All change at the water’s edge: invasion by non-native riparian plants negatively impacts terrestrial invertebrates

Impacts of the Invasive Impatiens glandulifera: Lessons Learned from One of Europe's Top Invasive Species

Simple Summary

Plants and animals are a part of a larger system, commonly referred to as an ecosystem. This generally implies a balance existing between prey and predators. The unintentional introduction of a species in a new environment can lead to a significant alteration of the ecosystem(s) and the uncontrolled spread of the species. When this takes place, the introduced species is referred to as invasive. Invasives can affect the ecosystem in profound ways, and generally, negatively impacting on the native species. This manuscript reviewed the current knowledge of one of Europe’s top invasives, the Himalayan balsam (Impatiens glandulifera). It provides insights on the species and what have we learned from this invasive species.

Abstract

Biological invasions are renowned for their negative ecological and economic implications, however from studying invasions invaluable insights can be gained in the fields of ecology and evolution- potentially contributing towards conservation plans to deal, not only with biological invasion, but with other concerning issues, such as climate change. Impatiens glandulifera, or Himalayan balsam, is widely considered to be a highly problematic invasive, having spread across more than thirty countries during the past century. This paper will examine the findings which have arose from studying I. glandulifera and its impacts on the invaded ecosystem.

Differing impacts of two major plant invaders on urban plant-dwelling spiders (Araneae) during flowering season

Plant invasions can have major impacts on ecosystems and influence global species diversity. In Central Europe, Himalayan balsam (Impatiens glandulifera) and American goldenrods (Solidago canadensis and S. gigantea) are important invaders often establishing dense and homogeneous stands, especially in urban and other disturbed habitats. We investigated their impacts on plant-dwelling spiders (abundance, family structure, guild structure) and potential spider prey items during flowering season within an urbanized landscape using a paired design comparing invaded and native reference vegetation plots. In general, flowering American goldenrods and Himalayan balsam had no significant impacts on the spider family composition. Invasion of American goldenrods further had no effect on total spider abundance and potential prey item abundance. In contrast, goldenrods showed a significantly increased crab spider (Thomisidae) abundance while being less inhabited by web builders. Himalayan balsam negatively influenced free hunters and running crab spider (Philodromidae) abundance, while we found no effects on other groups and total spider abundance. For Himalayan balsam, potential prey item abundance was higher than in native vegetation stands. Notwithstanding that our results only represent a snapshot of the system, they suggest that large-scale removal of urban goldenrod stands during flowering season might negatively influence local spider abundance, especially of crab spiders. Management efforts should therefore be accompanied by compensation measures to avoid disruptive effects on local plant-dwelling spider communities.

Response of dominant plant species to periodic flooding in the riparian zone of the Three Gorges Reservoir (TGR), China

Human-induced disturbances such as dam construction and regulation often change the duration and frequency of flooding and thus notably influence plant dominance in riparian zones. Even though numerous studies have indicated that the oxidative stress and antioxidative stress systems are essential for plant defenses against adverse flooding stress, the mechanism of vegetation distribution due to hydrological regimes is still unclear. In the current study, the riparian zone of the Three Gorges Reservoir (TGR), which experiences seasonal and anti-seasonal water-level fluctuations, was used to investigate the dominant species. To our knowledge, this is the first study that links molecular-physiological-morphological mechanisms to explore the development of flooding tolerance of dominant riparian species. Physiological traits (e.g., chlorophyll and protein contents), morphological traits (e.g., leaf length), and molecular traits (e.g., enzymatic antioxidant activity and the malondialdehyde content) were analyzed at different water-level gradient zones of the dominant species to evaluate the influence of flooding. To explore the regulation mechanisms of submergence for the vegetation distribution, correlation analysis, PCA (principal component analysis) and laboratory flooding experiments were conducted. The results showed that Cynodon dactylon, which has a rapid antioxidative system, was the dominant species in the riparian zone of the TGR. The leaf length varied significantly along with water level gradients (p < 0.05) with the minimum values appearing in the lowest part of the riparian zone and the maximum values observed in the highest areas. The chlorophyll and protein contents fluctuated in different water level gradient zones, but significant differences were not observed. Within the antioxidative system, catalase was found to be essential for riparian plants in their response to flooding. The current study could provide insight to explore the specific mechanism of resistance for dominant plants to periodic flooding, and the reason why dominant species can survive adverse stress.

Perceived socio-economic impacts of the marbled crayfish invasion in Madagascar

The negative environmental and economic impacts of many invasive species are well known. However, given the increased homogenization of global biota, and the difficulty of eradicating species once established, a balanced approach to considering the impacts of invasive species is needed. The marbled crayfish (Procambarus virginalis) is a parthenogenetic freshwater crayfish that was first observed in Madagascar around 2005 and has spread rapidly. We present the results of a socio-economic survey (n = 385) in three regions of Madagascar that vary in terms of when the marbled crayfish first arrived. Respondents generally considered marbled crayfish to have a negative impact on rice agriculture and fishing, however the animals were seen as making a positive contribution to household economy and food security. Regression modeling showed that respondents in regions with longer experience of marbled crayfish have more positive perceptions. Unsurprisingly, considering the perception that crayfish negatively impact rice agriculture, those not involved in crayfish harvesting and trading had more negative views towards the crayfish than those involved in crayfish-related activities. Food preference ranking and market surveys revealed the acceptance of marbled crayfish as a cheap source of animal protein; a clear positive in a country with widespread malnutrition. While data on biodiversity impacts of the marbled crayfish invasion in Madagascar are still completely lacking, this study provides insight into the socio-economic impacts of the dramatic spread of this unique invasive species. “Biby kely tsy fantam-piaviana, mahavelona fianakaviana” (a small animal coming from who knows where which supports the needs of the family). Government worker Analamanga, Madagascar.