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Islands are particularly noteworthy for global conservation because of the high number of species they host, the high levels of species endemism, and the large number and proportion of species at risk of extinction. Much of the conservation threat on islands is from invasive species. Whilst biosecurity is an increasing focus of attention for authorities globally, species are continuing to establish in new locations outside of their native ranges. Among invasive species, ants are a prominent taxon, especially on islands. Over the past decade, following the detection of one of the world’s worst invasive ant species, African big-headed ant Pheidole megacephala, the environmental management authority on world-heritage-listed Lord Howe Island has focused attention on invasive ants. This detection influenced the creation of biosecurity measures to prevent further incursions of exotic species, particularly ants. Despite these efforts, over the following decade numerous ant species were collected on the island for the first time, indicating a serious biosecurity problem. Here, we investigate the chronosequence of ant introductions to Lord Howe Island to quantify the extent and nature of the island’s ant biosecurity problem. A total of 45 species have been collected on the island and of these, 12 are considered to be endemic, and a further seven are possibly native. Nineteen of the 26 introduced species (42% of the total fauna and 73% of the introduced fauna) were only found for the first time in the last 15 years. All but two of the species that are not native to Lord Howe Island are native to the Australian mainland, indicating that the biosecurity threat comes from the transport of goods from the Australian mainland. We suggest that the pattern of accelerating ant species accumulation on Lord Howe Island is probably not an isolated phenomenon, and that it is probably occurring on most islands globally that are habitable by ants and visited by people.
We argue that human-mediated invasions are part of the spectrum of species movements, not a unique phenomenon, because species self-dispersing into novel environments are subject to the same barriers of survival, reproduction, dispersal and further range expansion as those assisted by people. Species changing their distributions by human-mediated and non-human mediated modes should be of identical scientific interest to invasion ecology and ecology. Distinctions between human-mediated invasions and natural colonisations are very valid for management and policy, but we argue that these are value-laden distinctions and not necessarily an appropriate division for science, which instead should focus on distinctions based on processes and mechanisms. We propose an all-encompassing framework of species range expansion. This does not detract from the importance of invasion biology as a discipline, but instead will help bring together research being conducted on multiple taxa, and by multiple disciplines, including epidemiology, that are often focused on an identical phenomenon: colonisation.
In our recent Discussion paper, we presented our view that the only real distinction between biological invasions and natural colonisations is the human element. We agree that invasion science is a very important science, not only to better understand the role that human mediation plays for colonisation, but also for many other science fields. We agree with all invasion researchers that the human influence can result in spectacular differences, including in rates of species movement, rates of successful colonisation, the particular species being moved, the biogeography of dispersal pathways and rates of any resulting ecological disturbance and biodiversity loss. Our deep point is that that species dispersed by human-mediation or natural colonisation are all subject to the same basic laws and rules of ecology, identical to many other phenomenon that occur naturally and can be greatly influenced by people. The human dimension is merely a mechanistic distinction, albeit important because it exposes insights about the colonisation process that cannot be seen by the study of natural colonisations alone. We provide 10 hypotheses that can be scientifically tested to determine whether biological invasions and natural colonisations are two separate processes or the same process being influenced by different mechanisms.
Die Bergbaufolgelandschaft stellt in Mitteleuropa die einzigartige Möglichkeit dar, den Prozess der Primärsukzession großflächig zu beobachten. Hierbei können z.B. Veränderungen in der Artenanzahl, der Artenzusammensetzung oder in der Struktur der Lebensgemeinschaften untersucht werden. Die bergbauliche Inanspruchnahme der Flächen führt zu einer extremen Störung. Nach erfolgter Verkippung des Abraumes können ökologische Prozesse wie Bodenbildung und Sukzession auf den neu entstandenen Flächen jedoch häufig relativ ungestört ablaufen. Um den Prozess der Besiedlung dieser Flächen zu analysieren, wurde die Laufkäferart Calathus erratus (SAHLBERG, 1827) als Modellart ausgewählt. Mittels genetischer Methoden wurde die Besiedlung großflächiger gestörter Offenlandbereiche im andschaftsmaßstab untersucht. Hierzu wurden Tagebaustandorte verschiedenen Alters und Entfernung zum unverritzten Land als Untersuchungsgebiete gewählt. Als Vergleichsstandorte dienten ehemalige Truppenübungsplätze. Die Käferpopulationen der verschiedenen Untersuchungsstandorte wurden hinsichtlich ihrer genetischen Variabilität mittels molekularer Marker untersucht. Von den genetischen Untersuchungen zur Populationsstruktur der Laufkäferart Calathus erratus werden Rückschlüsse auf die Entwicklung der genetischen Variabilität in gestörten und fragmentierten Landschaften erwartet.
Dynamics of juvenile woody plant communities on termite mounds in a West African savanna landscape
(2014)
Termites are keystone species in savanna ecology, and their mounds are thought to be an important source of habitat heterogeneity and structural complexity of the savanna. Macrotermes termitaria have been shown to allow woody plant colonisation of landscapes otherwise dominated by C4 grasses. In this study, we assess how resource-rich Macrotermes mounds affect juvenile woody plant and non-woody plant species diversity, community composition, biomass and population dynamics. We repeatedly sampled paired termite mound and savanna plots in Pendjari National Park (Sudanian vegetation zone, North Benin, West Africa) over the course of two years. Despite considerable overlap in their species pools, plant communities of mound and savanna plots were clearly separated in ordinations. Species richness and diversity of juvenile woody plants was consistently higher on termite mounds, while no differences could be detected for non-woody plants. Evenness of juvenile woody plants was generally lower on mounds, whereas density and basal area were higher on mounds. In contrast, we did not detect any influence of the mound microhabitat on colonisation, mortality and turnover of woody juveniles. Therefore, we suggest that differences in the communities on and off mounds should be strongly influenced by directed diaspore dispersal through zoochory.