AIM: Correlative models that forecast extinction risk from climate change and invasion risks following species introductions, depend on the assumption that species' current distributions reflect ...their climate tolerances (‘climatic equilibrium’). This assumption has rarely been tested with independent distribution data, and studies that have done so have focused on species that are widespread or weedy in their native range. We use independent data to test climatic equilibrium for a broadly representative group of species, and ask whether there are any general indicators that can be used to identify when equilibrium occurs. LOCATION: Europe and contiguous USA. METHODS: We contrasted the climate conditions occupied by 51 plant species in their native (European) and naturalized (USA) distributions by applying kernel smoothers to species' occurrence densities. We asked whether species had naturalized in climate conditions that differ from their native ranges, suggesting climatic disequilibrium in the native range, and whether characteristics of species' native distributions correspond with climatic equilibrium. RESULTS: A large proportion of species' naturalized distributions occurred outside the climatic conditions occupied in their native ranges: for 22 species, the majority of their naturalized ranges fell outside their native climate conditions. Our analyses revealed large areas in Europe that species do not occupy, but which match climatic conditions occupied in the USA, suggesting a high degree of climatic disequilibrium in the native range. Disequilibrium was most severe for species with native ranges that are small and occupy a narrow range of climatic conditions. MAIN CONCLUSIONS: Our results demonstrate that the direct effects of climate on species distributions have been widely overestimated, and that previous large‐scale validations of the equilibrium assumption using species' native and naturalized distributions are not generally applicable. Non‐climatic range limitations are likely to be the norm, rather than the exception, and pose added risks for species under climate change.
Predation by exotic species has caused the extinction of many native animal species on islands, whereas competition from exotic plants has caused few native plant extinctions. Exotic plant addition ...to islands is highly nonrandom, with an almost perfect 1 to 1 match between the number of naturalized and native plant species on oceanic islands. Here, we evaluate several alternative implications of these findings. Does the consistency of increase in plant richness across islands imply that a saturation point in species richness has been reached? If not, should we expect total plant richness to continue to increase as new species are added? Finally, is the rarity of native plant extinctions to date a misleading measure of the impact of past invasions, one that hides an extinction debt that will be paid in the future? By analyzing historical records, we show that the number of naturalized plant species has increased linearly over time on many individual islands. Further, the mean ratio of naturalized to native plant species across islands has changed steadily for nearly two centuries. These patterns suggest that many more species will become naturalized on islands in the future. We also discuss how dynamics of invasion bear upon alternative saturation scenarios and the implications these scenarios have for the future retention or extinction of native plant species. Finally, we identify invasion-motivated research gaps (propagule pressure, time-lags to extinction, abundance shifts, and loss of area) that can aid in forecasting extinction and in developing a more comprehensive theory of species extinctions.
•Species can survive beyond the bounds of the fundamental niche.•The ‘tolerance niche’ informs extinction risk and management options.•Relations among the realized, fundamental, and tolerance niche ...can be examined.•These ‘niche syndromes’ have not previously been characterized.•Characterizing niche syndromes can advance basic and applied research goals.
The current distributions of species are often assumed to correspond with the total set of environmental conditions under which species can persist. When this assumption is incorrect, extinction risk estimated from species distribution models can be misleading. The degree to which species can tolerate or even thrive under conditions found beyond their current distributions alters extinction risks, time lags in realizing those risks, and the usefulness of alternative management strategies. To inform these issues, we propose a conceptual framework within which empirical data could be used to generate hypotheses regarding the realized, fundamental, and ‘tolerance’ niche of species. Although these niche components have rarely been characterized over geographic scales, we suggest that this could be done for many plant species by comparing native, naturalized, and horticultural distributions.
Non-native species can cause the loss of biological diversity (i.e., genetic, species, and ecosystem diversity) and threaten the well-being of humans when they become invasive. In some cases, ...however, they can also provide conservation benefits. We examined the ways in which non-native species currently contribute to conservation objectives. These include, for example, providing habitat or food resources to rare species, serving as functional substitutes for extinct taxa, and providing desirable ecosystem functions. We speculate that non-native species might contribute to achieving conservation goals in the future because they may be more likely than native species to persist and provide ecosystem services in areas where climate and land use are changing rapidly and because they may evolve into new and endemic taxa. The management of non-native species and their potential integration into conservation plans depends on how conservation goals are set in the future. A fraction of non-native species will continue to cause biological and economic damage, and substantial uncertainty surrounds the potential future effects of all non-native species. Nevertheless, we predict the proportion of non-native species that are viewed as benign or even desirable will slowly increase over time as their potential contributions to society and to achieving conservation objectives become well recognized and realized. Las especies exóticas pueden causar la pérdida de diversidad biológica (i. e., diversidad genética, de especies y ecosistemas) y amenazar el bienestar de humanos cuando se vuelven invasoras. Sin embargo, en algunos casos también pueden proporcionar beneficios de conservación. Examinamos las formas en que las especies exóticas contribuyen actualmente a objetivos de conservación. Estos incluyen, por ejemplo, proporcionar hábitat o recursos alimenticios para especies raras, fungir como sustitutos funcionales de taxa extintos y proporcionar funciones ecosistémicas deseables. Especulamos que las especies exóticas pueden contribuir a lograr metas de conservación en el futuro porque su probabilidad de persistir y proporcionar servicios ecosistémicos es mayor que la de especies nativas en áreas donde el clima y el uso de suelos están cambiando rápidamente y porque pueden evolucionar hacia taxa nuevos y endémicos. El manejo de especies exóticas y su potencial integración en planes de conservación depende de cómo se definen las metas de conservación en el futuro. Una fracción de especies exóticas continuará causando daños biológicos y económicos, y una considerable incertidumbre rodea a los futuros efectos potenciales de todas las especies exóticas. Sin embargo, pronosticamos que la proporción de especies exóticas que son vistas como benignas o aun deseables incrementará lentamente con el tiempo a medida que sus contribuciones potenciales a la sociedad y al logro de objetivos de conservación sean bien reconocidas y entendidas.
Abstract Climate change is conjectured to endanger tropical species, particularly in biodiverse montane regions, but accurate estimates of extinction risk are limited by a lack of empirical data ...demonstrating tropical species’ sensitivity to climate. To fill this gap, studies could match high-quality distribution data with multi-year transplant experiments. Here, we conduct field surveys of epiphyte distributions on three mountains in Central America and perform reciprocal transplant experiments on one mountain across sites that varied in elevation, temperature and aridity. We find that most species are unable to survive outside of their narrow elevational distributions. Additionally, our findings suggest starkly different outcomes from temperature conditions expected by 2100 under different climate change scenarios. Under temperatures associated with low-emission scenarios, most tropical montane epiphyte species will survive, but under emission scenarios that are moderately high, 5-36% of our study species may go extinct and 10-55% of populations may be lost. Using a test of tropical species’ climate tolerances from a large field experiment, paired with detailed species distribution data across multiple mountains, our work strengthens earlier conjecture about risks of wide-spread extinctions from climate change in tropical montane ecosystems.
AIM: A major implication of natural selection is that species from different parts of the world will vary in their efficiency in converting resources into offspring for a given type of environment. ...This insight, articulated by Darwin, is usually overlooked in more recent studies of invasion biology that are often based on the more modern Eltonian perspective of imbalanced ecosystems. We formulate a renewed Darwinian framework for invasion biology, the evolutionary imbalance hypothesis (EIH), based only on the action of natural selection in historically isolated populations operating within a global network of repeated environments. This framework predicts that successful invaders are more likely to come from biotic regions of high genetic potential (with independent lineages of large population size), experiencing a given environment for many generations and under strong competition from other lineages. LOCATION: Global. METHODS: We test the predictive power of this framework by examining disparities in recent species exchanges between global biotic regions, including patterns of plant invasions across temperate regions and exchanges of aquatic fauna as a result of modern canal building. RESULTS: Our framework successfully predicts global invasion patterns using phylogenetic diversity of the world's biotic regions as a proxy that reflects their genetic potential, historical stability and competitive intensity, in line with the Darwinian expectation. Floristic regions of higher phylogenetic diversity are more likely to be source areas of invasive plants, and regions of lower phylogenetic diversity are more likely to be invaded. Similar patterns are evident for formerly isolated marine or freshwater assemblages that have been connected via canals. MAIN CONCLUSIONS: We advocate an approach to understanding modern species invasions that recognizes the potential significance of both the original Darwinian explanation and the more modern view that emphasizes novel ecological or evolutionary mechanisms arising in the introduced range. Moreover, if biological invasions are a natural outcome of Darwinian evolution in an increasingly connected world, then invasive species should continue to displace native species and drive widespread shifts in the functioning of ecosystems.
Plant communities have undergone dramatic changes in recent centuries, although not all such changes fit with the dominant biodiversity-crisis narrative used to describe them. At the global scale, ...future declines in plant species diversity are highly likely given habitat conversion in the tropics, although few extinctions have been documented for the Anthropocene to date (<0.1%). Nonnative species introductions have greatly increased plant species richness in many regions of the world at the same time that they have led to the creation of new hybrid polyploid species by bringing previously isolated congeners into close contact. At the local scale, conversion of primary vegetation to agriculture has decreased plant diversity, whereas other drivers of change-e.g., climate warming, habitat fragmentation, and nitrogen deposition-have highly context-dependent effects, resulting in a distribution of temporal trends with a mean close to zero. These results prompt a reassessment of how conservation goals are defined and justified.
Here, we outline a conceptual framework for biodiversity dynamics following environmental change. The model incorporates lags in extinction and immigration, which lead to extinction debt and ...immigration credit, respectively. Collectively, these concepts enable a balanced consideration of changes in biodiversity following climate change, habitat fragmentation and other forcing events. They also reveal transient phenomena, such as biodiversity surpluses and deficits, which have important ramifications for biological conservation and the preservation of ecosystem services. Predicting such transient dynamics poses a serious conservation challenge in a time of rapid environmental change.
While decision-making can benefit from considering positive and negative outcomes of change, over the past half-century, research on non-native species has focused predominately on their negative ...impacts. Here we provide a framework for considering the positive consequences of non-native species relative to relational, instrumental, and intrinsic values. We demonstrate that their beneficial outcomes are common and profoundly important for human well-being. Identified benefits include social cohesion, cultural identity, mental health, food and fuel production, regulation of clean waters, and attenuation of climate change. We argue that long-standing biases against non-native species within the literature have clouded the scientific process and hampered policy advances and sound public understanding. Future research should consider both costs and benefits of non-native species.
The study of non-native species has predominantly focused on quantifying the costs they inflict on people and nature.Recent decades have witnessed scientists acknowledging, and over the past few years increasingly investigating, the benefits that non-native species may provide.Here we provide a framework for considering the diversity of positive benefits supported by non-native species relative to relational, instrumental, and intrinsic values.Despite undoubted publication biases, we find that benefits of non-native species are diverse, frequent, and often of large magnitude.More research aimed at considering benefits of non-native species, and contrasting these benefits with costs is needed to advance our understanding of the impacts of non-native species and better contextualize management and policy decisions.
A major challenge in modern biology is to understand extinction risk from climate change across all realms. Recent research has revealed that physiological tolerance, behavioral thermoregulation, and ...small elevation shifts are dominant coping strategies on land, whereas large-scale latitudinal shifts are more important in the ocean. Freshwater taxa may face the highest global extinction risks. Nevertheless, some species in each realm face similar risks because of shared adaptive, dispersal, or physiological tolerances and abilities. Taking a cross-realm perspective offers unique research opportunities because confounding physical factors in one realm are often disaggregated in another realm. Cross-realm, across taxa, and other forms of climate change biology synthesis are needed to advance our understanding of emergent patterns of risk across all life.
An integrated perspective crossing terrestrial, freshwater, and marine realms is essential to understand where and why species are most vulnerable to climate change.The dominant ecoevolutionary processes for coping with climate change differ across realms.Cross-taxa and cross-realm research can provide unique insights and opportunities to advance our understanding of the processes and mechanisms threatening species survival.Academic culture and practice often impede cross-realm research, such that structural and cultural transitions are needed to advance a more unified field of climate change biology.
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