Tag Archives: Ecosystems

Half measures don’t work when restoring marine forests

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…

Kelp forest

Forest-like kelp at San Diego aquarium. Photo Swandieve/sxc.hu

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.

Correlation does not mean causation.

Image by Randall Munroe CC BY-NC.

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.


The Kelp Forest at an aquarium in San Diego. Photo © Swandieve/sxc.hu
Correlation. Image by Randall Munroe. This image licensed under a Creative Commons by-nc licence.

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Another reason not to poison ivy

Saving the bees is a popular cause, and with good reason. They’re essential for pollinating many important crops. However, we don’t always coördinate our aims and our actions. There are concerns that various chemical treatments, either neonicotinoid pesticides or fungicides could be responsible for the reducing the bee population in the UK. There’s probably many other reasons. 97% of lowland meadow in the UK has been lost, a scale of destruction that makes the loggers in the Amazon look amazingly unambitious. But there’s all sorts of little actions that make it worse.

Ivy is currently a villain. It climbs up walls and around trees. It doesn’t actually kill trees, but that gets overlooked. It can make damage on walls worse if the wall is already in a bad state. It can also insulate walls, so properly managed it will save you money. Recent research also shows that it undervalued in supporting bees. The title of a recent paper spells it out very clearly: Ivy: an underappreciated key resource to flower-visiting insects in autumn by Mihail Garbuzov and Francis Ratnieks at the University of Sussex.

Insects on ivy flowers

Insects on ivy flowers. Photo. tomylees/Flickr.

When I think of ivy I picture the lush green leaves, but it’s the small white flowers that are important. They appear in the autumn at a time when there are few other flowers. Garbuzov and Ratnieks examined hives around Brighton to find out what the bees were foraging for. The results surprised me. Honey bees need ivy, a LOT. During September and October Garbuzov and Ratnieks found that 89% of the pollen pellets the honey bees brought back were from ivy. They also found that the majority of honey bees and bumble bees were bringing back ivy nectar to build the winter honey stores. Ivy nectar is unusually high in sugars.

The key factor in ivy’s importance is timing. Spring brings out the blooms and it’s a feast for insects that are bringing up the next generations over the summer. Winter in contrast is a famine and hives need stocks and supplies. The late flowering of ivy provides a boost to bee hives to put them in a better position for surviving overwintering.

Garbuzov and Ratnieks go so far as to say that ivy may be a keystone species, a species that has a disproportionate effect on the local environment. Ivy’s ability to feed bees, wasps and flies in the autumn provides a better chance of survival and so more insects to reproduce in the spring, not simply to pollinate other flowers, but also to provide food for predator species.

There is no obvious connection between ivy and many other crops species, but it looks like Garbuzov and Ratnieks have shown that what looks like a very localised problem What do I do with my ivy? has consequences much further afield.

The Laboratory of Apiculture and Social Insects has produced this video on how to identify insects on ivy. The university has also blogged the paper with some nice photos.


Insects on ivy flowers. Photo tomylees/Flickr. This image licensed under a Creative Commons by-nc-sa licence.

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Stochastic modelling in ecosystems – progress but we are not there yet

Modelling Of Ecosystems: the Cycle, Inputs and Ouputs

Modelling Of Ecosystems: the Cycle, Inputs and Ouputs

Modelling of processes lets one understand the functions of interacting components, helps to identify parts of processes, and can predict outcomes of changes in the system. Unfortunately, what was a major area of financial modelling is now largely discredited, much to the cost of the rest of us; other areas such as insurance are becoming so constrained by rules and regulation as to be useless. Biological modelling, in contrast is advancing rapidly, whether with respect to subcellular events, whole organism development, or disease epidemiology. This week, Professor Xueron Mao has organized a meeting (previous blog post) at the University of Strathclyde in Glasgow, Scotland, on “Stochastic Modelling in Ecosystems” (link to meeting programme).

In the week marking the 20th anniversary of the 1992 United Nations Conference on Environment and Development (“Rio Summit”), I wondered about the impact of ecosystem modelling on the major policies being discussed at the Rio+20 summit in June 2012. Had I missed a whole area of literature in the last 10 years? Weekly, the news media tell us about the results from the latest models of climate change, while I read  papers every month about crop and photosynthesis models, not to say stunning work on many individual plant species, including special issues and collected papers from Annals of Botany. Like many UN-related organizations and meetings, the Sustainable Development conference has a large amount of underpinning ‘grey literature’ – commissioned reports and research with strong scientific content (albeit, often not complete or definitive, and hence not suitable for publication in refereed journals). However, a search of the UN website does not show any attempts at ecosystem modelling (or, indeed, ‘modeling’): the 14 discussions of the topic of modelling are all about economics and finance. The Google Scholar search shows few major papers in the last decade with keywords of modelling/modeling and ecosystems.

Maybe the challenge of modelling a whole ecosystem is too difficult: a model needs to define inputs, outputs and flux through a system. The ecosystem involves cycles and networks involving hundreds of species and millions of interactions from sub-cellular level upwards. In my own talk opening the meeting, I concluded that the outputs can be classified in three areas. Firstly, chemical energy, largely in the form of the fixed carbon that is used as food, feed, fibres and fuel outside the direct ecosystem. Secondly, a small but important fraction of the flux is removed from the system, particularly to the long-term carbon stores in limestone and fossil fuels. The final group of outputs can be considered as ‘ecosystem services’ including purified (or indeed polluted) water that is changed from the input state in both purity and flow rate, or oxygen reduced from carbon dioxide. The slides from my talk are on Slideshare.com under pathh, and maybe I will make a shortened commentary for YouTube at some point.

In the meeting, we were treated to a range of talks ranging from models of carbon cycles, through population and vegetation dynamics, through to disease epidemiology models. It is always exciting when different research communities come together, so it was very valuable to hear from and talk to the mathematicians at the meeting, even if there is some differences in our languages!
It is always invidious to pick out particular talks from a full programme, and the full listing is given here. Since this blog is plant-related, I will note the impressive talks from Mathew Williams (University of Edinburgh) discussing how gigatons of carbon move around the terrestrial (and indeed atmospheric) carbon cycles using global measurements in an experiment named FLUXNET, which, along with space-based measurements could examine large-scale forest biomass changes over timescales of only three years. My collaborator Jongrae Kim (University of Glasgow http://www.robustlab.org/) gave the next talk, discussing some formal approaches to modularization of complex networks in his talk on robustness analysis of community structures, of great relevance to making very large networks amenable to analysis. Francesco Accantino presented a model of abundance and changes of three Acacia species in humid savannas adding stochasticity to a matrix model, which linked nicely to Pierre Couteron (IRD, Montpellier) working at other sites in sub-Saharan Africa. Pierre modelled the distribution patterns of patchy vegetation, showing effects of rainfall and slope in both stable systems and the changes in the last 50 years. Remote sensing is giving much more data than ecologists have ever had, and interestingly Pierre is able to use freely available Google Earth for many of his analyses. After valuable talks related to aspects of epidemiology in several systems, the closing paper by Carlo de Michele (Politecnico di Milano, Italy) built on earlier talks about water as a main determinant of vegetation type – the topic of ecohydrology as the study of hydrology that underpins ecology. Like several other talks, modelling of water could give a bistable system with two solutions of bare soil (low rainfall) or of vegetative ground cover (high rainfall), taking into account the effects of rainfall stochasicity on soil water linked to vegetation systems. The surprise was that not only did the results describe behaviour of desert compared to topical forest ecosystems, but also annual changes in savannas with dry, bare periods followed by vegetation-covered wet seasons.

“Stochastic modelling in ecosystems” has some way to go before it becomes “Stochastic modelling of ecosystems”. Genetics, measurement methods and parameterization of properties are coming from the biologists are beginning to meet the modelling community with their increased understanding of robustness, oscillation and network reduction as well as computational approaches. I am looking forward to decisions at Rio+30 being underpinned by recommendations based on rigorous and robust models showing how we can exploit ecosystems without destroying the earth.

Stochastic Modelling in Ecosystems - University of Strathclyde - 2012 - Group Photograph

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