Modeling abundance using N-mixture models: the importance of considering ecological mechanisms

Predicting abundance across a species' distribution is useful for studies of ecology and biodiversity management. Modeling of survey data in relation to environmental variables can be a powerful method for extrapolating abundances across a species' distribution and, consequently, calculating total abundances and ultimately trends. Research in this area has demonstrated that models of abundance are often unstable and produce spurious estimates, and until recently our ability to remove detection error limited the development of accurate models. The N-mixture model accounts for detection and abundance simultaneously and has been a significant advance in abundance modeling. Case studies that have tested these new models have demonstrated success for some species, but doubt remains over the appropriateness of standard N-mixture models for many species. Here we develop the N-mixture model to accommodate zero-inflated data, a common occurrence in ecology, by employing zero-inflated count models. To our knowledge, this is the first application of this method to modeling count data. We use four variants of the N-mixture model (Poisson, zero-inflated Poisson, negative binomial, and zero-inflated negative binomial) to model abundance, occupancy (zero-inflated models only) and detection probability of six birds in South Australia. We assess models by their statistical fit and the ecological realism of the parameter estimates. Specifically, we assess the statistical fit with AIC and assess the ecological realism by comparing the parameter estimates with expected values derived from literature, ecological theory, and expert opinion. We demonstrate that, despite being frequently ranked the “best model” according to AIC, the negative binomial variants of the N-mixture often produce ecologically unrealistic parameter estimates. The zero-inflated Poisson variant is preferable to the negative binomial variants of the N-mixture, as it models an ecological mechanism rather than a statistical phenomenon and generates reasonable parameter estimates. Our results emphasize the need to include ecological reasoning when choosing appropriate models and highlight the dangers of modeling statistical properties of the data. We demonstrate that, to obtain ecologically realistic estimates of abundance, occupancy and detection probability, it is essential to understand the sources of variation in the data and then use this information to choose appropriate error distributions. Copyright ESA. All rights reserved

Predicting avian distributions to evaluate spatiotemporal overlap with locust control operations in eastern Australia

Locusts and grasshoppers cause considerable economic damage to agriculture worldwide. The Australian Plague Locust Commission uses multiple pesticides to control locusts in eastern Australia. Avian exposure to agricultural pesticides is of conservation concern, especially in the case of rare and threatened species. The aim of this study was to evaluate the probability of pesticide exposure of native avian species during operational locust control based on knowledge of species occurrence in areas and times of application. Using presence-absence data provided by the Birds Australia Atlas for 1998 to 2002, we developed a series of generalized linear models to predict avian occurrences on a monthly basis in 0.5 degrees grid cells for 280 species over 2 million km 2 in eastern Australia. We constructed species-specific models relating occupancy patterns to survey date and location, rainfall, and derived habitat preference. Model complexity depended on the number of observations available. Model output was the probability of occurrence for each species at times and locations of past locust control operations within the 5-year study period. Given the high spatiotemporal variability of locust control events, the variability in predicted bird species presence was high, with 108 of the total 280 species being included at least once in the top 20 predicted species for individual space-time events. The models were evaluated using field surveys collected between 2000 and 2005, at sites with and without locust outbreaks. Model strength varied among species. Some species were under- or over-predicted as times and locations of interest typically did not correspond to those in the prediction data set and certain species were likely attracted to locusts as a food source. Field surveys demonstrated the utility of the spatially explicit species lists derived from the models but also identified the presence of a number of previously unanticipated species. These results also emphasize the need for special consideration of rare and threatened species that are poorly predicted by presence-absence models. This modeling exercise was a useful a priori approach in species risk assessments to identify species present at times and locations of locust control applications, and to discover gaps in our knowledge and need for further focused data collection Copyright 2009 by the Ecological Society ot America

Rethinking journalism practice through innovative approaches to post conflict reporting

Journalism has a long history of interviewing vulnerable people caught up in natural disasters, conflict or tragedy. While it is widely recognised that journalists have an important role to play in telling the stories of those traumatised by such events, the concepts of ‘peace journalism’ or ‘journalism of attachment’ have often elicited a negative reaction in traditional journalistic circles. Drawing on the authors’ research project working with young people embroiled in Colombia’s civil conflict, this paper sets out an alternative and innovative approach to the retelling of the stories of others. It outlines how the research team engaged with the young people, some of whom had operated as child soldiers before Colombia’s peace accord with FARC rebels, and encouraged them to narrate their own stories in their own style. Through a series of workshops, the team experimented with oral and visual representations of their experiences, staying close to their accounts, enabling their voices to be heard. The participants combined traditional narrative with animation to produce a short documentary setting out their hopes for peace and reconciliation. This project, with its focus on immersion and listening, offers an alternative approach for journalists trying to relay the experiences of traumatised individuals marginalised in society as a result of their participation in the armed conflict. While the project was located in the specific context of Colombia, the paper argues that the journalistic approaches used could be applied more widely to the reporting of trauma in post conflict or marginalised communities

Outside the gate: sub-urban legal practices in early medieval England

Many aspects of English early medieval (Anglo-Saxon) legal landscapes can be discerned in archaeological and toponymic evidence, ranging from the locations of legislative councils and judicial assemblies to sites of capital punishment. Among the corpus of such sites a striking group can be detected at the periphery of urban spaces. Gates into a number of towns appear to have functioned as legislative meeting-places, and even gave their names to some legally constituted communities, while suburban locations also feature prominently as sites of gallows and public punishment. In this paper historical, archaeological and toponymic evidence is used to examine this phenomenon of suburban legal practices and to pose questions about the wider dimensions of the early medieval legal landscape

Forest landscape ecology and global change: an introduction

Forest landscape ecology examines broad-scale patterns and processes and their interactions in forested systems and informs the management of these ecosystems. Beyond being among the richest and the most complex terrestrial systems, forest landscapes serve society by providing an array of products and services and, if managed properly, can do so sustainably. In this chapter, we provide an overview of the field of forest landscape ecology, including major historical and present topics of research, approaches, scales, and applications, particularly those concerning edges, fragmentation, connectivity, disturbance, and biodiversity. In addition, we discuss causes of change in forest landscapes, particularly land-use and management changes, and the expected structural and functional consequences that may result from these drivers. This chapter is intended to set the context and provide an overview for the remainder of the book and poses a broad set of questions related to forest landscape ecology and global change that need answers