Taxonomic sufficiency in biodiversity research: Is it always necessary to identify species?

It’s been a successful few weeks in the lab!  Two weeks ago I promoted an exciting paper about spider silk and herbivory and just after that paper come out, another publication from our lab was published, titled: “Does species-level resolution matter? Taxonomic sufficiency in terrestrial arthropod biodiversity studies“.  This paper evolved out of a past graduate-level class in Forest Entomology at McGill, and was re-worked and re-written by post-doc Laura Timms, former Phd student Joseph Bowden, and my colleague Keith Summerville.

Let me provide a plain language summary of this work and I will also touch upon some of the controversy that has arisen because of this paper:

Biodiversity science is about the discovery and description of all the different kinds (species) of organisms living on our planet.  It is a vitally important area of research because different species play important roles in our ecosystems, and as a consequence, are important to us.  The different number of species in an area can also inform us about how we might be harming or helping ecosystems.  This is an active area of study in the context of forestry, since some forest practices (for example, cutting all the trees down in an area) can cause changes in the number of species (and whether they are rare or common) and these changes can inform us about whether our forestry practices are harming our ecosystems.  All of this kind of work, however, depends on the ability of scientists to collect, sort, and identify different kinds of species.  Since most described species on the planet are Arthropods (e.g., spiders, insects, and their relatives), these animals are often used as a way to indicate how biodiversity might be affected by environmental change.  However, there is a problem: it takes a very long time to identify different arthropods, and it is costly and difficult – requiring highly specialized training, by people known as taxonomists.  In our research project, we asked whether not you always need to know the exact differences between insects and spiders  in order to tell if a disturbance is affecting biodiversity.  We did this by looking at a series of data-sets about beetles (Coleoptera), moths & butterflies (Lepidoptera), and spiders (Araneae). These data-sets were from past research projects about how forest disturbance affects biodiversity.

Here is how we did the work: Different kinds of organisms are classified using a two-part name:  the genus and the species.  There can be many different species within one genus.  You can then classify different genera (the plural of genus) into grouping called Families.  For example, all wolf spiders are in the Family Lycosidae.  A common genus within this family is Pardosa – there are dozens of species of Pardosa in Canada; Pardosa mackenziana, Pardosa moesta, Pardosa hyperborea, etc.  We first took our big data-sets and using the lowest level of naming (the species) we asked whether forest disturbance affected biodiversity.  We then grouped all our species into their respective genera -this meant that the data-sets got smaller (i.e., there are necessarily fewer genera than species).  We did the same analysis to see if we could still get a signal about the effects of disturbance on biodiversity, but now with the ‘reduced’ data.  We did this again at the family level.  We did this because we wanted to know if you could take a short-cut. Stated another way, if you don’t have the time or ability to figure out all the species in your research project, can you still see if there is an effect of forestry on biodiversity?

A wolf spider (Lycosidae)

A wolf spider – do you need to know its name?

Our results showed that in most cases, you do not need to know the species identity to see the effects of forestry practices on the biodiversity of spiders, beetles and moths & butterflies – you do not get as clear answers when things were grouped into Families, but the datasets with species grouped into genera were almost as good as when you group things into species.  This was surprising, because an assumption in biodiversity science is that species-level identifications are necessary and should be the ‘gold standard’ for this kind of research.  We showed that in many cases, you can get your answer by identifying arthropods to the generic level:  this can save you a lot of time (and money).   Some researchers (including taxonomists) may not be thrilled with this result as it might suggest that species are not important, and specialized taxonomic knowledge is not essential to complete biodiversity research.  This is certainly not the case, which leads me to the caveats:

1) Our results do not mean species are not important!  Instead, we are saying that if there are logistical and financial constraints, you might be able to answer your research question without having to identify all the species.   If you have a project about large-scale disturbance and are looking to see whether there are any broad affects on biodiversity, our approach might work.   However, you might miss some subtle effects, so this approach must be taken with caution.  Although our suggestion is a short-cut, it would still be important to save all the samples, and at a later time (as money and expertise permits) the species could be determined.

2) Our study is specifically geared towards research about insects and spiders in relation to large-scale forestry disturbances.  We are not saying that this will work in all situations and with all different kinds of organisms! The context is important.  Related to this, if an overarching research question is about species in an ecosystem, species-level identifications are essential.  Everything depends on the research question and the research context.

3) This general approach that we have discussed is highly dependent on what kind of organisms you are studying.  If you are working with a group of organisms that do not have too many different species within a genus, our approach may work.  If, however, there are many species within a single genus, our suggestion will not work as well.  Therefore, a researcher should look at the general relationship between the number of species per genus for their study organisms and use this ratio as a guide when thinking about taking the short-cut that we discussed in the research.

In sum, we are quite excited about this research – we think it will provide more opportunities for biodiversity projects to get done, and will help answer certain research questions when there are substantial constraints on time and money.  This is one way to be pragmatic about biodiversity research.

Please share your thoughts!

Reference:

Timms, L., Bowden, J., Summerville, K., & Buddle, C. (2012). Does species-level resolution matter? Taxonomic sufficiency in terrestrial arthropod biodiversity studies Insect Conservation and Diversity DOI: 10.1111/icad.12004

A walk in the woods

Last week I had the opportunity to visit my PhD student Dorothy Maguire at her field sites south of Montreal.  It was a glorious summer day, and given the construction holiday in Quebec, the travel time was quick and effortless (for Montrealers, you know what I am talking about!).  I have briefly described Dorothy’s research in a previous post, and during the field visit, I was able to see Dorothy and her two field assistants ‘in action’.  This included checking samples from an aerial malaise trap, beating the foliage (for herbivores) in the forest canopy, and checking contents of a Lindgren funnel (set up in the canopy to collect flying insects, including beetles).

Thomas and Camille checking the contents of the aerial malaise trap

It was an amazing day for natural history.  In fact, I sometimes think my graduate students cannot stand spending time in the field with me, since I tend to walk slowly, vial in hand, stopping all the time to pick up a spider or beetle, or to turn over a log to search for pseudoscorpions.    I’m probably much more of a burden than a help in the field, and this probably leads to some resentment (ha ha).

Anyway – it was great to get into the forest again after time in the Arctic, and I was thrilled at all the biodiversity starting me in the face.

What did I see?

A dozen or more species of trees, including shagbark hickory, ironwood, and the usual suspects (American beech, sugar maple, red maple, some oaks)

Some stunning underwing moths (Catocala) (although they were somewhat less stunning than usual since they were dead, in a Lindgren funnel!)

The BIGGEST horsefly that I have ever seen (probably Tabanus atratus).  Yikes – I captured it before it bit me – it could have hurt.  A lot.

The big, nasty horse fly (Tabanidae)

Butterflies, butterflies, butterflies!  Including the beautiful great spangled fritillary (Speyeria cybele) and the northern pearly-eyed (Enodia anthedon)- the latter is one of the few shade-loving butterflies in this part of the world

Hundreds of sap beetles (family Nitidulidae) – these were very common in the aerial malaise traps, but were also flying into us much of the day

Some GIANT Scarabaeidae beetles – I don’t know the species but they were robust and impressive; masters of their universe.

Dozens of Harvestmen (Opiliones), which I later identified as Leiobunum aldrichi – I have now started a colony at home (much to my children’s delight).

Female (l) and male (r) Gypsy moth, caught in the act.

Gypsy moth (Lymantria dispar) – a lot of gypsy moth.  This species in an invasive, introduced species.  Gypsy moth caterpillars can feed on hundreds of species of trees, including our beloved Sugar maple.  This is one species that I am not happy about seeing, and its numbers this year are certainly higher than last year.

And to top it all off.. Antlions (Neuroptera: Myrmeleontidae).  Yes, Antlions!!  These are among the most fascinating of the insects -the larvae build conical sand-pits and await ants that happen to slip into the pit and fall down into the waiting predator.  I have lived in the Montreal area for over 10 years and I had no idea that Antlions existed this far north.  Wow.

Quebec Antlion “trap”, photographed just south of Montreal

This is only part of the list, but one thing is clear – a hot, mid-summer day in a Montreal-area forest is full of the wonders of Nature.  I didn’t have to look very far, and I didn’t have to look very hard.  Furthermore, most of what I mentioned was all from a rather small forest fragment surrounded by agricultural lands.   We must study, document, quantify the biodiversity within these forest fragments – they are very special, and they host a diverse and fascinating flora and fauna.

 Take a walk in your local woods, and see what you can find under leaves, bark, climbing up trees and catching a few rays of sun in a small clearing.  It’s a nice way to spend a summer day.

Holistic views of ecosystems: linking salmon and butterflies

Beautiful Anchorage, Alaska

I’ve spent most of my week in beautiful Anchorage, Alaska.  I was attending a workshop that brought together scientists from Northern countries to discuss an Arctic Terrestrial Biodiversity Monitoring Plan. The goal of this ambitious plan is to include all key taxa, include all northern countries, and find ways to standardize methods and harmonize data.   There were a half dozen bird experts around the table, numerous experts on Arctic vegetation, a large contingent of mammal experts, and one arthropod expert (me).  This is a situation I have been in before, and will be in again in the future – largely because arthropods are not “charismatic” nor do they typically fall into management plans.  Regardless, I welcomed the opportunity to discuss ways that Arthropods can and should fit into large-scale, and long-term monitoring plans in the Arctic (there are, by the way, some tremendous arthropod monitoring programs underway – the Zackenberg research station in Greenland, for example, has been collecting arthropods using standardized protocols for almost 20 years)

The workshop was exciting, challenging, motivating, and overall a wonderful opportunity to discuss the interdisciplinary concept of biodiversity monitoring.   A great example of an interdisciplinary approach was a presentation we heard about using traditional knowledge to understand the Natural Indicators of the Salmon run in the Yukon River, a river that drains out to the ocean in Alaska. This was organized/facilitated by the Yukon River Drainage Fisheries Association.  This presentation highlighted a project where Elders were asked about what helped them understand the Salmon run in the river – a critically important process for people living in this part of Alaska.  I was amazed to hear that for some Elders, the appearance and activity of certain species of butterflies (and sometimes biting flies) was one of the indicators that was used to predict when the Salmon would run.

An Arctic Butterfly

Yes, you read correctly: Butterfly activity indicates the Salmon run.   The claim that activity of insects relates to the Salmon run is not a direct connection as the insect activity was considered as a “Correlative indicator”.  The observation is that when certain insects appeared and were active, so were Salmon, hence the correlation.  This does make some biological sense as many of the environmental factors affecting butterflies are probably also important to salmon.

The Yukon River Drainage Association went on help to produce a children’s book titled When Will the Salmon Come?. This is a richly illustrated, beautiful book that discusses all the Natural Indicators that Elders use to know when Salmon will appear on the river, and the insect activity is highlighted.   A children’s book is a wonderful way to connect with a broad audience.

When will the salmon come? (the book cover)

Being a skeptical scientist, I went and searched the literature for anything ‘published’ on the topic of Salmon and butterflies, and I could not find anything.  This does NOT mean it’s not a real and important observation. It means that it is a truly fascinating and curious correlation that was observed by Elders living close to the river, and by people who likely approach nature from a holistic standpoint.  I need to do this more; we all need to do this more. Natural systems are interdisciplinary yet we often study them in silos, defined by a specific taxon or system.

In sum, I was most pleased to be the lone entomologist in a large interdisciplinary workshop  about biodiversity monitoring in the fragile Arctic – my horizons were certainly broadened.  The story of butterflies and salmon made me take a step back and consider how different groups of people can bring different perspectives and all are equally valid.  In other words, keep an open mind, and think of this story when you see some butterflies passing by…they could be telling you an important story – you just have to listen.