Indirect biotic interactions of plant invasions with native plants and animals.

Author(s):  
Warwick J. Allen

Abstract Invasive plants often occur at high densities and tend to be highly generalist in their interactions with herbivores, pathogens, mycorrhiza, endophytes and pollinators. These characteristics mean that invasive plants should frequently participate in diverse indirect biotic interactions with the surrounding community, mediated by their direct interaction partners (e.g. antagonists and mutualists). Indirect interactions play an important role in many ecological processes, yet we still lack a systematic understanding of the circumstances under which they influence the success and impacts of invasive species. In this chapter, I first describe several of the indirect interaction pathways that are commonly encountered in invasion biology and review their contribution to the impacts of plant invasions on co-occurring species. The literature review revealed that there are now many case studies describing various indirect impacts of invasive plants. However, identical interaction motifs (e.g. plant-enemy-plant, plant-mutualist-plant) can bring about several possible outcomes, depending upon each species' provenance, relative abundances and interaction strengths, abiotic resource availability, spatial and temporal scale and the influence of other species. Moreover, knowledge gaps identified include a lack of studies of indirect facilitation outside of plant-pollinator systems, limited consideration of indirect invader impacts on other non-native species, and the scarcity of generalizable results to date. Second, I integrate the literature with some trending research areas in invasion biology (interaction networks, biogeography, invasion dynamics) and identify some potential future research directions. Finally, I discuss how knowledge about indirect biotic interactions could be incorporated into the management of invasive plants.

Author(s):  
Warwick J. Allen ◽  

Invasive plants often occur at high densities and tend to be highly generalist in their interactions with herbivores, pathogens, mycorrhiza, endophytes and pollinators. These characteristics mean that invasive plants should frequently participate in diverse indirect biotic interactions with the surrounding community, mediated by their direct interaction partners (e.g. antagonists and mutualists). Indirect interactions play an important role in many ecological processes, yet we still lack a systematic understanding of the circumstances under which they influence the success and impacts of invasive species. In this chapter, I first describe several of the indirect interaction pathways that are commonly encountered in invasion biology and review their contribution to the impacts of plant invasions on co-occurring species. The literature review revealed that there are now many case studies describing various indirect impacts of invasive plants. However, identical interaction motifs (e.g. plant-enemy-plant, plant-mutualist-plant) can bring about several possible outcomes, depending upon each species' provenance, relative abundances and interaction strengths, abiotic resource availability, spatial and temporal scale and the influence of other species. Moreover, knowledge gaps identified include a lack of studies of indirect facilitation outside of plant-pollinator systems, limited consideration of indirect invader impacts on other non-native species, and the scarcity of generalizable results to date. Second, I integrate the literature with some trending research areas in invasion biology (interaction networks, biogeography, invasion dynamics) and identify some potential future research directions. Finally, I discuss how knowledge about indirect biotic interactions could be incorporated into the management of invasive plants.


Author(s):  
Anna Traveset ◽  
David M. Richardson

Abstract Diverse biotic interactions between non-native plant species and other species from all taxonomic groups are crucial mediators of the dynamics of plant invasions. This chapter reviews the key hypotheses in invasion ecology that invoke biotic interactions to explain aspects of plant invasion dynamics. We examine the historical context of these hypotheses and assess the evidence for accepting or rejecting their predictions. Most hypotheses invoke antagonistic interactions, mainly competition, predation, herbivory interactions and the role of pathogens. Only in the last two decades have positive (facilitative/mutualistic) interactions been explicitly included in invasion biology theory (as in ecological theory in general). Much information has accumulated in testing hypotheses relating to biotic resistance and Enemy Release Theory, although many of the emerging generalizations are still contentious. There is growing consensus that other drivers of plant invasion success, such as propagule pressure and disturbance, mediate the outcome of biotic interactions, thereby complicating our ability to make predictions, but these have rarely been assessed in both native and adventive ranges of non-native invasive species. It is also widely acknowledged that biogeographic comparisons, more than common garden experiments, are needed to shed light on many of the contradictory results. Contrasting findings have also emerged in exploring the roles of positive interactions. Despite strong evidence that such interactions are crucial in many communities, more work is needed to elucidate the factors that influence the relative importance of positive and negative interactions in different ecosystems. Different types of evidence in support of invasional meltdown have emerged for diverse habitats and across spatial scales. In light of increasing evidence that biotic indirect effects are crucial determinants of the structure, dynamics and evolution of ecological communities, both direct and indirect interactions involving native and non-native species must be considered to determine how they shape plant invasion patterns and the ecological impacts of non-native species on recipient communities. Research that examines both biotic interactions and the factors that mediate their strength and alter interaction outcomes is needed to improve our ability to predict the effects of novel interactions between native and non-native species, and to envisage how existing invaded communities will respond to changing environmental conditions. Many opportunities exist for manipulating biotic interactions as part of integrated control strategies to reduce the extent, density and impacts of non-native plant invasions. These include the introduction of species from the native range of the non-native plant for biological control, diverse manipulations of plant - herbivore interactions and many types of interaction to enhance biotic resistance and steer vegetation recovery following non-native plant control.


2021 ◽  
Author(s):  
Michaeline B. N. Albright ◽  
Stilianos Louca ◽  
Daniel E. Winkler ◽  
Kelli L. Feeser ◽  
Sarah-Jane Haig ◽  
...  

AbstractMicrobiome engineering is increasingly being employed as a solution to challenges in health, agriculture, and climate. Often manipulation involves inoculation of new microbes designed to improve function into a preexisting microbial community. Despite, increased efforts in microbiome engineering inoculants frequently fail to establish and/or confer long-lasting modifications on ecosystem function. We posit that one underlying cause of these shortfalls is the failure to consider barriers to organism establishment. This is a key challenge and focus of macroecology research, specifically invasion biology and restoration ecology. We adopt a framework from invasion biology that summarizes establishment barriers in three categories: (1) propagule pressure, (2) environmental filtering, and (3) biotic interactions factors. We suggest that biotic interactions is the most neglected factor in microbiome engineering research, and we recommend a number of actions to accelerate engineering solutions.


2021 ◽  
Author(s):  
Jiang Wang ◽  
Yuan Ge ◽  
J. Hans C. Cornelissen ◽  
Xiaoyan Wang ◽  
Song Gao ◽  
...  

Abstract Biodiversity loss, exotic plant invasions and climatic change are currently the three major challenges to our globe and can each affect various ecological processes, including litter composition. To gain a better understanding of global change impacts on ecological processes, these three global change components need to be considered simultaneously. Here we assembled experimental plant communities with species richness levels (1, 2, 4, 8 or 16) and subjected them to drought (no, moderate or intensive drought) and invasion (invasion by the exotic annual plant Symphyotrichum subulatum or not). We collected litter of the native plant communities and let it decompose for nine months within the communities. Drought decreased litter decomposition, while the exotic plant invasion had no impact. Increasing species richness decreased litter decomposition under the mesic condition (no drought), but had little impact under moderate and intensive drought. A structural equation model showed that drought and species richness affected litter decomposition mainly via influencing litter nitrogen concentration, but not via altering the quantity and diversity of soil meso-fauna or soil physio-chemical properties. The negative impact of species diversity on litter decomposition under the mesic condition was mainly ascribed to a sampling effect, i.e. via particularly low litter nitrogen concentrations in the two dominant species. Our results indicate that species richness can interact with drought to affect litter decomposition via effect on litter nitrogen. We conclude that nitrogen-dependent litter decomposition should be a mechanism to predict integrated effects of plant diversity loss, exotic plant invasions and climatic change on litter decomposition.


Author(s):  
Johannes J. le Roux

Abstract Microbes are omnipresent, yet their interactions with invasive plants remain understudied. This is surprising, given the importance of microbes in plant community ecology and their influence on plant performance in new environments. Recent advances in molecular genetic approaches have opened the door to studying this unseen majority in great detail and to understand how they fit into ecological interaction networks. Molecular approaches allow rapid assessments of microbial diversity at reasonable cost while providing both taxonomic and evolutionary information. Here I discuss how these approaches have contributed to a better understanding of plant-microbial interactions in the context of biological invasions. By drawing insights from various case studies, I illustrate how next-generation sequencing (DNA barcoding) has revolutionized the way we understand such interactions. Tight-knit and coevolved mutualist (e.g. mycorrhizal) and antagonist (e.g. pathogen) interactions appear particularly promising to understand the structure and function of invasive plant-microbial interaction networks, the impacts of invasive plants on native networks and the vulnerability of native networks to infiltration by non-native species. I also discuss novel ways in which molecular data can aid the study of invasive plant-microbial interactions, such as incorporating phylogenetic data into network analyses to better understand the role of evolutionary history in network dynamics and how such dynamics respond to plant invasions. DNA barcoding of microbes also presents unique challenges to the study of network ecology, such as uncertainty in the legitimacy and efficiency of interactions. Future research should incorporate overall plant-associated microbial communities (microbiomes) into interaction networks to better understand the role microbes play during plant invasions.


Author(s):  
Amy E. Kendig ◽  
S. Luke Flory ◽  
Erica M. Goss ◽  
Robert D. Holt ◽  
Keith Clay ◽  
...  

Abstract Plant-pathogen interactions occur throughout the process of plant invasion: pathogens can acutely influence plant survival and reproduction, while the large densities and spatial distributions of invasive plant species can influence pathogen communities. However, interactions between invasive plants and pathogens are often overlooked during the early stages of invasion. As with introductions of invasive plants, the introduction of agricultural crops to new areas can also generate novel host-pathogen interactions. The close monitoring of agricultural plants and resulting insights can inform hypotheses for invasive plants where research on pathogen interactions is lacking. This chapter reviews the known and hypothesized effects of pathogens on the invasion process and the effects of plant invasion on pathogens and infectious disease dynamics throughout the process of invasion. Initially, pathogens may inhibit the transport of potentially invasive plants. After arrival in a new range, pathogens can facilitate or inhibit establishment success of introduced plants depending on their relative impacts on the introduced plants and resident species. As invasive plants spread, they may encounter novel pathogens and alter the abundance and geographic range of pathogens. Pathogens can mediate interactions between invasive plants and resident species and may influence the long-term impacts of invasive plants on ecosystems. As invasive plants shift the composition of pathogen communities, resident species could be subject to higher disease risk. We highlight gaps in invasion biology research by providing examples from the agricultural literature and propose topics that have received little attention from either field.


Author(s):  
Carine Emer ◽  
◽  
Sérgio Timóteo ◽  
◽  

Every organism on Earth, whether in natural or anthropogenic environments, is connected to a complex web of life, the famous 'entangled bank' coined by Darwin in 1859. Non-native species can integrate into local 'banks' by establishing novel associations with the resident species. In that context, network ecology has been an important tool to study the interactions of non-native species and the effects on recipient communities due to its ability to simultaneously investigate the assembly and disassembly of species interactions as well as their functional roles. Its visually appealing tools and relatively simple metrics gained momentum among scientists and are increasingly applied in different areas of ecology, from the more theoretical grounds to applied research on restoration and conservation. A network approach helps us to understand how plant invasions may or may not form novel species associations, how they change the structure of invaded communities, the outcomes for ecosystem functionality and, ultimately, the implications for the conservation of ecological interactions. Networks have been widely used on pollination studies, especially from temperate zones, unveiling their nested patterns and the mechanisms by which non-native plants integrate into local communities. Yet, very few papers have used network approaches to assess plant invasion effects in other systems such as plant-herbivore, plant-pathogen or seed-dispersal processes. Here we describe how joining network ecology with plant invasion biology started and how it has developed over the last few decades. We show the extent of its contribution, despite contradictory results and biases, to a better understanding of the role of non-native plant species in shaping community structure. Finally, we explore how it can be further improved to answer emerging questions.


Author(s):  
John D. Parker ◽  
◽  
John L. Devaney ◽  
Nathan P. Lemoine ◽  
◽  
...  

Biotic resistance to plant invasions takes many forms: consumption by native herbivores, competition with native plants and infection by native pathogens. But how often does biotic resistance prevent the damaging monocultures that typify the most problematic plant invaders, and how often is biotic resistance overwhelmed by the direct and indirect impacts of human activities? This chapter attempts to answer these questions, drawing on the long history of research into biotic resistance. We first briefly describe the major forms of biotic resistance to exotic plant invasions as an antecedent to other, more detailed chapters on competition, herbivory and pathogens. We then describe a new neutral model where variance in disturbance promotes invasions over the short term, but over longer timescales only propagule pressure drives invasions. These findings are a cautionary tale; pending increases in global trade and travel, particularly to the tropics, may provide the prerequisite disturbance and propagule pressure needed to ultimately stoke further invasions. Finally, we highlight case studies where invasions have been mitigated by restoration of biotic resistance from native herbivores and competitors. These studies provide strong empirical support that conservation of native biodiversity can be a nature-based solution to some invasions, although it remains to be seen if climate change will alter these effects over longer timescales.


Forests ◽  
2018 ◽  
Vol 9 (11) ◽  
pp. 723 ◽  
Author(s):  
Kurt Riitters ◽  
Kevin Potter ◽  
Basil Iannone ◽  
Christopher Oswalt ◽  
Qinfeng Guo ◽  
...  

Research Highlights: We demonstrate a macroscale framework combining an invasibility model with forest inventory data, and evaluate regional forest exposure to harmful invasive plants under different types of forest protection. Background and Objectives: Protected areas are a fundamental component of natural resource conservation. The exposure of protected forests to invasive plants can impede achievement of conservation goals, and the effectiveness of protection for limiting forest invasions is uncertain. We conducted a macroscale assessment of the exposure of protected and unprotected forests to harmful invasive plants in the eastern United States. Materials and Methods: Invasibility (the probability that a forest site has been invaded) was estimated for 82,506 inventory plots from site and landscape attributes. The invaded forest area was estimated by using the inventory sample design to scale up plot invasibility estimates to all forest area. We compared the invasibility and the invaded forest area of seven categories of protection with that of de facto protected (publicly owned) forest and unprotected forest in 13 ecological provinces. Results: We estimate approximately 51% of the total forest area has been exposed to harmful invasive plants, including 30% of the protected forest, 38% of the de facto protected forest, and 56% of the unprotected forest. Based on cumulative invasibility, the relative exposure of protection categories depended on the assumed invasibility threshold. Based on the invaded forest area, the five least-exposed protection categories were wilderness area (13% invaded), national park (18%), sustainable use (26%), nature reserve (31%), and de facto protected Federal land (36%). Of the total uninvaded forest area, only 15% was protected and 14% had de facto protection. Conclusions: Any protection is better than none, and public ownership alone is as effective as some types of formal protection. Since most of the remaining uninvaded forest area is unprotected, landscape-level management strategies will provide the most opportunities to conserve it.


2019 ◽  
Vol 190 (4) ◽  
pp. 333-344 ◽  
Author(s):  
Hong Qian ◽  
Brody Sandel ◽  
Tao Deng ◽  
Ole R Vetaas

AbstractEcologists have embraced phylogenetic measures of assemblage structure, in large part for the promise of better mechanistic inferences. However, phylogenetic structure is driven by a wide array of factors from local biotic interactions to biogeographical history, complicating the mechanistic interpretation of a pattern. This may be particularly problematic along elevational gradients, where rapidly changing physical and biological conditions overlap with geological and biogeographical history, potentially producing complex patterns of phylogenetic dispersion (relatedness). We focus on the longest elevational gradient of vegetation in the world (i.e. c. 6000 m in Nepal) to explore patterns of phylogenetic dispersion for angiosperms (flowering plants) along this elevational gradient. We used the net relatedness index to quantify phylogenetic dispersion for each elevational band of 100 m. We found a zig-zag pattern of phylogenetic dispersion along this elevational gradient. With increasing elevation, the phylogenetic relatedness of species decreased for the elevational segment between 0 and c. 2100 m, increased for the elevational segment between 2100 and c. 4200 m, and decreased for the elevational segment above c. 4200 m. We consider this pattern to be a result of the interaction of geophysical (e.g. plate tectonics) and eco-evolutionary processes (e.g. niche conservatism and trait convergence). We speculate on the mechanisms that might have generated this zig-zag pattern of phylogenetic dispersion.


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