No abstract

Species interactions are responsible for many key mechanisms that govern the dynamics of ecological communities. Variation in the way interactions are organized among species results in different network structures, which translates into a community's ability to resist collapse and change. To better understand the factors involved in dictating ongoing dynamics in a community at a given time, we must unravel how interactions affect the assembly process. Here, we build a novel, integrative conceptual model for understanding how ecological communities assemble that combines ecological networks and island biogeography theory, as well as the principles of niche theory. Through our conceptual model, we show how the rate of species turnover and gene flow within communities will influence the structure of ecological networks. We conduct a preliminary test of our predictions using plant-herbivore networks from differently-aged sites in the Hawaiian archipelago. Our approach will allow future modeling and empirical studies to develop a better understanding of the role of the assembly process in shaping patterns of biodiversity.

Within ecological communities, species engage in myriad interaction types, yet empirical examples of hybrid species interaction networks composed of multiple types of interactions are still scarce. A key knowledge gap is understanding how the structure and stability of such hybrid networks are affected by anthropogenic disturbance. Using 15,169 interaction observations, we constructed 16 hybrid herbivore‐plant‐pollinator networks along an agricultural intensification gradient to explore changes in network structure and robustness to local extinctions. We found that agricultural intensification led to declines in modularity but increases in nestedness and connectance. Notably, network connectance, a structural feature typically thought to increase robustness, caused declines in hybrid network robustness, but the directionality of changes in robustness along the gradient depended on the order of local species extinctions. Our results not only demonstrate the impacts of anthropogenic disturbance on hybrid network structure, but they also provide unexpected insights into the structure‐stability relationship of hybrid networks.

Species interaction networks, which govern the maintenance of biodiversity and ecosystem processes within ecological communities, are being rapidly altered by anthropogenic activities worldwide. Studies on the response of species interaction networks to anthropogenic disturbance have almost exclusively focused on one interaction type at a time, such as mutualistic or antagonistic interactions, making it challenging to decipher how networks of different interaction types respond to the same anthropogenic disturbance. Moreover, few studies have simultaneously focused on the two main components of network structure: network topology (i.e., architecture) and network ecology (i.e., species identities and interaction turnover), thereby limiting our understanding of the ecological drivers underlying changes in network topology in response to anthropogenic disturbance. Here, we used 16,400 plant-pollinator and plant-herbivore interaction observations from 16 sites along an agricultural intensification gradient to compare changes in network topology and ecology between mutualistic and antagonistic networks. We measured two aspects of network topology-nestedness and modularity-and found that although the mutualistic networks were consistently more nested than antagonistic networks and antagonistic networks were consistently more modular, the rate of change in nestedness and modularity along the gradient was comparable between the two network types. Change in network ecology, however, was distinct between mutualistic and antagonistic networks, with partner switching making a significantly larger contribution to interaction turnover in the mutualistic networks than in the antagonistic networks, and species turnover being a strong contributor to interaction turnover in the antagonistic networks. The ecological and topological changes we observed in the antagonistic and mutualistic networks have different implications for pollinator and herbivore communities in agricultural landscapes, and support the idea that pollinators are more labile in their interaction partner choice, whereas herbivores form more reciprocally specialized, and therefore more vulnerable, interactions. Our results also demonstrate that studying both topological and ecological network structure can help to elucidate the effects of anthropogenic disturbance on ecological communities, with applications for conservation and restoration of species interactions and the ecosystem processes they maintain.

Deforestation transforms habitats, displacing vertebrates and the other dimensions of biodiversity they support through their interactions. Few empirical studies have quantified the effect deforestation has on vertebrate–pollinator interaction networks. Here we quantify how hummingbird–plant networks change in relation to hummingbird diversity across a deforestation gradient. We found that, overall, hummingbird–plant interactions were significantly more specialized in forests and specialized interactions decayed rapidly with the loss of tree cover at small spatial scales. Hummingbird species interaction specialization was also higher in forest habitats compared to coffee plantations, but we found no support for a morphological hummingbird trait that predicted interaction specialization or forest dependence. Finally, we developed spatially explicit models for quantifying impacts of land-use decisions on hummingbird species and the biodiversity they support. These tools can be used to identify and prioritize important habitats for conservation activities, like creating new protected areas and improving agricultural lands for biodiversity.

3Determining linkage rules that govern the formation of species interactions is a critical goal of 4 ecologists, especially considering that biodiversity, species interactions, and the ecosystem processes they 5 maintain are changing at rapid rate worldwide. Species traits and abundance play a role in determining 6 plant-pollinator interactions, but we illustrate here that linkage rules of plant-pollinator interactions 7 change with disturbance context, switching from predominantly trait-based linkage rules in undisturbed, 8 natural habitats, to abundance-based linkage rules in intensive agricultural habitats. The transition from 9 trait-based to abundance-based linkage rules corresponds with a decline in floral trait diversity and an 10 increase in opportunistic interaction behavior as agricultural intensification increases. These findings 11 suggest that agricultural intensification is changing the very rules determining the realization of 12 interactions and the formation of communities, making it challenging to use the structure of undisturbed 13 systems to predict interactions within disturbed communities. 14 15

Objective: Opioid use is a continuing problem for the United States. Individuals who use opioids have a high risk of misuse, especially with prescription opioids. Substances that are often used in combination with opioids include methamphetamines, sedatives, and benzodiazepines, as well as tobacco, alcohol, and marijuana, but not in a medical setting. We sought to determine (a) the relationship between various drugs (eg, methamphetamine, benzodiazepines) and opioid use, as well as (b) the relationship between polysubstance use and opioid use.Design: We created a screening instrument that requested the patients seeking medical care at Federally Qualified Health Centers (FQHC) and Veterans Affairs (VA) hospitals in West Alabama self-report their substance usage.Setting: This study took place in outpatient primary care settings (FQHCs and VA hospitals) in west Alabama.Participants: De-identified electronic health records for 346 adults were obtained from consenting medical facilities. Missing data were found in 33 of the records obtained. The final usable sample for this study was 311.Main Outcome Measure: The screening tool was comprised of five sections: demographics, tobacco use, alcohol abuse, drug use, and mental health. The primary outcome measure of this study was the number of days of opioid use in the past 30 days.Results: Thirteen individuals (4.18 percent) reported opioid use in the last 30 days. While polysubstance or dual substance use was not in the majority of the participant responses, the significant substances that were used in conjunction with opioids were methamphetamine, hallucinogens, and benzodiazepines.Conclusions: Individuals who are polysubstance users have a higher likelihood of opioid use. Interventions that target opioid use would serve the population stronger by including screenings and potential treatments for polysubstance use additionally.

Global climate change threatens to substantially rearrange species interactions, yet we lack clear predictions on how these changes will cascade through communities. Many perturbations associated with climate change, such as droughts, will change resource levels, with consequences for species interactions and thus ecological network structure. Diet theory predicts foraging niche expansion when preferred resources are scarce, yet under severe resource reduction interspecific competition could alternatively increase niche partitioning. Such niche expansion and/or contraction could profoundly shape ecological network structure following perturbations, but whether these predictions hold at the community level is unclear. We studied the impacts of drought on plant–pollinator networks in long‐lived perennial plant communities in which drought affects flower and floral reward production. We assessed whether drought effects on available floral resources altered pollinator dietary niche breadth to drive higher network‐level generalization. Accounting for interaction abundance and species turnover, we compared plant–pollinator networks in two drought years and three non‐drought years. We found that drought restructured plant–pollinator networks, resulting in more generalization in terms of presence–absence of links, yet more specialization when accounting for quantitative network intensities. Our results support the application of diet theory to understanding how perturbations may impact ecological network structure.