Genetic diversity tends to decrease and genetic differentiation tends to increase towards the periphery of a species’ range, but this has rarely been tested for plants of azonal habitats such as rocky slopes or screes. Pouget et al. study a narrow endemic Mediterranean plant, Arenaria provincialis (Caryophyllaceae), across its geographic range and find that despite its narrow distribution it has a high level of molecular variation. As predicted by the central–marginal theory, the areas characterized by the highest genetic diversity are centrally located. The current range size and abundance patterns are not sufficient to predict the organization of genetic diversity, which can only be explained by phylogeographic analysis of the long-term history of migrations and persistence.
Would you recognise a desert if it was covered in water? What I mean by that is if somewhere that should be covered in forest were barren and empty, would you notice? A paper in PLOS One outlines why it matters.
Seaweeds (macroalgae) are the “trees” of the oceans, providing habitat structure, food and shelter for other marine organisms…
It’s easy to overlook the importance of marine plants if you’re not a scuba diver. From the shore one patch of sea looks much the same as another. Obviously if you’re underwater then things look different. Towards Restoration of Missing Underwater Forests by Campbell et al. is a paper looking at the missing forests of Phyllospora comosa, a brown algae that should be found of the coast of Sydney.
The seaweed disappeared with increasing pollution from the city but, despite an increase in water quality, the forests have not returned. Why?
Campbell and her team transplanted Phyllospora into sites at Long Bay and Cape Banks near Sydney. They observed the algae to see how they survived. They also watched plants at the donor sites for comparison. The results were mixed.
They did well at Long Bay. Better than well, in fact. They were reproducing better than the control sites, which suggests that the only reason there weren’t Phyllospora at Long Bay is that there weren’t any. That’s tautological, but obviously in nature you get new Phyllospora from older Phyllospora. A colonisation effort in Long Bay would get the re-establishment of the seaweed started.
Things did not go so well at Cape Banks. Here Phyllospora did much worse than at Long Bay or the original populations. What this did see were that the transplanted algae were short and had a lot of bite marks from fish. What they suggest here is that the reason there isn’t Phyllospora on site is because there isn’t enough. Small colonies are suitable for snacking, but because they’re so small all the plants get damaged. A larger area might be so large that not all the plants suffer and that leaves enough for reproduction of the next generation.
They also found the new plants were concentrated in, or at the edge of the adult population. That suggests that the lone colonist plant will not flourish by itself, what matters isn’t just the plant but the whole community.
What I particularly liked about this paper is that there’s a classic example of scientists being scientists in it.
The disappearance of Phyllospora from reefs in Sydney coincided with a peak in high volume, near-shore sewage outfall discharges along the metropolitan coastline during the 1970s and 1980s (Coleman et al. 2008). Although causation has not been formally established, embryos of this species are particularly susceptible to pollutants commonly found in sewage, to the extent that they are used as a test species in standard ecotoxicological assessments.
They’re susceptible to pollutants. There were pollutants in the area, but that’s a correlation, not a proven causation. A causal link between pollution and the demise of the algae would be extremely convenient for anyone wanting to argue now is the time to restore the forests, and it’s not a ridiculous leap to make, but they still point out that it’s still not fully proven.
What the paper shows is an example of discontinuity in ecosystems. The results show that it’s not simply a question of degree of forestation, but that you either have enough Phyllospora to make a viable forest system or you don’t. The amount you need might vary from place to place, but spending half the money isn’t going to give you half the result.
It’s also something that requires close examination. For plants that you don’t see from the shore, it’s easy not miss them when they’re gone. There are knock-on effects in how the loss of habitat affects other organisms. but that might appear a long way from the site where the root problem is.
Campbell A.H., Marzinelli E.M., Vergés A., Coleman M.A. & Steinberg P.D. (2014). Towards Restoration of Missing Underwater Forests, PLoS ONE, 9 (1) e84106 DOI: 10.1371/journal.pone.0084106
Conservation of the unique biodiversity of mountain ecosystems needs trans-disciplinary approaches to succeed in a crowded world. Geographers, conservationists, ecologists and social scientists have, in the past, had the same conservation goals but have tended to work independently. This recent review in Annals of Botany underlines the need to integrate different conservation criteria and methodologies and offers new criteria for prioritizing species and habitats for conservation in montane ecosystems that combine both ecological and social data.
Mountain ecosystems are hot spots for plant conservation efforts because they hold a high overall plant diversity as communities replace each other along altitudinal and climatic gradients, including a high proportion of endemic species. This review contributes an enhanced understanding of plant diversity in mountain ecosystems with special reference to the western Himalayas; ethnobotanical and ecosystem service values of mountain vegetation within the context of anthropogenic impacts; and local and regional plant conservation strategies and priorities.
Khan S.M., Page S.E., Ahmad H. & Harper D.M. (2013). Sustainable utilization and conservation of plant biodiversity in montane ecosystems: the western Himalayas as a case study, Annals of Botany, 112 (3) 479-501 DOI: 10.1093/aob/mct125
There were a couple of stories in the Atlantic a few months ago on the American Chestnut, Castanea dentata. The tree used to be abundant across the eastern United States, even just a hundred years ago. Writing in last year’s special issue on Root Biology, Rout and Callaway said it was effectively extinct in the wild, thanks to Cryphonectria parasitica. C. parasitica is a fungus that Asian chestnuts can fight, but that kills many sweet chestnut trees. It arrived in the USA in the 1870s (and in the UK in 2011).
One story in the Atlantic is about what the loss of the American chestnut means. Corby Kummer concentrates on the social side, particularly on chestnut as a staple food. One route to reintroducing chestnuts to their native habitat is cross breeding them with Asian chestnuts. Obviously an Asian chestnut is not an American chestnut, so there’s a long and careful programme of cross-breeding to select for blight resistance, but still keeping the American character of the tree, as much as is possible.
The other story is a different approach. Rebecca J. Rosen reports on research to splice the right genes into the American chestnut genome. Unlike backcrossing with Asian chestnuts, this could be a more targeted approach to preserving the American chestnut, without carrying over extra genetic baggage. However, when I say that Transgenic Research, then there might be another issue that needs to be tackled. Will the public accept transgenic trees?
One reason they might not is that they might not accept trees anyway. No trees is the new normal, what Randy Olsen has called a ‘shifting baseline’. Trees will be a change anyway and people tend to be wary of change. Genetic manipulation might be a convenient focal point, for somehow claiming these are not real chestnuts. But even if you think altered trees don’t count for conservation, the project still has a big positive contribution to make. A paper published in Nature earlier this year alerted me to a concept I’d not come across before “functional extinction”.
C. dentata could be said to be functionally extinct, because there are now whole swathes of chestnutless land. The altered trees, whether they’re backcrosses or transgenic, can fill the chestnut’s function in the ecosystem. It used to be said that a squirrel could travel from Georgia to Maine without ever putting its foot on the ground. It’s unlikely that such a squirrel would grumble that the 1/16 Asian chestnut genes in the trees somehow devalued the experience.
A more serious issue is exactly what trees do you plant? Will the new trees suffer from a genetic bottleneck? Karl Haro von Mogel of the Biofortified blog will be travelling to hear what’s happening with the latest research and you can help get him there. If you do, you can ask him to put forward any questions you have with a clear conscience.
Normally when someone asks a dramatic question in a headline the answer is no. This time though it’s different. A paper in the new open-access journal Conservation Physiology shows that some plants in a biodiversity hotspot are under threat from a common conservation practice, as well as development of surrounding regions.
‘Phosphorus nutrition of phosphorus-sensitive Australian native plants: threats to plant communities in a global biodiversity hotspot‘ by Lambers et al. highlights an odd problem. Plants need phosphorus for growth. It’s a big component of many fertilisers. So for somewhere like phosphorus-poor soils in southwest Australia, you’d expect an increase in phosphorus to be good news. In fact it’s not.
There are a couple of problems.
One is that to survive in phosphorus-poor soils you need special skills. Utricularia menziesii, for example is one of the fastest plants on the planet. The speed isn’t in growth or seed dispersal. It is a bladderwort. It has bladders that act as traps for insects. The speed these traps work at is astonishing. An insect can be swept from outside to inside faster than a human could blink an eye. There are plenty of adaptations you can make to live in low phosphorus soils, but these have costs. You wouldn’t be able to compete against other plants in soils with more phosphorus, which is just one reason why many plants found in these soils are rare.
Another is that some plants have no self control. If you live in place where phosphorus is limited, you’ll want to grab all that you can. If there’s a boom in phosphorus, that ability to grab it becomes a glut and you’re in deep trouble.
Lambers et al. show that one of the most interesting feature of the southwest Australian plants isn’t simply that they live in low-phosphorus soils. It’s also that they do it alone. Plants often work with fungi to build what is called mycorrhizal symbiosis. This is where a fungus provides nutrients in exchange for carbohydrates from the plant. It makes plant-fungus interactions part of much wider ecosystem, so it’s noteworthy that many of the plants in this region do not have mycorrhizal partners. It seems that a variety of phosphorus gathering strategies can be used by neighbouring plants.
In this situation then it’s clear that run-off of phosophorus-rich fertilizer is a problem. What Lambers et. al. also highlight as a potential problem is the fight against Phytophthora cinnamomi.
P. cinnamomi is a mould responsible for root rot. It’s one of the most invasive pathogens in the world, so it’s no surprise that humans have developed a counter-measure. Unfortunately the best way to fight P. cinnamomi is with phosphite. As the name suggests, it’s a phosphorus salt. It acts to slow the spread of P. cinnamomi but a strong application of phosphite to an area will also increase the phosphorus levels of local soils. In southwest Australia where many native plants are susceptible to P. cinnamomi, the cure is as fatal as the disease.
It’s a knotty problem and Lambers et al. point out that while the plants in southwest Australia are unique, the problem itself is not. They point to a similar problem in the fynbos of South Africa and the cerrado of Brazil.
Lambers H., Ahmedi I., Berkowitz O., Dunne C., Finnegan P.M., Hardy G.E.S.J., Jost R., Laliberte E., Pearse S.J. & Teste F.P. (2013). Phosphorus nutrition of phosphorus-sensitive Australian native plants: threats to plant communities in a global biodiversity hotspot, Conservation Physiology, 1 (1) cot010-cot010 DOI: 10.1093/conphys/cot010
The causes of the high genetic diversity in most Canarian endemic plants are still poorly understood. Pérez de Paz and Caujapé-Castells use the allozyme dataset for 123 taxa of the archipelago’s endemic flora to find that genetic diversity levels and structuring are phylogenetically constrained by the traits of the colonizing lineages, although also influenced by distances to the mainland. Threat to conservation is only reflected in genetic variation under intensive population sampling designs, and is not related to small population sizes. The need for habitat protection, reproductive studies and ex situ conservation are emphasized, especially in endangered taxa, whereas prior multi-disciplinary research is needed for effective conservation of less-endangered endemics.