Due to anthropogenic pressure some species have declined whereas others have increased within their native ranges. Simultaneously, many species introduced by humans have established self-sustaining populations elsewhere (i.e. have become naturalized aliens). Previous studies have shown that particularly plant species that are common within their native range have become naturalized elsewhere. However, how changes in native distributions correlate with naturalization elsewhere is unknown. We compare data on grid-cell occupancy of native vascular plant species over time for 10 European regions (countries or parts thereof). For nine regions, both early occupancy and occupancy change correlate positively with global naturalization success (quantified as naturalization in any administrative region and as the number of such regions). In other words, many plant species spreading globally as naturalized aliens are also expanding within their native regions. This implies that integrating data on native occupancy dynamics in invasion risk assessments might help prevent new invasions.
Humans have spread plants globally for millennia, inadvertently causing ecological disruptions. Apart from their negative effects, biological invasions provide a unique opportunity to study how species modify their niche when confronted with novel environments. Focusing on the Mediterranean Basin, we assessed (1) which traits influence niche dynamics, and (2) whether niche conservatism or niche shift promotes invasion success. We selected the 80 most widespread alien vascular plant species in Mediterranean Europe and compiled data on their distributions in their native and invaded ranges. We then tested how a species' residence time, biogeographic origin, dispersal ability, functional traits, and intraspecific trait variability (ITV) influence its niche dynamics following invasion. Using already published independent data, we finally assessed whether niche dynamics can explain different dimensions of invasion success (quantified as regional spread or local abundance). We found that niche shifts were common (71% of species) and were mostly driven by species failing to occupy all suitable environments in their invaded range (unfilling), regardless of residence time. Niche unfilling and niche expansion were more important in species with high intraspecific trait variability introduced from non-Mediterranean biomes (temperate or tropical). Niche expansion was also greater in species with long-distance dispersal, a narrow native niche, and bigger seeds. Interestingly, invasion success correlated more with a species' ability to conserve its niche and residence time than with niche expansion. Niche shifts were better predicted by species traits than residence time. For example, high adaptive and acclimatization potential (inferred from high intraspecific trait variability) favored niche shifts in general, and long-distance dispersal favored niche expansion. Understanding how these traits relate to niche dynamics is important since a species' ability to conserve and fill its niche is, in turn, a good predictor of invasion success.
- Keywords
- acclimatization, invasion success, invasive species, niche dynamics, niche filling, phenotypic plasticity, rapid adaptation, species traits,
- MeSH
- Plant Dispersal * MeSH
- Ecosystem * MeSH
- Plants * classification MeSH
- Introduced Species * MeSH
- Publication type
- Journal Article MeSH
- Geographicals
- Europe MeSH
- Mediterranean Region MeSH
Numerous plant species are expanding their native ranges due to anthropogenic environmental change. Because cytotypes of polyploid complexes often show similar morphologies, there may be unnoticed range expansions (i.e. cryptic invasions) of one cytotype into regions where only the other cytotype is native. We critically revised herbarium specimens of diploid and tetraploid Centaurea stoebe, collected across Europe between 1790 and 2023. Based on their distribution in natural and relict habitats and phylogeographic data, we estimated the native ranges of both cytotypes. Diploids are native across their entire European range, whereas tetraploids are native only to South-Eastern Europe and have recently expanded their range toward Central Europe. The proportion of tetraploids has exponentially increased over time in their expanded but not in their native range. This cryptic invasion predominantly occurred in ruderal habitats and enlarged the climatic niche of tetraploids toward a more oceanic climate. We conclude that spatio-temporally explicit assessments of range shifts, habitat preferences and niche evolution can improve our understanding of cryptic invasions. We also emphasize the value of herbarium specimens for accurate estimation of species´ native ranges, with fundamental implications for the design of research studies and the assessment of biodiversity trends.
- Keywords
- Centaurea stoebe (spotted knapweed), climatic niche, colonization ability, cryptic invasion, herbarium specimens, polyploidy, range expansion, ruderal habitats,
- MeSH
- Centaurea * genetics physiology MeSH
- Diploidy MeSH
- Ecosystem MeSH
- Phylogeography MeSH
- Polyploidy * MeSH
- Introduced Species * MeSH
- Publication type
- Journal Article MeSH
- Geographicals
- Europe MeSH
Invasions by nonnative insect species can massively disrupt ecological processes, often leading to serious economic impacts. Previous work has identified propagule pressure as important driver of the trend of increasing numbers of insect invasions worldwide. In the present article, we propose an alternative hypothesis-that insect invasions are being driven by the proliferation of nonnative plants, which create niches for insect specialists and facilitate their establishment outside their native ranges where their hosts are planted or are invasive. We synthesize mechanisms by which plant invasions facilitate insect invasions, macroecological patterns supporting the tight link between plant and insect invasions, and case studies of plant invasions having facilitated subsequent insect establishment. This body of evidence indicates that plant invasions are a major driver of insect invasions. Consequently, the benefits of limiting the spread of nonnative plants include averting the proliferation of nonnative insects and their spillover onto native plant species.
- Keywords
- empty niche, enemy release, facilitation, human-mediated dispersal, introduction pathways,
- Publication type
- Journal Article MeSH
- Review MeSH
Successful alien species may experience a period of quiescence, known as the lag phase, before becoming invasive and widespread. The existence of lags introduces severe uncertainty in risk analyses of aliens as the present state of species is a poor predictor of future distributions, invasion success and impact. Predicting a species' ability to invade and pose negative impacts requires a quantitative understanding of the commonality and magnitude of lags, environmental factors and mechanisms likely to terminate lag. Using herbarium and climate data, we analysed over 5,700 time series (species × regions) in 3,505 naturalized plant species from nine regions in temperate and tropical climates to quantify lags and test whether there have been shifts in the species' climatic space during the transition from the lag phase to the expansion phase. Lags were identified in 35% of the assessed invasion events. We detected phylogenetic signals for lag phases in temperate climate regions and that annual self-fertilizing species were less likely to experience lags. Where lags existed, they had an average length of 40 years and a maximum of 320 years. Lengthy lags (>100 years) were more likely to occur in perennial plants and less frequent in self-pollinating species. For 98% of the species with a lag phase, the climate spaces sampled during the lag period differed from those in the expansion phase based on the assessment of centroid shifts or degree of climate space overlap. Our results highlight the importance of functional traits for the onset of the expansion phase and suggest that climate discovery may play a role in terminating the lag phase. However, other possibilities, such as sampling issues and climate niche shifts, cannot be ruled out.
- MeSH
- Phylogeny MeSH
- Climate Change * MeSH
- Plants MeSH
- Tropical Climate MeSH
- Introduced Species * MeSH
- Publication type
- Journal Article MeSH
Darwin's naturalization conundrum describes two seemingly contradictory hypotheses regarding whether alien species closely or distantly related to native species should be more likely to naturalize in regional floras. Both expectations have accumulated empirical support, and whether such apparent inconsistency can be reconciled at the global scale is unclear. Here, using 219,520 native and 9,531 naturalized alien plant species across 487 globally distributed regions, we found a latitudinal gradient in Darwin's naturalization conundrum. Naturalized alien plant species are more closely related to native species at higher latitudes than they are at lower latitudes, indicating a greater influence of preadaptation in harsher climates. Human landscape modification resulted in even steeper latitudinal clines by selecting aliens distantly related to natives in warmer and drier regions. Our results demonstrate that joint consideration of climatic and anthropogenic conditions is critical to reconciling Darwin's naturalization conundrum.
- MeSH
- Ecosystem * MeSH
- Humans MeSH
- Magnoliopsida * MeSH
- Plants MeSH
- Citizenship MeSH
- Introduced Species MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Plant introductions outside their native ranges by humans have led to substantial ecological consequences. While we have gained considerable knowledge about intercontinental introductions, the distribution and determinants of intracontinental aliens remain poorly understood. Here, we studied naturalized (i.e., self-sustaining) intracontinental aliens using native and alien floras of 243 mainland regions in North America, South America, Europe, and Australia. We revealed that 4510 plant species had intracontinental origins, accounting for 3.9% of all plant species and 56.7% of all naturalized species in these continents. In North America and Europe, the numbers of intracontinental aliens peaked at mid-latitudes, while the proportion peaked at high latitudes in Europe. Notably, we found predominant poleward naturalization, primarily due to larger native species pools in low-latitudes. Geographic and climatic distances constrained the naturalization of intracontinental aliens in Australia, Europe, and North America, but not in South America. These findings suggest that poleward naturalizations will accelerate, as high latitudes become suitable for more plant species due to climate change.
- MeSH
- Ecosystem MeSH
- Climate Change * MeSH
- Humans MeSH
- Plants MeSH
- Citizenship * MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Geographicals
- Europe MeSH
- North America MeSH
Human activities are causing global biotic redistribution, translocating species and providing them with opportunities to establish populations beyond their native ranges. Species originating from certain global regions, however, are disproportionately represented among naturalized aliens. The evolutionary imbalance hypothesis posits that differences in absolute fitness among biogeographic divisions determine outcomes when biotas mix. Here, we compile data from native and alien distributions for nearly the entire global seed plant flora and find that biogeographic conditions predicted to drive evolutionary imbalance act alongside climate and anthropogenic factors to shape flows of successful aliens among regional biotas. Successful aliens tend to originate from large, biodiverse regions that support abundant populations and where species evolve against a diverse backdrop of competitors and enemies. We also reveal that these same native distribution characteristics are shared among the plants that humans select for cultivation and economic use. In addition to influencing species' innate potentials as invaders, we therefore suggest that evolutionary imbalance shapes plants' relationships with humans, impacting which species are translocated beyond their native distributions.
- MeSH
- Biodiversity * MeSH
- Humans MeSH
- Climate MeSH
- Plants MeSH
- Seeds MeSH
- Introduced Species * MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Thousands of insect species have been introduced outside of their native ranges, and some of them strongly impact ecosystems and human societies. Because a large fraction of insects feed on or are associated with plants, nonnative plants provide habitat and resources for invading insects, thereby facilitating their establishment. Furthermore, plant imports represent one of the main pathways for accidental nonnative insect introductions. Here, we tested the hypothesis that plant invasions precede and promote insect invasions. We found that geographical variation in current nonnative insect flows was best explained by nonnative plant flows dating back to 1900 rather than by more recent plant flows. Interestingly, nonnative plant flows were a better predictor of insect invasions than potentially confounding socioeconomic variables. Based on the observed time lag between plant and insect invasions, we estimated that the global insect invasion debt consists of 3,442 region-level introductions, representing a potential increase of 35% of insect invasions. This debt was most important in the Afrotropics, the Neotropics, and Indomalaya, where we expect a 10 to 20-fold increase in discoveries of new nonnative insect species. Overall, our results highlight the strong link between plant and insect invasions and show that limiting the spread of nonnative plants might be key to preventing future invasions of both plants and insects.
- Keywords
- invasion debt, nonnative insects, nonnative plants, species flow, time lag,
- MeSH
- Insecta * MeSH
- Plants MeSH
- Introduced Species * MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Grasses (Family Poaceae) are among the most successful invasive plants in the world. Here we evaluate phylogenetic and biogeographic patterns of emergence of naturalized and invasive species among grasses globally. In our data, circa 19% of the grasses are currently catalogued as invasive and almost 38% are listed as naturalized; these are among the highest ratios for single families of organisms. Remarkably, most tribes of grasses contain numerous naturalized and invasive species, suggesting that the invasion success is rooted broadly in ancestral traits in the Poaceae. Moreover, the probability of invasiveness is positively related to the diversification rates in the family also suggesting a link with recent radiation events. The phylogenetic distribution of the invasive condition is neither strongly conserved nor purely random. Phylogenetic clumping levels also vary between Poaceae subclades. We postulate that this diffuse clumping could be partially attributed to the expression of labile traits that contribute to species invasiveness. In addition, floristic regions (biomes and biogeographic realms) have different proportions of invasive species, with the temperate Palearctic region having the highest ratio of invasive vs. non-invasive species. The phylodiversity of aliens across regions is also variable in space. Comparison of alien phylodiversity levels across biogeographic realms and biomes reveals regions producing highly restricted invasive lineages and others where the diversity of aliens exported is no different from global mean diversity levels in grasses. Elucidating the evolutionary patterns and drivers of invasiveness is useful for understanding and managing invasions, with the low phylogenetic structure of alien grasses warning of their overall high invasiveness potential.
- Publication type
- Journal Article MeSH
