented? Oryx 40: 266-278

Hoffmann M et al 2010. The impact of conservation on the status of the World’s vertebrates. Science – published online 26 Oct 2010 (doi 10.1126/science.1194442)

IUCN Red Data category specifications

Pimm SL et al 1995. The future of biodiversity. Science 269: 347-350

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The estuarine, or saltwater, crocodile (Crocodylus porosus) is the largest reptile in the world at around 4.5m in length, and with individuals over 7m long spotted.  They are found in freshwater and estuarine habitats such as mangroves, rivers and estuaries, from India through SE Asia and along the island chains to Australia and the South-east Pacific. This wide distribution of one species, with considerable tracts of open ocean in-between populations that should be un-navigable to the crocodiles, set Australian scientists wondering why this saltwater barrier has not lead to the separated populations becoming different species (‘speciation’). Their recent work has demonstrated that estuarine crocodiles can travel vast distances across the oceans by using water currents to speed up their journeys, enabling the seemingly unconnected populations to intermingle and breed. Yes, surfing crocodiles exist!

The team captured and radio-tagged 27 estuarine crocodiles in Australia then followed their satellite-tracked movements and compared their travels to the water speed and direction in that section of the river or ocean at that time. Their data showed that the crocodiles had two distinct travel modes:

(1) a short-range movement of around 1-3km per day in one direction; this was their typical daily pattern and is likely to have been day-to-day travel within their home range, and

(2) a less frequent long-range movement of more than 25km per day in a constant direction (although for the analysis all journeys of over 10km per day were included as long-range).

Intriguingly, while short-distance travel did not follow a set tidal pattern, long journeys were always started within one hour of the tide changing direction, giving the crocodile 6-8 hours travelling with a ‘tailwind’ current helping them along (less than 4% of long-distance travel was against the current and this dramatically reduced their travel speed). When the tide turned against them again, the crocodiles would stop their journey and climb out or dive to the bottom of the river, resting while the tide was not in their favour.

Some of the crocodiles travelled incredible distances – one taking an ocean voyage that coincided with a strong sea current that helped him travel 590km in 25 days, entering a different river along the Australian coastline. Another moved more than 411km in 19 days, later returning all the way back to the exact location within the river where it was originally captured – so they are excellent navigators as well.

The researchers suggest that using the ocean and river currents for migratory travel allows the crocodiles to travel far further than they would be able to do under their own power as crocodiles, despite being aquatic, are not really well-built for swimming – either in speed or efficiency. Both males and females made these long-distance journeys but the purpose of the travel is not yet known although it may be to take advantage of fish migrations. These travels do mean, however, that throughout their 10,000sq km range the ocean does not act as a barrier to gene flow between the various populations of estuarine crocodiles, maintaining the population as one species despite the ocean barriers in between.

Reference

Campbell HA, Watts ME, Sullivan S, Read MA, Choukroun S, Irwin SR & Franklin CE. 2010. Estuarine crocodiles ride surface currents to facilitate long-distance travel. Journal of Animal Ecology 79: 955-964

Further info

Ecology Asia

Unique Australian animals

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An article in The Times today mentioned an unusual wildlife sighting by a British photographer. On the crowded beaches of South Georgia a young king penguin apparently decided it had had enough of being blocked from reaching its water hunting grounds by a female elephant seal. In a rather surprising David vs Goliath fit of pique, the 2kg penguin slapped the 650kg seal round the face with its flipper before presumably realising its chances didn’t look too promising and leaving to find a different route to the ocean.

OK, so it’s a massively anthropomorphic view of events, but the mental image of this unlikely encounter certainly gave me a bit of a giggle!

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Scorpion glowing in UV light

This fortnight’s animal photo is of a scorpion glowing under ultraviolet (UV) light by Marlin Harms.  

All scorpions glow in UV light due to a protein in their exoskeleton – and although scientists have plenty of ideas, they have no definitive answer as to why scorpions have this brilliant quirk.

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Today the BBC’s ‘Horizon’ programme focuses on the recently-finished census of our planet’s seas and oceans. Ten years of research by over 2,700 scientists collaborating from 80 countries around the globe, have lead to discoveries of more than 1,200 new species and the rediscovery of others thought to have gone extinct years ago – 50 million years ago in the case of one shrimp. New marine habitats and ecosystems were found, as well as a greater insight into the state of the world’s oceans and the effects on marine life today. I’ll certainly be tuning in to BBC2 at 9pm tonight – after all, you can’t go wrong when David Attenborough’s narrating!!

Further Info:

BBC Horizon Programme Info
Census of Marine Life: A decade of discovery – official website 
BBC News: “Marine census publication marks ‘decade of discovery’ “

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