Quantifying levels of biological invasion: towards the objective classification of invaded and invasible ecosystems

Biological invasions are a global phenomenon that threatens biodiversity, and few, if any, ecosystems are free from alien species. The outcome of human‐mediated introductions is affected by the invasiveness of species and invasibility of ecosystems, but research has primarily focused on defining, characterizing and identifying invasive species; ecosystem invasibility has received much less attention. A prerequisite for characterizing invasibility is the ability to compare levels of invasion across ecosystems. In this paper, we aim to identify the best way to quantify the level of invasion by nonnative animals and plants by reviewing the advantages and disadvantages of different metrics. We explore how interpretation and choice of these measures can depend on the objective of a study or management intervention. Based on our review, we recommend two invasion indices and illustrate their use by applying them to two case studies. Relative alien species richness and relative alien species abundance indicate the contribution that alien species make to a community. They are easy to measure, can be applied to various taxa, are independent of scale and are comparable across regions and ecosystems, and historical data are often available. The relationship between relative alien richness and abundance can indicate the presence of dominant alien species and the trajectory of invasion over time, and can highlight ecosystems and sites that are heavily invaded or especially susceptible to invasion. Splitting species into functional groups and examining invasion patterns of transformer species may be particularly instructive for gauging effects of alien invasion on ecosystem structure and function. Establishing standard, transparent ways to define and quantify invasion level will facilitate meaningful comparisons among studies, ecosystem types and regions. It is essential for progress in ecology and will help guide ecosystem restoration and management.

[1]  T. Hoffman.  Fifty Years of Invasion Ecology: The Legacy of Charles Elton , 2012 .

[2]  Isabelle Reginster,et al.  Projecting trends in plant invasions in Europe under different scenarios of future land-use change , 2012 .

[3]  Brendan A. Wintle,et al.  Hotspots of plant invasion predicted by propagule pressure and ecosystem characteristics , 2011 .

[4]  E. Zavaleta,et al.  A global review of the impacts of invasive cats on island endangered vertebrates , 2011 .

[5]  D. Richardson,et al.  Predicting invasiveness of Australian acacias on the basis of their native climatic affinities, life history traits and human use , 2011 .

[6]  M. Vilà,et al.  Ecological impacts of invasive alien plants: a meta-analysis of their effects on species, communities and ecosystems. , 2011, Ecology letters.

[7]  Petr Pyšek,et al.  A proposed unified framework for biological invasions. , 2011, Trends in ecology & evolution.

[8]  J. Battles,et al.  The importance of quantifying propagule pressure to understand invasion: an examination of riparian forest invasibility. , 2011, Ecology.

[9]  Julian D Olden,et al.  The Potential Conservation Value of Non‐Native Species , 2011, Conservation biology : the journal of the Society for Conservation Biology.

[10]  Peter A. Vesk,et al.  Flow regulation reduces native plant cover and facilitates exotic invasion in riparian wetlands , 2011 .

[11]  A. Nicotra,et al.  Do invasive species show higher phenotypic plasticity than native species and, if so, is it adaptive? A meta-analysis. , 2011, Ecology letters.

[12]  I. Chades,et al.  Optimally managing under imperfect detection: A method for plant invasions , 2011 .

[13]  Wolfgang Nentwig,et al.  Socioeconomic legacy yields an invasion debt , 2010, Proceedings of the National Academy of Sciences.

[14]  Petr Pyšek,et al.  A compendium of essential concepts and terminology in invasion ecology , 2010 .

[15]  Petr Pyšek,et al.  Invasive Species, Environmental Change and Management, and Health , 2010 .

[16]  Wolfgang Nentwig,et al.  Disentangling the role of environmental and human pressures on biological invasions across Europe , 2010, Proceedings of the National Academy of Sciences.

[17]  J. E. Byers,et al.  Variable direct and indirect effects of a habitat-modifying invasive species on mortality of native fauna. , 2010, Ecology.

[18]  R. Chisholm.  Invasion Biology , 2010 .

[19]  M. Vilà,et al.  How well do we understand the impacts of alien species on ecosystem services? A pan-European, cross-taxa assessment , 2010 .

[20]  Wolfgang Nentwig,et al.  A Generic Impact‐Scoring System Applied to Alien Mammals in Europe , 2010, Conservation biology : the journal of the Society for Conservation Biology.

[21]  M. Fischer,et al.  A meta-analysis of trait differences between invasive and non-invasive plant species. , 2010, Ecology letters.

[22]  J. Catford,et al.  Using multi‐scale species distribution data to infer drivers of biological invasion in riparian wetlands , 2010 .

[23]  Wolfgang Nentwig,et al.  Alien species in a warmer world: risks and opportunities. , 2009, Trends in ecology & evolution.

[24]  D. Richardson,et al.  Biogeographic concepts define invasion biology , 2009 .

[25]  R. Hobbs,et al.  Novel ecosystems: implications for conservation and restoration. , 2009, Trends in ecology & evolution.

[26]  P. Hulme,et al.  Learning from failures: testing broad taxonomic hypotheses about plant naturalization. , 2009, Ecology letters.

[27]  T. Blackburn,et al.  The more you introduce the more you get: the role of colonization pressure and propagule pressure in invasion ecology , 2009 .

[28]  I. Kühn,et al.  The global invasion success of Central European plants is related to distribution characteristics in their native range and species traits , 2009 .

[29]  Petr Pyšek,et al.  Impact of invasive plants on the species richness, diversity and composition of invaded communities , 2009 .

[30]  D. Wilcove,et al.  Assessing the Threat Status of Ecological Communities , 2009, Conservation biology : the journal of the Society for Conservation Biology.

[31]  Hugh P Possingham,et al.  Managing the impact of invasive species: the value of knowing the density-impact curve. , 2009, Ecological applications : a publication of the Ecological Society of America.

[32]  C. Nilsson,et al.  Reducing redundancy in invasion ecology by integrating hypotheses into a single theoretical framework , 2009 .

[33]  Petr Pyšek,et al.  European map of alien plant invasions based on the quantitative assessment across habitats , 2009 .

[34]  D. Richardson,et al.  Subjectivity and flexibility in invasion terminology: too much of a good thing? , 2009, Biological Invasions.

[35]  B. Graae,et al.  A hierarchical framework for integrating invasibility experiments incorporating different factors and spatial scales , 2009, Biological Invasions.

[36]  J. E. Byers,et al.  Community impacts of two invasive crabs: the interactive roles of density, prey recruitment, and indirect effects , 2009, Biological Invasions.

[37]  Brendan A. Wintle,et al.  When have we looked hard enough? A novel method for setting minimum survey effort protocols for flora surveys , 2008 .

[38]  Katherine N. Suding,et al.  Restoration through reassembly: plant traits and invasion resistance. , 2008, Trends in ecology & evolution.

[39]  T. E. Martin,et al.  Introduced Mammalian Predators Induce Behavioural Changes in Parental Care in an Endemic New Zealand Bird , 2008, PloS one.

[40]  Vojtech Jarosik,et al.  Separating habitat invasibility by alien plants from the actual level of invasion. , 2008, Ecology.

[41]  Xavier Font,et al.  Habitat invasions by alien plants: a quantitative comparison among Mediterranean, subcontinental and oceanic regions of Europe , 2008 .

[42]  J C Stout,et al.  Factors Associated with Alien Plants Transitioning from Casual, to Naturalized, to Invasive , 2008, Conservation biology : the journal of the Society for Conservation Biology.

[43]  O. Pybus,et al.  Phylogeny, niches, and relative abundance in natural communities. , 2008, Ecology.

[44]  Doria R. Gordon,et al.  Consistent accuracy of the Australian weed risk assessment system across varied geographies , 2008 .

[45]  C. Canham,et al.  NEIGHBORHOOD MODELS OF THE EFFECTS OF INVASIVE TREE SPECIES ON ECOSYSTEM PROCESSES , 2008 .

[46]  Petr Pyšek,et al.  Traits Associated with Invasiveness in Alien Plants: Where Do we Stand? , 2008 .

[47]  D. Simberloff,et al.  In search of a real definition of the biological invasion phenomenon itself , 2008, Biological Invasions.

[48]  A. Ricciardi,et al.  Predicting the number of ecologically harmful exotic species in an aquatic system , 2007 .

[49]  L. Herborg,et al.  Predicting invasion risk using measures of introduction effort and environmental niche models. , 2007, Ecological applications : a publication of the Ecological Society of America.

[50]  Karen J. Esler,et al.  Riparian vegetation: degradation, alien plant invasions, and restoration prospects , 2007 .

[51]  R. Randall,et al.  The introduced flora of Australia and its weed status. , 2007 .

[52]  Alan Hastings,et al.  Invasion in a heterogeneous world: resistance, coexistence or hostile takeover? , 2007, Ecology letters.

[53]  T J Stohlgren,et al.  The invasion paradox: reconciling pattern and process in species invasions. , 2007, Ecology.

[54]  D. Richardson,et al.  The biogeography of naturalization in alien plants , 2006 .

[55]  J. Wilson,et al.  Biotic indirect effects: a neglected concept in invasion biology , 2006 .

[56]  D. Richardson,et al.  Plant invasions: merging the concepts of species invasiveness and community invasibility , 2006 .

[57]  A. Agrawal,et al.  Biotic interactions and plant invasions. , 2006, Ecology letters.

[58]  J. Balch,et al.  Assessing extinction risk in the absence of species-level data: quantitative criteria for terrestrial ecosystems , 2006, Biodiversity and Conservation.

[59]  D. Richardson,et al.  Novel ecosystems: theoretical and management aspects of the new ecological world order , 2006 .

[60]  D. Pearson,et al.  WEAK VS. STRONG INVADERS OF NATURAL PLANT COMMUNITIES: ASSESSING INVASIBILITY AND IMPACT , 2005 .

[61]  X. Font,et al.  Large-scale correlates of alien plant invasion in Catalonia (NE of Spain) , 2005 .

[62]  M. Williamson,et al.  Invaders, weeds and the risk from genetically manipulated organisms , 1993, Experientia.

[63]  M. Rejmánek,et al.  The total number of naturalized species can be a reliable predictor of the number of alien pest species , 2004 .

[64]  Francis E. Putz,et al.  A place for alien species in ecosystem restoration , 2004 .

[65]  Robert I. Colautti,et al.  A neutral terminology to define ‘invasive’ species , 2004 .

[66]  S. Pickett,et al.  Beyond biodiversity: individualistic controls of invasion in a self‐assembled community , 2004 .

[67]  P. Kareiva,et al.  Impact: Toward a Framework for Understanding the Ecological Effects of Invaders , 1999, Biological Invasions.

[68]  D. Simberloff,et al.  Positive Interactions of Nonindigenous Species: Invasional Meltdown? , 1999, Biological Invasions.

[69]  P. Mccormick,et al.  A proposed framework for developing indicators of ecosystem health , 1993, Hydrobiologia.

[70]  C. Daehler.  PERFORMANCE COMPARISONS OF Co-OCCURRING NATIVE AND ALIEN INVASIVE PLANTS: Implications for Conservation and Restoration , 2003 .

[71]  A. Lausch,et al.  Native and alien plant species richness in relation to spatial heterogeneity on a regional scale in Germany , 2003 .

[72]  David Cheal,et al.  Assessing the quality of native vegetation: The 'habitat hectares' approach , 2003 .

[73]  Thomas J. Stohlgren,et al.  The rich get richer: patterns of plant invasions in the United States , 2003 .

[74]  P. Chesson,et al.  Community ecology theory as a framework for biological invasions , 2002 .

[75]  A. Chanzy,et al.  The role of stones in soil water retention , 2002 .

[76]  D. C. L. Maitrea,et al.  Invasive alien trees and water resources in South Africa : case studies of the costs and benefits of management , 2002 .

[77]  Steven I. Higgins,et al.  USING A DYNAMIC LANDSCAPE MODEL FOR PLANNING THE MANAGEMENT OF ALIEN PLANT INVASIONS , 2000 .

[78]  D. Richardson,et al.  Recovery of South African fynbos vegetation following alien woody plant clearing and fire: implications for restoration , 2000 .

[79]  M. Rejmánek.  Invasive plants: approaches and predictions , 2000 .

[80]  Mark A. Davis,et al.  Fluctuating resources in plant communities: a general theory of invasibility , 2000 .

[81]  C. J. West,et al.  Naturalization and invasion of alien plants: concepts and definitions , 2000 .

[82]  P. Alpert,et al.  Perspectives in Plant Ecology, Evolution and Systematics Invasiveness, Invasibility and the Role of Environmental Stress in the Spread of Non-native Plants , 2022 .

[83]  P. Pheloung,et al.  A weed risk assessment model for use as a biosecurity tool evaluating plant introductions , 1999 .

[84]  W. M. Lonsdale,et al.  GLOBAL PATTERNS OF PLANT INVASIONS AND THE CONCEPT OF INVASIBILITY , 1999 .

[85]  Andrew J. Boulton,et al.  An overview of river health assessment: philosophies, practice, problems and prognosis , 1999 .

[86]  Thomas J. Stohlgren,et al.  EXOTIC PLANT SPECIES INVADE HOT SPOTS OF NATIVE PLANT DIVERSITY , 1999 .

[87]  Benjamin Smith,et al.  A consumer's guide to evenness indices , 1996 .

[88]  Surprising Behavior from a Familiar Model and Implications for Competition Theory , 1995, The American Naturalist.

[89]  I. Kowarik,et al.  Time lags in biological invasions with regard to the success and failure of alien species. , 1995 .

[90]  D. Richardson,et al.  Why Is Mountain Fynbos Invasible and Which Species Invade , 1992 .

[91]  Tarald O. Kvålseth,et al.  Note on biological diversity, evenness, and homogeneity measures , 1991 .

[92]  F. Castri,et al.  Biological Invasions: A Global Perspective , 1989 .

[93]  Marcel Rejmánek,et al.  Invasibility of plant communities , 1989 .

[94]  J. Wiens.  Spatial Scaling in Ecology , 1989 .

[95]  James A. Drake,et al.  Biological invasions : a global perspective , 1989 .

[96]  P. Vitousek,et al.  Biological Invasion by Myrica faya Alters Ecosystem Development in Hawaii , 1987, Science.

[97]  B. Mckenzie,et al.  A possible explanation for the lack of trees in the fynbos, Cape Province, South Africa , 1980 .

[98]  Robert K. Peet,et al.  The Measurement of Species Diversity , 1974 .