Integrated landscape genetics of the mountain pine beetle system
The mountain pine beetle (MPB; Dendroctonus ponderasae) outbreak in western Canada has had significant ecological and economic consequences. Outbreak dynamics are the product of interactions among the beetle itself, associated pathogenic fungi (Ophiostomaspp.), host trees (Pinus spp.), physical landscape features, and climate. As part of the TRIA project, a large interdisciplinary NSERC Strategic Network, this research uses genetic data to investigate the spatial interactions among species in the beetle-fungi-pine complex and relate them to landscape features to better understand the causes and consequences of outbreaks and to inform risk management models.
We are also interested in the question of whether rapid evolution has played a role in the expansion of the MPB into novel habitats. The first step to address such a question is to identify loci that are potentially under selection. However, demographic processes such as rapid range expansion can create spatial patterns in allele frequencies that mimic those created by adaptive processes. Landscape genomics endeavours to identify loci potentially under selection through correlations between allele frequencies and environmental heterogeneity but do not necessarily consider the influence of this potentially confounding demographic context. Using a simulation approach, we are examining how range expansion, population dynamics, and spatial context affect our capacity to meaningfully identify loci under selection.
Scanning electron microscopy image of an adult mountain pine beetle, Dendroctonus ponderosae. Photo credit: Janice Cooke
Parasitoid meta-community dynamics
Theory and empirical data indicate that forest structure (i.e., composition and configuration) can affect insect population dynamics and thus has the potential to modulate the severity and extent of forest insect outbreaks. Forest structure affects population irruptions directly through the availability and connectivity of suitable host trees. However, the forest can also indirectly affect outbreaks through its effects on predator (parasitoid) community diversity, abundances, and mobility. This project combines tools and techniques from community ecology and landscape genetics to evaluate the relative contributions of direct and indirect factors on insect trophic dynamics and outbreaks. Specifically, we are evaluating the relative importance of the “silvicultural” and “natural enemies” hypothesis of spruce budworm (SBW) outbreaks.
To address this idea, SBW larvae were collected in the summer of 2014 from 30 sites across Quebec in regions currently affected by the SBW. Larvae were reared and emerged parasitoids were identified. In total, or 50 000 larvae were individually reared which provided over 7000 parasitoids of over 15 species of hymenoptera and diptera.
Current projects using these data include:
1) Assessing how forest structure affects spatial variation in parasitism rates at different spatial scales using remotely sensed data.
2) Determining the relative importance of spatial context, environmental variation, and outbreak characteristics of parasitoid community beta-diversity at broad spatial scales.
3) Investigating how climate driven phenological mismatches between SBW and parasitoids may affect future outbreak dynamics in northern forests.
4) Characterizing the spatial genetic structure and estimating dispersal capacity of two parasitoid species: Apanteles fumiferanae & Glypta fumiferanae.
5) Assessing the context-dependent drivers of community assembly in the SBW parasitoid complex.
We hope that our results will contribute to our understanding of the diversity-stability relationships in forest insects systems and to provide recommendations for spatial management strategies that will allow us to augment the control that parasitoid populations exert on outbreaking populations and thus to reduce forest losses.
Students: Olivier Pontbriand-Paré, Simon Legault, Ronan Marrec
Photo credit: Simon Legault
Photo credit: Simon Legault
Using spatial genetics to characterize spruce budworm dispersal
The spruce budworm (SBW; Choristoneura fumiferana) is a lepidopteran forest pest that devastates huge areas of spruce and fir forest during its periodic outbreaks. SBW outbreak dynamics are shaped by the complex interactions among climate, forest structure, communities of natural enemies, and dispersal. Despite the significance of movement to the spatial dynamics of SBW outbreaks, little is known about SBW dispersal, how it varies with spatial context and over course of an outbreak, and how it affects spatial synchrony in outbreak dynamics. This research applies tools and methods from spatial population genetics to characterize genetic connectivity among outbreak patches in the current outbreak in eastern north America. Using this information on genetic connectivity, and how it varies within and among years, we will infer patterns of gene flow and dispersal and how it varies as a function of intervening land-cover (isolation by resistance) and local environmental conditions (isolation by environment). Concurrently, we are developing dispersal models using predicted phenology (BioSIM) and demographic data collected from pheromone traps (adult males). Together, this work will increase our knowledge of how SBW movement varies in different forest and landscape contexts and will be used to improve simulation models that predict insect population dynamics and forecast future outbreak risk. This work will also address the important question of the potential efficacy of currently proposed early intervention strategies.
Check out our photo gallery illustrating our sampling network and developing results.
Students: Simon Legault
Collaborators: Rob Johns (CFS, AFC), Colin Garroway (UManitoba), Deepa Pureswaran (CFS, LFC), D. Kneeshaw (UQAM), F. Sperling (UofA), M. Cusson (CFS), R. Levesque (U. Laval), L. Lumley (RAM, AB), B. Brunet (UofA).
SBW larva hanging by a thread. Photo: Olivier Pontbriand-Paré
Spatial genetic structure is influenced by ecological context. Genetic structure in cyclic and irruptive populations will depend on the timing of data collection (peak or trough), context-dependent dispersal in the species, as well as the amplitude and frequency of population oscillations. See James et al (2014). for more details.
Periodic outbreaks of the spruce budworm (SBW; Choristoneura fumiferana) in eastern Canada create large patches of standing dead spruce and fir forest. Of particular concern to forest and fire managers is whether these patches of standing dead timber represent areas of significantly greater fire risk, for how long such increased risk persists, and how these relationships vary through space and time. Using historical data on fire ignitions and spruce budworm defoliation this research examines the relationship between defoliation and fire in the province of Ontario, Canada. Previous work has suggested a temporary increase in flammability in budworm-killed forests but regional and seasonal variability in these relationships has not been examined.
We are currently modelling how the probability of lightning-caused ignition, the probability of escape from initial control, and final fire size vary as a function of a set of spatial and temporal covariates, including SBW defoliation up to 10 years prior to ignition. Our goal is to create predictive spatial models that can be used in combination with forecasted future climate and fire weather to predict changes in fire risk. Through this research we hope to develop a better understanding of the contribution of insect outbreaks to fire risk in boreal and mixed-wood forest systems. In the context of recent increases in the extent and severity of insect outbreaks in northern forests, this work is relevant to quantify the potential for increased insect-related lightning-caused fire risk that may be further exacerbated by drier and warmer conditions due to climate change.
Students : Louis-Etienne Robert
Collaborators : Mike Wotton (CFS, UofT), Dave Martell (UofT), Rich Fleming (CFS)
Photo credit: Terry Chapin. http://www.lternet.edu/node/49513.
Forest ecosystem modelling
Researchers are often faced with questions at spatial and temporal scales that exceed our manipulative capacities. For example, understanding the long term consequences of climate change or different forest management regimes on forest dynamics requires data at spatial and temporal scales much larger than are usually feasible in traditional ecological studies. Spatially explicit simulation modelling can be used to address these questions, with the caveat that models are not reality, but instead represent a simplified version of reality containing the main processes in which we are interested. In this way, simulation models should be considered as a way for us to observe the consequences of our assumptions about how systems work even when direct manipulation and observation may not be possible.
This research theme focuses on the long term consequences of forest management on landscape composition and configuration and how these spatial patterns affect habitat availability, landscape connectivity, and biodiversity conservation. Using spatially explicit simulation models and the SELES simulation platform, we examine how interactions between the spatial legacies created by forest management policies affect other ecological processes such as climate, fire and insect disturbance, forest succession, as well as community and population dynamics.
Much of the other ongoing research in the lab will contribute new parameters, sub-models, and conceptual frameworks to current models of forest ecosystem dynamics and will improve their capacity to evaluate the sustainability of current land-management practices.
Irruptive population dynamics are affected by both bottom-up and top-down processes. However, trophic chains such as this do not exist in isolation. Indeed, the food webs in which irruptive taxa are nested include multiple connections with and between trophic levels. We are investigating how variation in the amount of available host affects irruptive population dynamics when assuming that a reduction in the amount of host (e.g., confiers) increases the availability non-host (e.g., deciduous species) available for other herbivores, which in turn serves as a reservoir for shared natural enemies. This work is motivated by the spruce budworm outbreak system in which forest diversity has been shown to reduce the intensity of defoliation, presumabley thorugh an influence on a diverse community of associated generalist parasitoids. Using mathematical models (ODEs) to formalize this conceptual model, we are specifically investigating under what conditions a manipulation of in host and non-host density can modulate the intensity of defoliator outbreaks.
Collaborators: V. Krivan (CAS), É. Filotas (TELUQ)