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

Meet the lab: Crystal Ernst

This is the first in a series of posts where each Arthropod Ecology lab member can introduce themselves. First up is PhD student Crystal Ernst:

I’m a Ph.D. candidate in the final stages of my program: these days I’m crunching out analyses and writing papers as I prepare to submit my thesis at the end of the term. As a community ecologist, I spend a lot of time thinking about how and why different species assemble together in space and time. These questions are foundational to the study of ecology and provide the overall framework for my research program, which uses beetles and other ground-dwelling arthropods to study the structure and determinants of terrestrial animal assemblages.

PhD student Crystal Ernst installing pan traps along the Dempster Highway (Yukon)

PhD student Crystal Ernst installing pan traps along the Dempster Highway (Yukon)

I have spent my summers conducting field research in gorgeous, remote regions of our northern territories, including Kugluktuk Nunavut and the Dempster Highway in the Yukon. My colleagues, members of the Northern Biodiversity Program, have contributed to the collection efforts as well, resulting in specimens being obtained from twelve different locations in the boreal forest, the subarctic and high arctic, spanning Canada coast to coast. I’m now neck-deep in the joy of interpreting the stories contained in my collection of specimens.

Specimens in pan trap (photo by C Ernst)

Specimens in pan trap (photo by C Ernst)

 

Sorting specimens back in the lab

Sorting specimens back in the lab

I’ve taken two approaches with this work. First, I’ve used a fairly traditional taxonomic approach to studying these animals: by identifying them morphologically (with a microscope and identification keys), I can associate each individual with a known insect species – although some new species have also been discovered! With this information I can describe the species richness (diversity) and distributions of different beetles in the north, and see which species are associated with each other at different northern locations. Secondly, I’ve looked at my arthropods from the perspective of their ecological functions – their roles in their environments. For example, some insects are responsible for pollenating plants, others are important decomposers, and others still are predators; arthropod assemblages can therefore be described in terms of the diversity and dominance of different functional groups. I am in the process of comparing taxonomic and functional assemblages found across northern Canada, and working to determine what aspects of their ecosystems (things like: temperature, wind, and sunlight; the diversity and structure of the plant community in which they live; soil characteristics) are associated with the way these assemblages are structured, and how they change over time and across space.

Three color morphs of Blethisa catenaria, a rare subarctic species (H. Goulet)

Three color morphs of Blethisa catenaria, a rare subarctic species (H. Goulet)

A fun complementary topic I’ve researched is the relationships between some high arctic ground beetles and a fascinating group of parasites called hairworms. I found a number of beetles from different locations to be infested with these worms; in one instance almost a quarter of the beetles were infected! The parasites are aquatic as adults and must first infect an aquatic insect (like a mosquito larva) before being transmitted to a terrestrial host (like a beetle) via the predation of the aquatic host by the terrestrial insect. To complete their life cycles, the worms somehow compel the beetles to enter the water, effectively forcing them to drown themselves so that the worms can emerge safely into their aquatic habitat. This discovery suggests an important link between the creatures living in terrestrial habitats and those in aquatic habitats and tells us about the arctic food chain: beetles must be eating mosquitos or other insects that have aquatic larval/immature stages. These prey items may, in fact, be a very important source of food. More work needs to be done to confirm this! In the meantime, I am excited to have found these associations – the fact that these particular species of beetles can be hosts for hairworm parasites is new information, and it appears that the parasite itself is a new species!

Pterostichus caribou with hairworms (C. Ernst)

Pterostichus caribou with hairworms (C. Ernst)

When I’m not writing my thesis or putting obscure little black beetles on pins, you can probably find me working at McGill’s Teaching and Learning Services, enjoying my time as a teaching assistant, networking on Twitter, mucking around in my vegetable garden (or putting said veggies in jars), walking my dogs, enjoying nature while canoe tripping with my partner, poking wildlife, or lifting heavy things at the gym. I’m on the hunt for a fantastic postdoctoral position that will allow me to continue studying different communities of living things in other ecosystems, and that factors that affect how they’re put together, and I’m excited about the many opportunities out there!

Meet the 2014 Arthropod Ecology Lab!

Welcome back to the new Academic term!  We had our first lab meeting yesterday, and made sure to run outside to get a “Start of year” lab photo:

The Arthropod Ecology Lab (2014)

The Arthropod Ecology Lab (2014)

From left to right we are: Yifu Wang, Anne-Sophie Caron, Sarah Loboda, Shaun Turney, Chris Buddle, Elyssa Cameron, Jessica Turgeon, Crystal Ernst, Etienne Normandin, and Chris Cloutier.  (missing is Dorothy Maguire)

We are smiling for good reason: September brings enthusiasm, and optimism. We are ready to have an exciting year. Learning from each other, doing science, and sharing our passion for arthropods.  This year, this blog will hopefully host a lot of news from the lab, and will include posts from many of the students. Starting next week, we will roll out “Meet the lab” posts, where each student will write a short post about themselves, and about their projects.  Stay tuned!

Quiescence

Quiescence is defined as a period of rest; being quiet, still or inactive. It’s often used to describe period of inactivity in insects, but I think also applies well to my current of state of blogging, and what I see as the state of my blogging into the near future.  This short post is really just to update my followers and readers, and to explain my current situation.

Life has ups and downs, and cycles around a career and work similarly have periods of intense activity, change, and new challenges. As many of you know, I’ve taken on a role as an Associate Dean in my Faculty, and coupled with upcoming (remote) field work to Nunavut, summer vacation, and conferences in the summer, I must admit that regular blogging over the next little just isn’t going to be possible.

 

Nunavut awaits...

Nunavut awaits…

It’s hard to admit defeat, and face the reality that it’s just not possible to do everything I would like to do. I’ve always prided myself of being a regular blogger (until recently, I’ve posted once or more per week, for over two years, on this blog or on my other blogs), and I was even was bold enough to proclaim that my new administrative position wouldn’t interfere with science blogging! However, it’s just not fair to my readers to publish just for the sake of posting, as quick, hurried posts will certainly suffer in quality. It’s also not appropriate for me to feel guilty for not blogging (heck, I do not get paid to blog!), and even though it’s something I love to do, I just can’t make it work right now.

To my followers: I am sorry that this blog will be quiet for a while, and I must thank you all sincerely for all the support and positive feedback: regular blogging is fun and validating because of all of you.

All that being said, I would like to continue with the ‘ten facts’ series on Expiscor, so if you would like to contribute to that, drop me a line! I’m also very excited about some other ongoing outreach and science communication projects – stay tuned for news about these initiatives.

Quiescence is a wonderful state: it’s a calming, soothing place, and unlike diapause, doesn’t have an end-date. It’s without pressure, without expectation and without stress. It’s a state that I need as I strive to balance life and work, and it will help me slow down.  I do look forward to returning to regular blogging, but I just can’t promise when this will be.  For now, please follow me on Twitter for updates and news.

As they byline of Expiscor states: there are many legs out there in the world of arthropods, and many stories to be told. Discoveries certainly await, but they can also wait!

 

 

 

 

 

Congratulations to the new Doctor of spider behaviour

I’m delighted to announce that lab member Raphaël Royauté successfully defended his PhD yesterday….  and he did it with grace, maturity, and poise. The defence was fair, but tough, and Raphael was able to show his breadth and depth of expertise on the broad topic of behaviour in arthropods.

Raphaël’s thesis was titled “Factors influencing behavioural variation in apple orchard populations of the jumping spider Eris militaris (Araneae: Salticidae)” and the during the defence, he was asked (not by me, remarkably!) to offer a ‘tweet’ of the his thesis. Here it is, coming in at almost exactly 140 characters.

Raph's thesis, in a tweet.

Raph’s thesis, in a tweet.

So, his research looked at behavioural syndromes in this remarkable jumping spider: Raphaël collected spiders in apple orchards, maintained them in a laboratory and ran them through a battery of behavioural test. He defined behaviours, looked at correlations among these behaviours (sometimes called ‘personality’), and how these traits varied during the development of individuals, consistency of these behaviours and whether behaviours differed depending on whether the spiders came from insecticide-free on insecticide-treated orchards.  Raphaël also looked at the direct effect of sub-lethel effects of insecticides on behaviour and will soon be publishing the ways that insecticides mess up their personalities.

Raphaël has really done incredible work – but looking back, I should not be surprised. Soon after he arrived in the lab we worked together on a short project about the activity of spiders right after snowmelt, at at that point, I was impressed with his intellectual curiosity, drive and motivation, and overall approach to scientific research.

Raphael and me, in 2008

Working together on Raph’s first project at McGill

After that first project, Raphaël came back to McGill to work on a PhD with me and Dr. Charles Vincent as co-supervisors. And now, many years later, he is now successfully defended a PhD. What a marvellous journey, and I can honestly say that I’ve learned far more from Raphaël than he could have learned from me.

Good luck Raph! (And you’ll be missed in the lab)

Charles Vincent (l), Raphaël (c) and me (r), just after the Defence (17 March 2014)

Charles Vincent (l), Raphaël (c) and me (r), just after the Defence (17 March 2014)

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

Expiscor (11 Nov. 2013): Changes

Expiscor is moving!

It’s been fun bringing you Expiscor each week, but things are changing and this blog feature has found a new home. Starting later this week, I’ll be blogging over at SciLogs.com.

Yes, I’m excited. 

Excited!

Excited!

It is truly an honour and a thrill to be invited to join the cast of impressive science bloggers, from Malcolm Campbell and his “Six Incredible Things Before Breakfast”, to Paige Brown’s “From the Lab Bench” to GrrlScientist’s “Maniraptora” and  Matt Shipman’s Communication Breakdown 

Expiscor will also change its style; I don’t provide nearly as good a “link-fest” as other people do (e.g., Ed’s and Malcolm’s are amazing!) and so instead of a weekly set of links, I will bring what I view as a short-list of fascinating discoveries, mostly from the world of Arthropods. These highlights, to be posted on Monday (as usual), will be more than a list, as I will try to provide a bit of context and opinion around each story. I see opportunity in the blogosphere to highlight new findings, stories, and photos related to the natural history and biology of spiders, insects, and their relatives.  In addition to these weekly highlights, I will write semi-regular long-form posts, again with a focus on arthropods, and some of these will be cross-posted on arthropodecology.com.

Don’t worry, you’ll still see amazing photos on Expiscor, like this one from Nash Turley:

Expiscor is flying away to SciLogs (photo by N. Turley, reproduced here with permission)

Expiscor is flying away to SciLogs (photo by N. Turley, reproduced here with permission)

You might wonder why I have opted to move Expiscor from its current home to a community blog. For me, it’s about continuing to improve and expand the blogging side of my academic life, and working alongside the other bloggers on SciLogs.com, I think, will help further hone my skills. More importantly, however, is that this move will allow me to reach out and connect with a very broad and interdisciplinary audience. Science communication, to me, is all about continually pushing the limits, expanding, thinking about and re-working the ways to bring exciting scientific discoveries to the world, and SciLogs is exactly aligned with this belief, as its mission statement highlights:

The SciLogs combine the strengths of both science culture and the blog medium. They provide scientists and those interested in science with the opportunity to interact in interdisciplinary discussions about science in all its forms… 

ArthropodEcology.com will remain active, although it certainly won’t be as active as it has been over the past year. The original idea behind the arthropod ecology blog was to highlight research activities within my laboratory, and to provide a forum for writing and discussing Higher Education. It’s grown a lot since then, and in some ways, the site will return to its roots, and I hope to get my graduate students and other people within my local community interested in writing their own posts under the arthropod ecology banner.

To my loyal readers, followers and friends: I must thank you for continued interest and support. The community of people associated with this blog is truly tremendous, and you give me energy, ideas and support every day. You help me uncover fascinating stories, provide me with terrific content, including photographs. You have made me a better scientist and a better person.

In sum, I pledge to continue to fish out discoveries and bring them to you; what’s changing is the location, and I do hope you will keep following along over at Expiscor’s new home.

And I know you want it… here’s your tweet of the week, from Minibeast Mayhem. Yeah, invertebrates are awesome.

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