http://www.youtube.com/watch?v=HBxn56l9WcUI’ve always liked frogs. I remember, when I was probably around 4 years old, being fascinated by the tadpoles that Dad brought home in a big jar from a farm pond. Mum explained about how they’d gradually metamorphose (thought I doubt she used that word!) & we watched their legs slowly grow & their tails disappear as they swam around in an old tub, until the point where they became frogs. Frogs are amphibians, along with newts & mud-puppies & axolotls and the legless caecilians (which look like a cross between an eel and an earthworm). As a group, frogs are much younger – in geological terms – than the others: most fossil frogs date back only about 50 million years, although the earliest-known frog-like creature, Triadobatrachus, lived about 250 mya in the early Triassic. Like almost all terrestrial amphibians, adult frogs use not only lungs for gas exchange, but also their skin and the membranous lining of their mouths. (Lungless salamanders are an exception – as the name suggests, they must rely on their skin alone, which is very convenient for those researching amphibian gas exchange.) This reliance on transcutaneous respiration has meant that amphibians are very susceptible to harm due to to chytrid fungus infection, which severely damages the skin and markedly reduces the animals’ ability to exchange O2 & CO2 with the atmosphere. In addition, using your skin as a gas exchange surface means that you have to keep it moist. This means that we’d expect to find frogs only in environments that are humid and damp year-round, & in general that’s the case. But there are always exceptions. and the desert rain frog is one of them. Breviceps macrops lives in one of the most inhospitable environments there is, a dry coastal strip of land in Namibia & South Africa. Hardly a place for a frog! It spends most of its time in burrows dug deep enough to reach into moist sand, but comes out at night when the air is cooler & more humid. While there’s very little actual rain, moisture-bearing sea fogs roll in from the ocean on at least 100 nights each year, bringing some water to the habitat as the fogs condense onto dunes & vegetation – enough to allow these little amphibians to survive. (There’s no actual tadpole stage in their life cycle; little froglets develop directly from eggs in the burrows.) And like other amphibians, they vocalise to advertise their presence. I hesitate to say the sound is a croak. In fact, it drove my dog to distraction when I played the following clip. I give you – ‘the sonorous war cry of a very angry frog‘.
Posts Tagged ecology
only the bones remained Feb 19No Comments
And at the end, there weren’t many of those.
One of the things we talk about in biology class is the importance of decomposers. Most students think in terms of bacteria when this topic’s raised, & maybe things like fungi. But there is more to the breakdown of a body than those microorganisms.
Think worms, for example. In his final bookA, Charles Darwin highlighted the significant role played by earthworms in breaking down ‘vegetable matter’ (eg leaves) to produce what he called ‘vegetable mould’.
And of course there are ants. While we may think of them as those irritating little critters that overrun the kitchen if they find a food source, & produce anthillsB of sand in the cracks in paving, they also act as what could be called macro-decomposers. As this video demonstrates:
B Those with small children (&/or a fondness for kinetic sand!) might enjoy this blog post about ants, kinetic sand, & learning opportunities :)
I do enjoy asapSCIENCE – their videos are quirky, entertaining, & informative, and can provide some great talking points for science classes. But for this one, add poignant to the adjectives.
sticky little lizard feet Oct 312 Comments
Evolutionary change can be fast – Peter and Rosemary Grant’s long-term & ongoing research project on the Galapagos finches documented rapid responses to environmental changes, for example, as does the recent work on cane toads in Australia. And biologists have known since Darwin’s time that competition can be a strong driver of evolutionary change. (Take Gause’s principle of competitive exclusion & its implications, for example.) A just-published paper about Anolis lizards demonstrates this very well (Stuart et al., 2014).
The way in which different species of this little lizard divvy up their habitat is used as an illustration of niche partitioning by many textbooks (you’ll find an example here). Stuart & his co-authors describe some elegant experimental work over a period of 15 years, on artificial islands in a Florida lagoon. Initially they used six of these islands, all of which were already colonised by the green native anole, Anolis carolinensis: three of the islands acted as controls, while brown anoles from Cuba (Anolis sagrei) were introduced to the other three. The two species are described as being “very similar in habitat use and ecology”, including diet, so they’d be expected to compete fairly strongly when brought together.
In other areas where the two species are found together, A.sagrei perches lower in trees than carolinensis, which left to itself would occupy most of the tree. So the prediction was that on islands where sagrei was introduced the same thing would happen: carolinensis would come to occupy a reduced niche, perching higher than the ‘invader’. And this is indeed what happened, in the space of three months:
by August 1995,on treatment islands already showed a significant perch height increase relative to controls, which was maintained through the study.
The researchers also predicted that this change in niche would be accompanied by a change in morphology; specifically, that there would be selection for larger, sticker feet in A.carolinensis, on the basis that
[toepad] area and lamella number (body-size corrected) correlate positively with perch height among anole species, and larger and better-developed toepads improve clinging ability, permitting anoles to better grasp unstable, narrow, and smooth arboreal perches.
This prediction was tested through observations on 11 islands, five with only the native species and six with both the native and the Cuban invader. Again, carolinensis perched significantly higher in trees on islands where sagrei was also present – and on those islands carolinensis anoles also had “larger toepads and more lamellae” than were found on the same species living without the competitor (an example of character displacement) – and this happened within about 20 lizard generations.
Careful analyses allowed the researchers to rule out other explanations:
In sum, alternative hypotheses of phenotypic plasticity, environmental heterogeneity, ecological sorting, nonrandom migration, and chance are not supported; our data suggest strongly that interactions with A. sagrei have led to evolution of adaptive toepad divergence in A. carolinensis.
So, just as with the cane toads, we are seeing rapid evolutionary change in real time.
Y.E.Stuart, T.S.Campbell, P.A.Hohenlohe, R.G.Reynolds, L.J.Revell & J.B.Losos (2014) Rapid evolution of a native species following invasion by a congener. Science 346 (6208): 463-466. doi: 10.1126/science.1257008
In their first-year microbiology lectures. our students hear about Helicobacter pylori, the bacterium associated with the development of gastric ulcers (a discovery that eventually saw Barry Marshall and Robin Warren receive the 2005 Nobel Prize for Physology or Medicine). The trouble is, I suspect that this is all that they hear about a story that is considerably more complex.
The story of H.pylori is just one part of Jessica Snyder Sach’s highly readable and thoroughly-referenced book, Good Germs, Bad Germs, which introduces the reader to the complexities of the human microbiome: the intricate microbial ecosystems found on and within the human body.
Good Germs, Bad Germs: health and survival in a bacterial world. Jessica Snyder Sachs (2008) pub. Hill & Wang. ISBN (e-book): 0809016427
The book begins with the harrowing tale of a young man’s death from a rampant MRSA infection, and of a child living with multiple life-threatening allergies.- two tales linked by the unforseen effects of our overuse of anitbiotics and our fixation on hygiene. (Actually, the former was not entirely unseen: in his 1945 Nobel Prize lecture, Alexander Fleming commented on the possibility that overuse of penicillin could see the development of resistant bacteria. Unfortunately, at the time this warning went unheeded – if indeed it was really heard – for example, penicillin was available as an over-the-counter drug in the US for almost a decade after its introduction in the 1950s, which would undoubtedly have contributed to the development of resistant strains of microbes.)
Then, after an introduction to the “war on germs” and scientists’ search for the ‘magic bullets’ that would (it was hoped) allow us to vanquish them forever, it’s on to “life on man”. Wherein I learned heaps, including the thought-provoking suggestion that there may be some adaptive significance to the fact that babies usually exit the vagina with their heads face backwards, towards the mother’s anus. For babies guts are colonised by bacteria very soon after birth – & they may receive an inoculum of faecal matter on the way out, to join the lactobacilli from the vagina itself and bifiobacteria from breast milk.
Incidentally, while all this may sound uncomfortably germy, there’s good evidence that the gut microflora are essential for survival. Lab animals reared in absolutely germ-free conditions, & whose guts never develop a microbial flora, fail to thrive. What’s more, Snyder Sachs comments that the combined acction of several species of intestinal bacteria “liberate as much as 30 percent of the calories a person absorbs from food, especially from high carbohydrate meals.”
Reading on – and it was really hard to put this book down! – you’ll hear about the hygiene hypothesis, which suggests that many of the inflammatory diseases that plague us today are an unforeseen result of lives that are too clean. Along with this is the ‘dirt vaccine’: the idea that vaccination with a mycoplasma may help to redirect the overzealous immune response underlying many allergies. Then it’s on to a deeper look at the development of antibiotic resistance and the rise of the superbugs, which has been exacerbated by the widespread use of antibiotics in farm animals. (Encouragingly, Snyder Sachs notes that banning this use, as in the Netherlands, can lead to a reduction in ‘superbug’ prevalence.) And finally, we look at our options for the future, and whether we can find a way to live in balance with our burgeoning microbial ecosystems.
And H.pylori? It turns out that this particular bacterium has been with us for at least 60,000 years, something that’s been used to track human migration patterns that began when Homo sapiens first left Africa. H.pylori colonises the stomach in the first few months of life, before gastric acid secretion really ramps up, and can actually affect that acid secretion, lowering the pH enough that Helicobacter can survive but most other species are killed. There is a plus to this: the lowered pH reduces the effects of acid reflux & the development of oesophageal cancer. But then, there’s those gastric ulcers – which apparently didn’t really become an issue until the 1830s, when this was mainly a disease of the upper classes, possibly linked to a decline in colonisation related to improved sanitation and the use of early antibiotic products. And gastric ulcers
remain virtually unknown in undeveloped regions of the world such as Africa, where most people become colonised in infancy. It may be that delaying or disrupting H.pylori colonisation with water sanitation or antibiotics has somehow altered the immunological ‘truce’ that this microbe forged with our immune systems over thousands, possibly millions, of years.
I like the full, more complex story; it’s so much more satisfying than the ‘helicobacter – bad’ version, and it’s a much better reflection of the dynamic relationship between humans and the microbes that call us home.
most excellent epiphytes Mar 28No Comments
A couple of years ago I spent a lovely afternoon in the huge domed glasshouses of Singapore's "Gardens on the Bay". The 'cloud forest' was my favourite – both for the concept & for the wonderful range of epiphytes on show there.
So you'll understand that I enjoyed reading about it again on this blog, written for the New Zealand Epiphyte Network. Anyone with even a passing interest in New Zealand's native plants should drop by the site. And maybe sign up to be part of their citizen science project while you're there?
Go on, you know you want to :)
Crocodiles (& their relatives, alligators) are generally viewed as top predators. They're 'ambush' hunters1, lunging up out of the water to snatch at their prey at the last moment.
But sometimes, they come off second-best. Check out this video on the National Geographic site, of a jaguar stalking, catching, & killing a caiman.
1 Having said that, when I was writing this post I came across the intriguing suggestion that some crocodilians use sticks to lure birds within lunging distance ie that they use tools. They've been observed doing this only during the birds' breeding season, when their feathery cousins2 are looking around for sticks to use in nest-building.
2 Taxonomically speaking, crocs and birds are both archosaurs. Early crocodilians – the pseudosuchians – were a predatory force to be reckoned with & it's possible that the pseudosuchians' demise, in the mass extinction that marked the end of the Triassic, was a factor that opened things up for the expansion of the dinosaur lineages.
Whales – competing with us for food, or helping to sustain the phytoplankton production on which most life in the oceans depends? The story and video at this link make a good case for the latter.
Then there's the wolves – their return to Yellowstone Park in the US has led to a whole cascade of environmental changes: changes that are very much for the better. Because the wolves keep the elk population moving around & to some degree under control in terms of population size, the vegetation has had a chance to recover from overgrazing. Forest regrowth along the riverbanks has stabilised those banks and contributed to an improvement in water quality. Beaver populations have bounced back & their activity has further altered the landscape in ways that have seen other species return or recover. The wolves have benefited the park's ecosystem in ways that nobody had predicted.
As for the final topic, well… I have occasionally been asked by much younger, smaller persons how hedgehogs "do it" (the answer being, "carefully!"). In fact Nanny Ogg had a hum'rous song on that very topic. Brian Switek discusses the issue as it might relate to stegasaurs in My Beloved Brontosaurus. And then there are porcupines, animals for whom it seems all coitus must be consensual (unlike ducks, bedbugs, & dolphins, to name just three). Because anything else really wouldn't work…
For the last few years our Centre for e-Learning has run WCeLfest – a day of presentations & discussion around using various technology tools to enhance teaching & learning. I always find these sessions very valuable as there are a lot of people doing some really interesting things in their classrooms, & there’s always something new to learn & try out myself. I offered to run a session myself this year, which is what I’m going to talk about here, but I was also asked to be on the panel for a discussion around what universities might look like in the future, and that was heaps of fun too.
My WCeLfest session was billed as a workshop, so to kick things off I explained that the attendees were going to experience being in what is effectively a ‘flipped’ class, getting the students’ perspective, and why I’d developed the class in the way that I had. (I added that feedback on that experience was welcome!) I think there was one biologist in the room, so for most of those present the things they’d be doing would be just as novel as they will be for many of my students.
First, my ‘class’ got some extra background information. If previous years are anything to go by, then about a third of the students in my first-year biology class won’t have studied the year 12 Achievement Standards related to plants1. This always poses something of a challenge as we run the ‘plants’ part of the paper first, flowers & fruit being readily available in late summer (& I doubt things would be different if we taught it later in the paper). So I’m always thinking about improved ways to bridge students into the subject without boring those who have a reasonable background in things botanical.
The first lecture looks at what plants are & why they’re important, both ecologically & in terms of human history. For the last 2-3 years I’ve used an active learning exercise, putting up a graph on changes in atmospheric oxygen over the 4.5 billion years of Earth’s existence and asking the students to interpret and discuss the information it shows. But, using the same graph with a different group of learners, I realised that some of my students might not even know what photosynthesis entails, which would rather destroy the purpose of that part of the class.
So this year, they’re getting homework for the night before: this video. And at WCeLfest, we watched it together.
As you’ll have seen, there are a few, very basic, questions at the end of the video, but we stopped the video before reaching the quiz & instead briefly discussed and answered each question in groups, plus there were some additional queries, which was great. The original set of questions reinforce the basic concepts & give those students who were unfamiliar with them a bit of confidence that they’re prepared for the next step.
Now, for my ‘real’ class I’ll be showing an additional, more complex video, but for this shorter session we just moved on to the data interpretation.
Again, I explained the rationale behind this part of the session. I’d decided to do this exercise with my first-year students for a couple of reasons: firstly, to break up the class and get them actively engaged in the learning process; and secondly, to give practice in the process skills needed to interpret information provided in graphical form. The question they needed to address, using their knowledge from the video and the data in the graph, was: without plants, life as we know it wouldn’t have evolved in the first place. Why not?
As I do in my normal classes, while the class split into groups to come up with an answer, I circulated between those groups2 in order to hear what was going on & field any additional questions. “What was the atmosphere made of before photosynthesis began?” was one, which led to a brief consideration of how the Earth formed. And I needed to explain oxidised/oxidation, as well. This was a really valuable process for me as it’s highlighted a couple of areas where I need to do a little more background work with my first-years.
A quick summary of the class discussion: the ‘oxidation’ part is important because that’s how we know when oxygen generation began – iron-rich rocks began to rust. It wasn’t until the exposed rocks had been oxidised and the ocean had become saturated with oxygen, that oxygen began to be released into the atmosphere, as evidenced by more oxidised rock. As O2 accumulated in the atmosphere, the ozone layer formed, offering protection from the sun’s UV radiation & allowing living things to move onto the land.
And we finished with a quick look at the ‘design-an-organism’ class that I’ve previously blogged about.
The feedback was very positive, with several people saying that they could see how they might use the flipped classroom technique in their own teaching. It was also lovely to hear someone say that they’d got a bit worried when they realised we’d be talking science, but that they’d really enjoyed the experience and learned some new things along the way. And I’d learned ways to improve the exercise, so the enjoyment & learning were mutual
1 These are AS91155 Demonstrate understanding of adaptation of plants or animals to their way of life, and AS91156 Demonstrate understanding of life processes at the cellular level. You’ll find them here on the NZQA website.
2 In my ideal class3 there’d be an ‘aisle’ between every 2 rows of seating, to allow teachers/facilitators to move more freely among the students.
3 I can dream, can’t I?
Any discussion around water fluoridation will bring up quite a number of concerns, but increasingly – on-line anyway – conspiracy theories also come to the fore. I think the latter need to be addressed, but not at the risk of ignoring or failing to address the former. Worrying about the nature of what’s in our water supply, & its possible health impacts, is both natural and understandable – especially given that there’s so much information (of varying quality) out there, & sometimes the people you hear are the ones who shout the loudest. Which is not necessarily the same as those who have the strongest case. As I’ve said before, that’s what drew me into this debate in the first place: the way science has been misrepresented by those wishing to bolster a case against water fluoridation.
My own personal opinion is that the issue should really be addressed in terms of ethics and societal responsibilities, and it’s sad to see that attempts to have this discussion (on-line, anyway) are so often diverted yet again to a you-said-we-said about the science. I do wonder what this does for those ‘lurkers’ who may be following the to-&-fro – & I see I’m in good company in that respect.
Actually, it must get really confusing, for reading some of the on-line comments about fluoridation, I’m still surprised at how often conspiracy theories crop up. (I shouldn’t be, I suppose, but I am.) The pharma shill gambit is quite common: the idea that people holding views that differ from the speaker’s, must be being paid to hold them. In the case of fluoridation, I think people need to do their sums. In Hamilton, the cost of buying HFA to add to municipal water supplies was around $48,000 each year. That’s not a lot to go around all the local scientists, dentists, healthcare workers, and humble bloggers accused of being bought by big business by anti-fluoride activists… (This is something also addressed in Harriet Hall’s excellent post over at Science-Based Medicine. Bob Park’s ‘seven signs of bogus science’ is also relevant.)
One might well ask why our opinions need to be bought. I’ve asked this more than once. One commenter told me darkly that all would be revealed in due course. (I’m still waiting.) The usual reason is some unspecified conspiracy by big business and government agencies, although again, it’s not at all clear what they’re getting out of it.
Unless, of course, the population is being dumbed down to blindly accept all sorts of attacks on our liberties. This seems to be linked to the fact that the tranquiliser prozac contains fluoride, & to the ‘Hitler/the Nazis used it’ meme – a claim, Ken Perrott notes, that was trotted out in the Hamilton City Council’s ‘tribunal’ on water fluoridation.. Unfortunately for this one, Hitler didn’t, & prozac contains much higher amounts of fluoride than town supply water would. (There have also been attempts to link fluoride with the nerve gas sarin; a sort of slur by association. Yes, there’s a fluorine atom in there. There’s also carbon, hydrogen, oxygen, & phosphorus: the formula for sarin is C4H10FO2P.)
Or perhaps it’s all a plot to reduce the world’s population! This one seems to be based on the observation that at high concentrations fluoride does affect the endocrine system: levels much higher than those found in town supply water. This means that fluoride’s hardly an effective tool for population control if no-one’s adding it at the requisite concentration. (China, with its one-child policy, doesn’t fluoridate at all, at least in part because in some regions water fluoride concentrations are already elevated.) This ‘theory’ is further based on major misunderstandings of work by John Holdren, who with Paul & Anne Erlich discussed the burgeoning human population & various actions that might curb its growth in the book Ecoscience: Population, Resources, Environment. At one point they noted that a population of around 1 billion might be optimal in ecological terms (we’re already at 7 billion & counting). This has been (mis)interpreted as advocacy for deliberately reducing the population to this level and, because of the known impact of high levels of fluoride on endocrine functioning, then gasp! fluoride must be part of the plot.
Ultimately, all these conspiracy theories require that an awful lot of people should be corrupt. Tens, perhaps hundreds of thousands of scientists, falsifying their research, hiding the bits that don’t fit the story, suborning new researchers as they come along. They’d have to be in every research institution in the world. It would cost ridiculously large amounts of money (money, in the case of fluoridation of water, that simply isn’t there.) Governments and the media would have to be in on it as well. And that’s not possible. Someone, somewhere, would provide evidence of what was going on.
And indeed, the various conspiracies can’t be all that good, if various brave mavericks are able to a) recognise what’s going on and b) spread their findings (on the internet & elsewhere) without the men in black turning up & carrying them away.