Models for Pooled Time-Series Cross-Section Data

Several models are available for the analysis of pooled time-series cross-section (TSCS) data, defined as “repeated observations on fixed units” (Beck and Katz 1995). In this paper, we run the following models: (1) a completely pooled model, (2) fixed effects models, and (3) multi-level/hierarchical linear models. To illustrate these models, we use a Generalized Least Squares (GLS) estimator with cross-section weights and panel-corrected standard errors (with EViews 8) on the cross-national homicide trends data of forty countries from 1950 to 2005, which we source from published research (Messner et al. 2011). We describe and discuss the similarities and differences between the models, and what information each can contribute to help answer substantive research questions. We conclude with a discussion of how the models we present may help to mitigate validity threats inherent in pooled time-series cross-section data analysis

Shifting baseline in macroecology? Unraveling the influence of human impact on mammalian body mass

Aim Human activities have led to hundreds of species extinctions and have narrowed the distribution of many of the remaining species. These changes influence our understanding of global macroecological patterns, but their effects have been rarely explored. One of these patterns, the Bergmann’s rule, has been largely investigated in macroecology, but often under the assumption that observed patterns reflect “natural” processes. We assessed the extent to which humans have re-shaped the observable patterns of body mass distribution in terrestrial mammals, and how this has altered the macroecological baseline. Location Global Methods Using a comprehensive set of ecological, climatic, and anthropogenic variables we tested several alternative hypotheses to explain the body mass pattern observed in terrestrial mammals assemblages at a 1-degree resolution. We then explored how model predictions and the Bergmann’s latitudinal pattern are affected by the inclusion of human impact variables, and identified areas where predicted body mass differs from the expected due to human impact. Results Our model suggests that median and maximum body mass predicted in grid cells would be higher, and skewness in local mass distributions reduced, if human impacts were minimal, especially in areas that are highly accessible to humans and where natural land cover has been converted for human activities. Main conclusions Our study provides evidence of the pervasive effects of anthropogenic impact on nature, and shows human-induced distortion of global macroecological patterns. This extends the notion of “shifting baseline”, suggesting that when the first macroecological investigations started, our understanding of global geographic patterns was based on a situation which was already compromised. While in the short term human impact is causing species decline and extinction, in the long term it is causing a broad re-shaping of animal communities with yet unpredicted ecological implications

Resource Selection and Its Implications for Wide-Ranging Mammals of the Brazilian Cerrado

Conserving animals beyond protected areas is critical because even the largest reserves may be too small to maintain viable populations for many wide-ranging species. Identification of landscape features that will promote persistence of a diverse array of species is a high priority, particularly, for protected areas that reside in regions of otherwise extensive habitat loss. This is the case for Emas National Park, a small but important protected area located in the Brazilian Cerrado, the world's most biologically diverse savanna. Emas Park is a large-mammal global conservation priority area but is too small to protect wide-ranging mammals for the long-term and conserving these populations will depend on the landscape surrounding the park. We employed novel, noninvasive methods to determine the relative importance of resources found within the park, as well as identify landscape features that promote persistence of wide-ranging mammals outside reserve borders. We used scat detection dogs to survey for five large mammals of conservation concern: giant armadillo (Priodontes maximus), giant anteater (Myrmecophaga tridactyla), maned wolf (Chrysocyon brachyurus), jaguar (Panthera onca), and puma (Puma concolor). We estimated resource selection probability functions for each species from 1,572 scat locations and 434 giant armadillo burrow locations. Results indicate that giant armadillos and jaguars are highly selective of natural habitats, which makes both species sensitive to landscape change from agricultural development. Due to the high amount of such development outside of the Emas Park boundary, the park provides rare resource conditions that are particularly important for these two species. We also reveal that both woodland and forest vegetation remnants enable use of the agricultural landscape as a whole for maned wolves, pumas, and giant anteaters. We identify those features and their landscape compositions that should be prioritized for conservation, arguing that a multi-faceted approach is required to protect these species