Climate change, phenology match and the big unknown

This year was crazy in Seville with plants flowering 2-3 months earlier than last year. So we went to sample, and guess what: bees were there too. Despite expectations about phenological “mis-match” are raised here and there, we don’t find a big phenological mismatch between plants and pollinators*. I am not talking here of specific species, but taking a community approach. However, this is not the end of the story. Is good that plants and pollinators are in sync, but this alone doesn’t warrants a healthy ecosystem functioning.

Why not? My main worry is that after a mild January and beginning of February, we have now “normal cold days” again. Consequently, we also find little bee activity (today we are sampling at 14ºC just to make sure this is true). Hence, both plants and bees are likely to suffer. The demographic implications of this are hard to predict, maybe is not a big deal if it happens only one year, but if it happens often, I presume can be quite bad. All in all its hard to quantify, but I suspect that we need to go back to population dynamics if we want to understand climate change impacts beyond phenological overlaps.

*Don’t take this blog as word, there are plenty of good papers showing it (here and here), including my own (here and here), and very little showing a clear mismatch, most of those on specialized systems.

Advertisements

Why do we need to protect bees?

This is a very tricky question. Recent media coverage and policy makers are increasingly using the “ecosystem services” argument to justify the conservation of bee populations. Bees are indeed providing us with a precious service, the pollination of 75% of our crops. However, “bees” are a diverse group of more than 20.000 species. David Kleijn had the wonderful idea to check how many of those bee species are responsible of crop pollination and I was more than happy to help him find out. This is the resulting paper. Surprisingly very few species made most of the crop pollination job. Moreover, those species are the ones of least conservation concern, as I already showed here.

What does this means? We should enhance agro-ecosystems to maximize crop pollination by bees. There is no doubt about this and repeated papers had shown that more green infrastructure enhance pollinator densities and thereby pollination. BUT if we want to protect the bee species that really need our help, other measures and incentives are needed beyond ecosystem service delivery. Those threatened species pollinate wild plants, parasite other bees (potentially regulating populations) or are part of larger food webs. Conserving rare bees and other animals should be done without an economical incentive in mind, otherwise, conservationists selling the idea that biodiversity should be conserved because it provide us with services may end up shooting them selfs in the foot by allowing policy makers to protect only the species that are of any immediate use.

Marking bees with glow-in-the-dark powder

Lab notebook style post to keep record of pilot experiments I run. We used one day this spring to see if we can track what bumblebee queens are doing. We captured queens and applied a colored powder to them. The idea is to see if we can find the powder in flowers after that, to see where and what they visit.

Lessons learned:

  • Capturing queens is time-consuming. 12 queens – 6 hours.
  • Marking them is super easy. Only a tiny bit of powder in the vial is enough. Inside the vial bees buzz and cover themselves completely.
  • First tests with too much powder were bad (bees too covered, see photo below)
  • We used glowing in the dark powder (sold in 8 colors in amazon) in case it helps spot it later with a UV light (also very cheap at amazon).
  • Very few flowers are open at this stage of the year, so we targeted a few Salix at different distances from the marking area along a power line corridor, and look for powder in Salix flowers after 6 hours.
  • We recovered a single flower with powder, but was in a Salix 500m down the corridor (not bad)
  • Not convinced on this technique for queens, but may work better for workers, when you can mark 100’s of bees.

As always we only had bad phone cameras, here is a photo of the first trial with way too much powder used. This bee was seen 1 h. after the release flying happily.Bee_glow

 

Biodiversity insurance hypothesis in the real world

This year is being great and we have another great publication in Ecology Letters. We use long-term plant and pollinator data to show that high levels of biodiversity ensure plant pollinator matching over time despite climate change.

The story behind the paper starts 2 years ago (yes, it always take time!) when we did a paper showing that in general, plants and bees are advancing its phenology due to climate change at similar rates. The problem of this general patterns is that we don’t present data on any particular case study to show how this “general pattern” translates to a given system. My idea was doing a small follow-up using apple orchards as a case study. I ran the first analysis and saw that indeed, apple flowering and bee pollinators are advancing at similar rates. Cool, We can now provide a case study that validates the pattern observed! But then I went further and tried to see what happens when the main apple pollinators are analyzed one by one. Here the things got interesting because some bee species DO show a phenological mismatch with apple, but the total synchrony is stable at the community level because the effects of individual species cancel out. When I showed the results to Rachael, she immediately related them to the biodiversity insurance hypothesis, and we start working on validating this idea. That meant looking for more data, including a simulation, and a lot of fun reading the biodiversity ecosystem function literature. Is amazing how much of what we know relating biodiversity and ecosystem functioning is based on experiments in grasslands, so applying those concepts to real world trophic interactions was intellectually very stimulating. I like a lot the final paper and I am looking forward to work more on this topic, hopefully with less complex data.

More on Pollinator declines

We have a new correspondence article about bee declines that tries to walk the fine line between a non-helping pessimistic attitude about pollinator declines and an unrealistic optimism. As I said before, I think is easier to defend a black or white position about the pollinator crisis, but I think is time to discuss the grey areas. So here I go:

We show two straight forward things. First, that recent papers showing 50% of bee extinctions and papers showing moderate 15% declines (that’s our paper!) are not reporting conflicting results. Is just a matter of scale. Local scale extinctions in heavily altered habitats translate into population declining trends at the regional scale. To read it in positive, we are still on time to revert this declining trends, because the species are there!

Second, we show that not all species respond equally to global change threads, for example some species love agricultural areas. Most important, seems that the species that thrive in crop fields, are the ones responsable of increasing crop production, so the best current ecosystem service providers (a.k.a. bees that visit crops) may be not as threatened as other bees. But please do not take that as “we don’t have to worry at all”. This is the “grey area” where we need to be clear that highly intensified agricultural areas (e.g. huge almond fields in California) may still suffer pollinator shortages. Similarly, we are talking here about crop pollination, but there is a growing evidence that all species are important to maintain (and stabilize) ecosystem functioning in natural areas. So the good news are only partial.

Read it, is a very short piece and is Open access. If someone is curious about F1000Research, just two lines to say that we choose it for the flexibility of formats they allow, the speed of publication and because I was very eager to see how post peer review works. So far we had two very positive reviewers (which made the article indexed in less than 24 Hours!), but no more comments. Is also a short piece so maybe there is not much else to comment?

Native bees buffer the negative impact of climate warming on honey bee pollination

We have a new paper in GCB lead by Romina. In this paper we do a very cool thing. We characterize the daily activity period of a bunch of bee species and how this activity is modulated by temperature. We show that while honeybees decrease visitation to watermelon at very high temperatures (literature suggest that the reason is that honeybees need to go for water more often when hot, hence have less time to visit flowers), some native bees concentrate its visits on the warmer hours. I think that understanding behavioural differences among species is neat to answer BEF questions.

wtbeeIn addition, we play a bit with future temperature scenarios to see if (all else being equal) visitation and pollen deposition will change with warmer temperatures. We show that the visitation reduction predicted for honeybees is compensated by an increased visitation rate by native bees (taken altogether). Despite this predictions should be interpreted with care, it adds up to the several lines of evidence suggesting that conserving all species is needed in order to have flexible ecosystems able to cope with environmental change.

 

 

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: