Epanchin P.N.,University of California at Davis |
Epanchin P.N.,University of California at Berkeley |
Knapp R.A.,University of the Sierra |
Lawler S.P.,University of California at Davis
Ecology | Year: 2010
Adjacent food webs may be linked by cross-boundary subsidies: moreproductive donor systems can subsidize consumers in less-productive neighboring recipient systems. Introduced species are known to have direct effects on organisms within invaded communities. However, few studies have addressed the indirect effects of nonnative species in donor systems on organisms in recipient systems. We studied the direct role of introduced trout in altering a lake-derived resource subsidy and their indirect effects in altering a passerine bird's response to that subsidy. We compared the abundance of aquatic insects and foraging Gray-crowned Rosy-Finches (Leucosticte tephrocotis dawsoni, "Rosy-Finch") at fishcontaining vs. fishless lakes in the Sierra Nevada Mountains of California (USA). Introduced trout outcompeted Rosy-Finches for emerging aquatic insects (i.e., mayflies). Fish-containing lakes had 98% fewer mayflies than did fishless lakes. In lakes without fish, Rosy-Finches showed an aggregative response to emerging aquatic insects with 5.9 times more Rosy-Finches at fishless lakes than at fish-containing lakes. Therefore, the introduction of nonnative fish into the donor system reduced both the magnitude of the resource subsidy and the strength of cross-boundary trophic interactions. Importantly, the timing of the subsidy occurs when Rosy-Finches feed their young. If Rosy-Finches rely on aquatic-insect subsidies to fledge their young, reductions in the subsidy by introduced trout may have decreased Rosy-Finch abundances from historic levels. We recommend that terrestrial recipients of aquatic subsidies be included in conservation and restoration plans for ecosystems with alpine lakes. © 2010 by the Ecological Society of America.
Zhou H.,University of South Carolina |
Hanson T.,University of South Carolina |
Knapp R.,University of the Sierra
Biometrics | Year: 2015
The global emergence of Batrachochytrium dendrobatidis (Bd) has caused the extinction of hundreds of amphibian species worldwide. It has become increasingly important to be able to precisely predict time to Bd arrival in a population. The data analyzed herein present a unique challenge in terms of modeling because there is a strong spatial component to Bd arrival time and the traditional proportional hazards assumption is grossly violated. To address these concerns, we develop a novel marginal Bayesian nonparametric survival model for spatially correlated right-censored data. This class of models assumes that the logarithm of survival times marginally follow a mixture of normal densities with a linear-dependent Dirichlet process prior as the random mixing measure, and their joint distribution is induced by a Gaussian copula model with a spatial correlation structure. To invert high-dimensional spatial correlation matrices, we adopt a full-scale approximation that can capture both large- and small-scale spatial dependence. An efficient Markov chain Monte Carlo algorithm with delayed rejection is proposed for posterior computation, and an R package spBayesSurv is provided to fit the model. This approach is first evaluated through simulations, then applied to threatened frog populations in Sequoia-Kings Canyon National Park. © 2015, The International Biometric Society.
Murphy L.M.,University of the Sierra
Violence and Victims | Year: 2011
Using a nationally representative sample of participants, this study investigates childhood victimization in the home and adolescent violent victimization in the community on the risk of being a victim of intimate partner violence (IPV), general violence, or both during early adulthood. The study findings indicate being left home alone and being physically abused during childhood, and adolescent violent victimization in the community had strong independent effects on an individual's likelihood of becoming a victim of IPV, general violence, or both in early adulthood. The study findings suggest a consistent pattern of victimization across the life course, and intervention programs need to be developed that address the specific needs of children and adolescents at high risk for home and community violent victimization. © 2011 Springer Publishing Company.
Sesay M.,Shenzhen University |
Sesay M.,University of the Sierra |
Jin X.,Shenzhen University |
Ouyang Z.,Shenzhen University
Journal of the Optical Society of America B: Optical Physics | Year: 2013
In this paper, we design a polarization splitter by combining a photonic crystal waveguide and internal polarization- selective rods leading to a spatial separation of two orthogonal polarizations for mid-infrared applications. The performance of the splitter is investigated by tuning the length of the polarization-selection rods or defect rods for both the polarization extinction ratio (PER) and degree of polarization (DoP). At optimized parameter of the selective rods, the DoP obtained a high value as 1 and the PER obtained a higher value greater than 30 dB for both TE- and TM-polarized lights. © 2013 Optical Society of America.
Maconachie R.,University of Bath |
Binns T.,University of Otago |
Tengbe P.,University of the Sierra
Cities | Year: 2012
As skyrocketing global food and energy prices have recently triggered a stream of riots in urban centres across sub-Saharan Africa, underscoring the desperation of urban residents as food becomes unobtainable, cities in the West African country of Sierra Leone face a series of new challenges as the country emerges from a decade of civil war during the 1990s. Focusing on the question of urban food security in and around Sierra Leone's capital city, Freetown, this paper explores the proliferation of urban and peri-urban agriculture (UPA) as a response to the rising demand for food and employment. In this context, the paper examines a recent upsurge in cooperative activity associated with UPA in Freetown, drawing upon the knowledge and perceptions of those involved in urban farming associations. In seeking to better understand the associational and livelihood strategies of urban residents in the post-war era, the paper highlights how UPA activities are currently driving a resurgence in community-based cooperation, a development which could play an important role in safeguarding livelihoods and urban food security during a particularly critical point in the country's post-conflict recovery trajectory. © 2011 Elsevier Ltd.