Abstract
Growing travel and trade threatens biodiversity as it increases the rate of biological invasions globally, either by accidental or intentional introduction. Therefore, avoiding these impacts by forecasting invasions and impeding further spread is of utmost importance. In this study, three forecasting approaches were tested and combined to predict the invasive behaviour of the alien macrophyte Lemna minuta in comparison with the native Lemna minor: the functional response (FR) and relative growth rate (RGR), supplemented with a combined biomass-based nutrient removal (BBNR). Based on the idea that widespread invasive species are more successful competitors than local, native species, a higher FR and RGR were expected for the invasive compared to the native species. Five different nutrient concentrations were tested, ranging from low (4 mgN.L-1 and 1 mgP.L-1) to high (70 mgN.L-1 and 21 mgP.L-1). After four days, a significant amount of nutrients was removed by both Lemna spp., though significant differences among L. minor and L. minuta were only observed at lower nutrient concentrations (lower than 17 mgN.L-1 and 6 mgP.L-1) with higher nutrient removal exerted by L. minor. The derived FR did not show a clear dominance of the invasive L. minuta, contradicting field observations. Similarly, the RGR ranged from 0.4 to 0.6 d-1, but did not show a biomass-based dominance of L. minuta (0.5 ± 0.1 d-1 versus 0.63 ± 0.09 d-1 for L. minor). BBNR showed similar results as the FR. Contrary to our expectations, all three approaches resulted in higher values for L. minor. Consequently, based on our results FR is sensitive to differences, though contradicted the expectations, while RGR and BBNR do not provide sufficient power to differentiate between a native and an invasive alien macrophyte and should be supplemented with additional ecosystem-based experiments to determine the invasion impact.
Highlights
Environmental degradation and biodiversity loss are considered to be important consequences of the globally increasing rate of biological invasions [1, 2]
Nutrient analyses performed at day 0 and day 4 resulted in the average nutrient concentrations provided in Supporting Information (S1 and S2 Tables) for total nitrogen (TN) and total phosphorus (TP), respectively
Nutrient masses were inferred from the measured nutrient concentrations, resulting in a similar nutrient content for L. minor and L. minuta. Both total nitrogen and total phosphorus differed significantly (p-values < 0.01) from the initial mass when L. minor or L. minuta was present at high or low nutrient concentrations
Summary
Environmental degradation and biodiversity loss are considered to be important consequences of the globally increasing rate of biological invasions [1, 2]. FR and RGR of Invasive Lemna minuta accidentally [3] Introduction of such an alien organism in a yet non-colonized environment can, subsequently, result in its establishment and spread, thereby threatening current communities, economic activities and human health [4,5,6]. The ability to forecast and impede future introductions, establishment and spread of alien species is of utmost importance to develop time- and cost-reducing measures. Identifying potential introductions, avoiding establishment and impeding further spread of invasive alien species (IAS) by detection and subsequent large-scale eradication requires financial input and highly destructive measures [5]. Understanding the process of invasion provides the possibility of counteractive management to limit invasion impact and re-establish native communities [9, 10] on a large scale. Small-scale eradication of invasive species is a more preferred action as it is less destructive and can be successfully applied when an alien species is discovered rapidly [5], though it requires a lot of time, effort and capital [11]
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