Showing posts with label bdelloid rotifer. Show all posts
Showing posts with label bdelloid rotifer. Show all posts

Wednesday 15 February 2017

Backyard bonanza: collating stats for a predator-free future

I've previously discussed how a lack of understanding of statistics can cause consumers to make poor choices, so it would seem that increasing the public's understanding of them can only be a good thing. Therefore, along the lines of New Zealand's annual garden bird survey, I decided to do a bit of citizen science. My aim was to record the highest number of each fauna species seen at one time, either actually in my garden or seen from my garden. The time frame was a calendar year, so as to take into account seasonal migrations and food availability. As an aside, it might have been easier to count flora (after all, it doesn't move very fast) but with Auckland being the weediest city in the world and my floral knowledge much weaker than my recognition of fauna, I opted for the easier option of any animal that I could see without using a microscope.

A meta-analysis released this month states that almost twenty-five percent of birds on the IUCN Red List of Threatened Species are being affected by climate change. In addition, with last years' announcement to make New Zealand predator-free by 2050, such surveys might be useful for locating concentrations of introduced pest species. In a way, I'm providing a guide that anyone can follow with the minimum of effort (hint, hint). So here are my results, followed by some more information:


Class/species Native/self-introduced Number seen
Insecta
Ant (unknown species) Yes Numerous
Asian paper wasp No 3
Black field cricket Yes 4
Bumble bee No 1
Bush cockroach Yes 14
Cabbage tree moth Yes 7
Cabbage white butterfly No 2
Cicada Yes 2
Click beetle Yes 2
Common bag moth Yes 1
Crane fly Yes 1
European earwig No 1
Ground beetle Yes 2
Honey bee No 1
Housefly No 7
Ladybird Yes 2
Monarch butterfly Yes 17
Shield bug Yes 3
South African praying mantis No 22
Tree weta Yes 18
Arachnida
Bird dropping spider Yes 1
Black cobweb spider Yes 1
Black house spider Yes 1
Daddy long-legs Yes 3
Jumping spider Yes 1
Nurseryweb spider Yes 1
Slater spider Yes 1
White tail spider No 1
Annelida
Earthworm No 5
Tiger worm No Numerous
Hexapoda
Springtail No Numerous
Chilopoda
Centipede Yes 3
Mollusca
Common garden snail No 9
Reptilia
Rainbow skink No 2
Aves
Australasian hawk Yes 1
Blackbird No 2
Black headed gull Yes 3
Eastern rosella No 4
Fantail Yes 2
Goldfinch No 3
Greenfinch No 2
House sparrow No 14
Myna bird No 4
Rock pigeon No 5
Silvereye Yes 7
Song thrush No 1
Spotted dove No 1
Starling No 4
Tui Yes 1
Mammalia
Cat No 2
Chicken No 1
Dog No 1
Hedgehog No 1
Mouse No 1
Rabbit No 1


The first thing that seems obvious is just how many non-native species I observed, some deliberate introductions whilst others accidentally brought to New Zealand, but all within the past two centuries.

Now for some interesting comments about how statistics can be (mis)interpreted:

1) The method I chose to order the table by could affect how easy it is to find key points of interest. Alphabetical order is familiar but is simply a well-known form of cataloging. Therefore it can be seen as a neutral form of presentation, not emphasising any particular pattern of the results. Had I ordered by native/non-native, it might have become more apparent how many of the latter bird species there are. If I had ordered all species in one list by this method, rather than in separate classes, the pattern would have been obscured again. So simply by selecting a certain order, results can appear to support a certain notion.

2) How useful is this data if it lacks supporting information? By this, I mean factors that might affect the count: Is it a common or garden (yes, that's a pun) location or an highly unusual one? Is the locale urban or rural? What are the surroundings? How big is the garden and how much vegetation is there? Is the vegetation primarily native or non-native? I could go on like for this ages, but clearly to get a more sophisticated understanding of the causes behind the figures, this information is necessary. Even then, two locations that are almost identical to a casual observer might appear profoundly different from the vantage point of say, earthworms. I will admit to (a) having built 2 weta motels and a bug motel; and (b) feeding silvereyes in winter; and (c) having made a tui sugar water feeder that has been totally ignored. Go figure!

3) Are there any other obvious factors that could affect wildlife? How managed is the location? Are chemicals such as weedkiller used or is the garden solely organic? Again, this can have a massive effect on wildlife, such as pesticides that remove insects at the base of food webs. On the one hand, if mine is an organic garden surrounding by neighbours who spray their foliage, then it could be an island of suitability in a comparatively barren terrain. But alternatively, if most of the neighbourhood isn't fauna-friendly, how likely would my garden get visited even on the off-chance by animals that can't live in the wider area?

4) Of course there's also contingency within natural selection. For example, quite by chance some species can survive on foods not native to their ecosystem. Although stick insect numbers in New Zealand were drastically reduced thanks to DDT, gardens don't need to contain their native food plants in order to support them. In the south-west of England, three species of accidentally-introduced New Zealand stick insect have flourished for decades on the likes of roses! Also, unusual events can affect populations: in this case, the two rainbow skinks appeared several months' after laying some ready lawn so I can only assume their eggs arrived with the turf, the previous five years having seen no skinks whatsoever.

5) When it comes to surveys, timing is also important. As you might expect, most of my observations took place during the day, with the only nocturnal ventures being on clear nights when using my telescope. The moths and hedgehogs were mostly seen at night, whilst had I included birds I could hear as well as see, then a morepork would have been added to the list. Again a simple prejudice, in this case sight over sound, has skewed the statistics. The large number of mantises were not adults but nymphs all hatching from a single ootheca. As for the monarch butterflies, they were a combination of caterpillars, chrysalis and adults, having appeared in much greater numbers this year than previous, despite no additional swan plants (their only food). Interesting, a clump of twenty or so mature swan plants a few streets away hasn't yielded any monarchs in any of the three stages. Presumably, predators such as wasps are responsible.

The sheer randomness of nature is exciting, but doesn't exactly help to uncover why populations are such as they are found via small-scale studies. Oh, and further to the damage invasive species have wrought on native wildlife, you may be interested to learn that none of the mammals belonged to me, the cats and dog being owned by friends and neighbours whilst the rabbit was an escapee from a dozen houses away!

6) Finally, there's the scale prejudice. Although I have a basic microscope, I didn't include such tiny wonders as tardigrades and bdelloid rotifers, even though garden moss and leaf litter respectively has revealed these wee critters. My page of nature photographs shows this prejudice, with microscopic fauna getting their own page.

So, what can we learn from this, apart from the large number of non-native species commonly found in Auckland? Perhaps that raw data can be presented in ways to obscure patterns or suggest others, should the publisher have an agenda. Furthermore, without access to highly detailed meta data, the statistics by themselves tell only a small part of the story and as such are open to wide-ranging interpretation by the reader. Therefore the next time you read about some percentage or other, remember that even without manipulation or omission, survey data is not necessarily pure, unsullied and free of bias.

Saturday 28 May 2011

Amazing animalcules: or how to create a jungle in a coffee jar

With frequently cloudy night skies preventing astrophotography of Saturn (even a few clouds are enough to ruin seeing, since they reflect the light pollution over London) I decided to head in the other direction, so to speak, and investigate the world of the very small. Last year my daughters and I had mixed success raising a batch of tadpole shrimp, a.k.a. Triops longicaudatus. Having seen the creatures lay their eggs in the adult tank, I kept some of the substrate in case we wanted to try round two this year. Therefore having had some warmer weather recently, I thought last week would be a good time for Triops Trek: the Next Generation.

Some enthusiasts - I can't really call them owners/keepers for such short-lived 'pets' - sift the half-millimetre diameter triops eggs from their tank substrate as if gold panning, but with the coral sand I used that frankly looked far too much like hard work. Therefore I just added about a 5mm deep layer of last year's substrate into a hatching tank of deionised water and hoped for the best. And...

...Success! Out of the thirty-five or so that hatched about half are still alive a week later, which surprised the hell out of me. The only problem being that the main tank is really only big enough for five or six adults. That is if they survive the transition and don't fall prey to problems with osmotic pressure, Ph balance, the nitrification cycle, etc, ad nauseum.

Meanwhile, a bit of research later, I discovered that each adult female (and most are) T. longicaudatus lays between 60 to 200 eggs per clutch. With up to one clutch a day, that's potentially an enormous number of eggs in my substrate. Looking at the nursery tank today I could see about sixty unhatched eggs stuck to the sides just above the water line, the latter having dropped slightly due to evaporation. All I have to do now is find a way of scraping them out...
Triops longicaudatus A.K.A. tadpole shrimps
Back to the current batch. The first problem was what to feed the nauplii (hatchlings for the uninitiated), as for the first few days they are too small to manage the shrimp food left over from last year's kit and I certainly wasn't going to bother buying anything. Luckily, last year I had found grow-your-own-infusoria instructions so had collected dried leaves from the local park during winter. So here's my recipe for happy hatchlings: collect some dead leaves, the more spore-covered the better; tear them into small pieces; soak them in rain or mineral water for three or four hours in a clean jar (e.g. coffee jar); tip out the water and dry the leaves; add them back to jar with fresh rain or mineral water and leave for three to four days. Voila - infusoria in abundance!

For those like me not in possession of a microscope, the best way to observe your new ecosystem (a slight Dr Frankensteinian moment) is at night. Place the jar against a dark background, turn off all the lights and view them via a torch and a magnifying glass with at least 3 times magnification. You'll be amazed at all the activity, especially the spiralling dance of the bdelloid rotifer. These half-millimetre creatures are extremely common but at this size it's perhaps not surprising that I've never noticed them before. There are hundreds of species, all of which seem to be asexual (or entirely female, depending on your viewpoint). But even these are just the tip of the diversity iceberg that is the world of the neo-microscopic. NASA has been experimenting on other similar-sized denizens, tardigrades, which can survive exposure to the vacuum, extreme temperatures and radiation of space. Otherwise known as water bears (despite their eight legs) tardigrades look more like a something off The Muppet Show than Doctor Who, but research has shown they can survive hundreds of times the lethal X-ray dose for humans, so perhaps long-duration spaceflights in the future will in some way benefit from the current endurance-testing of these remarkable little animals.

Back to the home-grown micro-jungle. Having reared a jarful of infusoria, I happily injected a few siphons' worth into the triops hatching tank. And then I felt a bit uneasy. I had heard that some fresh water aquarium owners breed triops just as food for their fish - perish the thought. And yet here I was, happily throwing the seals into the shark tank, as it were. Last year I had allowed a fairy shrimp and clam shrimp to go to their doom, along with countless daphnia (water fleas). So why was I worried now? Is there a threshold above which I consider a species should not become food (triops, obviously), whilst those below it can be eaten without qualms (clearly daphnia) and presumably bdelloid rotifers?

As a Westerner, I haven't grown up with Buddhist or other Eastern notions concerning animal welfare, ranging from veganism to reincarnation (although the latter clearly has self-interest at its core). Morals and empathy have a place in science too, and I consider pharmaceutical experimentation on animals as a necessary evil not to be thought about too often, but with the home-grown infusoria was it a case of size-based vulnerability or just cuteness that worried me how easily I had bred one animal as lunch for another? I suppose it's easy to argue that daphnia have the stigma of the name 'flea' with all its connotations, but the triops kit literature has an interestingly dismissive approach about associated fauna: it states that they won't live long (compared to triops, that is), but fails to mention that a primary reason for this is that the triops will hoover up the smaller species in next to no time.

Perhaps it was nothing more than the graceful, balletic movements of the rotifers that gave me pangs of guilt about serving them at the Café de Triops, but next time you pass a small puddle of dirty rainwater why not spare a moment's thought for the astonishing animalcules that live, largely unobserved, all around us? It really is a jungle out there!