Ecosystem-level consequences of invasions by native species as a way to investigate relationships between evenness and ecosystem function

Abstract

Biodiversity is currently undermined worldwide principally as a result of human activities. The irreversibility of species extinction has encouraged the research community to investigate the potential effect of declining species or functional group diversity and/or composition on ecosystem function since the beginning of the 1990s. However, while changes in relative abundance among species (i.e., evenness) are more frequent than extinction of species and are able to cause important changes in ecosystem function, most studies have curiously not examined thoroughly the potential role of that diversity component. The few small-scale experimental manipulations that have so far examined the relationship between evenness and ecosystem function have produced ambiguous results, sometimes indicating an effect on selected functions, and sometimes not. Because one reason for the inconsistency of the previous results may be scale-dependency issues, we propose here an alternative approach, investigation of this relationship directly at the system-level through the opportunity offered by field studies of ecosystemlevel consequences of invasions by native species. Indeed, the specificities of changes in ecosystem structure induced by native invaders compared to exotic ones could constitute a useful tool to improve our understanding of the relationship between evenness and ecosystem function as well as to evaluate the importance of the spatial arrangement of species in the stability of ecosystems.

Long-term spatio-temporal expansion of the native-invasive Retama monosperma on coastal dunes: Importance of land-use and natural dispersal vectors

“…In agreement with Valéry et al (2009), this study supports the idea that the expansion of native-invasive species may have negative effects on ecosystem diversity and stability. In addition, it may have great relevance for the conservation of properties and processes within the ecosystems under R. monosperma invasion, likewise as it would be the case of an invasive spread of alien species.…”

“…In recent years, the importance of the expansion of exotic species in coastal dunes and their potential to induce changes in the structure and functioning of resident communities, have been recognized (Sakai et al, 2001;Valéry et al, 2009). A limited number of studies deal with the invasive expansion of native species within their natural area of distribution (Peters et al, 2006;Van Auken, 2000).…”

“…Such studies are particularly scarce in the case of coastal dunes (Isermann et al, 2007;Isermann, 2008;Nielsen et al, 2011), where the rapid expansion and increase in coverage of some species, particularly shrubs, significantly contributes to the dune stabilization process, altering the functioning of the entire ecosystem. An analysis of historical invasions, spread rates and patterns, conducted at the landscape scale, can be linked to proximate causes and can contribute to an understanding of how changes in structure and functioning of dune ecosystems occur (Valéry et al, 2009;Vilà and Ibáñez, 2011). Such analyses can also be used to model future spread (Kollmann et al, 2009), as well as help to determine the effectiveness of different management practices (Ansley et al, 2001).…”

Are the ecological impacts of alien species misrepresented? A review of the “native good, alien bad” philosophy

“…Thus, while rapid increases in population or 252 distribution are more common in alien species (due to a lack of predators, pathogens and parasites; a concept summarised in the enemy release hypothesis), the real issue is often not alien status itself, but the presence of biological traits that encourage invasiveness/expansiveness. Investigating how expansive native species affect their own ecosystems would be helpful in separating the effects of alien species 256 from invasive behaviour alone (Valéry et al 2009). …”

Deficit Watering Reduces Plant Growth to a Smaller Extent With Arbuscular Mycorrhizal Association Than Without It for Non-Invasive Grass Species but Not for Invasive Grass Species

“…Biological invasion phenomena, however, are not restricted to alien species as native species may also overwhelm new habitats (i.e. native invasive species, Valéry et al, 2008Valéry et al, , 2009. Hereafter species will be shortly referred to by their genus name.…”