People have moved species from one part of the globe to another throughout human history. For the most part species introductions have been deliberate—most of the food we eat, the fibers we use, the plants in our gardens, have their origins in distant parts of the world. Occasionally, species introductions have been inadvertent or accidental—as hitchhikers on deliberate introductions, or, increasingly, as collateral to growing global travel and trade. Every so often, an introduced species tends to become dominant in its de novo environment, competing with native species, altering the structure and functioning of native ecosystems, and doing untold ecological and economic damage: the arrival of avian malaria in the Hawaiian islands led to the extinction of several bird species unique to the archipelago, and to the decline of many others; introduced grasses have altered !re regimes, thereby changing ecosystem structure, composition, and dynamics in the Americas; introduced trees are reducing water flow into aquifers and a$ecting water supply to Cape Town in South Africa. These are examples of what have come to be known as invasive alien species, ‘invasive’ a reference to the ecological damage they cause, and ‘alien’ a reference to their non-native biogeographical provenance. So great is the concern about invasive alien species today, that the international Convention on Biological Diversity has ranked them amongst the foremost threats to biodiversity and ecosystem functioning.
A British biologist, Charles Elton, was amongst the earliest to draw attention to the problem of invasive species in the late 1950s. He was concerned that with increasing human- aided movement of species around the planet, the uniqueness and distinctness of biodiversity in different parts of the world was in danger of being homogenised. He cautioned that though not all alien species were necessarily invasive, those that were could have devastating impacts. He also cautioned that the potential danger from invasive alien species was likely to be greatest on oceanic islands, with their unique but vulnerable biota, and in disturbed environments, where available resources could be readily preempted by invasive species.
Today there is a great deal of interest, both in what makes certain species more invasive than others, and in what makes certain ecosystems more vulnerable to invasion than others—questions that can provide insights into how ecosystems are assembled. These questions also have tremendous practical significance for the conservation of biodiversity and the services that society derives from ecosystems, as they can provide us with tools to predict which species are most likely to become invasive, and can enable us to model invasive species spread and to prioritise management interventions. #ere is also growing interest in evaluating the economic consequences of invasive species for human well being, and in developing appropriate policies and capacities for invasive species prevention, control, or mitigation.
This special feature brings together a collection of articles that showcases a diversity of concerns related to invasive alien species. Perrings et al. examine the economic and policy aspects of the problem of biological invasions at a global scale, especially with respect to global trade. The authors include microorganisms in their definition of biological invasive species, thus encompassing issues of emergent and recurrent human diseases. Their assertion, that the problem of invasive species is the most significant environmental issue facing humanity, is therefore not surprising.
Volin reviews work on Lygodium micro-phyllum, a climbing fern native to the Old World and now widespread in the southeastern USA. #is article illustrates the kinds of information, across scales, required to understand the ecological underpinnings of a species’ invasiveness; such information can aid the search for appropriate control methods and enable predictive modeling of the species’ spread, of value for managers and policymakers.
Three of the articles focus on Lantana camara in India, undoubtedly a reflection of lantana’s status as amongst India’s most widespread terrestrial invasive species. However, they examine very di$erent aspects of lantana—Sharma and Raghubanshi focus on its ecological impacts, Babu et al. talk about mitigation and control, and Shaanker et al. propose adaptation and related livelihoods. The article by Sharma and Raghubanshi draws on their work on the impacts of lantana on biodiversity and ecosystem functioning. They also propose that lantana’s invasive success may not be explained by any one characteristic of the species but rather, could be attributed to multiple mechanisms. Babu et al. describe a method they have designed to control lantana and restore native species and ecosystem functioning, which may have high benefits, particularly in protected areas.
The management of invasive species can have complex effects on livelihoods and ecology, as illustrated by both Shaanker et al. and by Shackleton and Gambiza. Shaanker et al. argue that once an invasive species has become widespread it may be best to live with it and enable local communities to draw a livelihood from it, thus reducing the costs of control. Shackleton and Gambiza draw our attention to Euryops floribundus, a native invasive species in South Africa; its eradication, though of bene!t to livestock owners, would adversely a$ect women who depend on it for fuel.
Rauf Ali is dismissive of the focus on what he terms the ‘page 3 species,’ including lantana. Instead, he draws attention to the vulnerability of island eco-systems, in this case, the Andaman islands, to invasions. His choice of invasive species—both elephants and chital are native to the Indian mainland— helps underscore an important point, that ‘alien’ is a biogeographical rather than a political concept. His choice of invasive species also underscores the cultural obstacles to our dealing with animal invasive species.
Namboothri and Shanker draw our attention to Kappaphycus alvarezii, a marine invasive species, and its relationship with the industrial production of soft drinks. Cola production has created an economic interest in the species, to the extent that arguments are made contesting the species’ invasiveness. Who bears the burden of proof? Should we adopt the precautionary principle? #is collection of summaries informs us that there are a great diversity of biologically invasive species and contexts, with some fundamental uncertainties but possibly great implications for human welfare.
Ankila Hiremath is a Fellow at ATREE, New Delhi, India. Mail at hiremath@atree.org
Vikram Dayal is an Associate Professor at the Institute of Economic Growth, Delhi, India.
Illustrator: Kalyani Ganapathy
