Category: GSO Paper

Effective conservation of freshwater biodiversity requires spatially explicit investigations of how dams and hydroclimatic alterations among climate regions may interact to drive species to extinction. We investigated how dams and hydroclimatic alterations interact with species ecological and life history traits to influence past extirpation probabilities of native freshwater fishes in river basins in the southwestern and southeastern US. Using long-term data from stream and river gages, we related extirpation probabilities of native fishes in both regions to streamflow anomalies, river basin characteristics, species traits, and non-native species richness using binomial logistic regression. Extirpations in the Southwest were highest in lowland mainstem rivers impacted by large dams and in desert springs. Dampened flow seasonality, increased longevity (i.e., delayed reproduction), and decreased fish egg sizes (i.e., lower parental care) were related to elevated fish extirpation probability in the Southwest. Extirpations in the Southeast were most prevalent in upland rivers in species with flow dependency, greater age and length at maturity, isolation by dams, and at a greater distance upstream. Our results confirm that dams are an overriding driver of native fish species losses, irrespective of basin-wide differences in native or non-native species richness. Dams and hydrologic alterations interact with species traits to influence community disassembly, and very high extirpation risks in the Southeast are due to interactions between high dam density and species restricted ranges. Given global surges in dam building and retrofitting, increased extirpation risks should be expected unless management strategies that balance flow regulation with ecological outcomes are widely implemented.

See full text at: https://doi.org/10.1111/gcb.13940

Kominoski, J.S., Ruhí, A., Hagler, M.M., Petersen, Kelly, Sabo, J.L., Sinha, T., Sankarasubramanian, A., & Olden, J.D. (2018). Patterns and drivers of fish extirpations in rivers of the American Southwest and Southeast. Global Change Biology, 24(3), 1175-1185.

Long-distance animal movements can increase exposure to diverse parasites, but can also reduce infection risk through escape from contaminated habitats or culling of infected individuals. These mechanisms have been demonstrated within and between populations in single-host/single-parasite interactions, but how long-distance movement behaviours shape parasite diversity and prevalence across host taxa is largely unknown. Using a comparative approach, we analyse the parasite communities of 93 migratory, nomadic and resident ungulate species. We find that migrants have higher parasite species richness than residents or nomads, even after considering other factors known to influence parasite diversity, such as body size and host geographical range area. Further analyses support a novel ‘environmental tracking’ hypothesis, whereby migration allows parasites to experience environments favourable to transmission year-round. In addition, the social aggregation and large group sizes that facilitate migration might increase infection risk for migrants. By contrast, we find little support for previously proposed hypotheses, including migratory escape and culling, in explaining the relationship between host movement and parasitism in mammals at this cross-species scale. Our findings, which support mechanistic links between long-distance movement and increased parasite richness at the species level, could help predict the effects of future environmental change on parasitism in migratory animals.

See full text at: https://doi.org/10.1098/rspb.2018.0089

Teitelbaum, C.S., Huang, S., Hall, R.J. & Altizer, S. (2018). Migratory behaviour predicts greater parasite diversity in ungulates. Proceedings of the Royal Society B: Biological Sciences, 285(1875), 1-8.

Interaction modifications arise when a third species alters the strength and direction of a pairwise interaction. One way in which an interaction modifier can influence an interaction is through changing the physical environment and creating conditions that favor one species over another. On coral reefs, coral-algal competition is a wide-spread phenomenon that can be modified by water flow. Additionally, sessile (stationary), net-producing vermetid gastropods can be ubiquitous and known to negatively affect coral growth and survival. Although the putative mechanism underlying the snail’s effect is the mucus net, how the net may affect corals was unknown. In our paper, we showed that the mucus net modified water flow and the thickness of the diffusive boundary layer (the region in which molecular transport occurs) over corals and over coral-algal interactions. Our results suggest that the negative effects of vermetids on corals are due to the trapping of noxious conditions over coral surfaces, which likely intensifies competition between corals and algae.

See full text at: https://doi.org/10.1007/s00442-018-4091-9

Brown, A.L. & Osenberg, C.W. (2018). Vermetid gastropods modify physical and chemical conditions above coral–algal interactions. Oecologia (online early).

Many wildlife species persist on a network of ephemerally occupied habitat patches connected by dispersal. Provisioning of food and other resources for conservation management or recreation is frequently used to improve local habitat quality and attract wildlife. Resource improvement can also facilitate local pathogen transmission, but the landscape-level consequences of provisioning for pathogen spread and habitat occupancy are poorly understood. Here, we develop a simple metapopulation model to investigate how heterogeneity in patch quality resulting from resource improvement influences long-term metapopulation occupancy in the presence of a virulent pathogen. We derive expressions for equilibrium host–pathogen outcomes in terms of provisioning effects on individual patches (through decreased patch extinction rates) and at the landscape level (the fraction of high-quality, provisioned patches), and highlight two cases of practical concern. First, if occupancy in the unprovisioned metapopulation is sufficiently low, a local maximum in occupancy occurs for mixtures of high- and low-quality patches, such that further increasing the number of high-quality patches both lowers occupancy and allows pathogen invasion. Second, if the pathogen persists in the unprovisioned metapopulation, further provisioning can result in all patches becoming infected and in a global minimum in occupancy. This work highlights the need for more empirical research on landscape-level impacts of local resource provisioning on pathogen dynamics.

Mercury is a widespread and pervasive contaminant, and chronic exposure to mercury can impair host immune defense and susceptibility to infections. However, the relationship between mercury and immunity is unknown for bats, which appear immunologically distinct from other mammals and are reservoirs of many pathogens important to human and animal health. Our study quantified mercury in hair collected from blood-feeding vampire bats (Desmodus rotundus) in two populations from Belize. Bats that foraged more consistently on domestic animals exhibited higher mercury. However, relationships between diet and mercury were evident only in 2015 but not in 2014, which could reflect recent environmental perturbations associated with agriculture. Mercury concentrations were low relative to values observed in other bat species but still correlated with vampire bat immunity. Bats with higher mercury had more neutrophils, weaker bacterial killing ability, and impaired innate immunity. These patterns suggest that temporal variation in mercury exposure may impair bat innate immunity and increase susceptibility to pathogens such as bacteria. Unexpected associations between low-level mercury exposure and immune function underscore the need to better understand the environmental sources of mercury exposure in bats and the consequences for bat immunity and susceptibility

Road salts and brines can help keep roads passable during winter weather, but road salts are also affecting lake chloride concentrations through runoff. A new study completed as part of the GLEON Fellowship Program, and just published in PNAS, found that increasing lake salinity may be widespread, particularly in north temperate ecosystems, which are home to the highest densities of lakes on Earth. Led by Hilary Dugan, the team, including GSO member Kait Farrell, identified decadal trends in chloride concentrations from 371 North American lakes, and found that impervious surface cover, or the amount of paved surfaces in a watershed, is a strong predictor of chloride trends in lakes. Worryingly, as little as 1% impervious surface cover near a lake may increase the risk of long-term salinization, and the potential for steady and long-term salinization of many lakes in the US is high. Even in Georgia, where we apply less road salt than in the focal study area, it is important to track long-term chloride trends in lakes and reservoirs, as urbanization and agriculture can also contribute to increasing salinization, which can diminish the ecosystem services lakes and reservoirs provide.

Read the full article at https://doi.org/10.1073/pnas.1620211114

Animal migration patterns are changing in response to changes in climate and land use, and these changes could be important for survival of migratory species. These changes, which are adaptations to a changing environment, can happen very quickly, but so far studies have focused on evolutionary changes, which may be too slow to be effective in a rapidly changing world. We used long-term monitoring data of whooping cranes to show that migration patterns can change within an individual’s life and, further, that these changes are initiated by older, experienced birds and then spread to younger birds. This results suggests that maintaining older individuals in a population may be important for effective behavioral adaptation to changing environments.

Read the full article at https://doi.org/10.1038/ncomms12793

Mosquito-borne diseases are emerging and spreading to new areas each year, often catching us unaware.  Zika virus, for example, although discovered in 1947, was relatively unknown until it spread to the Americas in 2014, where it caused over 100,000 cases in Brazil alone. While we now recognize the public health importance of Zika, we still know little about the ecology of the disease, including which mosquitoes are capable of transmitting it. There are hundreds of mosquito species, and testing all of them is difficult, if not impossible. To identify unknown vectors of Zika, we developed a model linking vector species and the Zika virus via vector-virus trait combinations that confer a propensity toward associations in an an ecological network connecting flaviviruses and their mosquito vectors. Our model predicts that thirty-five species may be able to transmit the virus, seven of which are found in the continental United States, including Culex quinquefasciatus and Cx. pipiens. Together, the ranges of the seven American species encompass the whole United States, suggesting Zika virus could affect a much larger area than previously anticipated. We suggest that empirical studies prioritize these species to confirm predictions of vector competence, enabling the correct identification of populations at risk for transmission within the United States.

Read the full article at http://dx.doi.org/10.7554/eLife.22053

Evans, Michelle V., Tad A. Dallas, Barbara A. Han, Courtney C. Murdock, and John M. Drake. 2017. “Data-Driven Identification of Potential Zika Virus Vectors.” eLife 6 (February): e22053. doi:10.7554/eLife.22053.

Every population has a basic set of requirements needed to survive, like having at least two individuals: a male and female. The concept of a minimum number of individuals needed for population survival or an Allee effect applies beyond reproduction. For example, meerkats cooperate to detect predators. More meerkats means individuals can spend more time foraging, taking care of young, etc. There are many examples for large species, but what about bacteria? We demonstrate that an Allee effect can also impact asexual bacterial populations, which were previously thought to be exempt. This will impact how scientists manage harmful and helpful bacterial populations.

Read the full article at https://doi.org/10.1098/rsbl.2016.0070

R. B. Kaul, A. M. Kramer, F. C. Dobbs, and J. M. Drake. Experimental demonstration of an Allee effect in microbial populations. Biology Letters, 12(4) Apr. 2016. ISSN 1545-7885.