Invasive water boatman alters the coexistence of native species in Spanish and Moroccan freshwaters
José Antonio Carbonell collecting macroinvertebrate samples. Image: Raquel López
A guest post by Tano Gutiérrez-Cánovas and José Antonio Carbonell.
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Biological invasions are one of the most important causes of biodiversity loss and ecosystem change worldwide, and can be especially damaging in aquatic habitats.
However, it is still unclear how biological invasions may interact with local abiotic stressors such as salinity and land-use intensification, which are expected to increase as global change intensifies. We know little about the response of native communities of insects to biological invasions, despite the huge contribution of insects to global animal biodiversity, especially in freshwater ecosystems.
The alien species Trichocorixa verticalis verticalis. Image: José Antonio Carbonell
So far, the study of the ‘invasiveness’ of alien species has been focused mainly on isolated biological characteristics (e.g. body size, trophic strategy) and the specific ecosystem impacts induced by alien species. Yet it remains unclear how the ecological and biological similarity between native and alien species may influence the success and the impact of biological invasions, especially when subject to intense environmental stressors.
In a new study recently published in the Functional Ecology, we investigated the impact of an invasive water boatman (Trichocorixa verticalis verticalis) on the coexistence patterns of three native boatman Sigara species (Sigara lateralis, Sigara scripta and Sigara selecta) along a salinity gradient.
Trichocorixa verticalis verticalis, originally distributed in North America and the Caribbean, has been recorded as an alien species in South Africa, New Caledonia, Morocco, Spain and Portugal, being the only water bug recognised as an alien species in Europe.
In our study, we characterised the habitat specialisation and functional niches of each species from physiological and biological characteristics, respectively, and their degree of overlap. The physiological characteristic studied was the salinity tolerance of the different life stages (eggs, nymphs and adults) of each species. On the other hand, the biological characteristics selected were fecundity, dispersal ability, feeding strategy, life cycle and size.
One of the surveyed wetlands at the Doñana National Park in Spain. Image: José Antonio Carbonell
After characterising the habitat specialisation and functional niches of the boatman species, we used field data (salinity and species presence) to compare their coexistence patterns of native and invasive species in invaded (south-western Iberia and northern Morocco) and non-invaded (south-eastern Iberia) freshwater ecosystems.
Finally, we tested if habitat filtering (where stress gradients segregate species into different habitats allowing regional coexistence) or niche differentiation (different resource exploitation allows the coexistence of species) affected the species’ coexistence.
The three native boatman species: A) Sigara lateralis, B) Sigara scripta, C) Sigara selecta. Image: José Antonio Carbonell
Our results showed that the presence of the invasive insect modifies the distribution and coexistence patterns of native boatmen. We found that in non-invaded areas habitat filtering drives habitat segregation of the native species along the salinity gradient, with a lower contribution of niche differentiation.
On the other hand, in invaded areas niche differentiation seems to be the main mechanism preventing competition among the invasive and native species, enabling coexistence and resource partitioning along the salinity gradient.
The present work makes a novel contribution to the study of the impacts of invasive species at the community level through the integration of habitat specialisation and functional niche approaches with field occurrence data. We showed how the presence of the invasive species T. v. verticalis can modify the distribution and co-occurrence patterns of native Sigara species along the salinity gradient, as well as the main assembly rules that shape the assemblages in non-invaded and invaded areas.
Our approach may prove useful in helping scientists anticipate the consequences of ecologically novel invaders for native communities at structural and functional levels in a global change context.
The Freshwater Blog 