Defining the Impact of Non‐Native Species

Non‐native species cause changes in the ecosystems to which they are introduced. These changes, or some of them, are usually termed impacts; they can be manifold and potentially damaging to ecosystems and biodiversity. However, the impacts of most non‐native species are poorly understood, and a synthesis of available information is being hindered because authors often do not clearly define impact. We argue that explicitly defining the impact of non‐native species will promote progress toward a better understanding of the implications of changes to biodiversity and ecosystems caused by non‐native species; help disentangle which aspects of scientific debates about non‐native species are due to disparate definitions and which represent true scientific discord; and improve communication between scientists from different research disciplines and between scientists, managers, and policy makers. For these reasons and based on examples from the literature, we devised seven key questions that fall into 4 categories: directionality, classification and measurement, ecological or socio‐economic changes, and scale. These questions should help in formulating clear and practical definitions of impact to suit specific scientific, stakeholder, or legislative contexts. Definiendo el Impacto de las Especies No‐Nativas     

Protected‐Area Boundaries as Filters of Plant Invasions

Abstract: Human land uses surrounding protected areas provide propagules for colonization of these areas by non‐native species, and corridors between protected‐area networks and drainage systems of rivers provide pathways for long‐distance dispersal of non‐native species. Nevertheless, the influence of protected‐area boundaries on colonization of protected areas by invasive non‐native species is unknown. We drew on a spatially explicit data set of more than 27,000 non‐native plant presence records for South Africa's Kruger National Park to examine the role of boundaries in preventing colonization of protected areas by non‐native species. The number of records of non‐native invasive plants declined rapidly beyond 1500 m inside the park; thus, we believe that the park boundary limited the spread of non‐native plants. The number of non‐native invasive plants inside the park was a function of the amount of water runoff, density of major roads, and the presence of natural vegetation outside the park. Of the types of human‐induced disturbance, only the density of major roads outside the protected area significantly increased the number of non‐native plant records. Our findings suggest that the probability of incursion of invasive plants into protected areas can be quantified reliably.     

Assessing the effects of the three herbicides acetochlor, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 2,4-dichlorophenoxyacetic acid on the compound action potential of the sciatic nerve of the frog (Rana ridibunda)

To assess the relative toxicity of the herbicides acetochlor and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) on the nervous system, the sciatic nerve of the frog (Rana ridibunda) nerve was incubated in saline inside a specially designed recording chamber. This chamber permits monitoring of the evoked compound action potential (CAP) of the nerve, a parameter that could be used to quantify the vitality of the nerve in normal conditions as well as when the nerve was exposed to the compounds under investigation. Thus, when the nerve was exposed to acetochlor, the EC(50) was estimated to be 0.22mM, while for 2,4,5-T the EC(50) was 0.90mM. Using the identical nerve preparation, the EC(50) of 2,4-D was estimated to be 3.80mM [Kouri, G., Theophilidis, G., 2002. The action of the herbicide 2,4-dichlorophenoxyacetic acid on the isolated sciatic nerve of the frog (Rana ridibunda). Neurotoxicol. Res. 4, 25-32]. The ratio of the relative toxicity for acetochlor, 2,4,5-T and 2,4-D was found to be 1:4:17.2. However, because it is well-known that the action of 2,4-D is dependent on the pH, the relative toxicity of the three compounds was tested at pH 3.3, since it has been found that the sciatic nerve of the frog is tolerant of such a low pH. Under these conditions, the EC(50) was 0.77mM (from 0.22mM at pH 7.2) for acetochlor, 0.20mM (from 0.90mM) for 2,4,5-T and 0.24mM (from 3.80mM at pH 7.2) for 2,4-D. Thus, the relative toxicity of the three compounds changed drastically to 1:0.25:0.31. This change in the relative toxicity is due not only to the increase in the toxicity of 2,4,5-T and 2,4-D at low pH levels, but also to the decrease in the toxicity of acetochlor at pH 3.3.