Résumé :
|
One of the main current threats to biodiversity and ecosystem function is the introduction of invasive species. We received 26 variables on the life-history, ecology and human use of the 69 inland fish species of the Iberian Peninsula reporting that the phylogeny, variability (in addition to central tendency) and human use are needed to a better understanding of the differences between native and invasive species. The taxonomic distribution of invasive fish species deviated significantly from world freshwater richness and in contrast to native species, invasive fish belonged to only five taxonomic orders but a wide spectrum of families not native to the Iberian Peninsula. The life-history traits were highly dependent on taxonomy since after accounting for phylogeny, invasive species displayed differences in reproductive season. Human use was also significantly different between native and invasive taxonomic distribution because of the high diversity of species introduced. We show that accounting for taxonomy and studying variability in addition to central tendency is important in the comparison of life-history traits between native and invasive species. Some of the species most threatened by invasive fish species, mainly the mosquitofish (Gambusia holbrooki), are the Mediterranean native cyprinodontiforms. We report the first data on the use of occasionally-inundated habitats, the diet and prey electivity of the Spanish toothcarp contrasting habitats: mats of green macroalgae, open water, and glasswort (that is occasionally inundated). The three habitats differed is density and species composition, with algal mats showing higher invertebrate biomasses and glasswort higher organisms diversity. Glasswort presented the highest density of mature toothcarp, whilst immature fish were similarly abundant in the glasswort and algal mat habitats. Condition (weight-length relationship) and food biomass in the gut contents of immature toothcarp were higher in algal mats than in glasswort, whereas there were no differences for mature fish. Glasswort was positively selected by mature fish but seemed a disadvantageous habitat for immature toothcarp. In general, toothcarp's diet was omnivorous, dominated by harpacticoid copepods, copepod nauplii and detritus. However, diet composition varied among habitats, depending on prey availability. Although a benthic feeding habitat has previously been suggested, in our study the diet was based rather on water column organisms for both glasswort and algal mat habitats. There was also an ontogenic diet shift, with an increase of mean prey length with fish length, clearly linked to a microhabitat change? Smaller fish showed positive electivity on planktonic prey, while larger fish elected more benthic organisms. Mosquitofish (Gambusia hobrooki) is one of the worst species worldwide with strong impacts on ecosystem functioning and native species. It has been previously hypothesized, based on field observations, that salinity limits the invasive success of mosquitofish and constitutes a refuge for native cyprinodontiforms. However, there are few studies on how salinity affects its ecology and biology and whether it mediates the behavioral interactions with native species is largely unknown. In the last part of this work we report information to understand the role of salinity in the invasive success of mosquitofish. We examined differences on mosquitofish life history traits inhabitating from fresh (near ca. 0,2% of salinity) to polysaline waters (ca. 23%). Salinity affected density and life history traits of both male and female mosquitofish. Both mosquitofish sexes decreased they density and increased reproductive investment with salinity at the cost of somatic condition in females. Females from higher salinity waters reproduced earlier, since presented embryos on advanced developmental stages, and presented heavier embryos (independently of the maturation state, after correction for brood and fish size). Furthermore, our data showed that some mosquitofish can adopt a matrotrophic strategy although it has previously been considered a lecithrotrophic species. On the other hand, we experimentally tested the role of salinity on the agonistic behaviour and food competition between mosquitofish and an endangered cyprinodont, demonstrating that mosquitofish decreased its agressive behaviour towards the toothcarp and captured less prey, reducing its efficiency with salinity increases. In contrast, toothcarp did not change its behaviour with different salinity treatments. Therefore, the effects of salinity on mosquitofish life history and behavioural traits confirm previous field observations that salinity limits mosquitofish invasive success.
|