Null models of exotic invasion and scale-dependent patterns of native and exotic species richness

Jason D. Fridley, Rebecca L. Brown, John F. Bruno

Research output: Contribution to journalReview articlepeer-review

123 Scopus citations


Surveys of natural habitats often indicate that native and exotic species richness are positively correlated at large scales and negatively correlated at small scales. The small-scale relationship is often presented as evidence that native richness can repel invasion or conversely that exotic invasions can reduce native diversity. The larger scale pattern has been interpreted as evidence of the importance of facilitation, variable habitat quality, propagule supply, and other ecological phenomena. However, these explanations fail to consider expected native-exotic richness relationships under a null model assuming no species interactions. We show via simulation that the null expectation for a randomly assembled community is a negative relationship between native and exotic species richness at the smallest scales and, when plots vary in total richness, a positive relationship at larger scales. We outline a procedure to compare observational data to this null expectation using a permutation test of labels of species origin (native or exotic). Our use of this technique on plant community data indicates that patterns of native and exotic richness are remarkably similar to those generated by a null model. We argue that a null model approach is needed to evaluate whether observed native-exotic richness data deviate significantly from expected patterns generated by sampling and statistical artifacts.

Original languageEnglish (US)
Pages (from-to)3215-3222
Number of pages8
Issue number12
StatePublished - Dec 2004
Externally publishedYes


  • Assembly rules
  • Ecosystem functioning
  • Invasion biology
  • Invasion frequency
  • Permutation test
  • Plant diversity
  • Riparian plant communities
  • Scale dependence
  • Strandline plant communities

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


Dive into the research topics of 'Null models of exotic invasion and scale-dependent patterns of native and exotic species richness'. Together they form a unique fingerprint.

Cite this