Search

Invasive plants directly and indirectly disrupt the ecosystem functioning, of which indirect effects, for example, through trophic cascades, are particularly difficult to predict. It is frequently assumed that the impact of an invading species on the ecosystem is proportional (linearly related) to its density or abundance in a habitat, but this assumption has rarely been tested. We hypothesised that abundance and richness of plants and potentially pollinators of wet meadows change as a result of invasion of steeplebush Spiraea tomentosa and that these changes are proportional to the density of the shrub. We selected 27 sites amongst wet meadows habitats invaded by S. tomentosa with coverage ranging from 0% to 100% and examined the diversity of plants, as well as the abundance and diversity of flower visitors (bees, butterflies with moths and flies). Our results showed that the richness of plants, as well as the richness and number of individuals of flower visitors, decrease significantly and linearly with an increase of the S. tomentosa cover. This finding supports the hypothesis that the impact of an invasive species can be proportional to their population density, especially if this species is limiting the available resources without supplying others. Our study is the first to show such an unequivocal negative, linear effect of an invasive shrub on the abundance and richness of potential pollinators. It proves that the negative impact of S. tomentosa on the wetland ecosystem appears even with a minor coverage of the invader, which should be taken into account when planning activities aimed at controlling the population of this transformer species. The simultaneously detected linear dependence allows us to assume that the benefits of controlling secondary populations of the shrub can be proportional to the incurred effort. [ABSTRACT FROM AUTHOR]

Biological invasions are a major human induced global change that is threatening global biodiversity by homogenizing the world's fauna and flora. Species spread because humans have moved species across geographical boundaries and have changed ecological factors that structure ecosystems, such as nitrogen deposition, disturbance, etc. Many biological invasions are caused accidentally, as a byproduct of human travel and commerce driven product shipping. However, humans also have spread many species intentionally because of perceived benefits. Of interest is the role of the recent exponential growth in information exchange via internet social media in driving biological invasions. To date, this has not been examined. Here, we show that for one such invasive species, goldenrod, social networks spread misleading and incomplete information that is enhancing the spread of goldenrod invasions into new environments. We show that the notion of goldenrod honey as a "superfood" with unsupported healing properties is driving a demand that leads beekeepers to produce goldenrod honey. Social networks provide a forum for such information exchange and this is leading to further spread of goldenrod in many countries where goldenrod is not native, such as Poland. However, this informal social information exchange ignores laws that focus on preventing the further spread of invasive species and the strong negative effects that goldenrod has on native ecosystems, including floral resources that negatively impact honeybee performance. Thus, scientifically unsupported information on "superfoods" such as goldenrod honey that is disseminated through social internet networks has real world consequences such as increased goldenrod invasions into novel geographical regions which decreases native biodiversity. [ABSTRACT FROM AUTHOR]

The response of animals to the edge reveals the potential mechanism underlying the impact of invasive plants on native pollinators. Many invasive plants flower only during a part of the growing season, which creates a temporal pattern of the availability of resources. This can lead to the emergence or disappearance of the edge effect in the pollinator community in the patches dominated by alien plants.We tested whether the variability in the supply of flower resources created by dense stands of flowering invasive goldenrods could create a temporal edge effect for pollinating insects in a grassland landscape. We surveyed pollinator communities along transects perpendicular to the goldenrod‐grassland edge. To understand the variation in edge effects, we surveyed the number of flowers, which are the main food resources for pollinators.We found positive edge responses of abundance and species richness of all pollinator groups from the edges to the grassland interior before the goldenrod flowering period. During the goldenrod flowering period abundance and species richness of bees showed a neutral edge response, the response of butterflies and hoverflies towards the centre of the goldenrod patch were negative and positive respectively.Our results revealed that the emergence of the edge effect in a pollinating insect community is associated with temporal usability of invasive plants as a food source. Thus, the combined outcome of the available resources and invasion of alien plants can help to understand the edge effect on pollinator distributions in the invaded landscapes. [ABSTRACT FROM AUTHOR]

The invasion of Solidago is one of the main threats to the biodiversity of natural meadows, leading to changes in animal and plant communities, as well as soil features. We compared effects of soil microclimatic conditions (temperature and moisture) and the availability of potential protein sources (dry mass of epigean invertebrates) on ants between meadows invaded by Solidago altissima and S. canadensis and those uninvaded. Our results showed that the ant communities were different between the uninvaded and invaded meadows, with reduction of ant abundance and species richness in the latter. Myrmica spp. were abundant in the uninvaded meadows, whereas Lasius niger was the dominant species in the invaded ones. We found that the lower moisture negatively influenced the abundance of Myrmica species in the Solidago-invaded meadows. Moreover, the epigean invertebrate dry mass, as an estimation of the availability of protein sources, varied between the two types of meadows, with a higher abundance in the uninvaded ones. The abundance of Myrmica ants with narrower ecological requirements showed a positive correlation with the invertebrate biomass in the invaded meadows. In contrast, the abundance of L. niger with broad ecological requirements was negatively correlated with the invertebrate biomass in the invaded meadows, possibly as a strategy to reduce interspecific competition. Our study showed that the invasion of Solidago plants caused changes in the abundance and species composition of ant communities through modification in microhabitat conditions, that is, decreasing soil moisture, reducing biomass and changing distribution of prey invertebrates. [ABSTRACT FROM AUTHOR]

Abstract: Plant invasions are affected by many factors that must be favourable in order for invasions to occur. Factors can be grouped into three major categories: propagule pressure, biotic factors and abiotic characteristics; all may be moderated by human activity. However, studies examining all factors simultaneously are rare, and most are limited to a single factor. This hampers our understanding of the mechanisms driving invasions. In recent decades, an alien walnut (Juglans regia) has become invasive in Central Europe due to an increase in the populations of native dispersers, rooks (Corvus frugilegus) and political changes that have resulted in the abandonment of farmland. Here, we test whether increased propagule pressure resulting from the presence of seed‐bearing walnuts in abandoned fields interacts with native forest seed‐dispersing animals (biotic factors), landscape structure and management, and passive secondary dispersal by gravity (abiotic factors) to facilitate the further invasion of walnuts into forests. Seed‐dispersing animals were observed visiting walnuts growing in abandoned fields and in human settlements. Walnuts and seed dispersers were surveyed in 102 forest patches. Forest characteristics were examined, and field experiments examining passive dispersal were conducted. Walnut seeds were carried into forests by native birds, jays (Garrulus glandarius). Jays harvested seeds from both wild walnuts growing in abandoned fields and walnuts planted in human settlements. The density of walnuts in forest patches was correlated with jay density. Forest occupancy by walnuts and walnut densities were correlated with the cover of abandoned fields and human settlements containing seed‐bearing walnuts. Secondary seed dispersal also affected forest colonization. Walnut seeds hidden by native rooks in sloping, arable fields may be transported passively to forest edges. Synthesis. Our results show that this invasion is a multifaceted process in which human‐related alterations to propagule pressure and biotic and abiotic factors have led to the spread of alien walnuts from human settlements and abandoned fields into forest ecosystems. Thus, politically related land use changes can create an invasion debt that causes unexpected linkages among the invasive plant, native dispersers, land management and topography that together can cause cascading changes in ecosystems. [ABSTRACT FROM AUTHOR]

1. Plant communities influence the availability of important resources for ants, such as nest sites and food, as well as environmental conditions. Thus, plants affect the abundance and distribution of ants. 2. In a field experiment, the influence of plant cover on the settlement of nest sites and per-capita productivity of sexual individuals by the ant Temnothorax crassispinus was analysed. In July 2014, in five areas with patches of alien balsam Impatiens parviflora, and another five of native balsam I. noli-tangere, transects composed of artificial nests were established; the nest sites were situated inside patches of balsams, and outside of them. Four hundred and forty artificial nests were used. One year later, the nests were collected. 3. Colonies of the ants three times more often inhabited nest sites outside the patches of both balsams. Besides, colonies with queens were more frequently found in nest sites located away from balsams. The per-capita productivity of sexual individuals was higher in nests collected in patches of balsam, and the colonies from patches of alien balsam produced a more female-biased sex ratio. 4. In terms of the impact on the ant, no clear differences were found between the alien balsam and the native one. The most important factor affecting the fitness of ants in areas dominated by balsams is the presence of herbaceous plant cover rather than whether the plant is alien or native. [ABSTRACT FROM AUTHOR]