Who’s where? Ecological uncertainty shapes neophobic predator avoidance in Trinidadian guppies

Behavioral Ecology and Sociobiology - Behavioural diversity is a basic component of biodiversity, with implications in ecological interactions at the intra- and interspecific levels. The...     

Song overproduction and selective attrition lead to song sharing in the field sparrow (Spizella pusilla)

Summary Male field sparrows settling on particular territories for the first time often sing two or more song types. Vocal experience with neighboring males then leads in most cases to the deletion from the male's repertoires of all but one song type. In 2 years, settling males retained the song type that most closely resembled that of a neighbor. Focal observations in 1 year revealed that the most actively singing neighbor was the one the new birds resembled. Songs were not selected on the basis of their absolute acoustic characteristics, but rather by their resemblance to neighbors' songs. After the attrition process is complete, males retain their song for the rest of their lives. Evidence supports the hypothesis that the actual acquisition of a song need not take place at the time and place as males occupy territories. Rather, males may acquire an abundance of song models earlier in life and then select songs from this repertoire that most closely resemble those of their neighbors. The development of mature repertoires and of local dialects is the outcome of one process in this species.     

Suppression of soybean aphid by generalist predators results in a trophic cascade in soybeans.

Top-down regulation of herbivores in terrestrial ecosystems is pervasive and can lead to trophic cascades that release plants from herbivory. Due to their relatively simplified food webs, agroecosystems may be particularly prone to trophic cascades, a rationale that underlies biological control. However, theoretical and empirical studies show that, within multiple enemy assemblages, intraguild predation (IGP) may lead to a disruption of top-down control by predators. We conducted a factorial field study to test the separate and combined effects of predators and parasitoids in a system with asymmetric IGP. Specifically we combined ambient levels of generalist predators (mainly Coccinellidae) of the soybean aphid, Aphis glycines Matsumura, with controlled releases of the native parasitoid Lysiphlebus testaceipes (Cresson) and measured their impact on aphid population growth and soybean biomass and yield. We found that generalist predators provided strong, season-long aphid suppression, which resulted in a trophic cascade that doubled soybean biomass and yield. However, contrary to our expectations, L. testaceipes provided minor aphid suppression and only when predators were excluded, which resulted in nonadditive effects when both groups were combined. We found direct and indirect evidence of IGP, but because percentage parasitism did not differ between predator exclusion and ambient predator treatments, we concluded that IGP did not disrupt parasitism during this study. Our results support theoretical predictions that intraguild predators which also provide strong herbivore suppression do not disrupt top-down control of herbivores.     

Evaluating CO2 reduction strategies in the US

We constructed a model to simulate emissions of CO₂ from electricity generation in the US and, using the model, we developed 20-year projections of emissions under various regulatory scenarios.     

A bioeconomic model for estimating the benefits of acid rain abatement to Salmon fishing: a case study in South West Scotland

The United Kingdom, under the Large Combustion Plant Directive of the European Community, is committed to cutting sulphur dioxide (SO2) emissions by 60% of 1980 levels by the year 2003. In order to justify this action and to support new decisions on further emission reductions, policy makers require knowledge of the economic benefits of abatement. Benefit estimates for the recovery of freshwater fish populations present difficulties since the effect of reduced acid deposition on environmental processes is complex and because fishery records are often inadequate or absent. This paper predicts the economic benefits of acid rain abatement to the rod and line salmon fishery of Galloway, South West Scotland. It achieves this by linking output on long term changes in water chemistry and fish population status from MAGIC, a process based catchment model for acidification, with catch and market value data. Predicted increases in the market value of the fishery are presented and the role of the model in economic analysis of environmental policy discussed.     

Multivariate Bayesian analysis of atmosphere–ocean general circulation models

Numerical experiments based on atmosphere–ocean general circulation models (AOGCMs) are one of the primary tools in deriving projections for future climate change. Although each AOGCM has the same underlying partial differential equations modeling large scale effects, they have different small scale parameterizations and different discretizations to solve the equations, resulting in different climate projections. This motivates climate projections synthesized from results of several AOGCMs’ output. We combine present day observations, present day and future climate projections in a single highdimensional hierarchical Bayes model. The challenging aspect is the modeling of the spatial processes on the sphere, the number of parameters and the amount of data involved. We pursue a Bayesian hierarchical model that separates the spatial response into a large scale climate change signal and an isotropic process representing small scale variability among AOGCMs. Samples from the posterior distributions are obtained with computer-intensive MCMC simulations. The novelty of our approach is that we use gridded, high resolution data covering the entire sphere within a spatial hierarchical framework. The primary data source is provided by the Coupled Model Intercomparison Project (CMIP) and consists of 9 AOGCMs on a 2.8 by 2.8 degree grid under several different emission scenarios. In this article we consider mean seasonal surface temperature and precipitation as climate variables. Extensions to our model are also discussed.     

Optimal resource management control for CO2 emission and reduction of the greenhouse effect

In recent years, the world has witnessed an ever-growing concern towards global warming caused by greenhouse gases, such as carbon dioxide (CO₂). In order to reduce the emissions of CO₂ without limiting economic growth, substantial investments should target the development of clean technology and the expansion of forested areas. Considering the limited availability of resources, investments must be used in the most effective way. The present work proposes a method to efficiently manage these resources by applying the optimal control theory to a new mathematical model that describes the dynamics of the atmospheric CO₂. The contributions of this work are twofold: (1) present a model that describes the dynamic relation of CO₂ emission with investment in reforestation and clean technology and (2) present a method to efficiently manage the available resources by casting an optimal control problem. The mathematical model uses ordinary differential equations to relate the production of CO₂ with forest area and Gross Domestic Product (GDP). The model parameters are adjusted to fit the actual published data. Given an appropriate performance index, the optimal solution is found by numerically solving the Two-Point Boundary Value Problem (TPBVP) that arises from the application of Pontriagyn's Maximum Principle. The sensitivity of the obtained numerical solution is evaluated with respect to the uncertainties in the model parameters. The main objective of this work is to provide a quantitative tool for the efficient allocation of resources to reduce the greenhouse effect caused CO₂ emissions.