RESEARCH PROJECTS
Temperature and herbivory as drivers of demography across species' ranges
Across species' ranges the environment changes drastically, reaching a point where certain aspects become so limiting that they exceed a species' tolerance and form range limits. In particular, temperature and herbivory can both shape species ranges and may interact where the impact of herbivory on plants can vary with the abiotic environment. For my Ph.D. with Dr. Amy Angert, we installed a factorial field experiment in 2021 to determine how temperature and herbivory scale up to drive observed variation in demography across the elevational range of broadleaf lupine (Lupinus latifolius) in the North Cascades, BC. Findings will inform how plant population responses to biotic interactions, such as herbivory, depend on the abiotic environment, and the underlying mechanisms driving this relationship (e.g., life history variation, spatial variation in species interaction intensity, abiotic stress and the ability to recover or resist a negative species' interaction)​
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(Left) Open-topped warming chambers and herbivore exclosures to determine how temperature and herbivory drive demogrgaphy across the species' range. (Top-Middle) Broadleaf lupine subalpine meadow in E.C. Manning Provincial Park, BC. (Bottom-Middle) Broadleaf lupine plants; photo by E. Menchions. (Right) Me installing an open-topped warming chamber; photo by J. Malloff.
Demographic lags and microclimatic buffering to explain species' range stasis
Ongoing climate change is causing many species' ranges to shift upslope to higher elevations. However, many species have not shifted in pace with recent warming (i.e., ‘range stasis’), possibly due either to demographic lags or microclimatic buffering. The ‘lagged-response hypothesis’ posits that range stasis disguises an underlying climatic sensitivity if range shifts lag the velocity of climate change due to slow colonization or mortality. Alternatively, the ‘microclimatic buffering hypothesis’ proposes that small-scale variation within the landscape, such as canopy cover, creates patches of suitable habitat within otherwise unsuitable macroclimates that create climate refugia and buffer range contractions. To test these two hypotheses, we combined a large seed addition experiment of 25 plant species across macro- and micro-scale climate gradients with local herbaria records to compare patterns of seedling recruitment relative to adult ranges and microclimate in the North Cascades, USA. We found support for the lagged response hypothesis, where adult ranges are in disequilibrium. Specifically, species' optimum shifted towards cooler regions and recruited beyond their cool edge. Meanwhile, we found trailing range dynamics are not limited by seedling recruitment. By contrast, we were unable to detect evidence of microclimatic buffering due to canopy cover. Combined, our results suggest apparent range stasis in our system is a lagged response to climate change at the cool ends of species ranges, with range expansions likely to occur slowly or in a punctuated fashion. Preprint here!
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(Left) Hiking in the North Cascades. (Centre) Viewpoint. (Right) Tagged seedlings in the seed addition experiment.
What stages of a species' life cycle drive range dynamics?
Species' respond in different ways to their environment throughout their life cycle. It remains unclear which parts of the life cycle are most important in shaping future climate-driven range shifts. For my M.Sc. with Dr. Carissa Brown, we looked at life-stage specific environmental requirements for black spruce (Picea mariana) at the northern range edge in Yukon. We identified strict microsite associations for successful seed production in adult trees and a lack of suitable substrates available for early recruitment at treeline. You can check out the paper here.
I am further exploring this concept in my Ph.D. and am building population models (i.e., integral projection models) to assess life-history variation across the elevational range of broadleaf lupine. By determining which parts of the life cycle contribute most to population performance (i.e., population growth rate [λ]) across the range, we will identify which life stages are most important in shaping species' distributions and how sensitive populations may be to different abiotic and biotic factors across the range. For example, a given amount of seed predation will have a larger effect in populations where reproduction contributes more to population performance.
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(Top Left) Gravel pit camping on the dempster highway, Yukon. (Bottom Left) Tombstone Territorial Park. (Centre) Black spruce seedling. (Top Right) Black spruce adult. (Bottom Right) Pingo in Tuktoyaktuk, NWT.