Dynamic spatial interactions between the native invader Brown-headed Cowbird and its hosts

AimWe investigated the contribution of parasitism by the Brown-headed Cowbird (Molothrus ater) to its host population dynamics at a subcontinental scale. We predicted that the growth rate of cowbirds would be most strongly related to the abundance of forest insectivorous hosts and that landscape fragmentation would have opposite effects on the parasite and its hosts. Furthermore, due to the species' sedentarity and low rates of adult dispersal, we expected that cowbird population dynamics would be structured at local, rather than large spatial scales.LocationThe Great Plains, United States.MethodsWe modelled jointly the population dynamics of cowbird and its 58 most common hosts, accounting for effects of landscape fragmentation and cowbird dispersal. We used Bayesian inference to evaluate this model on 76 routes of the North American Breeding Bird Survey (BBS), surveyed each year from 2001 to 2011. We then analysed covariations between the demographic dynamics of cowbirds and their hosts in a multivariate ecological trait space.ResultsContrary to most of its hosts, the cowbird had positive growth rates in man-disturbed, fragmented landscapes, which covaried at small spatial scales. The large-scale effects of parasitism were limited, as few host species affected, or were affected by cowbird growth rates. However, significant cowbird–host relationships were structured by ecological traits: cowbird growth rates were most increased by the abundance of ecological generalists, while hosts were affected by cowbird abundance irrespective of their position in the functional space.Main conclusionsCowbirds parasitize opportunistically the hosts occurring in disturbed landscapes. The large-scale effects of nest parasitism therefore depend probably on landscape structure and other environmental factors operating at local scales. We suggest that efforts to counter the local and continental declines of many passerine species should include parasitism among the biotic components of landscape disturbance

Residential winter kWh responsiveness under optional time-varying pricing in British Columbia

A large sample of daily electricity consumption and pricing data are available from a pilot study conducted by BC Hydro in British Columbia (Canada) of its residential customers under optional time-varying pricing and remotely-activated load-control devices for the four winter months of November 2007-February 2008. We use those data to estimate the elasticity of substitution σ, defined as the negative of the percentage change in the peak-to-off-peak kW. h ratio due to a 1% change in the peak-to-off-peak price ratio. Our estimates of σ characterize residential price responsiveness with and without load control during cold-weather months. While the estimates of σ sans load control are highly statistically significant (α=0.01), they are less than 0.07. With load control in place, however, these σ estimates more than triple. Finally, we show that time-varying pricing sans load control causes a peak kW. h reduction of 2.6% at the 2:1 peak-to-off-peak price ratio to 9.2% at the 12:1 peak-to-off-peak price ratio. Load control raises these reduction estimates to 9.2% and 30.7%.School of Accounting and Financ

Power-use profile analysis of non-domestic consumers for electricity tariff switching

For both domestic and non-domestic consumers, dynamic electricity tariffs have been proposed as a way to reduce their energy costs and to facilitate demand-side response. It is difficult for businesses which are tenants to adopt energy efficiency measures; thus, tariff switching is the easier option. Therefore, understanding the limits of the cost saving offered by tariff switching is an important step. This raises two questions: by how much could bills be reduced, and would all consumers benefit equally? Using a dataset of half-hourly electricity readings from more than 7500 British businesses, we performed an empirical analysis to discover which types of businesses might have lower or higher costs when changing between static and real-time tariffs. We identified differences in demand profiles that demonstrate that the decision whether to switch tariff types is a subtle one which may have a significant cost impact. The dataset was aggregated into five categories: Entertainment, Industry, Retail, Social, and Other. Our analytical methods can be used to distinguish the differences between typical electricity demand profiles for small- to medium-sized businesses and sectors in different market options. Our analyses of switching to a real-time tariff suggest that most of those small- to medium-sized businesses that would reduce their annual electricity bill would gain by no more than 10 %. Most of these businesses would gain by less than 5 %. This, we suggest, sets a realistic upper limit of the likely cash savings before energy efficiency, or other measures must be taken to further reduce bills.This work was supported by an UK Engineering and Physical Science Research Council grant (EP/I000194/1)