Month: March 2017

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Do low oxygen environments facilitate marine invasions? Relative tolerance of native and invasive species to low oxygen conditions

Authors: Marcelo E Lagos, Diego R Barneche, Craig R White, and Dustin J Marshall

Published in: Global Change Biology (early view)

Abstract

Biological invasions are one of the biggest threats to global biodiversity.

Marine artificial structures are proliferating worldwide and provide a haven for marine invasive species. Such structures disrupt local hydrodynamics, which can lead to the formation of oxygen-depleted microsites.

The extent to which native fauna can cope with such low oxygen conditions, and whether invasive species, long associated with artificial structures in flow-restricted habitats, have adapted to these conditions remains unclear.

We measured water flow and oxygen availability in marinas and piers at the scales relevant to sessile marine invertebrates (mm). We then measured the capacity of invasive and native marine invertebrates to maintain metabolic rates under decreasing levels of oxygen using standard laboratory assays.

We found that marinas reduce water flow relative to piers, and that local oxygen levels can be zero in low flow conditions. We also found that for species with erect growth forms, invasive species can tolerate much lower levels of oxygen relative to native species.

Integrating the field and laboratory data showed that up to 30% of available microhabitats within low flow environments are physiologically stressful for native species, while only 18% of the same habitat is physiologically stressful for invasive species.

These results suggest that invasive species have adapted to low oxygen habitats associated with manmade habitats, and artificial structures may be creating niche opportunities for invasive species.

Citation

Lagos ME, Barneche DR, White CR, Marshall DJ (2017) Do low oxygen environments facilitate marine invasions? Relative tolerance of native and invasive species to low oxygen conditions. Global Change Biology PDF 1 MB doi:10.1111/gcb.13668

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Field manipulations of resources mediate the transition from intraspecific competition to facilitation

Authors: Karin Svanfeldt, Keyne Monro, and Dustin J Marshall

Published in: Journal of Animal Ecology, volume 86, issue 3 (May 2017)

Summary

Population density affects individual performance, though its effects are often mixed. For sessile species, increases in population density typically reduce performance. Still, cases of positive density-dependence do occur in sessile systems and demand explanation. The stress gradient hypothesis (SGH) predicts that under stressful conditions, positive effects of facilitation may outweigh the negative effects of competition.

While some elements of the SGH are well studied, its potential to explain intraspecific facilitation has received little attention. Further, there have been questions regarding whether the SGH holds if the stressor is a resource. Most studies of interactions between the environment and intraspecific facilitation have relied on natural environmental gradients; manipulative studies are much rarer.

To test the effects of intraspecific density and resources, we manipulated resource availability over natural population densities for the marine bryozoan Watersipora subtorquata.

We found negative effects of density on colony performance in low resource environments, but mainly positive density-dependence in high resource environments. By adding resources, competition effects were reduced and the positive effects of facilitation were revealed.

Our results suggest that resource availability mediates the relative strength of competition and facilitation in our system. We also suggest that intraspecific facilitation is more common than may be appreciated and that environmental variation may mediate the balance between negative and positive density-dependence.

Citation

Svanfeldt K, Monro K, Marshall DJ (2017) Field manipulations of resources mediate the transition from intraspecific competition to facilitation. Journal of Animal Ecology, PDF 233 KB doi:10.1111/1365-2656.12644

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Estimating monotonic rates from biological data using local linear regression

Authors: Colin Olito, Craig R White, Dustin J Marshall and Diego R Barneche

Published in: Journal of Experimental Biology, volume 220, number 5 (March 2017)

Abstract

Accessing many fundamental questions in biology begins with empirical estimation of simple monotonic rates of underlying biological processes. Across a variety of disciplines, ranging from physiology to biogeochemistry, these rates are routinely estimated from non-linear and noisy time series data using linear regression and ad hoc manual truncation of non-linearities.

Here, we introduce the R package LoLinR, a flexible toolkit to implement local linear regression techniques to objectively and reproducibly estimate monotonic biological rates from non-linear time series data, and demonstrate possible applications using metabolic rate data.

LoLinR provides methods to easily and reliably estimate monotonic rates from time series data in a way that is statistically robust, facilitates reproducible research and is applicable to a wide variety of research disciplines in the biological sciences.

Citation

Olito C, White CR, Marshall DJ, Barneche DR (2017) Estimating monotonic rates from biological data using local linear regression, Journal of Experimental Biology, 220: 759‒764 PDF 617 KB doi: 10.1242/jeb.148775