Author: Claire Teitelbaum

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).