Global warming strains at species interactions

R.G. Bijlsma).

(a) Freshly emerging pedunculate oak leaves (Quercus robur) in spring (Photo credit: C. Both). (b) Caterpillar of the winter moth (Operophtera brumata) foraging on oak leaves (Photo credit: M.E. Visser). (c) Male pied flycatcher (Ficedula hypoleuca) entering a nest box with several winter moth caterpillars to feed his chicks (Photo credit: C. Both). (d) Newly hatched European sparrowhawk chicks (Accipiter nisus) waiting for passerine prey to arrive (Photo credit: R.G. Bijlsma).

Climate change is like a stalking predator, a threat that first crept up, and then swiftly leapt out at the ecological science community. There is no doubt it was an issue around which there was a simmering awareness for decades. However, recent detailed multidisciplinary studies, which have pored over numerous long-term datasets (most compiled for reasons unconnected to climate change monitoring), have forced a re-appraisal of the magnitude and pace of the challenge that global warming represents to both geophysical systems (e.g., ice sheets, mountain glaciers, sea level) and to biodiversity in already stressed environments.

One of the clearest ‘attribution fingerprints’ of global warming on biological systems is the advance of reproductive events to earlier in the breeding season. Species that take their cue to mate or migrate from climatic phenomenon (e.g., average or extreme temperature, or rainfall), rather than non-climatic triggers (e.g., length of day), are predicted to respond most readily to climate change.

For most species, this is exactly what is seen, with the most commonly observed changes manifested in the advance of spring events, delay of autumn events, shortening of life-stages and changes in migration patterns.

However, this is not a universal response — which raises a number of interesting possibilities. Perhaps some (mostly larger-bodied) species are unable to adapt quickly enough, due to long generation lengths? Others, especially those threatened by other human-induced factors such as habitat loss or over-exploitation, may lack sufficient standing genetic diversity or behavioural flexibility to respond effectively. In other cases, there may be advantages in quite different types of adaptation (e.g., breeding earlier to keep up with the food supply, or breeding later and having less food, but avoiding the breeding season of the predator).

I recently wrote an In Focus review for Journal of Animal Ecology, which took a reflective look at a recent paper published in the journal, which considers some of these issues of ecosystem adaptation to climate change (the above and below are edited excerpts from it). The excellent paper I describe is by some Dutch ecologists who have a long-established track record studying the ecosystem of Hoge Veluwe National Park in the Gelderland province of the Netherlands.

The system is a European mixed woodland food web. Oak and pine dominate the study site. During bud burst, the deciduous oak trees are food for moth caterpillars, which are, in turn, predated upon by a number of bird species. These songbirds, and especially their fledglings, are targeted as prey by Eurasian sparrowhawks. Two decades of data (1985 to 2005) have been collected from this community, monitoring everything from flowering and breeding times to the birth and death rates of individual species. Previously published work has shown that the component species are individual reacting to climate change.

The recent work is particularly interesting. It goes beyond a simplified one- or two-species response (whereby, for instance, the timing of peak caterpillar numbers induces songbirds such as pied flycatchers and blue tits, to breed earlier to keep up the food supply). Instead they consider adaptation pressures and inter-species relationships, from caterpillars grazing on oak, songbirds eating caterpillars, and predatory sparrowhawks picking off the songbirds. Quite a complex set of interactions, as is typical of ecosystem studies.

The researchers showed that all components of this system: tree budburst, peak caterpillar numbers, songbird hatching dates, and sparrowhawk hatching dates, are happening earlier and earlier over time. This statistical analysis shows the smallest response was for the sparrowhawk (0.9 days advance in breeding per decade), then budburst (almost twice that rate, at 1.7 days), a big change for songbirds (3.5 days for coal and great tits and 5 days for flycatchers and blue tits) and a whopping 7.5 days per decade for the caterpillars. At that rate, the peak of caterpillar numbers will occur a full month earlier within the space of 40 years – and that’s at the current pace of warming, which is expected to accelerate considerably without emissions reductions.

What would a decade worth of change do? Well, the peak of caterpillar numbers would have advanced almost 8 days, the songbirds which feed on them only half that, and the sparrowhawks a mere 1 day. Over time, this would put strain on the species interactions, and would inexorably pull the species interactions apart, due to mismatches in the timing of breeding and maximum food availability. This could, in turn lead to outbreaks in caterpillar numbers, because they are being fed to fewer songbird chicks. More caterpillars would mean more of the oaks are heavily grazed, which could damage the forest structure. The ecosystem starts to unravel…

So what might these different rates among the different component species of this food web indicate? It’s difficult to be sure, but the authors have some interesting ideas.

One possibility is that the larger species, because of their longer generations, aren’t able to adapt to the changes in climate as quickly as the fast breeding species. Another is what’s termed ‘weak predictability’ — animal’s decision-making (when the birds choose to lay their clutch) is simply too far separated in time from the key selection environment (when the caterpillars peak – driven by climate warming). So they can’t react to cues because they’d have to have some window into the future (the build-up of caterpillar eggs, or perhaps the size of the previous season’s crop of grubs might do it, but this type of forecasting would take considerable time to evolve).

Or perhaps there is a strong pressure from natural selection for prey to outpace their predators by breeding earlier (since climate conditions now allow this). This would explain why the caterpillars have advanced more rapidly than the tree budburst (they trade-off having less available food because this also reduces the number of them that end up getting eaten by songbird chicks). The songbirds are probably trying to both keep up with their caterpillars and escape being eaten by sparrowhawks, and so are adapting as fast as they can (which is slower than the caterpillars, who have shorter generation times and enhanced growth rates under warmer conditions). The sparrowhawks eat many species besides songbirds, and so the pressure on them to respond to indirect changes in caterpillars and budburst is quite weak. It’s an intriguing idea.

As I’ve noted previously on BNC, the pressures faced by biodiversity are multiple and they tend to reinforce each other to make the whole situation that much worse. For instance, heatwaves and droughts tend to exacerbate forest fires, and habitat fragmentation can mean that species find it difficult to move through urban and agricultural landscapes to reach new areas that are become climatically suitable to them as the average temperature warms. They get anchored in patchy environments that become increasingly unsuitable for them over time.

We need more studies like this, to help us better understand the variety of responses ecosystems are likely to experience under global change (climate warming and other human impacts such as deforestation and the spread of invasive species). Certainly there are still large gaps in knowledge, especially in areas such as southern hemisphere biological communities (yes, even Australia). But I suspect the answers are out there, buried in the literature and in government and research organisation databases, just waiting to be properly analysed to tease out the climate change signals. My team of postdocs and PhD students at University of Adelaide are hard at this task.

Stay tuned, I’ll certainly be reporting back here in the future about what we found!



  1. Barry,
    I’m afraid that the denialists will say that since we don’t know everything, by a leap of non-logic we therefore must know nothing.

    Then, by the same logic, they then construct a great edifice of denial founded upon nothing at all. [well it must be nothing because they said so].

    Thanks Barry for this and your other fascinating and informative posts.

  2. Chris,
    Maybe they will just say that the extreme pressure of biodiversity merely to survive is more a function of weather rather than climate and even if AGW is happening would they not have to be currently ignoring it in the NH?

  3. An all to frequent retort from climate change deniers, is that what is occurring, is within “natural variability”. For decades plant and animal behaviour, be it changes in reproduction timing, or species shift to higher latitudes and altitudes, has been happening from the Arctic to the Antarctic. Though documented, much of the information on this subject, is fragmented and difficult to access. There needs to be greater effort put into gathering and collating this information, into a user friendly data base, giving us the big picture.

  4. I’m thinking that the movement of farming will amplify problems. e.g., Suppose your farm in the Murray Darling Basin is no longer viable because the water has “moved” north. So you follow the water and move your crops/livestock north. Where you used to farm has been alienated (to some extent) from wildlife and will not simply recover to its original state when abandoned. Net result is decreased space for wildlife.

  5. Yes Nick @ 5 Chapter 1 AR4 does have a lot information, but in a form that is not necessarily user friendly. When debating a climate sceptic it would nice to be able to easiy reference for example, that the range of the Arctic Fox has shrunk by x amount km’s while the range of the Red Fox has advanced by x amount km’s. Or the range of the Adelie Penguins is decreasing while that of sub Antarctic Penguins is increasing. A lot of this information does exist in science journals, which too often one finds to be subscription only, after following the links.

  6. I am presenting this paper at the Minding Animals Conference in Newcastle 13 – 18 July

    I realise that the topic is a bit ‘out there’ but as a transdisciplinary philospher I am willing to give it a go. Any thoughts from non-denialists/non-sceptics on the phenology-mental health issues would be gratefully received.


    As development pressure increases and global climate changes, there are psychoterratic or earth-related psychic disturbances to human well-being. I have created the concept of solastalgia, defined as the melancholia or homesickness you have when you are still at home, to account for the direct experience of such negatively perceived change in humans. The threat to one’s sense of place leads to an assault on one’s psychic identity. The concept of solastalgia has its genesis in the human response to large scale development pressures such as open cut (pit) mining and coal-fired power station fallout, but it is also applicable to anthropogenic climate change pressures. Humans experience the melancholia of nostalgia when they become completely removed, displaced, detached or alienated from loved landscapes and the home environment. They have the melancholia of solastalgia at the lived experience of the degradation and desolation of their home environment, including the loss of its biodiversity. As global warming and subsequent climate change shift eco-climatic zones away from their former locations, non-human animals experience a mismatch between their eco-evolutionary niche and the transformed home environment. Some species are capable of adaptation by migration with the direction of change. Movement further up mountains, for example, is a limited adaptation strategy for an alpine species in the face of a warming clime. However, many species cannot adapt to rapid change and become threatened or face extinction. The case for the relevance of psychoterratic or earth related mental health syndromes affecting human well-being has now been put (Albrecht et al 2007), and in this paper I explore the idea that non-human animals are already, or are likely to experience in the near future, negative impacts on their psychic integrity and well-being as a result of habitat contraction, destruction and climate change. A changing phenology of place is likely to have profound implications for animal psychology. From the early C19 onwards there has been academic speculation on manias, disturbances, delirium, melancholia and psychoparalysis in animals. More recent research on animals in held in captivity and domesticity has noted a range of psychological disorders including stereotypical actions, anxiety and the symptoms of depression. The endemic sense of place held by wild animals is likely to be strongly felt and if threatened, a source of profound distress. Psychoterratic illness such as nostalgia and solastalgia in non-human animals is likely to be just as serious a threat to their mental integrity as that to be found in humans. The emergent field of comparative, interspecies, psychoterratic mental health studies shall be openly explored in this paper.

  7. Pingback: Climate change basics III – environmental impacts and tipping points « BraveNewClimate

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