Mucus-net producing snails modify water flow and molecular transport potential over corals and coral-algal interactions

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.

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

Native Lake Sturgeon eat more fish (and sooner) in response to Round Goby invasion: A silver lining to an invasive cloud?

Species invasions are ubiquitous in ecosystems across the world, and the Laurentian Great Lakes ecosystem is no exception. Round Goby, a small benthic fish species, have invaded each of the Great Lakes, spreading to Lake Ontario by 2002. The Great Lakes are home to a number of native fish species that are imperiled and of high conservation interest. One of these is the Lake Sturgeon, of which relatively few relict populations still persist, and for which population densities are far below historical records. This paper presents evidence that invasive Round Goby in Lake Ontario are not only eaten by Lake Sturgeon, a large-bodied benthic consumer and putative invertivore, they’ve allowed Lake Sturgeon to shift feeding ecology toward increased predation on fish at smaller size and younger age. The net effect of Round Goby on Lake Sturgeon in this system is still poorly understood: the effects of other species interactions between Round Goby and Lake Sturgeon, and the indirect effects of shifting food web structure on Lake Sturgeon are unknown. However, the shift in feeding ontogeny we document may actually have a positive effect on Lake Sturgeon access higher-quality prey (namely Round Goby) at smaller size and younger age; thereby eating more fish, and sooner. This highlights the complexity of ecosystem responses to species invasions. Though Round Goby have had a strong negative overall effect on the Great Lakes system, the shift in Lake Sturgeon feeding ecology we observe may have a positive effect on this native species.

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Jacobs, G. R., Bruestle, E. L., Hussey, A., Gorsky, D., & Fisk, A. T. (2017). Invasive species alter ontogenetic shifts in the trophic ecology of Lake Sturgeon (Acipenser fulvescens) in the Niagara River and Lake Ontario. Biological Invasions, 10(5), 1533–1546.

Photos from the 2017 Graduate Student Symposium

GSS 2017 was on January 27 and 28. Here are a few photos of the talks, posters and activities from the weekend.

Heterogeneity in patch quality buffers metapopulations from pathogen impacts

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.

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Becker, D.J., and Hall, R.J. (2016). Heterogeneity in patch quality buffers metapopulations from pathogen impacts. Theoretical Ecology 9, 197–205.

Predictors and immunological correlates of sublethal mercury exposure in vampire bats

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

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Becker, D.J., Chumchal, M.M., Bentz, A.B., Platt, S.G., Czirják, G.Á., Rainwater, T.R., Altizer, S., and Streicker, D.G. (2017). Predictors and immunological correlates of sublethal mercury exposure in vampire bats. Royal Society Open Science 4, 170073.

North America’s freshwater lakes are getting saltier

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.

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Dugan, H.A., Bartlett, S.L., Burke, S.M., Doubek, J.P., Krivak-Tetley, F.E., Skaff, N.K., Summers, J.C., Farrell, K.J., McCullough, I.M., Morales-Williams, A.M., et al. (2017). Salting our freshwater lakes. PNAS 201620211.

Experience drives innovation of new migration patterns of whooping cranes in response to global change

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.

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Teitelbaum, Claire S., Sarah J. Converse, William F. Fagan, Katrin Böhning-Gaese, Robert B. O’Hara, Anne E. Lacy, and Thomas Mueller. “Experience Drives Innovation of New Migration Patterns of Whooping Cranes in Response to Global Change.” Nature Communications 7 (September 6, 2016): 12793. doi:10.1038/ncomms12793.