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.
Abstract: There is an increasing interest in recording early colonisation of organisms when studying changes in distribution ranges induced by climate change. Here, I describe one population of Mentha cervina L. (Hart’s pennyroyal), naturalising in the wild at South Gare, v.c.62 North-east Yorkshire. Two other populations have been reported in Britain and none are known from Ireland. Of the three populations ever reported from the wild in Britain, two are still extant. It is unclear what vectors disperse M. cervina in Britain and whether the species is becoming increasingly naturalised or not. Diagnostic characters: digitate bracteoles and four calyx teeth, are provided to facilitate the recording of this mint species by field botanists.
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!
This post highlights another project Carl Sayer, Lake BESS’s principal investigator, is involved with: The Norfolk Pond Project. Ponds sustain a major share of freshwater diversity yet they have been subjected to near-systematic destruction, pollution or abandonment since WWII.
After years of neglect by conservation and research compared to other habitats, ponds are finally being incorporated into UK aquatic conservation approaches and the Norfolk Pond Project is an excellent example:
“Norfolk holds more ponds than any other English county with an estimated 23,000 ponds present. Most of these ponds are located in farmland, and have their origins as marl or clay pits and in some cases livestock-watering ponds dug in the 17th to 19th centuries. “
“In addition the Brecks, west Norfolk and sites north of Norwich are home to some of the most amazingly diverse ancient ponds in the UK, pingos – ponds that occupy ice depressions formed during the last great ice age. A great place to see pingos is at Norfolk Wildlife Trust’s nature reserve, Thompson Common.”
The Lake BESS team has just spent four full days on the water to collect bryozoans statoblasts from 14 different Norfolk broads. You will find more information about our work on bryozoans in this previous post.
The aim of this sampling is to gather evidence regarding how connectivity between lakes influences the movement of aquatic biodiversity, in particular bryozoan population genetics.
We were extremely privileged to be shown around by Geoff Philips, who greatly facilitated this field work with his knowledge of the area and of the people managing The Broads – at the Broads Authority, the Norfolk Wildlife trust, etc.
Last summer, we collected similar samples from the Upper Lough Erne region, Northern Ireland. With this trip in the Broads we completed the sampling of bryozoans for our project. We used an Ekman grab from our boat to retrieve lake surface sediment, i.e. oozy mud.
But collecting the mud is only the first step of the sampling. Back on the shore, our bryozoans expert Beth screened the sediments through a microscope to pick out individuals statoblasts (the dormant phase of bryozoans measuring less than 1 mm in diameter). These individual statoblasts are going to be sent off for their DNA to be extracted.
We are expecting to find out that isolated broads have bryozoans population with more distinct genetics than those from broads connected to the river systems. But we are really not sure how the gene flow within the Broads will compare with that experienced within the Upper Lough Erne region, so we are looking forward to get our results – and we are hope to be surprised!
Many thanks for the many people who helped making this sampling possible!
Lakes are inspirational places for people enjoying outdoor activities and they are cherished by local communities and holiday-makers alike. However, lake ecosystems are threatened by environmental change and loss of biodiversity that can have cascading and catastrophic effects.
The LakeBESS project, run from the Environmental Change Research Centre (ECRC) at UCL, is focussed on two lake districts, the Broads in East Anglia and the Upper Lough Erne district in Northern Ireland.
We are looking into how biodiversity regulates ecological balance within lakes and would like to assess the consequences of biodiversity loss for the provision of ecosystem services. Ecosystem services from lakes are extremely diverse: recreation, tourism, water purification, flood prevention, provision of fish for anglers and fisheries and other supporting services such as carbon storage for climate mitigation.
Because of this variety, changes in lake ecological functioning may affect the different services in different ways, rendering best practices for restoration and management difficult to establish.
One aspect we are particularly interested to develop in LakeBESS is the importance of ecological connectivity between lakes for their biodiversity. Connectivity may be a major factor determining lake ecosystem resilience because it counter-balances the negative effect of local extinction by increasing species re-colonisation.
Another aspect of interest is the consequences of biological invasions by organisms such as zebra mussel and Canadian pondweed.
We have just started this project as part of the Biodiveristy, Ecosystem Services and Sustainablility (BESS) research programme funded by the UK Natural Environment Research Council (NERC).
Our team is composed of Carl Sayer, Helen Bennion, Jorge Salgado and Ambroise Baker at UCL, Tom Davidson at the University of Aarhus (Denmark), Beth Okamura at the Natural History Museum and Nigel Willby at Stirling University. We are looking forward to a field campaign this summer and to presenting the result of our work to the numerous stakeholders in both lake districts.
We also would love to hear your take on how changes in lakes, or in a particular lake, can affect people’s lives.