1
Invasive Alien Species : A Prodigious Global Threat in the Anthropocene

Michael R. Ielmini1 and K.V. Sankaran2

1 National Forest System Headquarters, USDA Forest Service, Washington, DC, USA

2 Kerala Forest Research Institute, Peechi, Kerala, India

1.1 Introduction

Invasive alien species (IAS), introduced intentionally or inadvertently, are one of the main drivers of global environmental change and cause significant ecological and economic damage (Vitousek et al. 1996, 1997; Mckinney and Lockwood 1999; Sala et al. 1999; Pimentel et al. 2000; Hurka 2002; Dukes and Mooney 2004; Mooney et al. 2004). A widely accepted definition of IAS is that they are introduced species of exotic (non-native, alien, non-indigenous) origin, which through the various mechanisms of invasion outcompete native species, causing harm to the health and function of the invaded ecosystems; affect plant and animal health; and threaten or negatively impact cultures or communities and the economy or productivity of these systems. IAS tend to establish and spread far and wide in natural and planted forests, agriculture lands, marginal lands, aquatic systems, and areas close to settlements. Evidence abounds in the literature on the invasion of thousands of exotic plants, insects, fishes, mollusks, crustaceans, microbes, mammals, birds, reptiles, and amphibians, which adversely impact hundreds of millions of hectares of land and water across the globe (Newsome and Noble 1986; Kurdila 1995). Lonsdale (1999) has modeled invasibility around the globe and found that there were significant differences among biomes, but not between continents, in the level of invasion. Worldwide, native forests, prairies, deserts, mountains, wetlands, rivers, lakes, and seas have all been invaded by a broad array of insidious harmful exotic species. Islands are particularly at risk of invasion and impact (Vitousek 1988; D'Antonio and Dudley 1995). This book provides examples of this broad spectrum of invasive threats, documents many national assessments and status reports on IAS, and discusses management preparedness across continents.

IAS are the second major cause of the loss of global biodiversity, after habitat loss (Hurka 2002). IAS, the movement of which are often accelerated through human activities (Cushman and Meentemeyer 2008; Simberloff et al. 2013), are very adaptable to diverse soil and climatic conditions, and they compete with native species for resources and have contributed to significant population declines in many native species. The data are not definitive on the specific number of native species that have been driven to extinction due to alien species invasions, but evidence exists for a clear relationship.

Human population growth, together with an increased globalization, has led to the significant rise in the number of alien species worldwide (di Castri 1989). One of the results of this globalization is that species distribution becomes more homogeneous and species composition shrinks from one location to the other. The threat to indigenous biodiversity from IAS has helped attract wider attention to the impacts of globalization, and as a result, many countries have worked out their own regulatory-type lists (aka "black lists") of unwanted or high-risk non-native species that they want to prevent entering their territories, establishing, and spreading within their borders (Bevanger et al. 2007).

Human-assisted movement of species across countries and continents has a long history. Movement of species across countries and continents has a long history. It began when humans started travel and trade. Intentional movement of plant and animal species has a correlation with the foundations of agriculture and animal husbandry - based on ancient habits of favoring certain species and their habitats over others for food, fiber, and medicine (Flannery 1973). From the invasive plant standpoint, the number of potential threats is astounding. At least 13?168 species of vascular plants have been naturalized, outside their native habitats or ranges; and a total of 4979 species are documented as invasive species (RBG Kew 2016). In The Global Compendium of Weeds (Randall 2012), there are almost 21?000 entries and an index of over 15?000 synonyms and 27?000 common names used in different countries. Randall (2012) noted that previously the most significant coverage of the world's weed flora was by Holm et al. (1979) in the Geographical Atlas of World Weeds (1979), which listed 6400 weeds. A final species count will be possible only after the synonyms are cross-indexed against other entries, but there will be well over 18?500 discrete weedy taxa. According to Pimentel et al. (1999), about 50?000 non-native species have been introduced in the United States. Many of these were deliberately introduced for erosion control (kudzu vine, Pueraria lobata), for food purposes and fishing (brown trout, Salmo trutta), as agricultural crops (Johnson grass, Sorghum halepense), or as ornamental trees and landscape plants (purple loosestrife, Lythrum salicaria). Some of the major invasive microbes and invertebrates were introduced inadvertently through various pathways and vectors, such as the chestnut blight pathogen (Cryphonectria parasitica), West Nile virus (Flavivirus sp.), gypsy moth (Lymantria dispar), emerald ash borer (Agrilus planipennis), and zebra mussel (Dreissena polymorpha) (Pimentel et al. 1999). Purple loosestrife was introduced into the United States as an ornamental in the early nineteenth century. It is widespread in riparian habitats throughout the continental United States, and control costs are an estimated US$45 million per year. Riparian areas, as in other countries, are extremely valuable to native plants and animals, and the invasion by the plant poses a serious threat to numerous riparian-dependent species (Pimentel et al. 1999).

Certain other invasive plants, such as cheatgrass (Bromus tectorum), have almost entirely displaced sagebrush-grassland plants and associated animals in the United States. Cheatgrass has also seriously altered the fire regime from an average return interval of 60-110?years to 0-3?years. It is a good example of the adverse impacts an introduced species can have on the environment. Scientists and resource managers estimate that the plant has invaded 100 million acres of grassland-steppe in the western United States. Cheatgrass forms a dense, uniform carpet that outcompetes native grasses and shrubs. It flushes quickly and dries likewise, producing very flammable cover that often burns completely and intensely, consuming all native flora and fauna that cannot escape these catastrophic wildfires. In pinyon-juniper woodlands, the combination of cheatgrass and fire prevents the reestablishment of the original sites (Mitchell 2000).

In Africa and the Asia-Pacific region, invasive plants such as Chromolaena odorata (Siam weed), Lantana camara (common lantana or tickberry), Parthenium hysterophorus (Santa Maria feverfew or parthenium weed), Prosopis juliflora (mesquite), and Leucaena leucocephala (river tamarind) and the aquatic weed Pontederia crassipes cause heavy damage to the ecology of the invaded areas, affect ecosystem services, and reduce the productivity of agricultural crops. In Europe, another group of plants including Fallopia japonica (Japanese knotweed), Impatiens glandulifera (Himalayan balsam), Ambrosia artemisiifolia (annual ragweed), and Ailanthus altissima (tree of heaven) cause similar damage. Records of invasive mammals, birds, reptiles, amphibians, fishes, insects, and microbes, also widespread across these regions, are growing, degrading all ecosystems invaded. Impacts of the insect box tree moth (Cydalima perspectalis) and spotted-wing drosophila (Drosophila suzukii) in Europe; the black rat (Rattus rattus), European starling (Sturnus vulgaris), brown tree snake, Nile perch (Lates niloticus), giant African snail (Lissachatina fulica), and Argentine ant in Africa; and the coconut leaf beetle (Brontispa longissima), pine wood nematode (Bursaphelenchus xylophilus), red imported fire ant (Solenopsis invicta), papaya mealybug (Paracoccus marginatus), and golden apple snail (Pomacea canaliculata) in the Asia-Pacific form good examples of these.

IAS also cause economic losses to invaded areas and communities (Pimentel et al. 2005). It has, for instance, become evident that agriculture, forestry, and fisheries suffer very high costs, and human health is greatly compromised as well. Estimates show that IAS inflict an annual economic loss close to US$120 billion in the United States (Pimentel 2002), and approximately 46% of the plants and animals federally listed as endangered species in the United States have been negatively impacted by invasive species (Wilcove et al. 1998). In Europe, Genovesi et al. (2015) reported that 354 threatened species (229 animals, 124 plants, and 1 fungus) are specifically affected by IAS, which accounts for 19% of all threatened species in Europe. Globally, the annual impacts and control costs...