Asynchronous Fluctuations Research Articles

Abundance, habitat distribution and content of reserve energy substances in shrews (Sorex caecutiens, Sorex isodon) within the Seymchan-Buyundinskaya Depression (Upper Kolyma River region)

This research examined the influence of interspecific interactions among shrew species on their territorial distribution and trophic conditions within larch and poplar-chosenia forests along the upper Kolyma River. The study specifically analyzed the biotopic characteristics associated with the relative abundance and energy reserve content, including fat tissue mass and glycogen levels in the liver, of Sorex caecutiens and S. isodon. Fieldwork was conducted in the Seymchan- Buyunda depression during July and August in 2003 and 2010. A total of 1,588 individuals from both species were captured using pitfall traps. The assessment of energy reserve content in S. caecutiens (n = 736) and S. isodon (n = 113) was carried out between 2006 and 2010. The abundance of S. caecutiens in the examined habitats exhibited consistent trends and a strong correlation (RS = 0.95, p < 0.01). Conversely, S. isodon displayed asynchronous fluctuations in abundance across various habitats, likely attributable to competition with Laxmann’s shrew, which tends to displace S. isodon from its preferred larch forest during periods of elevated population density. The interannual variations in energy reserve content for both shrew species were remarkably similar, with no significant differences observed between habitats. The nature of these variations suggested insufficient feeding conditions for the animals during years of high overall abundance, with the dominant species, S. caecutiens, contributing most significantly to this phenomenon in both habitats of the upper Kolyma. The results indicate that interspecific relationships play a crucial role in shaping both territorial distribution and food availability for these shrew species.

Asynchronous abundance fluctuations can drive giant genotype frequency fluctuations.

Large stochastic population abundance fluctuations are ubiquitous across the tree of life1-7, impacting the predictability of population dynamics and influencing eco-evolutionary outcomes. It has generally been thought that these large abundance fluctuations do not strongly impact evolution, as the relative frequencies of alleles in the population will be unaffected if the abundance of all alleles fluctuate in unison. However, we argue that large abundance fluctuations can lead to significant genotype frequency fluctuations if different genotypes within a population experience these fluctuations asynchronously. By serially diluting mixtures of two closely related E. coli strains, we show that such asynchrony can occur, leading to giant frequency fluctuations that far exceed expectations from models of genetic drift. We develop a flexible, effective model that explains the abundance fluctuations as arising from correlated offspring numbers between individuals, and the large frequency fluctuations result from even slight decoupling in offspring numbers between genotypes. This model accurately describes the observed abundance and frequency fluctuation scaling behaviors. Our findings suggest chaotic dynamics underpin these giant fluctuations, causing initially similar trajectories to diverge exponentially; subtle environmental changes can be magnified, leading to batch correlations in identical growth conditions. Furthermore, we present evidence that such decoupling noise is also present in mixed-genotype S. cerevisiae populations. We demonstrate that such decoupling noise can strongly influence evolutionary outcomes, in a manner distinct from genetic drift. Given the generic nature of asynchronous fluctuations, we anticipate that they are widespread in biological populations, significantly affecting evolutionary and ecological dynamics.

Marine protected areas promote stability of reef fish communities under climate warming

Protection from direct human impacts can safeguard marine life, yet ocean warming crosses marine protected area boundaries. Here, we test whether protection offers resilience to marine heatwaves from local to network scales. We examine 71,269 timeseries of population abundances for 2269 reef fish species surveyed in 357 protected versus 747 open sites worldwide. We quantify the stability of reef fish abundance from populations to metacommunities, considering responses of species and functional diversity including thermal affinity of different trophic groups. Overall, protection mitigates adverse effects of marine heatwaves on fish abundance, community stability, asynchronous fluctuations and functional richness. We find that local stability is positively related to distance from centers of high human density only in protected areas. We provide evidence that networks of protected areas have persistent reef fish communities in warming oceans by maintaining large populations and promoting stability at different levels of biological organization.

No positive effects of biodiversity on ecological resilience of lake ecosystems

<p>Ecological resilience is critical for ecosystems to persist in the face of perturbations without shifting to a different state. Global biodiversity loss in multiple ecosystems is considered to be associated with decreasing ecological resilience and increasing the risk of ecosystem collapse. However, how temporal changes in biodiversity affect ecological resilience in natural ecosystems remains poorly elucidated. By analyzing subfossil records of diatoms, chironomids, and cladocerans from 53 lake sediment cores across the globe, we found that species richness showed an increasing trend with time, while beta diversity and ecological resilience presented a decreasing temporal trend when ecosystems are approaching the abrupt shift. Asynchronous fluctuations among species and temporal stability at species level are suggested to be the mechanisms that contribute to the maintenance of temporal community stability. We found species richness and beta diversity have positive effects on species asynchrony but negative effects on species stability. However, we found that species asynchrony and species stability had negative relationships with ecological resilience, with species richness and beta diversity overall having no positive effects on ecological resilience. We highlighted that biodiversity effects on ecological resilience are not only the role of species richness, but also the species assemblage and network complexity of species-species interactions. Our study indicates that increased species diversity and community heterogeneity may be not beneficial for the ecosystem to recover from disturbances at a lake ecosystem scale, which has great implications for the assessment of ecological resilience and predicting ecosystem collapse in future global environmental change scenarios.</p>

Integrating Information from the Past into Oyster Management

In the United States, the eastern oyster (Crassostrea virginica) is an economically, culturally, and ecologically important oyster species that ranges from Maine to Texas. Eastern oyster populations are managed by a variety of federal, state, and local governments as well as non-governmental organizations. In addition, the long history of oyster harvesting and coastal land use change in the United States, and asynchronous fluctuations in abundance across the species range due to diverse pressures (e.g., hydrological changes, pollution, disease, overharvesting), combined with often scarce historical monitoring records documenting the timing and magnitude of the changes, have challenged oyster applied professionals for well over a century. The Oysters Past Working Group (OPWG) brings together academic researchers (paleoecologists, archaeologists, and historical ecologists) and applied professionals, representing federal, state, and local government and non-governmental organizations tasked with conserving, managing, and/or restoring oyster populations and habitat. The primary goals of the OPWG are to: 1) identify priority research directions for academic researchers by evaluating the information needs among applied professionals and the types of information from the past that may be able to address them; 2) create a guidance document on best practices for applying information from the past to oyster management; and 3) build trust and commitment to promote longer-lasting and sustained collaboration between academic researchers and applied professionals.

Implementation of the Stabilizing Function of a Fiscal Policy in the Eurozone Countries

The implementation of a stabilizing fiscal policy is of particular importance to the eurozone countries, which do not have the ability to make autonomous decisions in the scope of their monetary policy in order to ease fluctuations of an economic cycle. The aim of this research was to evaluate the implementation of a discretionary fiscal policy in selected countries of this bloc. The ex post analysis of the approaches to national fiscal policies, with a division into two research sub-periods, was conducted with statistical methods. Based on the official forecasts by the European Commission, a “real time analysis” was also made, which to some extent enables gaining an insight into plans and intentions of the governments at the moment of making budgetary decisions. The results call into question the use of discretionary fiscal policies in stabilizing the economic cycle at the national level in the studied Eurozone countries. It can be said that the reforms implemented after the financial and economic crisis had a limited impact on the intentions and the actual implementation of the fiscal policies in an anti-cyclical manner. It is then sensible to consider alternative mechanisms, which could successfully lessen the asynchronous fluctuations in production within the European monetary union.

The portfolio effect in a small-scale fishery reduces catch and fishing income variability in a highly dynamic ecosystem.

It is an increasingly accepted idea that biological diversity stabilizes ecosystem processes and the services they provide to society. By reducing biomass fluctuation, biodiversity could mitigate the impact of changing environmental conditions on rural incomes as long as people exploits a diverse set of natural assets. This effect is analogous to the risk-spreading function of financial portfolios. This paper presents evidence of the portfolio effect for an open-access artisanal fishery in an estuarine ecosystem, located in a Colombian Biosphere Reserve. Using catch statistics from 2002 to 2018, we evaluate the contribution of catch diversity to the stabilization of fishing income. We find that changes in catch composition are related to seasonal and interannual variations in salinity conditions. The portfolio effect arises from asynchronous fluctuations of fish species due to fluctuating environmental conditions. Catch diversification, instead of specialization, help achieve resilient fisheries.

Independent Effects of Species Removal and Asynchrony on Invariability of an Intertidal Rocky Shore Community

Ecological stability depends on interactions between different levels of biological organization. The insurance effects occur when increasing species diversity leads to more temporally invariable (i.e., more stable) community-level properties, due in part to asynchronous population-level fluctuations. While the study of insurance effects has received considerable attention, the role of dominant species that contribute with particular functional traits across different level of organizations is less understood. Using a field-based manipulative experiment, we investigated how species richness and different types of parameters at the population level, such as the invariability of dominants, population invariability, and population asynchrony, influence the community invariability. The experiment involved the repetitive removal of the canopy forming algaMazzaella laminarioides(hereafter “Mazzaella”) during 32 months in two rocky intertidal sites of northern-central Chile. We predicted that the invariability of dominants enhances community invariability, that the effect of multispecies population-level parameters on community invariability are dependent on species richness, and that subdominant algae are unable to fully compensate the loss of canopies of the dominant species. Biomass of algae and mobile invertebrates was quantified over time. We observed independent effects ofMazzaellaremoval and community-wide asynchrony on community invariability. While canopy removal reduced community invariability, population asynchrony boosted community invariability regardless of the presence of canopies. In addition, filamentous and foliose algae were unable to compensate the loss of biomass triggered by the experimental removal ofMazzaella. Canopy removal led to a severe decrement in the biomass of macrograzers, while, at the same time, increased the biomass of mesograzers. Asynchrony stemmed from compensatory trophic responses of mesograzers to increased abundances of opportunistic algae. Thus, further work on consumer-resource interactions will improve our understanding of the links between population- and community-level aspects of stability.

Influence of soil and relief on productivity of clover-timothy herbage

Relevance. The article is devoted to the topical problem of studying the influence of soil conditions and the relief of an agricultural landscape on the yield of clover-timothy herbage on drained soils, knowledge of which makes it possible to optimize the production process of crops in the mode of adaptive landscape farming.Methods and results. The studies were carried out in 1998–2020 at the test site of the All-Russian Research Institute of Reclaimed Lands (VNIIMZ) – a branch of the Federal Research Centre Soil Science Institute named after V.V. Dokuchaev (Tver region), located within the end-moraine hill. The purpose of the research is to study the influence of soil conditions and the relief of the agricultural landscape on the yield of clover-timothy herbage of 1 year of use. Grass productivity monitoring was carried out on a transect – a field crossing the main microlandscape positions (relief elements) and elementary soil combinations of the agrolandscape. Crop productivity and other parameters of the vegetation and soil cover on the transect were taken into account on 30 systematically located plots, within which there are 4 replicates, 23 m2 in area, spaced 10 m from each other.Results of studies on productivity were processed by correlation and multivariate analysis of variance. Studies have shown that the relief and soil features of the agricultural landscape have almost the same effect on the crop yield. Each of these factors, on average, determined 18–16% of the spatial variability in productivity. About 2/3 of the variability in the yield of herbs depends on factors that are difficult to take into account. It was found that the degree of influence of the relief and soils on the yield of grasses is not constant over time and ranges from 2 to 33%. In the time series of observations, periods of synchronous and asynchronous fluctuations in the degrees of influence of soil and relief on the yield were distinguished. Synchronization of temporal fluctuations in the degrees of impact on the productivity of grasses of different elements of the landscape occurs with a decrease in the amount of precipitation and active temperatures. On the basis of the revealed patterns, it is possible to develop measures to adapt technologies for growing perennial grasses to the natural conditions of farms in the mode of adaptive landscape fodder production.

Functional redundancy and stability in a subtidal macroalgal community in the Southwestern Atlantic coast

Functional redundancy can stabilize ecological functions as asynchronous fluctuations among functionally similar species may buffer environmental changes. We investigated the temporal dynamics of a subtidal macroalgal community in the warm temperate Southwestern Atlantic coast (SWA) to evaluate whether functional redundancy stabilize ecosystems functions through compensatory dynamics under realistic environmental scenarios. Despite temporal variations in the community structure occurred, a high stability in macroalgal coverage was found at the community-level driven by taxa asynchronous fluctuations. No relationship between functional redundancy and stability occurred, suggesting that functional compensation cannot surpass the influence of environmental fluctuations on the performance of ecological functions. Declines in Sargassum species abundance, along with its low functional redundancy, indicate that this canopy-forming algae must be prioritized in conservation efforts in the SWA. Our study adds to the comprehension and generalization of biodiversity-stability findings in natural systems across distinct geographical areas, also contributing to their operationalization in marine ecosystems.

Perceptual Fluctuations within the Entrepreneurial Journey: Experience from Process-Based Entrepreneurship Training

The entrepreneurial idea and opportunity are formed in the entrepreneurial process, which is characterized by entrepreneurial learning. During the entrepreneurial journey, the entrepreneur repeatedly reassesses the maturity of his business/venture idea and venture creation process to enter the market. The entrepreneur’s decisions are influenced by both objective and affective circumstances. This study aims to identify and map the fluctuations of idea–opportunity perception and affection by a student entrepreneur throughout the entrepreneurial learning journey simulating a genuine entrepreneurial (learning) process. The data collection of variables took place during an entrepreneurship course that modeled the entrepreneurial journey via process-based entrepreneurship training and applying feasibility and attractiveness self-assessment, observation and in-depth interviews. A small group of doctoral students developed their business ideas during a process-based entrepreneurship course. After each lesson and homework, they assessed the feasibility and attractiveness of their idea and opportunity. The results showed asynchronous fluctuations in these individual context-based perception variables, frequently depending on the progression of the entrepreneurial journey. The study added the concept of affective artifact and some generalizing dimensions to describe the entrepreneurial journey. Recommendations are given for the implementation and research of entrepreneurial process-based training.

Predator avoidance and foraging for food shape synchrony and response to perturbations in trophic metacommunities

The response of species to perturbations strongly depends on spatial aspects in populations connected by dispersal. Asynchronous fluctuations in biomass among populations lower the risk of simultaneous local extinctions and thus reduce the regional extinction risk. However, dispersal is often seen as passive diffusion that balances species abundance between distant patches, whereas ecological constraints, such as predator avoidance or foraging for food, trigger the movement of individuals. Here, we propose a model in which dispersal rates depend on the abundance of the species interacting with the dispersing species (e.g., prey or predators) to determine how density-dependent dispersal shapes spatial synchrony in trophic metacommunities in response to stochastic perturbations. Thus, unlike those with passive dispersal, this model with density-dependent dispersal bypasses the classic vertical transmission of perturbations due to trophic interactions and deeply alters synchrony patterns. We show that the species with the highest coefficient of variation of biomass governs the dispersal rate of the dispersing species and determines the synchrony of its populations. In addition, we show that this mechanism can be modulated by the relative impact of each species on the growth rate of the dispersing species. Species affected by several constraints disperse to mitigate the strongest constraints (e.g., predation), which does not necessarily experience the highest variations due to perturbations. Our approach can disentangle the joint effects of several factors implied in dispersal and provides a more accurate description of dispersal and its consequences on metacommunity dynamics.

Diets of the Barents Sea cod (<i>Gadus morhua</i>) from the 1930s to 2018

Abstract. A new dataset on the diet of Atlantic cod in the Barents Sea from the 1930s to the present day has been compiled to produce one of the largest fish diet datasets available globally. Atlantic cod is one of the most ecologically and commercially important fish species in the North Atlantic. The stock in the Barents Sea is by far the largest, as a result of both successful management and favourable environmental conditions since the early 2000s. As a top predator, cod plays a key role in the Barents Sea ecosystem. The species has a broad diet consisting mainly of crustaceans and teleost fish, and both the amount and type of prey vary in space and time. The data – from Russia, Norway and the United Kingdom – represent quantitative stomach content records from more than 400 000 fish and qualitative data from 2.5 million fish. Many of the data are from joint collaborative surveys between Norway and Russia. The sampling was conducted throughout each year, allowing for seasonal, annual and decadal comparisons to be made. Visual analysis shows cod diets have changed considerably from the start of the dataset in the 1930s to the present day. There was a large proportion of herring in the diets in the 1930s, whereas in more recent decades capelin, invertebrates and other fish dominate. There are also significant interannual asynchronous fluctuations in prey, particularly capelin and euphausiids. Combining these datasets can help us understand how the environment and ecosystems are responding to climatic changes, and what influences the diet and prey switching of cod. Trends in temperature and variability indices can be tested against the occurrence of different prey items, and the effects of fishing pressure on cod and prey stocks on diet composition could be investigated. The dataset will also enable us to improve parametrization of food web models and to forecast how Barents Sea fisheries may respond in the future to management and to climate change. The Russian data are available through joint projects with the Polar Branch of the Russian Federal Research Institute of Fisheries and Oceanography (VNIRO). The UK and Norwegian data (Townhill et al., 2020) are being released with this paper at https://doi.org/10.21335/NMDC-2139169383.

Complementary mechanisms stabilize national food production

Ensuring the temporal stability of national food production is crucial for avoiding sharp drops in domestic food availability. The average stability of individual crop yields and asynchrony among crop yield fluctuations are two candidate mechanisms to stabilize national food production. However, the quantification of their respective influence on the stability of national food production is lacking, as is the identification of the factors regulating both mechanisms. Using yield data for 138 crops and 115 countries over a 50-year period, we first show that the stability of total national yield mostly relies on the fluctuations of the yield of crops covering the largest share of cropland. The average yield stability of these crops exert a stabilizing effect on national food production that is twice as important as the one of the asynchronous yield fluctuations among them. Climate variability reduces the stability of national food production by synchronizing yield fluctuations among crops and destabilizing the yield of individual crops. However, our results suggest that increasing crop diversity can counteract the synchronizing effects of climate variability by enhancing asynchronous dynamics among crops. Irrigation can promote the average stability of individual crop yields but cannot compensate for the destabilizing effect of climate variability. Considering both the response of each crop to climatic variations and the dynamics emerging from crop baskets will help agricultural policies to ensure stable food supply at the national level.

Research long-term fluctuations in winter temperatures. Methods for analyzing the intensities and synchronicities of fluctuations in fuel consumption

The article deals with the problem of assessing the deviations of the meteorological characteristics of the heating season. The usual method of calculating the relative deviations of indicators from the arithmetic mean is not suitable. A requirement is imposed on the “new” averages and estimates of deviations of meteorological characteristics, which follows from their properties: the duration multiplied by the average daily temperature difference for the heating period should be equal to the integral temperature difference. The application of this property to the means and to the very estimates of the deviations of meteorological characteristics makes it difficult to determine the latter. A method is being developed to determine the intensities of fluctuations in the meteorological characteristics of the heating season. Intensities show how much, on average, the duration, average daily and integral temperature differences for the heating period can deviate from the average expected level. A technique is being developed for reflecting synchronous and asynchronous fluctuations in deviations of meteorological characteristics, and the contributions of these fluctuations are determined.

On the origin of ultraslow spontaneous Na+ fluctuations in neurons of the neonatal forebrain.

Spontaneous neuronal and astrocytic activity in the neonate forebrain is believed to drive the maturation of individual cells and their integration into complex brain-region-specific networks. The previously reported forms include bursts of electrical activity and oscillations in intracellular Ca2+ concentration. Here, we use ratiometric Na+ imaging to demonstrate spontaneous fluctuations in the intracellular Na+ concentration of CA1 pyramidal neurons and astrocytes in tissue slices obtained from the hippocampus of mice at postnatal days 2-4 (P2-4). These occur at very low frequency (∼2/h), can last minutes with amplitudes up to several millimolar, and mostly disappear after the first postnatal week. To further investigate their mechanisms, we model a network consisting of pyramidal neurons and interneurons. Experimentally observed Na+ fluctuations are mimicked when GABAergic inhibition in the simulated network is made depolarizing. Both our experiments and computational model show that blocking voltage-gated Na+ channels or GABAergic signaling significantly diminish the neuronal Na+ fluctuations. On the other hand, blocking a variety of other ion channels, receptors, or transporters including glutamatergic pathways does not have significant effects. Our model also shows that the amplitude and duration of Na+ fluctuations decrease as we increase the strength of glial K+ uptake. Furthermore, neurons with smaller somatic volumes exhibit fluctuations with higher frequency and amplitude. As opposed to this, larger extracellular to intracellular volume ratio observed in neonatal brain exerts a dampening effect. Finally, our model predicts that these periods of spontaneous Na+ influx leave neonatal neuronal networks more vulnerable to seizure-like states when compared with mature brain.NEW & NOTEWORTHY Spontaneous activity in the neonate forebrain plays a key role in cell maturation and brain development. We report spontaneous, ultraslow, asynchronous fluctuations in the intracellular Na+ concentration of neurons and astrocytes. We show that this activity is not correlated with the previously reported synchronous neuronal population bursting or Ca2+ oscillations, both of which occur at much faster timescales. Furthermore, extracellular K+ concentration remains nearly constant. The spontaneous Na+ fluctuations disappear after the first postnatal week.

Disentangling local, metapopulation, and cross-community sources of stabilization and asynchrony in metacommunities.

Asynchronous fluctuations of populations are essential for maintaining stable levels of bio-mass and ecosystem function in landscapes. Yet, understanding the stabilization of metacommunities by asynchrony is complicated by the existence of multiple forms of asynchrony that are typically studied independently: Community ecologists, for instance, focus on asynchrony within and among local communities, while population ecologists emphasize asynchrony of populations in metapopulations. Still, other forms of asynchrony, such as that which underlies the spatial insurance effect, are not captured by any existing analytical frameworks. We therefore developed a framework that would in one analysis unmask the stabilizing roles of local communities and metapopulations and so unify these perspectives. Our framework shows that metacommunity stabilization arises from one local and two regional forms of asynchrony: (1) asynchrony among species of a local community, (2) asynchrony among populations of a metapopulation, and (3) cross-community asynchrony, which is between different species in different local communities and underlies spatial insurance. For each type of stabilization, we derived links to diversity indices and associated diversity-stability relationships. We deployed this framework in a set of rock pool invertebrate metacommunities in Discovery Bay, Jamaica, to partition sources of stabilization and test their dependence on diversity. Cross-community asynchrony was the dominant form of stabilization, accounting for >60% of total metacommunity stabilization despite being undetectable with existing frameworks. Environmental variation influenced types of stabilization through different mechanisms. pH and dissolved oxygen, for example, increased asynchrony by decorrelating local species, while salinity did so by changing the abundance structure of metapopulations. Lastly, all types of asynchrony depended strongly on different types of diversity (alpha, metapopulation, and beta diversity drove local, metapopulation, and cross-community asynchrony, respectively) to produce multiple diversity-stability relationships within metacommunities. Our new partition of metacommunity dynamics highlights how different elements—from local communities to metapopulations—combine to stabilize metacommunities and depend critically on contrasting environmental regimes and diversities. Understanding and balancing these sources of stability in dynamic landscapes is a looming challenge for the future. We suggest that synthetic frameworks which merge ecological perspectives will be essential for grasping and safeguarding the stability of natural systems.

Limited evidence for sardine and anchovy asynchrony: re-examining an old story.

Asynchronous fluctuations in abundance between species with similar ecological roles can stabilize food webs and support coexistence. Sardine (Sardinops spp.) and anchovy (Engraulis spp.) have long been used as an example of this pattern because low-frequency variation in catches of these species appears to occur out of phase, suggesting that fisheries and generalist predators could be buffered against shifts in productivity of a single species. Using landings data and biomass and recruitment estimates from five regions, we find that species do not have equivalent peak abundances, suggesting that high abundance in one species does not compensate for low abundance in the other. We find that globally there is a stronger pattern of asynchrony in landings compared to biomass, such that landings data have exaggerated the patterns of asynchrony. Finally, we show that power to detect decadal asynchrony is poor, requiring a time series more than twice the length of the period of fluctuation. These results indicate that it is unlikely that the dynamics of these two species are compensatory enough to buffer fisheries and predators from changes in abundance, and that the measurements of asynchrony have largely been a statistical artefact of using short time series and landings data to infer ecology.

Local species diversity, β-diversity and climate influence the regional stability of bird biomass across North America.

Biodiversity often stabilizes aggregate ecosystem properties (e.g. biomass) at small spatial scales. However, the importance of species diversity within communities and variation in species composition among communities (β-diversity) for stability at larger scales remains unclear. Using a continental-scale analysis of 1657 North American breeding-bird communities spanning 20-years and 35 ecoregions, we show local species diversity and β-diversity influence two components of regional stability: local stability (stability of bird biomass within sites) and spatial asynchrony (asynchronous fluctuations in biomass among sites). We found spatial asynchrony explained three times more variation in regional stability of bird biomass than did local stability. This result contrasts with studies at smaller spatial scales-typically plant metacommunities under 1 ha-that find local stability to be more important than spatial asynchrony. Moreover, spatial asynchrony of bird biomass increased with bird β-diversity and climate heterogeneity (temperature and precipitation), while local stability increased with species diversity. Our study reveals new insights into the scale-dependent processes regulating ecosystem stability, providing evidence that both local biodiversity loss and homogenization can destabilize ecosystem processes at biogeographic scales.

Mediterranean landscape change during the Holocene: Synthesis, comparison and regional trends in population, land cover and climate

This synthesis paper offers a comparative perspective on how seven different Mediterranean regions, from Iberia and Morocco to the Levant, have been transformed by human and natural agencies during the past 10 millennia. It draws on a range of data sources: notably (1) archaeological site surveys ( n = 32,000) and 14C dates ( n = 12,000) as proxies for long-term population change, (2) pollen records as a proxy for past vegetation and land cover ( n = 253) and (3) proxies, such as stable isotopes, from lake, cave and marine records as indicators of hydro-climate ( n = 47). Where possible, these data sets have been made spatially and temporally congruent in order to examine relationships between them statistically and graphically. Data have been aggregated or averaged for each region/sub-region and put into 200-year time windows. Archaeo-demographic data show a clear increase at the start of Neolithic farming, followed by a series of regionally asynchronous fluctuations in population, prior to a pan-Mediterranean Roman settlement maximum. Pollen data indicate a late-Holocene decline in %Arboreal Pollen in those regions that were initially well wooded, but not in drier regions of the southern/eastern Mediterranean. Overall, the clearest palynological proxy for human land cover change is provided by the OJCV (tree crop) index. The cultivation of these trees in the eastern Mediterranean after 6500 cal. yr BP may have been an adaptive response to mid-Holocene climatic desiccation. These anthropogenic pollen indicators correlate more closely with trends in population than with regional hydro-climatic z scores, implying that they reflect primarily human activities. During the mid Holocene, most Mediterranean landscapes were transformed by a combination of climate and rural land use, but after ~3500 cal. yr BP, human actions became increasingly dominant in determining land cover. During the past 1500 years, the dominant landscape trajectory in the eastern Mediterranean was markedly different to that in the central/western Mediterranean.