Landscape Partnership Resources Library
Generic Indicators for Loss of Resilience Before a Tipping Point Leading to Population Collapse
Theory predicts that the approach of catastrophic thresholds in natural systems (e.g., ecosystems, the climate) may result in an increasingly slow recovery from small perturbations, a phenomenon called critical slowing down. We used replicate laboratory populations of the budding yeast Saccharomyces cerevisiae for direct observation of critical slowing down before population collapse. We mapped the bifurcation diagram experimentally and found that the populations became more vulnerable to disturbance closer to the tipping point. Fluctuations of population density increased in size and duration near the tipping point, in agreement with the theory. Our results suggest that indicators of critical slowing down can provide advance warning of catastrophic thresholds and loss of resilience in a variety of dynamical systems. SCIENCE VOL 336 1
Impacts of Biodiversity Loss
How much diversity is needed to maintain the productivity of ecosystems? VOL 336 SCIENCE
Navigating the Anthropocene: Improving Earth System Governance
The United Nations conference in Rio de Janeiro in June is an important opportunity to improve the institutional framework for sustainable development. VOL 335 SCIENCE
The Global Extent and Determinants of Savanna and Forest as Alternative Biome States
Theoretically, fire–tree cover feedbacks can maintain savanna and forest as alternative stable states. However, the global extent of fire-driven discontinuities in tree cover is unknown, especially accounting for seasonality and soils. We use tree cover, climate, fire, and soils data sets to show that tree cover is globally discontinuous. Climate influences tree cover globally but, at intermediate rainfall (1000 to 2500 millimeters) with mild seasonality (less than 7 months), tree cover is bimodal, and only fire differentiates between savanna and forest. These may be alternative states over large areas, including parts of Amazonia and the Congo. Changes in biome distributions, whether at the cost of savanna (due to fragmentation) or forest (due to climate), will be neither smooth nor easily reversible.
The 2010 Amazon Drought
Several global circulation models (GCMs) project an increase in the frequency and severity of drought events affecting the Amazon region as a consequence of anthropogenic greenhouse gas emissions (1). The proximate cause is twofold, increasing Pacific sea surface temperatures (SSTs), which may intensify El Niño Southern Oscillation events and associated periodic Amazon droughts, and an increase in the frequency of historically rarer droughts associated with high Atlantic SSTs and northwest displacement of the intertropical convergence zone (1, 2). Such droughts may lead to a loss of some Amazon forests, which would accelerate climate change (3). In 2005, a major Atlantic SST–associated drought occurred, identified as a 1-in-100-year event (2). Here, we report on a second drought in 2010, when Atlantic SSTs were again high.
Time to Adapt to a Warming World, But Where’s the Science?
With dangerous global warming seemingly inevitable, users of climate information— from water utilities to international aid workers—are turning to climate scientists for guidance. But usable knowledge is in short supply VOL 334 SCIENCE
Global Resilience of Tropical Forest and Savanna to Critical Transitions
It has been suggested that tropical forest and savanna could represent alternative stable states, implying critical transitions at tipping points in response to altered climate or other drivers. So far, evidence for this idea has remained elusive, and integrated climate models assume smooth vegetation responses. We analyzed data on the distribution of tree cover in Africa, Australia, and South America to reveal strong evidence for the existence of three distinct attractors: forest, savanna, and a treeless state. Empirical reconstruction of the basins of attraction indicates that the resilience of the states varies in a universal way with precipitation. These results allow the identification of regions where forest or savanna may most easily tip into an alternative state, and they pave the way to a new generation of coupled climate models.
Modeling Effects of Environmental Change on Wolf Population Dynamics, Trait Evolution, and Life History
Environmental change has been observed to generate simultaneous responses in population dynamics, life history, gene frequencies, and morphology in a number of species. But how common are such eco-evolutionary responses to environmental change likely to be? Are they inevitable, or do they require a specific type of change? Can we accurately predict eco-evolutionary responses? We address these questions using theory and data from the study of Yellowstone wolves. We show that environmental change is expected to generate eco-evolutionary change, that changes in the average environment will affect wolves to a greater extent than changes in how variable it is, and that accurate prediction of the consequences of environmental change will probably prove elusive.
Stationarity Is Dead: Whither Water Management?
Climate change undermines a basic assumption that historically has facilitated management of water supplies, demands, and risks. SCIENCE VOL 319
Reducing Greenhouse Gas Emissions from Deforestation and ForestDegradation: Global Land-Use Implications
Recent climate talks in Bali have made progress toward action on deforestation and forest degradation in developing countries, within the anticipated post-Kyoto emissions reduction agreements. As a result of such action, many forests will be better protected, but some land-use change will be displaced to other locations. The demonstration phase launched at Bali offers an opportunity to examine potential outcomes for biodiversity and ecosystem services. Research will be needed into selection of priority areas for reducing emissions from deforestation and forest degradation to deliver multiple benefits, on-the-ground methods to best ensure these benefits, and minimization of displaced land-use change into nontarget countries and ecosystems, including through revised conservation investments
Warming Up Food Webs
How do predator-prey interactions influence Warming Up Food Webs ecosystem responses to climate change? VOL 323 SCIENCE
Megafaunal Decline and Fall
Declines in North American megafauna populations began before the Clovis period and were the cause, not the result, of vegetation changes and increased fires.
Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America
Although the North American megafaunal extinctions and the formation of novel plant communities are well-known features of the last deglaciation, the causal relationships between these phenomena are unclear. Using the dung fungus Sporormiella and other paleoecological proxies from Appleman Lake, Indiana, and several New York sites, we established that the megafaunal decline closely preceded enhanced fire regimes and the development of plant communities that have no modern analogs. The loss of keystone megaherbivores may thus have altered ecosystem structure and function by the release of palatable hardwoods from herbivory pressure and by fuel accumulation. Megafaunal populations collapsed from 14,800 to 13,700 years ago, well before the final extinctions and during the BøllingAllerød warm period. Human impacts remain plausible, but the decline predates Younger Dryas cooling and the extraterrestrial impact event proposed to have occurred 12,900 years ago.
The Last Glacial Maximum
We used 5704 14C, 10Be, and 3 He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level ~14.5 ka.
Seasons and Life Cycles
A conceptual framework. This table is a guide to determining how individual species are responding to an extended growing season by observing the duration of peak season. The life history of a species—from the onset of greening through the end of senescence—is illustrated by the length of the solid lines. Each case represents a shift in the timing (columns) and duration (rows) of one or more species in a hypothetical three-species community that includes an early-, mid-, and late-season species. The growing season begins when the first species greens and ends when the last species senesces. The peak season (gray shaded area) occurs when all species have started and none have completed their life history. Reproductive life history events likely begin before the peak season and are completed before its end. The final row and column list changes that can be observed through frequent observations of surface greenness.
Risks of Climate Engineering
Observations indicate that attempts to limit climate warming by reducing incoming shortwave radiation risk major precipitation changes.
Phenology Feedbacks on Climate Change
A longer growing season as a result of climate change will in turn affect climate through biogeochemical and biophysical effects. SCIENCE VOL 324
The Genetic Architecture of Maize Flowering Time
Flowering time is a complex trait that controls adaptation of plants to their local environment in the outcrossing species Zea mays (maize). We dissected variation for flowering time with a set of 5000 recombinant inbred lines (maize Nested Association Mapping population, NAM). Nearly a million plants were assayed in eight environments but showed no evidence for any single largeeffect quantitative trait loci (QTLs). Instead, we identified evidence for numerous small-effect QTLs shared among families; however, allelic effects differ across founder lines. We identified no individual QTLs at which allelic effects are determined by geographic origin or large effects for epistasis or environmental interactions. Thus, a simple additive model accurately predicts flowering time for maize, in contrast to the genetic architecture observed in the selfing plant species rice and Arabidopsis.
Peatland Response to Global Change
Peatlands can buffer the impact of external perturbations, but can also rapidly shift to a new ecosystem type, with large gains or losses of stored carbon. VOL 326 SCIENCE
Impact of a Century of Climate Change on Small-Mammal Communities in Yosemite National Park, USA
We provide a century-scale view of small-mammal responses to global warming, without confounding effects of land-use change, by repeating Grinnell’s early–20th century survey across a 3000-meter-elevation gradient that spans Yosemite National Park, California, USA. Using occupancy modeling to control for variation in detectability, we show substantial (~500 meters on average) upward changes in elevational limits for half of 28 species monitored, consistent with the observed ~3°C increase in minimum temperatures. Formerly low-elevation species expanded their ranges and high-elevation species contracted theirs, leading to changed community composition at mid- and high elevations. Elevational replacement among congeners changed because species’ responses were idiosyncratic. Though some high-elevation species are threatened, protection of elevation gradients allows other species to respond via migration
