Food webs: reconciling the structure and function of biodiversity. Really?

I read this paper (Food webs: reconciling the structure and function of biodiversity; Thomson et al. 2012 Trends in Ecology & Evolution, 27(12):689-697) with great interest because the title is really promising. Indeed it is nice overview of what’s out there in terms of network and functioning, but not much reconciliation. First I have the feeling that community ecologists (even if they don’t use network metrics) are already (and have been for a long time) on the framework they describe in Table 1C. But my main concern is that I missed an answer to the question: What can a network approach add to the study of ecosystem functioning?

Well, I have two ideas that can help answering that.

1) Network approach can be very useful when the function itself is defined by the network. If you are studying pollination or pest control, the actual function delivered is contained in the network structure, hence species richness, diversity or composition (or new metrics, like FD) can be unable to fully explain functionality  because what confers high levels of function (or stability) to the community is the network properties (e.g if it’s modular, generalized or well connected). I know some pople is on that path, so I am looking forward to see what they find.

2) Another situation where networks can make the difference is when indirect interactions modulate the function, but are too complex to track them one by one. Networks can describe better phenomenons like apparent competition or cascading effects than any other classical approach. If this type of complex interactions are relevant for the level of functioning measured (e.g. productivity of the basal level), then, adding the network perspective can be more informative than classical approaches.

May be what I am saying is too obvious, so the authors didn’t cover it, or I may be missing something, but this is the direction I would like to see things moving.

Is there a pollination crisis?

After some months writing this blog, finally I can do some self-promotion and post about our new article just published in PNAS.

Do you think we are experiencing a pollinator crisis? Take note of your answer and keep reading.

In this paper, we show that most Northeastern US bee species persisted along the last 100 year. And those are 100 years that has transformed the landscape dramatically. However, we show that community composition changed markedly. The loser species are some big species, often specialists and with short activity periods. See a quick figure I made trying to capture the essence to outreach people who only have one minute to spare.

BartomeusPNAS

So, what that tell us about a possible pollination crisis? A crisis is something that leads to an unstable and dangerous situation, in this case regarding the fate of pollinators and the service they deliver. Nobody talks about a bird crisis. Some bird species are doing great, some are threatened with extinction, but nobody would dare to generalize about the fate of all bird species as a whole. I think is time we take the same approach with such a diverse group as the pollinators (including bats, birds, butterflies, bees and a long etc…). In this paper we show that some bumblebees (e.g. Bombus impatiens) are doing great, while others are on the brink of extinction (e.g. Bombus affinis). We need to understand better species responses and stop crying wolf for all pollinators. There is a fine line between raising general aware among citizens about the importance of pollinators and their conservation and an overestimated alarmist call. Every time a farmer reads about the pollination crisis while seeing that his field is full of bees buzzing around, we (scientists) are loosing credibility.

Moreover, if is crop pollination and food security what concerns you, it may be that the winner pollinator species, those that thrive in human dominated landscapes, are also the best ecosystem service providers. And if it’s biodiversity (and its overall functioning) what you want to protect, then we should look at which species/habitats needs maximum conservation. We need to move forward and pose the relevant questions, instead of looking for a general declining pattern that hopefully is not really there.

I am expanding too much for my taste, so more on that next week. But to make clear my point: we need to keep studying pollinators (keep funding me!), but next time you cite worldwide pollinator declines, cite me also (i.e. Pots et al 2010, but see Bartomeus et al 2013).

Bartomeus I., Ascher J.S., Gibbs J., Danforth B.N., Wagner D.L., Hedtke S.M. & Winfree R.  Historical changes in northeastern US bee pollinators related to shared ecological traits, Proceedings of the National Academy of Sciences,   DOI:

*Giving the importance of the subject, it was specially important for us to make all historical bee data available @datadryad (dx.doi.org/10.5061/dryad.…) for further analysis and replicability.

We know nothing

Today I read a paper about bee population dynamics published in Ecology (Franzen and Nilsson 2013). Given the current concern about bee declines (more on that in a few weeks) one can assume we (scientists) understand the basic dynamics of bee populations, or at least we have an idea of their life histories. Well, the paper monitored one metapopulation of one species during 9 years and found that fluctuations on the number of nests among years are huge (more than one order of magnitude). Why? We don’t know and It is not correlated with floral resources or climate. Some speculations include source-sink dynamics, a prolonged diapause or bet hedging strategies to avoid natural enemies. We know nothing. And you may ask, why is this published in Ecology? Well, because I think is a good paper that at least shows some data. That means that given the knowledge we currently have, this tiny bit of information advances our understanding.

Really basic research is not sexy but can we (and I am the first guilty) understand a pollinator crisis if we don’t know if it is predation or it is competition what is driving bee fitness. Or can we understand the actual structure of plant-pollinator networks, which are characterised by an incredible turn over among years, without knowing if bed hedging strategies are the norm or the exception (Danforth 1999). Can we assess the effect of landscape configuration on bee populations without the basic natural history information like eggs per female, or growth rates?

Image

Franzen M. & Nilsson S.G. (2013). High population variability and source-sink dynamics in a solitary bee species, Ecology, 130204095918002. DOI:

Why analysing your data is like being in a romantic relationship

Last year I was working on a big dataset to assess how bee phenology has changed over time. Here it is the first cool figure I produced. I was quite excited so I didn’t even bother to make beautiful axes.

I am pretty sure the stats I finally used changed quite a lot, and I also added many more data points before publishing the results (it toke me a year to sort out all details), but the main result held. Bees are emerging earlier in recent time periods that they used to emerge. The final published figure looks like that:

While cleaning my computer today, I realised that my first plot looks way more colourful and exciting than the final figure I ended up publishing. Then, I remembered a text I wrote about analyzing data…

“I almost forgot the fun of first analysis when everything is new and exciting, when you want to know everything about “data” and you learn from “her” everyday… it’s a shame that after that it becomes repetitive and monotonous. You’ve lost the magic, but on the other hand, it’s also nice to really get to know each other, you gain compromise and confident results.”

So maybe my own plots can prove I was right, and Data analysis is like a love story. Are your first drafts also more pasional than the final version?

 

keep up with the literature…

sciseekclaimtoken-50660e34020be

I just find a 2009 paper I missed. How many of those will be out there? I did a commentary (Bartomeus & Winfree 2011) last year on how to track bee movements along different habitats. I did a quite intense literature research and I still missed this very relevant paper (Brosi et al 2009). Sorry, I have no excuses for not citing the paper on the commentary, and despite is true that I don’t usually read that Journal, I like a lot the first author work, so here my little amend:

I would like to have highlighted the paper in my commentary because despite the promising ideas it contains, no advance has been made in this direction in the subsequent years. Maybe other researchers missed that paper too? The paper propose using stable isotopes to track habitat use by pollinators. Despite the known correlation between habitat structure and pollinator diversity and abundance, little is known on which habitats use different pollinator species and specially in which proportions. This knowledge is important to understand the effect of land use change on pollinator persistence, but can be used for answering multiple questions ranging from ecosystem services to pollinator population dynamics. The main limitation faced by researchers so far is the inherent difficulty to track individual specimens movements.

The goal of the paper is to utilize the naturally occurring differences in isotopic composition among habitats to characterize habitat-based bee foraging changes within a landscape context. In this case they characterize the use of agricultural or forested areas. The researchers found a significant relationships between the carbon and nitrogen isotope signals on bees depending on the season, the landscape context and the local biotic context. Though they could not estimate proportions of different habitat uses due to high variances in the stable isotopes signal, they claim that this important step can be achieved in other systems. If so, the ability to calculate isotope mixing models (which estimate the proportion of different habitats use) would be useful for most investigations of pollinator foraging in the context of ecosystem services.

References:

Bartomeus I., Winfree, R. (2011) The Circe Principle: Are Pollinators Waylaid by Attractive Habitats? Current Biology 21(17): 653-655

Brosi, B.J., Daily, G.C., Chamberlain, C.P. & Mills, M. (2009). Detecting changes in habitat-scale bee foraging in a tropical fragmented landscape using stable isotopes, Forest Ecology and Management, 258 (9) 1855. DOI: 10.1016/j.foreco.2009.02.027