Santa Fe Institute

About: Santa Fe Institute is a nonprofit organization based out in Santa Fe, New Mexico, United States. It is known for research contribution in the topics: Population & Context (language use). The organization has 558 authors who have published 4558 publications receiving 396015 citations. The organization is also known as: SFI.

Plant community composition mediates both large transient decline and predicted long‐term recovery of soil carbon under climate warming

Abstract: [1] We integrated two methods, experimental heating and observations across natural climate gradients, to elucidate both short- and long-term climatic controls on ecosystem carbon storage and to investigate carbon-cycle feedbacks to climate in montane meadows. A 10-year heating experiment warmed and dried heated plot soils and substantially decreased (by ∼200 ± 150 g C m−2) the amount of carbon stored in soil organic matter, a positive feedback to warming. In situ CO2 flux measurements, laboratory soil incubations, and a heating-induced shift in vegetation community composition from high- to low-productivity species indicate that a decline in community productivity and resultant decrease in soil inputs from plant litter caused most of the soil carbon decrease. An alternative widely hypothesized mechanism for soil carbon decrease under warming is stimulation of soil respiration, but we observed no increase in seasonally integrated soil respiration in our experiment (soil drying inhibited microbial decomposition even as soil warming stimulated it). To extend our analysis from the short-term transient response represented by the heating experiment to the presumed long-term approximate steady state represented by natural climate gradients, we tested a hypothesized relation between vegetation community composition (which controls both litter input rate and average litter quality) and soil carbon along the climate gradient. The gradient analysis implies that the experimentally induced decline in soil carbon is transient and will eventually reverse as lower quality litter inputs from the increasingly dominant low-productivity species reduce soil respiration losses. This work shows that ecological processes can control both short- and long-term responses to climate change, confirming some model-based predictions about the importance of vegetation shifts, but challenging the widely held hypothesis that the effect of temperature change on respiration will dominate soil carbon changes.

Sensitive intervention points in the post-carbon transition.

Abstract: We must exploit socioeconomic tipping points and amplifiers Conventional approaches to mitigating climate change are not working. Despite the actions pledged under the 2015 Paris Agreement, actual progress is falling well short (1). Given limited time and resources, traditional efforts such as the climate stabilization wedge approach (2) are unlikely to be effective on their own. Physical science has shown how complex adaptive systems can cross critical thresholds (“tipping points”) (3), such that a relatively small change can trigger a larger change that becomes irreversible (4), where nonlinear feedback effects act as amplifiers (5). We propose to examine how to exploit similar sensitive intervention points (SIPs) and amplification mechanisms in socioeconomic, technological, and political systems to advance climate change mitigation. We focus on research and policies in which an intervention kicks or shifts the system so that the initial change is amplified by feedback effects that deliver outsized impact.

Metastable Evolutionary Dynamics: Crossing Fitness Barriers or Escaping via Neutral Paths?

Abstract: We analytically study the dynamics of evolving populations that exhibit metastability on the level of phenotype or fitness. In constant selective environments, such metastable behavior is caused by two qualitatively different mechanisms. One the one hand, populations may become pinned at a local fitness optimum, being separated from higher-fitness genotypes by a {\em fitness barrier} of low-fitness genotypes. On the other hand, the population may only be metastable on the level of phenotype or fitness while, at the same time, diffusing over {\em neutral networks} of selectively neutral genotypes. Metastability occurs in this case because the population is separated from higher-fitness genotypes by an {\em entropy barrier}: The population must explore large portions of these neutral networks before it discovers a rare connection to fitter phenotypes. We derive analytical expressions for the barrier crossing times in both the fitness barrier and entropy barrier regime. In contrast with ``landscape'' evolutionary models, we show that the waiting times to reach higher fitness depend strongly on the width of a fitness barrier and much less on its height. The analysis further shows that crossing entropy barriers is faster by orders of magnitude than fitness barrier crossing. Thus, when populations are trapped in a metastable phenotypic state, they are most likely to escape by crossing an entropy barrier, along a neutral path in genotype space. If no such escape route along a neutral path exists, a population is most likely to cross a fitness barrier where the barrier is {\em narrowest}, rather than where the barrier is shallowest.

Zones of Cooperation in Demographic Prisoner's Dilemma

Abstract: The emergence of cooperation in Prisoner's Dilemma (PD) games is generally assumed to require repeated play (and strategies such as Tit-For-Tat, involving memory of previous interactions) or features ("tags") permitting cooperators and defectors to distinguish one another. In the Demographic Prisoner's Dilemma, neither assumption is made: agents with finite vision move to random sites on a lattice and play a fixed culturally-inherited zero-memory strategy of cooperate (C) or defect (D) against neighbors. Agents are indistinguishable to one another--they are "tagless". Positive payoffs accrue to agents playing C against C, or D against C. Negative payoffs accrue to agents playing C against D, or D against D. Payoffs accumulate. If accumulated payoffs exceed some threshold, agents clone offspring of the same strategy onto neighboring sites and continue play. If accumulated payoffs are negative, agents die and are removed. Spatial zones of cooperation emerge.

Integrating computational thinking across the K--8 curriculum

Abstract: The excitement around K-12 Computing Education in the United States is rapidly increasing and K-8 holds great potential as the entry point for the integration of computing. We examine how young learners can gain early exposure and engage in rich computational experiences in K-8. These experiences can build students’ computational thinking, understanding of CS concepts, experience with collecting and analyzing data, programming skills and confidence as critical thinkers. We discuss how three types of computational activities: digital storytelling, data collection and analysis, and computational science investigations, can be used to incorporate computational thinking (CT) across the curriculum.