How many species are there on Earth?

This article surveys current answers to the factual question posed in the title and reviews the kinds of information that are needed to make these answers more precise. Various factors affecting diversity are also reviewed. These include the structure of food webs, the relative abundance of species, the number of species and of individuals in different categories of body size, along with other determinants of the commonness and rarity of organisms.     

Transitions to sustainability: a change in thinking about food systems change?

In the present context of intertwined and intensifying economic, environmental and climate challenges and crisis, we need to enlarge our thinking about food systems change. One way to do so is by considering intersections between our longstanding interdisciplinary interest in food and agriculture and new scholarship and practice centered on transitions to sustainability. The general idea of transition references change in a wide range of fields and contexts, and has gained prominence most recently as a way to discuss and address sustainability challenges. To explore connections to food systems change, I highlight two broad approaches in the sustainability transitions research field. First is a multi-level perspective that examines sustainability innovation pathways and second is a social practices approach that illuminates the possibilities (or not) for shifts in normal everyday routines and practices. Taken together, these approaches offer different and useful ways to think about the dynamics, durability and significance of innovations in food and agriculture, and the part they play in transitions to sustainability. Numerous opportunities exist to forge more productive links between work on food systems change and the broad and growing sustainability transitions field. First, our research and practice insights about the importance of politics, governance, values and ethics in food and agriculture could help to strengthen the sustainability transitions field, which initially underplayed such questions. Second, the sustainability transitions field’s implicit systems sensibility and its futures orientation could help to widen the scope of inquiry and the contribution to policy and planning of research and practice on food systems change.     

Mars: change in axial tilt due to climate?

The average tilt of Mars' equator with respect to its orbital plane may have increased significantly over the age of the solar system. Obliquity oscillations might have induced changes in the climate, which altered the mass distribution and hence the solar torque on the planet. Viscous deformation attributable to loading by the large polar caps expected at low obliquity may have induced secular changes in the axial tilt. Earth-like effective viscosities can account for virtually the entire present obliquity of 24.4 degrees. Thus the present average tilt of Mars may not be primordial.     

Why do farmers decide to produce meat goats? Evidence from the United States

This paper addresses the reasons why US meat goat producers selected to engage in meat goat production. A mail survey of US meat goat producers was conducted. Potential reasons for entering meat goat production included those associated with lifestyle, farm management, productivity, and economics. Reasons for entering meat goat production were assessed and analyzed using ordered probit models. The most important reasons for entering meat goat production included enjoyment working with goats, goat production fitting well into the farm management plan, goats could be raised on a relatively small acreage, goat grazing preferences were different from other species, and the family could be involved in the goat enterprise. The 12th and 13th most important reasons were goat production profitability and low cost associated with purchasing and raising goats. Larger-scale farmers were more likely to have selected meat goat production for profitability and productivity reasons while smaller-scale farmers were more likely to have selected it for lifestyle reasons. Farmer demographics, farm characteristics, and farm location also impacted reasons why the farmer selected the goat enterprise. Results have implications for development of the meat goat industry.