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Entries in diversity (17)

Thursday
Apr082010

What's a Manta do?

ResearchBlogging.org

Manta rays (Manta birostris) surely vie for the title most spectacular among the large animals in the ocean. Not only do they grow to enormous sizes, but they are placid, graceful, and generally unafraid of humans, which means we can get close to them in the water and really appreciate how incredible they are, up nice and personal. I always thought that mantas were a one-of-a-kind species - the only member of its genus - like humans, whale sharks, koala bears or killer whales. Luckily, Andrea Marshall is not like me. She and her colleagues took a closer look at the body features, colours and patterns on lots of mantas from all around the world and they concluded that there are at least two, and possibly even three, manta ray species. They’re not the first people to propose this, so technically what they have done is “resurrect” the name Manta alfredi, the Prince Alfred manta, which had been made a synonym of Manta birostris some time ago (read the paper for the full sordid taxonomic history of mantas). The differences between the two species are subtle and mostly to do with the colour of the lips, wings and shoulders, the spots on the belly and the presence or absence of a bony mass near the base of the tail, but nonetheless they probably reflect real differences between the animals and, under the current definition of “species”, they probably cannot successfully interbreed. The third potential species they call “Manta sp. cf. birostris” which is taxonomist shorthand for “as-yet undescribed manta species sort-of like M. birostris”.

If you have ever been to the Georgia Aquarium, you may have seen one or both of their mantas in the Ocean Voyager exhibit. If you look closely at these and compare them to the Marshall paper, you’ll see that one (called “Nandi”) is Manta alfredi and the other (“Tallulah”) is more like Manta sp. cf. birostris. Its slightly ironic that in light of this new paper, neither of them is the “actual” or original “manta ray”.  Of course, they are both still spectacular animals!

Who cares about all this anyway? What does it matter if there’s one or three or a dozen manta species? As it happens, it matters a great deal! Taxonomy underlies everything else in biology. What good is a population estimate, for example, if that estimate confuses two species? We would grossly overestimate both, potentially leading to overexploitation. More generally, how can we understand migration patterns, breeding grounds, diets, ecological roles or behaviour, if we are constantly confounded? These are, of course, somewhat self-centered concerns about the quality of our science or management decisions; a species count is about the most fundamental measure of nature that we have, and those sorts of diversity stats are predicated on a decent taxonomy. Consider this: how much of a ginormous “oops!” would it be if we were to protect a species in one area of ocean, only to learn that the animal in the area we didn’t protect was actually a different species?   Perhaps a more important reason it matters is for the mantas themselves and the rest of their ecosystem.  Each species has an intrinsic right to exist and a value to the ecosystem its part of. 

I just love the idea that even for familiar, charismatic mega-animals like mantas, if we look a little closer, nature shows us hidden diversity: surprising, unexpected, and exciting.

Marhsall, Andrea D., Compagno, Leonard J.V., & Bennett, Michael B. (2009). Redescription of the genus Manta with resurrection of Manta alfredi (Krefft, 1868) (Chondrichthyes; Myliobatoidei; Mobulidae) Zootaxa, 2301, 1-28

Tuesday
Apr062010

Explosive radiation (in) rocks!

ResearchBlogging.org

Much like internal waves, I always loved the idea of explosive radiation.  Not the nasty, pernicious Chernobyl kind; I mean the rapid evolution of a whole bunch of species from a common ancestor, over a relatively short period of time.   There's a few textbook examples of explosive radiations, but none so well-worn (possibly even hackneyed) as that of the cichlid fishes in the rift lakes of eastern Africa.  The startling diversity of these little fishes in lakes Tanganyika, Malawi and Victoria has kept evolutionary biologists busy (and Africans fed) for years.  See for example, the paper by Elmer and colleagues cited below, which points out that due to the drying-out of Lake Victoria 15-18,000 years ago, either all the cichlids there evolved since then based on stock that re-colonised from Lake Tanganyika, or they sought refuge elsewhere during the dry spell and returned when the lake refilled.

Cichlids are nice and all, but if you look around, you start to see radiations all over the place.  Turtles, bivalves and salamanders in the US south-east; tetras in the Amazon, eleotrid gudgeons in Australia, and gobies on coral reefs are just a handful of aquatic examples that are still with us, but there are many others in the fossil record too (hence my title) including trilobites and ammonoids and lots more.  Presumably these are the sorts of patterns that led Stephen Jay Gould and Niles Eldredge to develop the concept of punctuated equilibrium back in the 70's: theirs was the idea that evolution proceeds not gradually, but in fits and starts, in response to dramatic environmental changes and chance events.  The way I see this idea, most of the species we observe around us are the dregs of explosive radiations past, whittled away by extinctions to just the most successful few, either gradually or equally punctuated.  Cases like the rift-lake cichlids are just ones in which relatively few have gone extinct yet (but see the effects of the introduced Nile perch!)

All of this was just a preamble for what I really wanted to post about, which was about a radiation I only heard about recently.  Late last year I was at a scientific exchange  of US and Russian fish health researchers organised by the National Fish Health Research Laboratories and sponsored by the Living Oceans Foundation, at which one of the Russian speakers  Maxim Timofeev introduced us the radiation of several groups, including amphipods, in Russia.  Amphipods are (usually) tiny shrimp-like animals that live on the bottom or among dense plants or algae; read more about them in the Väinölä paper cited below.  Well, in Siberia's Lake Baikal, the worlds oldest, largest and deepest freshwater lake, they underwent a remarkable radiation, to produce over 300 species (a third of the worlds entire fauna), including spectacular beasts such as the fish predator (!) shown here. I mean, HOW AWESOME IS THAT THING?  Freaks me almost as much as giant wetas used to do, when I was younger (if you don't dig on bugs, I recommend not clicking that link...).  Anyway, I had no idea these things existed until Maxim gave his talk.  Don't you just love discovering new critters you never knew about before?  And not just one, but hundreds.

(Check out this link about Baikal fauna too; the language is just terrific.  Try this turn of phrase on for size: "When it comes to tenderness and gustatory qualities of meat, the omul knows no rivals")

Elmer, K., Reggio, C., Wirth, T., Verheyen, E., Salzburger, W., & Meyer, A. (2009). Pleistocene desiccation in East Africa bottlenecked but did not extirpate the adaptive radiation of Lake Victoria haplochromine cichlid fishes Proceedings of the National Academy of Sciences, 106 (32), 13404-13409 DOI: 10.1073/pnas.0902299106

Väinölä, R., Witt, J., Grabowski, M., Bradbury, J., Jazdzewski, K., & Sket, B. (2007). Global diversity of amphipods (Amphipoda; Crustacea) in freshwater Hydrobiologia, 595 (1), 241-255 DOI: 10.1007/s10750-007-9020-6

Wednesday
Mar312010

When can we stop sampling and have a beer?

This post was chosen as an Editor's Selection for ResearchBlogging.orgResearchBlogging.org

Yesterday I got a very kind email from a fellow scientist, Eric Seabloom at Oregon State University, letting me know that a paper I wrote with my PhD advisor Tom Cribb (University of Queensland) a few years ago had influenced a recent publication of his.  My paper was about one of those patterns in nature that just seem to be universal.  They're called species accumulation curves and, at the heart of it, they represent the "law of diminishing returns"* as it applies to sampling animals in nature. Basically, they show that when you first start looking for animals - maybe in a net, a trap or a quadrat - pretty much everything you find is new to you, but as you go along, you find fewer and fewer new species, until eventually you don't find any more new species.  Simple, maybe even obvious, right?  Well it turns out that that simple observation has embedded within it all sorts of useful information about the way animal diversity is spread around, and even about how animals interact with each other in nature.  Consider the figure on the above right, which represents two sets of 5 samples (the tall boxes), containing different animal species (the smaller coloured boxes).  The first thing to note is that both set (a) and set (b) consist of 5 samples, and both have a total diversity of 5 species (i.e. 5 different colours).  In set (a), all the diversity is present in every sample, but in set (b) there's only one species per sample, so you have to look at all 5 samples before you find all 5 species.  If you were to plot a graph of these findings, you'd get very different species accumulation curves; they would both end at 5 species, but they would be shaped differently.  They'd look much like what you see below:

 Set (a) would be more like the curve on the left (in fact, it would be a perfect right angle), while set (b) would be more like the curve on the right (in fact, it would be a straight diagonal line).  You can see some other properties on the two types of curves above also, for the more ecologically inclined, but the gist is, the shape of the curves means something about the communities they describe.

Tom and I wrote our paper after many nights in the field spent dissecting coral reef fishes to recover new species of parasitic worms - a time consuming and sometimes tedious process (sometimes thrilling too, depending on what you do or don't find).  We were often motivated by another far more important factor too - when can we stop all this bloody sampling so that we can go and have a beer on the beach?!?   Species accumulation curves therefore have a very practical aspect to them - they tell you when its OK to stop sampling because you've either sampled all the available species, OR, you've sampled enough to extrapolate a good estimate of how many species there might be.

Back to Eric Seabloom.  He and his colleagues wrote a paper about the diversity of aphid-borne viruses infecting grasses of the US Pacific northwest and Canada.  While the environment that they sampled was about as far away as its possible to be from the coral reefs that Tom and I looked at, the patterns of saturated and unsaturated communities they observed were the same. I get a huge buzz out of that, and that out of the morass of published science out there, Dr. Seabloom found a scientific kindred spirit who had had the same thoughts and ideas about nature, however different the specific areas of study.  While Tom and I sipped beers on the beach and watched the sunset over the reef, I wonder if Eric and his colleagues blew the froth off a few while they watched the wind waves spread across the grasslands.  There's something so unifying about science; it can give you common ground with someone you never would have otherwise known, and that's just one reason why I love it so much.

*The tendency for a continuing application of effort or skill toward a particular project or goal to decline in effectiveness after a certain level of result has been achieved. Answers.com 

DOVE, A., & CRIBB, T. (2006). Species accumulation curves and their applications in parasite ecology Trends in Parasitology, 22 (12), 568-574 DOI: 10.1016/j.pt.2006.09.008

ERIC W. SEABLOOM, ELIZABETH T. BORER, CHARLES E. MITCHELL, & ALISON G. POWER (2010). Viral diversity and prevalence gradients in North American Pacific Coast grasslands Ecology, 91 (3), 721-732 (doi:10.1890/08-2170.1)

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