A naturalist and his moquitoes

This is another in the “meet the lab” series – here’s a feature by MSc student Chris Cloutier:

I can’t remember a time when I wasn’t fascinated by the world of creepy crawly things. For as long as I have been able to grasp and crawl I have been collecting and observing insects and spiders. Although my mother wasn’t always fond of the critters I would trek through the house, my parents were very supportive of my curiosities and did their best to nurture my interests. As a family we would go camping and fishing often, introducing me to the world outside of our backyard and ultimately landing me where I am today.
My passion for studying insects began many years ago with my first entomology course in CEGEP. After completion of that program I enrolled at Macdonald campus of McGill University. Before I even started my first semester I got my first real taste of applied entomology, when Chris Buddle hired me for several months during the summer to be his field and lab technician. Let’s just say that from that point onward I was hooked.

While studying at Mac I really started to discover where my interests were in this very diverse field. I was intrigued with the ecology and natural history of insects and the amazing things that they do. I really enjoyed learning about insect-human interaction, and for some reason I was very interested in disease transmission and parasitism and the amazing enzootic pathways they can take.

Chris Cloutier: the man, the naturalist, the legend.

Chris Cloutier: the man, the naturalist, the legend.

My Master’s research began in early 2014. I had been working for several years at the Morgan Arboretum, a forested property owned by McGill, when my employer, and now co-supervisor, Dr. Jim Fyles approached me with the idea of performing some graduate research using the Arboretum as a study area. I jumped at the idea of doing this, and we got Chris Buddle on board right away. My thesis will be analysing the temporal variation of mosquito community composition across a habitat gradient which includes suburban areas, fields and various forested sites within the Morgan Arboretum. One of the reasons for this research is the fact that in many suburban and forested areas around Montreal, mosquito densities reach near intolerable levels during the summer months. This, coupled with the increasing number of cases of arbovirus (arthropod-borne viruses) infections, such as West Nile Virus, the importance of understanding where mosquitoes are located, and when, as well as which species are present is becoming more and more important.
Collection of mosquitoes takes place for 24h once a week for the entire frost free period, typically from April to November in Montreal. The traps I use to collect mosquitoes are quite specialized and are designed to capture only females which are seeking a blood meal (the ones that we worry about on our strolls through the woods!). These traps use a combination of LED light and carbon dioxide to attract the insects. The LED lights draw in mosquitoes from quite some distance, and the CO2, produced with the help of a few kilograms of dry ice, draws them ever closer to the trap. Once in range, a tiny fan sucks them into a mesh catch-bag and they are trapped.

Chris in the field, checking a trap.

Chris in the field, checking a trap.

When not out in the field, I spend most of my time with my eyes firmly attached to a microscope, sorting, identifying, and counting mosquitoes. After my first field season, I have collected just over 43,000 mosquitoes representing 9 genera and approximately 28 species. I am now faced with the task of analysing the data and making sense of all those numbers, which in fact has revealed some interesting patterns already. I’m looking forward to heading out next spring to start all over again.

The hard work.

The hard work.

I consider myself to be a “geek of all trades” with interests in everything from birding, to plants, herps and pretty much everything in between. I rarely leave home without my binoculars, and during the summer I almost always carry some vials, an aerial net and several field guides (yes, I often get some strange looks…). I’m also a husband and more recently, a father too. My wife still hates mosquitoes but I feel her coming around slowly, and my daughter doesn’t know it yet, but she will be spending an awful lot of time outdoors with us.
Follow me on twitter @C_Cloutier15 or email me at christopher.cloutier@mail.mcgill.ca if you would like to know more about what I am up to and how things are going with my research.

Studying natural history by stealth

Natural history can be defined as the search for, and description of, patterns in nature. I see natural history research as a more formal and structured approach to studying and recording the natural world. I also see this kind of research as a branch science that is often driven by pure curiosity. Many well-known and popular scientists are naturalists (ever hear of David Attenborough or E.O. Wilson?), and we can see that curiosity is one of the underpinnings of their work and personalities. Natural history research is, without doubt, very important, but in world of academic research, it sure doesn’t headline as pulling in multi-million dollar grants, nor does “natural history” appear in the titles of high profile research papers.

Is there a place for curiosity-driven natural-history research in today’s science? If so, how do we study it in the current climate of research?

Arctic wildflowers. Worthy of research... just because?

Arctic wildflowers. Worthy of research… just because?

This is big question, and one that we grapple with occasionally during my lab meetings. Most recently this came up because I challenged one of my students when they wrote about how important their research was because “…it hadn’t been done before“. In the margin of their work, I wrote “…so what? You need to explain how your work advances the discipline, and the explicit reasons how your research is important independent of whether or not it has been done before“.

Am I wrong? Is it acceptable to justify our research endeavours because they haven’t been done before?

The context matters, of course: some disciplines are very applied, and the funding model may be such that all or most research is directed, project-oriented. The research may have specific deliverables that have importance because of, perhaps, broader policies, stakeholder interests, or needs of industry. In other fields, this is less clear, and when working in the area of biodiversity science, such as I do, we constantly stumble across things that are new because they haven’t been studied before. And a lot of these ‘discoveries’ result from asking some rather basic questions about the natural history or distribution of a species. These are often things that were not part of the original research objectives for a project. Much of natural history research is about discovering things that have never been known before and this may be part of the reason why natural history research isn’t particularly high-profile.

Here are just a few examples of interesting natural history observations from our work in the Arctic:

This is the first time we observed the spider species Pachygnatha clerki on the Arctic islands!

Wow, we now know that an unknown parasitoid species frequently parasitizes the egg sacs of a northern wolf spider species!

Females of this little pseudoscorpion species produce far more offspring than what had been previously documented!

Now, if I wanted to follow-up on any of these observations, I think it’s fair to state that the research would be curiosity-driven, and not necessarily grounded in a theoretical or conceptual framework. It’s the kind of research that can be rather difficult to get funded. It’s also the kind of research that is fulfilling, and a heck of a lot fun.

I'm likin' these lichens. And surely data about them is required...

I’m likin’ these lichens. And surely data about them is required…

How then do you study such fascinating aspects of natural history? How do you get out to the field to just watch stuff; record observations just for the sake of it; spend time tabulating life history parameters of a species just because it’s interesting?

Perhaps you have the luxury of doing natural history research as your full-time job: You may be able to sit back and have people send you specimens from around the world, and maybe go out on an extended collecting trip yourself. You may be lucky enough (and wealthy enough?) to devote serious amounts of time to “think”, measure and record data about species. Perhaps you can even take a long walk each day to mull over your observations. Maybe you will gather enough observations to eventually pull together some generalities and theories, and perhaps you will get around to writing a book or manuscript about this….

Reality check: Most of us don’t have that luxury. Instead, we chase grants, supervise students, do projects that fit in with our unit’s research area, and publish-or-perish in the current model of academic research. Despite how we might long for the “good old days” of academia, they are gone (at least in my discipline). It’s rare that a University Professor or research scientist is hired to do stuff just to satisfy her or his own curiosity.

That main sound depressing to some, and hopeless, but it’s not meant to be. I do believe there are still ways to do exciting and interesting natural history research, and we can call it research by stealth.

In my field of study, establishing a research programs means getting grant money, and these are often aligned with priorities that matter to government, to policy, or to a particular environmental threat such as climate change or invasive species. It’s important to get these grants, and work with students and collaborators to try to solve some of the large and complex problems of the world. I am not advocating avoiding this. Instead, as we move along with these big projects, there are also countless opportunities to do a little natural history research, by stealth. Our first priority may not be the collection of natural history data, but nothing stops us from finding creative ways to make careful and meaningful natural history observations.

When taking a lunch break on the tundra, take a little longer to watch the Bombus flying by, or write down some observations about the bird fauna in your local study site, even if you aren’t an ornithologist. Keep a journal or sketch a few observations while you are sitting in the back of the field truck on that long drive up to the black spruce bogs. Each year, buy a field guide for a different taxon, and learn new stuff alongside your focused project. This ‘spirit’ of natural history observation is one that I promote to my own students, and I encourage them to follow up on some of these as a side-project to their main thesis research. Often, these end up being published, and end up in a thesis, and they certainly end up informing us more about our study species or study area.

Lunch break on the tundra: an opportunity for natural history observations

Lunch break on the tundra: an opportunity for natural history observations

Despite writing all of this, I still think my comment in my student’s writing will remain: we have to look at the importance of our research in the context of the bigger picture – it’s not enough to say something is important because it hasn’t been done before, and I’m not sure a PhD thesis can (or should) be entirely based on natural history observation. I would not be doing my job as a supervisor if I promoted curiosity-driven natural history research as the top priority for my student’s projects. To be candid: they won’t get jobs or publish papers in the higher profile journals (i.e., those ones that matter to search committees), and they won’t be well equipped when they leave my lab and head to another institution.

…But I will promote natural history research by stealth.

I think there is loads of room for curiosity-driven natural history research in today’s science. We may need to be creative in how we approach this, but, in the end, it will be worth it. We satisfy our curiosity, and learn a little more about the world along the way. We will also gain perspective and experience, and my students will be well equipped for a future in which natural history research is valued more highly then it is now.

Meet the lab: Elyssa Cameron

Here’s another in the “Meet the lab” series – written by Master’s student Elyssa Cameron.

Like many in my field, my love of nature and the creatures which inhabit it began much earlier than I can remember. From camping trips to day camps to museums and everything in between, I have always been passionate about understanding the world around me. Whether I was catching butterflies, trying to identify an elusive bird, exploring a new place or simply basking the in the beauty and wonder of an unaltered landscape, I knew that I wanted to be an advocate for nature.

Elyssa

Elyssa Cameron, with a furry friend.

In 2011, this led me to pursue an undergraduate degree at McGill University in Environmental Biology, specializing in wildlife. Here I learned the skills and thought processes that would help guide me on my journey. This is also where I feel in love with ecology and ecosystem dynamics. I was humbled by the enormous web of complexity which governs our world and sought to discover where exactly my interests lay. My search took me to South Africa, where I spent 3 week learning about wildlife management, game ranching, governance of national parks, and the challenges in maintaining healthy, safe, sustainable populations and ecosystems. It was during this trip that I realised that the management and conservation of any ecosystem needed to rest upon a solid understanding of the ecology of the system as well as the interactions of individual species, between different species and between species and their environment. Without this basic knowledge of how something works, one cannot hope to protect it.

giraffe

With this newfound drive for management and conservation through a better understanding of ecosystem ecology, I signed on to do a Master’s project with Chris Buddle (McGill University) on arctic arthropods in 2014. Having never truly worked on insects and spiders before, I knew such an undertaking would be a challenge; but one that I was excited to take on! The aim of this project is to establish a more comprehensive long-term ecological monitoring program in Cambridge Bay, Nunavut, by linking patterns of vegetation and habitat diversity to arthropod diversity. In this way, we can examine the arctic ecosystem in a more complete way and not as a series of individual pieces. This will allow for more effective management in this rapidly changing ecosystem and will hopefully provide more predictive power for models and policies.

However, to obtain these baseline conditions, we must first collect the data. This took me on my second great adventure – a summer in Canada’s high arctic! For those of you who have not yet experienced the vast and diverse beauty of Canada, it is something I cannot recommend enough. But be forewarned, there are LOTS of bugs – which was great for the Bug Team! Working in association with CHARS (Canadian High Arctic Research Station) the Bug Team was part of a unit of researchers set on better understanding the arctic ecosystem and promoting interdisciplinary collaboration. We sampled spiders, flies, beetles, wasps and others to try and get the most complete view of the species diversity and community structure as we could in such a short summer.

Arctic

Elyssa’s Arctic Adventures!

While there, we also did a number of community outreach programs to try and get the locals interested in science. We participated in a science night, made insect and butterfly collections to leave at the high school and Sarah Loboda (one of my wonderful lab mates!) organized day camp activities for the kids.

Now back at McGill, I spend most of my days in the lab looking through a microscope. With the general sorting of samples now complete, I am about to embark on my biggest challenge yet: species identifications! Both scary and exciting; but with the great support system here, I’m not worried.

As of January, I will also be co-supervising an intern from the Vanier Wildlife Technicians program with Chris Cloutier (the lab’s resident mosquito expert).

Trophic cascades in fragmented forests

Many birds eat insects and spiders. Some of these insects and spider are themselves predators, feeding on critters lower down in the food web. Some of the insects that are fed upon by birds, or other predators, also play important roles in forest, such as munching upon the fresh, green leaves of young trees (here’s a reminder).

Munch, munch, munch. The hungry caterpillar. (photo by Sean McCann, reproduced here with permission)

Munch, munch, munch. The hungry caterpillar. (photo by Sean McCann, reproduced here with permission)

These interactions are ongoing, all the time, in forests around the world. These forests, however, are changing in important ways. Some of them are getting smaller and smaller as humans continue to encroach on the land, via urbanization or agriculture. This results in a ‘fragmented’ landscape. A landscape with small forest patches, perhaps no bigger than your back yard. A landscape with larger forests, perhaps one in which you could get lost in. These forests are themselves connected to each other –sometimes directly by a corridor or hedgerow.

This is the context for PhD student Dorothy Maguire’s research. Within that context, Dorothy tackled a fascinating project, one that was just recently published. In this work, Dorothy and co-authors (including me, an undergrad at that time, Thomas Nicole, and McGill Professor Elena Bennett) put cages around small trees in different types of forests SW of Montreal. The cages (made of chicken wire) were in place to test the effects of ‘predator exclusions’ on the insects and spiders occurring on saplings. The prediction is that if you exclude larger predators, such as birds, this may allow a ‘release’ of other insects and spiders. In turn, this release may have trickle-down effects on an important process occurring in young trees: herbivory. For example, if a predator is more common because it’s not being eaten by birds, perhaps it will eat more caterpillars, which may mean the leaves on trees will be eaten less frequently. In ecology this is dubbed a ‘trophic cascade’. Dorothy did this work in the context of fragmented forests, and she worked in forests that were either small and isolated from other forests, or in forests that were large and connected to other forests. This was done because there’s an expectation that these ecological effects will be different depending on the degree of fragmentation happening on the landscape. For example, insectivorous birds may decrease in abundance in small, isolated patches, which means their effects on insect prey (and perhaps herbivory) may be reduced relative to effects in larger patches of forest.

Dorothy Maguire, working in a forest fragment.

Dorothy Maguire, working in a forest fragment.

During one summer field season, Dorothy and Thomas wrapped up some small sugar maple trees in chicken wire, left some alone as controls, counted insects and spiders over the summer months, and measured herbivory on the trees themselves. As expected, the effects of the ‘cage’ was significant: when you put a cage around a tree, you end up with more arthropods living on those trees. This confirms other papers which report a similar effect: insectivorous birds (and perhaps other vertebrate predators) have a significant, and meaningful impact on the insects and spiders living on trees. Or, stated another way, birds eat critters living on trees, and without these birds, there would certainly be more arthropods around!

Dorothy did not uncover a strong effect on the process of insect herbivory: although more insects and spiders were living in the trees protected by chicken wire, the leaves themselves were not affected. This could be because more insect predators were around, and thus compensating for the lack of birds, and eating just as many herbivorious insects (e.g., caterpillars) as the birds might have eaten.

The lanscape of southern Quebec. Lots of agriculture, some patches of forest.

The lanscape of southern Quebec. Lots of agriculture, some patches of forest.

Scaling up to the landscape context, there were no overall significant effects of the cage treatments in relation to the forest type, nor was the level of herbivory dependent on the landscape context. The general results for large, connected patches were no different than for small, isolated patches. However, the magnitude of the effect was marginally affected by the landscape context for the cage exclusion: vertebrate predator may have a more significant impact in smaller, isolated patches.

As with all research projects, this work resulted with as many questions as answers, which is equally frustrating and fascinating. It’s clear that vertebrate predators are important in these systems, but more work is needed to fully assess whether these effects are truly affected by the degree of forest fragmentation on the landscape. The lack of effects on the process of herbivory itself was equally intriguing – there are clearly many complex interactions occurring on small maple trees. Some of these interactions involve top-down predation events, but there are likely a suite of ‘bottom-up’ effects that are also influencing the system.

Reference:

MAGUIRE, D. Y., NICOLE, T., BUDDLE, C. M. and BENNETT, E. M. (2014), Effect of fragmentation on predation pressure of insect herbivores in a north temperate deciduous forest ecosystem. Ecological Entomology. doi: 10.1111/een.12166

The effect of insecticides on jumping spider personalities

This post was written by C. Buddle and R. Royaute (a PhD student in the Arthropod Ecology lab).

We are pleased to announce a recent publication from our lab, titled Interpopulation variations in behavioral syndromes of a jumping spider from insecticide-treated and insecticide-free Orchards.  As is traditional in the lab, here’s a plain language summary of the work:

Agriculture has strongly intensified in the last 60 years, causing major concerns the sustainability of biodiversity. Agricultural practices can reduce habitats available for wildlife and also release toxins in the environment through the use of pesticides. Not all organisms living in agricultural fields are harmful, and many predators, including spiders, can help to reduce pest density. We have a relatively good knowledge that the diversity of spider species in agriculture, especially under our temperate latitudes, can help reduce pest damage. However, many of the factors that influence spider predation on pests depend on the outcome of behavioural interactions and we don’t know much about that topic. Spiders are often cannibalistic and aggressive with one another and these types of behaviours may limit their efficiency for pest control. We also need to understand if these aggressive tendencies vary depending on the type of agricultural field considered, a pesticide treated field may favour very different behaviours than one that is managed organically. Another important point is that populations are composed by a multitude of individuals, each with its own behavioural tendencies. Some individuals take more risks when confronted with predators (i.e. they are more bold), others are more active and explore larger areas or consume more prey. These tendencies – often referred to as personality traits – may also be correlated with one another.

In the context of agriculture, this may mean that certain individual spiders may contribute more to biocontrol because they consume more prey, or that certain individuals are more at risk of being in contact with pesticides because they are more active. To understand, how agricultural practices, and particularly insecticidal applications, affects personality and behavioural syndromes in spiders, we focused on the jumping spider Eris militaris, an abundant and charming jumping spider occurring in apple orchards in Quebec. Here’s a lovely photo from Crystal Ernst to illustrate how attractive they are: (thanks, Crystal, for permission to post the photo here!)

Screen Shot 2013-11-26 at 3.34.45 PM

We collected spiders from pesticide-treated and pesticide-free orchards, brought them back to the laboratory, and did a number of behavioural tests on the individuals from the two populations. Compared to the insecticide-free populations, we document that individuals from orchards that did receive insecticides experienced a shift in their behaviours syndromes. The overall shape of this syndrome is multidimensional, but it suffices to say that the correlations among different behaviours (the ‘syndromes’, otherwise known as the ‘personality’) differed depending on where the population came from.

A 'mirror test' - used to study behaviour in E. militaris (photo by R. Royaute)

A ‘mirror test’ – used to study behaviour in E. militaris (photo by R. Royaute)

In sum, the personality shifts that we documented for E. militaris are potentially quite important since the relationships between different behaviours may affect a spider’s ability to be an effective generalist predator in apple orchards. We need to consider how management  (including use of insecticides) may affect specific behaviours, and more importantly, the relationships between the different behaviours.

Reference

Royaute, R., C.M. Buddle & C. Vincent. 2013.  Interpopulation Variations in Behavioral Syndromes of a Jumping Spider from Insecticide-Treated and Insecticide-Free Orchards. Ethology. doi: 10.1111/eth.12185

Arthropod Ecology Mission Statement

Last week, during our laboratory meeting, we worked to develop a laboratory mission statement. My real inspiration for this came from my friend and colleague Elena Bennett – she also got me connected to Jessica Hellmann’s excellent post on the topic.  A mission statement is really just a way to clearly define who we are, what we do, and why we do the sorts of things that we do. From a research laboratory’s point of view, the goal of the exercise is (in part) to help all members of the laboratory feel part of something bigger. Something that has broad relevance to a community that extends far beyond the walls of our institution, and far beyond the boundaries of our own specific research projects.

As Jessica states clearly in her post, a Mission Statement  “…is a description of the purpose for your organization, primarily as it now is and/or will be within the next few years. A good mission statement should accurately explain why your organization exists and what it hopes to achieve in the near future. It articulates the organization’s essential nature, its values, and its work. The statement should resonate with the people working in and for the organization, as well as with the different constituencies that the organization hopes to affect. It must express the organization’s purpose in a way that inspires commitment, innovation, and courage.”.  A mission statement should be short, easily remembered, jargon-free, proactive, and readable to people outside of our organization.

Here’s what we did to come up with our (draft) statement:

1) We each wrote down a few words or a short sentence on an index card. We tried to write things that we felt described what the laboratory does in a broader sense (i.e. beyond our own specific interests). Here’s an example:

Screen Shot 2013-10-09 at 10.04.24 AM

2) We mixed up these cards and each person took someone else’s card. We then went around the table and read what was on the cards. This allowed us a terrific jumping off point for the discussion and generated the necessary words and ideas.

3) The ‘scribe’ (in this case, it was me) wrote down each descriptive word (in our case, things like ‘arthropods‘, ‘human disturbance‘, ‘biodiversity‘ came up a lot), and as a group, we wrote down some verbs to help us think about the ‘action’ that we take with the things we do. Here, verbs like ‘explore‘, ‘quantify‘, ‘share’ came up a lot.

4) We wrote the mission statement – in two parts. (a) We tried to provide a few sentence of context, and to ground our laboratory in the ‘why‘ and the ‘what‘; (b) We wrote a few sentence of ‘how‘ we do our research.

5) Edit, edit, edit. This was done during the lab meeting, but also over email

Here’s the end result:

Mission Statement:

Arthropods (insects, spiders and their relatives) comprise most of the known biodiversity on the planet. Human activities are rapidly changing our environment, from climate change to landscape fragmentation and urbanization, with unknown consequences for local and global biodiversity. Arthropods have profound effects on ecosystem function, human health, goods and services, and culture. Our well-being is connected to this “smaller majority”, yet we know little about where they live, what they do, and how their diversity is changing. In our laboratory we: 1) Quantify patterns of terrestrial arthropod biodiversity across a suite of ecosystems, over a range of spatial and temporal scales; 2) Explore how arthropods respond to and are affected by human-induced environmental changes; 3) Investigate the interaction between arthropods and ecological processes; 4) Share our knowledge, ideas, and passion about arthropods.

How did we do? We would love your feedback on this.

Here are a few thoughts and reflections:

  • This was a very worthwhile process – it was an amazing discussion and gave as opportunity to really delve into areas that were well beyond our individual research interests.
  • I have always believed that ‘patterns in terrestrial arthropod biodiversity’ was really what I spend my research time thinking about; it’s good that the collaborative process of developing a mission statement ended up reflecting that!
  • Any specific habitat (e.g., canopy systems, the Arctic), or even any type of arthropod (e.g., beetles, spiders) never remained in our final mission statement. This is terrific, and shows well that the laboratory has diverse interests, but more importantly, that we encourage research in different places and with different model taxa.
  • Yes, jargon remains. This is difficult. We agreed, as a laboratory, that our mission statement would be aimed at a ‘scientifically literate’ audience.
  • I’m an ecologists and we do ecology, yet that word did not end up in the final product. Curious.
  • We ALL agreed about the importance of ‘sharing’ and engagement with a broader audience -many of us do various kinds of outreach, from blogs and tweets to volunteering to talk about insects in local elementary schools. I was extremely pleased and proud that our laboratory sees this is a core activity.

This process if far from over: the next step is a “Vision Statement“. As Jessica points out, a Mission statement is more about what we “do” and why, whereas a Vision Statement “...looks at least five years into the future and defines a future state. It is an articulation of a world that the organization and people are working toward, not what is expected to happen now“. Ok, that’s a task for a future lab meeting!

(BIG thanks to my amazing laboratory for helping develop a mission statement)

Lunch in the tree-tops for the birds and the bugs

A few weeks ago, our laboratory published a paper in PeerJ (an open-access journal) titled “Vertical heterogeneity in predation pressure in a temperate forest canopy“. This work resulted from a project by former Master’s student Kathleen Aikens. She graduated a little while ago, and although we published one of her thesis chapters in 2012, it took another year to get this paper out, in part because Kathleen and I both become too busy.  Thankfully, post-doc Dr. Laura Timms agreed to help us finish up the paper, and she worked with me and Kathleen to re-analyze the data, re-write some sections, and whip it into shape.

As is now traditional for my laboratory, here’s a plain-language summary of the paper:

Tree canopies, including those in deciduous forests in southern Quebec, are important for many different animals, including insects and spiders. These small, marvelous creatures crawl up and down trees with regularity, feed upon the leaves of trees, feed upon each other, and are food for animals such as birds and bats. Past research has shown that many species of insects and spiders live in tree canopies, and in general, more insects and spiders are found closer to the ground compared to the very tops of the trees. This makes sense, since deciduous tree canopies often need to be recolonized each spring, and tree canopies are relatively harsh environments – they are windy, hot, and often-dry places as compared to the forest floor.  What we don’t know, however, is whether the insects and spiders avoid the tree canopies because they may be eaten more frequently in the canopy as compared to the understory. The objective of this research was to test this question directly, and find out whether insects and spiders are arranging themselves, vertically, because predators may be preferentially feeding on them along this vertical gradient. This is a very important area of study since biodiversity is highly valued and important in forests, but we cannot fully appreciate the status of this diversity without discovering what controls it.

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Our mobile aerial lift platform. TO THE CANOPY!

We did this work by using two experiments that involved manipulating different factors so we could get at our question in the most direct way possible. In the first experiment, we made ‘cages’ out of chicken wire and enclosed branches of sugar maple trees in the cages. We did this at the ground level all the way to the tops of trees, using a ‘mobile aerial lift platform’. These cages acted to keep out large predators, such as birds, but allowed insects and spiders to live normally on the vegetation. We counted, identified, and tracked the insects and spiders both within these cages, and in adjacent branches that did not have cages (the ‘control’). By comparing the control to the cage, we could find out whether feeding activity by larger vertebrate predators affected insects and spiders, and whether this differed when comparing the ground to the top of the trees. In the second experiment, we used small pins and attached live mealy worms (larvae of beetles) to the trunks of trees, and we did this in the understory all the way up to the canopy. We watched what happened to these mealy worms, and compared what happened during the day and overnight. This is called a ‘bait trial’, and let us figure out what sort of predators are out there in the environment, and in our case, whether they fed more often in the canopy compared to the ground-level. This second experiment was designed for seeing the effects of insect and spider predators along a vertical gradient whereas the first experiment was focused more on vertebrate predators (e.g., birds).

image

Munch munch. Carpenter ants feeding on mealworms.

Our results from the first experiment showed that the cages had an effect: more insects and spiders were found when they were protected from predation by birds. Birds are playing a big role in forest canopies: they are feeding on insects and spiders, and in the absence of vertebrate predators, you might speculate more insects and spiders would occupy trees. Our second experiment showed that ants were important predators along the tree trunks, and overall, the most invertebrate predators were found in the lower canopy. Both experiments, together, confirmed that the understory contained the most insects and spiders, and was also the place with the highest amount of predation pressure.  The take-home message is that there is an effect of predation on insects and spiders in deciduous forests, and this effect changes if you are in the understory as compared to the top of the canopy. We also learned and confirmed that insects and spiders remain a key element of a ‘whole tree’ food web that includes vertebrates such as birds, and that predators in trees tend to feed on insects and spiders along a gradient. Where there is more food, there is more predation pressure! Our work was unique and novel because this is the first time a study of predation pressure was done along a vertical gradient in deciduous forests. It will help better guide our understanding of forest biodiversity, and the processes that govern this diversity.

A more detailed discussion of this work is posted on the PeerJ blog.