Costs and benefits of capsaicin-mediated control of gut retention in dispersers of wild chilies

A fundamental way in which animal-dispersed plants can influence the viability and distribution of dispersed seeds is through control of retention time in the guts of dispersers. Using two species of wild chilies and their dispersers, we examined how chemical and physical properties of fruits and seeds mediate this interaction. Capsicum chacoense is polymorphic for pungency, occurs in Bolivia, and is dispersed mostly by elaenias. Capsicum annuum is not polymorphic, occurs in Arizona (USA), and is dispersed mostly by thrashers. We first tested whether capsaicin, the substance responsible for the pungency of chilies, affects gut retention time of seeds in primary dispersers. Capsaicin slowed gut passage of seeds but did so in a manner that differed greatly between bird species because the constipative effects of capsaicin occurred only after an 80-minute time lag. Elaenias in Bolivia held only 6% of C. chacoense seeds for > 80 minutes, whereas thrashers in Arizona held 78% of C. annuum seeds for > 80 minutes. Next we examined the effects of retention time on seed viability and germination. Increased retention resulted in a greater proportion of seeds germinating in C. annuum, had no effects on non-pungent C. chacoense, and had negative effects on pungent C. chacoense. These divergent effects are explained by differences in seed coat morphology: seed coats of pungent C. chacoense are 10-12% thinner than those of the other two types of seeds. Thus, longer retention times damaged seeds with the thinnest seed coats. In C. annuum, seed viability remained high regardless of retention time, but germination increased with retention, suggesting a role for scarification. Thus, in C. annuum, fruit chemistry appears well matched with seed morphology and disperser physiology: capsaicin extends gut retention for most seeds, resulting in greater seed scarification and higher germination rates. Increased retention of pungent C. chacoense seeds is detrimental, but because the primary consumers have short retention times, capsaicin slows only a small proportion of seeds, minimizing negative effects. These results illustrate the importance of context in studies of fruit secondary metabolites. The same chemical can have different impacts on plant fitness depending on its morphological, physiological, and ecological context.     

Invasion patterns inferred from cytochrome oxidase I sequences in three bryozoans, Bugula neritina, Watersipora subtorquata, and Watersipora arcuata

Nucleotide variation in cytochrome c oxidase subunit I (COI) was used to examine population structure in three invasive bryozoans: Bugula neritina (Linnaeus, 1758), Watersipora subtorquata (d’Orbigny, 1852), and W. arcuata (Banta, 1969). These species are found on ship hulls and have a short (≤2 days) larval phase. Samples were collected from 1998–2001 at multiple sites in Australia, and in Hong Kong, New Zealand, Hawaii, California, Curaçao, and England. B. neritina is known to include three cryptic species, including species Type S (Davidson and Haygood in Biol Bull 196:273–280, 1999) which occurs on the east and west coasts of the USA. One haplotype recorded previously in the USA, S1, was found to be widespread, occurring throughout Australia and in Hong Kong, Curaçao, Hawaii, and England. W. subtorquata, a Caribbean–Atlantic species which has invaded southern Australia, New Zealand, and California, had low nucleotide diversity in these areas (π=0.0016±0.0014), consisting of three haplotypes connected by one or two nucleotide mutations. W. arcuata, an Eastern-Pacific native, had comparatively high diversity (π=0.0221±0.0115) in introduced populations from Australia and Hawaii. In each species, identical haplotypes were identified on separate coastlines providing evidence of widespread, rather than genetically independent, introductions. The major contrast in nucleotide diversity suggests that different propagule-source models explain introductions.     

Modeling the nexus between coal consumption,FDI inflow and economic expansion: does industrialization matter in South Africa?

Environmental Science and Pollution Research - This study examines the role of industrialization in the energy-growth-FDI nexus for the case of South Africa using data over the period 1970 to 2018....     

Optimal Environmental Health Regulations with Heterogeneous Populations: Treatment versus “Tagging”

In this paper, we develop a model of population level environmental health risk with individuals that are heterogeneous in their susceptibility to environmental toxins. This framework allows us to determine when it is optimal to target vulnerable subgroups of the population with special exposure-reducing treatments. Our analytic results show that the potential economic gains from targeted policies will depend critically on the quality of existing capital, the degree of returns to scale in treatment technologies, and the size and sensitivity of the vulnerable population. An empirical application of the model is extended to the case of cryptosporidium in drinking water supplies.     

Divergence in sink contributions to population persistence

Population sinks present unique conservation challenges. The loss of individuals in sinks can compromise persistence; but conversely, sinks can improve viability by improving connectivity and facilitating the recolonization of vacant sources. To assess the contribution of sinks to regional population persistence of declining populations, we simulated source–sink dynamics for 3 very different endangered species: Black‐capped Vireos (Vireo atricapilla) at Fort Hood, Texas, Ord's kangaroo rats (Dipodomys ordii) in Alberta, and Northern Spotted Owls (Strix occidentalis caurina) in the northwestern United States. We used empirical data from these case studies to parameterize spatially explicit individual‐based models. We then used the models to quantify population abundance and persistence with and without long‐term sinks. The contributions of sink habitats varied widely. Sinks were detrimental, particularly when they functioned as strong sinks with few emigrants in declining populations (e.g., Alberta's Ord's kangaroo rat) and benign in robust populations (e.g., Black‐capped Vireos) when Brown‐headed Cowbird (Molothrus ater) parasitism was controlled. Sinks, including ecological traps, were also crucial in delaying declines when there were few sources (e.g., in Black‐capped Vireo populations with no Cowbird control). Sink contributions were also nuanced. For example, sinks that supported large, variable populations were subject to greater extinction risk (e.g., Northern Spotted Owls). In each of our case studies, new context‐dependent sinks emerged, underscoring the dynamic nature of sources and sinks and the need for frequent re‐assessment. Our results imply that management actions based on assumptions that sink habitats are generally harmful or helpful risk undermining conservation efforts for declining populations.     

INFLUENCES OF SOIL DATASET RESOLUTION ON HYDROLOGIC MODELING1

ABSTRACT: Soils represent a fundamental abiotic parameter in defining the characteristics of an ecosystem. The U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) produces the most detailed digital spatial soil datasets that are publicly available. The Soil Survey Geographic (SSURGO) database contains basic attributes for the continuous coverage of soils across the United States. In its standard format, the SSURGO database is incompatible for use within the ArcView Soil and Water Assessment Tool (SWAT). A modified version of the State Soil and Geographic (STATSGO) database is the template soils dataset used by ArcView SWAT. This paper presents the methodology and development of a SSURGO database preprocessor extension for the ArcView SWAT model. A case study for the Upper Sabinal River Watershed near Uvalde, Texas, is given. Results indicate that hydro‐logic output parameter differences occur when comparing the STATSGO and SSURGO database information in the ArcView SWAT model under identical modeling conditions. Specifically, the SSURGO model produced a greater daily mean water yield with evapotranspiration and surface runoff being found consistently lower across the watershed. The most likely causes assigned to this phenomenon were higher percolation and resulting ground water return flow values due to significantly larger saturated hydraulic conductivity values associated with the SSURGO 2.x database.     

Building phenological models from presence/absence data for a butterfly fauna.

Species phenology is increasingly being used to explore the effects of climate change and other environmental stressors. Long-term monitoring data sets are essential for understanding both patterns manifest by individual species and more complex patterns evident at the community level. This study used records of 78 butterfly species observed on 626 days across 27 years at a site in northern California, USA, to build quadratic logistic regression models of the observation probability of each species for each day of the year. Daily species probabilities were summed to develop a potential aggregate species richness (PASR) model, indicating expected daily species richness. Daily positive and negative contributions to PASR were calculated, which can be used to target optimum sampling time frames. Residuals to PASR indicate a rate of decline of 0.12 species per year over the course of the study. When PASR was calculated for wet and dry years, wet years were found to delay group phenology by up to 17 days and reduce the maximum annual expected species from 32.36 to 30. Three tests to determine how well the PASR model reflected the butterfly fauna dynamics were all positive: We correlated probabilities developed with species presence/absence data to observed abundance by species, tested species' predicted phenological patterns against known biological characteristics, and compared the PASR curve to a spline-fitted curve calculated from the original species richness observations. Modeling individual species' flight windows was possible from presence/absence data, an approach that could be used on other similar records for butterfly communities with seasonal phenologies, and for common species with far fewer dates than used here. It also provided a method to assess sample frequency guidelines for other butterfly monitoring programs.     

The use of Monte Carlo simulation techniques to predict population blood lead levels

Effective management of the risks posed by lead depends on an understanding of the relationship between exposure (the presence and accessibility of lead in the environment) and dose (blood lead levels). Our paper begins by outlining the type of information most valuable to a decision maker addressing the lead problem. A useful exposure-dose characterisation must address multiple contamination sources simultaneously, provide estimates of the number of people with blood lead levels exceeding critical thresholds, and assess the influence of modifying factors (e.g. the soil and dust ingestion rate) on population blood lead variability. We describe a pilot effort to develop an urban setting lead exposure-dose model, and use this model to compare three approaches for generating model input quantities: (1) worst-case estimates, (2) central estimates and (3) Monte Carlo simulation. Using the criteria outlined above, we find that the Monte Carlo technique provides the most useful model output. We describe the population blood lead level distribution generated by the model, as well as the relative influence of environmental and behavioural factors on the variability of the population distribution. Finally, we assess the impact of parameter uncertainty on the model output, and contend this type of information can help identify areas in which further empirical study would be most valuable.