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Climate Change and Biological Invasions in South Africa
Abstract
South Africa is a mega-diverse country situated at the southern tip of Africa flanked by two unique marine systems, one cool and one warm. Species introductions to the region have also been diverse. Given the major and growing threat to biodiversity and ecosystem functioning from biological invasions, there has been significant research on this topic. Biological invasions continue to expand and new species continue to arrive. Climate change is expected to affect invasions directly, influencing species’ distributions according to individual species’ tolerances and interactions with other species; and indirectly, through new introductions, and by altered pathways linked to human responses to climate change. The uncertainty relating to climate projections has narrowed considerably since the release of the Intergovernmental Panel on Climate Change Sixth Assessment Report, permitting a more focused assessment of its potential interaction with the impacts of biological invasions than was possible before. This chapter summarizes the projected changes for rainfall and temperature in the medium and long term using a middle-of-the-road socio-economic scenario based on ‘downscaled’ projections. Overall, projected shifts in climate, even over the long term, are less extreme than had previously been projected in national and regional assessments for South Africa, although the rate and extent of change is projected to be more extreme for southern African regions north of South Africa. Future biological invasions can be divided into: (i) expansion of existing invasions; (ii) new invasions that result from changes in the nature, volume and timing of trade and travel; and (iii) invasions that result from climate change mitigation and adaptation such as carbon sequestration projects and assisted migration. Expansion of native species, notably ‘bush encroachment’ in savannas, is also predicted to increase. We discuss likely patterns of change in terrestrial, freshwater and marine systems, considering first the change in current invasions and native species and then changes in pathways that are likely to affect future invasions in each realm. Species losses and gains are expected in all realms. On land, rising atmospheric CO2 has likely already facilitated widespread increases in cover of indigenous tree and shrub species, and may also exacerbate invasions of alien woody plants. Managing invasions in the future will require significant efforts in pathway control. Careful balance in permitting and even facilitating range expansions, while controlling undesirable native range expansions and preventing the introduction and expansion of generalist, highly invasive alien species is paramount. Policies aimed at using indigenous species in rehabilitation and carbon sequestration projects, as well as cross-border collaboration on biosecurity and biodiversity safeguards, are critical.
... Climate shifts are predicted to lead to more stochastic weather patterns, resulting in more extreme hydrological events such as droughts and severe flooding (Lennox et al. 2019). These changes are likely to affect both native and invasive species range distributions, especially in South African freshwaters characterised by Mediterranean climates (Broom, Weyl & South 2023;van Wilgen et al. 2022). Hydrological alterations will increase or decrease available aquatic habitat and connectivity dynamics, which will inevitably mediate or facilitate invasion processes (Guareschi & South 2024;Rahel & Olden 2008;van Wilgen et al. 2022;Winder, Jassby & Mac Nally 2011). ...
... These changes are likely to affect both native and invasive species range distributions, especially in South African freshwaters characterised by Mediterranean climates (Broom, Weyl & South 2023;van Wilgen et al. 2022). Hydrological alterations will increase or decrease available aquatic habitat and connectivity dynamics, which will inevitably mediate or facilitate invasion processes (Guareschi & South 2024;Rahel & Olden 2008;van Wilgen et al. 2022;Winder, Jassby & Mac Nally 2011). ...
... Drying-wetting regimes of riverine systems have been overlooked in invasion science but may be both a barrier and facilitator to invasive species spread (Guareschi & South 2024). This case study in ANEP exemplifies the complex dynamics, which are predicted to become more common in this region (van Wilgen et al. 2022). The two major droughts over the research period of 2007-2019 resulted in its tributary streams becoming disconnected and, in some instances, almost completely dry apart from key deep water refugia for much of this 12-year period. ...
Invasive freshwater fish can often have severe negative effects on native fishes in river systems. The interactions between hydrology and habitat variability can mediate the speed and success of individual invasions and the consequent impact on biodiversity. The rivers within Addo Elephant National Park (AENP) in the Eastern Cape, South Africa experience cyclical droughts and wet periods and as a result are naturally episodic. These rivers were recently invaded by three non-native species, the invasive largemouth bass (Micropterus salmoides) as well as the extralimital sharptooth catfish (Clarias gariepinus) and Mozambique tilapia (Oreochromis mossambicus). Monitoring of key sampling sites along two rivers over a 12-year period that included two major droughts revealed unexpected patterns in the spread of these species and their interactions with native fishes. On the Coerney River, C. gariepinus repeatedly invaded and was extirpated from a seasonal reach of the river, wherein O. mossambicus was only occasionally captured. On the Wit River, two apparently independent introductions of M. salmoides in the lower and upper reaches of the river resulted in patchy habitat occupancy over the course of 12 years. While C. gariepinus regularly co-occurred with native species, M. salmoides appeared to locally extirpate the endangered Eastern Cape redfin (Pseudobarbus afer). During drought, both species persisted in close but disconnected pools, suggesting that the episodic hydrology and geomorphology of these rivers may offer temporary predation refugia for native species during drought.
Conservation implications: Drought in episodic rivers can mitigate against the impact and spread of freshwater invasions within protected areas. Effects of drying on invasion corridors and spatial interactions with native species should be taken into consideration when managing such invasions. Severe droughts also offer an opportunity to actively control invasive species when they are confined to accessible drought refugia within the protected area.
... Invasive Alien Plants (IAPs) have a threat to the natural ecosystem and global biodiversity. Hence, it is considered one of the drivers of biodiversity and alters the ecosystem services and socio-economic conditions of an ecosystem [1][2][3][4]. The actors and information are a diverse and scattered, necessitating collaboration with regard to IAPs management. ...
... As a result, the CASt idea encourages a wide range of actors, disciplines, and stakeholders, including private landowners, to participate in the integrated IAPs management. These species have an impact on many ecosystems, ecosystem services (e.g., water), native species (e.g., flora and fauna), and risks from fire and flood [1][2][3]5,[8][9][10][11][12][13][14]. Many international agreements (e.g., the Convention on Biological Diversity) have been signed by the country, and it has met the Aichi Biodiversity Target 9 for the control and management of IAPs [15]. ...
... IAPs management is critical on a global scale as invasive species have threatened native biodiversity and adversely impacted water resources and ecosystem services [1,3,4,6,[9][10][11][12]14,[16][17][18][19][20][21]. The Working for Water Programme in South Africa (1995) aimed to manage IAPs in order to achieve environmental (e.g., soil and water conservation, biodiversity conservation) and social (e.g., green job creation, skills and capacity building, and inclusion of marginalised and disadvantaged communities) sustainability goals [7,22,23]. ...
This study examined the knowledge of Collaborative Adaptive Stewardship (CASt) to advance Invasive Alien Plants (IAPs) management in South Africa. This concept promotes the involvement of private landowners and other stakeholders in the management and action processes, hence promoting social inclusivity, job creation, and sustainable biodiversity stewardship. It demonstrates that landowners are major stakeholders in IAPs management, thereby practising biodiversity stewardship in the 80% of privately owned lands of the country. The involvement of landowners in the management process aids in the prevention of further expansion of IAPs, the mitiga-tion of risks (such as fire and flooding), and the maintenance of ecosystem functionality and landscape scale connectivity. CASt fosters synergy among many stakeholders for the management of IAPs and long-term sustainable biodiversity stewardship. In South Africa, a number of landowners have entered into stewardship agreements as a result of incentives and subsidies for IAPs management. The benefits should be contingent on private landowner actions to IAPs management; this will support biodiversity stewardship. This study serves as a foundation for collaborative IAPs management and will be crucial in achieving long-term sustainability goals (e.g., economy, society and environment) to protect biodiversity and ecosystem services.
... The outcomes and implications of anthropogenically driven climate change may directly influence biological invasions through the creation of previously inaccessible trading routes, by creating favorable conditions for generalist invasive species (e.g., extreme events increasing stress on resident taxa), and by modifying trophic networks or species life cycles (e.g., populational outbreaks; e.g., Hulme 2017, van Wilgen et al. 2022. For these reasons, the management of invasive species would benefit from the incorporation of climate change scenarios as a prerequisite to facilitate better decision-making processes (Robinson et al. 2020, Bradley et al. 2022. ...
... However, nonnative species do not always benefit from climate change. For example, the distributions of some invasive ants, European plant species, and trout species in Africa are expected to potentially decline in some future climate change scenarios (e.g., Peterson et al. 2008, Bertelsmeier et al. 2015, van Wilgen et al. 2022. The examples discussed in the present article, spanning different environments, illustrate the difficulty of simple generalizations and therefore the importance of adjusting the lens of invasion science when focusing on the implications of climate-driven range shifts. ...
In a hyperconnected world, framing and managing biological invasions poses complex and contentious challenges, affecting socioeconomic and environmental sectors. This complexity distinguishes the field and fuels polarized debates. In the present article, we synthesize four contentious issues in invasion science that are rarely addressed together: vocabulary usage, the potential benefits of nonnative species, perceptions shifting because of global change, and rewilding practices and biological invasions. Researchers have predominantly focused on single issues; few have addressed multiple components of the debate within or across disciplinary boundaries. Ignoring the interconnected nature of these issues risks overlooking crucial cross-links. We advocate for interdisciplinary approaches that better integrate social and natural sciences. Although they are challenging, interdisciplinary collaborations offer hope to overcome polarization issues in invasion science. These may bridge disagreements, facilitate knowledge exchange, and reshape invasion science narratives. Finally, we present a contemporary agenda to advance future research, management, and constructive dialogue.
... This phenomenon has emerged as one of the most important problems of the rangelands. This impact will increase in the future, affecting the species distribution and altering the interactions between plant communities, soil, and fauna dynamics (Van Wilgen et al. 2022;Weber-Grullon et al. 2022). ...
Senegalia mellifera (Benth) Seigler & Ebinger., Dichrostachys cinerea (L.) Wight & Arn. and Terminalia sericea Burch. Ex DC., are three important bush encroacher species that contribute to the well-known ecological process named “thicketization” in Southern Africa. This issue has persisted for many years, impacting species distribution, plant communities, soil, and fauna dynamics. According to climate change projections, Southern Africa is expected to become drier and warmer in future scenarios, creating favourable conditions for proliferation of bush encroacher species. MaxEnt is a general-purpose machine learning method widely utilized in various ecological and biological scenarios to predict the potential suitable habitat of species. This is achieved by incorporating presence-only occurrence records and bioclimatic, and topographic variables. The analysis was performed in a Geographic Information System based on the current and future suitable areas for the respective Shared Socioeconomic Pathways (SSP) scenarios according to INM-CM5-0, UK-ESM1-0-LL and MPIES-M1-2-HR climate models. This was done to assess the potential effects of climate change on the distribution patterns of bush encroacher species. Model performance was assessed by the area under the curve (AUC) of the receiver operator characteristic (ROC), with 0.836, 0.822 and 0.738 as results to Terminalia sericea , Dichrostachys cinerea and Senegalia mellifera respectively. The current results show that Senegalia mellifera presents a habitat suitability of 56% (1,460,353 km²) of the total area, while Terminalia sericea and Dichrostachys cinerea have suitability over 37.9% (996,168 km²) and 43.9% (1,154,645 km²) of the area, respectively. These findings indicate that precipitation and temperature variables are the most important factors in explaining the spatial distribution of the bush encroacher species, predicting a future increase between 8–29.4%, 2.8–24%, and 3–24.2% for Senegalia mellifera , Terminalia sericea , and Dichrostachys cinerea respectively. Furthermore, each species has its own set of important variables and different ecological behaviour patterns. These results imply that an improved understanding of the response of woody species to a changing climate is important for managing bush encroachment in savanna ecosystems.
Based on our analysis, Senegalia mellifera is currently suitable in 56% of the total area; while 43.9% of the total area is suitable for Dichrostachys cinerea , and 37.87% of the total area is currently suitable for Terminalia sericea . In the future scenarios, the habitat suitability increases for all three species compared to the current state.
The unsuitable areas decrease in all the proposed scenarios with respect to the present, predicting a shrub expansion in the future throughout southern Africa. Furthermore, our results imply that Senegalia mellifera is the most potentially affected by bush encroachment in future changes, with a larger distribution area in future scenarios. These findings are supported by many studies, which indicate the probable increase of woody cover and loss of grasslands.
Temperature and precipitation patterns are the main drivers behind the distribution of these bush encroachers, increasing or decreasing the competitiveness of these species according to these variables and their phenotypic plasticity.
The increase in habitat suitability occurs throughout the case study, but there is a clear trend of shrub expansion towards the south of the case study. The change maps show a pattern of shrub movement towards South Africa and Botswana. This would fit with climate predictions for South Africa, which predict a decrease in rainfall in the east and north of the country, being more suitable for shrub competitive species.
... They are amply living up to the prognosis for the future made in 2008 that by 2025 their rate of spread would have radically increased (Branch et al., 2008a). In South Africa alone, the rate at which alien species have been recorded has escalated exponentially from just one in 1950 to 95 by 2023 (Robinson et al., 2005;Griffiths et al., 2009;Mead et al., 2011a;Mead et al., 2011b;Robinson et al., 2016;Robinson et al., 2020;Van Wilgen et al., 2023). Jennsen (2015) expresses a pessimistic view: 'You have loosed a chaotic, unstable element into the Mosaic. ...
Integrating observations and experiments, we address the progressive effects of three alien species, the mussels Mytilus galloprovincialis and Semimytilus patagonicus, and the barnacle Balanus glandula, on limpet species in South Africa. We describe four aspects: (1) Interactions among algae, the limpet Scutellastra granularis and M. galloprovincialis. (2) The influences of B. glandula on S. granularis and on the periwinkle Afrolittorina knysnaensis. (3) Transformation of the zonation of S. granularis by the successive arrival of these three aliens. (4) Assessment of how effective the published predictors of the effects of M. galloprovincialis have been when applied to S. patagonicus. We conclude: (a) Scutellastra granularis improves mussel survival and condition by regulating algae that would otherwise overgrow and smother the mussels. (b) Balanus glandula has largely occupied the upper half of rocky shores, and at high densities depletes or eliminates suitable bare-rock habitat for S. granularis. However, it has positive effects on another gastropod, A. knysnaensis. (c) Mytilus galloprovincialis dominates the midshore and has positive effects on the recruitment of S. granularis, but negatively influences adults of this limpet, so that its size composition, density, reproductive output and zonation are all altered by this mussel. (d) Semimytilus patagonicus presents different challenges to those created by M. galloprovincialis, settling at much greater densities, lower down the shore, and reaching smaller maximum sizes. Rather than generating a favourable habitat for epizootic S. granularis recruits and juveniles, it almost completely excludes that limpet. We conclude that the influences of alien species are not readily predictable, depending on the nature of the invader and recipient species, environmental conditions and complex interactions among species. Collectively, the three alien species now cover almost all zones on wave-exposed rocky shores, completing the ‘zonation squeeze’ on limpets, but are less influential on wave-sheltered shores and in years when recruitment is low.
There is an ongoing debate about the potential of localized conservation efforts to address the ecological challenges brought about by global climate shifts. Among these challenges, biological invasion negatively affects ecosystem health and biodiversity. In this study, we assessed the potential impact of global climate changes and human activities on the spread of the invasive species Broussonetia papyrifera in Pakistan's subtropical region. Jackknife analysis indicated that, among the climatic variables studied, the maximum temperature of the warmest month (bio05) made the most significant contribution, accounting for 25.6 % of the model's predictive capacity. Potential highly invaded regions are located in the territory of Islamabad, Rawalpindi, Attock, Nowshera, Swabi, Haripur, and Mardan. Some patches were also found to be invaded in Khyber Pakhtunkhwa (Abbottabad, Buner, Tor Ghar, and Peshawar) and Punjab (Narowal, Sialkot, Gujrat, Jhelum, and Chakwal). Specifically, based on all four Shared Socioeconomic Pathways (SSPs) scenarios for the 2050 s and 2070 s, the highly invaded regions of B. papyrifera are predicted to shift Northern Punjab, Eastern Khyber Pakhtunkhwa, and Northern Kashmir. Based on the SSPs 245 and 585 scenarios, the majority of highly invaded regions are projected to expand by 2050. Similarly, within these regions, the potentially invaded land area is estimated to increase to 2.74 % under SSPs 585 in the 2050 s, 5.29 % under SSPs 245 in the 2070 s, and 6.27 % under SSPs 585 in the 2070 s. Applying circuit theory and ecological resistance, a surface connectivity map of the species revealed that Rawalpindi and Sargodha in Punjab had the most prominent corridors, with rates being highest where ecological patches continually merged. This study is the first to predict B. papyrifera distribution in Pakistan under current and future climate change scenarios. Implementing nationwide guidelines comprehensively may curb the spread of invasive species and protect native plant diversity from extinction. The findings of this study will aid in timely monitoring and surveillance of B. papyrifera and in formulating integrated management plans at the national level to prevent its invasion, spread, and potential harm to newly projected regions.
The transport of non-indigenous species in ship’s ballast water represents a threat to marine biodiversity. This study is the first on marine bioinvasion in Sub-Saharan Africa. The Port of Douala (PoD), located in the Gulf of Guinea, is experiencing increasing maritime traffic, hence the importance of preventing biological invasions. PoD received ballast water from 41 ports and 20 ecoregions during the study period (2018–2021). We used a biological invasion model and showed that ships from the ports of Antwerp, Durban, Dar es Salaam, Pointe-Noire (Southern Gulf of Guinea) and Dakar (Sahelian Upwelling), with their associated ecoregions present a major invasion risk. Treating ballast water from these ships to IMO D-2 standards could reduce their probability of biological invasion by 97.18, 98.43, 98.80, 98.77 and 98.84 %, respectively. Climate change may also mitigate the risk of biological invasion, particularly for ships in the North Sea ecoregion from the port of Antwerp.
Attacks on humans by wild pigs (Sus scrofa) have been documented since ancient times. However, studies characterizing these incidents are lacking. In an effort to better understand this phenomenon , information was collected from 412 wild pig attacks on humans. Similar to studies of large predator attacks on humans, data came from a variety of sources. The various attacks compiled occurred in seven zoogeographic realms. Most attacks occurred within the species native range, and specifically in rural areas. The occurrence was highest during the winter months and daylight hours. Most happened under non-hunting circumstances and appeared to be unprovoked. Wounded animals were the chief cause of these attacks in hunting situations. The animals involved were typically solitary, male and large in size. The fate of the wild pigs involved in these attacks varied depending upon the circumstances, however , most escaped uninjured. Most human victims were adult males traveling on foot and alone. The most frequent outcome for these victims was physical contact/mauling. The severity of resulting injuries ranged from minor to fatal. Most of the mauled victims had injuries to only one part of their bodies, with legs/feet being the most frequent body part injured. Injuries were primarily in the form of lacerations and punctures. Fatalities were typically due to blood loss. In some cases, serious infections or toxemia resulted from the injuries. Other species (i.e., pets and livestock) were also accompanying some of the humans during these attacks. The fates of these animals varied from escaping uninjured to being killed. Frequency data on both non-hunting and hunting incidents of wild pig attacks on humans at the Savannah River Site, South Carolina, showed quantitatively that such incidents are rare.
Wild pig (Sus scrofa) collisions with vehicles are known to occur in the United States, but only minimal information describing these accidents has been reported. In an effort to better characterize these accidents, data were collected from 179 wild pig-vehicle collisions from a location in west central South Carolina. Data included accident parameters pertaining to the animals involved, time, location, and human impacts. The age structure of the animals involved was significantly older than that found in the population. Most collisions involved single animals; however, up to seven animals were involved in individual accidents. As the number of animals per collision increased, the age and body mass of the individuals involved decreased. The percentage of males was significantly higher in the single-animal accidents. Annual attrition due to vehicle collisions averaged 0.8 percent of the population. Wild pig-vehicle collisions occurred year-round and throughout the 24-hour daily time period. Most accidents were at night. The presence of lateral barriers was significantly more frequent at the collision locations. Human injuries were infrequent but potentially serious. The mean vehicle damage estimate was $1,173.
Fisheries are among the human activities that are most strongly affected by ongoing climate-related changes in the presence and abundance of fish species across the globe. The ecological and social repercussions of such changes for recreational fisheries are however still poorly understood. Here, we compare selected ecological and social dimensions of both recreational angling and spearfishing targeting the bluefish (Pomatomus saltatrix) in Italy. The bluefish has undergone a northward expansion in the region over the last 20–30 years, during which it reached new areas and increased in abundance. Using digital videos and their associated data published by both recreational anglers and spearfishers on YouTube we characterized ecological and social dimensions using a culturomics approach. Specifically, we focused on harvesting patterns, social engagement and sentiments related to the bluefish. Our study revealed four major results: (1) similar harvesting patterns (i.e., declared mass and seasonal upload patterns) related to videos by both recreational anglers and spearfishers; (2) higher social engagement (i.e., number of views and likes) for videos by recreational anglers than spearfishers; (3) differences in themes of discussion, with anglers being mainly interested in fishing strategy and gears and spearfishers being more interested in fishing actions shown on the videos; (4) positive and negative sentiments of both recreational anglers and spearfishers towards the invasiveness and aggressiveness of the species. The latter represents an interesting trade-off associated with recreational fishing of the bluefish: it is perceived as an invasive species, but it is also a valued target fish because its voracity contributes to the quality of the recreational fishing experience. Our study showcases the value of exploring social media and associated data to better understand the ecological and human dimensions of marine recreational fisheries in relation to distributional range shifts of species associated with climate change.
Rodents living alongside humans increases the probability of encounter and also the transmission of rodent-borne diseases. Singapore’s cosmopolitan urban landscape provides a perfect setting to study the prevalence of four rodent-borne pathogens: Seoul hantavirus (SEOV), Leptospira species, Rickettsia typhi and Yersinia pestis, and identify the potential risk factors which may influence rodent density and transmission of rodent-borne diseases. A total of 1143 rodents were trapped from 10 unique landscape structures throughout Singapore. Real-time quantitative Polymerase Chain Reactions were used to detect pathogenic and intermediate Leptospira spp. and Yersinia pestis, whereas the seroprevalence of SEOV and R. typhi were analysed by Enzyme-Linked Immunosorbent Assay and Immunofluorescence Assay respectively. Multivariable logistic regression analysis was used to evaluate the association between prevalence of infection in rodent reservoirs and risk factors. Most of the rodents were caught in public residential developments (62.2%). Among the tested rodents, 42.4% were infected with Leptospira spp., while 35.5% and 32.2% were seropositive for SEOV and R. typhi respectively, whereas Yersinia pestis was not detected. Furthermore, risk factors including habitat, species, gender, and weight of rodents, influenced prevalence of infection to a varying extent. This study highlights the presence of Leptospira spp., SEOV and R. typhi in Singapore’s rodent population, suggesting the need for effective rodent management and sanitation strategies to prevent further circulation and transmission to humans.
Commercial harvests have been effectively employed to manage wildlife populations across the world. Although commercial harvesting of the nonnative, invasive axis deer (Axis axis) in Maui, Hawaii, occurs at small scales and only on private lands, there is potential for large-scale implementation to be used as a population management tool. To investigate local stakeholder interest in a hypothetical, large-scale commercial harvest of axis deer, we used an online survey of individuals and businesses in Maui to analyze their attitudes towards axis deer populations and management, their experiences with axis deer, and potential to utilize axis deer venison and products, as relevant. We found evidence of public support for commercial harvesting to be employed as one of the many tools available to manage axis deer populations. Additionally, we documented support on both the supply-side and demand-side for axis deer-derived products that may be available if large-scale commercialized harvesting were implemented. We leverage these results to contribute to conversations about commercial wildlife harvesting in the United States by challenging assumptions that the practice is inconsistent with the public’s perceptions of the North American Model of Wildlife Conservation and suggesting policies and programs that would ease axis deer commercial harvest growing pains.
Narrowing the communication and knowledge gap between producers and users of scientific data is a longstanding problem in ecological conservation and land management. Decision support tools (DSTs), including websites or interactive web applications, provide platforms that can help bridge this gap. DSTs can most effectively disseminate and translate research results when producers and users collaboratively and iteratively design content and features. One data resource seldom incorporated into DSTs are species distribution models (SDMs), which can produce spatial predictions of habitat suitability. Outputs from SDMs can inform management decisions, but their complexity and inaccessibility can limit their use by resource managers or policy makers. To overcome these limitations, we present the Invasive Species Habitat Tool (INHABIT), a novel, web-based DST built with R Shiny to display spatial predictions and tabular summaries of habitat suitability from SDMs for invasive plants across the contiguous United States. INHABIT provides actionable science to support the prevention and management of invasive species. Two case studies demonstrate the important role of end user feedback in confirming INHABIT’s credibility, utility, and relevance.
Agricultural biosecurity interventions are aimed at minimizing introductions of harmful non‐native organisms to new areas via agricultural trade. To prioritize such interventions, historical data on interceptions have been used to elucidate which factors determine the likelihood that a particular import is carrying a harmful organism. Here we use an interception data set of arthropod contaminants recorded on plant imports arriving in South Africa from 2005 to 2019, comprising 13,566 samples inspected for arthropod contaminants, of which 4902 were positive for the presence of at least one arthropod. We tested 29 predictor variables that have previously been used to explain variation in rates of detection and three variables describing possible sources of additional variation and grouped these into six mutually exclusive “factor classes.” We used boosted regression trees as a non‐parametric stochastic machine‐learning method to build models for each factor class and interactions between them. We explored the influence of these variables with data split either randomly or chronologically. While we identified some specific patterns that could be explained post‐hoc by historical events, only inspected volumes were reliably correlated with detection of arthropod contaminants across the whole data set. However, inspected volumes could not predict future interceptions of arthropods, which instead relied on contextual factors such as country, crop or year of import. This suggests that, although certain factors may be important in certain circumstances or for particular crops or commodities, there is little general predictive power in the current data. Instead, an idiographic approach would be most beneficial in biosecurity to ascertain the details of why a particular pest arrived on a particular pathway and how it might move (and be stopped) in future.
Background:
With the current climate change crisis and its influence on infectious disease transmission there is an increased desire to understand its impact on infectious diseases globally. Hantaviruses are found worldwide, causing infectious diseases such as haemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS)/hantavirus pulmonary syndrome (HPS) in tropical regions such as Latin America and the Caribbean (LAC). These regions are inherently vulnerable to climate change impacts, infectious disease outbreaks and natural disasters. Hantaviruses are zoonotic viruses present in multiple rodent hosts resident in Neotropical ecosystems within LAC and are involved in hantavirus transmission.
Methods:
We conducted a systematic review to assess the association of climatic factors with human hantavirus infections in the LAC region. Literature searches were conducted on MEDLINE and Web of Science databases for published studies according to Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) criteria. The inclusion criteria included at least eight human hantavirus cases, at least one climatic factor and study from > 1 LAC geographical location.
Results:
In total, 383 papers were identified within the search criteria, but 13 studies met the inclusion criteria ranging from Brazil, Chile, Argentina, Bolivia and Panama in Latin America and a single study from Barbados in the Caribbean. Multiple mathematical models were utilized in the selected studies with varying power to generate robust risk and case estimates of human hantavirus infections linked to climatic factors. Strong evidence of hantavirus disease association with precipitation and habitat type factors were observed, but mixed evidence was observed for temperature and humidity.
Conclusions:
The interaction of climate and hantavirus diseases in LAC is likely complex due to the unknown identity of all vertebrate host reservoirs, circulation of multiple hantavirus strains, agricultural practices, climatic changes and challenged public health systems. There is an increasing need for more detailed systematic research on the influence of climate and other co-related social, abiotic, and biotic factors on infectious diseases in LAC to understand the complexity of vector-borne disease transmission in the Neotropics.
Axis deer (Axis axis) are invasive species that threaten native ecosystems and agriculture on Maui Island. To mitigate negative effects, it is necessary to understand current abundance, population trajectory, and how to most effectively reduce the population. Our objectives were to examine the population history of Maui axis deer, estimate observed population growth, and use species-specific demographic parameters in a VORTEX population viability analysis to examine removal scenarios that would most effectively reduce the population. Only nine deer were introduced in 1959, but recent estimates of >10,000 deer suggest population growth rates (r) ranging between 0.147 and 0.160 even though >11,200 have been removed by hunters and resource managers. In VORTEX simulations, we evaluated an initial population size of 6,000 females and 4,000 males, reflecting the probable 3F:2M sex ratio, with annual removal rates of 10%, 20%, and 30% over a 10-year period. A removal rate of 10% resulted in a positive growth rate of 0.103 ± 0.001. A 20% removal rate resulted in only a slightly negative growth, while a 30% removal rate resulted in -0.130 ± 0.004. By increasing the ratio of females removed to 4F:1M in the 30% harvest scenario, the decline nearly doubled, resulting in -0.223 ± 0.004. Effectively reducing axis deer will most likely require an annual removal of approximately 20–30% of the population and with a greater proportion of females to increase the population decline. Selective removal of males may not only be inefficient, but also counterproductive to population reduction goals.
In the southwestern United States, non-native grass invasions have increased wildfire occurrence in deserts and the likelihood of fire spread to and from other biomes with disparate fire regimes. The elevational transition between desertscrub and montane grasslands, woodlands, and forests generally occurs at ∼1,200 masl and has experienced fast suburbanization and an expanding wildland-urban interface (WUI). In summer 2020, the Bighorn Fire in the Santa Catalina Mountains burned 486 km² and prompted alerts and evacuations along a 40-km stretch of WUI below 1,200 masl on the outskirts of Tucson, Arizona, a metropolitan area of >1M people. To better understand the changing nature of the WUI here and elsewhere in the region, we took a multidimensional and timely approach to assess fire dynamics along the Desertscrub-Semi-desert Grassland ecotone in the Catalina foothills, which is in various stages of non-native grass invasion. The Bighorn Fire was principally a forest fire driven by a long-history of fire suppression, accumulation of fine fuels following a wet winter and spring, and two decades of hotter droughts, culminating in the hottest and second driest summer in the 125-yr Tucson weather record. Saguaro (Carnegia gigantea), a giant columnar cactus, experienced high mortality. Resprouting by several desert shrub species may confer some post-fire resiliency in desertscrub. Buffelgrass and other non-native species played a minor role in carrying the fire due to the patchiness of infestation at the upper edge of the Desertscrub biome. Coupled state-and-transition fire-spread simulation models suggest a marked increase in both burned area and fire frequency if buffelgrass patches continue to expand and coalesce at the Desertscrub/Semi-desert Grassland interface. A survey of area residents six months after the fire showed awareness of buffelgrass was significantly higher among residents that were evacuated or lost recreation access, with higher awareness of fire risk, saguaro loss and declining property values, in that order. Sustained and timely efforts to document and assess fast-evolving fire connectivity due to grass invasions, and social awareness and perceptions, are needed to understand and motivate mitigation of an increasingly fire-prone future in the region.
Non-technical summary
We summarize some of the past year's most important findings within climate change-related research. New research has improved our understanding about the remaining options to achieve the Paris Agreement goals, through overcoming political barriers to carbon pricing, taking into account non-CO 2 factors, a well-designed implementation of demand-side and nature-based solutions, resilience building of ecosystems and the recognition that climate change mitigation costs can be justified by benefits to the health of humans and nature alone. We consider new insights about what to expect if we fail to include a new dimension of fire extremes and the prospect of cascading climate tipping elements.
Technical summary
A synthesis is made of 10 topics within climate research, where there have been significant advances since January 2020. The insights are based on input from an international open call with broad disciplinary scope. Findings include: (1) the options to still keep global warming below 1.5 °C; (2) the impact of non-CO 2 factors in global warming; (3) a new dimension of fire extremes forced by climate change; (4) the increasing pressure on interconnected climate tipping elements; (5) the dimensions of climate justice; (6) political challenges impeding the effectiveness of carbon pricing; (7) demand-side solutions as vehicles of climate mitigation; (8) the potentials and caveats of nature-based solutions; (9) how building resilience of marine ecosystems is possible; and (10) that the costs of climate change mitigation policies can be more than justified by the benefits to the health of humans and nature.
Social media summary
How do we limit global warming to 1.5 °C and why is it crucial? See highlights of latest climate science.
Species distribution modeling (SDM) is widely used in ecology and conservation. Currently, the most available data for SDM are species presence‐only records (available through digital databases). There have been many studies comparing the performance of alternative algorithms for modeling presence‐only data. Among these, a 2006 paper from Elith and colleagues has been particularly influential in the field, partly because they used several novel methods (at the time) on a global data set that included independent presence–absence records for model evaluation. Since its publication, some of the algorithms have been further developed and new ones have emerged. In this paper, we explore patterns in predictive performance across methods, by reanalyzing the same data set (225 species from six different regions) using updated modeling knowledge and practices. We apply well‐established methods such as generalized additive models and MaxEnt, alongside others that have received attention more recently, including regularized regressions, point‐process weighted regressions, random forests, XGBoost, support vector machines, and the ensemble modeling framework biomod. All the methods we use include background samples (a sample of environments in the landscape) for model fitting. We explore impacts of using weights on the presence and background points in model fitting. We introduce new ways of evaluating models fitted to these data, using the area under the precision‐recall gain curve, and focusing on the rank of results. We find that the way models are fitted matters. The top method was an ensemble of tuned individual models. In contrast, ensembles built using the biomod framework with default parameters performed no better than single moderate performing models. Similarly, the second top performing method was a random forest parameterized to deal with many background samples (contrasted to relatively few presence records), which substantially outperformed other random forest implementations. We find that, in general, nonparametric techniques with the capability of controlling for model complexity outperformed traditional regression methods, with MaxEnt and boosted regression trees still among the top performing models. All the data and code with working examples are provided to make this study fully reproducible.
Tropical fruit flies are considered among the most economically important invasive species detected in temperate areas of the United States and the European Union. Detections often trigger quarantine and eradication programs that are conducted without a holistic understanding of the threat posed. Weather-driven physiologically-based demographic models are used to estimate the geographic range, relative abundance, and threat posed by four tropical tephritid fruit flies (Mediterranean fruit fly, melon fly, oriental fruit fly, and Mexican fruit fly) in North and Central America, and the European-Mediterranean region under extant and climate change weather (RCP8.5 and A1B scenarios). Most temperate areas under tropical fruit fly propagule pressure have not been suitable for establishment, but suitability is predicted to increase in some areas with climate change. To meet this ongoing challenge, investments are needed to collect sound biological data to develop mechanistic models to predict the geographic range and relative abundance of these and other invasive species, and to put eradication policies on a scientific basis. Gutierrez et al. model the potential geographic range in temperate regions of four species of invasive tropical fruit flies under extant weather and climate change using physiologically-based demographic models. Their models show increased habitat suitability for many areas under climate change.
Crop production is a constant battle with weeds, in which weeds, generally, are victorious. Therefore, rather than channeling our efforts into the development of a “silver bullet” to control weeds, the focus should be on sustainable weed management in both natural- and agro-ecosystems. However, sustainable weed management can be a challenge in the context of global climate change. Over the past few decades, global climate change, mostly indicated by phenomena such as increased atmospheric temperature and elevated CO2 levels, is evident due to human activities and natural events. These phenomena also affect regional/local climate, resulting in significant influences on the agricultural systems of a particular region. Rising CO2 levels may give comparative advantages to C3 plants through increased photosynthesis, biomass production and yield, compared to C4 plants. Plants with C4 photosynthetic pathways, on the other hand, are likely to benefit more from rising global temperatures than C3 plants. Thus, the differential responses of C3 and C4 plants to climate change may alter crop–weed interactions and competition outcomes, most likely at the expense of the crop. Climate change will likely cause shifts in weed community compositions, their population dynamics, life cycle, phenology, and infestation pressure. Some weed species may go extinct, while some others may become more aggressive invaders. Weeds are, generally, colonizers and have some unique biological traits and ecological amplitudes that enable them to successfully dominate crops in a habitat with changed environmental conditions. Moreover, climate shifts, especially erratic rainfall and drought, may affect herbicide selectivity and efficacy or the success of bio-control agents resulting in an establishment of a mixed and complex population of C3 and C4 weed species adding to the complexity of weed management. Although elevated CO2 levels will stimulate the productivity of major C3 crops, most troublesome agricultural weeds will likely be more responsive to a rise in CO2 than crops, and thus may dominate the agro-ecosystem. It is predicted that, as temperature rises, the majority of the C4 weeds will flourish and will pose serious crop yield losses. Understanding and assessment of the impact of simultaneous changes in multiple climate factors and their complex interactions on crops and weeds are therefore necessary to formulate an adaptive weed management approach and build resilience. Moreover, strategic policies and strong actions need to be taken to reduce the root causes of CO2 and other greenhouse gas emissions to minimize the impact of climate change on weed biology and management.
Increased adoption of crops with stacked traits conferring glyphosate and dicamba resistance, and recent confirmation of kochia [Bassia scoparia (L.) A.J. Scott] biotypes resistant to these herbicides in Alberta and Saskatchewan, warrant surveillance of herbicide-resistant kochia in Manitoba. A randomized–stratified survey of 315 sites in Manitoba was conducted in the fall of 2018. Overall, 58% of the kochia populations tested were glyphosate-resistant, while 1% were dicamba-resistant. This survey documents rapid increase in glyphosate-resistant kochia over a five-year time frame, and also confirms the first cases of kochia in Manitoba with dicamba resistance alone and in combination with glyphosate resistance.
Climate change has the potential to change the distribution of pests globally and their resistance to pesticides, thereby threatening global food security in the 21st century. However, predicting where these changes occur and how they will influence current pest control efforts is a challenge. Using experimentally parameterised and field-tested models, we show that climate change over the past 50 years increased the overwintering range of a global agricultural insect pest, the diamondback moth ( Plutella xylostella ), by ~2.4 million km ² worldwide. Our analysis of global data sets revealed that pesticide resistance levels are linked to the species’ overwintering range: mean pesticide resistance was 158 times higher in overwintering sites compared to sites with only seasonal occurrence. By facilitating local persistence all year round, climate change can promote and expand pesticide resistance of this destructive species globally. These ecological and evolutionary changes would severely impede effectiveness of current pest control efforts and potentially cause large economic losses.
Indo-Pacific lionfish (Pterois volitans and P. miles) are the first marine teleost to become established in the Western Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. Lionfish have been labeled a global conservation issue and pose major threats to local economies. To test whether commercial harvest of lionfish is a socially accepted management approach in Texas, we measured the components of an environmental behavior intention model with survey responses of Texas Gulf Coast residents (n = 420). Regression analyses of survey responses indicate that individuals were significantly more willing to consume lionfish if they had a high level of concern for the environmental problems posed by the invasive species and were more knowledgeable about the fish. Participation in an educational program that addresses lionfish was also found to be associated with greater willingness to consume lionfish among those who are moderately to highly concerned about the issue. The originality of this study is related to its contribution in identifying social factors that contribute to an individual’s willingness to consume lionfish. Insights from this study demonstrate the attitudinal and behavioral mechanisms that can be addressed to increase acceptance of using consumption as a sustainable management strategy to combat marine fish invasions.
Both weed interference and adverse weather can cause significant maize yield losses. However, most climate change projections on maize yields ignore the fact that weeds are widespread in maize production. Herein, we examine the effects of weed control and weather variability on maize yield loss due to weeds by using machine learning techniques on an expansive database of herbicide efficacy trials spanning 205 weather environments and 27 years. Late‐season control of all weed species was the most important driver of maize yield loss due to weeds according to multiple analyses. Average yield losses of 50% were observed with little to no weed control. Furthermore, when the highest levels of weed control were not achieved, drier, hotter conditions just before and during silking exacerbated maize yield losses due to weeds. Current climate predictions suggest much of the U.S. maize growing regions will experience warmer, drier summers. This, coupled with growing prevalence of herbicide resistance, increases the risk of maize yield loss due to weeds in the future without transformational change in weed management systems.
The sale of ornamental nonnative plants is a primary pathway of invasive plant introduction into the US. As a result, many nonnative plants have been identified as noxious weeds by federal and state governments, or as problematic invasive plants by agencies and nonprofit organizations. However, it is unclear whether identifying a species as invasive has curtailed its sale as an ornamental. Using the Google search engine and a database of nursery catalogs, we found that 61% of 1285 plant species identified as invasive in the US remain available through the plant trade, including 50% of state‐regulated species and 20% of federal noxious weeds. Vendors offering invasive plants were located in all lower 48 states. The widespread availability of invasive plants in the US is likely a symptom of disjointed state regulations that fail to protect ecosystems and economies. Regional regulation coupled with outreach to growers and consumers is needed to reduce the ongoing propagation of invasive plants in the US.
One of the possible consequences of projected global warming is the progressive enlargement of drylands. This study investigates to what extent population and land-use (forests, pastures, and croplands) are likely to be in areas turning arid in the 21st century. The first part of the study focuses on the climatological enlargement of arid areas at global, macro-regional, and high-resolution (0.44°) scales. To do so we analysed a large ensemble of CORDEX climate simulations, combined three indicators (FAO-UNEP aridity index, Köppen-Geiger climate classification, and Holdridge life zones), and quantified the areas turning from climatologically not arid into climatologically arid (and vice-versa) from recent past (1981–2010) to four projected global warming levels (GWLs) from 1.5°C to 4°C. In the second part, we used population and land-use projections to analyze their exposure to progressive shifts to drier or wetter climate. Both types of projections follow five socio-economic scenarios (SSPs from SSP1 to SSP5). We present results for the viable combinations between SSPs and GWLs. Depending on GWL, the projected drying patterns show regional differences but, overall, the negative consequences of climate change are clear. Already at 1.5°C warming, approximately 2 million km2 (1.4% of global land) are likely to become arid; at 2°C this area corresponds to 2.6 million km2 (2.7%), at 3°C to 5.2 million km2 (3.5%), and at 4°C to 6.8 million km2 (4.5%), an area that can be ranked the seventh largest country in the World. Such drying is particular strong over South America and southern Europe. In the worst-case scenario (SSP3, regional rivalry, at 4°C), approximately 500 million people will live in areas shifting towards arid climate. Forest areas are likely to be more affected in South America, pastures in Africa, and croplands in the Northern Hemisphere. For land-use, the worst-case scenarios are SSP3 and SSP5 (fossil-fuel based future): at GWL 4°C, about 0.5 million km2 of forests and 1.2 million km2 of both pastures and croplands are likely to be in areas shifting to arid climate.
Aims
Shifts in the realized niches of exotic species may play an important role in their invasion. Galinsoga quadriradiata has invaded China widely and occupied many climate zones that are different from its native range. We addressed the climatic niche shift of G. quadriradiata, and evaluated how this could contribute to its invasion in China.
Methods
We used the Maxent model to predict the potential distribution of G. quadriradiata using its native and invaded range occurrences and climatic variables. Principal component analysis was conducted to measure climatic niche shifts of G. quadriradiata during its invasion in China.
Important Findings
The models revealed only 32.7% niche overlap between the native and invasive populations. The niche similarity of the two populations was significantly low (Schoener’s D = 0.093, P<0.005), suggesting the occurrence of a niche shift. The envelop and center of the realized climatic niche in China has shifted to lower temperature and less precipitation compared to that in its native range. The majority of invaded areas in southern China are in the stabilizing zone, whereas the colonization and adaptation zones are predicted to be at the leading edge of G. quadriradiata invasion in northern China. This suggests that the regional distribution of G. quadriradiata may be in a quasi-equilibrium state, and that the species continues to invade environmentally suitable areas. Alterations in G. quadriradiata’s niche would help to explain why this species is so invasive in China.
Invasion, spread and establishment of invasive alien species in a new environment causes serious ecosystem perturbation and native species extinctions. The problem is further aggravated under climate change as some invasive alien species perform better under elevated temperature and carbon dioxide regimes. Currently unsuitable regions such as high-altitude areas and mountains are likely to become more suited to invasion under future climatic conditions. We have modelled the distribution of one of the most invasive alien species, parthenium weed ( Parthenium hysterophorus L.) which is rapidly colonizing different parts of Bhutan. We have implemented ensemble modelling approach using the BIOMOD2 package in R environment. Under current climate scenario, about 2.83% (1, 099.01 km 2 ) of the country’s total area is predicted to be suitable for parthenium weed invasion, covering 17 out of the 20 districts in Bhutan. Under future climate scenarios, the highest suitability is predicted under RCP4.5 2050 period with about 5, 419.69 km 2 anticipated to be suitable. Except for Bumthang, all districts show suitability to invasions under future climate scenarios. Generally, districts located in the west and south show more suitability than those in the east and central region. The highest elevation of suitability is predicted to be at 2, 931 m above sea level; an upward shift of about 753 m. Based on these findings, there is an urgent need to develop management programs and raise public awareness on the adverse impacts of parthenium weed in Bhutan.
Recent confirmation of dicamba-resistant kochia [Bassia scoparia (L.) A.J. Scott] in Alberta warrants investigation of resistance to other commonly used synthetic auxin herbicides like fluroxypyr. A randomized-stratified survey of 305 sites in Alberta was conducted in 2017 to determine the status of fluroxypyr-resistant kochia. Overall, 13% of the kochia populations were fluroxypyr-resistant. Only 4% of the populations were both fluroxypyr- and dicamba-resistant, indicating that different mechanisms may confer resistance to these herbicides. When combined with estimates of dicamba resistance, about 28% of the kochia populations sampled in Alberta in 2017 were resistant to at least one synthetic auxin herbicide.
Western North American sagebrush shrublands and steppe face accelerating risks from fire-driven feedback loops that transition these ecosystems into self-reinforcing states dominated by invasive annual grasses. In response, sagebrush conservation decision-making is increasingly done through the lens of resilience to fire and annual grass invasion resistance. Operationalizing resilience and resistance concepts requires place-based understanding of resilience and resistance variation among landscapes over time. Place-based insights allow for landscape prioritization in targeted areas of significance such as such as protected-area sagebrush ecosystems that exhibit inherently low resilience and are therefore at high risk of loss. We used a multi-scale approach to evaluate sagebrush resiliency and strategic planning across 1) the US National Park system, 2) a regional suite of five parks, and 3) for two specific park case studies. First, we summarized broad patterns of relative resilience to fire and resistance to annual grass invasion across all parks with sagebrush ecosystems. We found that national parks represented ~11% of US protected-area sagebrush ecosystems and reflected a similar low-resilience bias that occurs across the biome, broadly. Climate change is likely to shift both low- and high-resilience park sagebrush ecosystems towards moderate resiliency, creating new opportunities and constraints for park conservation. Approximately seventy park units include at least some sagebrush shrublands or steppe, but we identified 40 parks with substantial amounts (>20% of park area) that can be included in an agency-wide conservation strategy. Second, we examined detailed patterns of resilience and resistance, fire history and fire risk, cheatgrass (Bromus tectorum) invasion, and sagebrush shrub (Artemisia spp.) persistence in five national park units in Columbia Basin and Snake River Plain sagebrush steppe, contextualized by the broader summary. In these five parks, fire frequency and size increased in recent decades. Cheatgrass invasion and sagebrush persistence correlated strongly with resilience, burn frequency (0-3 fires since ~1940), and burn probability, but with important variation, in part mediated by local-scale topography. Third, we used these insights to assemble strategic sagebrush ecosystem fire protection mapping scenarios in two additional parks – Lava Beds National Monument and Great Basin National Park. Readily available and periodically updated geospatial data including soil surveys, fire histories, vegetation inventories, and long-term monitoring support resiliency-based adaptive management through tactical pre-fire protection, post-fire restoration, and triage. Our assessment establishes the precarious importance of the US national park system to sagebrush ecosystem conservation and an operational strategy for place-based and science-supported conservation.
Unmanned aerial vehicle (UAV) imaging is a promising data acquisition technique for image-based plant phenotyping. However, UAV images have a lower spatial resolution than similarly equipped in field ground-based vehicle systems, such as carts, because of their distance from the crop canopy, which can be particularly problematic for measuring small-sized plant features. In this study, the performance of three deep learning-based super resolution models, employed as a pre-processing tool to enhance the spatial resolution of low resolution images of three different kinds of crops were evaluated. To train a super resolution model, aerial images employing two separate sensors co-mounted on a UAV flown over lentil, wheat and canola breeding trials were collected. A software workflow to pre-process and align real-world low resolution and high-resolution images and use them as inputs and targets for training super resolution models was created. To demonstrate the effectiveness of real-world images, three different experiments employing synthetic images, manually downsampled high resolution images, or real-world low resolution images as input to the models were conducted. The performance of the super resolution models demonstrates that the models trained with synthetic images cannot generalize to real-world images and fail to reproduce comparable images with the targets. However, the same models trained with real-world datasets can reconstruct higher-fidelity outputs, which are better suited for measuring plant phenotypes.
Many weed biological control programs suffer from large-scale spatial variation in success due to restricted distributions or abundances of agents in temperate climates. For some of the world’s worst aquatic weeds, agents are established but overwintering conditions limit their survival in higher latitudes or elevations. The resulting need is for new or improved site- or region-specific biological control tools. Here, we review this challenge with a focus on low-temperature limitations of agents and propose a roadmap for improving success. Investigations across spatial scales, from global (e.g., foreign exploration), to local (selective breeding), to individual organisms (molecular modification), are discussed. A combination of traditional (foreign) and non-traditional (introduced range) exploration may lead to the discovery and development of better-adapted agent genotypes. A multivariate approach using ecologically relevant metrics to quantify and compare cold tolerance among agent populations is likely required. These data can be used to inform environmental niche modeling combined with mechanistic modeling of species’ fundamental climate niches and life histories to predict where, when, and at what abundance agents will occur. Finally, synthetic and systems biology approaches in conjunction with advanced modern genomics, gene silencing and gene editing technologies may be used to identify and alter the expression of genes enhancing cold tolerance, but this technology in the context of weed biological control has not been fully explored.
We quantify long-run adaptation of U.S. corn and soybean yields to changes in temperature and precipitation over 1951–2017. Results show that although the two crops became more heat- and drought-tolerant, their productivity under normal temperature and precipitation conditions decreased. Over 1951–2017, heat- and drought-tolerance increased corn and soybean yields by 33% and 20%, whereas maladaptation to normal conditions reduced yields by 41% and 87%, respectively, with large spatial variations in effects. Changes in climate are projected to reduce average corn and soybean yields by 39–68% and 86–92%, respectively, by 2050 relative to 2013–2017 depending on the warming scenario. After incorporating estimated effects of climate-neutral technological advances, the net change in yield ranges from (−)13 to 62% for corn and (−)57 to (−)26% for soybeans in 2050 relative to 2013–2017. Our analysis uncovers the inherent trade-offs and limitations of existing approaches to crop adaptation.
Antarctica is increasingly vulnerable to climate change impacts, with the continent predicted to warm by ∼4 °C by 2100 under a ‘business as usual’ greenhouse gas emission scenario. Simultaneously, human activity, primarily in the form of scientific research and the fishing and tourism industries, is putting increasing pressure on Antarctic and Southern Ocean environments and ecosystems. We evaluate the effectiveness of the Antarctic area protection system in promoting resilience to climate change impacts. Under the framework of the Antarctic Treaty System (ATS), terrestrial and marine areas can be designated to protect locations of scientific, environmental, historic and intrinsic value and to facilitate operational coordination to minimise environmental impact. However, climate change is not mentioned explicitly in the Protocol on Environmental Protection to the Antarctic Treaty and is little considered in guidelines for the designation and management of the region’s existing protected areas. Climate change impacts are considered in only 17% of Antarctic Specially Protected Area (ASPA) management plans and, at a time when threats to Antarctic environments are increasing, the last decade has seen an 84% decline in ASPA designation rate compared with levels in the 1980s. Nevertheless, momentum is building within the Scientific Committee on Antarctic Research (SCAR) and the ATS’s Committee on Environmental Protection (CEP) to deliver an evidence-based, integrated response to climate change that includes the use of protected areas. The Antarctic scientific community is well-placed to support decision-makers in the use of existing conservation management tools through provision of climate change forecasts at sub-regional scales, data on anticipated environmental change, and predicted species and ecosystems responses. Ultimately, reducing global greenhouse gas emission will provide the greatest protection from climate change impacts within Antarctica.
Background
Invasive alien species (IAS) cause significant economic losses in all parts of the world. Although IAS are widespread in Africa and cause serious negative impacts on livelihoods as a result of yield losses and increased labour costs associated with IAS management, few data on the impacts are available in the literature and the magnitude and extent of the costs are largely unknown. We estimated the cost of IAS to agriculture, the most important economic sector in Africa.
Methods
Data on the monetary costs of IAS to mainland Africa as well as information about the presence and abundance of the most important IAS were collected through literature review and an online survey among a wide variety of stakeholders. Using this and additional data from publicly available sources we estimated yield losses and management costs due to IAS in agriculture for individual countries and the entire continent. Where the data allowed, the costs for selected IAS or crops were estimated separately. The estimates were extrapolated using production and distribution data and/or matching of agro-ecological zones.
Results
The total estimated annual cost of IAS to agriculture in Africa is USD 65.58 Bn. Management costs (comprising mainly labour costs associated with weeding), crop yield losses and reductions in livestock derived income constitute the majority of the estimated cost (55.42, 44.31 and 0.26 percent, respectively). The IAS causing the highest yield losses was Spodoptera frugiperda (USD 9.4 Bn).
Conclusions
This study reveals the extent and scale of the economic impacts of IAS in the agricultural sector in one of the least studied continents. Although the cost estimate presented here is significant, IAS also cause major costs to other sectors which could not be assessed due to data deficit. The results highlight the need for pre-emptive management options, such as prevention and early detection and rapid response to reduce huge potential future costs, as well as measures that contribute to large-scale control of widely established IAS at little cost to farmers and other affected land users, to reduce losses and improve livelihoods.
The negative impacts of invasive animals ripple throughout the 417 sites of the National Park System and threaten the ability for the National Park Service (NPS) to achieve its legislated mission. Momentum has been building throughout the country and the NPS to more comprehensively address the threat posed by invasive species. A national approach by the NPS is needed to increase the effectiveness of preventing invasions, control and slow the spread of existing invasions, and provide a central hub to ensure that these efforts are coordinated and cost effective. This report takes the initial step in presenting the state of the knowledge of invasive animals in the NPS by summarizing the occurrence
of invasive animals in parks and the needs and efforts at the park, regional, and national level to address them.
Mountainous areas and their endemic plant diversity are threatened by global climate change and invasive species. Mountain plant invasions have historically been minimal, however, climate change and increased anthropogenic activity (e.g. roads and vehicles) are amplifying invasion pressure. We assessed plant performance (stem density and fruit production) of the invasive non-native forb Linaria dalmatica along three mountain roads, over an eight-year period (2008–2015) in the Greater Yellowstone Ecosystem (GYE), USA. We evaluated how L. dalmatica performed in response to elevation, changed over time, responded to climate and how the climate of our sites has changed, and compared elevation, climate, micro-topography (slope aspect and angle), and fruit production among sites with differing temporal trends. Linaria dalmatica stem density and fruit production increased with elevation and demonstrated two temporal groups, those populations where stem densities shrank and those that remained stable or grew over time. Stem density demonstrated a hump-shaped response to summer mean temperature, while fruit production decreased with summer mean maximum temperature and showed a hump-shaped response to winter precipitation. Analysis of both short and long-term climate data from our sites, demonstrated that summer temperatures have been increasing and winters getting wetter. The shrinking population group had a lower mean elevation, hotter summer temperatures, drier winters, had plots that differed in slope aspect and angle from the stable/growing group, and produced less fruit. Regional climate projections predict that the observed climate trends will continue, which will likely benefit L. dalmatica populations at higher elevations. We conclude that L. dalmatica may persist at lower elevations where it poses little invasive threat, and its invasion into the mountains will continue along roadways, expanding into higher elevations of the GYE.
Parthenium weed (Parthenium hysterophorus L.) is an invasive alien plant species that is spreading rapidly all over the world. With globalization and climate change, it will continue to spread, posing threats to agriculture, biodiversity and the environment. To determine its invasion and impacts in Bhutan, an investigation was undertaken in West-Central Bhutan using a questionnaire survey, complemented by MaxEnt modelling. Most farmers (19–30%) recall having seen parthenium for the last 11–15 years, or more. Infestations of parthenium differed significantly (P < 0.05) across three districts for dryland, orchards, fallow land and pastures, but not in rice fields and on roadsides. The most intensely invaded land types were fallow land, pastures, and roadsides, with farmers perceiving it as ‘somewhat common’(score ~ 3) and ‘common’ (score ~ 4) weed. Farmers’ perceptions of the invasiveness of parthenium weed were high at 77% (Wangdue), 80% (Punakha), and 88% (Tsirang), considering it as at least ‘somewhat invasive’, or higher. Only 13–25% of respondents scored the weed as ‘highly invasive’. Parthenium invasion significantly (P < 0.01 to 0.001) escalated the cost of production, reduced fodder quality, supressed native species and caused allergies to the locals in the study districts. Further, MaxEnt modelling of parthenium distribution was undertaken, using the parthenium presence-only data and bioclimatic variables, under 2 CO2 emission scenarios of the Intergovernmental Panel on Climate Change (IPCC), i.e. Representative Concentration Pathways (RCP2.6 and 8.5). The projections showed discernible spatial changes in climate suitability over 2070, mostly in the mid- and high-altitude zones, indicating aggressive incursion into Bhutan’s important agro-ecological landscapes. The findings, highlight the urgent need to initiate parthenium management strategies for food production and natural resources.
Focusing on extreme climatic events in India’s Western Ghats Biodiversity Hotspot, we demonstrate that unmanaged aquaculture and unregulated fisheries can often combine with ECE in exacerbating biological invasions through the unexpected introduction and escape of novel alien species. High magnitude flooding events in August 2018 and 2019 resulted in the escape of at least ten alien fish species that were recorded for the first time, from the natural waters of the Western Ghats. Illegal farming systems, aqua-tourism destinations and amusement parks, as well as reservoirs, facilitated the escape of alien species during the ECE. Despite expanding invasions, unmanaged stocking and aquaculture using alien species continue in the Western Ghats, necessitating urgent management and policy interventions.
Although evolution has been often seen as a gradual process through a Darwinian lens, far more rapid evolutionary change has been observed in recent times. Recent examples documenting the potential speed of invasive plant evolution have included: latitudinal flowering clines, life history shifts, or abrupt changes in morphology. The timescales for such observations range from centuries down to <5 years. Invasive weeds provide good models for the rapid changes, partly because invasive weeds exhibit unique evolutionary mechanisms integral to their success. For example, purging of their genetic load may enable invasive plants to adapt more rapidly. Other genetic mechanisms include plasticity as an evolved trait, hybridization, polyploidy, epigenetics, and clonal division of labor. It is well-demonstrated that anthropogenic stressors such as habitat disturbance or herbicide use may work synergistically with climate change stressors in fostering rapid weed evolution. Changing temperatures, moisture regimes and extreme climate events operate universally, but invasive plant species are generally better equipped than native plants to adapt. Research on this potential for rapid evolution is critical to developing more proactive management approaches that anticipate new invasive plant ecotypes adapted to changing climatic conditions.
Biological invasions are responsible for substantial biodiversity declines as well as high economic losses to society and monetary expenditures associated with the management of these invasions1,2. The InvaCost database has enabled the generation of a reliable, comprehensive, standardized and easily updatable synthesis of the monetary costs of biological invasions worldwide3. Here we found that the total reported costs of invasions reached a minimum of US26.8 billion. Moreover, we estimate that the annual mean cost could reach US$162.7 billion in 2017. These costs remain strongly underestimated and do not show any sign of slowing down, exhibiting a consistent threefold increase per decade. We show that the documented costs are widely distributed and have strong gaps at regional and taxonomic scales, with damage costs being an order of magnitude higher than management expenditures. Research approaches that document the costs of biological invasions need to be further improved. Nonetheless, our findings call for the implementation of consistent management actions and international policy agreements that aim to reduce the burden of invasive alien species. Analysis of the InvaCost database shows that the costs of biological invasions have markedly increased between 1970 and 2017 and show no sign of slowing down, highlighting the importance of evidence-based and cost-effective management actions.
The Antarctic Peninsula is under pressure from non-native plants and this risk is expected to increase under climate warming. Establishment and subsequent range expansion of non-native plants depend in part on germination ability under Antarctic conditions, but quantifying these processes has yet to receive detailed study. Viability testing and plant growth responses under simulated Antarctic soil surface conditions over an annual cycle show that 16 non-native species, including grasses, herbs, rushes and a succulent, germinated and continued development under a warming scenario. Thermal germination requirement (degree day sum) was calculated for each species and field soil-temperature recordings indicate that this is satisfied as far south as 72° S. Here, we show that the establishment potential of non-native species, in number and geographical range, is considerably greater than currently suggested by species distribution modelling approaches, with important implications for risk assessments of non-native species along the Antarctic Peninsula.
Aim
Temperature is fundamental to the physiological and ecological performance of marine organisms, but its role in modulating the magnitude of ecological impacts by exotic species remains unresolved. Here, we examine the relationship between thermal regimes in the range of origin of marine exotic species and sites of measured impact, after human‐induced introduction. We compare this relationship with the magnitude of impact exerted by exotic species on native ecosystems.
Location
Global.
Time period
1977–2017 (meta‐analysis).
Major taxa studied
Marine exotic species.
Methods
Quantitative impacts of exotic species in marine ecosystems were obtained from a global database. The native range of origin of exotic species was used to estimate the realized thermal niche for each species and compared with the latitude and climatic conditions in recipient sites of recorded impact of exotic species. The difference in median temperatures between recipient sites and the thermal range of origin (i.e., thermal midpoint anomaly) was compared with the magnitude of effect sizes by exotic species on native species, communities and ecosystems.
Results
Recorded impacts occurred predominantly within the thermal niche of origin of exotic species, albeit with a tendency toward higher latitudes and slightly cooler conditions. The severity of impacts by exotic species on abundance of native taxa displayed a hump‐shaped relationship with temperature. Peak impacts were recorded in recipient sites that were 2.2°C cooler than the thermal midpoint of the range of origin of exotic species, and impacts decreased in magnitude toward higher and lower thermal anomalies.
Main conclusions
Our findings highlight how temperature and climatic context influence ecological impacts by exotic species in marine ecosystems and the implications for existing and novel species interactions under climate change.
Insect pests are the major biotic fauna that reduces the production of different crops.
On average, pests account for 20-40% of yield losses worldwide. Farmers rely heavily on
chemical control, generally practiced for higher gains and management of insect-pests, but
improperly by its injudicious application. The sole reliance on chemical pesticides has led to
the problem of 3 R’s viz., Resistance, Resurgence and Residues. Even with chemical
methods, the pest could not be managed, and now the cost of input exceeds the yield. When
the idea of the "green revolution" emerged, the assured irrigation regions were discovered
and solutions were found to boost productivity there. Water plays an important role to reduce
or increase the pest population. Heavy rainfall with high intensity wash out the pest
population from crop during rainy season. For some pests, water stress play important role for
the management of the insect pest. Therefore, the paper is aimed to combine all available
techniques, whether they were for a specific pest or all pests of a crop.
As part of the 2015 Paris Agreement, countries agreed to regularly revisit and enhance their national climate strategies and, every 5 years, to offer new emissions targets in the form of nationally determined contributions (NDCs) (1). This year’s 26th Conference of Parties provides a waypoint in this updating process as countries have been offering enhanced or completely new NDCs (2, 3) (henceforth, updated pledges) (4). We find that compared with the 2015 pledges, the updated pledges suggest a strengthening of ambition through 2030. By calculating probabilistic temperature outcomes over the 21st century for five emissions scenarios (see the figure and table S1), we find that the updated pledges provide a stronger near-term foundation to deliver on the long-term goals of the Paris Agreement of reducing the probability of the worst levels of temperature change this century and increasing the likelihood of limiting temperature change to well below 2°C.
Ceratapion basicorne (Illiger) is a recently approved univoltine biological control agent that develops inside the rosette of yellow starthistle (Centaurea solstitialis L.), an invasive annual plant. Adult weevils normally emerge in early summer, and females are thought to be in reproductive diapause until the following spring, when they oviposit in rosettes. The long period of reproductive diapause constrains mass-rearing this weevil because only one generation per year can be produced. Determining the environmental conditions that regulate diapause termination may enable shortening diapause under laboratory conditions to increase production of adults to release. We tested three hibernating conditions (greenhouse [ambient temperature and photoperiod], glass door refrigerator [5°C and ambient photoperiod], and growth chamber [5°C and 24 h dark]) for three durations (4, 8, 11 wk). The highest proportion of females laying eggs came from the growth chamber, with 40% terminating diapause after 4 wk, 80% after 8 wk, and 95% after 11 wk of exposure. Our study demonstrates that duration of cold temperature is an important stimulus to terminate reproductive diapause of C. basicorne, and that exposure to ambient light had no effect at 5°C. However, 47% of females held at ambient greenhouse conditions, without any chilling period, completed diapause within 11 wk. Thus, a cold period can accelerate diapause development, but it is not necessary for its completion. Reducing the winter diapause period from about 6 mo to 11 wk should enable the production of multiple generations per year to increase the number of insects available to release.
This book is part of the "CABI Invasive Series", which addresses all topics relating to invasive species, including biosecurity surveillance, mapping and modelling, economics of invasive species and species interactions in plant invasions. Aimed at researchers, upper-level students and policy makers, titles in the series provide international coverage of topics related to invasive species, including both a synthesis of facts and discussions of future research perspectives and possible solutions. This book specifically aims to examine the nexus of climate change and biological invasions, and the resulting impacts, and to identify means to reduce the vulnerability and increase the resiliency of managed and unmanaged ecosystems. It is divided into four parts: (i) the dimensions of the problem: background and science; (ii) case studies; (iii) management: detection and prevention; and (iv) management: control and adaptation.
Increasing atmospheric carbon dioxide concentrations [CO2] and climate change are impacting farming worldwide. Ecological weed management (EWM) principles, including use of diverse tactics already employed by many farmers, may assist in adapting to and mitigating climate change. We systematically reviewed the literature on EWM and climate change and here summarise practical considerations related to changing efficacy and utility of non-chemical EWM practices. Localised changes in precipitation will affect tillage and cultivation. We expect that mulching, transplanting and some weed seedbank management strategies, which add resiliency to a weed management programme, may show increased utility in a future with more extreme and variable weather. Innovations in autonomous robotic weeding technologies and cultivation tool design show promise in helping to overcome challenges related to low and variable cultivation efficacy and traditionally slow working rates. EWM practices that help farmers achieve multiple objectives and provide benefits beyond climate change adaptation, such as financial gains, may be most advantageous, the development of which could be facilitated by interdisciplinary research and outreach efforts. Overall, we conclude that in an increasingly variable climate, farmers will have to employ a greater diversity of weed management tactics in order to spread risk and enable climate resilience through farming systems diversification.
Most of Earth's terrestrial carbon is stored in the soil and can be released as carbon dioxide (CO2) when disturbed. Although humans are known to exacerbate soil CO2 emissions through land-use change, we know little about the global carbon footprint of invasive species. We predict the soil area disturbed and resulting CO2 emissions from wild pigs (Sus scrofa), a pervasive human-spread vertebrate that uproots soil. We do this using models of wild pig population density, soil damage, and their effect on soil carbon emissions. Our models suggest that wild pigs are uprooting a median area of 36,214 km2 (mean of 123,517 km2) in their non-native range, with a 95% prediction interval (PI) of 14,208 km2–634,238 km2. This soil disturbance results in median emissions of 4.9 million metric tonnes (MMT) CO2 per year (equivalent to 1.1 million passenger vehicles or 0.4% of annual emissions from land use, land-use change, and forestry; mean of 16.7 MMT) but that it is highly uncertain (95% PI, 0.3–94 MMT CO2) due to variability in wild pig density and soil dynamics. This uncertainty points to an urgent need for more research on the contribution of wild pigs to soil damage, not only for the reduction of anthropogenically related carbon emissions, but also for co-benefits to biodiversity and food security that are crucial for sustainable development.
South Africa’s colonial past has shaped its environmental history, including introductions of alien plants. Indentured Indian labourers, mainly from Tamil Nadu, that were brought to South Africa in the 1860s, acquired knowledge of Zulu healing practices and plants. This translocation of traditional medical knowledge (mostly Ayurvedic), and the adoption of new plants and traditions of practice, led to these migrants opening up some of the first muthi (traditional medicine) shops in South Africa, and also to importing and incorporat- ing Indian medicinal plants within South African healing traditions. Given this role of traditional medicine in the introduction of alien plant taxa, we gathered data on them from published literature (including market surveys) and from a survey of 77 muthi outlets in three South African cities. There were 301 alien taxa from 76 families, of which 81 taxa were recorded in trade. Sixty-nine of the traded taxa were identified to species, of which 20 have a declared legal status requiring some form of control. Of the 81 traded taxa, 44% were sold in a non-viable form and 29% were seeds or fruit that could be germinated; the remaining 28% were sold as live plants. Seeds of these alien taxa constituted the greatest quantity and most widely traded plant part of the taxa recorded. The survey of muthi outlets generated 36 alien plant taxa, of which 26 were new records in the trade. Plant origins recorded in this survey revealed that 41% of plants were harvested in South Africa, 35% imported from India, and 24% were of unknown origin. The importance of this trade as a pathway for introduction of alien species is discussed.
This UN Decade on Ecosystem Restoration highlights the capacity of restoration to mitigate trends in biodiversity loss and land degradation. However, many managers lack the tools they need to systematically and comprehensively identify degraded sites to prioritize restoration efforts given limited resources. We developed a novel, inexpensive, low-tech approach for training and engaging citizen scientists to identify recreational impacts and other degraded areas within a defined unforested area. The mapping process follows four phases: 1) Landscape scans by citizen scientists using Google Earth Pro imagery; 2) A second scan of all marked sites based on high resolution aerial photography; 3) Compilation of basic information about the degraded sites; 4) Addition of associated soil type and plant communities. In the 12,375 ha McDowell Sonoran Preserve (Scottsdale, Arizona) we detected 67 new sites not previously identified by land managers, using an estimated 305 citizen scientist hours and only 30 staff hours. Each site has accompanying information including distance from nearest access point, cause of degradation, and plant and soils detail. After completion, we conducted independent field visits of 33% of the detected sites and verified degradation in all cases. We found that the remotely sensed approach provided better perspective to accurately measure the scale and original source of degradation compared with field visits. The approach can be conducted over a short period of time using citizen scientists; allows managers to undertake landscape level restoration prioritization and planning; and, if repeated, can be used to monitor changes in degradation and restoration over time.
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Uncontrolled biological invasions have direct and indirect impacts on the structure and functioning of soil invertebrate communities in Antarctica. Among others, invasion success is strongly determined by the ability of species to tolerate broad thermal ranges. Yet, few studies have compared the thermal niches of native and invasive species. Physiological characterizations of upper and lower thermal tolerances are essential to test the extent to which eurythermality can benefit invasive species in a context of changing climates. Here, we compare cold and heat tolerance between adults of the alien winter crane fly Trichocera maculipennis and the native winged midge Parochlus steinenii in Antarctica. Specimens were collected in the field during the 2019/2020 austral summer, and ramping experiments controlling heating and cooling rates were performed to estimate upper and lower critical thermal limits of the two Diptera insect species. Adults of the alien fly remained active between − 5.3 °C and 30.1 °C. In turn, the native midge was active between − 5.0 °C and 28.6 °C. We observed no significant interspecific differences between lower critical thermal limits, but upper thermal limits were significantly higher for the alien species. Hence, the capacity to endure low summer temperatures in most of the Antarctic Peninsula is similar for adults of both species, but the alien crane fly is readily adapted to withstand warming scenarios. Therefore, the broad thermal tolerances exhibited by the alien crane fly can be taken as evidence to predict geographic range expansions, while also warn of high biosecurity risks for all operating research stations in Antarctica.
Climate change affects life at global scales and across systems but is of special concern in areas that are disproportionately rich in biological diversity and uniqueness. Using a meta-analytical approach, we analysed >8000 risk projections of the projected impact of climate change on 273 areas of exceptional biodiversity, including terrestrial and marine environments. We found that climate change is projected to negatively impact all assessed areas, but endemic species are consistently more adversely impacted. Terrestrial endemics are projected to be 2.7 and 10 times more impacted than non-endemic natives and introduced species respectively, the latter being overall unaffected by climate change. We defined a high risk of extinction as a loss of >80% due to climate change alone. Of endemic species, 34% and 46% in terrestrial and marine ecosystems, and 100% and 84% of island and mountain species were projected to face high extinction risk respectively. A doubling of warming is projected to disproportionately increase extinction risks for endemic and non-endemic native species. Thus, reducing extinction risks requires both adaptation responses in biodiversity rich-spots and enhanced climate change mitigation.