Bee and butterfly records indicate diversity losses in western and southern North America, but extensive knowledge gaps remain.

Pollinator losses threaten ecosystems and food security, diminishing gene flow and reproductive output for ecological communities and impacting ecosystem services broadly. For four focal families of bees and butterflies, we constructed over 1400 ensemble species distribution models over two time periods for North America. Models indicated disproportionally increased richness in eastern North America over time, with decreases in richness over time in the western US and southern Mexico. To further pinpoint geographic areas of vulnerability, we mapped records of potential pollinator species of conservation concern and found high concentrations of detections in the Great Lakes region, US East Coast, and southern Canada. Finally, we estimated asymptotic diversity indices for genera known to include species that visit flowers and may carry pollen for ecoregions across two time periods. Patterns of generic diversity through time mirrored those of species-level analyses, again indicating a decline in pollinators in the western U.S. Increases in generic diversity were observed in cooler and wetter ecoregions. Overall, changes in pollinator diversity appear to reflect changes in climate, though other factors such as land use change may also explain regional shifts. While statistical methods were employed to account for unequal sampling effort across regions and time, improved monitoring efforts with rigorous sampling designs would provide a deeper understanding of pollinator communities and their responses to ongoing environmental change.

The interaction between administrative jurisdiction and disturbance on public lands: Emerging socioecological feedbacks and dynamics.

Disturbance is one of the fundamental shapers of ecological communities, redistributing resources and resetting successional pathways. Human activities including resources management can influence disturbance regimes and trajectories by actively imposing or suppressing disturbance events or shaping ecosystem recovery via disturbance response. Furthermore, different management objectives may drive different disturbance responses. This suggests that the management jurisdiction to which a land parcel is assigned is likely to influence disturbance management and therefore ecological conditions within that parcel. Here, we combined two exploratory approaches to investigate this linkage. First, we used a systematic literature review to develop a typology of reported disturbance response types and strategies by federal land management agencies in the US. Second, we used Forest Inventory and Analysis (FIA) plot data in five multi-jurisdictional ecosystems containing national parks to investigate the relationship between land ownership and large disturbance occurrence and between disturbance and tree growth rate. We found that agencies vary in the diversity of disturbance response tactics they are reported to employ, and disturbance types vary in the diversity of responses reported in the literature. Disturbance occurrence varied by land ownership type across the FIA dataset, and the direction of tree growth rate was influenced by the interaction between ownership type and disturbance occurrence in two of five examined ecosystems. Although our mixed methods approach was purely exploratory and not mechanistic, our findings suggest that disturbance response is one possible route by which management regimes may influence ecological conditions. Efforts to understand and predict ecological heterogeneity across large landscapes must consider variation in the social system as a potential contributor to such patterns.

Decreased bee emergence along an elevation gradient: Implications for climate change revealed by a transplant experiment.

Bees experience differences in thermal tolerance based on their geographical range; however, there are virtually no studies that examine how overwintering temperatures may influence immature survival rates. Here, we conducted a transplant experiment along an elevation gradient to test for climate-change effects on immature overwinter survival using movement along elevational gradient for a community of 26 cavity-nesting bee species in the family Megachilidae along the San Francisco Peaks, Arizona elevational gradient. In each of three years, we placed nest blocks at three elevations, to be colonized by native Megachilidae. Colonized blocks were then (1) moved to lower (warmer) elevations; (2) moved to higher (cooler) elevations; or (3) left in their natal habitat (no change in temperature). Because Megachilidae occupy high elevations with colder temperatures more than any other family of bees, we predicted that emergence would decrease in nest blocks moved to lower elevations, but that we would find no differences in emergence when nest blocks were moved to higher elevations. We found three major results: (1) Bee species moved to lower (warmer) habitats exhibited a 30% decrease in emergence compared with species moved within their natal habitat. (2) Habitat generalists were more likely than habitat specialists to emerge when moved up or down in elevation regardless of their natal life zones. (3) At our highest elevation treatment, emergence increased when blocks were moved to higher elevations, indicating that at least some Megachilidae species can survive at colder temperatures. Our results suggest that direct effects of warming temperatures will have negative impacts on the overall survival of Megachilidae. Additionally, above the tree line, low availability of wood-nesting resources is a probable limiting factor on bees moving up in elevation.

Invasive predators affect community-wide pollinator visitation.

Disruption of plant-pollinator interactions by invasive predators is poorly understood but may pose a critical threat for native ecosystems. In a multiyear field experiment in Hawai'i, we suppressed abundances of globally invasive predators and then observed insect visitation to flowers of six native plant species. Three plant species are federally endangered (Haplostachys haplostachya, Silene lanceolata, Tetramolopium arenarium) and three are common throughout their range (Bidens menziesii, Dubautia linearis, Sida fallax). Insect visitors were primarily generalist pollinators, including taxa that occur worldwide such as solitary bees (e.g., Lasioglossum impavidum), social bees (e.g., Apis mellifera), and syrphid flies (e.g., Allograpta exotica). We found that suppressing invasive rats (Rattus rattus), mice (Mus musculus), ants (Linepithema humile, Tapinoma melanocephalum), and yellowjacket wasps (Vespula pensylvanica) had positive effects on pollinator visitation to plants in 16 of 19 significant predator-pollinator-plant interactions. We found only positive effects of suppressing rats and ants, and both positive and negative effects of suppressing mice and yellowjacket wasps, on the frequency of interactions between pollinators and plants. Model results predicted that predator eradication could increase the frequency of insect visitation to flowering species, in some cases by more than 90%. Previous results from the system showed that these flowering species produced significantly more seed when flowers were allowed to outcross than when flowers were bagged to exclude pollinators, indicating limited autogamy. Our findings highlight the potential benefits of suppression or eradication of invasive rodents, ants, and yellowjackets to reverse pollination disruption, particularly in locations with high numbers of at-risk plant species or already imperiled pollinator populations.

Landowners' Socio-Cultural Valuation of Ecosystem Services Provided by Trees in Costa Rican Agricultural Landscapes.

Over one-fourth of the world's land area is dedicated to agriculture, and these lands provide important ecosystem services (ES). Trees are a key component of agricultural ecosystems' ability to provide ES, especially in tropical regions. Agricultural landowners' evaluation of the ES provided by trees influences management decisions, impacting tree cover at large scales. Using a case study approach, we conducted semi-structured interviews with four types of agricultural landowners in southern Costa Rica to better understand how they value ES provided by trees. We used a socio-cultural valuation method, which revealed that landowners highly valued regulating and provisioning ES provided by trees and that the number and type of ES identified was influenced by the principle economic activity. Those farmers with larger amounts of forests on their properties more often identified cultural ES. The socio-cultural valuation methods revealed that respondents valued trees as wildlife habitat, coupling supporting and cultural services with both material (e.g., tourism) and non-material benefits (e.g., beauty). Few farmers in the study benefited from payment for ecosystem services programs, but the high value farmers placed on trees indicates there are other opportunities to increase tree cover on farms, such as promotion of live fencing and expanded riparian corridors. Results from this work can help improve conservation outcomes by shifting the focus of ecosystem service valuation to the needs and concerns of small-scale farmers in the development of outreach programs, management plans, and policies aimed at increasing tree cover on private lands in agricultural landscapes.

Estimating social-ecological resilience: fire management futures in the Sonoran Desert.

Resilience quantifies the ability of a system to remain in or return to its current state following disturbance. Due to inconsistent terminology and usage of resilience frameworks, quantitative resilience studies are challenging, and resilience is often treated as an abstract concept rather than a measurable system characteristic. We used a novel, spatially explicit stakeholder engagement process to quantify social-ecological resilience to fire, in light of modeled social-ecological fire risk, across the non-fire-adapted Sonoran Desert Ecosystem in Arizona, USA. Depending on its severity and the characteristics of the ecosystem, fire as a disturbance has the potential to drive ecological state change. As a result, fire regime change is of increasing concern as global change and management legacies alter the distribution and flammability of fuels. Because management and use decisions impact resources and ecological processes, social and ecological factors must be evaluated together to predict resilience to fire. We found highest fire risk in the central and eastern portions of the study area, where flammable fuels occur with greater density and frequency and managers reported fewer management resources than in other locations. We found lowest fire resilience in the southeastern portion of the study area, where combined ecological and social factors, including abundant fuels, few management resources, and little evidence of past institutional adaptability, indicated that sites were least likely to retain their current characteristics and permit achievement of current management objectives. Analyzing ecological and social characteristics together permits regional managers to predict the effects of changing fire regimes across large, multi-jurisdictional landscapes and to consider where to direct resources. This study brought social and ecological factors together into a common spatial framework to produce vulnerability maps; our methods may inform researchers and managers in other systems facing novel disturbance and spatially variable resilience.

Land management objectives and activities in the face of projected fire regime change in the Sonoran desert.

As a multi-jurisdictional, non-fire-adapted region, the Sonoran Desert Ecoregion is a complex, social-ecological system faced increasingly with no-analogue conditions. A diversity of management objectives and activities form the socioecological landscape of fire management. Different managers have different objectives, resources, and constraints, and each therefore applies different activities. As a result, it can be difficult to predict the regional consequences of changing fire regimes. We interviewed and surveyed managers of 53 million acres of government-managed lands across the Sonoran Desert Ecoregion of Arizona, asking them to describe their management objectives and activities as well as expected changes in the face of projected fire regime change across the region. If current activities were deemed unlikely to meet objectives into the future, this represents a likely adaptation turning point, where new activities are required in order to meet objectives. If no potential activity will meet an objective, it may be necessary to select a new objective, indicating an adaptation tipping point. Here, we report which current objectives and activities are deemed by managers most likely and least likely to succeed. We also discuss constraints reported by managers from different jurisdictions. We find that agriculture, military, and resource extraction objectives are perceived by managers as most likely to be met, whereas conservation of natural and cultural resources is considered least likely to be achieved. Federal land managers reported higher likelihood of both achieving current objectives and adopting new activities than did non-federal land managers. This study illustrates how rapid global change is affecting the ability of land managers differing in missions, mandates, and resources to achieve their central objectives, as well as the constraints and opportunities they face. Our results indicate that changing environmental conditions are unlikely to affect all management entities equally and for some jurisdictions may result in adaptation turning points or tipping points in natural and cultural resource conservation.

Introduction to the Special Issue: The role of seed dispersal in plant populations: perspectives and advances in a changing world.

Despite the importance of seed dispersal as a driving process behind plant community assembly, our understanding of the role of seed dispersal in plant population persistence and spread remains incomplete. As a result, our ability to predict the effects of global change on plant populations is hampered. We need to better understand the fundamental link between seed dispersal and population dynamics in order to make predictive generalizations across species and systems, to better understand plant community structure and function, and to make appropriate conservation and management responses related to seed dispersal. To tackle these important knowledge gaps, we established the CoDisperse Network and convened an interdisciplinary, NSF-sponsored Seed Dispersal Workshop in 2016, during which we explored the role of seed dispersal in plant population dynamics (NSF DEB Award # 1548194). In this Special Issue, we consider the current state of seed dispersal ecology and identify the following collaborative research needs: (i) the development of a mechanistic understanding of the movement process influencing dispersal of seeds; (ii) improved quantification of the relative influence of seed dispersal on plant fitness compared to processes occurring at other life history stages; (iii) an ability to scale from individual plants to ecosystems to quantify the influence of dispersal on ecosystem function; and (iv) the incorporation of seed dispersal ecology into conservation and management strategies.

Advancing an interdisciplinary framework to study seed dispersal ecology.

Although dispersal is generally viewed as a crucial determinant for the fitness of any organism, our understanding of its role in the persistence and spread of plant populations remains incomplete. Generalizing and predicting dispersal processes are challenging due to context dependence of seed dispersal, environmental heterogeneity and interdependent processes occurring over multiple spatial and temporal scales. Current population models often use simple phenomenological descriptions of dispersal processes, limiting their ability to examine the role of population persistence and spread, especially under global change. To move seed dispersal ecology forward, we need to evaluate the impact of any single seed dispersal event within the full spatial and temporal context of a plant's life history and environmental variability that ultimately influences a population's ability to persist and spread. In this perspective, we provide guidance on integrating empirical and theoretical approaches that account for the context dependency of seed dispersal to improve our ability to generalize and predict the consequences of dispersal, and its anthropogenic alteration, across systems. We synthesize suitable theoretical frameworks for this work and discuss concepts, approaches and available data from diverse subdisciplines to help operationalize concepts, highlight recent breakthroughs across research areas and discuss ongoing challenges and open questions. We address knowledge gaps in the movement ecology of seeds and the integration of dispersal and demography that could benefit from such a synthesis. With an interdisciplinary perspective, we will be able to better understand how global change will impact seed dispersal processes, and potential cascading effects on plant population persistence, spread and biodiversity.

Intrinsic and extrinsic drivers of intraspecific variation in seed dispersal are diverse and pervasive.

There is growing realization that intraspecific variation in seed dispersal can have important ecological and evolutionary consequences. However, we do not have a good understanding of the drivers or causes of intraspecific variation in dispersal, how strong an effect these drivers have, and how widespread they are across dispersal modes. As a first step to developing a better understanding, we present a broad, but not exhaustive, review of what is known about the drivers of intraspecific variation in seed dispersal, and what remains uncertain. We start by decomposing 'drivers of intraspecific variation in seed dispersal' into intrinsic drivers (i.e. variation in traits of individual plants) and extrinsic drivers (i.e. variation in ecological context). For intrinsic traits, we further decompose intraspecific variation into variation among individuals and variation of trait values within individuals. We then review our understanding of the major intrinsic and extrinsic drivers of intraspecific variation in seed dispersal, with an emphasis on variation among individuals. Crop size is the best-supported and best-understood intrinsic driver of variation across dispersal modes; overall, more seeds are dispersed as more seeds are produced, even in cases where per seed dispersal rates decline. Fruit/seed size is the second most widely studied intrinsic driver, and is also relevant to a broad range of seed dispersal modes. Remaining intrinsic drivers are poorly understood, and range from effects that are probably widespread, such as plant height, to drivers that are most likely sporadic, such as fruit or seed colour polymorphism. Primary extrinsic drivers of variation in seed dispersal include local environmental conditions and habitat structure. Finally, we present a selection of outstanding questions as a starting point to advance our understanding of individual variation in seed dispersal.

Implications of non-native species for mutualistic network resistance and resilience.

Resilience theory aims to understand and predict ecosystem state changes resulting from disturbances. Non-native species are ubiquitous in ecological communities and integrated into many described ecological interaction networks, including mutualisms. By altering the fitness landscape and rewiring species interactions, such network invasion may carry important implications for ecosystem resistance and resilience under continued environmental change. Here, I hypothesize that the tendency of established non-native species to be generalists may make them more likely than natives to occupy central network roles and may link them to the resistance and resilience of the overall network. I use a quantitative research synthesis of 58 empirical pollination and seed dispersal networks, along with extinction simulations, to examine the roles of known non-natives in networks. I show that non-native species in networks enhance network redundancy and may thereby bolster the ecological resistance or functional persistence of ecosystems in the face of disturbance. At the same time, non-natives are unlikely to partner with specialist natives, thus failing to support the resilience of native species assemblages. Non-natives significantly exceed natives in network centrality, normalized degree, and Pollination Service Index. Networks containing non-natives exhibit lower connectance, more links on average, and higher generality and vulnerability than networks lacking non-natives. As environmental change progresses, specialists are particularly likely to be impacted, reducing species diversity in many communities and network types. This work implies that functional diversity may be retained but taxonomic diversity decline as non-native species become established in networks worldwide.

Employing plant functional groups to advance seed dispersal ecology and conservation.

Seed dispersal enables plants to reach hospitable germination sites and escape natural enemies. Understanding when and how much seed dispersal matters to plant fitness is critical for understanding plant population and community dynamics. At the same time, the complexity of factors that determine if a seed will be successfully dispersed and subsequently develop into a reproductive plant is daunting. Quantifying all factors that may influence seed dispersal effectiveness for any potential seed-vector relationship would require an unrealistically large amount of time, materials and financial resources. On the other hand, being able to make dispersal predictions is critical for predicting whether single species and entire ecosystems will be resilient to global change. Building on current frameworks, we here posit that seed dispersal ecology should adopt plant functional groups as analytical units to reduce this complexity to manageable levels. Functional groups can be used to distinguish, for their constituent species, whether it matters (i) if seeds are dispersed, (ii) into what context they are dispersed and (iii) what vectors disperse them. To avoid overgeneralization, we propose that the utility of these functional groups may be assessed by generating predictions based on the groups and then testing those predictions against species-specific data. We suggest that data collection and analysis can then be guided by robust functional group definitions. Generalizing across similar species in this way could help us to better understand the population and community dynamics of plants and tackle the complexity of seed dispersal as well as its disruption.

Non-native insects dominate daytime pollination in a high-elevation Hawaiian dryland ecosystem.

PREMISE OF THE STUDY: Over one-third of the native flowering plant species in the Hawaiian Islands are listed as federally threatened or endangered. Lack of sufficient pollination could contribute to reductions in populations, reproduction, and genetic diversity among these species but has been little studied. METHODS: We used systematic observations and manual flower treatments to quantify flower visitation and outcrossing dependency of eight native (including four endangered) plant species in a dryland ecosystem in Hawaii: Argemone glauca, Bidens menziesii, Dubautia linearis, Haplostachys haplostachya, Sida fallax, Silene lanceolata, Stenogyne angustifolia, and Tetramolopium arenarium. KEY RESULTS: During 576.36 h of flower observations, only insects visited the flowers. Out of all recorded flower visits, 85% were performed by non-native species, particularly the honeybee (Apis mellifera) and flies in the family Syrphidae. Some plant species received little visitation (e.g., S. angustifolia received one visit in 120 h of observation), whereas others were visited by a wide diversity of insects. The endangered plant species were visited by fewer visitor taxa than were the common native plant species. For six of the focal plant species, bagging of flowers to exclude pollinators resulted in significant reductions in seed set. CONCLUSIONS: The flower visitor community in this system, although heavily dominated by non-native insects, appears to be facilitating pollination for multiple plant species. Non-native insects may thus be sustaining biotic interactions otherwise threatened with disruption in this island ecosystem. This may be particularly important for the studied endangered plant species, which exhibit fewer partners than the more common plant species.

Management thresholds stemming from altered fire dynamics in present-day arid and semi-arid environments.

Changes in fire frequency, size, and severity are driving ecological transformations in many systems. In arid and semi-arid regions that are adapted to fire, long-term fire exclusion by managers leads to declines in fire frequency, altered fire size distribution, and increased proportion of high severity fires. In arid and semi-arid systems where fire was historically rare, factors such as invasion by highly combustible non-native plants elevate fire frequency and size, elevating mortality of native species. Altered temperature and precipitation regimes may exacerbate these changes by increasing biomass and flammability. Current transformation in fire dynamics carry social as well as ecological consequences. Human cultures, livelihoods, values, and management behaviors are attuned to fire dynamics. Changes can make it costly or impossible to maintain traditional landscape use and economic activities. We review the ecological and social science literature to examine drivers of altered fire dynamics in arid and semi-arid systems worldwide and the conditions representing fire dynamics thresholds-points at which altered conditions may make it difficult or impossible to achieve management objectives, even via traditional adaptive management focusing on alternative management activities to achieve objectives. Such thresholds could force a wholesale shift in management objectives and practices and a new approach to adaptive management that redefines objectives when no viable adaptive action can be undertaken.

Benefits to poorly studied taxa of conservation of bird and mammal diversity on islands.

Protected area delineation and conservation action are urgently needed on marine islands, but the potential biodiversity benefits of these activities can be difficult to assess due to lack of species diversity information for lesser known taxa. We used linear mixed effects modeling and simple spatial analyses to investigate whether conservation activities based on the diversity of well-known insular taxa (birds and mammals) are likely to also capture the diversity of lesser known taxa (reptiles, amphibians, vascular land plants, ants, land snails, butterflies, and tenebrionid beetles). We assembled total, threatened, and endemic diversity data for both well-known and lesser known taxa and combined these with physical island biogeography characteristics for 1190 islands from 109 archipelagos. Among physical island biogeography factors, island area was the best indicator of diversity of both well-known and little-known taxa. Among taxonomic factors, total mammal species richness was the best indicator of total diversity of lesser known taxa, and the combination of threatened mammal and threatened bird diversity was the best indicator of lesser known endemic richness. The results of other intertaxon diversity comparisons were highly variable, however. Based on our results, we suggest that protecting islands above a certain minimum threshold area may be the most efficient use of conservation resources. For example, using our island database, if the threshold were set at 10 km(2) and the smallest 10% of islands greater than this threshold were protected, 119 islands would be protected. The islands would range in size from 10 to 29 km(2) and would include 268 lesser known species endemic to a single island, along with 11 bird and mammal species endemic to a single island. Our results suggest that for islands of equivalent size, prioritization based on total or threatened bird and mammal diversity may also capture opportunities to protect lesser known species endemic to islands.

Secondary extinctions of biodiversity.

Extinctions beget further extinctions when species lose obligate mutualists, predators, prey, or hosts. Here, we develop a conceptual model of species and community attributes affecting secondary extinction likelihood, incorporating mechanisms that buffer organisms against partner loss. Specialized interactors, including 'cryptic specialists' with diverse but nonredundant partner assemblages, incur elevated risk. Risk is also higher for species that cannot either evolve new traits following partner loss or obtain novel partners in communities reorganizing under changing environmental conditions. Partner loss occurs alongside other anthropogenic impacts; multiple stressors can circumvent ecological buffers, enhancing secondary extinction risk. Stressors can also offset each other, reducing secondary extinction risk, a hitherto unappreciated phenomenon. This synthesis suggests improved conservation planning tactics and critical directions for research on secondary extinctions.

Cultivating creativity in conservation science.

Conservation practitioners and scientists are often faced with seemingly intractable problems in which traditional approaches fail. While other sectors (e.g., business) frequently emphasize creative thinking to overcome complex challenges, creativity is rarely identified as an essential skill for conservationists. Yet more creative approaches are urgently needed in the effort to sustain Earth's biodiversity. We identified 4 strategies to develop skills in creative thinking and discuss underlying research and examples supporting each strategy. First, by breaking down barriers between disciplines and surrounding oneself with unfamiliar people, concepts, and perspectives, one can expand base knowledge and experiences and increase the potential for new combinations of ideas. Second, by meeting people where they are (both literally and figuratively), one exposes oneself to new environments and perspectives, which again broadens experiences and increases ability to communicate effectively with stakeholders. Third, by embracing risk responsibly, one is more likely to develop new, nontraditional solutions and be open to high-impact outcomes. Finally, by following a cycle of learning, struggle, and reflection, one can trigger neurophysiological changes that allow the brain to become more creative. Creativity is a learned trait, rather than an innate skill. It can be actively developed at both the individual and institutional levels, and learning to navigate the relevant social and practical barriers is key to the process. To maximize the success of conservation in the face of escalating challenges, one must take advantage of what has been learned from other disciplines and foster creativity as both a professional skill and an essential component of career training and individual development.

Imperfect replacement of native species by non-native species as pollinators of endemic Hawaiian plants.

Native plant species that have lost their mutualist partners may require non-native pollinators or seed dispersers to maintain reproduction. When natives are highly specialized, however, it appears doubtful that introduced generalists will partner effectively with them. We used visitation observations and pollination treatments (experimental manipulations of pollen transfer) to examine relationships between the introduced, generalist Japanese White-eye (Zosterops japonicus) and 3 endemic Hawaiian plant species (Clermontia parviflora, C. montis-loa, and C. hawaiiensis). These plants are characterized by curved, tubular flowers, apparently adapted for pollination by curve-billed Hawaiian honeycreepers. Z. japonicus were responsible for over 80% of visits to flowers of the small-flowered C. parviflora and the midsize-flowered C. montis-loa. Z. japonicus-visited flowers set significantly more seed than did bagged flowers. Z. japonicus also demonstrated the potential to act as an occasional Clermontia seed disperser, although ground-based frugivory by non-native mammals likely dominates seed dispersal. The large-flowered C. hawaiiensis received no visitation by any birds during observations. Unmanipulated and bagged C. hawaiiensis flowers set similar numbers of seeds. Direct examination of Z. japonicus and Clermontia morphologies suggests a mismatch between Z. japonicus bill morphology and C. hawaiiensis flower morphology. In combination, our results suggest that Z. japonicus has established an effective pollination relationship with C. parviflora and C. montis-loa and that the large flowers of C. hawaiiensis preclude effective visitation by Z. japonicus.

Mutualism Disruption Threatens Global Plant Biodiversity: A Systematic Review.

BACKGROUND: As global environmental change accelerates, biodiversity losses can disrupt interspecific interactions. Extinctions of mutualist partners can create "widow" species, which may face reduced ecological fitness. Hypothetically, such mutualism disruptions could have cascading effects on biodiversity by causing additional species coextinctions. However, the scope of this problem - the magnitude of biodiversity that may lose mutualist partners and the consequences of these losses - remains unknown. METHODOLOGY/PRINCIPAL FINDINGS: We conducted a systematic review and synthesis of data from a broad range of sources to estimate the threat posed by vertebrate extinctions to the global biodiversity of vertebrate-dispersed and -pollinated plants. Though enormous research gaps persist, our analysis identified Africa, Asia, the Caribbean, and global oceanic islands as geographic regions at particular risk of disruption of these mutualisms; within these regions, percentages of plant species likely affected range from 2.1-4.5%. Widowed plants are likely to experience reproductive declines of 40-58%, potentially threatening their persistence in the context of other global change stresses. CONCLUSIONS: Our systematic approach demonstrates that thousands of species may be impacted by disruption in one class of mutualisms, but extinctions will likely disrupt other mutualisms, as well. Although uncertainty is high, there is evidence that mutualism disruption directly threatens significant biodiversity in some geographic regions. Conservation measures with explicit focus on mutualistic functions could be necessary to bolster populations of widowed species and maintain ecosystem functions.