Update: climate change can cause extinction

Have a look at this article on the bitsofscience website. An interesting update to the earlier post about 'mass extinction', this article mentions the Permian and other mass extinctions linked to climatic changes, but it seems that there is more certainty that past climate change was the dominant reason for biodiversity loss for more recent, smaller extinction events. 

European fish species are in a tricky stituation...

The BioFresh project mentioned earlier hosts a blog on the topic of freshwater ecosystems, and their latest post caught my eye. It picks up of the publication of the newest International Union for Conservation of Nature's Red List, which identifies the European species threatened with extinction, and highlights the particularly vulnerable status of Europe's freshwater fishes and lampreys. The Red List has had news coverage by the BBC and Telegraph too. Most interesting in the BioFresh blog is the list of the main threats to these rare freshwater fish species that were identified by IUCN... climate change is not on the list. Instead, fairly unsurprisingly, pollution, overfishing, dams, water abstraction and invasives seem to be the factors most putting these species at risk.

Some of the at-risk species include the critically endangered European eel (top); the Chornaya gudgeon (middle), found only in Ukraine; and the Jarabugo (bottom), found in Spain and Portugal. I wonder if the 'main threats' list will have changed in the future, or if perhaps these species will be long gone before climatic changes become a significant factor? Certainly climate change could indirectly already be taking effect; we know it's linked to invasive species, and I have already mentioned that dam construction projects are undertaken to safeguard water security. As this is Europe we are talking about, perhaps a more likely driver of dam building is political pressure for 'green' carbon neutral HEP energy.

Global Warming = Mass Extinction?

I've been looking at a rather sensationalist news story from the Guardian back in 2003, where the first line states that:

"Rising global temperatures over the next century could trigger a catastrophe to rival the worst mass extinction in the history of the planet"

My first reaction was skeptical, but on inspection of next few lines it seems this bold statement was actually based on some logic. Bristol based scientists had found that the Permian mass extinction 250 MYA, which saw 95% of Earth's species go extinct, was caused by only 6º C of warming. Worryingly, 6º C is the maximum warming predicted by the Intergovernmental Panel on Climate Change for a business as usual scenario... !

However, if you continue reading it turns out that the Permian extinctions were caused by massive volcanic activity, the greenhouse gas emissions of which triggered the warming. This seems rather misleading; what about the effects of huge eruptions and giant ash clouds upon dinosaur death? Don't volcanic eruptions cool the planet anyway, as the dust filled atmosphere reflects the Sun's energy back out to space? While it's arguable that reporting a "looming catastrophe" for biodiversity because of climate change will stir preventative action, I consider articles like these to simply erode public trust in climate change scientists. The article did get me thinking though - is there past evidence of climate change causing significant biodiversity loss, preferably without volcanoes muddying the waters?

Preparing European lakes and rivers for climate change

This website gives a good overview of how the current assessment systems under the Water Framework Directive are addressing the effects of climate change for aquatic environments in Europe. 

A paleoecological perspective

This post stays on the subject of global biodiversity, as I think an interesting additional perspective to the theoretical one in the last post can be found in Willis et al. (2010). This paper reviews the use of paleoecological archives to understand the rates and nature of ecological responses to climate change, partly with the aim of assessing the reliability of climate-biodiversity models with real data. Willis et al. note a huge discrepancy between a modeled and historical scenario.


Models predict that rising temperatures and CO² could transform 80% of Earth's tropical rain forest into savannah in the next 50 years; this would be a severe loss of biodiversity. However, pollen and plant macrofossils from dated tropical lake archives show that during the Eocene thermal maximum, a period with higher temperature and CO² levels than those predicted by the models for 50 years time, extremely diverse tropical rain forest extended far further over the globe than it does today. Willis et al. suggest the reason behind this is a lack of understanding of atmospheric dynamics (with regard to CO²) in the model in question. I think this real-data perspective is a hopeful one; perhaps climate change would actually increase global biodiversity if other anthropogenic threats could be 'treated'.

References:

Willis, K.J., R.M. Bailey, S.A. Bhagwat and H.J.B. Birks (2010) 'Biodiversity baselines, thresholds and resilience: testing predictions and assumptions using palaeoecological data', Trends in Ecology & Evolution, 25, 10, 583-91.

What are the prospects for global biodiversity?

I've talked about how threatened freshwater biodiversity is and what threatens it now. In this post I want to consider the outlook for global biodiversity in the future. I don't think we are yet in a state of 'biodiversity crisis' (a term frequently used on blogs and forums) as there are still hotspots of amazing diversity on the planet. Are we heading for crisis however? If so, how quickly? 

I'll look at Jenkins' (2003) paper Prospects for Biodiversity, which has been cited 103 times. This theoretical study tackles the above questions for global biodiversity by looking at what to expect by 2050. Jenkins presents an overview of other research in the area, focusing on extinction risk and population reduction in birds, terrestrial and marine mammals and freshwater fishes, habitat losses to agriculture, forest cover and wilderness. Assumptions include around 9 billion people by 2050, that IPCC predictions on climate change hold true and that humans don't behave very differently.

A key theme is huge biodiversity losses in developing countries in tropical regions as they develop. These areas - South America, sub-Saharan Africa, Indonesia and the Philippines - have suitable forested land available for conversion to agriculture, which will be needed to feed and clothe an increasing global population. Deforestation here will take a heavy toll on global biodiversity, as many of these areas are highly biodiverse with high endemism. Developed countries on the other hand, are predicted changes in distribution of species with climate change, but a fairly stable biodiversity overall. Temperature forest cover should rise and species loss in developed farmland areas slow - but these are dependent on the current green movement retaining momentum and working long term.

A recurring element is the scarcity of large animal species, in the remaining tropical forest and in the oceans, due to resource overexploitation. Freshwater biodiversity is predicted to particularly suffer. Jenkins cites WWF Living Planet Index data from 1970 - 2000 that shows freshwater biodiversity falling far faster than marine or forest, and states that human pressures on freshwater habitats will only increase. The greatest freshwater biodiversity losses will take place in urban tropical and arid areas, mainly from pollution, overfishing and water abstraction, and even in developed countries aquatic biodiversity is still predicted to worsen, this time due to invasive species.

All in all, a rather bleak picture for global biodiversity; monumental reductions in species diversity, particularly for certain types of ecosystem or taxa. Jenkins of course points out the difficulties in prediction; extinction rates are a simple concept, but deciding what they are likely to be in future is stymied by lack of knowledge. We are ignorant of the actual species diversity out there, unable to comprehensively monitor extinction in discovered species and uncertain of how many species we may save in the future.

Perhaps the most interesting point Jenkin's makes is that the predicted shift to "biotically impoverished" habitats is not expected to cause problems for humanity. This is quite contrary to much of the wider literature which cites biodiversity as hugely important for humanity as a provider of natural services (such as nutrient recycling, flood control or carbon sequestration), having important aesthetic and cultural value and as a provider of food, building and trade resources. Have a look at this and this website, which give the classic breakdown of 'why save biodiversity'.

However, "biotically impoverished" doesn't mean no biota, just a less diverse range of species. Jenkins' point does make sense; you don't really need a wide range of tree species to soak up CO², intercept rainwater or provide timber. He suggests that ecologists have yet to find compelling evidence that wild systems are better at the above mentioned functions/values than human modified ones. A person's concept of an aesthetically pleasing environment is often not a natural one - mine is the Somerset countryside, for example, a man-made landscape with far lower biodiversity than the pre-agricultral ecosystem. If conservationists fail to show that high biodiversity is highly important for human prosperity, I imagine the prospects for global biodiversity to become even more bleak.

One aspect of biodiversity Jenkins fails to mention: it's inherent value as a 'database' of genetic information and chemical products. This must be considered as having value like an insurance policy; a high biodiversity is worth maintaining just in case humans need to use it for new medicines or genetic code in the future. Finally, is this the reason we 'need' to save natural ecosystems? A key unknown in Jenkins predictions is us - he has assumed our attitude and behavior will not change "radically". Are humans prepared to make big changes to save biodiversity 'just in case' we need it later on?

References:

Jenkins, M. (2003) 'Prospects for Biodiversity', Science, 302, 1175-7.

In preparation for next time...

The last post was unplanned, but it actually sets up the next topic nicely, as I will be looking at one of those theoretical (modeling!) studies that attempt to predict how biodiversity will fare in the future. I'll be looking at the big picture: global rather than just freshwater biodiversity, as much of the literature around the future impact of climate change on biodiversity is at this scale. In preparation, it's worth considering a few things about the relationship between climate change and biodiversity.

The Convention on Biological Diversity's website provides a nice overview of climate change and it's relationships with biodiversity; some key points are summarized in this paragraph. Cycles of climatic changes are a big part of life's evolutionary history, with periods of rapid climate change often driving migration, behavioral adaptation and evolution of new physical characteristics to survive. Key concerns for the current warming is that it's happening very quickly, will reach higher levels than seen in the last 1.8 million years and is happening alongside other anthropogenic pressures (such as pollution or hunting), all of which could result in far more extinction than in previous warming periods. The article uses the term biodiversity to mean 'all life', and hence suggests that biodiversity can impact climate change, as more photosynthesizing biota would remove CO₂ from the atmosphere, so slow climatic change. It's not clear to me that this relationship exists when you consider biodiversity to mean the diversity of life, as a carbon sink does not need to be species rich to be effective.

It's important to consider that extinctions of vulnerable species doesn't necessarily lead to a significant long-term loss of biota, just biodiversity. Climate change may may not reduce the biomass of the plant, just it's heterogeneity, and there may well be areas where new conditions drive the introduction or evolution of new species leading higher local biodiversity. All that is certain is that the planet's biotic communities will be altered (in content and distribution), and that many current species are likely to be lost.

Something that got my attention...

A New Scientist article from the issue 4 weeks ago has an interesting special report describing what is 'known' about climate change and what is still 'unknown', in other words which topics science has reached consensus on. The question "How serious a threat is global warming to life?" is considered unanswered, although the author Michael Le Page seems certain that climate change will present a huge challenge to life on Earth. In my opinion, anything that is sure to present a 'huge' challenge is surely a very serious threat, but what Le Page is getting at is that although science knows that rapid climate change will challenge species survival, it doesn't know how successfully life will overcome this challenge, and so the long term impacts of climate change on global biodiversity are unknown.

The argument presented to show that science doesn't know how successfully non-human life will adapt is summarized as follows: theoretical studies predict very serious impacts for biodiversity (as many species won't be able to adapt), and these are so far backed by real world studies, but on the other hand a warmer wetter planet with more CO²  available for plants to photosynthesize should support more life. When I first read this, it seemed silly; how could peer-reviewed studies which do provide answers to "How serious is climate change for life?" be given so little weight? If studies conclusively show that climate change will have severe impact on biodiversity, then surely we do know how successfully life will meet the challenge of climate change, and so be able to assess how serious a threat it is.

Ultimately, the reason this article got me thinking is because it's description of "How serious a threat is global warming to life?" as 'unknown' is contrary to the main aim of this blog; to explore the affect global warming will have on aquatic life! I am expecting there to be a wealth of scientific understanding about what a warmer future holds for aquatic life. There may be uncertainties and gaps in our knowledge, but we do have a wealth of information about the workings of aquatic habitats, flora and fauna, as well as the modeling tools and measured data to predict what may happen and then validate or discard these predictions as time goes on. 

References:
Le Page, M. (2011) 'Special report: Climate change: What we do know - and what we don't', New Scientist, 22 October, 36-43.

BioFresh

Check out the website of BioFresh, a project devoted entirely to freshwater biodiversity with some really interesting information, particularly on conservation priorities and trends.

What threatens freshwater biodiversity? Climate change has some destructive allies...

The IPCC underlines that although climate change will affect biodiversity directly (through rising temperatures, changing rainfall patterns and habitat loss through sea level rise), many of it's negative effects will have come about in conjunction with other anthropogenic pressures to biodiversity (IPCC, 2002). It's important to remember that anthropogenic impact has a history far longer than recent concern about climate change, and that these pressures have already lead to biodiversity loss - I think climate change can only exacerbate damage already done. In this post I'll build on themes mentioned in the introduction to look at the important 'other' biodiversity threats specific to just freshwaters, and their likely interactions with climate change. 

Perhaps the largest threat suggested by the literature is habitat disturbance, fragmentation and loss. Groombridgeand Jenkins (1998) consider the habitat loss from draining wetland environments and building on floodplains, as well as the creation of poor habitat by water management strategies such as channel straightening and reservoir creation. Projects like these clearly remove habitat, but also make travel between remaining habitat difficult as a barrier of unsuitable conditions lies in between (for example an area that is too shallow to too exposed to terrestrial predators). Another water management strategy, increasingly common in countries experiencing seasonal water shortage, are dams - these physical barriers are well-known to adversely affect migratory species. It's these types of fragmentation that will interact most negatively for biodiversity with climate change, preventing vulnerable species from migrating away from areas where climatic conditions are unsuitable.

It's a peculiar situation in freshwaters that while strategies to manage water resources leave biodiversity vulnerable to climate change, as shown above, these strategies can be vital to prevent human vulnerability to climate change. As Vörösmarty et al. (2010) point out, most development projects to increase water security for people have negative impact on biodiversity. As adequate legal protection measures are not in place to protect freshwater biodiversity, and the future financial resources for water security will likely be far greater than for conservation (Vörösmarty et al., 2010), biodiversity needs are unlikely to be prioritised. Here, climate change will threaten biodiversity indirectly - as precipitation patterns change, creating water shortage in some parts of the world, more dams (and other water management projects) will go ahead, adding extra pressure to species already pressured by the direct physical and chemical impacts of climate change.

Pollution is another key threat, particularly in some parts of the world; 45% of China's major rivers were moderately to badly polluted in 2008 (Vörösmarty et al., 2010). Pollution can derive from diffuse sources, usually agricultural fertilizer and pesticide run-off, or point sources, such as waste dumps and effluent pipes. The study by Vörösmarty et al. (2010) found that downstream proximity to urban areas was a reliable predictor for pollution, although river habitat far upstream could be affected by urbanization at the river mouth. Pollution problems in freshwater systems make the community more vulnerable to climate change, as it may already be in an unstable state, with threatened species. Climate change is also likely to increase loading of pollutants like nitrates and phosphates (responsible for eutrophication) as warmer temperatures release organic material from permafrost and increase soil and sediment erosion.

Invasive species can cause huge problems in freshwater systems by competing for native species for resources, spreading disease or introducing parasites. Much literature has focused on this, for example, Dextrase and Mandrak (2006) found alien species to be the second largest threat to Canadian freshwater fishes after habitat degradation. Gurevitch and Padilla (2004) suggest that exotic species do cause dramatic ecosystem alterations, although little evidence shows they are solely responsible for the extinction of native species. Just like pollution, however, this pressure could combine with climate change to reduce biodiversity, and will also increase with warmer temperatures as species shift towards higher, cooler latitudes.

Ultimately, the take home message is that the future impact of climate change upon freshwater biodiversity will be complex, and that it won't be enough to try and fix any one aspect of the problem, as all anthropogenic pressures are interlinked.

References:

Dextrase, A.J and N.E. Mandrak (2006) 'Impacts of alien invasive species on freshwater fauna at risk in Canada', Biological Invasions, 8, 1, 13-24.

Groombridge and Jenkins (1998) Freshwater Biodiversity: A Preliminary Global Assessment, Biodiversity Series No. 8, Cambridge: World Conservation Monitoring Centre. 

Gurevitch, J. and D.K. Padilla (2004) 'Are invasive species a major cause of extinctions?', TRENDS in Ecology and Evolution, 19, 9, 470-4.

IPCC (2002) Climate Change and Biodiversity, IPCC Technical Paper V.

Vörösmarty, C. J., P. B. McIntyre, M. O. Gessner, D. Dudgeon, A. Prusevich, P. Green, S. Glidden, S. E. Bunn, C. A. Sullivan, C. Reidy Liermann and P. M. Davies (2010) 'Global threats to human water security and river biodiversity', Nature, 467, 555-60.

How is current freshwater biodiversity faring?

Define biodiversity?

The term is used in many different contexts - perhaps because it comes from the conservationist movement rather than biology - but is usually taken to mean the variety of all life on Earth. Broadly, the classic definition is: biological diversity is the genetic diversity within species, the diversity of different species and the variety of ecosystems on Earth (UN, 1992).

What's the current state of biodiversity for freshwater habitats?

Relative to the spatial extent of habitat, the species richness of freshwaters is very high in comparison to marine or terrestrial environments, and the bounded nature of lakes and rivers has lead to high levels of endemism (Groombridge and Jenkins, 1998). Unsurprising then, that Myers (2003) highlights the obligation to more thoroughly and extensively document freshwater species, suggesting that freshwater ecosystems could turn out to be crucial biodiversity 'hotspots' for conservation. Despite these gaps in the data the importance of freshwater biodiversity is well-known, and it's already a high priority for most conservation efforts. For example it's first on the agenda for the International Decade for Action from 2005-15 (Dudgeon et al., 2006).

Unfortunately this high conservation priority is not just down to the natural richness of freshwaters. In a recent study by Vörösmarty et al. (2010) which used threat indices to map global incident biodiversity threat, it's only a tiny percentage of the world's rivers that remain unaffected by people. Freshwater habitat is among the worst threatened by humans (Myers, 2003), and as a result it's quality is in decline; most monitored freshwater species populations are falling (Groombridge and Jenkins, 1998). Freshwater fish in particular are known to be highly threatened (Groombridge and Jenkins, 1998) and as these are often the only taxa monitored, many conservationists assume that fish species declines are indicative of increasingly poor freshwater ecosystem health in general.

References:

Dudgeon, D., A.H. Arthington, M.O. Gessner, Z.I. Kawabata, D.J. Knowler, C. Lévêque, R.J. Naiman, A.H. Prieur-Richard, D. Soto, M.L.J. Stiassny and C.A. Sullivan (2006) 'Freshwater biodiversity: importance, threats, status and conservation challenges', Biological Reviews, 81, 163-82.

Groombridge and Jenkins (1998) Freshwater Biodiversity: A Preliminary Global Assessment, Biodiversity Series No. 8, Cambridge: World Conservation Monitoring Centre. 

Myers (2003) 'Biodiversity Hotspots Revisited', BioScience, 53(10):916-917.

UN Conference on Environment and Development (1992) Convention on Biological Diversity, Rio de Janeiro: UN Conference on Environment and Development.

Vörösmarty, C. J., P. B. McIntyre, M. O. Gessner, D. Dudgeon, A. Prusevich, P. Green, S. Glidden, S. E. Bunn, C. A. Sullivan, C. Reidy Liermann and P. M. Davies (2010) 'Global threats to human water security and river biodiversity', Nature, 467, 555-60.

An Introduction to HotFrog

I consider anthropogenic climate change to be one of the largest challenges facing Earth’s environment and society. I’m not alone in this concern; climate change is a topic that increasingly dominates the news, politics, scientific research and popular media, and this trend shows little sign of abating. As a geographer who is leaning precariously towards aquatic ecology, I find climate change most interesting within the context of its effect upon Earth’s fauna and flora, and in particular it’s freshwater aquatic communities.

There have already been measurable impacts from climatic change across all varieties of ecosystem, such as changes in spring phenology for birds and rapid range shifts to higher altitude and latitude for butterflies; both of these well documented (Walther et al., 2002). Possibly the greatest concern that conservation ecologists have about climate change however, is its potential to threaten global biodiversity. There is concern that the twin threats of habitat loss and climate change will prevent vulnerable species from adapting to a warming planet, as they could become trapped in areas of unsuitable conditions, leading to extinction.  

This blog aims to explore the impact climate change could have upon freshwater aquatic ecosystem biodiversity, asking questions like “Will climate change really cause ‘mass extinctions' of freshwater species, or is this unrealistic?” and “How will the ecosystem structure and function of freshwater environments be affected by climate change?”.  I hope that I will be able to provide some degree of answer!

Of course, its important to recognize that there more threats to freshwater biodiversity than just climate change and habitat loss, and that all these pressures will affect future biodiversity. As a reminder of some of the threats to general aquatic biodiversity have a look at this highly informative and well researched video:

References:
Walther, G., E. Post, P. Convey, A.Menzel, C.Parmesank, T.J.CBeebee, J. Fromentin, O.Hoegh-GuldbergI& F.Bairlein (2002)‘Ecological responses to recent climate change’, Nature, 416, 389-95.