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The enterprise of conservation is inherently ethical, requiring conservationists to navigate morally challenging problems. Working together, conservationists and ethicists have developed the field of conservation ethics. Yet, due to the deeply interdisciplinary nature of the field, conservation ethics faces a unique set of challenges. We first comment on the harm caused by reciprocal ignorance between some practicing conservationists and ethicists. We then explore the difficulties of creating a widely applied ethic, examining conversations surrounding the recently emerged virtue ethic, Compassionate Conservation. By bringing attention to these challenges, and highlighting medical bioethics as a touchstone of productive applied ethical theory, we can help the field avoid unproductive pitfalls, as well as facilitate positive and productive communication and collaboration between the various members of the different disciplines involved.

We present four datasets that provide information on primary production, nitrogen (N) uptake and allocation in two salt marsh grasses, short-form Spartina alterniflora and Distichlis spicata. These four datasets were generated during a month-long stable isotope (15N) tracer study described in the companion manuscript (Hill et al., 2018). They include an allometry dataset containing mass and height data for individual plants harvested from Colt State Park, Bristol, Rhode Island and used to nondestructively estimate plant masses. A second dataset contains weekly stem height measurements collected over the course of the 15N tracer study. Also included are high resolution data from 49 vegetated compartments (leaves, stems, fine/coarse roots, rhizomes) and bulk sediment depth intervals, reporting the mass, carbon and N concentrations, and stable isotope ratios measured following the harvest of cores over time. Additionally, we provide a complementary dataset with estimates of microbial removal from potential and ambient denitrification enzyme assays. These data, along with source code used in their analysis, are compiled in the NitrogenUptake2016 R package available from the Comprehensive R Archive Network.

Background In old field systems, the common woodlouse may have an indirect effect on a nursery web spider. Woodlice and nursery web spiders feed in different food chains, yet previous work demonstrated that the presence of woodlice is correlated with higher predation success by nursery web spiders upon their grasshopper prey. This finding suggested a new hypothesis which links two seemingly disparate food chains: when woodlice are present, the spider predator or the grasshopper prey changes their location in the vegetative canopy in a way that increases their spatial overlap and therefore predation rate. However, warming temperatures may complicate this phenomenon. The spider cannot tolerate thermal stress, meaning warming temperatures may cause the spider to move downwards in the vegetative canopy or otherwise alter its response to woodlice. Therefore, we would expect warming and woodlice presence to have an interactive effect on predation rate. Methods We conducted behavioral experiments in 2015, 2017, and 2018 to track habitat domains—the use of the vegetative canopy space by grasshoppers and spiders—in experimental cages. Then, we used three models of spider movement to try to explain the response of spiders to woodlice: expected net energy gain, signal detection theory, and individual-based modelling. Results Habitat domain observations revealed that spiders shift upward in the canopy when woodlice are present, but the corresponding effect on grasshopper prey survival was variable over the different years of study. Under warming conditions, spiders remained lower in the canopy regardless of the presence of woodlice, suggesting that thermal stress is more important than the effect of woodlice. Our modelling results suggest that spiders do not need to move away from woodlice to maximize net energy gain (expected net energy gain and signal detection theory models). Instead spider behavior is consistent with the null hypothesis that they move away from unsuccessful encounters with woodlice (individual-based simulation). We conclude that mapping how predator behavior changes across biotic (e.g. woodlouse presence) and abiotic conditions (e.g. temperature) may be critical to anticipate changes in ecosystem dynamics.

Salt marshes have the potential to intercept nitrogen that could otherwise impact coastal water quality. Salt marsh plants play a central role in nutrient interception by retaining N in above- and belowground tissues. We examine N uptake and allocation in two dominant salt marsh plants, short-form Spartina alterniflora and Distichlis spicata. Nitrogen uptake was measured using 15N tracer experiments conducted over a four-week period, supplemented with stem-level growth rates, primary production, and microbial denitrification assays. By varying experiment duration, we identify the importance of a rarely-measured aspect of experimental design in 15N tracer studies. Experiment duration had a greater impact on quantitative N uptake estimates than primary production or stem-level relative growth rates. Rapid initial scavenging of added 15N caused apparent nitrogen uptake rates to decline by a factor of two as experiment duration increased from one week to one month, although each experiment shared the qualitative conclusion that Distichlis roots scavenged N approximately twice as rapidly as Spartina. We estimate total N uptake into above- and belowground tissues as 154 and 277 mg N·m-2·d-1 for Spartina and Distichlis, respectively. Driving this pattern were higher N content in Distichlis leaves and belowground tissue and strong differences in primary production; Spartina and Distichlis produced 8.8 and 14.7 g biomass·m-2·d-1. Denitrification potentials were similar in sediment associated with both species, but the strong species-specific difference in N uptake suggests that Distichlis-dominated marshes are likely to intercept more N from coastal waters than are short-form Spartina marshes. The data and source code for this manuscript are available as an R package from https://github.com/troyhill/NitrogenUptake2016.

Classic bottom-up theory predicts that increased resource availability (for example, nutrients) at the base of the food web will stimulate primary production and, in turn, secondary production. Recent studies, however, indicate that bottom-up controls on food web production can be modified by other factors, such as landscape configuration and continuity. As part of a 10-year ecosystem-scale experiment in a New England salt marsh, we investigated the response of secondary consumers, specifically a fish, the mummichog (Fundulus heteroclitus), to nutrient enrichment. In the first 6 years, we observed a classic bottom-up response of increased production of algae, invertebrate prey, and mummichogs. After the sixth year, however, mummichog biomass declined to below reference levels by the eighth year. This decline in mummichog biomass coincided with nutrient-induced collapse of the low-marsh habitat. Based on stable isotope analyses, field surveys, and small-scale experiments, we suggest that the geomorphic changes induced a trophic decoupling between creek and marsh habitats, thereby reducing mummichog access to prey in the intermittently flooded marsh. Thus, despite continued stimulation of algal and invertebrate prey production, fish abundances declined to below pre-enrichment levels. Our results demonstrate how geomorphic controls can override classic bottom-up control and emphasize the importance of long-term studies in detecting the response of slow-turnover phenomena (for example, changing landscapes).

Salt marshes have the potential to intercept nitrogen that could otherwise impact coastal water quality. Salt marsh plants play a central role in nutrient interception by retaining N in above- and belowground tissues. We examine N uptake and allocation in two dominant salt marsh plants, short-form Spartina alterniflora and Distichlis spicata. Nitrogen uptake was measured using (15)N tracer experiments conducted over a four-week period, supplemented with stem-level growth rates, primary production, and microbial denitrification assays. By varying experiment duration, we identify the importance of a rarely-measured aspect of experimental design in (15)N tracer studies. Experiment duration had a greater impact on quantitative N uptake estimates than primary production or stem-level relative growth rates. Rapid initial scavenging of added (15)N caused apparent nitrogen uptake rates to decline by a factor of two as experiment duration increased from one week to one month, although each experiment shared the qualitative conclusion that Distichlis roots scavenged N approximately twice as rapidly as Spartina. We estimate total N uptake into above- and belowground tissues as 154 and 277 mg N·m(−2)·d(−1) for Spartina and Distichlis, respectively. Driving this pattern were higher N content in Distichlis leaves and belowground tissue and strong differences in primary production; Spartina and Distichlis produced 8.8 and 14.7 g biomass·m(−2)·d(−1). Denitrification potentials were similar in sediment associated with both species, but the strong species-specific difference in N uptake suggests that Distichlis-dominated marshes are likely to intercept more N from coastal waters than are short-form Spartina marshes. The data and source code for this manuscript are available as an R package from https://github.com/troyhill/NitrogenUptake2016.

We present four datasets that provide information on primary production, nitrogen (N) uptake and allocation in two salt marsh grasses, short-form Spartina alterniflora and Distichlis spicata. These four datasets were generated during a month-long stable isotope (15N) tracer study described in the companion manuscript (Hill et al., 2018). They include an allometry dataset containing mass and height data for individual plants harvested from Colt State Park, Bristol, Rhode Island and used to nondestructively estimate plant masses. A second dataset contains weekly stem height measurements collected over the course of the 15N tracer study. Also included are high resolution data from 49 vegetated compartments (leaves, stems, fine/coarse roots, rhizomes) and bulk sediment depth intervals, reporting the mass, carbon and N concentrations, and stable isotope ratios measured following the harvest of cores over time. Additionally, we provide a complementary dataset with estimates of microbial removal from potential and ambient denitrification enzyme assays. These data, along with source code used in their analysis, are compiled in the NitrogenUptake2016 R package available from the Comprehensive R Archive Network.