The role of species traits and taxonomic patterns in alien bird impacts

Aim To test whether the distribution of alien bird impacts varies across bird families and regions of origin, and to investigate whether species traits associated with successful introductions can predict which species will have negative impacts in the new area of introduction. Location Europe and the Mediterranean Basin. Methods Combining historical information and published literature about negative economic, biological and human health impacts, we compared the distribution of impacts among bird families and native origins of bird species for three major types of impact (economic, biodiversity and human health). We examined the relationships between ecological, biological and reproductive characteristics of species and the severity of the impacts. Results The majority of alien species with reported impacts originated from the Afrotropical, Indo‐Malayan and Palaearctic biogeographical regions. The distribution of alien bird species in Europe with reported impacts shows a taxonomic bias and largely mirrors patterns of establishment. While most species had primarily either economic or biodiversity impacts, several species in the Anatidae, Corvidae, Passeridae, Phasianidae and Sturnidae families were associated with moderate to serious negative impacts on both economic resources and native biodiversity. After controlling for taxonomic effects, species with the greatest overall impacts were habitat generalists and multi‐brooded, while species with smaller bodies and the tendency to form large feeding or roosting flocks were linked with greater impacts on native biodiversity. Main conclusions This study presents the first synthesis of published impact data for alien birds and provides a broad‐scale perspective on factors that contribute to their impacts. The results show that accounting for both species traits and taxonomy improves our ability to predict the impacts of alien bird species. Because several species are currently in the early stages of establishment in Europe, there may be an opportunity to limit negative impacts with efforts that promote proactive strategies against species and families possessing the above characteristics.     

What determines the impact of alien birds and mammals in Europe?

An often-cited reason for studying the process of invasion by alien species is that the understanding sought can be used to mitigate the impacts of the invaders. Here, we present an analysis of the correlates of local impacts of established alien bird and mammal species in Europe, using a recently described metric to quantify impact. Large-bodied, habitat generalist bird and mammal species that are widespread in their native range, have the greatest impacts in their alien European ranges, supporting our hypothesis that surrogates for the breadth and the amount of resources a species uses are good indicators of its impact. However, not all surrogates are equally suitable. Impacts are generally greater for mammal species giving birth to larger litters, but in contrast are greater for bird species laying smaller clutches. There is no effect of diet breadth on impacts in birds or mammals. On average, mammals have higher impacts than birds. However, the relationships between impact and several traits show common slopes for birds and mammals, and relationships between impact and body mass and latitude do not differ between birds and mammals. These results may help to anticipate which species would have large impacts if introduced, and so direct efforts to prevent such introductions.     

Weak or strong invaders? A comparison of impact between the native and invaded ranges of mammals and birds alien to Europe

Aim Species introduced to an area outside of their native range are often thought to have higher impact in this new area. We examined whether this is really the case in mammals and birds and to what extent. In particular, we explored how impacts of alien species vary in relationship to invader identity and type of impact. Location Global. Methods We conducted a thorough review of the literature to compare the impact of alien European mammals and birds in their native and invaded ranges. Based on a series of environmental and economic impact scores, we ordered species along a continuum from weak invaders, which have lower impact in the invaded range, to strong invaders, which have higher impact in the invaded range. Results We found that nearly 80% of the mammals are strong invaders, but only half of the birds. Members of these two classes also affect their communities in different ways; birds more often have an impact via hybridization, whereas mammals have stronger impacts via herbivory, transmission of diseases to wildlife and their effects on agriculture, livestock and forestry. Main conclusions Generally, mammals and birds have different impacts when invading new regions. Although there are some bird species that are strong invaders, these remain the exception among birds, whereas most mammals increase their impact in the invaded range. This study provides a deeper insight into patterns of impact in the invaded range.     

Little,but increasing evidence of impacts by alien bryophytes

Based on data of bryophyte invasions into 82 regions on five continents of both hemispheres, we aim here at a first comprehensive overview of the impacts that bryophytes may have on biodiversity and socio-economy. Of the 139 bryophytes species which are alien in the study regions seven cause negative impacts on biodiversity in 26 regions, whereas three species cause negative impacts on socio-economic sectors in five regions. The vast majority of impacts stem from anecdotal observations, whereas only 14 field or experimental studies (mostly on Campylopus introflexus in Europe) have quantitatively assessed the impacts of an alien bryophyte. The main documented type of impact on biodiversity is competition (8 alien bryophytes), with native cryptogams being most affected. In particular, C. introflexus (9 regions) and Pseudoscleropodium purum (7 regions) affect resident species composition. The few socio-economic impacts are caused by alien bryophytes which form dense mats in lawns and are then considered a nuisance. Most negative impacts on biodiversity have been recorded in natural grasslands, forests, and wetlands. Impacts of alien bryophytes on biodiversity and socio-economy are a recent phenomenon, with >85 % of impacts on biodiversity, and 80 % of impacts on socio-economy recorded since 1990. On average, 40 years (impacts on biodiversity) and 25 years (impacts on socio-economy) elapsed between the year a bryophyte species has been first recorded as alien in a region and the year impacts have been recorded first. Taking into account the substantial time lag between first record and first recorded impact in a region, it seems to be likely that the currently moderate impacts of alien bryophytes will continue to increase. As quantitative studies on impacts of alien bryophytes are rare and restricted to few environments and biogeographic regions, there is a need for addressing potential impacts of alien bryophytes in yet understudied settings.     

Identifying the factors that determine the severity and type of alien bird impacts

Aim

To identify traits related to the severity and type of environmental impacts generated by alien bird species, in order to improve our ability to predict which species may have the most damaging impacts.

Location

Global.

Methods

Information on traits hypothesized to influence the severity and type of alien bird impacts was collated for 113 bird species. These data were analysed using mixed effects models accounting for phylogenetic non‐independence of species.

Results

The severity and type of impacts generated by alien bird species are not randomly distributed with respect to their traits. Alien range size and habitat breadth were strongly associated with impact severity. Predation impacts were strongly associated with dietary preference, but also with alien range size, relative brain size and residence time. Impacts mediated by interactions with other alien species were related to alien range size and diet breadth.

Main conclusions

Widely distributed generalist alien birds have the most severe environmental impacts. This may be because these species have greater opportunity to cause environmental impacts through their sheer number and ubiquity, but this could also be because they are more likely to be identified and studied. Our study found little evidence for an effect of per capita impact on impact severity.

     

Bergmann's rule in alien birds

Native bird species show latitudinal gradients in body size across species (Bergmann's rule), but whether or not such gradients are recapitulated in the alien distributions of bird species are unknown. Here, we test for the existence of Bergmann's rule in alien bird species worldwide, and investigate the causes of the observed patterns. Published databases were used to obtain the worldwide distributions of established alien bird populations, the locations of alien bird introductions, and bird body masses. Randomisation tests and linear models were used to assess latitudinal patterns in the body masses of introduced and established alien bird populations. Established alien bird species exhibit Bergmann's rule, but this is largely explained by where alien bird species have been introduced: latitudinal variation in the body masses of established alien bird species simply reflects latitudinal variation in the body masses of introduced species. There is some evidence that body mass is implicated in whether or not established species’ alien ranges spread towards or contract away from the Equator following establishment. However, most alien bird ranges are encompassed by the latitudinal band(s) to which the species was introduced. Bergmann's rule in alien birds is therefore a consequence of where humans have introduced different species, rather than of natural processes operating after population introduction.     

Comparing determinants of alien bird impacts across two continents: implications for risk assessment and management

Invasive alien species can have serious adverse impacts on both the environment and the economy. Being able to predict the impacts of an alien species could assist in preventing or reducing these impacts. This study aimed to establish whether there are any life history traits consistently correlated with the impacts of alien birds across two continents, Europe and Australia, as a first step toward identifying life history traits that may have the potential to be adopted as predictors of alien bird impacts. A recently established impact scoring system was used in combination with a literature review to allocate impact scores to alien bird species with self‐sustaining populations in Australia. These scores were then tested for correlation with a series of life history traits. The results were compared to data from a previous study in Europe, undertaken using the same methodology, in order to establish whether there are any life history traits consistently correlated with impact across both continents. Habitat generalism was the only life history trait found to be consistently correlated with impact in both Europe and Australia. This trait shows promise as a potential predictor of alien bird impacts. The results support the findings of previous studies in this field, and could be used to inform decisions regarding the prevention and management of future invasions.     

Will climate change promote future invasions?

Biological invasion is increasingly recognized as one of the greatest threats to biodiversity. Using ensemble forecasts from species distribution models to project future suitable areas of the 100 of the world's worst invasive species defined by the International Union for the Conservation of Nature, we show that both climate and land use changes will likely cause drastic species range shifts. Looking at potential spatial aggregation of invasive species, we identify three future hotspots of invasion in Europe, northeastern North America, and Oceania. We also emphasize that some regions could lose a significant number of invasive alien species, creating opportunities for ecosystem restoration. From the list of 100, scenarios of potential range distributions show a consistent shrinking for invasive amphibians and birds, while for aquatic and terrestrial invertebrates distributions are projected to substantially increase in most cases. Given the harmful impacts these invasive species currently have on ecosystems, these species will likely dramatically influence the future of biodiversity.     

Assessing the impact of revegetation and weed control on urban sensitive bird species

Nature in cities is concentrated in urban green spaces, which are key areas for urban biodiversity and also important areas to connect people with nature. To conserve urban biodiversity within these natural refugia, habitat restoration such as weed control and revegetation is often implemented. These actions are expected to benefit biodiversity, although species known to be affected by urbanization may not be interacting with restoration in the ways we anticipate. In this study, we use a case study to explore how urban restoration activities impact different bird species. Birds were grouped into urban sensitivity categories and species abundance, and richness was then calculated using a hierarchical species community model for individual species responses, with “urban class” used as the hierarchical parameter. We highlight variable responses of birds to revegetation and weed control based on their level of urban sensitivity. Revegetation of open grassy areas delivers significant bird conservation outcomes, but the effects of weed control are neutral or in some cases negative. Specifically, the species most reliant on remnant vegetation in cities seem to remain stable or decline in abundance in areas with weed control, which we suspect is the result of a simplification of the understorey. The literature reports mixed benefits of weed control between taxa and between locations. We recommend, in our case study site, that weed control be implemented in concert with replanting of native vegetation to provide the understory structure preferred by urban sensitive birds. Understanding the impacts of revegetation and weed control on different bird species is important information for practitioners to make restoration decisions about the allocation of funds for conservation action. This new knowledge can be used both for threatened species and invasive species management.     

Livestock grazing constrains bird abundance and species richness: A global meta-analysis

Balancing food production and biodiversity conservation is a global challenge today. Livestock grazing is one of the main activities triggering habitat degradation and land-use change around the world. Its effects on biodiversity have been widely explored, with birds being the most studied vertebrates. However, its impact seems to be contradictory given the disparity of the results. To understand the influence of livestock grazing on birds, we conducted a meta-analysis exploring the effects of several grazing characteristics on bird abundance and species richness. Our results showed that livestock grazing has a significant negative effect on bird abundance (mean effect size -0.422 ± 0.140), and species richness (mean effect size -0.391 ± 0.141). Livestock grazing affected negatively the bird abundance in riparian habitats in contrast to the other habitat types. Species richness was negatively affected by grazing in woody habitats and Afrotropical and Neotropical regions. Grazing by cattle was more detrimental for both bird richness and abundance than sheep grazing or a mixture of domestic livestock. Moreover, intermediate grazing intensity seems appropriate to maintain bird abundance and richness, as high grazing intensity dropped both bird abundance and species richness substantially, and low grazing intensity reduced bird species richness. This pattern supposes a non-linear effect of grazing intensity on birds. Therefore, the management of grazing intensity and type of livestock could help to reduce the negative effect on bird abundance and richness, as moderate grazing intensities and mix of livestock types appear to have a minor or null impact on bird abundance and richness. Future studies should explore in-depth the effect of moderate grazing intensities on bird diversity and composition to provide better management recommendations to enhance avian conservation in rangelands.     

Sugarcane and Eucalyptus plantation equally limit the movement of two forest‐dependent understory bird species

Habitat fragmentation results in landscape configuration, which affects the species that inhabit it. As a consequence, natural habitat is replaced by different anthropogenic plantation types (e.g. pasture, agriculture, forestry plantations and urban areas). Anthropogenic plantations are important for biodiversity maintenance because some species or functional groups can use it as a complementary habitat. However, depending on plantation permeability, it can act as a barrier to the movement of organisms between habitat patches, such as forest fragments, reducing functional connectivity for many species. Anthropogenic plantations are becoming the most common land use and cover type in the Anthropocene and biodiversity conservation in fragmented landscapes requires information on how different plantation types affect the capacity of the species to move through the landscape. In this study, we evaluated the influence of the type and structure of plantations on the movement of two forest‐dependent understory bird species – plain antvireo (Dysithamnus mentalis) and flavescent warbler (Myiothlyps flaveola) – within a highly fragmented landscape of Atlantic Forest hotspot. Knowing that forestry plantation is assumed to be more permeable to dependent forest bird species than open ones, we selected six study areas containing a forest fragment and surrounding plantation: three with sugarcane plantation and three with Eucalyptus sp. plantation. We used playback calls to stimulate the birds to leave forest fragments and traverse the plantations. Control trials were also carried out inside the forest fragments to compare the distances crossed. We observed that individuals moved longer distances inside forest than between plantation types, which demonstrate that plantations do constrict the movements of both species. The two plantation types equally impeded the movements of the species, suggesting the opposite of the general assumption that forestry plantations are more permeable. Our results indicate that, for generalist species, plantation type does not matter, but its presence negatively impacts movement of these bird species. We highlight that plantations have negative influences on the movements of common bird species, and discuss why this is important when setting conservation priorities.     

The EICAT+ framework enables classification of positive impacts of alien taxa on native biodiversity

Species introduced through human-related activities beyond their native range, termed alien species, have various impacts worldwide. The IUCN Environmental Impact Classification for Alien Taxa (EICAT) is a global standard to assess negative impacts of alien species on native biodiversity. Alien species can also positively affect biodiversity (for instance, through food and habitat provisioning or dispersal facilitation) but there is currently no standardized and evidence-based system to classify positive impacts. We fill this gap by proposing EICAT+, which uses 5 semiquantitative scenarios to categorize the magnitude of positive impacts, and describes underlying mechanisms. EICAT+ can be applied to all alien taxa at different spatial and organizational scales. The application of EICAT+ expands our understanding of the consequences of biological invasions and can inform conservation decisions.

Various schemes assess negative impacts of alien species on native biodiversity, but alien species can also positively affect biodiversity. This Consensus View proposes EICAT+, a scheme which uses five semi-quantitative scenarios to categorise positive impacts, describes underlying mechanisms, and can be applied to all alien taxa and across various invasion contexts.     

Climate change and birds: perspectives and prospects from southern Africa

Global climate warming, now conclusively linked to anthropogenically-increased CO₂ levels in the earth's atmosphere, has already had impacts on the earth's biodiversity and is predicted to threaten more than 1 million species with extinction by 2050. Climate change in southern Africa is expected to involve higher temperatures and lower rainfall, with less predictability and a greater frequency of severe storms, fires and El Niño events. The predicted changes to birds in Africa — the continent most at risk from climate change — have hardly been explored, yet birds and many other vertebrates face uncertain futures. Here, in one of the first focused analyses of the correlates of climate change vulnerability in southern African birds, we offer a wide-ranging perspective on which species may be most at risk, and explore which traits may influence the adaptability or extinction risk of bird species.

Our review suggests that small nomadic species with short generation times may be least at risk. While larger-bodied species may be physiologically buffered against environmental change, their longer generation times may make them less able to adapt evolutionarily to climate change. Migrant species, and those with specialised feeding niches such as pollinators, are also predicted to be at risk of population declines, based on low ability to adapt to new environments when introduced there as aliens. Species with small ranges (<50 000km²) restricted to the two southern African biodiversity hotspots most at risk from climate change — the Cape Floral Kingdom and the Succulent Karoo — are ranked according to low, medium or high risk of extinction. Those restricted to mountain slopes, mountain tops or islands, and those occurring mainly at the southern or western extremes of these biomes, are ranked as highest risk. These include endemic sunbirds, warblers and rock-jumpers — none of which are currently recognised Red Data species. Using climate envelopes we modelled the possible range shifts by 2050 of three pairs of species found in habitats considered to be at risk: fynbos, mountain and arid Karoo. All six species lost substantial portions of their range (x = 40%), with the montane Drakensberg Rock-jumper Chaetops aurantius losing most (69%). Significant reductions of available climate space in all species may interact with life history characteristics to threaten many southern African bird species unable to shift geographic range or adapt to novel resource conditions. We conclude with a list of research priorities and testable hypotheses which may advance our understanding of the complex influence that climate change is likely to have on African, particularly southern African, birds.     

The climatic drivers of long-term population changes in rainforest montane birds

Climate-driven biodiversity erosion is escalating at an alarming rate. The pressure imposed by climate change is exceptionally high in tropical ecosystems, where species adapted to narrow environmental ranges exhibit strong physiological constraints. Despite the observed detrimental effect of climate change on ecosystems at a global scale, our understanding of the extent to which multiple climatic drivers affect population dynamics is limited. Here, we disentangle the impact of different climatic stressors on 47 rainforest birds inhabiting the mountains of the Australian Wet Tropics using hierarchical population models. We estimate the effect of spatiotemporal changes in temperature, precipitation, heatwaves, droughts and cyclones on the population dynamics of rainforest birds between 2000 and 2016. We find a strong effect of warming and changes in rainfall patterns across the elevational-segregated bird communities, with lowland populations benefiting from increasing temperature and precipitation, while upland species show an inverse strong negative response to the same drivers. Additionally, we find a negative effect of heatwaves on lowland populations, a pattern associated with the observed distribution of these extreme events across elevations. In contrast, cyclones and droughts have a marginal effect on spatiotemporal changes in rainforest bird communities, suggesting a species-specific response unrelated to the elevational gradient. This study demonstrated the importance of unravelling the drivers of climate change impacts on population changes, providing significant insight into the mechanisms accelerating climate-induced biodiversity degradation.     

Trends and characteristics of imports of live CITES‐listed bird species into Japan

Understanding the characteristics of the international bird trade is critical for preventing the traffic of endangered species. Japan is the second largest importer of birds for the pet industry globally, yet little research has examined its role in the international trade of live exotic birds. We used reports to the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) Trade Database to conduct the first quantitative analysis of the live commercial bird imports to Japan. We also investigated whether the volume of import is influenced by factors related to species availability. We analysed close to 2 million live bird imports by Japan from 1979 to 2015. The volume of imports peaked in 1999 and then declined until 2008, when imports increased again. Japan imported 603 bird species, mostly parrots (64%), owls (11%) and raptors (9%), from 92 different countries. Most imported birds were reported to be captive‐bred (70%), and key exporters were Belgium (23%), the Netherlands (15%) and Singapore (12%). The most frequently imported bird species had widespread distributions and were not of high conservation concern, so we concluded that bird imports were restricted by the availability of bird species to the international market. Research effort in countries that engage heavily in wildlife trade is necessary to understand the impacts of the trade on bird conservation, and to monitor captive bird populations outside their native ranges.     

Does migration promote or restrict circumpolar breeding ranges of arctic birds?

Aim Migration has been suggested to promote large breeding ranges among birds because of the greater mobility of migratory compared with non‐migratory species, but migration has also been suggested to restrict breeding ranges because of evolutionary constraints imposed by the genetically based migration control programme. We aim to investigate the association between migration and the breeding ranges of both land birds and pelagic birds breeding in the Arctic region. Location The Arctic region. Methods Information on breeding and wintering ranges and migratory status of bird species breeding in the arctic tundra biome was compiled from the literature. The association between breeding range, migration distance and primary winter habitat was tested using multivariate generalized linear models and pair‐wise Mann–Whitney U‐tests. Phylogenetic effects were tested for using Mantel’s permutation tests. Results We found different relationships depending on the species’ major winter habitat. Among birds that are pelagic during winter, long‐distance migrants have the largest breeding ranges, while among terrestrial birds, residents and short‐distance migrants have the largest breeding ranges. Breeding ranges of coastal birds of all migratory distance classes are comparatively restricted. Main conclusions As a new explanation for this pattern we suggest that the possibility of colonizing large winter ranges is a key factor for the subsequent expansion of breeding ranges in arctic bird communities and possibly also in bird communities of other regions of the world. Because of the reversal in the relative extent of continents and oceans between the hemispheres, longitudinally wide winter ranges are more likely for long‐distance than short‐distance migrants among pelagic birds, while the reverse holds true for birds that use terrestrial winter habitats. For coastal birds both continents and oceans form barriers restricting colonization of extensive winter quarters and consequently also of extensive breeding ranges, regardless of the distance to the winter quarters.     

Continental‐scale determinants of population trends in European amphibians and reptiles

The continuous decline of biodiversity is determined by the complex and joint effects of multiple environmental drivers. Still, a large part of past global change studies reporting and explaining biodiversity trends have focused on a single driver. Therefore, we are often unable to attribute biodiversity changes to different drivers, since a multivariable design is required to disentangle joint effects and interactions. In this work, we used a meta‐regression within a Bayesian framework to analyze 843 time series of population abundance from 17 European amphibian and reptile species over the last 45 years. We investigated the relative effects of climate change, alien species, habitat availability, and habitat change in driving trends of population abundance over time, and evaluated how the importance of these factors differs across species. A large number of populations (54%) declined, but differences between species were strong, with some species showing positive trends. Populations declined more often in areas with a high number of alien species, and in areas where climate change has caused loss of suitability. Habitat features showed small variation over the last 25 years, with an average loss of suitable habitat of 0.1%/year per population. Still, a strong interaction between habitat availability and the richness of alien species indicated that the negative impact of alien species was particularly strong for populations living in landscapes with less suitable habitat. Furthermore, when excluding the two commonest species, habitat loss was the main correlate of negative population trends for the remaining species. By analyzing trends for multiple species across a broad spatial scale, we identify alien species, climate change, and habitat changes as the major drivers of European amphibian and reptile decline.     

Breeding success of an endangered island endemic kestrel increases with extent of invasion by an alien plant species

The Mauritius Kestrel Falco punctatus, once the rarest kestrel worldwide, became an icon of bird conservation after it recovered from four to six individuals in 1974 to some 800 by 2005 following intense conservation management. Its population however then halved within about a decade prompting a re-evaluation of the IUCN status and up listing of the species in 2014 and an increased conservation attention. Drivers of this new decline are unclear and the influence of habitat structure and diet on breeding success may be important contributors but have received relatively little attention, particularly in the way they may interact to influence production of new fledglings. We address this knowledge gap by studying whether breeding success is influenced by habitat structure (in terms of cover of the invasive Ravenala in native habitats, an alien plant causing strong structural shift in the forests that it invades, and extent of cleared area), diet composition and food pass frequency (as a proxy for food intake) and food quality at 28 nests of a re-introduced kestrel population in south east Mauritius during the 2015–2016 breeding season. The kestrel’s diet comprised native and alien birds, reptiles, insects, and small alien mammals, with a disproportionately high proportion of Phelsuma gecko. A higher frequency of food provisioning and percentage cover of Ravenala both contributed to higher breeding success. Ravenala may increase gecko density or increase gecko detectability and predation by the kestrel, or both, while changed land use (pasture and sugar cane fields) may increase prey diversity in the form of non-forest prey known to be eaten by Kestrels (e.g. alien agamids, small mammals and birds). These prey related influences on breeding suggest that the Bambou mountain range provides a human-generated novel ecosystem altering food availability and increasing the kestrel’s breeding success. However, Ravenala is an invasive alien species harmful to the wider forest biodiversity. Progressive weeding of Ravenala and concurrent re-introduction and augmentation of native palms and Pandanus species which geckos can use at comparable densities to Ravenala, is recommended. This would likely improve the kestrel’s hunting habitat quality and maintain high gecko density or detectability and the vegetation structure required for hunting manoeuvrability and prey availability without the negative consequences of invasive Ravenala.     

Impact of Non-Native Birds on Native Ecosystems: A Global Analysis

Introduction and naturalization of non-native species is one of the most important threats to global biodiversity. Birds have been widely introduced worldwide, but their impacts on populations, communities, and ecosystems have not received as much attention as those of other groups. This work is a global synthesis of the impact of nonnative birds on native ecosystems to determine (1) what groups, impacts, and locations have been best studied; (2) which taxonomic groups and which impacts have greatest effects on ecosystems, (3) how important are bird impacts at the community and ecosystem levels, and (4) what are the known benefits of nonnative birds to natural ecosystems. We conducted an extensive literature search that yielded 148 articles covering 39 species belonging to 18 families -18% of all known naturalized species. Studies were classified according to where they were conducted: Africa, Asia, Australasia, Europe, North America, South America, Islands of the Indian, of the Pacific, and of the Atlantic Ocean. Seven types of impact on native ecosystems were evaluated: competition, disease transmission, chemical, physical, or structural impact on ecosystem, grazing/ herbivory/ browsing, hybridization, predation, and interaction with other non-native species. Hybridization and disease transmission were the most important impacts, affecting the population and community levels. Ecosystem-level impacts, such as structural and chemical impacts were detected. Seven species were found to have positive impacts aside from negative ones. We provide suggestions for future studies focused on mechanisms of impact, regions, and understudied taxonomic groups.     

Direct and indirect effects of anthropogenic bird food on population dynamics of a songbird

Anthropogenic bird foods are frequently credited with affecting avian population dynamics, but few studies have tested this assertion over broad spatial scales. Human-derived foods could directly impact population sizes or indirectly affect them by mediating the influence of another factor, such as disease. In 1994, a novel disease outbreak (mycoplasmal conjunctivitis) substantially reduced populations of the house finch (Haemorhous mexicanus) in the eastern United States, creating an opportunity to test whether bird feeding indirectly exacerbated or ameliorated the impacts of the disease. We assessed the effects of bird food availability on house finch populations using data from the National Survey on Fishing, Hunting, and Wildlife-associated Recreation and the Christmas Bird Count. House finch densities were positively related to the density of people providing food for birds prior to the spread of mycoplasmal conjunctivitis, suggesting that the availability of bird seed can limit the size of finch populations. Following the disease epidemic, house finch declines were greatest where the density of people feeding birds also fell dramatically. This pattern suggests that bird food could have a positive indirect effect on disease-related mortality. Our findings suggest that the collective actions of individual people have the potential to influence resource availability and population dynamics of wildlife in human-modified landscapes.