Habitat loss, trophic collapse, and the decline of ecosystem services

The provisioning of sustaining goods and services that we obtain from natural ecosystems is a strong economic justification for the conservation of biological diversity. Understanding the relationship between these goods and services and changes in the size, arrangement, and quality of natural habitats is a fundamental challenge of natural resource management. In this paper, we describe a new approach to assessing the implications of habitat loss for loss of ecosystem services by examining how the provision of different ecosystem services is dominated by species from different trophic levels. We then develop a mathematical model that illustrates how declines in habitat quality and quantity lead to sequential losses of trophic diversity. The model suggests that declines in the provisioning of services will initially be slow but will then accelerate as species from higher trophic levels are lost at faster rates. Comparison of these patterns with empirical examples of ecosystem collapse (and assembly) suggest similar patterns occur in natural systems impacted by anthropogenic change. In general, ecosystem goods and services provided by species in the upper trophic levels will be lost before those provided by species lower in the food chain. The decrease in terrestrial food chain length predicted by the model parallels that observed in the oceans following overexploitation. The large area requirements of higher trophic levels make them as susceptible to extinction as they are in marine systems where they are systematically exploited. Whereas the traditional species-area curve suggests that 50% of species are driven extinct by an order-of-magnitude decline in habitat abundance, this magnitude of loss may represent the loss of an entire trophic level and all the ecosystem services performed by the species on this trophic level.     

Antenatal screening for fetal trisomies using microarray-based cell-free DNA testing: A systematic review and meta-analysis

Objective

To evaluate the test accuracy of non-invasive prenatal testing (NIPT) for fetal trisomy 21, 18, and 13 using cell-free (cf) DNA analysis in maternal plasma with microarray quantitation.

Method

Systematic review and meta-analysis. Searches in MEDLINE, Pre-MEDLINE, EMBASE, Web of Science, and the Cochrane Library to 09.07.2018.

Results

Five studies analyzing 3074 samples, including 187 trisomy 21, 43 trisomy 18, and 19 trisomy 13 cases, were identified. Risk of bias was high in all studies, introduced particularly by exclusions from analysis and by the role of the sponsor. Sensitivity of microarray-based cfDNA testing was 99.5% (95%CI 96.3%-99.9%) for trisomy 21, 97.7% (95%CI 87.9%-99.6%) for trisomy 18, and 100% (95%CI 83.2%-100%) for trisomy 13. Specificity was 100% (95% CI 99.87%-100%) for trisomy 21, 99.97% (95%CI 99.81%-99.99%) for trisomy 18, and 99.97% (95%CI 99.81%-99.99%) for trisomy 13. Pooled test failure rate was 1.1%. A direct comparison of microarray- and sequencing-based cfDNA found equivalent test accuracy.

Conclusion

Included studies suggest that NIPT using microarray-based cfDNA testing has high sensitivity and specificity for detecting fetal trisomy 21, 18, and 13. However, the evidence base is small and at high risk of bias.     

Quantification of pore clogging characteristics in potential permeable reactive barrier (PRB) substrates using image analysis

Permeable reactive barriers (PRBs) are now an established approach for groundwater remediation. However, one concern is the deterioration of barrier material performance due to pore clogging. This study sought to quantify the effect of pore clogging on the alteration of the physical porous architecture of two novel potential PRB materials (clinoptilolite and calcified seaweed) using image analysis of SEM-derived images. Results after a water treatment contaminated with heavy metals over periods of up to 10 months identified a decrease in porosity from c. 22% to c. 15% for calcified seaweed and from c. 22% to c. 18% for clinoptilolite. Porosity was reduced by as much as 37% in a calcified seaweed column that clogged. The mean pore size (2D) of both materials slightly decreased after water treatment with c. 11% reduction in calcified seaweed and c. 7% reduction in clinoptilolite. An increase in the proportion of crack-shaped pores was observed in both materials after the contaminated water treatment, most noticeably in the bottom of columns where contaminated water first reacted with the material. The distribution of pores (within a given image) derived from the distance transform indicated the largest morphological differences in materials was recorded in calcified seaweed columns, which is likely to impact significantly on their performance as barrier materials. The magnitude of porosity reduction over a short time period in relation to predicted barrier longevity suggest these and similar materials may be unsuited for barrier installation in their present form.     

Beyond the money shot; or how framing nature matters? Locating Green at Wildscreen

ABSTRACT

Natural history films use technological mediations to frame aspects of nature so as to communicate information, in part through engendering particular viewer affects. As an entertainment industry embedded in capitalist social relations and concerned with competition for finance and ratings, natural history film-making is also a search for “the money shot” – associated with extremes including rarity, sensational behavior, and otherwise un(fore)seen views. I highlight this sensationalizing impetus through ethnographic fieldwork conducted at the biannual UK Wildscreen film festival in 2010. Here, wildlife films were frequently presented as action dramas with a rhythm of anticipation, climax and satisfaction. I argue that, through stimulating significantly disconnective affects, such framing may work against composition of a caring ecocultural ethics that entwines human with more-than-human natures and futures; and that this tendency parallels the similarly disconnecting effects documented for pornographic film. In contrast, I engage with the differently constructive frames guiding the low budget, open access, activist film Green, which, perhaps paradoxically given the thrust of much of the natural history film industry, won the prestigious WWF Gold Panda Award at Wildscreen 2010. I follow framing theorist George Lakoff to emphasize that since cognition is both embodied and embedded in diverse inter-relationships, affective registers generating mimetic connection are as significant in communicating information regarding “the environment” as the text and words by which nature might be framed. I conclude that attention to affective registers and embodied (dis)connections in natural history film may enhance a turning of capitalist spectacle against itself, so as to work more effectively in service to the composition of abundant socionatural futures.     

Quantification of changes in zero valent iron morphology using X-ray computed tomography

Morphological changes within the porous architecture of laboratory scale zero valent iron （ZVI） permeable reactive barriers （PRBs）, after exposure to different groundwater conditions, have been quantified experimentally for different ZVI/sand ratios （10%, 50% and 100%, W/W） with the aim of inferring porosity changes in field barriers. Column studies were conducted to simulate interaction with different water chemistries, a synthetic groundwater, acidic drainage and deionised （DI） water as control. Morphological changes, in terms of pore size and distribution, were measured using X-ray computed tomography （CT）. CT image analysis revealed significant morphological changes in columns treated with different water chemistries. For example, 100% ZVI （W/W） columns had a higher frequency of small pores （0.6 mm） was observed in ZVI grains reacted with typical groundwater, resulting in a porosity of 27%, compared to 32% when exposed to DI water. In comparison, ZVI grains treated with the acidic drainage had higher porosity （44%） and larger average pore size （2.8 mm）. 10% ZVI PRB barrier material had the highest mean porosity （56%） after exposure to any water chemistry whilst 100% ZVI （W/W） columns always had the lowest （34%） with the 50% ZVI （W/W） in between （40%）. These results agree with previously published PRB field data and simultaneously conducted geochemical monitoring and mass balance calculation, indicating that both the geochemical and hydraulic environment of the PRB play an important role in determining barrier lifespan. This study suggests that X-ray CT image analysis is a powerful tool for studying the detailed inter pores between ZVI grains within PRBs.     

Gastropod herbivory in response to elevated CO2 and N addition impacts plant community composition

In this study, the influence of elevated carbon dioxide (CO2) and nitrogen (N) deposition on gastropod herbivory was investigated for six annual species in a California annual grassland community. These experimentally simulated global changes increased availability of important resources for plant growth, leading to the hypothesis that species with the most positive growth and foliar nutrient responses would experience the greatest increase in herbivory. Counter to the expectations, shifts in tissue N and growth rates caused by N deposition did not predict shifts in herbivore consumption rates. N deposition increased seedling N concentrations and growth rates but did not increase herbivore consumption overall, or for any individual species. Elevated CO2 did not influence growth rates nor have a statistically significant influence on seedling N concentrations. Elevated CO2 at ambient N levels caused a decline in the number of seedlings consumed, but the interaction between CO2 and N addition differed among species. The results of this study indicate that shifting patterns of herbivory will likely influence species composition as environmental conditions change in the future; however, a simple trade-off between shifting growth rates and palatability is not evident.     

The disruption of an ant-aphid mutualism increases the effects of birds on pine herbivores

Predators affect herbivores directly and indirectly, by consumptive and nonconsumptive effects, and the combined influence of multiple predators is shaped by interactions among predators. I documented the individual and combined effects of birds (chickadees, nuthatches, warblers) and ants (Formica podzolica) on arthropods residing in pine (Pinus ponderosa) canopies in a factorial field experiment. Birds and ants removed herbivores but simultaneously benefited them by removing predatory arthropods. Birds and ants had net negative and positive effects, respectively, on the abundance of herbivore prey, supporting the notion that vertebrate predators have stronger negative effects on herbivores than do arthropod predators. Aphids (ant-tended and untended species) constituted three-quarters of herbivore biomass. The effect of birds on ant-tended aphids was twice that on untended aphid species or tended aphid species without ants. This was not due to there being more ant-tended aphids for birds to prey on; tended and untended aphid species were in similar abundances in the absence of birds. Instead, the effects of birds were strengthened by attributes of the mutualism that rendered tended aphids susceptible to predation. These dynamics led to nonadditive effects of birds and ants: birds only reduced tended aphid species and total herbivore abundances on trees with ants, while ants only increased tended aphid species and total herbivore abundances in the absence of birds. Consequently, top predators in this system only influenced total herbivore abundance when they disrupted an ant-aphid mutualism.