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Dr. W. Bölsche
(1895)
Auf Anregung des naturwissenschaftlichen Vereins zu Osnabrück habe ich die seit längeren Jahren von mir im sogen. Artlande und angrenzenden Gebieten beobachteten Säugetiere, Vögel, Reptilien und Fische zusammengestellt. Das Artland bilden die Kirchspiele Badbergen, Gehrde, Menslage und das Stadtgebiet Quakenbrück. Mit den angrenzenden Gebieten würde das Artland den größten Teil der Mittel- und einen Teil der Nieder-Hase umfassen, ein Gebiet, welches ich kurz folgendermaßen schildern möchte. Außer einem unbedeutenden Höhenzug als letzten Ausläufer des Osnings ins nordwestdeutsche Tiefland, der sich bis Börstel ausdehnt, besteht dasselbe nur aus Flachland. Ausgedehnte Wiesenflächen, Brüche wechseln mit Ackerland und Waldungen, Haiden mit Sümpfen und Moor.
In dieser kleinen Arbeit übergebe ich den Hymenopterologen den 1. Teil einer Hymenopterenfauna von Iburg und seiner nächsten Umgebung. Das Sammelgebiet ist verhältnismäßig recht klein. Denkt man sich mit einem Radius von höchstens 1 1/2 km einen Halbkreis nach Süden gelegt, dessen Mittelpunkt sich in Iburg selbst befindet, so wird südlich das ganze Jagdgebiet von demselben eingeschlossen. Nach Osten, Norden und Westen würde wegen der angrenzenden Wälder und Gebirge der Radius, eines nach diesen Richtungen gezogenen Halbkreises kaum 1 km betragen. Innerhalb der Grenzen dieser beiden Halbkreise wurden die nachfolgend verzeichneten Arten gesammelt, doch lieferte der südliche Teil gewiss 9/10 derselben, da die Terrainverhältnisse des nördlichen Halbkreises den Wespen außerordentlich wenig Nistplätze bieten.
Recently, Müller and Nentwig (2011) reviewed the plant pathogens that have been considered for biological control of the weed Cirsium arvense (L.) Scop. (Canada thistle, Californian thistle, creeping thistle), and concluded that the prospects have been largely overestimated. The premise of their conclusion is that no bioherbicide products have achieved marketability, which they surmise is due to lack of host specificity, effectiveness, and issues with application. While it is true that no microbial products have achieved marketability for this weed, we believe their reasoning for this is erroneous, and likely due to lack of distinction between two biocontrol approaches, specifically classical biocontrol, and innundative biocontrol (often referred to as the biopesticide approach). These two different types of biocontrol have different goals, and are applied in different ways.
Invasive knotweeds, native to Eastern Asia, are among the most dominant plant invaders of European and North American temperate ecosystems. Recent studies indicate that one cause of this dominance might be allelopathy, but the possible sources and modes of action of this allelopathy are insufficiently understood. Here, we asked whether the invasive knotweed Fallopia × bohemica can exert allelopathic effects on native plants also through its leaf litter, or through persistent soil contaminants, and whether these affect the germination or growth of native plants. In a germination experiment with nine native species neither litter leachate, an aqueous extract of knotweed leaves added to the soil, nor trained soil with a history of Fallopia pre-cultivation suppressed the germination or early growth of natives. A mesocosm study with experimental native communities showed that the presence of F. × bohemica, although not a dominant in these communities, caused significant shifts of life-history strategy in two dominant natives, and that similar effects could be elicited through litter leachates or trained soil alone. However, there were hardly any effects on the biomass of natives. Our study indicates that knotweed allelopathy acts on the growth rather than germination of natives, and that soil contamination through persistent allelochemicals may not be a significant problem in habitat restoration. It also shows that allelopathic effects can sometimes be subtle changes in life-history and allocation patterns of the affected species.
Many successful invasions involve long initial periods in which the invader exists at low densities followed by sudden population increases. The reasons for such time-lags remain poorly understood. Here we document a sudden increase in density of the introduced Japanese white-eye (Zosterops japonicus) in a restoration area contiguous with old-growth forest at Hakalau Forest National Wildlife Refuge on the Island of Hawaii. The refuge, with very high density of native birds, existed in a pocket of low whiteeye density that persisted for at least 20 years since the late 1970s. The refuge began an extensive native trees restoration project in 1989 within a 1314 ha abandoned pasture above old-growth forest. This area was soon colonized by white-eyes and their population grew exponentially once the trees had grown tall enough to develop a canopy. This increase was in turn followed by significantly more white-eyes in the open and closed forests adjacent to the restoration area. Competition between white-eyes and native species was documented on study sites within these forests. Density data indicate that competition was more widespread, with loss of tens of thousands of native birds in the 5371 ha area surveyed. Our results are consistent with the view that ecological barriers may delay the population increase of invaders and that human-derived activities may help invaders cross these barriers by creating new ecological opportunities. Control of white-eye numbers may be essential for recovery of native species.