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Abstract Host populations often vary in the magnitude of coinfection they experience across environmental gradients. Furthermore, coinfection often occurs sequentially, with a second parasite infecting the host after the first has established a primary infection. Because the local environment and interactions between coinfecting parasites can both drive patterns of coinfection, it is important to disentangle the relative contributions of environmental factors and within‐host interactions to patterns of coinfection.Here, we develop a conceptual framework and present an empirical case study to disentangle these facets of coinfection. Across multiple lakes, we surveyed populations of five damselfly (host) species and quantified primary parasitism by aquatic, ectoparasitic water mites and secondary parasitism by terrestrial, endoparasitic gregarines. We first asked if coinfection is predicted by abiotic and biotic factors within the local environment, finding that the probability of coinfection decreased for all host species as pH increased. We then asked if primary infection by aquatic water mites mediated the relationship between pH and secondary infection by terrestrial gregarines.Contrary to our expectations, we found no evidence for a water mite‐mediated relationship between pH and gregarines. Instead, the intensity of gregarine infection correlated solely with the local environment, with the magnitude and direction of these relationships varying among environmental predictors.Our findings emphasize the role of the local environment in shaping infection dynamics that set the stage for coinfection. Although we did not detect within‐host interactions, the approach herein can be applied to other systems to elucidate the nature of interactions between hosts and coinfecting parasites within complex ecological communities. 

Abstract AimGlobal interspecific body size distributions have been suggested to be shaped by selection pressures arising from biotic and abiotic factors such as temperature, predation and parasitism. Here, we investigated the ecological and evolutionary drivers of global latitudinal size gradients in an old insect order. LocationGlobal. TaxonOdonata (dragonflies and damselflies). MethodsWe compiled data on interspecific variation in extant and extinct body sizes of Odonata, using an already existing database (The Odonate Phenotypic Database) and fossil data (The Paleobiology Database). We combined such body size data with latitudinal information and data on biotic and abiotic environmental variables across the globe to investigate and quantify interspecific latitudinal size‐gradients (“Bergmann's Rule”) and their environmental determinants. We used phylogenetic comparative methods and a global published phylogeny of Odonata to address these questions. ResultsPhylogenetic comparative analyses revealed that global size variation of extant Odonata taxa is negatively influenced by both regional avian diversity and temperature, with larger‐bodied species in the suborder Anisoptera (dragonflies) showing a steeper size‐latitude relationship than smaller‐bodied species in the suborder Zygoptera (damselflies). Interestingly, fossil data show that the relationship between wing size and latitude has shifted: latitudinal size trends had initially negative slopes but became shallower or positive following the evolutionary emergence and radiation of birds. Main ConclusionsThe changing size‐latitude trends over geological and macroevolutionary time were likely driven by a combination of predation from birds and maybe pterosaurs and high dispersal ability of large dragonflies. Our study reveals that a simple version of Bergmann's Rule based on temperature alone is not sufficient to explain interspecific size‐latitude trends in Odonata. Our results instead suggest that latitudinal size gradients were shaped not only by temperature but also by avian predators, potentially driving the dispersal of large‐sized clades out of the tropics and into the temperate zone. 

Abstract Numerous mechanisms can promote competitor coexistence. Yet, these mechanisms are often considered in isolation from one another. Consequently, whether multiple mechanisms shaping coexistence combine to promote or constrain species coexistence remains an open question.Here, we aim to understand how multiple mechanisms interact within and between life stages to determine frequency‐dependent population growth, which has a key role stabilizing local competitor coexistence.We conducted field experiments in three lakes manipulating relative frequencies of twoEnallagmadamselfly species to evaluate demographic contributions of three mechanisms affecting different fitness components across the life cycle: the effect of resource competition on individual growth rate, predation shaping mortality rates, and mating harassment determining fecundity. We then used a demographic model that incorporates carry‐over effects between life stages to decompose the relative effect of each fitness component generating frequency‐dependent population growth.This decomposition showed that fitness components combined to increase population growth rates for one species when rare, but they combined to decrease population growth rates for the other species when rare, leading to predicted exclusion in most lakes.Because interactions between fitness components within and between life stages vary among populations, these results show that local coexistence is population specific. Moreover, we show that multiple mechanisms do not necessarily increase competitor coexistence, as they can also combine to yield exclusion. Identifying coexistence mechanisms in other systems will require greater focus on determining contributions of different fitness components across the life cycle shaping competitor coexistence in a way that captures the potential for population‐level variation. 

Abstract Despite the ubiquitous nature of parasitism, how parasitism alters the outcome of host–species interactions such as competition, mutualism and predation remains unknown. Using a phylogenetically informed meta‐analysis of 154 studies, we examined how the mean and variance in the outcomes of species interactions differed between parasitized and non‐parasitized hosts. Overall, parasitism did not significantly affect the mean or variance of host–species interaction outcomes, nor did the shared evolutionary histories of hosts and parasites have an effect. Instead, there was considerable variation in outcomes, ranging from strongly detrimental to strongly beneficial for infected hosts. Trophically‐transmitted parasites increased the negative effects of predation, parasites increased and decreased the negative effects of interspecific competition for parasitized and non‐parasitized heterospecifics, respectively, and parasites had particularly strong negative effects on host species interactions in freshwater and marine habitats, yet were beneficial in terrestrial environments. Our results illuminate the diverse ways in which parasites modify critical linkages in ecological networks, implying that whether the cumulative effects of parasitism are considered detrimental depends not only on the interactions between hosts and their parasites but also on the many other interactions that hosts experience. 

Abstract The extent and magnitude of parasitism often vary among closely related host species and across populations within species. Determining the ecological basis for this species and population‐level variation in parasitism is critical for understanding infection dynamics in multi‐host–parasite systems. To investigate such ecological underpinnings of variation in parasitism, we studiedEnallagmadamselfly host species and their water mite (Arrenurusspp.) ectoparasites in lakes.We first evaluated how host identity and density could shape parasitism. To test the effects of con‐ and heterospecific host density on parasitism, we used a field experiment withEnallagma basidensandE. signatum. We found that parasitism did not vary with con‐ or heterospecific density and was determined by host identity alone, with no spillover effects.We also evaluated the potential role of local adaptation and resource availability in shaping parasitism. To do so, we usedE. signatumin a reciprocal transplant experiment crossed with a prey resource‐level manipulation. This experiment revealed that parasitism declined sharply for one host population in its non‐local lake, but not the other source population, with no effects of prey levels. This asymmetry implies that damselflies express enhanced defences against parasitism that are neither population‐specific nor dependent on resource abundance, or that mites developed heightened local host specificity.The results of multivariate modeling from an observational study generally supported these experimental findings: neither host density nor resource abundance strongly explained among‐population variation in parasitism. Instead, local abiotic conditions (pH) had the strongest relationship with parasitism, with minimal associations with predator density, temperature and a measure of immune function.Collectively, our findings suggest a crucial role for the local environment in shaping host–parasite interactions within multi‐host–parasite systems. More generally, these results show that research at the intersection of community ecology and disease ecology is critical for understanding host–parasite dynamics within natural communities. 

Abstract The neutral theory of biodiversity explored the structure of a community of ecologically equivalent species. Such species are expected to display community drift dynamics analogous to neutral alleles undergoing genetic drift. While entire communities of species are not ecologically equivalent, recent field experiments have documented the existence of guilds of such neutral species embedded in real food webs.What demographic outcomes of the interactions within and between species in these guilds are expected to produce ecological drift versus coexistence remains unclear. To address this issue, and guide empirical testing, we consider models of a guild of ecologically equivalent competitors feeding on a single resource to explore when community drift should manifest.We show that community drift dynamics only emerge when the density‐dependent effects of each species on itself are identical to its density‐dependent effects on every other guild member. In contrast, if each guild member directly limits itself more than it limits the abundance of other guild members, all species in the guild are coexisting, even though they all are ecologically equivalent with respect to their interactions with species outside the guild (i.e. resources, predators, mutualists). Hence, considering only interspecific ecological differences generating density dependence, and not fully accounting for the preponderance of mechanisms causing intraspecific density dependence, will provide an incomplete picture for segregating between neutrality and coexistence. We also identify critical experiments necessary to disentangle guilds of ecologically equivalent species from those experiencing ecological drift, as well as provide an overview of ways of incorporating a mechanistic basis into studies of species coexistence and neutrality.Identifying these characteristics, and the mechanistic basis underlying community structure, is not merely an exercise in clarifying the semantics of coexistence and neutral theories, but rather reflects key differences that must exist among community members in order to determine how and why communities are structured. 

Undergraduate science students who volunteer within a research laboratory group, or participate in funded research opportunities, in general are those who have the opportunity to engage in authentic research. In this article, we report the findings from two different iterations of a semester-long collaboration between a biology faculty member and a science education faculty member at a major research institution in the Southeastern United States. Specifically, the faculty members designed an ecology laboratory course for upper-level undergraduate students (primarily biology majors) where they would engage in an original and highly authentic ecological research project. The goal of this course was to have students explicitly learn about the nature of science (NOS), and authentic scientific practices such as inquiry and experimentation in the context of their own research. In the second year of the course, the global COVID-19 pandemic forced us to modify our approach to accomplish the same goals, but now in a remote and online format. Using questionnaires, concept inventories, and semi-structured interviews, the impact of the course on students’ understandings of NOS, inquiry, and experimentation, in addition to their perspectives on the experience within the course compared to prior laboratory coursework, was investigated. We found that students showed modest gains in each of the aforementioned desirable outcomes. These gains were generally comparable in both face-to-face and remote course settings. Additionally, students shared with us their preference for authentic laboratory work as compared with the typical laboratory work with its given research question and step-by-step instructions. Our research demonstrates what is possible in both face-to-face and remote undergraduate laboratory courses in biology and the positive impact that was observed in our students. We hope it serves as a model for other scientists and science educators as they collaborate to design authentic research-based coursework for undergraduate biology students.