Aliens in caves: the global dimension of biological invasions in subterranean ecosystems

Alien species are a significant threat to natural ecosystems and human economies. Despite global efforts to address this challenge, the documented number of alien species is rapidly increasing worldwide. However, the magnitude of the impact of alien species may vary significantly across habitats. For example, some habitats are naturally less prone to biological invasions due to stringent abiotic and biotic characteristics, selecting for a limited number of introduced species possessing traits closely related to the native organisms. Subterranean ecosystems are quintessential examples of habitats with strong environmental filters (e.g. lack of light and scarcity of food), driving convergent adaptations in species that have successfully adapted to life in darkness. Despite these stringent environmental constraints, the number of records of alien species in subterranean ecosystems has increased in recent decades, but the relevant literature remains largely fragmented and mostly anecdotal. Therefore, even though caves are generally considered very fragile ecosystems, their susceptibility to impacts by alien species remains untested other than for some very specific cases. We provide the first systematic literature survey to synthesise available knowledge on alien species in subterranean ecosystems globally. This review is supported by a database summarising the available literature, aiming to identify gaps in the distribution and spread of alien invertebrate species in subterranean habitats, and laying the foundations for future management practices and interventions. First, we quantitatively assessed the current knowledge of alien species in subterranean ecosystems to shed light on broader questions about taxonomic biases, geographical patterns, modes of dispersal, pathways for introductions and potential impacts. Secondly, we collected species-specific traits for each recorded alien species and tested whether subterranean habitats act as ecological filters for their establishment, favouring organisms with pre-adaptive traits suitable for subterranean life. We found information on the presence of 246 subterranean alien species belonging to 18 different classes. The dominant alien species were invertebrates, especially insects and arachnids. Most species were reported in terrestrial subterranean habitats from all continents except Antarctica. Palaearctic and Nearctic biogeographic regions represented the main source of alien species. The main routes of introductions into the recipient country are linked to commercial activities (84.3% of cases for which there was information available). Negative impacts have been documented for a small number of case studies (22.7%), mostly related to increased competition with native species. For a limited number of case studies (6.1%), management strategies were reported but the effectiveness of these interventions has rarely been quantified. Accordingly, information on costs is very limited. Approximately half of the species in our database can be considered established in subterranean habitats. According to our results, the presence of suitable traits grants access to the stringent environmental filter posed by subterranean environments, facilitating establishment in the new habitat. We recommend that future studies deepen the understanding of invasiveness into subterranean habitats, raising public and scientific community awareness of preserving these fragile ecosystems.     

The evolutionary consequences of biological invasions

A major challenge of invasion biology is the development of a predictive framework that prevents new invasions. This is inherently difficult because different biological characteristics are important at the different stages of invasion: opportunity/transport, establishment and spread. Here, we draw from recent research on a variety of taxa to examine the evolutionary causes and consequences of biological invasions. The process of introduction may favour species with characteristics that promote success in highly disturbed, human-dominated landscapes, thus exerting novel forms of selection on introduced populations. Moreover, evidence is accumulating that multiple introductions can often be critical to the successful establishment and spread of introduced species, as they may be important sources of genetic variation necessary for adaptation in new environments or may permit the introduction of novel traits. Thus, not only should the introduction of new species be prevented, but substantial effort should also be directed to preventing the secondary introduction of previously established species (and even movement of individuals among introduced populations). Modern molecular techniques can take advantage of genetic changes postintroduction to determine the source of introduced populations and their vectors of spread, and to elucidate the mechanisms of success of some invasive species. Moreover, the growing availability of genomic tools will permit the identification of underlying genetic causes of invasive success.     

The intermediate distance hypothesis of biological invasions

Biological invasions are a worldwide phenomenon, but the global flows between native and alien regions have rarely been investigated in a cross‐taxonomic study. We therefore lack a thorough understanding of the global patterns of alien species spread. Using native and alien ranges of 1380 alien species, we show that the number of alien species follows a hump‐shaped function of geographic distance. We observe distinct variations in the relationship between alien species exchanges and distance among taxonomic groups, which relate to the taxa‐specific dispersal modes and their pathways of introduction. We formulate a simple statistical model, combining trade volume and biogeographic dissimilarity, which reproduces the observed pattern in good agreement with reported data and even captures variations among taxonomic groups. This study demonstrates the universality of the intermediate distance hypothesis of alien species spread across taxonomic groups, which will help to improve the predictability of new alien species arrivals.     

The nature of economic costs of biological invasions

Biological Invasions - The management of invasive alien species (IAS) is complex and requires consideration of intertwined ecological and economic dimensions. Given the wide variety of costing...     

生物入侵对鸟类的生态影响

生物入侵是全球生物多样性面临的最主要威胁之一, 入侵种在改变入侵地环境的同时也使当地的生物受到极大影响。鸟类在生态系统中处于较高的营养级, 生态系统中任何一个环节的变化都可能对鸟类造成一定的影响。本文回顾了哺乳动物、鸟类、无脊椎动物和植物等不同生物类群的入侵对本地鸟类生态影响方面的研究进展。外来生物对鸟类的影响主要表现在以下几方面: (1)外来哺乳动物对成鸟、幼鸟或鸟卵的捕食作用; (2)外来鸟类与本地鸟类竞争栖息地和食物资源, 与当地的近缘种杂交而造成基因流失; (3)外来无脊椎动物改变本地鸟类的栖息环境和食物状况, 甚至直接捕食本地鸟类; (4)外来植物入侵改变入侵地的植物群落组成和结构, 造成本地鸟类的栖息地丧失或破碎化, 并通过改变入侵地生态系统的食物链结构而对高营养级的鸟类产生影响。最后, 作者还提出了该领域有待解决的问题和今后可能的研究方向。     

The biological aspects of botfly invasions in reindeer]

Field and laboratory studies established the development time of all the phases of Oedemagena tarandi and Cephenemyia trompe in different climatic zones of their habitat. The phenological and ecological features of O. tarandi and C. trompe in the aforesaid zones were identified which are the basis for scientifically grounded prophylactic measures. Data on potential and actual fecundity make it possible to calculate their reproduction potential and to forecast the invasion intensity of the reindeer in the next season.     

Allee effects in biological invasions

Understanding the dynamics of small populations is obviously important for declining or rare species but is also particularly important for invading species. The Allee effect, where fitness is reduced when conspecific density is low, can dramatically affect the dynamics of biological invasions. Here, we summarize the literature of Allee effects in biological invasions, revealing an extensive theory of the consequences of the Allee effect in invading species and some empirical support for the theory. Allee effects cause longer lag times, slower spread and decreased establishment likelihood of invasive species. Expected spatial ranges, distributions and patterns of species may be altered when an Allee effect is present. We examine how the theory can and has been used to detect Allee effects in invasive species and we discuss how the presence of an Allee effect and its successful or unsuccessful detection may affect management of invasives. The Allee effect has been shown to change optimal control decisions, costs of control and the estimation of the risk posed by potentially invasive species. Numerous ways in which the Allee effect can influence the efficacy of biological control are discussed.     

Global change and biological invasions

Invasion by exotic species is one of the serious socio-economic, environmental and ecological problems currently faced by mankind. Biological invasions have changed the species composition, structure and function of ecosystems, and are seriously threatening global biodiversity, economy and human health (Iqbal et al. 2021; Wang et al. 2020; Yang et al. 2021; Zhao et al. 2020; Zheng et al. 2015). Biological invasions have resulted in an economic loss of at least US$ 1.288 trillion over the past few decades worldwide (Diagne et al. 2021). As a consequence of these far-reaching impacts, biological invasions have become a hot research topic in modern ecology, and attract major attention from international organizations, governments and scientists all over the world. There is a complex interaction between biological invasions and global environmental change. Biological invasions are not only passengers of global change, but can also be major drivers of global change (MacDougall and Turkington 2005). Other components of global change, such as atmospheric CO₂ enrichment, global warming, nitrogen deposition, changes in precipitation regimes, habitat fragmentation and land-use change, affect species distributions and resource dynamics of ecosystems, and consequently drive invasion success of many exotic species. On the other hand, invasion by exotic species can also alter basic ecosystem properties, which in turn affect many components of global change. Research on the patterns, processes and mechanisms of biological invasion can shed light on the drivers and consequences of biological invasions in the light of global change, and serve as a scientific basis for forward-thinking management plans. The overarching challenge is to understand the basic ecological interactions of, e.g., invasive and native species, plants and soil, and plants and animals.     

Evolutionary indirect effects of biological invasions

Just as ecological indirect effects can have a wide range of consequences for community structure and ecosystem function, theory suggests that evolutionary indirect effects can also influence community dynamics and the outcome of species interactions. There is little empirical evidence documenting such effects, however. Here, I use a multi-generation selection experiment in the field to investigate: (1) how the exotic plant Medicago polymorpha and the exotic insect herbivore Hypera brunneipennis affect the evolution of anti-herbivore resistance traits in the native plant Lotus wrangelianus and (2) how observed Lotus evolutionary responses to Hypera alter interactions between Lotus and other members of the herbivore community. In one of two study populations, I document rapid evolutionary changes in Lotus resistance to Hypera in response to insecticide treatments that experimentally reduced Hypera abundance, and in response to Medicago-removal treatments that also reduced Hypera abundance. These evolutionary changes in response to Hypera result in reduced attack by aphids. Thus, an evolutionary change caused by one herbivore species alters interactions with other herbivore taxa, an example of an eco-evolutionary feedback. Given that many traits mediate interactions with multiple species, the effects of evolutionary changes in response to one key biotic selective agent may often cascade through interaction webs to influence additional community members.     

An evolutionary perspective of biological invasions

The workshop on the Evolutionary Perspective of Biological Invasions in Terrestrial Ecosystems was held in Halle, Germany from 30 September to 3 October 2002.     

Antarctica: The final frontier for marine biological invasions

Antarctica is experiencing significant ecological and environmental change, which may facilitate the establishment of non‐native marine species. Non‐native marine species will interact with other anthropogenic stressors affecting Antarctic ecosystems, such as climate change (warming, ocean acidification) and pollution, with irreversible ramifications for biodiversity and ecosystem services. We review current knowledge of non‐native marine species in the Antarctic region, the physical and physiological factors that resist establishment of non‐native marine species, changes to resistance under climate change, the role of legislation in limiting marine introductions, and the effect of increasing human activity on vectors and pathways of introduction. Evidence of non‐native marine species is limited: just four marine non‐native and one cryptogenic species that were likely introduced anthropogenically have been reported freely living in Antarctic or sub‐Antarctic waters, but no established populations have been reported; an additional six species have been observed in pathways to Antarctica that are potentially at risk of becoming invasive. We present estimates of the intensity of ship activity across fishing, tourism and research sectors: there may be approximately 180 vessels and 500+ voyages in Antarctic waters annually. However, these estimates are necessarily speculative because relevant data are scarce. To facilitate well‐informed policy and management, we make recommendations for future research into the likelihood of marine biological invasions in the Antarctic region.     

对生物入侵的几点思考

生物入侵涉及异地迁徙及建群等复杂问题,涉及个体、种群、群落、生态系统等生态学的各个层次,又必不可少地要深入地去探索生物入侵过程中的快速进化和分子生态学基础。生物系统的超级复杂性加上环境和人为因素的极度随机性,充分显示了在这一领域从事研究的艰巨性和挑战性。入侵种具有两面性,因此,预防比治理更为关键。为了应对生物入侵,有待建立完善的国家和地区的防控系统、提高技术水平并加强有关诸多经济因素对生物入侵的影响的研究。     

Historical perspectives on human-assisted biological invasions

Of all the things we have done to the Earth so far, which one is likely to make the most indelible mark? I have been posing this question to students and colleagues for some time, and usually receive one of three reasonable replies: habitat destruction, human overpopulation, or global climate change. Yet as bad as all these maladies are, they are, to some extent, reversible on time scales to which we can relate. The remedies for these problems, despite mammoth cultural and economic obstacles, can be visualized generally in terms of technology and scientific theory. Only the will is lacking. On longer geological and evolutionary time scales, most such human impacts, if corrected soon, would be mere blips, perturbations of the ecosphere that would leave only a few detectable traces in the fossil record a million years hence.     

The role of aggression in range expansion and biological invasions

Traits that aid in the invasion process should exhibit a gradient across the expansion range in response to changing selection pressures. Aggression has been repeatedly associated with invasion success in many taxa, as it may help invaders to wrestle the resources from other species which enhances their success in a novel environment. However, aggression primarily al lows individuals to overcome conspecific rivals, providing advantages in competition over resources. Agonistic prowess could therefore increase fitness at both ends of the expansion gradient. Here we review the role of aggression in range expansion of in vasive species, and its potential role as a driver of range expansion. We analyze how these different mechanisms could affect trait variation in expanding and invasive populations. Specifically, we look at how aggression could help dilate the edges of a popula tion through niche competition, as well as lead to exclusion from the center （Le. areas of high population density） by the conspe cities. Both of these processes will result in a characteristic spatial distribution of phenotypes related to aggression that could provide insights into the ecological pressures and dynamics of expanding populations, potentially providing clues to their success as niche competitors and invasive species     

媒介昆虫-病毒-植物互作对生物入侵的影响

媒介昆虫-病毒-植物互作关系复杂多样。虽然相关的研究较多, 然而有关三者互作对于生物入侵的影响还知之甚少。已有证据表明, 寄主植物对病毒的敏感性和对媒介昆虫的适合性、媒介昆虫对寄主的适应能力等因素影响三者互作关系。当寄主植物易感病并且对媒介昆虫的适合性低, 而媒介昆虫对寄主植物的适应能力强时, 媒介昆虫与植物病毒之间很可能建立间接互惠关系, 这种互惠可促进媒介昆虫入侵和病毒病流行。此外, 媒介昆虫与植物病毒之间中性或偏害的互作关系对于外来生物入侵的促进作用也不容忽视。鉴于三者互作对于生物入侵的重要性, 今后需要对不同物种所组成的多种组合进行比较研究, 并采用多种方法揭示互作的生理和分子机制。     

Speciation genetics of biological invasions with hybridization

The negative effects of human‐induced habitat disturbance and modification on multiple dimensions of biological diversity are well chronicled ( Turner 1996 ; Harding et al. 1998 ; Lawton et al. 1998 ; Sakai et al. 2001 ). Among the more insidious consequences is secondary contact between formerly allopatric taxa ( Anderson & Hubricht 1938 ; Perry et al. 2002 ; Seehausen 2006 ). How the secondary contact will play out is unpredictable ( Ellstrand et al. 2010 ), but if the taxa are not fully reproductively isolated, hybridization is likely, and if the resulting progeny are fertile, the eventual outcome is often devastating from a conservation perspective ( Rhymer & Simberloff 1996 ; Wolf et al. 2001 ; McDonald et al. 2008 ). In this issue of Molecular Ecology, Steeves et al. (2010) present an analysis of hybridization between two avian species, one of which is critically endangered and the other of which is invasive. Their discovery that the endangered species has not yet been hybridized to extinction is promising and not what one would necessarily expect from theory.     

Impacts of biological invasions on disturbance regimes

Human management activities have altered the frequency and intensity of ecosystem disturbance often with enormous impacts on landscape structure and composition. One additional and under-appreciated way in which humans have altered disturbance regimes is through the introduction of invasive non-native species, themselves capable of modifying existing disturbance regimes or introducing entirely new disturbances. In many cases, modifications of disturbance regimes results in maintenance of ecosystems in a new or transitional state. There is now evidence that alteration of disturbance regime may be the most profound effect that a species or functional group can have on ecosystem structure and function.