climate change, islands, and the impending demise of tuatara?

Mitchell, N. J., Kearney, M. R., Nelson, N. J., and Porter, W. P. 2008. Predicting the fate of a living fossil: how will global warming affect sex determination and hatching phenology in tuatara? Proceedings of the Royal Society. Series B. Biological Sciences, Online version, doi: 10.1098/rspb.2008.0438.

tuatara sold separately
Originally uploaded by Mollivan Jon

This paper seems to have really touched a nerve on the web, with more than 50 media websites and blogs reporting that climate change will kill off the Brothers Island tuatara by 2080 by causing all eggs to develop into males. People, it seems, are now well primed to fear global warming. But is climate change now the number one challenge to tuatara conservation? Far from it.

This paper by Mitchell et al. (2008) was the topic of a recent ecology & evolution journal club at Lincoln University. While we were impressed with the techniques used to model soil temperature changes in Brothers Island, we were all skeptical of the conclusion, as paraphrased by the Nature news story, that "All tuatara could be born male — and thus doomed to extinction — within decades." By 2085, to be exact.

Brothers Island tuatara (Sphenodon guntheri) is a genetically distinct population of tuatara (the more widespread species being S. punctatus). Its only natural population is on the tiny (4 ha) Brothers Island in the Cook Strait, presumably the last remnant of a once much more widespread population, as tuatara remains have been recovered from throughout both main islands of New Zealand. Both species of tuatara, like many reptiles, have a temperature-dependent sex determination system. In the case of tuatara, their eggs are buried in the soil where warmer eggs develop into males and cooler eggs develop into females (the opposite of most reptiles).

With a temperature-dependent sex determination system, Mitchell et al. (2008) ask what global warming is likely to do to the tuatara sex ratios on Brothers Island. They combine an impressively detailed model of the soil temperatures on Brothers island with the sex-temperature relationship of the closely related and similar S. punctatus, to predict sex ratio shifts under two climate change scenarios. Under the more extreme of their two climate scenarios, a warming of 4° C., the tuatara are all males by 2085.

While we were all generally impressed with the methods used, none of us were particularly alarmed by the authors' conclusion. Why? Here are our reasons.

• Tuatara have survived numerous Ice Ages and interglacial periods in New Zealand's past, including the last glacial event that ended about 10,000 years ago and a warm period before 6,000 years ago that was perhaps 1.5°–3° warmer than now. At these times, tuatara were numerous and widespread, but still, the species have survived major fluctuations in climate in the past.


• The authors note that the Brothers Island female tuatara currently lay their eggs on northern and northeastern facing open slopes on the island, i.e., the warm places. They avoid the shade, i.e., cold places. The authors note that with shading, their models suggest that even a 4ºC rise in mean temperature would still result in mixed-sex nests. So, when the climate warms, all the females need do is change their behaviour to lay eggs in cooler, shaded places. Need shade? Plant native trees. Crisis averted.
  
• If human-driven accelerated climate change stopped tomorrow, the Brothers Island tuatara would still be in serious trouble. Their current predicament is not the result of climate change but the result of rat predation on mainland New Zealand combined with widespread habitat loss and modification in the lowlands. Climate change is just one of the many challenges now facing this tiny, isolated population. Inbreeding depression is another. Vulnerability to extinction following disturbance is another (e.g., a severe storm or drought could wipe them out). And, if rats arrived on the island, only immediate action would save the population.


• People will move this population to other locations and expand their numbers. This is not some small, obscure insect species. This is a high profile megafauna species that New Zealanders care about.

The media and bloggers are using this study as reason for urgent action to reduce the rate of climate change. While there are a great many reasons to reduce the currently alarming rate of climate change, what these tuatara need above anything else is a greater area of New Zealand habitat free from mammalian predators.

Beware the Australian ngaio-eating thrips

myoporum thrips attack! 1
Originally uploaded by Mollivan Jon

Mound, L. A., and Morris, D. C. 2007. A new thrips pest of Myoporum cultivars in California, in a new genus of leaf-galling Australian Phlaeothripidae (Thysanoptera). Zootaxa, 1495:35–45.

Mound and Morris (2007) describe a new species of thrips from California, Klambothrips myopori, where it is hammering the cultivated and wild Myoporum there, including New Zealand's ngaio tree. The species most certainly originates from Australia, or New Zealand. Its presence in California might not be such a bad thing, since ngaio was becoming widespread in the wild in parts of California and is on several Californian weed lists. The photo shows a typically damaged wild plant from the margins of the Upper Newport Bay Preserve wetland in southern California.

I've yet to see any damage comparable to this in New Zealand. It's well worth keeping an eye out for. If it is not a New Zealand native and can get from Australia to California, getting to New Zealand is perfectly feasible. Without natural controls, it is certainly capable of causing extensive damage to its host plants.

Mound and Morris's (2007) article is available, free, from http://www.mapress.com/zootaxa/2007f/zt01495p045.pdf (200 KB).

Weeds, weeds, weeds

Howell, C. 2008. Consolidated list of environmental weeds in New Zealand. DOC Research & Development Series 292, Department of Conservation, Wellington, New Zealand.

Clayson Howell of the Department of Conservation (DOC) has compiled a useful list of all the 328 vascular plant species that DOC regards as environmental weeds, and which are actively controlled on DOC-managed wildlands.

As Clayson writes, "New Zealand is a very weedy place" (p. 4). It's likely to become more so. It's well known now that naturalised exotic vascular plants in New Zealand have outnumbered native plants. There is something over two thousand native vascular plant species in New Zealand, almost all endemic (it's 2158 species according to de Lange et al.'s 2006 New Zealand indigenous plant checklist, published by the New Zealand Plant Conservation Network). Howell and Sawyer (2006, New Zealand naturalised vascular plant checklist, published by the New Zealand Plant Conservation Network) recognise 2391 naturalised exotic species. With DOC now managing 348 of these as weeds, that's 13% of New Zealand's naturalised plants that are nasty enough to justify control as environmental weeds. I recently combined the DOC list with all plants listed as pests on the Regional Council's various pest management strategies (RPMS), to get about 400 species. Add on that weeds being controlled by agriculture, horticulture, and forestry (plus private gardeners), and it is becoming clear that ecologist's "Tens Rule" of about 10% of naturalised plants becoming weeds (and 10% of introduced plants naturalising) is looking increasing optimistic for New Zealand.

While most of the report is a species list, Clayson also provides a useful overview of where and why these species are regarded by DOC as weeds, when they were first discovered in NZ, and an overview of which lifeforms are over- and under-repesented as weeds from the full naturalised flora.

The report is available from http://www.doc.govt.nz/upload/documents/science-and-technical/drds292.pdf (278 KB).

A glimpse of the past through kakapo poo

Horrocks, M., Salter, J., Braggins, J., Nichol, S., Moorhouse, R., and Elliott, G. 2008. Plant microfossil analysis of coprolites of the critically endangered kakapo (Strigops habroptilus) parrot from New Zealand. Review of Palaeobotany and Palynology, 149:229–245.

This paper was the subject of a recent ecology journal club at Lincoln University. In it, Horrocks et al. (2008) reconstruct the diet of New Zealand's flightless kakapo using coprolites (preserved faeces). Since New Zealand's bird fauna was decimated so recently, there are still faeces to be found in places where their makers are gone. Kakapo were once common throughout New Zealand, but have now been reduced to less than 100 individuals being intensively managed on offshore island reserves. This paper uses traditional methods of identifying plant microfossils (particularly the morphology of pollen and spores) to characterise what kakapo used to eat throughout their mainland New Zealand range. Not surprisingly, the kakapo diet was broader and more varied than what is now available in their offshore island sanctuaries. There are some good tips for what other foods these island birds could be offered.

What is difficult to obtain from this study is what foods were actively sought after by the kakapo rather than which were fed on proportional to their availability in these habitats. Comparing the plant composition of the kakapo faeces with the background levels of pollen and spores at or near these sites (with some undoubtedly tricky adjustments estimating relative plant abundance from pollen and spore counts) could be an interesting follow-on from this study.

The paper can be accessed from ScienceDirect (subscription required).

Leonard Cockayne on genetic engineering in agriculture

Cockayne, L. 1919. Presidential Address. Transactions and Proceedings of the Royal Society of New Zealand, 51:485–496. (http://rsnz.natlib.govt.nz/volume/rsnz_51/rsnz_51_00_006340.html)

The back issues of the Transactions and Proceedings of the Royal Society of New Zealand are now freely available online. I have been looking through some of the old publications of New Zealand's ecology greats, including the above presidential address by Leonard Cockayne.

In this presidential address, Cockayne makes the case for a strong investment in pure science in New Zealand. I was particularly struck by the following passage, in which Cockayne foresees the advent of genetic engineering and its potential value for plant breeding and agriculture. Keep in mind, while reading this, that it was written in 1919, just 19 years after Mendel's genetic experiments had been re-discovered, ten years after the words "gene", "genotype", and "phenotype" had been coined, a decade before the modern synthesis of evolution by natural selection, and almost 40 years before the genetic code was cracked.

"Our scientific duty as a nation is not only to apply to the best of our ability our present knowledge, but by means of purely academic investigations to discover further fundamental principles on which the greatly improved farming of the future will depend. Suppose, for example, such characters as we wished could be bestowed at will upon certain fodder plants or food plants—i.e., that the plant-breeder could by methods now unknown create exactly the plant suitable for a special environment, just as one can forge a special tool. Experiments of seemingly the most worthless kinds in genetics might lay the foundation for such knowledge, the value of which is beyond our wildest dreams."

The ghosts of Pacific avifauna

Diamond, J. 2007. Voices from Bird Bones. Science, 315:941–942. www.sciencemag.org (subscription required).

Jared Diamond reviews two recent publications on the Pacific's many extinct birds.

• "Extinct Birds of New Zealand" by Alan Tennyson and Paul Martinson (Te Papa Press, Wellington, New Zealand, 2006).


• "Extinction and Biogeography of Tropical Pacific Birds" by David W. Steadman (University of Chicago Press, Chicago, 2006).

The review of Tennyson and Martinson's attractive book is brief and complementary. "Martinson's gorgeously detailed paintings bring home the tragic loss of formerly breathing real animals in a way that descriptions of bones cannot achieve" (p. 941). Diamond presents it as a worthy companion to Trevor Worthy and Richard Holdaway's (2002) book, "The Lost World of the Moa".

"The New Zealand fossil avifauna is by far the most completely sampled in the world" (p. 941). Diamond is particularly fascinated by how the extinction of many of New Zealand's endemic birds was followed by a replacement by often related Australian species. He sees there being much to learn about the processes of community assembly from both the Pacific's prehistoric avifauna and the modern bird communities that have replaced them.

David Steadman's decades of excavations have revealed the details of how the Polynesian settlement of the Pacific Islands triggered a mass extinction of birds and other vertebrates. I well remember being stunned when I read Steadman's chapter in the 1997 book "Biodiversity II", with its description of the massive scale of bird extinctions in the Pacific following human arrival. Unfortunately, Diamond's opinion of Steadman's book is less than complementary, not due to any inaccuracies in the data behind the book, but rather regret at the superficial interpretation of this data. In Diamond's eyes, Steadman is stubbornly resistant to the modern analysis of his data and all the amazing things that could be learned from it. With the publication of "Extinction and Biogeography of Tropical Pacific Birds", this modern treatment may follow.

Darwin's visit to New Zealand, now online

Darwin, C. 1845. Journal of researches into the natural history and geology of the countries visited during the voyage of H.M.S. "Beagle" round the world, under the command of Capt. Fitz Roy, R.N. (8th edition, corrected and enlarged edition). Ward, Lock and Co, London, New York, and Melbourne. Electronic full text edition available at New Zealand Electronic Text Centre, www.nzetc.org/tm/scholarly/tei-DarJour.html

Charles Darwin's voyage of the Beagle, including his less than flattering account of his visit to New Zealand in 1835, is now readily accessible in this full text electronic version freely available on the internet.

"I believe we were all glad to leave New Zealand. It is not a pleasant place. Amongst the natives there is absent that charming simplicity which is found in Tahiti; and the greater part of the English are the very refuse of society. Neither is the country itself attractive."

Wright et al. (2006): The road from Santa Rosalia: A faster tempo of evolution in tropical climates.

Wright, S. D., J. Keeling, and L. N. Gillman. 2006. The road from Santa Rosalia: A faster tempo of evolution in tropical climates. Proceedings of the National Academy of Sciences, USA 103:7718-7722.

This study has demonstrated for the first time that molecular evolution proceeds at a faster tempo in the tropics than at higher latitudes. Forty-five woody rainforest plant genera were identified that have species occurring in both tropical and temperate climates. Numerous New Zealand species were included, in part because New Zealand carries into high latitudes a large number of woody plant genera that also occur in lowland tropical rainforest assemblages. For each genus one species was selected from the highest latitude and altitude possible and another selected from the lowest latitude and altitude possible. The ITS region of rDNA was then sequenced and substitution rates for each species pair were compared using a confamiliar outgroup. The rate of molecular evolution in the tropical species was found to be, on average, twice that in temperate species. Probably the most fundamental ecological pattern in nature is the declining species richness with increasing distance from the equator. It is suggested that differential rates of molecular evolution might provide the mechanism responsible for this pattern.

Introducing New Zealand Ecology Reviews

A few years back Alastair Robertson (Massey University) had the excellent idea of using the newsletter and website of the NZ Ecological Society to highlight important papers on New Zealand ecology that are published internationally. The project became known as HotScience and it invited members of the NZ Ecological Society to submit citations and summaries of the NZ ecology in such publications. It worked well for a while but submissions to the newsletter have dwindled recently and the society's overcommitted volunteer webmaster (me) got behind on updating the HotScience area of the society webpages (www.nzes.org.nz).

I am reviving the project with a new format and new optimism, as a web log ("blog"). A blog has two great advantages over our earlier system. It greatly streamlines the process of posting entries by allowing members to post their own summaries and/or reviews of NZ ecological science directly to the blog. It also allows members and other interested people to comment on these entries. Feel free to publicly disagree with what is posted. This is science, after all. Anyone can view the website and I have it currently set so that anyone can comment on posted articles. I will keep an eye on the posts and comments and only step in as moderator if necessary.

Because of the blog's ability to discuss and criticise papers as well as summarise them, I have renamed the project New Zealand Ecology Reviews. (The name Hotscience has also been subsequently adopted by a New Zealand website, www.hotscience.co.nz, which provides science resource for teachers.)

If you want to post a review or summary of a new article to New Zealand Ecology Reviews, you will need to be a member of this blog. This is free and easy but needs to be approved by a blog administrator (currently just me but easily expanded to others who wish to share the responsibility). Please contact me at webmaster [at] nzes.org.nz to request blog membership. Membership of the blog is restricted to NZ Ecological Society members. You can join the society at www.nzes.org.nz/join.html for a modest annual subscription.

I have posted all previous HotScience entries into New Zealand Ecology Reviews. I don't have a record of who sent these in so these are posted anonymously. If you originally sent a HotScience summary into the society newsletter and would like to be acknowledged in New Zealand Ecology Reviews for having done so, please contact me and I can make you the author of the post.

Efford et al. (2005): A field test of two methods for density estimation.

Efford, M.G., Warburton, B., Coleman, M. C. and Barker R. J. 2005. A field test of two methods for density estimation. Wildlife Society Bulletin 33: 731–738.

Population density estimation with a new spatially explicit capture–recapture method was tested in the field and compared to distance analysis of data from trapping webs. Brushtail possums were trapped in pine forest at Waitarere, near Foxton. Capture–recapture with hollow trapping squares gave an estimate (1.9/ha) that was close to the result from nearly complete removal (2.3/ha). Trapping webs gave highly biased estimates (6.5–8.0/ha), consistent with Monte Carlo simulations. The spatially explicit capture–recapture method places few constraints on the spatial configuration of sampling; dispersed configurations (e.g. randomly sited trap clusters) may be used to estimate mean density across landscapes. See www.landcareresearch.co.nz/services/software/density for software and a pdf of the paper.