Salgado, J., Sayer, C. D., Willby, N., Baker, A. G., Goldsmith, B., McGowan, S., Davidson, T. A., Bexell, P., Patmore, I. R. & Okamura, B. (2021) Habitat heterogeneity enables spatial and temporal coexistence of native and invasive macrophytes in shallow lake landscapes. River Research and Applications. https://doi.org/10.1002/rra.3839
First published: 15 July 2021
Macrophyte invasive alien species (IAS) fitness is often hypothesised to be associated with beneficial environmental conditions (environmental matching) or species-poor communities. However, positive correlations between macrophyte IAS abundance and native plant richness can also arise, due to habitat heterogeneity (defined here as variation in abiotic and native biotic conditions over space and time). We analysed survey and palaeoecological data for macrophytes in satellite lakes along the Upper Lough Erne (ULE) system (Northern Ireland, UK), covering a gradient of eutrophication and connectivity to partition how environmental conditions, macrophyte diversity and habitat heterogeneity explained the abundance of Elodea canadensis, a widely distributed non-native macrophyte in Europe. E. canadensis abundance positively correlated with macrophyte richness at both the within- and between-lake scales indicating coexistence of native and invasive species over time. E. canadensis was also more prolific in highly connected and macrophyte-rich lakes, but sparser in the more eutrophic-isolated ones. Partial boosted regression trees revealed that in eutrophic-isolated lakes, E. canadensis abundances correlated with water clarity (negatively), plant diversity (positively), and plant cover (negatively) whereas in diverse-connected lakes, beta diversity (both positively and negatively) related to most greatly E. canadensis abundance. Dense macrophyte cover and unfavourable environmental conditions thus appear to confer invasibility resistance and sufficient habitat heterogeneity to mask any single effect of native biodiversity or environmental matching in controlling E. canadensis abundance. Therefore, in shallow lake landscapes, habitat heterogeneity variously enables the coexistence of native macrophytes and E. canadensis, reducing the often-described homogenisation effects of invasive macrophytes.
Following the previous post, this is just to let you know that our trip to Northern Ireland was very successful. It gave us a chance to discuss our research results with many partners, stakeholders and members of the public. The interest we met makes us hope that our research will find direct applications on the ground.
We would like to thank the many people who made this trip possible at the Fermanagh and Omagh District Council, Waterways Ireland, the Northern Ireland Environmental Agency and Queen’s University Belfast.
The BBC reported today that Fermanagh is the happiest place in the UK according to a recent survey by the ONS. Is there a link with the exceptional freshwater biodiversity levels we found during our work in the Upper Lough Erne region, part of Co. Fermanagh? Our Lake BESS work is only a preliminary step towards answering such fundamental question: a whole new research agenda lies ahead of us to better understand the value of nature and ecosystems in what is often referred to as coupled human-environment systems.
Our data was a compilation of lake surveys in both lake districts and for two time periods: the 1980 and recent time (thanks you to all our partners who were willing to share their data, by the way!). Each lake survey comprises of:
Extensive botanical work, recording aquatic plants from the open water and the marginal zone, and
Collecting water samples that are later analysed in the lab for phytoplankton abundance, concentration of nutrients such as phosphorus and water chemistry in general.
Our data shows that nutrient pollution drives ecosystem functioning in both regions and during both time periods. This reminds us on the importance of good policies to protect freshwaters while maintaining thriving agriculture.
The situation with biodiversity is a bit different as it appears to be influenced both by the local conditions (lake size and shape, nutrients status) and landscape-wide connectivity. One main difference between the Upper Lough Erne lakes and the Broads is that flood connectivity in the Upper lough Erne is a major factor structuring in the aquatic plant communities there. Does this induce greater resilience? remains a pending question we are working on.
All these results are being written up into a scientific article, so please get in touch if you’d like to discuss or report them!
We’re just back from our very successful field work around the Upper Lough Erne, Co. Fermanagh, Northern Ireland. We managed to survey nearly 20 satellite loughs for aquatic plants, water chemistry and bryozoans (see this previous post).
The help we received from volunteers and project partners was absolutely tremendous! Over the two week we have been a dozen of us actively involved in this research campaign. We’d particularly like to thank Hannah, Robert, Tim and Stephen for joining our team at this occasion and also all the land owners who were kind enough to grant us access to the lakes we had targeted.
Battling through reed beds to get onto some of the lough with our boats was one of the striking aspects of this field work! But it was worth the effort and the diversity of aquatic plant observed over the two week is very impressive. For instance we have sightings for at least ten different Potamogeton species (see this previous post), an extremely good score!
We’ll post more picture and reports from this field work in the coming weeks.
The islands of Britain and Ireland have over 40 species or hybrids of pondweeds (genus Potamogeton). This diversity in pondweed is one of the highest in Europe with most European species being represented. Unfortunately local diversity and abundance of pondweeds have declined over the 20th Century, as a result of habitat destruction and pollution. The Upper Lough Erne region and The Broads are two areas of importance for the conservation of pondweed – but “what can we learn from these strongholds?” and “what measure could enhance their recovery nationally?” are questions we are trying to address part of the Lake BESS project. (Photo by Ambroise Baker: P. polygonifolius in full bloom).
Do not miss out on a good laugh and great shots of Crom Castle on the shore of Upper Lough Erne in the second series of BBC’s Blandings, an adaptation of PG Wodehouse celebrated stories. The whole series 2 can be watch on iplayer for two more weeks!
But is it a zebra or is it a butterfly? Project partner Jorge Salgado suggests: “It’s a unique butterfly species with mussel wings that only inhabits the the Upper Lough Erne.”
Zebra mussel is an invasive mussel that was first observed in Ireland in 1997 but is now becoming widespread. It can use native mussel shells as substrate, as shown on this photograph taken by Jorge Salgado.