Imagining the future improves saving in preschoolers.

Preschoolers are notoriously poor at delaying gratification and saving limited resources, yet evidence-based methods of improving these behaviors are lacking. Using the marble game saving paradigm, we examined whether young children's saving behavior would increase as a result of engaging in future-oriented imagination using a storyboard. Participants were 115 typically developing 4-year-olds from a midwestern U.S. metropolitan area (Mage = 53.48 months, SD = 4.14, range = 47-60; 54.8% female; 84.5% White; 7.3% Hispanic/Latino ethnicity; median annual household income = $150,000-$174,999). Children were randomly assigned to one of four storyboard conditions prior to the marble game: Positive Future Simulation, Negative Future Simulation, Positive Routine, or Negative Routine. In each condition, children were asked to imagine how they would feel in the future situation using a smiley face rating scale. Results showed that children were significantly more likely to save (and to save more marbles) in the experimental conditions compared with the control conditions (medium effect sizes). Moreover, imagining saving for the future (and how good that would feel) was more effective at increasing saving behaviors than imagining not saving (and how bad that would feel). Emotion ratings were consistent with the assigned condition, but positive emotion alone did not account for these effects. Results held after accounting for game order and verbal IQ. Implications of temporal psychological distancing and emotion anticipation for children's future-oriented decision making are discussed.

Closing the gap between science and management of cold-water refuges in rivers and streams.

Human activities and climate change threaten coldwater organisms in freshwater ecosystems by causing rivers and streams to warm, increasing the intensity and frequency of warm temperature events, and reducing thermal heterogeneity. Cold-water refuges are discrete patches of relatively cool water that are used by coldwater organisms for thermal relief and short-term survival. Globally, cohesive management approaches are needed that consider interlinked physical, biological, and social factors of cold-water refuges. We review current understanding of cold-water refuges, identify gaps between science and management, and evaluate policies aimed at protecting thermally sensitive species. Existing policies include designating cold-water habitats, restricting fishing during warm periods, and implementing threshold temperature standards or guidelines. However, these policies are rare and uncoordinated across spatial scales and often do not consider input from Indigenous peoples. We propose that cold-water refuges be managed as distinct operational landscape units, which provide a social and ecological context that is relevant at the watershed scale. These operational landscape units provide the foundation for an integrated framework that links science and management by (1) mapping and characterizing cold-water refuges to prioritize management and conservation actions, (2) leveraging existing and new policies, (3) improving coordination across jurisdictions, and (4) implementing adaptive management practices across scales. Our findings show that while there are many opportunities for scientific advancement, the current state of the sciences is sufficient to inform policy and management. Our proposed framework provides a path forward for managing and protecting cold-water refuges using existing and new policies to protect coldwater organisms in the face of global change.

Executive function and mathematics in preschool children: Training and transfer effects.

Identifying the underpinnings of mathematics proficiency is relevant for all societies. A growing literature supports a relation between executive function (EF) and mathematics across a wide age range, but causal links are not well understood. In the current study, typically developing preschool children (N = 104) were randomly assigned to one of four training conditions: EF, Number, EF + Number, or an active Control. They participated in three brief training sessions and pretest and posttest sessions measuring EF and mathematics skills. EF training improved EF skills on a task similar to the training but did not extend to an untrained EF task. In addition, the EF training improved number skills but not general mathematics skills. The EF + Number training improved number and general mathematics skills but not EF skills. The EF + Number training did not yield significantly greater benefits for EF and mathematics beyond other training conditions. Finally, differential training effects emerged, such that children with lower pretest EF skills had greater EF benefits on only the trained EF skill. In addition, children from lower versus higher socioeconomic households had greater gains in numerical skills following EF training. No training condition improved verbal knowledge, suggesting that results were specific to the targeted skills. These results extend prior findings on the effectiveness of improving EF and mathematical skills through short-term trainings during early childhood.

Evolutionary origins for ecological patterns in space.

Historically, many biologists assumed that evolution and ecology acted independently because evolution occurred over distances too great to influence most ecological patterns. Today, evidence indicates that evolution can operate over a range of spatial scales, including fine spatial scales. Thus, evolutionary divergence across space might frequently interact with the mechanisms that also determine spatial ecological patterns. Here, we synthesize insights from 500 eco-evolutionary studies and develop a predictive framework that seeks to understand whether and when evolution amplifies, dampens, or creates ecological patterns. We demonstrate that local adaptation can alter everything from spatial variation in population abundances to ecosystem properties. We uncover 14 mechanisms that can mediate the outcome of evolution on spatial ecological patterns. Sometimes, evolution amplifies environmental variation, especially when selection enhances resource uptake or patch selection. The local evolution of foundation or keystone species can create ecological patterns where none existed originally. However, most often, we find that evolution dampens existing environmental gradients, because local adaptation evens out fitness across environments and thus counteracts the variation in associated ecological patterns. Consequently, evolution generally smooths out the underlying heterogeneity in nature, making the world appear less ragged than it would be in the absence of evolution. We end by highlighting the future research needed to inform a fully integrated and predictive biology that accounts for eco-evolutionary interactions in both space and time.

Responding to joint attention as a developmental catalyst: Longitudinal associations with language and social responsiveness.

Joint attention (JA), infants' ability to engage in triadic attention with another person and a separate object or event, emerges in infancy. Responding to joint attention (RJA) develops earlier than initiating joint attention (IJA) and may benefit from a reconceptualization from a competence to a skill that varies in performance. Investigating associations between RJA performance and important skills of toddlerhood such as language, social responsiveness, and executive function (EF) in typically developing samples can better elucidate how RJA may serve as a developmental precursor to later dimensional skills, with implications for both typical and atypical development. Here, 210 (82% White) infants completed the Dimensional Joint Attention Assessment (DJAA), a naturalistic play-based assessment of RJA, at 8-15 months. At 16-38 months social responsiveness, verbal ability, and EF were assessed. Multilevel models showed that DJAA scores were associated with later verbal abilities and parent-reported social responsiveness. Exploratory analyses showed trend-level associations between RJA and EF. Results establish the content validity of the DJAA as a measure of RJA, and longitudinal associations with later verbal ability and social responsiveness. Future work should examine EF emergence and consolidation, and RJA and later EF associations.

Four decades of climatic fluctuations and fish recruitment stability across a marine-freshwater gradient.

Investigating the effects of climatic variability on biological diversity, productivity, and stability is key to understanding possible futures for ecosystems under accelerating climate change. A critical question for estuarine ecosystems is, how does climatic variability influence juvenile recruitment of different fish species and life histories that use estuaries as nurseries? Here we examined spatiotemporal abundance trends and environmental responses of 18 fish species that frequently spend the juvenile stage rearing in the San Francisco Estuary, CA, USA. First, we constructed multivariate autoregressive state-space models using age-0 fish abundance, freshwater flow (flow), and sea surface temperature data (SST) collected over four decades. Next, we calculated coefficients of variation (CV) to assess portfolio effects (1) within and among species, life histories (anadromous, marine opportunist, or estuarine dependent), and the whole community; and (2) within and among regions of the estuary. We found that species abundances varied over space and time (increasing, decreasing, or dynamically stable); and in 83% of cases, in response to environmental conditions (wet/dry, cool/warm periods). Anadromous species responded strongly to flow in the upper estuary, marine opportunist species responded to flow and/or SST in the lower estuary, and estuarine dependent species had diverse responses across the estuary. Overall, the whole community when considered across the entire estuary had the lowest CV, and life histories and species provided strong biological insurance to the portfolio (2.4- to 3.5-fold increases in stability, respectively). Spatial insurance also increased stability, although to a lesser extent (up to 1.6-fold increases). Our study advances the notion that fish recruitment stability in estuaries is controlled by biocomplexity-life history diversity and spatiotemporal variation in the environment. However, intensified drought and marine heatwaves may increase the risk of multiple consecutive recruitment failures by synchronizing species dynamics and trajectories via Moran effects, potentially diminishing estuarine nursery function.

Executive and Social Functioning Across Development in Children and Adolescents With Prenatal Alcohol Exposure.

BACKGROUND: Prenatal alcohol exposure (PAE) is linked to a variety of neurodevelopmental challenges, including social functioning (SF) and executive functioning (EF) deficits. These deficits present differently across developmental stages from preschool age to adolescence. METHODS: The post hoc analyses described here were conducted on data from 83 preschool-age children with PAE (early childhood group; ages 2.5 to 5.0) and 95 adolescents (49 with PAE, 46 controls; ages 8 to 16). Each child completed EF tasks as part of several prior studies. Parents completed social and communication inventories about their child's abilities. Thirty-three participants from the early childhood group returned for a 4-year follow-up and completed both SF and EF measures. RESULTS: Both the early childhood and adolescent groups with PAE showed deficits in SF and EF. There was a relationship between SF and EF within the adolescent PAE group that was not present in the adolescent control group or the early childhood PAE group. However, at the 4-year follow-up (Mage  = 8.45), participants originally in the early childhood PAE group also demonstrated this relationship. CONCLUSIONS: These findings support previous research on EF/SF deficits in adolescents with PAE while also addressing a gap in the literature concerning early childhood research on this topic. Additionally, these findings suggest that the relationship between EF and SF deficits may strengthen throughout development. This line of research highlights potential sensitive periods for SF and EF training in children with PAE and suggests that fetal alcohol spectrum disorders programs consider targeting EF training as a component of social skill interventions.

Children's screen and problematic media use in the United States before and during the COVID-19 pandemic.

This mixed methods study examined parent-reported child screen media use before and during the COVID-19 pandemic by examining 2019-2020 changes in parent perceptions of media, screen media use (SMU), and problematic media use (PMU) in children aged 2-13 years (N = 129; 64 boys, 64 girls, 1 nonbinary; 90.7% White, 4.6% Hispanic/Latino, 0.8% Black, 8.5% multiethnic; primarily middle-to-high income). Quantitative analyses showed a significant SMU and PMU increase (medium effect size). There was a steeper increase in PMU among school-age (older) children. Together, the qualitative and quantitative results suggest that the PMU and SMU increase were influenced by distal, proximal, and maintaining factors including the COVID-19 pandemic, distance learning, child behaviors, other children, parental mediation, and positive media reinforcement.

Individual differences in executive function and learning: The role of knowledge type and conflict with prior knowledge.

Executive function (EF) predicts children's academic achievement; however, less is known about the relation between EF and the actual learning process. The current study examined how aspects of the material to be learned-the type of information and the amount of conflict between the content to be learned and children's prior knowledge-influence the relation between individual differences in EF and learning. Typically developing 4-year-olds (N = 61) completed a battery of EF tasks and several animal learning tasks that varied on the type of information being learned (factual vs. conceptual) and the amount of conflict with the learners' prior knowledge (no prior knowledge vs. no conflicting prior knowledge vs. conflicting prior knowledge). Individual differences in EF predicted children's overall learning, controlling for age, verbal IQ, and prior knowledge. Children's working memory and cognitive flexibility skills predicted their conceptual learning, whereas children's inhibitory control skills predicted their factual learning. In addition, individual differences in EF mattered more for children's learning of information that conflicted with their prior knowledge. These findings suggest that there may be differential relations between EF and learning depending on whether factual or conceptual information is being taught and the degree of conceptual change that is required. A better understanding of these different relations serves as an essential foundation for future research designed to create more effective academic interventions to optimize children's learning.

Pretending with realistic and fantastical stories facilitates executive function in 3-year-old children.

Fictional stories can affect many aspects of children's behavior and cognition, yet little is known about how they might help or hinder children's executive function skills. The current study investigated the role of story content (fantasy or reality) and mode of engagement with the story (pretense or a non-pretense control) on children's inhibitory control, an important component of early executive function. A total of 60 3-year-olds were randomly assigned to hear a fantastical or realistic story and were encouraged to engage in either pretense or a non-pretense activity related to the story. They then completed the Less Is More task of inhibitory control. Story content had no impact on children's inhibitory control; children performed equally well after hearing a fantastical or realistic story. However, children who engaged in story-related pretend play showed greater inhibitory control than those who engaged in a non-pretense activity. We found no interaction between story content and play engagement type. These results held when controlling for baseline inhibitory control, receptive vocabulary, age, gender, affect, and propensity toward pretense. Therefore, mode of play engagement with a story was more important in promoting children's inhibitory control skills than the degree of realism in the story.

Self-regulation as promotive for academic achievement in young children across risk contexts.

The link between self-regulation and academic achievement in young children is well-documented. However, few studies have examined the extent to which different aspects of self-regulation are more important for early numeracy and literacy for those in contexts of high cumulative risk, such as children experiencing homelessness. In the current study, 116 children ages 4;0-7;1 years (58 residing in an emergency homeless shelter and 58 from a community participant pool) completed assessments of math and reading, as well as multiple measures of self-regulation: executive function (EF), emotion regulation (ER), and respiratory sinus arrhythmia (RSA). Parents completed a questionnaire about their children's behavioral regulation. We examined whether sample (i.e., shelter or community) moderated the association between each aspect of self-regulation and academic outcomes. Results showed a main effect of EF skills on early numeracy, and this relation did not differ across samples. Intervention efforts to promote academic competencies might specifically target EF in those who struggle with early EF skills regardless of risk context.

Temporal dynamics of migration-linked genetic variation are driven by streamflows and riverscape permeability.

Landscape permeability is often explored spatially, but may also vary temporally. Landscape permeability, including partial barriers, influences migratory animals that move across the landscape. Partial barriers are common in rivers where barrier passage varies with streamflow. We explore the influence of partial barriers on the spatial and temporal distribution of migration-linked genotypes of Oncorhynchus mykiss, a salmonid fish with co-occurring resident and migratory forms, in tributaries to the South Fork Eel River, California, USA, Elder and Fox Creeks. We genotyped >4,000 individuals using RAD-capture and classified individuals as resident, heterozygous or migratory genotypes using life history-associated loci. Across four years of study (2014-2017), the permeability of partial barriers varied across dry and wet years. In Elder Creek, the largest waterfall was passable for adults migrating up-river 4-39 days each year. In this stream, the overall spatial pattern, with fewer migratory genotypes above the waterfall, remained true across dry and wet years (67%-76% of migratory alleles were downstream of the waterfall). We also observed a strong relationship between distance upstream and proportion of migratory alleles. In Fox Creek, the primary barrier is at the mouth, and we found that the migratory allele frequency varied with the annual timing of high flow events. In years when rain events occurred during the peak breeding season, migratory allele frequency was high (60%-68%), but otherwise it was low (30% in two years). We highlight that partial barriers and landscape permeability can be temporally dynamic, and this effect can be observed through changing genotype frequencies in migratory animals.

Refuges and ecological traps: Extreme drought threatens persistence of an endangered fish in intermittent streams.

Recent droughts raise global concern over potential biodiversity loss and mitigating impacts to vulnerable species has become a management priority. However, drought impacts on populations are difficult to predict, in part, because habitat refuges can buffer organisms from harsh environmental conditions. In a global change context, more extreme droughts may turn previously suitable habitats into ecological traps, where vulnerable species can no longer persist. Here, we explore the impacts of California's recent record-breaking drought on endangered juvenile Coho salmon. We estimated the variability of cumulative salmon survival using mark-recapture of nearly 20,000 tagged fish in intermittent stream pools during a 7-year period encompassing drought and non-drought conditions. We then determined the relative importance of physical habitat, streamflow, precipitation, landscape, and biological characteristics that may limit survival during drought. Our most striking result was an increase in the number of pools with reduced or zero survival during drought years and a coincident increase in spatial variability in survival among study reaches. In nearly half of the stream pools, salmon survival during drought was similar to mean survival of pools assessed during non-drought years, indicating some pools had remarkable resistance (ability to withstand disturbance) to extreme drought. Lower survival was most attributable to longer duration of disconnection between upstream and downstream habitats, a consequence of increasing drought severity. Our results not only suggest that many pools sustain juvenile salmon in non-drought years transition into ecological traps during drought but also highlight that some pools serve as refuges even under extreme drought conditions. Projected increases in drought severity that lead to longer droughts and greater habitat fragmentation could transform an increasing proportion of suitable habitats into ecological traps. Predicting future impacts of drought on Coho salmon and other sensitive species will require identification and protection of drought refuges and management strategies that prevent further habitat fragmentation.

Unnatural selection of salmon life histories in a modified riverscape.

Altered river flows and fragmented habitats often simplify riverine communities and favor non-native fishes, but their influence on life-history expression and survival is less clear. Here, we quantified the expression and ultimate success of diverse salmon emigration behaviors in an anthropogenically altered California river system. We analyzed two decades of Chinook salmon monitoring data to explore the influence of regulated flows on juvenile emigration phenology, abundance, and recruitment. We then followed seven cohorts into adulthood using otolith (ear stone) chemical archives to identify patterns in time- and size-selective mortality along the migratory corridor. Suppressed winter flow cues were associated with delayed emigration timing, particularly in warm, dry years, which was also when selection against late migrants was the most extreme. Lower, less variable flows were also associated with reduced juvenile and adult production, highlighting the importance of streamflow for cohort success in these southernmost populations. While most juveniles emigrated from the natal stream as fry or smolts, the survivors were dominated by the rare few that left at intermediate sizes and times, coinciding with managed flows released before extreme summer temperatures. The consistent selection against early (small) and late (large) migrants counters prevailing ecological theory that predicts different traits to be favored under varying environmental conditions. Yet, even with this weakened portfolio, maintaining a broad distribution in migration traits still increased adult production and reduced variance. In years exhibiting large fry pulses, even marginal increases in their survival would have significantly boosted recruitment. However, management actions favoring any single phenotype could have negative evolutionary and demographic consequences, potentially reducing adaptability and population stability. To recover fish populations and support viable fisheries in a warming and increasingly unpredictable climate, coordinating flow and habitat management within and among watersheds will be critical to balance trait optimization versus diversification.

Protected areas buffer against harvest selection and rebuild phenotypic complexity.

Harvest mortality typically truncates the harvested species' size structure, thereby reducing phenotypic complexity, which can lead to reduced population productivity, increased population variability, and selection on an array of life history traits that can further alter these demographic processes. Marine protected areas (MPAs) are a potential tool to protect older, larger individuals and therefore mitigate such ecological and evolutionary effects of harvest, depending on the degree of connectivity among areas. Such MPA protection relies on a shift in size-dependent mortality, the measurement of which can therefore serve as an early indicator of whether MPAs might achieve the desired longer-term ecological and evolutionary responses. We directly measured MPA effects on size-selective mortality and associated size structure using mark-recapture data on European lobster (Homarus gammarus) collected at three MPA-control area pairs in southern Norway during one decade (n = 5,943). Mark-recapture modeling, accounting for variation in recapture probabilities, revealed (1) that annual mean survival was higher inside MPAs (0.592) vs. control areas (0.298) and (2) that significant negative relationships between survival and body size occurred at the control areas but not in the MPAs, where the effect of body size was predominantly positive. Additionally, we found (3) that mean and maximum body size increased over time inside MPAs but not in control areas. Overall, our results suggest that MPAs can rebuild phenotypic complexity (i.e., size structure) and provide protection from harvest selection.

Indirect genetic control of migration in a salmonid fish.

Migration is a complex trait that often has genetic underpinnings. However, it is unclear if migratory behaviour itself is inherited (direct genetic control), or if the decision to migrate is instead the outcome of a set of physiological traits (indirect genetic control). For steelhead/rainbow trout (Oncorhynchus mykiss), migration is strongly linked to a large genomic region across their range. Here, we demonstrate a shared allelic basis between early life growth rate and migratory behaviour. Next, we demonstrate that early life growth differs among resident/migratory genotypes in wild juveniles several months prior to migration, with resident genotypes achieving a larger size in their first few months of life than migratory genotypes. We suggest that the genetic basis of migration is likely indirect and mediated by physiological traits such as growth rate. Evolutionary benefits of this indirect genetic mechanism likely include flexibility among individuals and persistence of life-history diversity within and among populations.

No evidence that warmer temperatures are associated with selection for smaller body sizes.

Reductions in animal body size over recent decades are often interpreted as an adaptive evolutionary response to climate warming. However, for reductions in size to reflect adaptive evolution, directional selection on body size within populations must have become negative, or where already negative, to have become more so, as temperatures increased. To test this hypothesis, we performed traditional and phylogenetic meta-analyses of the association between annual estimates of directional selection on body size from wild populations and annual mean temperatures from 39 longitudinal studies. We found no evidence that warmer environments were associated with selection for smaller size. Instead, selection consistently favoured larger individuals, and was invariant to temperature. These patterns were similar in ectotherms and endotherms. An analysis using year rather than temperature revealed similar patterns, suggesting no evidence that selection has changed over time, and also indicating that the lack of association with annual temperature was not an artefact of choosing an erroneous time window for aggregating the temperature data. Although phenotypic trends in size will be driven by a combination of genetic and environmental factors, our results suggest little evidence for a necessary ingredient-negative directional selection-for declines in body size to be considered an adaptive evolutionary response to changing selection pressures.

Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter.

Climate change and human pressures are changing the global distribution and the extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico-chemical changes (preconditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale. We experimentally simulated, under standard laboratory conditions, rewetting of leaves, riverbed sediments, and epilithic biofilms collected during the dry phase across 205 IRES from five major climate zones. We determined the amounts and qualitative characteristics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds. In addition, we evaluated the variance in leachate characteristics in relation to selected environmental variables and substrate characteristics. We found that sediments, due to their large quantities within riverbeds, contribute most to the overall flux of dissolved substances during rewetting events (56%-98%), and that flux rates distinctly differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contributed most to the areal fluxes. The largest amounts of leached substances were found in the continental climate zone, coinciding with the lowest potential bioavailability of the leached OM. The opposite pattern was found in the arid zone. Environmental variables expected to be modified under climate change (i.e. potential evapotranspiration, aridity, dry period duration, land use) were correlated with the amount of leached substances, with the strongest relationship found for sediments. These results show that the role of IRES should be accounted for in global biogeochemical cycles, especially because prevalence of IRES will increase due to increasing severity of drying events.

Age-related change in brain rhythms from early to middle childhood: Links to executive function.

The connection between brain rhythms at rest and cognition remains poorly understood. This is especially true during early childhood in which neuroimaging data are relatively scarce. We developed a new method for collecting eyes closed and eyes open resting state electroencephalography (EEG) suitable for young children. We report results characterizing age-related change in power in multiple brain rhythms over frontal and posterior regions under eyes closed and open conditions of rest in 3-, 4-, 5- and 9-year-old children (N = 162). We observed two key patterns of results. First, with age theta decreased, alpha increased, and alpha peak frequency increased. Second, power was generally higher when eyes were closed than open for theta and alpha but higher when eyes were open than closed for beta and gamma. We also investigated the relation between resting state EEG activity and executive function (EF) using the Minnesota Executive Function Scale, a standardized behavioral measure of EF for ages 2 and up. Correlational and regression analyses showed that individual differences in the theta/beta ratio is associated with EF even after controlling for children's age and verbal abilities. We situate our results in a theoretical discussion of theta/beta and its role in control processes.

Recent shifts in the occurrence, cause, and magnitude of animal mass mortality events.

Mass mortality events (MMEs) are rapidly occurring catastrophic demographic events that punctuate background mortality levels. Individual MMEs are staggering in their observed magnitude: removing more than 90% of a population, resulting in the death of more than a billion individuals, or producing 700 million tons of dead biomass in a single event. Despite extensive documentation of individual MMEs, we have no understanding of the major features characterizing the occurrence and magnitude of MMEs, their causes, or trends through time. Thus, no framework exists for contextualizing MMEs in the wake of ongoing global and regional perturbations to natural systems. Here we present an analysis of 727 published MMEs from across the globe, affecting 2,407 animal populations. We show that the magnitude of MMEs has been intensifying for birds, fishes, and marine invertebrates; invariant for mammals; and decreasing for reptiles and amphibians. These shifts in magnitude proved robust when we accounted for an increase in the occurrence of MMEs since 1940. However, it remains unclear whether the increase in the occurrence of MMEs represents a true pattern or simply a perceived increase. Regardless, the increase in MMEs appears to be associated with a rise in disease emergence, biotoxicity, and events produced by multiple interacting stressors, yet temporal trends in MME causes varied among taxa and may be associated with increased detectability. In addition, MMEs with the largest magnitudes were those that resulted from multiple stressors, starvation, and disease. These results advance our understanding of rare demographic processes and their relationship to global and regional perturbations to natural systems.