Worldwide effects of non-native species on species-area relationships

Non-native species have invaded most parts of the world. Because many invading species are likely to become permanent inhabitants, the ways that scientists account for species richness, or the number of species found in different places, should account for non-native species. SRS scientists and collaborators undertook research to discover whether species invasion reshapes species diversity in predictable ways across the globe. They found that as the proportion of nonnatives grew, the species-area relationships for all species became stronger. And while invasions increased local diversity, the increases may be transitory. Better understanding species-area relationships has practical implications – for example, it may help predict the likelihood of future invasions and prepare for their consequences.

effects of non-natives on species area relationshipsThe number of species encountered in an area will grow as the area considered grows. This deceptively simple phenomenon, known to scientists as the species-area relationship (SAR), is one of the most well-studied aspects of ecosystems, and different ecosystems can have very different SARs. But SARs are likely changing as a result of nonnative species invasions. SRS scientists and university collaborators used published and newly compiled data (35 datasets worldwide) to examine how species invasions affect SARs across a variety taxonomic groups and ecosystems around the world. 
Examining SARs for native, non-native, and all species, the researchers investigated how the proportion of non-native species affected SARs. Post-invasion SARs for all species (native plus non-native) became stronger as the proportion of nonnatives grew, a pattern that held worldwide. There were some differences among non-native taxonomic groups in filling new niches and between islands and mainland ecosystems. The global study also produced evidence that invasions may increase local diversity. However, due to the highly dynamic nature of human-caused species introductions, as well as the possibility of local extinctions following invasion, it remains to be seen whether any increased diversity is transitory. 
Improved understanding of changing SARs has practical implications for conservation and ecosystem management—for example, it may help predict the likelihood of future invasions and to prepare for their consequences. Non-native species have invaded most parts of the world, and the invasion process is expected to accelerate, affecting many aspects of native ecosystems.

Pictured: A forest invaded by many nonnative species. Such extensive invasion can cause local extinctions and/or regional extinction debts of native species, potentially affecting species-area relationships in the future. USDA Forest Service image.

Related publications:

Partners: Duke University, University of North Carolina, University of Tennessee, Northeast Normal University

Contact: Qinfeng Guo, Eastern Forest Environmental Threat Assessment Center,

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