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Friday, June 24, 2016

Did Climate Change Drive the Bramble Cay Melomys to Extinction? Probably

Bramble Cay melomys (Melomys rubicola)
Credit Ian Bell/Queensland Department of Environment and Heritage Protection

 Melomys Rubicola has been declared extinct. Had it been something like a fuzzy koala or panda instead of a rat, the world might have taken more notice, but maybe not. A Google search on the topic goes over 20 pages deep. This seems to have struck a nerve.

It's possible that an undiscovered genetically identical population exists somewhere else. It's not unheard of for a species declared extinct to show up again. But if it has been on that tiny island off the coast of Papua New Guinea long enough for speciation to occur, then it is extinct because to repopulate someplace else a pregnant female would have needed to leave the island and establish itself elsewhere, and that is extremely unlikely.

There have been some dubious claims of extinctions caused by climate change, as one would expect, and I'm sure there will be many more. But little by little, the real extinctions will arrive.
I poked around on the internet for critiques of this announcement and found three, two of which were not worth bothering with (one confused the ozone problem with climate change) so I settled on the one at Energy Matters, which is an excellent blog and on my regular reading list. The analysis provided on this particular topic is characteristically thorough but not thorough enough to convince me.

Roger Andrews found that there has not been an increase in the number or intensity of cyclones in that area since 1969. He also looked up the tide gauge records for the area since 2000 and created a crude best fit line through it to determine that the ocean level in that part of the world may have only risen maybe 2.5 inches since 2000. His conclusion was that because the highest point on this island is about nine feet (even with the seasonal fifteen inch increase in sea level rise during cyclone season) sea level rise since 2000 would not have made much difference. And according to the authors' explanation, he's right. Temperature changes are likely the main driver, not sea level rise.

So there you have it. The demise of Melomys rubicola had nothing to do with temperature, rainfall or sea level rise. The animal was a victim of storm surges that progressively destroyed its habitat.

This is where Andrew lost me. The researchers are the ones who stated that Melomys rubicola was the victim of repeated storm surges over the last decade that progressively destroyed its habitat. Given time, this is how it will end for other island species.

No evidence – not even a climate model – is presented to support the claim that these storm surges had anything to do with increasing atmospheric CO2.

But the report does present evidence. Keeping in mind that CO2 levels not seen for 800,000 years have led to warmer temperatures which have in turn led to rates of ocean level increase not seen in millennia (all three of which are measured, not modeled) and contrary to the tidal and cyclone data presented by Andrew, the repeated storm surges at that island over the last decade were obviously severe enough to eventually wipe them out after having been there for at least 1.7 centuries.

On pages 24 through 26 of the report the authors list several severe surge events that occurred in the vicinity over this time frame and discussed how they are likely linked to climate change:

The increase in cyclonic activity on the east coast of Queensland since 2003 has been attributed to an alteration in the occurrences of El Niño and La Niña events under the influence of the Inter-decadal Pacific Oscillation (J.J. Callaghan, Appendix H in Harper2013). An analysis of three decades of data from across the entire Pacific Ocean basin determined that occurrences of coastal erosion and flooding are most closely tied to the El Niño/Southern Oscillation, with the Southern Hemisphere, including Australia, experiencing more severe conditions during La Niña due to increases in cyclonic activity, wave energy and sea surface elevation (Barnard et al.2015).The Torres Strait also experiences higher sea levels during La Niña years, whereas lower sea levels occur during El Niño years (Suppiah et al.2010). Clearly, the damaging impacts exerted on coastal areas by the changing weather regimes are being driven by climatic oscillations (Barnard et al. 2015). The trend towards a strengthening in the intensity of La Niña conditions until at least 2012 has been linked to climate change, specifically the increase in global mean temperature (L’Heureux et al.2013), with the frequency of extreme La Niña events predicted to increase (almost doubling) with greenhouse warming during this century (Cai et al. 2015).

The overall concern with climate change is that the contribution from anthropomorphic sources have increased the rates of change from geologic time scales to time scales that will affect our grandchildren. This would all be a moot point if there were not also a hypothesis that humanity can slow the change by ending fossil fuel use and the destruction of carbon sinks.

A population repeatedly devastated by increasing levels of seawater inundation and vegetation loss will one day fail to recover. That's how extinction generally happens. A population shrinks for some set of reasons to the point that it can't reproduce fast enough to recover from losses normally incurred by things like drought, disease, predation, annual inundation, etc.

I found myself in the middle of a feeding frenzy when I made the mistake of asking why storm surges didn't drive it to extinction millennia ago. What follows are some responses to my remark in the comment field:

Because this little sand spit probably wasn’t there millennia ago ...Bramble Cay is effectively a sand bar in the estuary of the Fly River ...While coral atolls have a self-regulating mechanism that maintains them at or around sea level sand spits are notorious for coming and going ... The Cay may not have existed in the past.

Photo on Bramble Cay from Gizmodo taken by Natalie Waller

The hypothesis that Bramble Cay is an ephemeral sand bar that comes and goes in a river estuary seems unlikely considering that the river ends about 40 miles away across the ocean. But I also found three sources stating that Bramble Cay is primarily composed of rock. So we can throw out the ephemeral sand bar hypothesis suggesting that the mammal could not have been there for very long (long enough for speciation to occur).

Alternately the species was wiped out by storm surges in the past, and repopulated the Cay when it was carried down on vegetation by the Fly River in flood.

The odds that this one species (instead of a different species) has repeatedly repopulated this cay seems very low to me. It was more likely a one-time event. And to ice that cake, from the official report:

...the Bramble Cay melomys population possessed only one mtDNA genotype, suggesting that a single colonisation event took place on the cay

Several commenters thought it was important to demonstrate with links to sources how a mammal could have arrived there by riding on vegetation drifts. Why they thought that mattered, I have no idea. That's a well documented phenomena. How it got there is irrelevant. How long it has been isolated there is what matters. A specimen was collected in 1845, suggesting that it has been surviving there for centuries.

From another commenter:

It isn’t a reasonable hypothesis when you have no evidence to back up the claim only supposition and conjecture. Do we know that the creature has lived there for millennia? If so, has it always been present on that island? Sea levels have been rising for considerably longer than we have been pumping CO2 into the atmosphere.

We know it has been there for centuries. As for changing sea levels, see chart below. And of course it hasn't always been present on that island. Tortoises have not always been present on the Galapagos Archipelago.

Graph adapted from Real Climate

From what I can gather, the melomys is common on islands in the region and is therefore not even extinct.

I’d have thought it almost certain that the Melomys are thriving in PNG. Where to hell do these biologists come from? Do they think the Melomys evolved from sea slugs on Bramble cay?

There are about 13 species of melomys (compare that to the six surviving species of tiger out of nine that existed just a short time ago).

I found the following comment somewhat appalling:

I live in a declared koala habitat where there are no koalas. Tabby (and Rover) can clean out more native fauna in a night than a year of floods or droughts.

Not that our modern activist researchers would ever obscure such an obvious causative factor just to get an appreciative moo from the herd.

The fact that our choice of pets is destroying species far faster than climate change at this time is irrelevant.

The following was a reasonable comment but if he was really so interested, why didn't he take thirty seconds to Google the answer like I did?

Sure would be interesting to know what characteristics separate this rodent from similar species on the PNG mainland.

Another commenter crafted a 462 word essay response, which I parse below. He accepts that the climate is warming but thinks it will be a good thing for nature. Although this view contradicts what some of the other commenters think, which is that climate change will have no meaningful impact, they all seem OK with his idea that it is already having a positive meaningful impact. The article author thanked him for what he thought was an "excellent response."

Despite the name you don’t know much about species. Do you?

His ability to extract so much information from my short comment and moniker is a true gift on par with that of Sherlock Holmes. But his insult skills need honing ; )

This is life at the edge. A small patch of land appears, and gets quickly colonized by a few species. Through founder effect, genetic drift, and specific conditions they quickly diverge, but their life is precarious. If conditions become slightly worse the population is wiped out, and this is not a loss to the parent species. This is evolution in action, and has nothing to do with us.

His above statement is accurate until the second half of the last sentence. The hypothesis is that the rapidly rising ocean levels caused by warmer temperatures caused by greenhouse gases from the obliteration of vast carbon sinks and industrial discharge of ancient fossil carbon stores back into the atmosphere has accelerated those conditions that have "become slightly worse [until] the population is wiped out." It's an old and well-known fact that, statistically speaking, island species have been and will continue to be the first ones to go.

...this is not a loss to the parent species.

I don't see the relevancy of that unless he's arguing that we should not strive to preserve subspecies because of the continued existence of parent species, be they melomys, zebra, or Galapagos tortoise.

And the main cause is invasive species ...Agricultural management and climatic change are the major drivers of biodiversity change in the UK

True but those particular strawman arguments are also irrelevant to the discussion. There are many causes. Reducing any of them would be a good thing.

If we discount these island species that we are losing, the idea of a mass extinction becomes silly.

Right, the idea that we might be causing a mass extinction is silly. He's now arguing that human activity has not and will not continue to accelerate extinction rates. I've read every book written by E.O. Wilson (including Super Organism), and have his latest one on my shelf. So, if I have to pick between biologists, I hope he pardons me if I side with one of the greatest since Darwin (and many in his time also thought his theories were bunk  ...and still do come to think of it) on the issue of the sixth extinction event.

As a biologist I am concerned that instead of dedicating our efforts to the protection of wild populations and ecosystems all over the planet, as we have been doing in the developed world, we dedicate the money to fight a climate change that it is having surprisingly little effect on the biology

I'm with him on that one. In fact, when you look at hydro electric dams, the damage being done to bat and raptor populations by improperly sited wind farms, the usurpation of desert tortoise habitat by solar thermal projects etc, one could hypothesize that we are accelerating damage to the ecosystem.

On the other hand, the billions being wasted in Germany in an attempt to decarbonize without nuclear is not going to be handed over to conservation organizations. I would think that a significant number of people would shiver at the site of a melomys (which looks pretty much like most rats) and wonder why we would bother to save it.

 ...and most of it [effects of climate change] positive ...Climatic change has had a wide range of impacts on species, with more species impacted positively than negatively in the short-term at least.

Assuming extinctions are going to result (and they are) he is essentially trading biodiversity for biomass. And being a rate problem, the phrase "in the short term at least" is all important. It's almost like he threw that line in as an afterthought when at some level of consciousness he realized that his logic chain was missing a link.

This was totally predictable. An increase in temperatures produces an increase in energy and water and together with an increase in CO2 produces more productive ecosystems. Some species might respond negatively to the changes, but most species will respond positively.

In the big picture, every species on the planet today will eventually go extinct. The vast majority of all species have gone extinct. Most certainly in a given boundary at a given time you can find a net positive. Species evolve to survive in a given environment. But change the environment fast enough, and that species will be driven to extinction. An increase in biomass at the expense of biodiversity is what biologists are hoping to avoid. In past climate changes some species were able to survive by shrinking in numbers and holing up in environmental strongholds (a last remaining few mountain rainforests, whatever) until they could expand again with a favorable change in the environment. Other species became much more common as their environment expanded. Many others became extinct. We have overrun the planet. Many species today have nowhere to run, nowhere to hide. The number of extinctions will be huge this time around and very fast paced on a geologic time scale.

Anthropogenic effect on species is greatly negative, but not due to climate change.

But earlier he said "Some species might respond negatively to the [climate] changes ..." And as is the case with the above sentence, most of the rest of his comment was a string of strawman arguments. I was not arguing which effect is greater at this point in time.

And finally, another commenter posited the following hypothesis:

May be a cat drifted out there and has since drifted on. As ridiculous as my suggestion is, it makes more sense than their explanation.

So, in the end, other than the drifting cat scenario, the other hypothesis presented in the comment field for why a mammal that has been on this cay for centuries is no longer there all had fatal flaws. Time will tell, as was the case with the ivory billed woodpecker and the passenger pigeon, if it is extinct.

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