A century of ecosystem change: human and seabird impacts on plant species extirpation and invasion on islands
- Published
- Accepted
- Subject Areas
- Conservation Biology, Ecology, Ecosystem Science, Coupled Natural and Human Systems
- Keywords
- native species extirpation, islands, exotic species invasion, Garry oak ecosystem, plant communities, seabirds, maritime meadow, soil nutrients
- Copyright
- © 2016 Lameris et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2016. A century of ecosystem change: human and seabird impacts on plant species extirpation and invasion on islands. PeerJ Preprints 4:e1787v1 https://doi.org/10.7287/peerj.preprints.1787v1
Abstract
We used 116-years of floral and faunal records from Mandarte Island, British Columbia, Canada, to estimate the indirect effects of humans on plant communities via their effects on the population size of a surface-nesting, colonial seabird, the Glaucous-winged gull (Larus glaucescens). Comparing current to historical records revealed 18 extirpations of native plant species (32% of species historically present), 31 exotic species introductions, and one case of exotic introduction followed by extirpation. Contemporary surveys indicated that native species cover declined dramatically from 1986 to 2006, coincident with the extirpation of ‘old-growth’ conifers. Because vegetation change co-occurred with an increasing gull population locally and regionally, we also tested predictions from the hypothesis that the presence and activities of seabirds help to explain those changes. Specifically, we predicted we would observe high nutrient loading and exotic plant species richness and cover on nearby islands with versus without gull colonies as a consequence of competitive dominance in species adapted to high soil nitrogen and trampling. As predicted, we found that native plant species cover and richness were lower, and exotic species cover and richness higher, on islands with versus without gull colonies. In addition, we found that soil carbon and nitrogen on islands with nesting gulls were positively related to soil depth and exotic species richness and cover across plots and islands. Our results suggest that gulls have the potential to drive rapid change in insular plant communities by increasing nutrients and disturbing vegetation. Because human activities have contributed to long-term change in gull populations, our results further suggest compelling, indirect links between human management decisions and plant community composition on islands of the Georgia Basin.
Author Comment
This is a preprint submission to PeerJ.
Supplemental Information
Plant species list of Mandarte Island recorded between 1896 - 2012
Includes a column for origin of species (native to coast British Columbia or exotic) and the current status on the island in comparison to 1896 (extinct, extant or introduced over the period between 1896 and 2012).
List of islands on which vegetation surveys used in this study have been conducted
Vegetation surveys have been conducted in 2007 and 2008 (Bennett et al. 2012) and 2012 (this study). Islands are classified as either supporting seabird colonies (‘gull islands’) or not (‘non-gull islands’).
Dataset of vegetation surveys on all islands (2007 - 2012) and on Mandarte Island (1986 & 2006)
In the first tab (vegetation surveys on all island 2007 - 2012) we included for every plot the data on number of species and cover of species, separated in exotic and native species groups. We give fraction of litter, rock, moss, lichens and bare ground cover. We give mean soil depth in the plot as well as % carbon and nitrogen in the soil sample of the plot. In the second and third tab (vegetation surveys Mandarte Island 1986 and 2006) we included for all plots on Mandarte Island the fraction of grass, rock and shrub cover, species cover specific (several species of plants) and soil depth.