Lac Hertel

Fussmann Lab
Department of Biology

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Michael Pedruski

Michael Pedruski PhD3 Student McGill Biology
(funded through an NSERC PGS-D Postgraduate Scholarship)
MSc Queen's University, Kingston
Co-supervisor: Prof. Andrew Gonzalez
Stewart Biology Building, N3/15
Phone: 514-398-3265
e-mail: michael.pedruski@mail.mcgill.ca

One of the most fascinating aspects of biotic life must surely be the immense diversity that characterizes it at almost every spatial scale. From well researched environments such as rainforests and coral reefs, to seemingly mundane habitats such as melt-water pools on urban soccer fields, the diversity of living organisms is often incredible. It seems only natural that in the face of such diversity we should ask how it arose, how it is maintained, and what would happen if it wasn't.

Competitive coexistence provides an intriguing problem in biodiversity research. While much research has suggested that species should not be able to coexist with other species that have the same niches or limiting resource, this contrasts with frequent observations of similar species co-ocurring. Recently, much debate has erupted between proponents of neutral and niche based theories of competitive coexistence over the extent to which these models are representative of natural communities. There is, however, increasing recognition that when considered in a framework of equalizing and stabilizing mechanisms (where equalizing mechanisms minimize fitness differences between competitors, and stabilizing mechanisms focus intraspecific competition relative to interspecific competition) neutral communities simply represent the extreme case of communities maintained by equalizing mechanisms alone, whereas niche structured communities involve both equalizing and stabilizing mechanisms. As such, the more pertinent question may not be the prevalence of neutral or niche structured communities, but rather the relative importance of equalizing and stabilizing mechanisms in competitive coexistence.

Over the course of my PhD at McGill under the supervision of Andrew Gonzalez and Gregor Fussmann I plan to conduct a series of experiments and theoretical studies in which I will manipulate the relative strength of equalizing and stabilizing mechanisms under resource competition in a freshwater diatom model system. I intend to examine how changing the relative importance of equalizing and stabilizing mechanisms alters the structure and function of the model communities. Furthermore I hope to investigate how evolutionary dynamics alters the balance between equalizing and stabilizing mechanisms given initial differences in their relative importance, and experimental variation in environmental constraints.

Through this research I hope to provide novel insights on the different ways that equalizing and stabilizing mechanisms can affect biotic communities, and ultimately elucidate the roles they play in nature.

Visit Paradox of Plankton for more on this project.

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Monica Granados

Monica Granados

PhD2 Student McGill Biology
MSc University of Toronto
Co-supervisor: Dr. Stéphane Plourde (Fisheries and Oceans Canada)
Stewart Biology Building, W6/13
Phone: 514-398-6725
e-mail: monica.granados@mail.mcgill.ca

The consequence of omnivory in food webs has a contentious history. Food web simulations by Pimm and Lawton in 1978 indicated the percentage of stable food webs with omnivory should be low. Yet, omnivory is prolific in real food webs. Reconstructions of terrestrial and marine ecosystems generated reticulate webs replete with omnivory. The disparity between real and simulated webs was reconciled in 1997 with the identification of weak interaction strength as the mechanism for the maintenance of omnivory. In simple, tri-trophic food webs with an omnivore, consumer and basal resource, weak omnivory reduces the attack rate on the consumer and reduces the growth rate of the basal resources resulting in increased stability.

While the current consensus is that the presence of omnivory is stabilizing, the consequence of introducing omnivory to a resident food web remains unknown. My research is motivated by the introduction of the blue mussel, Mytilus edulis, into the water column for aquaculture. Aquaculture transplants mussels from their natural benthic habitat to suspended lines consequently increasing the interaction rate between mussels and zooplankton. In this modified food web, mussels are omnivores consuming and competing with zooplankton for a common phytoplankton resource. For the first chapter of my thesis I performed experiments dissecting and manipulating the strength of predation and omnivory in an experimental food web consisting of a mussel, zooplankton and phytoplankton. The results were consistent with theoretical predictions - weak interactions promoted the persistence of zooplankton, whereas strong interactions drove zooplankton towards extinction. The experiment however, also revealed that the strength of omnivory and predation are not independent. The availability of algae, as a consequence of reducing omnivory, increased the rate of mussel predation on zooplankton.

My current research continues to investigate how omnivory mitigates stability. Presently I am performing experiments with ciliate communities to record the dynamics of consumer-resource oscillators along an omnivory gradient. I will also be conducting experiments to determine 1. the consequences of introducing omnivory to a predator-prey community and 2. how omnivory affects rates of invasion spread.

The results from these experiments will be coupled with models and metanalyses to elucidate the consequences of the propagation of omnivory.

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Sébastien Portalier

Sébastien Portalier

PhD3 Student McGill Biology
Co-supervisor: Prof. Michel Loreau
Stewart Biology Building, W3/1
Phone: 514-398-6697
e-mail: sebastien.portalier@mail.mcgill.ca

The topic of my PhD thesis is to model the evolution of food webs. It involves developing mathematical and computer models that represent food webs in which species are engaged in biotic interactions (like predator - prey, and competition) and exposed to the effects of important abiotic factors (e.g. gravity, light intensity). The food web structure is also affected by species evolution through time.

In summary, this approach tries to build more realistic food web models that include the effects of both environmental factors and evolution through some of the fundamental characteristics of species, such as their body size.

The models are then applied to investigate exciting and somewhat untracked issues. For example, the models investigate why, in pelagic food webs, predators usually have a larger body size than their preys, and why this pattern is not as obvious in continental food webs (in which predators can be smaller than their preys). Another aspect explored is the structure of food webs along the vertical dimension of space (especially in aquatic ecosystems) and the relative influence of several physical factors (such as light availability, gravity, turbulence) on this structure.

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Christina Tadiri

Christina Tadiri

PhD1 Student McGill Biology
BSc Biology McGill University
Stewart Biology Building, W3/2
Phone: 514-398-3153
e-mail: christina.tadiri@mail.mcgill.ca

In September 2012, I started as a PhD student working on parasite-host interactions in metacommunities.

I am using the guppy-Gyrodactylus system in the McGill Biology Phytotron.

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Egor Katkov

Egor Katkov

MSc 1 Student McGill Biology
Stewart Biology Building, W3/2
e-mail: egor.katkov@mail.mcgill.ca

Phytoplankton are sometimes called "The Forest of the Sea" because they are the most important primary producers of aquatic systems. I am currently looking at the effect of increasing CO2 levels in the atmosphere on communities of these organisms, which are at the base of aquatic ecosystems.

I am using an experimental dock located on Lake Hertel in McGill University's Gault Nature Reserve. The dock contains holes which accommodate 2500 L plastic bags that enclose parcels of the lake, called mesocosms. Apart from CO2 enrichment, I am also adding nitrogen and phosphorus to mimic agricultural runoff which can exacerbate the effects of carbon dioxide. The phytoplankton communities are quantified using a Fluoroprobe which allows me to quickly measure biomass of four different groups of phytoplankton: green algae, blue-green algae (cyanobacteria), diatoms and cryptophytes.

The goal of the research is to get an insight into the dynamics of phytoplankton communities with respect to nutrient limitation. This will allow us to infer how communities, including the larger non-photosynthetic organisms such as zooplankton and fish will react to the high CO2 levels in the atmosphere.

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