There has been a dramatic growth in research on biological invasions over the past 20 years, but a mature understanding of the field has been hampered because invasion biologists concerned with different taxa and different environments have largely adopted different model frameworks for the invasion process, resulting in a confusing range of concepts, terms and definitions. In this review, we propose a unified framework for biological invasions that reconciles and integrates the key features of the most commonly used invasion frameworks into a single conceptual model that can be applied to all human-mediated invasions. The unified framework combines previous stage-based and barrier models, and provides a terminology and categorisation for populations at different points in the invasion process.

A proposed unified framework for biological invasions.

How are garbage dumps impacting vertebrate demography, health, and conservation?

The migratory patterns of animals are changing in response to global environmental change with many species forming resident populations in areas where they were once migratory. The white stork (Ciconia ciconia) was wholly migratory in Europe but recently guaranteed, year-round food from landfill sites has facilitated the establishment of resident populations in Iberia. In this study 17 resident white storks were fitted with GPS/GSM data loggers (including accelerometer) and tracked for 9.1 ± 3.7 months to quantify the extent and consistency of landfill attendance by individuals during the non-breeding and breeding seasons and to assess the influence of landfill use on daily distances travelled, percentage of GPS fixes spent foraging and non-landfill foraging ranges. Resident white storks used landfill more during non-breeding (20.1 % ± 2.3 of foraging GPS fixes) than during breeding (14.9 % ± 2.2). Landfill attendance declined with increasing distance between nest and landfill in both seasons. During non-breeding a large percentage of GPS fixes occurred on the nest throughout the day (27 % ± 3.0 of fixes) in the majority of tagged storks. This study provides first confirmation of year-round nest use by resident white storks. The percentage of GPS fixes on the nest was not influenced by the distance between nest and the landfill site. Storks travelled up to 48.2 km to visit landfills during non-breeding and a maximum of 28.1 km during breeding, notably further than previous estimates. Storks nesting close to landfill sites used landfill more and had smaller foraging ranges in non-landfill habitat indicating higher reliance on landfill. The majority of non-landfill foraging occurred around the nest and long distance trips were made specifically to visit landfill. The continuous availability of food resources on landfill has facilitated year-round nest use in white storks and is influencing their home ranges and movement behaviour. White storks rely on landfill sites for foraging especially during the non-breeding season when other food resources are scarcer and this artificial food supplementation probably facilitated the establishment of resident populations. The closure of landfills, as required by EU Landfill Directives, will likely cause dramatic impacts on white stork populations.

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Are white storks addicted to junk food? Impacts of landfill use on the movement and behaviour of resident white storks (Ciconia ciconia) from a partially migratory population

Summary Biological invasions are synonymous with international trade. The direct effects of trade have largely been quantified using relationships between imports and the number of alien species in a region or patterns in the global spread of species linked to shipping and air traffic networks. But trade also has an indirect role on biological invasions by transforming the environments and societies of exporting and importing nations. Here, both the direct and indirect roles of trade on biological invasions, as well as their interaction, are examined for the first time. Future trends in international trade, including e-commerce, new trade routes, and major infrastructure developments, will lead to the pressure on national borders soon outstripping the resources available for intervention. The current legislative and scientific tools targeting biological invasions are insufficient to deal with this growing threat and require a new mindset that focuses on curbing the pandemic risk posed by alien species.

Unwelcome exchange: International trade as a direct and indirect driver of biological invasions worldwide

In the mid 1970s, the breeding populations of the migrant White Stork Ciconia ciconia were close to extinction in the northeastern region of France (Alsace). A re-introduction project was implemented, resulting in the year-round settlement of some individuals in the region, which rely on additional food supplied by humans during the winter. Today, both resident and migrant birds breed in the same areas and take food from rubbish dumps and humans (farmers). The effects of these anthropogenic influences, altering Stork behaviour, on Stork reproductive success are not known. The aim of this study was to test the influence of bird status (resident vs. migrant) and food availability (control nests vs. nests that benefit from high food supply) on reproductive success. In control nests, the mean laying date was earlier in resident than in migrant White Storks. There was also a clear seasonal decline in clutch size. For all nests, the numbers of eggs and hatchlings were higher in resident birds than in migrants, which can be attributed to the earlier breeding of resident Storks. The large broods of resident birds showed a high mortality rate, leading to the same fledgling success (fledglings/hatchlings) and number of fledglings as in migrants. Fledgling success and the number of fledglings were higher for nests close to a reliable food supply. In summary, although resident birds can breed earlier and produce more eggs than migrants, we found no advantage in terms of number of fledglings. The higher mortality rate of chicks found in pairs with a large brood could be caused by the deterioration of their habitat. Thus, the year-round settlement of Storks may not present a biological advantage if the quality of their habitat is not guaranteed by the conservation of their grasslands.

The effect of migration strategy and food availability on White Stork Ciconia ciconia breeding success

CapsuleFood independently affects both laying date and clutch size, suggesting that seasonal decline in clutch size is related to a decrease in food availability. Aim To test the effect of food abundance on laying date and clutch size of the White Stork and identify the cause of seasonal decline in the number of eggs laid. Methods During 1991 and 1996 we recorded clutch size and laying date of pairs breeding next to rubbish dumps (food abundant and constant throughout the breeding season) and birds breeding far from rubbish dumps (using natural food sources). Results In 1991 there was no difference in mean laying date between pairs nesting at rubbish dumps and control pairs. Clutch size was significantly larger at rubbish dump nests. In contrast, mean laying date was earlier in control pairs in 1996 and there was no significant differences in clutch sizes, even when controlling for laying date effect. Conclusion The results support the hypothesis that food availability independently affects both laying da...

Effect of food abundance on laying date and clutch size in the White Stork Ciconia ciconia

. Clutch size is an important life history trait, and factors such as nest predation and food availability can both be of crucial importance for its variation in nature. The aim of the present study was to evaluate the effects of extra food on clutch size, laying date and hatching success in the White Stork. Three different colonies of White Storks were studied in northern Algeria over a three-year period (2002–2004) that was characterised by considerable variation in both food availability and precipitation. This study demonstrated that an extra food supply during the pre-laying period had a positive effect on clutch size — nests with extra food had larger clutches. There was also an advance in laying date and a greater hatching success in nests with access to extra food. In addition to food supply, clutch size was independently affected by the year, which could have been due to differences in rainfall. Furthermore, the results of this study suggest that extra food during the incubation period co...

Food Supply and External Cues Limit the Clutch Size and Hatchability in the White Stork Ciconia ciconia

Hunting activities are responsible for the translocation and restocking of millions of animals throughout Europe, including the introduction of alien species. In a context of the growing use of game translocations and of increasing concern about the impact of biological invasions, our goal is to review the role of alien species introduced primarily for hunting purposes on the European scale. In particular, we explore: (1) the relative importance of game species in the context of alien species introductions; (2) the temporal evolution of the number of species introduced for hunting purposes; (3) the contribution of different taxa; (4) the pattern of introduced game species composition across countries (in terms of similarity), and (5) the underlying human demographic factors driving the diversity of introduced game species per country. According to our results, 24.3% of the mammals and 30.2% of the birds introduced into Europe during the last century were released primarily for hunting purposes, in total, 93 species (63 birds and 36 mammals), the most important taxa being Artiodactyls, Anseriformes and Galliformes. The species composition differed among countries, with a higher diversity of introduced game species in larger countries and in those with a higher human population density and proportion of hunters. This review stresses that hunting was a significant pathway for the introduction of invasive species into Europe in the last century. Since some of the game species introduced have had severe environmental impacts on many European regions, and introductions of non-native game species are still occurring, it is essential to improve regulations and increase public awareness regarding invasive game animals. This will help to preserve biodiversity and improve the sustainability of current hunting schemes in increasingly managed European ecosystems.

Hunting as a source of alien species: a European review

In a context of the growing concern about the impact of biological invasions, our objective is to review the role of those non-native species that have primarily been introduced for angling purposes in at least one European country. We are particularly interested in: (1) the relative role of sport fish species in the context of non-native species introductions; (2) assessing the relative importance of different fish taxa; (3) identifying similarity patterns in the composition of the angling fish species introduced throughout the continent, and (4) assessing the underlying factors that drive their diversity in Europe. According to our results, 23.6% of the freshwater fish introduced into Europe during the last century were released primarily for angling purposes. The species composition differed among countries, with a higher diversity of introduced angling species in larger countries and in those with a greater GDP per capita, along with a lower latitude. This review stresses that angling was a significant pathway for the introduction of invasive fish species into Europe in the last century. Furthermore, some of the introduced angling species had severe environmental impacts on many European regions. However, introductions of non-native angling species are still occurring. Therefore, existing EU regulations need better enforcement as well as to increase public awareness regarding invasive fish. This will help to preserve biodiversity and improve the sustainability of current angling schemes in increasingly managed European freshwater ecosystems. However, non-native fish could make angling sustainable, although not for biodiversity generally.

Angling as a source of non-native freshwater fish: a European review

The wild boar has, over the past few decades, undergone an expansion in Europe, which may have negatively affected ground-nesting bird populations and particularly those of wading birds. The aim of this study was to evaluate predation on waders’ nests by wild boar in Sweden, where this species has been increasing since its reintroduction. This was done by placing artificial nests in seven different study areas. A comparison was then made of predation rates of the nests placed on control plots (areas in which no wild boar were present but other predators were) and plots containing different abundances of wild boar. Contrary to our expectations, the proportion of nests predated was significantly lower in those areas in which wild boar were present, with a predation rate of 54 %, whereas the predation rate was 87.5 % in the others. The wild boar was identified as the second most important nest predator in the plots in which it was present, accounting for 18 % of the predated nests. The main predator on both types of plots was the red fox, which was responsible for 28 and 38.5 % of the predated nests on plots with/without wild boar, respectively. Interestingly, predation by badgers occurred principally in areas in which the wild boar was absent (34.5 % of the predated nests), whereas only one nest was predated by this predator in areas containing wild boar. It is not, however, possible to state whether predation by badgers was lower because of the presence of wild boar or whether this was owing to the fact that badgers do not select those particular patches because of habitat features.

Lars Hillström

Papers

Effect of food abundance on laying date and clutch size in the White Stork Ciconia ciconia

Food Supply and External Cues Limit the Clutch Size and Hatchability in the White Stork Ciconia ciconia

Hunting as a source of alien species: a European review

Angling as a source of non-native freshwater fish: a European review

Effects of wild boar predation on nests of wading birds in various Swedish habitats