David R. Williams

How can higher-yield farming help to spare nature?

Mechanisms to link yield increases with conservation Expansion of land area used for agriculture is a leading cause of biodiversity loss and greenhouse gas emissions, particularly in the tropics. One potential way to reduce these impacts is to increase food production per unit area (yield) on existing farmland, so as to minimize farmland area and to spare land for habitat conservation or restoration. There is now widespread evidence that such a strategy could benefit a large proportion of wild species, provided that spared land is conserved as natural habitat (1). However, the scope for yield growth to spare land by lowering food prices and, hence, incentives for clearance (“passive” land sparing) can be undermined if lower prices stimulate demand and if higher yields raise profits, encouraging agricultural expansion and increasing the opportunity cost of conservation (2, 3). We offer a first description of four categories of “active” land-sparing mechanisms that could overcome these rebound effects by linking yield increases with habitat protection or restoration (table S1). The effectiveness, limitations, and potential for unintended consequences of these mechanisms have yet to be systematically tested, but in each case, we describe real-world interventions that illustrate how intentional links between yield increases and land sparing might be developed.

Land-use strategies to balance livestock production, biodiversity conservation and carbon storage in Yucatán, Mexico.

Balancing the production of food, particularly meat, with preserving biodiversity and maintaining ecosystem services is a major societal challenge. Research into the contrasting strategies of land sparing and land sharing has suggested that land sparing-combining high-yield agriculture with the protection or restoration of natural habitats on nonfarmed land-will have lower environmental impacts than other strategies. Ecosystems with long histories of habitat disturbance, however, could be resilient to low-yield agriculture and thus fare better under land sharing. Using a wider suite of species (birds, dung beetles and trees) and a wider range of livestock-production systems than previous studies, we investigated the probable impacts of different land-use strategies on biodiversity and aboveground carbon stocks in the Yucatán Peninsula, Mexico-a region with a long history of habitat disturbance. By modelling the production of multiple products from interdependent land uses, we found that land sparing would allow larger estimated populations of most species and larger carbon stocks to persist than would land sharing or any intermediate strategy. This result held across all agricultural production targets despite the history of disturbance and despite species richness in low- and medium-yielding agriculture being not much lower than that in natural habitats. This highlights the importance, in evaluating the biodiversity impacts of land use, of measuring population densities of individual species, rather than simple species richness. The benefits of land sparing for both biodiversity and carbon storage suggest that safeguarding natural habitats for biodiversity protection and carbon storage alongside promoting areas of high-yield cattle production would be desirable. However, delivering such landscapes will probably require the explicit linkage of livestock yield increases with habitat protection or restoration, as well as a deeper understanding of the long-term sustainability of yields, and research into how other societal outcomes vary across land-use strategies.

The role of livestock intensification and landscape structure in maintaining tropical biodiversity

As tropical cattle ranching continues to expand, successful conservation will require an improved understanding of the relative impacts of different livestock systems and landscape structure on biodiversity. Here, we provide the first empirical and multi-scale assessment of the relative effects of livestock intensification and landscape structure on biodiversity in the threatened tropical dry forests of Mesoamerica. nWe used a dataset of dung beetles (169,372 individuals from 33 species) collected from 20 1-km2 landscapes, ranging from zero-yielding forest sites to high-yield cattle ranches and maize farms, to investigate the relative effect of livestock intensification (net cattle production; macrocyclic lactone use; annual dung production) and landscape structure (landscape composition and configuration) at multiple spatial scales on different attributes of dung beetle communities using a multi-model averaging approach. nDung beetle species richness, biomass and composition were more strongly related to landscape structure than to livestock intensification. nForest cover was the best predictor of dung beetle assemblages, being positively related to species diversity and biomass across multiple spatial scales. The use of macrocyclic lactones was strong and negatively related to dung beetle communities at the local scale. nSynthesis and applications: Maximising forest protection through a “land sparing” strategy is likely to be the best strategy for reducing negative impacts of cattle farming on Neotropical dung beetle communities. However, increasing or maintaining yields while reducing agrochemical inputs will be important for conserving on-farm biodiversity and the ecosystem services that dung beetles provide in livestock-dominated landscapes.

Reply to Lima-Ribeiro et al.: Human arrival scenarios have little influence on interpretations of late Quaternary extinctions

In a recent study (1), we analyzed the pattern of late Quaternary megafaunal extinctions in relation to changes in global climate and the timing of human arrival on different landmasses. Lima-Ribeiro et al. (2) write that some of the human arrival scenarios we considered are more plausible than others and that this affects the interpretation of our analysis. We incorporated a wide range of human arrival scenarios to allow precisely this sort of analysis, and we therefore welcome this contribution.nnTo clarify, we considered 32 human arrival scenarios not to … nn[↵][1]2To whom correspondence may be addressed. E-mail: davidrwilliams87{at}gmail.com or grahamprescott{at}gmail.com.nn [1]: #xref-corresp-1-1