Although most studies of factors contributing to successful establishment and spread of non-native species have focused on species traits and characteristics (both biotic and abiotic), increasing empirical and statistical evidence implicates propagule pressure—propagule sizes, propagule numbers, and temporal and spatial patterns of propagule arrival—as important in both facets of invasion. Increasing propagule size enhances establishment probability primarily by lessening effects of demographic stochasticity, whereas propagule number acts primarily by diminishing impacts of environmental stochasticity. A continuing rain of propagules, particularly from a variety of sources, may erase or vitiate the expected genetic bottleneck for invasions initiated by few individuals (as most are), thereby enhancing likelihood of survival. For a few species, recent molecular evidence suggests ongoing propagule pressure aids an invasion to spread by introducing genetic variation adaptive for new areas and habitats. This p...

http://www.radio.faced.ufba.br/twiki/pub/Ecologia/EdiTais/Texto_2_Simberlof-2009.pdf

The Role of Propagule Pressure in Biological Invasions

We describe here the ecological and evolutionary processes that modulate the effects of invasive species over time, and argue that such processes are so widespread and important that ecologists should adopt a long-term perspective on the effects of invasive species. These processes (including evolution, shifts in species composition, accumulation of materials and interactions with abiotic variables) can increase, decrease, or qualitatively change the impacts of an invader through time. However, most studies of the effects of invasive species have been brief and lack a temporal context; 40% of recent studies did not even state the amount of time that had passed since the invasion. Ecologists need theory and empirical data to enable prediction, understanding and management of the acute and chronic effects of species invasions.

/pdf/understanding-the-long-term-effects-of-species-invasions-2o20y8wczj.pdf

Understanding the long-term effects of species invasions.

A complete list of all alien taxa ever recorded in the flora of
the Czech Republic is presented as an update of the original
checklist published in 2002. New data accumulated in the last
decade are incorporated and the listing and status of some taxa
are reassessed based on improved knowledge. Alien flora of the
Czech Republic consists of 1454 taxa listed with information on
their taxonomic position, life history, geographic origin (or
mode of origin, distinguishing anecophyte and hybrid), invasive
status (casual; naturalized but not invasive; invasive),
residence time status (archaeophyte vs neophyte), mode of
introduction into the country (accidental, deliberate), and
date of the first record. Additional information on species
performance that was not part of the previous catalogue, i.e.
on the width of species’ habitat niches, their dominance in
invaded communities, and impact, is provided. The Czech alien
flora consists of 350 (24.1%) archaeophytes and 1104 (75.9%)
neophytes. The increase in the total number of taxa compared to
the previous catalogue (1378) is due to addition of 151 taxa
and removal of 75 (39 archaeophytes and 36 neophytes),
important part of the latter being the reclassification of 41
taxa as native, mostly based on archaeobotanical evidence. The
additions represent taxa newly recorded since 2002 and reported
in the national literature; taxa resulting from investigation
of sources omitted while preparing the previous catalogue;
redetermination of previously reported taxa; reassessment of
some taxa traditionally considered native for which the
evidence suggests the opposite; and inclusion of intraspecific
taxa previously not recognized in the flora. There are 44 taxa
on the list that are reported in the present study for the
first time as aliens introduced to the Czech Republic or
escaped from cultivation.

Catalogue of alien plants of the Czech Republic (2nd edition): checklist update, taxonomic diversity and invasion patterns

/pdf/catalogue-of-alien-plants-of-the-czech-republic-3rd-edition-1qup56n8.pdf

Catalogue of alien plants of the Czech Republic (3rd edition)

Biological invasions are a global consequence of an increasingly connected world and the rise in human population size The numbers of invasive alien species – the subset of alien species that spread widely in areas where they are not native, affecting the environment or human livelihoods – are increasing Synergies with other global changes are exacerbating current invasions and facilitating new ones, thereby escalating the extent and impacts of invaders Invasions have complex and often immense long‐term direct and indirect impacts In many cases, such impacts become apparent or problematic only when invaders are well established and have large ranges Invasive alien species break down biogeographic realms, affect native species richness and abundance, increase the risk of native species extinction, affect the genetic composition of native populations, change native animal behaviour, alter phylogenetic diversity across communities, and modify trophic networks Many invasive alien species also change ecosystem functioning and the delivery of ecosystem services by altering nutrient and contaminant cycling, hydrology, habitat structure, and disturbance regimes These biodiversity and ecosystem impacts are accelerating and will increase further in the future Scientific evidence has identified policy strategies to reduce future invasions, but these strategies are often insufficiently implemented For some nations, notably Australia and New Zealand, biosecurity has become a national priority There have been long‐term successes, such as eradication of rats and cats on increasingly large islands and biological control of weeds across continental areas However, in many countries, invasions receive little attention Improved international cooperation is crucial to reduce the impacts of invasive alien species on biodiversity, ecosystem services, and human livelihoods Countries can strengthen their biosecurity regulations to implement and enforce more effective management strategies that should also address other global changes that interact with invasions

/pdf/scientists-warning-on-invasive-alien-species-3lt6vsrc2u.pdf

Scientists' warning on invasive alien species.

Time lags can be found throughout the invasion process, including in the arrival, establishment, and impacts of invaders. While we often lack the information necessary to generate quantitative expectations of invader performance, some types of lags are not surprising. For example, populations often grow exponentially in the early phases of invasion, and this will give rise to an inherent lag. More broadly, early rates of anthropogenic invasion were much slower than what we are now witnessing, but as the vectors of invasion have also increased dramatically over time, this early lag is not unexpected. Many other lags, however, appear dramatically prolonged, and can come to an end with changes to the invader or its environment. For example, exotics can exist in relatively low numbers for decades before exploding, or invaders can become more aggressive over time and increase their impacts on native species. Invasion-related lags are critical for our efforts to manage invaders, as they may lead us to ...

https://bioone.org/journals/ecoscience/volume-12/issue-3/i1195-6860-12-3-316.1/Lag-times-and-exotic-species--The-ecology-and-management/10.2980/i1195-6860-12-3-316.1.pdf

Jeffrey A. Crooks

Papers

Lag times and exotic species: The ecology and management of biological invasions in slow-motion.