sábado, 7 de octubre de 2017

Biological invasions modify the coexistence of native species in aquatic ecosystems

Young limnologists link functional ecology and invasive species habitat niches to predict biodiversity losses

Version in Spanish and Portuguese

Biological invasions are one of the most important causes of biodiversity loss and ecosystem change worldwide, which are especially damaging in aquatic habitats. However, it is still unclear how biological invasions may interact with local abiotic stressors (e.g., salinity, land-use intensification), which are expected to increase as global change intensifies. Furthermore, 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.

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 in the presence of intense environmental stressors.

In a new study recently published in Functional Ecology, we investigated the impact of an invasive water boatman (Trichocorixa verticalis verticalis) on the co-existence 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.

Fig. 1. The alien species Trichocorixa verticalis verticalis

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.

Fig 2. One of the surveyed wetlands at the Doñana National Park (Spain)

After characterising the habitat specialisation and functional niches, we used field data (salinity and species presence) to compare the coexistence patterns of native and invasive species in invaded (south-western Iberia and northern Morocco) and non-invaded (south-eastern Iberia) areas.

Finally, we tested if habitat filtering (stress gradient segregates species into different habitats allowing regional coexistence) or niche differentiation (different resource exploitation allows the coexistence of species) assembly rules mediate their coexistence. To carry this out, we tested the actual co-occurrence values against the patterns found in simulated matrices created under null model scenarios of habitat filtering and niche differentiation.

Fig. 3. The three native boatman species. A) Sigara lateralis, B) Sigara scripta, C) Sigara selecta

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 by integrating 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 can also be useful to anticipate the consequences of ecologically novel invaders for native communities at structural and functional levels under a global change context.

Fig. 4. José Antonio Carbonell collecting macroinvertebrate samples

Carbonell, J. A., Velasco, J., Millán, A., Green, A. J., Coccia, C., Guareschi, S., & Gutiérrez-Cánovas, C. (2017). Biological invasion modifies the co-occurrence patterns of insects along a stress gradient. Functional Ecology. DOI: 10.1111/1365-2435.12884.