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Species Invasions (species + invasion)

Distribution by Scientific Domains

Life Sciences	72%
Humanities and Social Sciences	16%

Distribution within Life Sciences

Ecology & Organismal Biology	69%
Conservation Science	22%

Selected Abstracts

BIODIVERSITY RESEARCH: Native-exotic species richness relationships across spatial scales and biotic homogenization in wetland plant communities of Illinois, USA

DIVERSITY AND DISTRIBUTIONS, Issue 5 2010
Hua Chen
Abstract Aim, To examine native-exotic species richness relationships across spatial scales and corresponding biotic homogenization in wetland plant communities. Location, Illinois, USA. Methods, We analysed the native-exotic species richness relationship for vascular plants at three spatial scales (small, 0.25 m2 of sample area; medium, 1 m2 of sample area; large, 5 m2 of sample area) in 103 wetlands across Illinois. At each scale, Spearman's correlation coefficient between native and exotic richness was calculated. We also investigated the potential for biotic homogenization by comparing all species surveyed in a wetland community (from the large sample area) with the species composition in all other wetlands using paired comparisons of their Jaccard's and Simpson's similarity indices. Results, At large and medium scales, native richness was positively correlated with exotic richness, with the strength of the correlation decreasing from the large to the medium scale; at the smallest scale, the native-exotic richness correlation was negative. The average value for homogenization indices was 0.096 and 0.168, using Jaccard's and Simpson's indices, respectively, indicating that these wetland plant communities have been homogenized because of invasion by exotic species. Main Conclusions, Our study demonstrated a clear shift from a positive to a negative native-exotic species richness relationship from larger to smaller spatial scales. The negative native-exotic richness relationship that we found is suggested to result from direct biotic interactions (competitive exclusion) between native and exotic species, whereas positive correlations likely reflect the more prominent influence of habitat heterogeneity on richness at larger scales. Our finding of homogenization at the community level extends conclusions from previous studies having found this pattern at much larger spatial scales. Furthermore, these results suggest that even while exhibiting a positive native-exotic richness relationship, community level biotas can/are still being homogenized because of exotic species invasion. [source]

Assessing ecosystem threats from global and regional change: hierarchical modeling of risk to sagebrush ecosystems from climate change, land use and invasive species in Nevada, USA

ECOGRAPHY, Issue 1 2010
Bethany A. Bradley
Global change poses significant challenges for ecosystem conservation. At regional scales, climate change may lead to extensive shifts in species distributions and widespread extirpations or extinctions. At landscape scales, land use and invasive species disrupt ecosystem function and reduce species richness. However, a lack of spatially explicit models of risk to ecosystems makes it difficult for science to inform conservation planning and land management. Here, I model risk to sagebrush (Artemisia spp.) ecosystems in the state of Nevada, USA from climate change, land use/land cover change, and species invasion. Risk from climate change is based on an ensemble of 10 atmosphere-ocean general circulation model (AOGCM) projections applied to two bioclimatic envelope models (Mahalanobis distance and Maxent). Risk from land use is based on the distribution of roads, agriculture, and powerlines, and on the spatial relationships between land use and probability of cheatgrass Bromus tectorum invasion in Nevada. Risk from land cover change is based on probability and extent of pinyon-juniper (Pinus monophylla; Juniperus spp.) woodland expansion. Climate change is most likely to negatively impact sagebrush ecosystems at the edges of its current range, particularly in southern Nevada, southern Utah, and eastern Washington. Risk from land use and woodland expansion is pervasive throughout Nevada, while cheatgrass invasion is most problematic in the northern part of the state. Cumulatively, these changes pose major challenges for conservation of sagebrush and sagebrush obligate species. This type of comprehensive assessment of ecosystem risk provides managers with spatially explicit tools important for conservation planning. [source]

Interpreting temporal variation in omnivore foraging ecology via stable isotope modelling

FUNCTIONAL ECOLOGY, Issue 4 2009
Carolyn M. Kurle
Summary 1The use of stable carbon (C) and nitrogen (N) isotopes (,15N and ,13C, respectively) to delineate trophic patterns in wild animals is common in ecology. Their utility as a tool for interpreting temporal change in diet due to seasonality, migration, climate change or species invasion depends upon an understanding of the rates at which stable isotopes incorporate from diet into animal tissues. To best determine the foraging habits of invasive rats on island ecosystems and to illuminate the interpretation of wild omnivore diets in general, I investigated isotope incorporation rates of C and N in fur, liver, kidney, muscle, serum and red blood cells (RBC) from captive rats raised on a diet with low ,15N and ,13C values and switched to a diet with higher ,15N and ,13C values. 2I used the reaction progress variable method (RPVM), a linear fitting procedure, to estimate whether a single or multiple compartment model best described isotope turnover in each tissue. Small sample Akaike Information criterion (AICc) model comparison analysis indicated that 1 compartment nonlinear models best described isotope incorporation rates for liver, RBC, muscle, and fur, whereas 2 compartment nonlinear models were best for serum and kidney. 3I compared isotope incorporation rates using the RPVM versus nonlinear models. There were no differences in estimated isotope retention times between the model types for serum and kidney (except for N turnover in kidney from females). Isotope incorporation took longer when estimated using the nonlinear models for RBC, muscle, and fur, but was shorter for liver tissue. 4There were no statistical differences between sexes in the isotope incorporation rates. I also found that N and C isotope incorporation rates were decoupled for liver, with C incorporating into liver tissue faster than N. 5The data demonstrate the utility of analysing isotope ratios of multiple tissues from a single animal when estimating temporal variation in mammalian foraging ecology. [source]

COMPARING INVASIVE NETWORKS: CULTURAL AND POLITICAL BIOGRAPHIES OF INVASIVE SPECIES,

GEOGRAPHICAL REVIEW, Issue 2 2004
PAUL ROBBINS
ABSTRACT. Under what cultural and political conditions do certain species become successful invaders? What impact does species invasion have on human culture and politics? The work assembled in this special issue of the Geographical Review suggests complex interspecies interactions that complicate any answer to these questions. It demonstrates the need to advance a more integrative human/environment approach to species invasion than has hitherto been seen. Reviewing the concepts demonstrated in these articles and applying them to case histories of Mimosaceae (a family that includes genera such as Acacia, Prosopis, and Mimosa) invasion, two general principles become clear. The status and identification of any species as an invader, weed, or exotic are conditioned by cultural and political circumstances. Furthermore, because the human "preparation of landscape" is a prerequisite for most cases of invasion, and because species invasions impact local culture and politics in ways that often feed back into the environmental system, specific power-laden networks of human and non-human actors tend to create the momentum for invasion. It is therefore possible to argue a more general cultural and political account of contemporary species expansion: It is not species but sociobiological networks that are invasive. [source]

Prediction of Prosopis species invasion in Kenya using geographical information system techniques

AFRICAN JOURNAL OF ECOLOGY, Issue 3 2010
Gabriel M. Muturi
Abstract Tree species from Prosopis genus were widely planted for rehabilitation of degraded drylands of Kenya. However, they have invaded riverine ecosystems where they cause negative socio-economic and ecological impacts. GIS was used to estimate the reverine area threatened by Prosopis invasion in Kenya. Landsat satellite images, field surveys and past studies were also used to assess the resulting potential ecological impacts in the Turkwel ecosystem in Kenya. The study revealed that 3.0 to 27.7 million hectares are threatened by invasion, based on documented riverine forests width of 0.5,3 km. Image analysis showed that 34% of the sites under positive change were invaded, with most invasions occurring in natural forests and abandoned farms. Prosopis had overall occurrence of 39% in all the sampled sites in 2007, in contrast to 0% in 1990 that was reported in an earlier study. In these areas, Acacia tortilis occurrence dropped from 81% in 1990 to 43% in 2007, suggesting that Prosopis could be displacing it. Utilization of Prosopis for fodder, fuel wood and pods for animal feeds is recommended as a management tool to reverse the trend. The methods used in this study are also recommended for invasion prediction and management in other similar ecosystems. Résumé Pour la réhabilitation de zones arides dégradées au Kenya, on a abondamment planté trois espèces de Prosopis. Cependant, elles ont envahi des écosystèmes riverains où elles ont des impacts socioéconomiques et écologiques négatifs. On a utilisé un SIG pour estimer la superficie riveraine menacée par l'invasion des Prosopis au Kenya. Des images satellite Landsat, des études sur le terrain et les résultats de travaux antérieurs ont aussi été utilisés pour évaluer les éventuels impacts écologiques dans l'écosystème de Turkwel. L'étude a révélé qu'entre 3,0 et 27,7 millions d'hectares sont menacés d'invasion, si l'on se base sur la largeur de forêt riveraine documentée, qui est de 0,5 à 3 km. L'analyse des images a montré que 34% des sites en mutation positive étaient envahis, et que la plupart des invasions touchaient des forêts naturelles et des exploitations agricoles abandonnées. Les Prosopis avaient un taux d'occurrence global de 39% dans tous les sites échantillonnés en 2007, à comparer avec le chiffre de 0% rapporté en 1990 par une étude antérieure. Dans ces zones, la présence d'Acacia tortilis a chuté de 81% en 1990 à 43% en 2007, ce qui laisse penser que Prosopis pourrait être responsable de ce déplacement. On recommande d'utiliser Prosopis comme fourrage et bois de feu et de donner les gousses au bétail, ce qui serait une façon de les gérer pour inverser la tendance. Les méthodes utilisées dans cette étude sont aussi recommandées pour prédire et gérer les invasions dans des écosystèmes comparables. [source]

Structure and composition of vegetation along an elevational gradient in Puerto Rico

JOURNAL OF VEGETATION SCIENCE, Issue 5 2006
W.A. Gould
Liogier & Martorrell (1999) Abstract Question: What are the composition, conservation status, and structural and environmental characteristics of eight mature tropical forest plant communities that occur along an elevational gradient. Location: Northeastern Puerto Rico. Methods: We quantified the species composition, diversity, conservation status, and ecological attributes of eight mature tropical forest plant communities in replicated plots located to sample representative components of important forest types occurring along an elevational gradient. A suite of environmental and vegetation characteristics were sampled at each plot and summarized to characterize communities and analyse trends along the elevational gradient. Results: The set of communities included 374 species; 92% were native, 14% endemic, and 4% critical elements (locally endangered) to the island. All communities, occurring within a wide range of patch sizes and degree of conservation protection, showed a high percentage of native species (> 89% per plot). The lowland moist forest communities, occurring within a matrix of urbanization, agriculture, and disturbance, had the highest degree of invasion by exotics. Community descriptions were nested within a variety of hierarchies to facilitate extrapolation of community characteristics to larger ecosystem units. Basal area, above-ground biomass, canopy heights, and mean species richness peaked at mid elevations. Conclusions: It is significant that all of these forest communities continue to be dominated by native species while existing in a matrix of human and natural disturbance, species invasion, and forest regeneration from widespread agriculture. The lowland moist and dry forest types represent a minority of the protected forested areas in Puerto Rico, serve as unique genetic reservoirs, and should be protected. [source]

Control of plant species diversity and community invasibility by species immigration: seed richness versus seed density

OIKOS, Issue 1 2003
Rebecca L. Brown
Immigration rates of species into communities are widely understood to influence community diversity, which in turn is widely expected to influence the susceptibility of ecosystems to species invasion. For a given community, however, immigration processes may impact diversity by means of two separable components: the number of species represented in seed inputs and the density of seed per species. The independent effects of these components on plant species diversity and consequent rates of invasion are poorly understood. We constructed experimental plant communities through repeated seed additions to independently measure the effects of seed richness and seed density on the trajectory of species diversity during the development of annual plant communities. Because we sowed species not found in the immediate study area, we were able to assess the invasibility of the resulting communities by recording the rate of establishment of species from adjacent vegetation. Early in community development when species only weakly interacted, seed richness had a strong effect on community diversity whereas seed density had little effect. After the plants became established, the effect of seed richness on measured diversity strongly depended on seed density, and disappeared at the highest level of seed density. The ability of surrounding vegetation to invade the experimental communities was decreased by seed density but not by seed richness, primarily because the individual effects of a few sown species could explain the observed invasion rates. These results suggest that seed density is just as important as seed richness in the control of species diversity, and perhaps a more important determinant of community invasibility than seed richness in dynamic plant assemblages. [source]

The Role of Cloud Combing and Shading by Isolated Trees in the Succession from Maquis to Rain Forest in New Caledonia1

BIOTROPICA, Issue 2 2002
L. S. Rigg
ABSTRACT This study examined the role of shading and cloud combing of moisture by scattered trees of the emergent conifer Araucaria laubenfelsii (Corbass.) in montane shrubland-maquis at Mont Do, New Caledonia, in facilitating the succession from shrubland to rain forest. Water collection experiments showed that these trees combed significant amounts of water from low clouds on days when no rainfall was recorded and deposited this moisture on the ground beneath the tree canopy. Analysis of photosystem II function in A. laubenfelsii and five other plant species using fluorometry revealed much lower photosystem stress in plants beneath scattered A. laubenfelsii than for individuals exposed to full sunlight in the open maquis. Transition matrix analyses of vegetation change based on "the most likely recruit to succeed" indicated that the transition from maquis to forest was markedly faster when emergent trees of A. laubenfelsii acted as nuclei for forest species invasion of die maquis. On the basis of these lines of evidence, it is argued that increased moisture and shading supplied to the area directly below the crown of isolated A. laubenfelsii trees in the maquis facilitates the establishment of both conifer seedlings and other rain forest tree and shrub species. In the absence of fire, rain forest can reestablish through spread in two ways: first, by expansion from remnant patches, and second, from coalescence of small rain forest patches formed around individual trees of A. laubenfelsii. [source]

Nonindigenous Species: Ecological Explanation, Environmental Ethics, and Public Policy

CONSERVATION BIOLOGY, Issue 1 2003
David M. Lodge
Misunderstandings and tension exist regarding the science, values, environmental ethics, and public policy relevant to invasive species, which are the subset of nonindigenous species that cause economic or environmental damage. Although there is a natural background rate at which species invasions occur, it is much lower than the current human-induced rates at which species are being moved around the globe. Contrary to some recently voiced opinions , the fact that some species invasions occur without human assistance does not confer acceptability on all species invasions. Also, despite claims to the contrary, the reductions of native biodiversity caused by nonindigenous species are large and well documented. Even if that were not true, an emphasis on species numbers alone as a metric for the impact of nonindigenous species does not adequately incorporate the high value many humans place on the uniqueness of regional biota. Because regional biota are being homogenized by species invasions, it has become an appropriate and official public policy goal in the United States to reduce the harm done by invasive species. The goal is not, however, a reduction of numbers of nonindigenous species per se, as recently claimed by some authors, but a reduction in the damage caused by invasive species, including many sorts of environmental and economic damage. A major challenge remaining for ecology, environmental ethics, and public policy is therefore the development of widely applicable risk-assessment protocols that are acceptable to diverse constituencies. Despite apparent disagreements among scholars, little real disagreement exists about the occurrence, effects, or public-policy implications of nonindigenous species. Resumen: El público está recibiendo un mensaje confuso de ecologistas, otros académicos y periodistas sobre el tema de especies no nativas. Existen malos entendidos y tensión en relación con la ciencia, los valores, la ética ambiental y las políticas públicas relevantes a las especies invasoras, que son un subconjunto de las especies no nativas que causan daños económicos o ambientales. Aunque existe una tasa natural a la que ocurren invasiones, es mucho más baja que las actuales tasas, inducidas por humanos, a las que especies son movidas alrededor del mundo. Al contrario de algunos autores recientes, el hecho de que algunas invasiones de especies ocurren sin asistencia humana no le confiere aceptabilidad moral sobre todas las invasiones de especies. También, a pesar de recientes afirmaciones de lo contrario, las reducciones de biodiversidad nativa debido a especies no nativas son notables y están bien documentadas. Aún si no fuera verdad, el énfasis sólo en el número de especies como una medida del impacto de especies no nativas no incorpora adecuadamente el alto valor que muchos humanos reconocen en la singularidad de la biota regional. Debido a que la biota regional está siendo homogeneizada por invasiones de especies, la reducción del daño causado por especies invasoras se ha convertido en una política pública apropiada y oficial en los Estados Unidos. Sin embargo, la meta no es la reducción de especies no nativas, en si, como afirman algunos autores recientes, sino una reducción de los impactos dañinos de las especies invasoras, incluyendo muchos tipos de daño económico y ambiental. Por lo tanto, un reto mayor para la ecología, la ética ambiental y la política pública es el desarrollo de protocolos de evaluación de riesgos ampliamente aplicables que sean aceptables para electores diversos. A pesar de aparentes desacuerdos entre académicos, existe poco desacuerdo real acerca de la ocurrencia, el impacto o las implicancias en política pública de las especies no nativas. [source]

Elevated dominance of extrafloral nectary-bearing plants is associated with increased abundances of an invasive ant and reduced native ant richness

DIVERSITY AND DISTRIBUTIONS, Issue 5 2009
Amy M. Savage
Abstract Aim, Invasive ants can have substantial and detrimental effects on co-occurring community members, especially other ants. However, the ecological factors that promote both their population growth and their negative influences remain elusive. Opportunistic associations between invasive ants and extrafloral nectary (EFN)-bearing plants are common and may fuel population expansion and subsequent impacts of invasive ants on native communities. We examined three predictions of this hypothesis, compared ant assemblages between invaded and uninvaded sites and assessed the extent of this species in Samoa. Location, The Samoan Archipelago (six islands and 35 sites). Methods, We surveyed abundances of the invasive ant Anoplolepis gracilipes, other ant species and EFN-bearing plants. Results,Anoplolepis gracilipes was significantly more widely distributed in 2006 than in 1962, suggesting that the invasion of A. gracilipes in Samoa has progressed. Furthermore, (non- A. gracilipes) ant assemblages differed significantly between invaded and uninvaded sites. Anoplolepis gracilipes workers were found more frequently at nectaries than other plant parts, suggesting that nectar resources were important to this species. There was a strong, positive relationship between the dominance of EFN-bearing plants in the community and A. gracilipes abundance on plants, a relationship that co-occurring ants did not display. High abundances of A. gracilipes at sites dominated by EFN-bearing plants were associated with low species richness of native plant-visiting ant species. Anoplolepis gracilipes did not display any significant relationships with the diversity of other non-native ants. Main conclusions, Together, these data suggest that EFN-bearing plants may promote negative impacts of A. gracilipes on co-occurring ants across broad spatial scales. This study underscores the potential importance of positive interactions in the dynamics of species invasions. Furthermore, they suggest that conservation managers may benefit from explicit considerations of potential positive interactions in predicting the identities of problematic invaders or the outcomes of species invasions. [source]

The worldwide airline network and the dispersal of exotic species: 2007,2010

ECOGRAPHY, Issue 1 2009
Andrew J. Tatem
International air travel has played a significant role in driving recent increases in the rates of biological invasion and spread of infectious diseases. By providing high speed, busy transport links between spatially distant, but climatically similar regions of the world, the worldwide airline network (WAN) increases the risks of deliberate or accidental movements and establishment of climatically sensitive exotic organisms. With traffic levels continuing to rise and climates changing regionally, these risks will vary, both seasonally and year-by-year. Here, detailed estimates of air traffic trends and climate changes for the period 2007-2010 are used to examine the likely directions and magnitudes of changes in climatically sensitive organism invasion risk across the WAN. Analysis of over 144 million flights from 2007-2010 shows that by 2010, the WAN is likely to change little overall in terms of connecting regions with similar climates, but anticipated increases in traffic and local variations in climatic changes should increase the risks of exotic species movement on the WAN and establishment in new areas. These overall shifts mask spatially and temporally heterogenous changes across the WAN, where, for example, traffic increases and climatic convergence by July 2010 between parts of China and northern Europe and North America raise the likelihood of exotic species invasions, whereas anticipated climatic shifts may actually reduce invasion risks into much of eastern Europe. [source]

Effects of plant invasions on the species richness of abandoned agricultural land

ECOGRAPHY, Issue 6 2001
Scott J. Meiners
While exotic plant invasions are thought to lead to declines in native species, the long-term impacts of such invasions on community structure are poorly known. Furthermore, it is unknown how exotic plant invasions compare to invasions by native species. We present data from 40 yr of continuous vegetation sampling of 10 fields released from agriculture to examine the effects of invasions on species richness. The effects of both exotic and native species invasions on species richness were largely driven by variations among fields with most species not significantly affecting species richness. However, invasion and dominance by the exotics Agropyron repens, Lonicera japonica. Rosa multiflora. Trifolium pratense and the native Solidago canadensis were associated with declines in richness. Invasions by exotic and native species during old field succession have similar effects on species richness with dominance by species of either group being associated with loss of species richness. Exotic species invasions tended to have stronger effects on richness than native invasions. No evidence was found of residual effects of invasions because the impact of the invasion disappeared with the decline of the invading population. When pooled across species, heavy invasion by exotic species resulted in greater loss o species richness than invasion by native species. Studies of invasion that utilize multiple sites must account for variability among sites. In our study, had we no included field as a factor we would have incorrectly concluded that invasion consistently resulted in changes in species richness. [source]

Anthropogenic impacts upon plant species richness and net primary productivity in California

ECOLOGY LETTERS, Issue 2 2005
John W. Williams
Abstract We assess the importance of anthropogenic land-use, altered productivity, and species invasions for observed productivity,richness relationships in California. To this end, we model net primary productivity (NPP) c. 1750 AD and at present (1982,1999) and map native and exotic vascular plant richness for 230 subecoregions. NPP has increased up to 105% in semi-arid areas and decreased up to 48% in coastal urbanized areas. Exotic invasions have increased local species diversity up to 15%. Human activities have reinforced historical gradients in species richness but reduced the spatial heterogeneity of NPP. Structural equation modelling suggests that, prior to European settlement, NPP and richness were primarily controlled by precipitation and other abiotic variables, with NPP mediating richness. Abiotic variables remain the strongest predictors of present NPP and richness, but intermodel comparisons indicate a significant anthropogenic impact upon statewide distributions of NPP and richness. Exotic and native species each positively correlate to NPP after controlling for other variables, which may help explain recent reports of positively associated native and exotic richness. [source]

Coupling long-term studies with meta-analysis to investigate impacts of non-native crayfish on zoobenthic communities

FRESHWATER BIOLOGY, Issue 2 2006
JULIA M. MCCARTHY
Summary 1. Biological invasions are widely recognised as a significant component of human-caused environmental change and a primary threat to native biodiversity. The negative impacts of species invasions are particularly evident for freshwater crayfish faunas. 2. This study provides novel insight into the ecological effects of native and non-native crayfish on zoobenthic communities (with emphasis on the non-native rusty crayfish, Orconectes rusticus) across broad scales by combining a meta-analysis of small-scale experimental studies with a long-term observational study conducted over a 24 year period in Sparkling Lake, Wisconsin, U.S.A. (46°00,N, 89°42,W). 3. The meta-analysis summarised quantitatively the results of cage experiments for seven species of crayfish spanning four continents. We found that total zoobenthos densities (primarily Gastropoda and Diptera) were significantly lower in treatments containing crayfish relative to controls; a result that was significant for non-native crayfish but not for crayfish in their native range, perhaps owing to a small sample size. In contrast to other species, rusty crayfish were also negatively associated with Ephemeroptera. 4. Results from the time series analysis comparing temporal trends in rusty crayfish and invertebrate abundances from Sparkling Lake were consistent with the findings from the meta-analysis. Rusty crayfish were negatively correlated with the abundance of total zoobenthos, Diptera, Ephemeroptera and Odonata, as well as families of Trichoptera. 5. By coupling the results from short and long-term research, our study offers greater insight into the nature of crayfish-invertebrate interactions in aquatic systems, revealing consistent effects of invasive crayfish on native fauna. The control and management of invasive species is facilitated by the knowledge that well executed small-scale studies may be extrapolated to understand larger-scale ecological interactions. [source]

COMPARING INVASIVE NETWORKS: CULTURAL AND POLITICAL BIOGRAPHIES OF INVASIVE SPECIES,

Biotic homogenization: a new research agenda for conservation biogeography

JOURNAL OF BIOGEOGRAPHY, Issue 12 2006
Julian D. Olden
Abstract Aim, Biotic homogenization describes the process by which species invasions and extinctions increase the genetic, taxonomic or functional similarity of two or more biotas over a specified time interval. The study of biotic homogenization is a young and rapidly emerging research area in the budding field of conservation biogeography, and this paper aims to synthesize our current knowledge of this process and advocate a more systematic approach to its investigation. Methods, Based on a comprehensive examination of the primary literature this paper reviews the process of biotic homogenization, including its definition, quantification, underlying ecological mechanisms, environmental drivers, the empirical evidence for different taxonomic groups, and the potential ecological and evolutionary implications. Important gaps in our knowledge are then identified, and areas of new research that show the greatest promise for advancing our current thinking on biotic homogenization are highlighted. Results, Current knowledge of the patterns, mechanisms and implications of biotic homogenization is highly variable across taxonomic groups, but in general is incomplete. Quantitative estimates are almost exclusively limited to freshwater fishes and plants in the United States, and the principal mechanisms and drivers of homogenization remain elusive. To date research has focused on taxonomic homogenization, and genetic and functional homogenization has received inadequate attention. Trends over the past decade, however, suggest that biotic homogenization is emerging as a topic of greater research interest. Main conclusions, My investigation revealed a number of important knowledge gaps and priority research needs in the science of biotic homogenization. Future studies should examine the homogenization process for different community properties (species occurrence and abundance) at multiple spatial and temporal scales, with careful attention paid to the various biological mechanisms (invasions vs. extinctions) and environmental drivers (environmental alteration vs. biotic interactions) involved. Perhaps most importantly, this research should recognize that there are multiple possible outcomes resulting from the accumulation of species invasions and extinctions, including biotic differentiation whereby genetic, taxonomic or functional similarity of biotas decreases over time. [source]

The importance of biological inertia in plant community resistance to invasion

JOURNAL OF VEGETATION SCIENCE, Issue 3 2003
Betsy Von Holle
Abstract. Insights into the ecology of historic invasions by introduced species can be gained by studying long-term patterns of invasions by native species. In this paper, we review literature in palaeo-ecology, forest-stand simulation modelling, and historical studies of plant species invasions to illustrate the relevance of biological inertia in plant communities to invasion ecology. Resistance to invasion occurs in part because of environmental, demographic, and biotic factors influencing the arrival and establishment of invading species. We propose that biological inertia within the resident community is a fourth component of resistance to invasion, because of the lag time inherent in eliminating resident species and perhaps their traces after environmental conditions become suitable for invasion by immigrating species. Whether or not an introduced species invades can be conditioned by the presence of the pre-existing community (and/or its legacy) in addition to the other biotic and abiotic factors. [source]

From simple rules to cycling in community assembly

OIKOS, Issue 2 2004
Sebastian J. Schreiber
Simulation studies of community assembly have frequently observed two related phenomena: (1) the humpty dumpty effect in which communities can not be reconstructed by "sequential" invasions (i.e. single species invasions separated by long intervals of time) and (2) cycling between sub-communities. To better understand the mechanisms underlying these phenomena, we analyze a system consisting of two predators and two prey competing for a shared resource. We show how simple dominance rules (i.e. R* and P* rules) lead to cycling between sub-communities consisting of predator,prey pairs; predator and prey invasions alternatively lead to prey displacement via apparent competition and predator displacement via exploitative competition. We also show that these cycles are often dynamically unstable in the population phase space. More specifically, while for too slow invasion rates (i.e. "sequential" invasions) the system cycles indefinitely, faster invasion rates lead to coexistence of all species. In the later case, the assembly dynamics exhibit transient cycling between predator-prey subcommunities and the length of these transients decreases with the invasion rate and increases with habitat productivity. [source]