Abundance Of Alien Plant Species Research Articles

Functional trait variation predicts distribution of alien plant species across the light gradient in a temperate rainforest

Several interspecific studies have related functional traits to alien plant invasiveness. Few studies have explicitly addressed how intraspecific variation in functional traits influences alien plant distribution across environments. In an old-growth temperate rainforest, we evaluated alien plant distribution across the light gradient, its relationship with native plant diversity and abundance, and variation in functional traits related to light capture that could explain the ecological breadth of alien plant species across the light gradient. In addition, we estimated possible ecological and phylogenetic constraints to intraspecific variation in these functional traits. In sixty 8-m2 plots we recorded light availability together with richness and abundance of alien and native plant species. We measured in 14 alien plant species three functional traits (specific leaf area, chlorophyll content and root/shoot ratio) and calculated their coefficient of variation. We estimated ecological constraints by measuring correlations among traits that could limit functional responses to light. We assessed phylogenetic constraints by calculating the phylogenetic signal of those functional traits. Richness and abundance of alien plant species were positively associated with light availability, while abundance was negatively related to native plant species abundance. Dominance of alien species increased with light availability, but some of them were dominant even in the shade. Phenotypic variation of functional traits was positively associated with ecological breadth and dominance of alien plant species. We found little evidence of ecological or phylogenetic constraints on functional trait variation. Light availability and functional trait variation correlated with the distribution and dominance of alien plants in this temperate rainforest. Alien plant species showed considerable phenotypic variation in low light, which may facilitate colonization of the forest understory. This process would not be hindered by ecological or phylogenetic constraints. Intraspecific variation in functional traits can render insightful information on current and future alien plant distribution across environmental gradients.

Fire regulates the abundance of alien plant species around roads and settlements in the Serengeti National Park

Fire regulates the abundance of alien plant species around roads and settlements in the Serengeti National Park

Bees in disturbed habitats use, but do not prefer, alien plants

Alien plants form important interactions with flower visitors across many systems and are especially likely to dominate these interactions in disturbed habitats where native plants are rare. Most studies of alien plant–pollinator interactions have focused on the effects of alien plants on native plant reproduction; however, these alien plants may also be important food resources for native bees especially if they dominate the “floral market”. Dominance of alien species in the diet of bees could occur due to high relative density and abundance of alien plants and flowers, and/or to bee preference for alien plants when they are present. We investigated bees’ use of and preference for alien plants using two data sets from distinct regions of North America, central California and southern New Jersey. In each system, we sampled bees and flowering plants in multiple habitat types that differ in level of disturbance and in the relative abundance of alien plant species. Alien plants as a group dominated interactions with bee communities in more disturbed habitats. Importance, however, varied among plant species such that a subset of highly used plant species drove the overall pattern of use within the community. Despite higher use of alien plants in more disturbed sites, alien plants as a group were not more preferred. Rather, bees’ use of individual alien plants correlated with plant abundance in the community. Consistent with the interpretation that bees use, but do not prefer, alien plants, we found no effect of alien plant abundance or richness on bee abundance or richness.

Altitudinal distribution of alien plant species in the Swiss Alps

Abstract In summer 2003 we recorded the presence and abundance of alien plant species at 232 sites (107 railway stations and 125 road sites) along mountain passes in the Swiss Alps. The altitudinal distribution of species was related to the current abundance of the species in Switzerland and time since introduction. A total of 155 alien taxa were recorded. Numbers of species per site declined exponentially with altitude, and only a few species were found in the alpine zone (>2000 m). In contrast, species richness among comparable native taxa appeared to be nearly independent of altitude over the range investigated. Maximum altitude reached by alien species was related positively to both total area occupied in Switzerland and to time since introduction. A comparison of the results with earlier records suggests that many species, particularly those previously restricted to low or intermediate altitudes, have advanced their altitudinal limits over the past few decades. Various hypotheses are presented to explain the declining abundance of alien species with altitude: low-altitude filter effects, low propagule pressure, and genetic swamping of peripheral populations at higher altitudes. However, at present we do not have sufficient evidence to determine the relative importance of these effects. We conclude that invasion into mountain areas such as the Swiss Alps tends to proceed rather slowly, though the process may be accelerated by climatic warming. For this reason, further research to investigate the processes determining how plants invade mountain areas is urgently needed. And more generally, investigations into the distribution of alien species along strong altitudinal gradients may provide valuable insights into the mechanisms driving the spread of alien organisms.

Weeds and the monitoring of biodiversity in Australian rangelands

Abstract Monitoring the biodiversity of Australian rangelands has been identified as a means of informing policy and supporting funding decisions in relation to the conservation of biodiversity. Australian rangelands are subject to invasion by alien plants that have the potential to have major impacts on ecosystem function and biodiversity, although there has been little quantitative documentation of these effects. Research is needed to improve our understanding of how and to what extent alien plants affect biodiversity in Australian rangelands so that this relationship can be considered when developing and implementing programmes to monitor biodiversity. It is also important to consolidate existing efforts to quantify the extent of alien plant invasions and monitor their progress, thus documenting a process that threatens biodiversity. Information on the presence and abundance of alien plant species should be considered for inclusion as a component of biodiversity monitoring programmes that are undertaken. Monitoring components of biodiversity can itself provide a basis for evaluating weed management strategies.