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Ecology and Evolution of Shifting Range Margins in Glacier-fed Streams

Final Report Summary - SHIRMAN (Ecology and evolution of shifting range margins in glacier-fed streams)

The overarching research objective of the Marie Curie International Incoming Fellowships (IIF) 'Ecology and evolution of shifting range margins in glacier-fed streams' (SHIRMAN) project was to invoke a novel, multidisciplinary blend of ecological and molecular / evolutionary techniques to achieve a broad understanding of the dynamics of expanding species ranges at the their leading edges. Freshwater streams fed by glaciers are particularly relevant ecosystems for evaluating range expansions because glaciers worldwide are shrinking with a warming climate, often resulting in a replacement of ice with flowing-water habitat available for colonisation by aquatic biota such as fish, amphibians, and invertebrates.

The more detailed objectives / tasks of our project were split into two major themes:

(1) assessing various aspects of species ecology (including genetic diversity and feeding ecology) at the leading edge of an expanding geographic range compared to presumably more long-term stable locations within the range;
(2) quantifying regional-scale patterns of biological diversity (including genetic and species diversity) among streams occupying headwaters most influenced by glacial runoff vs. streams without significant glacial hydrology in more downstream locations of river basins.

We undertook the two research themes in two different geographical regions, each uniquely suited to addressing the respective research objectives. Theme 1 research was completed in Glacier Bay National Park in southeast Alaska (GBNP), which provided us an ideal space-for-time design with its natural age-sequence of whole stream catchments, the mouths of which have been free from glacial ice from 250 years (since the Little Ice Age) to very recently (40 years was our youngest stream). We undertook theme 2 research in the French Parc National des Pyrénées (PNP), which contains several small, relict alpine glaciers occupying the uppermost headwaters of extensive river networks.

Significant results have emerged from both research themes. The major findings from Theme 1 were that food-web complexity (as diet breadth of juvenile coho salmon, a generalist top predator in GBNP streams) peaked in intermediate-aged (approximately 150 - 200 years since ice cover) streams, but a genetic signature of demographic stability in this species varied only according to stream age (as would be expected if all habitats were otherwise equal). This pattern suggests that available prey diversity does not play a major role in limiting range distributions in coho salmon. Rather, simply the availability of a minimum of appropriate prey items, combined with suitable stream habitat conditions together appear to allow relatively rapid establishment of populations at the range margin. A high level of genetic diversity even in the youngest (40 years since glacial ice retreated from the stream mouth) GBNP stream also suggests the broader management implication that coho salmon and potentially other species with similar traits should capable of rapid recovery following habitat restoration activities such as dam removal.

Major results from theme 2 suggested that spatial patterns of biodiversity distribution are heavily influenced by glacial meltwater hydrology at the upper range limits of stream-dwelling species. Regional diversity (both total and site-to-site) estimates are significantly lower when the uppermost, highly meltwater-dominated stream sites are not included, a spatial pattern that predicts an analogous temporal pattern of significant decrease in aquatic biodiversity with the continued reduction and eventual loss of glacial runoff that is predicted with continued climate change. Another interesting ecological pattern from research conducted within theme 2 was that spatial patterns of diversity turnover were analogous for species diversity at the community level and genetic diversity of a widely distributed species. Hence: biodiversity at both levels is expected to be impacted as the small PNP glaciers are lost, in concert with loss of the unique marginal habitat conditions characteristic of sites highly influenced by glacial runoff.

We have worked and continue working with managers of the respective national parks to assist them with management and education / outreach activities related to results of this project. Our results are having an impact on the broader scientific community as well. We have already published the major results from theme 2 in a high-impact, peer-reviewed journal, and a second paper stemming from theme 2 is in preparation. The major results from theme 1 are also being prepared for submission to a high-impact journal. Furthermore, the project has contributed directly to education at the University of Birmingham. Both research themes directly involved Doctor of Philosophy (PhD) students whose own projects have benefited greatly from the mentoring associated with their involvement in this project.