Project Outline

PROJECT

When we consider species geographic range shifts with climate change, we often carry the preconceived notion that contemporary distribution boundaries are at equilibrium with current climate conditions. Dispersal limitation is difficult to quantify, but an important consideration when forecasting range shifts. With this study I plan to infer dispersal limitation through a series of reciprocal transplant projects at the northern range limit of Mimulus cardinalis (A riparian perennial found throughout California and up to southern Oregon). I will also be incorporating some of the now widely used species distribution models and empirically validating these methods through transplants across an environmental gradient.

•       Question 1: Can we infer dispersal limitation at the northern range margin through an ‘over the edge’ reciprocal transplant and demography survey?

•       Question 2: Can bioclimatic models be tested empirically? (Actual population viability vs. predicted) Transplant across an environmental gradient. 

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Question 1: Can we infer dispersal limitation at the northern range margin through an ‘over the edge’ reciprocal transplant and demography survey?

The general question “as new suitable habitats become available will species move to track these changes” has remained elusive (Corlett & Westcott, 2013). In addition to understanding how a species distribution will shift with future climates, it is just as important to understand the processes structuring their contemporary range limits. With a pilot study project initiated in the fall of 2013 we explore the role of dispersal limitation at the northern range margin using a reciprocal translocation project.

Transplant sites across central Oregon. Points denote site
locations while polygons delineate watersheds. (Blue - beyond the range;
Pink - source populations within the range; Green - sites within
the range, but unoccupied. 

Sites were selected both beyond and within the current range limit (defined by herbarium records & personal survey efforts). Sites within the current range were classified as either unoccupied or occupied, based on the presence of M.cardinalis within the watershed, allowing the study to also test for dispersal limitation at a more local spatial scale (attached map). At each site ~ 15 (4m/4m) plots were established along a 1 km reach of the stream in high gravel and cobble bars. Each plot contained 16 seedlings, giving a total of ~ 1200 seedlings planted. 

The outcome of this trail project will be used to direct future in-stream “over the range edge” transplants over the spring & summer of 2013. With future projects will be transplanted not only seedling, but taking a more demographic approach with the inclusion of multiple life stages.

Some of the transplant plot from the six sites.

Seedlings started from seed in greenhouse and transplanted when ~ 3 - 5 cm tall

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Question 2: Can bioclimatic models be tested empirically? (Actual population viability vs. predicted) Transplant across an environmental gradient.


If a plant species range limit is at a climatic equilibrium, then predicted suitability from ENMs should mirror real world population performance. If a range boundary is driven largely by dispersal limitation, then this correlative modeling approach will provide us with a false understanding of the niche limits and forecasted range shifts with climate change will be largely inaccurate. By transplanting populations across an environmental gradient & monitoring their subsequent performance I hope to test the accuracy of SDM/bioclimatic envelope models with real world population performance.