A delay, lots on the horizon!

There is a special issue coming out in Climate of the Past on Holocene climate changes in the central Mediterranean (here).  I’ve been involved with a number of the researchers for some time (and have commented on the serendipity of this relationship on this blog) and am pleased to have worked on several of the papers, although only one has made its way through the full review process (Joannin et al., 2013).

The papers resolve a longstanding conflict among records from the central Mediterranean, place regional Holocene climate changes into the context of global climatological systems and anthropogenic effects, explore several new multi and single proxy records from lake and marine sediments, and, ultimately, establish a synthesis.  But you’ve got to wait for that a little bit longer.

Figure 1.  The Cladoceran Daphnia.  Cladocerans may more broadly be useful for climate reconstruction if the results of a new study hold.
Figure 1. The Cladoceran Daphnia. Cladocerans may more broadly be useful for climate reconstruction if the results of a new study hold.

In other news, hey, there’s a new paleoclimatic proxy to use!  The Journal of Biogeography has an interesting early view article by Nevalainen et al. (here) about the use of Cladocrea as a climate proxy in Finland.  They fit GLMs to species response curves along climatic gradients and find good fit for a number of taxa.  I’m actually surprised, Hann, in the famous Methods in Quaternary Ecology, suggests that they’re not a particularly reliable climatic indicator (here) due to their strong relationships to the local aquatic environment (arguing that that local environment buffers climate change), but I’m willing to be swayed.

Once the special issue is released I’ll write more about climate in the central Mediterranean, and I’ve got good feedback on a paper we submitted recently, so I’ll be more productive on downwithtime soon.  Keep reading!

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Assistant scientist in the Department of Geography at the University of Wisconsin, Madison. Studying paleoecology and the challenges of large data synthesis.

4 thoughts on “A delay, lots on the horizon!”

  1. Simon, I need to read the paper, but I seriously doubt Cladocera have much use as a palaeoclimate indicator if by that one means as a proxy to derive quantitative temperature (related) information. These things respond to a wide range of factors some related to climate, many not, and I doubt many of these species are thermally restricted. Instead I wouldn’t be surprised if this was spurious correlation. Happy to be proved wrong, but from the information in the abstract I see nothing that would convince me otherwise.

    1. It looks like it’s not an assemblage level relationship, but rather a taxon by taxon relationship, so the general rule that they represent local environmental factors (that are buffered by broad-scale climate fluctuations, as suggested by Hann) could hold true. You’re such a pessimist! 🙂

      1. [Sorry, this is long…and not well structured…]

        They express everything as % relative abundance – and hence the values for one taxon are *not* independent of the others.

        They don’t have data on anything but gridded July temperature, elevation, lake area and sampling depth – so exactly how do they establish that the responses they claim to find in the data are unique climate effects sensu Juggins (2013)? When they do use subsets of data where they have some other limnological variables, there are strong explanatory variables exerting considerable influence on cladoceran composition – see the DO % variance explained in Table 2 (quite why this is labelled cumulative % variance explained is beyond me – each row, according to the table caption, is a separate RDA estimating the marginal effect). So out of 4 limnological variables present across the entire data set lo and behold they find July temperature the only one that is significant; well, you could have predicted that from just knowing the variables they *do* use. Their lakes vary massively across the geographical extent of Finland. Within regions elevation, sampling depth, area will vary and hence have noisy signals that don’t change consistently across ecoregions. July temp does, and so it comes out as significant but it is a surrogate variable encapsulating broader ecological and lake-type variation that is only partly related to a direct temperature effect.

        Their GLMs seem odd – you have a % relative abundance variable yet model it with a Poisson GLM? They don’t say what link – the true Gaussian model is fitted as a Poisson GLM with a log link, but that is for *abundance* data IIRC. Also, because they fitted these in Canoco and not a proper general purpose stats package, they don’t present residuals, confidence intervals etc that might allow us to judge whether these models are useful or not.

        Similar studies have also found a temperature effect on Cladocera – e.g. the Lotter et al study from the Swiss Alps. That data set was deployed at Krakenes to reconstruct temperature (alongside Chironomid-inferred temperature). Of the proxies used to “reconstruct” temperature in the synthesis study of Hilary Birks and colleagues, the cladoceran response was the most muted of the reconstructions. The broad pattern suggested some change, but you’d expect that just because the species composition had shifts in dominant taxa resulting from changes in the lake that whilst climate driven can easily be explained by other in-lake processes and changes in nutrient and habitat availability.

        The authors acknowledge this in the discussion stating:

        “The results shown here are not necessarily a reflection of direct temperature control, yet confirm the importance of temperature-associated limnological factors, such as nutrient availability and habitat quality (cf. Chen et al., 2010; Richard Albert et al., 2010). Although the results suggest that T July is an important forcing factor in shaping cladoceran communities across Finland, the wide variation in placing of the warmer study lakes along RDA axis 2 (Fig. 4a) implies that other limnological factors are major contributors to the distribution patterns observed (Table 2).” Nevalainen et al (2013, inpress)

        Many of the taxa they identify as representative of cold northern lakes are commonly found in nutrient poor temperate lakes – I found all those taxa in my UK lake training set from oligotrophic, circumneutral to acid lakes. So are the cladocerans responding to temperature or a complex of variables associated with nutrient availability, water colour/humic acids, plant-mediated habitat complexity… etc?

        The authors acknowledge that many species they pick out are strongly associated with aquatic macrophytes. It is widely acknowledged that plants play a strong role in shaping cladoceran assemblages through the structuring role they play in partitioning the water column into habitat parcels, providing refugia etc. Plant cover and type will be strongly correlated with their temperature gradient. We might reasonably ask therefore whether the identified “temperature” responses are not just a reflection of the changes in the plant cover/composition? It would be less controversial to note the thermal tolerances/limits of aquatic macrophytes than to ascribe the same tolerances/limits to Cladocera.

        Why not explain the observed results as Cladocera responding to changing nutrient availability and habitat structure/availability (which are being mediated by climate) than true temperature responses in these species? Well, they don’t have the data to show that this is a unique, temperature effect or to rule out complex correlated responses. And if you accept that these variables that can (and do) change independently of temperature, what utility this group as indicators of past, present or future climate?

        It is interesting that one acknowledged “cold-tolerant” taxon that I had heard of before (Acroperus harpae) doesn’t show up in their analysis… except as a “eurythermic” taxon!

        It is hard not to identify this work with the notion of “sick science” that Steve Juggins bemoans in his recent QSR paper. Where is the rigour in demonstrating the temperature effect independent of other important factors? Yes their equipment broke, but you can take a water sample and measure things in the lab, etc. Or if you don’t have the data to fully support bold claims, you don’t make bold claims – especially when they go against a lot of the existing knowledge of what structure cladoceran assemblages.

      2. You should just copy this and post it to your site, it’s a great breakdown of the paper. I was going to write up Steve’s paper in another post so maybe I need to get started on that.

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