Current occurrence and potential future climatic niche distribution of the invasive shrub Spiraea tomentosa L. in its native and non-native ranges

Linear scaling – negative effects of invasive Spiraea tomentosa (Rosaceae) on wetland plants and pollinator communities

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.

Quo vadis? Historical distribution and impact of climate change on the worldwide distribution of the Australasian fungus Clathrus archeri (Phallales, Basidiomycota)

Clathrus archeri is a fungus native to Australia and New Zealand that has started to expand into Europe, and it is considered a potentially invasive species. In this study, we examine the historical occurrence, current geographical range and potential future changes in the distribution of C. archeri using worldwide distribution data. Ecological modelling was used to assess the locations of the potential climatic niches of C. archeri within both its native and introduced ranges in the past, present and future. Our study clearly shows that the coverage of suitable habitats of this fungus has decreased since the last glacial maximum, and anthropogenic climate changes are accelerating the process of niche loss. The highest rate of C. archeri range contraction is expected in Australia, where the fungus should be considered a threatened species in the future. Highly valuable habitats will be available in Tasmania and New Zealand. However, a significant expansion rate of C. archeri will still probably be observed in Europe, where the climatic conditions preferred by the fungus will allow its quick expansion northeast into the continent.