Although most studies of factors contributing to successful establishment and spread of non-native species have focused on species traits and characteristics (both biotic and abiotic), increasing ...empirical and statistical evidence implicates propagule pressure—propagule sizes, propagule numbers, and temporal and spatial patterns of propagule arrival—as important in both facets of invasion. Increasing propagule size enhances establishment probability primarily by lessening effects of demographic stochasticity, whereas propagule number acts primarily by diminishing impacts of environmental stochasticity. A continuing rain of propagules, particularly from a variety of sources, may erase or vitiate the expected genetic bottleneck for invasions initiated by few individuals (as most are), thereby enhancing likelihood of survival. For a few species, recent molecular evidence suggests ongoing propagule pressure aids an invasion to spread by introducing genetic variation adaptive for new areas and habitats. This phenomenon may also explain some time lags between establishment of a non-native species and its spread to become an invasive pest.
The earliest concept of a balance of nature in Western thought saw it as being provided by gods but requiring human aid or encouragement for its maintenance. With the rise of Greek natural ...philosophy, emphasis shifted to traits gods endowed species with at the outset, rather than human actions, as key to maintaining the balance. The dominance of a constantly intervening God in the Middle Ages lessened interest in the inherent features of nature that would contribute to balance, but the Reformation led to renewed focus on such features, particularly traits of species that would maintain all of them but permit none to dominate nature. Darwin conceived of nature in balance, and his emphasis on competition and frequent tales of felicitous species interactions supported the idea of a balance of nature. But Darwin radically changed its underlying basis, from God to natural selection. Wallace was perhaps the first to challenge the very notion of a balance of nature as an undefined entity whose accuracy could not be tested. His skepticism was taken up again in the 20th century, culminating in a widespread rejection of the idea of a balance of nature by academic ecologists, who focus rather on a dynamic, often chaotic nature buffeted by constant disturbances. The balance-of-nature metaphor, however, lives on in large segments of the public, representing a fragile aspect of nature and biodiversity that it is our duty to protect.
Striking successes in classical biological control in agriculture and rangelands engender great interest in using this technology for wildlands conservation and environmental purposes. However, well ...known unintended consequences of several biological control projects have led to concern that possible environmental benefits do not warrant inherent risks. Four risks demand attention: (1) direct attack on non-targets; (2) indirect effects on non-targets; (3) dispersal of a biocontrol agent to a new area, either autonomously or with deliberate or inadvertent human assistance; (4) changed relationships between a control agent and a native species, particularly as generated by global climate change. Procedures for assessing risk of direct attack on non-targets by phytophagous biological control agents have steadily improved and an expanded centrifugal phylogenetic approach appears to provide adequate insight. Direct non-target impacts by entomophages are more difficult to predict. Myriad possible indirect effects, some subtle but nonetheless important, present a far greater challenge, and techniques of assessing such risks are in their earliest infancy and not as closely regulated. Despite prominent examples in both the general invasion literature and that for biological control, the risk that a species, once introduced, will spread beyond its intended range, and the consequences of such spread, are not routinely treated by risk assessors. This phenomenon deserves far more attention. Global changes—especially climate change—can lead to modified ranges and efficacies of introduced biological control agents and their targets. Although many examples show that climatic niches are often not conserved, an important first routine step would be to combine climatic envelopes with general circulation models for predicted future climates. Finally, actions based on a risk assessment are always implemented in a framework of predicted costs and benefits, which are inevitably asymmetric, so it is critically important that all stakeholders, including conservationists, participate in the decision-making process.
Increasing human population interacts with local and global environments to deplete biodiversity and resources humans depend on, thus challenging societal values centered on growth and relying on ...technology to mitigate environmental stress. Although the need to address the environmental crisis, central to conservation science, generated greener versions of the growth paradigm, we need fundamental shifts in values that ensure transition from a growth-centered society to one acknowledging biophysical limits and centered on human well-being and biodiversity conservation. We discuss the role conservation science can play in this transformation, which poses ethical challenges and obstacles. We analyze how conservation and economics can achieve better consonance, the extent to which technology should be part of the solution, and difficulties the “new conservation science” has generated. An expanded ambition for conservation science should reconcile day-today action within the current context with uncompromising, explicit advocacy for radical transitions in core attitudes and processes that govern our interactions with the biosphere. A widening of its focus to understand better the interconnectedness between human well-being and acknowledgment of the limits of an ecologically functional and diverse planet will need to integrate ecological and social sciences better. Although ecology can highlight limits to growth and consequences of ignoring them, social sciences are necessary to diagnose societal mechanisms at work, how to correct them, and potential drivers of social change.
Study of the population biology of introduced species has elucidated many fundamental questions in ecology and evolution. Detailed population biological research is likely to aid in fine-tuning ...control of widespread and/or long-established invasions, and it may lead to novel control methods. It will also contribute to an overall understanding of the invasion process that may aid in the formulation of policy and help to focus attention on invasions that are especially prone to becoming problematic. But the importance of intensive population biological research in dealing with introduced species, especially those recently introduced, is often limited. In the worst instances, the absence of population biological data can be an excuse for inaction, when a prudent decision or quick and dirty operation might have excluded or eliminated an invader. The most effective way to deal with invasive introduced species, short of keeping them out, is to discover them early and attempt to eradicate or at least contain them before they spread. This approach has often been successful, but its success has usually relied on brute-force chemical and mechanical techniques, not on population biological research.
Modern network science is a new and exciting research field that has transformed the study of complex systems over the last 2 decades. Of particular interest is the identification of small "network ...motifs" that might be embedded in a larger network and that indicate the presence of evolutionary design principles or have an overly influential role on system-wide dynamics. Motifs are patterns of interconnections, or subgraphs, that appear in an observed network significantly more often than in compatible randomized networks. The concept of network motifs was introduced into Systems Biology by Milo, Alon and colleagues in 2002, quickly revolutionized the field, and it has had a huge impact in wider scientific domains ever since. Here, we argue that the same concept and tools for the detection of motifs were well known in the ecological literature decades into the last century, a fact that is generally not recognized. We review the early history of network motifs, their evolution in the mathematics literature, and their recent rediscoveries.
Ecological character displacement, mostly seen as increased differences of size in sympatry between closely‐related or similar species, is a focal hypothesis assuming that species too similar to one ...another could not coexist without diverging, owing to interspecific competition. Thus, ecological character displacement and community‐wide character displacement (overdispersion in size of potential competitors within ecological guilds) were at the heart of the debate regarding the role of competition in structuring ecological communities. The debate has focused on the evidence presented in earlier studies and generated a new generation of rigorous, critical studies of communities. Character displacement research in the past two decades provides sound statistical support for the hypothesis in a wide variety of taxa, albeit with a phylogenetically skewed representation. A growing number of studies are strongly based in functional morphology, and some also demonstrate actual morphologically related resource partitioning. Phylogenetic models and experimental work have added to the scope and depth of earlier research, as have theoretical studies. However, many challenging ecological and evolutionary issues, regarding both selective forces (at the inter‐ and intraspecific level) and resultant patterns, remain to be addressed. Ecological character displacement and community‐wide character displacement are here to stay as the focus of much exciting research.
Although freshwater invasions have not been targeted for maintenance management or eradication as often as terrestrial invasions have, attempts to do so are frequent. Failures as well as successes ...abound, but several methods have been improved and new approaches are on the horizon. Many freshwater fish and plant invaders have been eliminated, especially by chemical and physical methods for fishes and herbicides for plants. Efforts to maintain invasive freshwater fishes at low levels have sometimes succeeded, although continuing the effort has proven challenging. By contrast, successful maintenance management of invasive freshwater plants is uncommon, although populations of several species have been managed by biological control. Invasive crayfish populations have rarely been controlled for long. Marine invasions have proven far less tractable than those in fresh water, with a few striking eradications of species detected before they had spread widely, and no marine invasions have been substantially managed for long at low levels. The rapid development of technologies based on genetics has engendered excitement about possibly eradicating or controlling terrestrial invaders, and such technologies may also prove useful for certain aquatic invaders. Methods of particular interest, alone or in various combinations, are gene-silencing, RNA-guided gene drives, and the use of transgenes.
Impacts of biological invasions: what's what and the way forward Simberloff, Daniel; Martin, Jean-Louis; Genovesi, Piero ...
Trends in ecology & evolution (Amsterdam),
January 2013, 2013, 2013-Jan, 2013-01-00, 20130101, 2013-01-01, Letnik:
28, Številka:
1
Journal Article
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Study of the impacts of biological invasions, a pervasive component of global change, has generated remarkable understanding of the mechanisms and consequences of the spread of introduced ...populations. The growing field of invasion science, poised at a crossroads where ecology, social sciences, resource management, and public perception meet, is increasingly exposed to critical scrutiny from several perspectives. Although the rate of biological invasions, elucidation of their consequences, and knowledge about mitigation are growing rapidly, the very need for invasion science is disputed. Here, we highlight recent progress in understanding invasion impacts and management, and discuss the challenges that the discipline faces in its science and interactions with society.
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