Environmental Synchrony Research Articles

Drivers and spatial patterns of population synchrony of fish species in a floodplain

Abstract Spatial synchrony is the correlation between the temporal dynamics of local populations. This pattern may be driven by spatially correlated environmental variation (i.e., Moran effect), dispersal and trophic interactions. Investigating geographic patterns of synchrony can help disentangle the relative importance of these drivers. Using fish abundance data from long‐term ecological research (17 years) in the Upper Paraná River floodplain, we studied the relative roles of dispersal distance, density dependence differences, and environmental synchrony in determining spatial synchrony of the most common species in this floodplain. We also investigated the geography of spatial synchrony by estimating modularity and site‐level contributions to synchrony and anti‐synchrony networks. We found positive spatial synchrony for most species, but levels were relatively low. For most species, our explanatory matrices were poorly related to spatial synchrony. We detected modular structures in some species networks, which reflected complex spatial patterns in synchrony. We also detected sites with high importance to spatial synchrony patterns that could be managed to increase metapopulation stability. The variable levels of spatial synchrony for fish species in the Upper Paraná River floodplain implies the need to monitor several sites to understand their dynamics in this region. Also, some migratory species of high importance to regional fisheries, such as Prochilodus lineatus, may deserve special monitoring attention due to the increased regional extinction risk associated with their high levels of spatial synchrony. Finally, we speculate that hydrological manipulation from upstream reservoirs should consider the timing of water releases to avoid spatially correlated population declines.

Scaling of population resilience with dispersal length and habitat size

Environmental fluctuations can create population-depleted areas and even extinct areas for the population. This effect is more severe in the presence of the Allee effect (decreasing growth rate at low population densities). Dispersal inside the habitat provides a rescue effect on population-depleted areas, enhancing the population resilience to environmental fluctuations. Habitat reduction decreases the effectiveness of the dispersal rescue mechanism. We report here how the population resilience to environmental fluctuations decreases when the dispersal length or the habitat size are reduced. The resilience reduction is characterized by a decrease of the extinction threshold for environmental fluctuations. The extinction threshold is shown to scale with the ratio between the dispersal length and the scale of environmental synchrony, i.e. it is the dispersal connection between non-environmentally-correlated regions that provides resilience to environmental fluctuations. Habitat reduction also decreases the resilience to environmental fluctuations, when the habitat size is similar to or smaller than the characteristic dispersal distances. The power laws of these scaling behaviors are characterized here. Alternative scaling functions with spatial scales of population synchrony are found to fit the simulations worse. These results support the dispersal length as the critical scale for extinction induced by habitat reduction.

Spatiotemporal variation in climatic conditions across ecosystems

Environmental variation in time and space affects biological processes such as extinction risk and speed of adaptation to environmental change. The spatial structure of environmental variation may vary among ecosystems, for instance due to differences in the flow of nutrients, genes and individuals. However, inferences about ecosystem spatial scale should also include spatial autocorrelation in environmental stochasticity, such as fluctuations in weather or climate. We used spatially structured time series (19-36 yr) on temperature from 4 different ecosystems (terrestrial, limnic, coastal sea and open ocean) to assess the spatiotemporal patterns of environmental variation over large geographical scales (up to 1900 km) during summer and winter. The distance of positive spatial autocorrelation in mean temperature was greatest for the terrestrial system (range: 592-622 km), and shorter for the open ocean (range: 472-414 km), coastal sea (range: 155-814 km) and the limnic systems (range: 51-324 km), suggesting a stronger spatial structure in environmental variation in the terrestrial system. The terrestrial system had high spatial synchrony in temperature (mean correlation: winter = 0.82, summer = 0.66) with a great spatial scaling (>650 km). Consequently, populations of terrestrial species experience similar environmental fluctuations even at distances up to 1000 km, compared to species in the aquatic systems (<500 km). There were clear seasonal differences in environmental synchrony in the terrestrial and limnic systems, but less so in the other systems. Our results suggest that biological processes affected by environmental stochasticity occur at the largest spatial scale in terrestrial systems, but their magnitude depends on whether the process is affected by winter or summer conditions.

Driving factors of synchronous dynamics in brown trout populations at the rear edge of their native distribution

AbstractThe classical debate about the roles of endogenous factors and external drivers in regulating populations continues to be a very active area of scientific research, and these roles are even more complex in populations located in geographically marginal areas. We tested three hypotheses on two separate brown trout populations inhabiting the southernmost basins of the Iberian Peninsula, with the aims of determining the relationships among (a) rainfall and air temperature for each season preceding fish sampling and the observed age group densities; (b) environmental synchrony and density synchrony for all possible pairs of sites; and (c) physical habitat similarity and the similarity of the density response to climatic drivers among pairs of sites. For this purpose, demographic series (98 surveys at 14 sampling sites), climatic conditions (rainfall and air temperature) and site habitat characteristics (physiogeographic and quality index values) were analysed between 2006 and 2014. The results show how the synchrony in the study populations is the result of a Moran effect directed mainly by winter precipitation and conditioned by the habitat similarity (highlighting the altitude, the distance to the upper limit and IHF index, along with the Euclidian distance among pairs of sites of the whole set of habitat variables). Preserving the heterogeneity of these habitat characteristics will increase the resilience of trout populations that inhabit this rear edge of distribution. The current context of global climate warming predicts extremely drastic changes in the dynamics of external drivers that regulate the trout populations in the study region.

Effects of environmental synchrony and density‐dependent dispersal on temporal and spatial slopes of Taylor's law

AbstractTaylor's law (TL) is an empirical rule that describes an approximate relationship between the variance and mean of population density: log10(variance) ≈ log10(a) + b × log10(mean). Population synchrony is another prevailing feature observed in empirical populations. This study investigated the effects of environmental synchrony and density‐dependent dispersal on the temporal (bT) and spatial (bS) slopes of TL, using an empirical dataset of gray‐sided vole populations and simulation analyses based on the second‐order autoregressive (AR) model. Eighty‐five empirical populations satisfied the temporal and spatial TLs with bT = 1.943 (±SE 0.143) and bS = 1.579 (±SE 0.136). The pairwise synchrony of population was 0.377 ± 0.199 (mean ± SD). Most simulated populations that obeyed the AR model satisfied the form of the temporal and spatial TLs without being affected by the environmental synchrony and density‐dependent dispersal; however, those simulated slopes were too steep. The incorporation of environmental synchrony resulted in reduced simulated slopes, but those slopes, too, were still unrealistically steep. By incorporating density‐dependent dispersal, simulated slopes decreased and fell within a realistic range. However, the simulated populations without environmental synchrony did not exhibit an adequate degree of density synchrony. In simulations that included both environmental synchrony and density‐dependent dispersal, 92.7% of the simulated datasets provided realistic values for bT, bS and population synchrony. Because the two slopes were more sensitive to the variation of density‐dependent dispersal than that of environmental synchrony, density‐dependent dispersal may be the key to the determination of bT and bS.

Potential mechanisms related to the spatial synchrony of phytoplankton is dependent on the type of data

Spatial synchrony occurs when the temporal dynamics of local populations are correlated. Correlated environmental variations (Moran effect), dispersal, and trophic interactions are theoretically the main mechanisms underlying population synchrony. We estimated spatial synchrony for total biomass, community density, densities of genera, and phytoplankton classes in a reservoir. We tested the hypotheses that synchrony levels would be high because all sites were sampled in a single waterbody; the Moran effect would be the main synchronizing mechanism; and synchrony should increase with environmental specialization of taxa. We also conducted an exploratory analysis to identify the regions of the reservoir contributing most to synchrony. We found low levels of synchrony, indicating that local factors were more important in controlling the dynamics of the local phytoplankton populations. Environmental synchrony and geographic distance were not significantly correlated with the synchrony matrices derived from genera data; however, synchrony matrices of the most abundant phytoplankton classes were mainly correlated with environmental synchrony. These results indicate that the detection of the Moran effect depends on the type of data used. As predicted, our results indicated that the dynamics of specialist genera were more synchronized than that of generalist genera. Finally, the lower reach of the reservoir contributed most to synchrony.

Spatial synchrony of zooplankton during the impoundment of amazonic reservoir

The escalating demand for energy and the strong political and economic pressure to explore the Amazon’s hydroelectric potential has led to the increase of hydroelectric reservoirs in the region. Reservoirs are artificial ecosystems that modify the structure of biological populations. Evaluating the spatial synchrony of populations and environmental variables in the development of reservoirs may reveal determinant factors and processes operating in these ecosystems. This may help understand the impacts, optimize monitoring systems and develop strategies to improve and maintain the ecological integrity (or stability) of these environments. In this study, we evaluated the spatial synchrony in zooplankton populations and limnological environmental variables during the implementation of a hydroelectric reservoir in the Amazon region, on the border of the states of Pará and Amapá. Synchrony was determined by mean cross-correlation between the pairs of points for each variable, followed by Mantel test to investigate its influencing factors. We observed spatial synchronous values for both population and limnological environmental variables. However, we could not identify the mechanisms that are operating, indicating that more than one factor may be influencing the ecosystem dynamics. Population synchrony increased after impoundment. Population synchrony may be associated with some limnological variables, such as the ones related to the amounts of nutrients, whereas environmental synchrony can be related to extrinsic factors, such as climatic variation, not tested this study. In order to increase the understanding of the mechanisms operating over population and environmental dynamics, we suggest that, besides evaluating limnological environmental variables and spatial synchrony, analyses should include meteorological and landscape data.

Environmental distances are more important than geographic distances when predicting spatial synchrony of zooplankton populations in a tropical reservoir

Abstract Several studies have shown that spatial synchrony, which is defined as the strength of the correlation between time series, is a common pattern that occurs in different regions, types of ecosystems and groups of organisms. In addition to applied research (optimisation of monitoring networks and population persistence), spatial synchrony has important implications for unravelling the processes underlying environmental and biological dynamics. We quantified the levels of synchrony among six sites in a tropical reservoir (Lajes Reservoir, Rio de Janeiro, Brazil) over 85 months (from August 2001 to December 2009) for twelve environmental variables, four broad zooplankton groups (testate amoebae, rotifers, cladocerans and copepods) and 23 abundant taxa. We hypothesised that (a) environmental synchrony would be higher than biological synchrony; (b) high synchrony would be found; and (c) biological synchrony matrices would be positively correlated with environmental synchrony and negatively correlated with both environmental and geographic distances. A strong relationship between biological synchrony and environmental matrices, when compared to geographic distance, would be consistent with the hypothesis that similar environmental variability synchronises the dynamics of local populations (Moran effect). In comparison to previous studies, we found high levels of synchrony. Environmental synchrony was often higher than biological synchrony, which was in line with our expectation and previous findings. The high levels of synchrony found in this study suggest that reservoir zonation was not enough to desynchronise the dynamics at the sites for both environmental and biological variables. Spatial synchrony in zooplankton populations declined more consistently with environmental distance than with geographic distance. Additionally, environmental distances were unrelated to geographic distances. Taken together, these results indicate a preponderant role of the Moran effect. Thus, as synchrony increases extinction rates, we speculate that novel ecosystems may be highly susceptible to regional‐wide changes in environmental factors.

Hard to predict: Synchrony in epiphytic biomass in a floodplain is independent of spatial proximity, environmental distance, and environmental synchrony

Population synchrony occurs when local population abundances increase and decrease simultaneously over time. In terms of other characteristics that can be measured in ecosystems, such as biomass and nutrient content, intrinsic and extrinsic processes have also been used to explain synchronic variation patterns. Synchrony may clarify whether regional processes are more important than local processes. This study used epiphytic biomass data (chlorophyll-a) collected from eight locations in a floodplain over 11 years. The goal was to estimate epiphytic biomass synchrony. We anticipated that high synchrony levels would be consistent with the strong impact of floods, which affect different floodplain habitats simultaneously. This is equivalent to the Moran effect. In contrast, low synchrony levels would be consistent with the hypothesis that the high environmental heterogeneity of floodplains hampers synchrony. Our results indicated low synchrony, and its variation was not correlated with geographic or environmental distances nor with environmental synchrony. Also, regression models demonstrated low predictive power of local environmental variables in predicting biomass variation in the different sites. In addition, we performed a meta-analysis that confirms the generality of our findings. In conclusion, these results challenge the efficiency of epiphytic biomass as an ecological indicator, at least in floodplain systems.

Regional‐scale extremes in river discharge and localised spawning stock abundance influence recruitment dynamics of a threatened freshwater fish

AbstractHighly variable recruitment is common for many riverine fish species, governed by a wide range of biotic and abiotic drivers that operate at local and regional scales. The dynamics and drivers of recruitment for many Australian freshwater fish species, particularly those that are rare and long‐lived, are relatively undescribed. This study describes the recruitment dynamics of an endangered riverine fish, Macquarie perch Macquaria australasica, across 5 isolated populations from southeastern Australia, and relates these dynamics to drivers that vary at local and regional scales. We hypothesised large flow events occurring during the core egg, and larval period would be negatively associated with recruitment strength and that recruitment patterns across populations would fluctuate in synchrony in response to extremes in river discharge resulting from regional‐scale climatic patterns.Discharge during the core egg and larval period, which was highly correlated across the region, and a local‐scale variable, spawning stock abundance, were the covariates most important in explaining recruitment strength. We also observed synchronised patterns in recruitment across our populations, thus conforming to predictions of the Moran effect (environmental synchrony). The findings suggest that most remnant populations of Macquarie perch, which are now predominantly isolated within small tributary systems characterised by highly variable flows, face a heightened risk of poor recruitment periods, particularly under climate change predictions. The synchronised patterns in recruitment suggest that threatened freshwater fishes such as Macquarie perch with highly fragmented isolated populations have an increased risk of the regional population becoming imperilled, thus the need for a coordinated multijurisdictional conservation approach.

The role of local and regional processes on population synchrony along the gradients of habitat specialization

AbstractMetacommunity perspective highlights the role of space as a factor contributing to local community structure and dynamics. Often tests of metacommunity models rely on snapshot patterns of species distribution and abundance. Such patterns may introduce biases because they overlook differences in responses of constituent species to changing environmental conditions, particularly when such responses override patterns predicted from dispersal and biotic interactions alone. This applies, for example, to habitat generalists, whose responses to environmental variations differ from those of habitat specialists, resulting in different snapshot patterns at different times. Synchronized (i.e., correlated among sites) environmental variation is perhaps the most obvious case of environmental variation that could generate regular differences among species of different specialization. We hypothesized that synchronized environmental variation synchronizes local populations of habitat specialists to a greater degree than it does for habitat generalists as experiments have shown that habitat generalists are less sensitive to changing environmental conditions. To test this in an empirical system, we used time series data (nine annual surveys) on an invertebrate metacommunity of 49 rock pools on the coast of Jamaica. We found that population synchrony of a significant portion of 24 species sharing these rock pools increased with habitat specialization in response to environmental synchrony (represented by synchrony of environment). However, distance among rock pools, which may affect dispersal or shared perturbations, was negatively correlated with population synchrony of individual species, irrespective of their specialization. As only habitat specialists showed increasing synchrony with environmental synchrony, and both generalist and specialist synchrony were negatively correlated with distance, we infer that habitat generalists must be synchronized more by space‐related processes while habitat specialists by a combination of environmental forcing and dispersal. Overall, the study suggests that species of different habitat specialization show consistent differences with respect to local processes involving environmental variations but show fewer differences with respect to regional processes involving distance, at least when long‐term dynamics are concerned. Furthermore, the study identifies a rarely recognized link between variation in space and its consequences for variation in time—a link much more expressed among spatially restricted species such as habitat specialists.

Influence of discharge, hydraulics, water temperature, and dispersal on density synchrony in brown trout populations (Salmo trutta)

Environmental factors may cause synchronous density variations between populations. A better understanding of the processes underlying synchrony is fundamental to predicting resilience loss in metapopulations subject to environmental change. The present study investigated the determinants of synchrony in density time series of three age groups of resident brown trout (Salmo trutta) (0+, 1+, and adults) in 36 stream reaches. A series of Mantel tests were implemented to disentangle the relative effects on trout synchrony of geographical proximity, environmental synchrony in key environmental variables affecting trout dynamics (discharge, water temperature, hydraulics, and spawning substrate mobility), and density-dependent dispersal. Results indicated that environmental synchrony strongly explained trout synchrony over distances less than 75 km. This effect was partly due to a negative influence on 0+ trout of strong discharges during the emergence period and a more complex influence of substrate mobility during the spawning period. Dispersal between reaches had a weak influence on results. Juvenile and adult densities were strongly driven by survival processes and were not influenced by environmental synchrony. The results suggest that the environment can have general effects on population dynamics that may influence the resilience of metapopulations.

Temporal variation in the synchrony of weather and its consequences for spatiotemporal population dynamics.

Over large areas, synchronous fluctuations in population density are often attributed to environmental stochasticity (e.g., weather) shared among local populations. This concept was first advanced by Patrick Moran who showed, based on several assumptions, that long-term population synchrony will equal the synchrony of environmental stochasticity among locations. We examine the consequences of violating one of Moran's assumptions, namely that environmental synchrony is constant through time. We demonstrate that the synchrony of weather conditions from regions across the United States varied considerably from 1895 to 2010. Using a simulation model modified from Moran's original study, we show that temporal variation in environmental synchrony can cause changes in population synchrony, which in turn can temporarily increase or decrease the amplitude of regional-scale population fluctuations. A case study using the gypsy moth (Lymantria dispar) provides empirical support for these predictions. This study provides theoretical and empirical evidence that temporal variation in environmental synchrony can be used to identify factors that synchronize population fluctuations and highlights a previously underappreciated cause of variability in population dynamics.

Patterns of zooplankton population synchrony in a tropical reservoir

The term “population synchrony” refers to the phenomenon of synchronous fluctuations of populations. The strength of this phenomenon may indicate the nature of the synchronizing mechanisms. In this study, we evaluated the relative importance of the Moran effect and dispersal on the levels of population synchrony in a zooplankton assemblage. We monitored the density of 36 taxa (27 genera, Bdelloidea, cyclopoid nauplii, calanoid nauplii, cyclopoid copepodites, calanoid copepodites and four broad taxonomic groups) at 7 sites through 19 months (from May 2004 through November 2009). For each taxon, we estimated the regional levels of synchrony as the mean Spearman correlation coefficient for all pairwise combinations of sites. These values were significant for 33 of the 36 taxa analyzed. Variations in synchrony were uncorrelated with hydrological or geographical distances. Environmental synchrony was unrelated to distance. The low relationship between synchrony (both environmental and population) and hydrological distance indicates the importance of the Moran effect. Nevertheless, climatic effects were not the main synchronizing mechanism. We suggest that damming was the main synchronizing force in this system.

Integrating demographic and genetic effects of connections on the viability of an endangered plant in a highly fragmented habitat

Classical ecological theories state that the viability of small metapopulations is critically related to: (1) the correlation of local population dynamics, (2) the possibility of extinct patch re-colonisation, and (3) the effects of genetic deterioration. Recent works suggested that these factors are not independent because dispersal might affect both re-colonisation and genetic rescue processes and because connectivity between habitat patches may be related to their environmental synchrony. Close patches may exhibit both high connectivity and synchronisation of their environments.Here, we examined these effects in the endangered plant Ranunculus nodiflorus that inhabits temporary water puddles, where water corridors constitute the vector (1) allowing seed dispersal throughout puddle networks and (2) leading to synchrony of local environmental factors. We utilised a demo-genetic metapopulation model to show how the antagonistic effects of connectivity and synchrony lead to complex interactions between the species’ biology and network configuration. We specifically demonstrated that (1) when an effective seed bank occurs, viability is maximised either for systems of numerous small independent networks (not connected and not synchronised), or for one single large network, while intermediate situations lead to a dramatic increase of the extinction risk; (2) genetic deterioration has notable negative effects on viability only in situations where environmentally driven extinction is buffered by the presence of a seed bank and network configuration; and (3) temporary connections among networks lead to a dramatic reduction of the extinction risk. The implementation of such connections is an efficient management option for the species.

Large-scale spatial synchrony and the stability of forest biodiversity revisited

Aims Mechanisms contributing to species coexistence have at least one of two modes of action: (i) stabilization of populations through restoring forces and (ii) equalization of fitness across individuals of different species. Recently, ecologists have begun gleaning the relative roles of these by testing the predictions of neutral theory, which predicts the properties of communities under pure fitness equalization. This null hypothesis was rejected for forests of southern Ontario based on large-scale (;100 km) spatial synchrony evident in the fossil pollen record over the entire Holocene, and the argument that a species’ relative abundance would instead vary independently at such distances in the absence of stabilizing mechanisms. This test of neutral theory was criticized based on the idea that the synchrony might be produced by dispersal alone. Here, I revisit this test of neutral theory by explicitly calculating the synchrony expected in these forests using a novel simulation method enabling examination of the distribution of a species over large spatial and temporal scales. Methods A novel neutral simulation algorithm tracking only the focal species was used to calculate the neutral expectation for spatial synchrony properties examined empirically by Clark and MacLachlan [(2003) Stability of forest biodiversity. Nature 423:635–8] using fossil pollen data from eight lake sites. The coefficient of variation (CV) in a species’ relative abundance across the eight sites (initiated at about 10% with a small CV) was calculated for 10 runs over a 10 000 year time interval. The CV reflects the level of spatial synchrony in that less synchronous dynamics should lead to more variation across space (a higher equilibrium CV), and in particular, a greater increase in the CV over time from a small initial value. A ‘two dimensional t’ fat-tailed dispersal kernel was assumed with parameters set to the median derived from seed trap data for deciduous wind-dispersed trees. Robustness of results to assumed dispersal distance, density of trees on the landscape, site sizes, age at maturity and starting spatial distribution were checked. Important Findings In contrast to the prediction of Clark and MacLachlan that, in the absence of stabilization, the CV across the sites should increase over time from levels observed at the beginning of the Holocene, under fat-tailed dispersal my neutral model robustly predicted only a brief (50 years) and small increase in the CV. I conclude that purely fitnessequalized species coexistence cannot be rejected based on the observed lack of increase in the CV across the eight sites in southern Ontario over the Holocene. Synchronous variation in environmental factors could alternatively explain the observed synchrony without the need for stabilization. However, neither dispersal nor environmental synchrony seems likely explanations for the quick widespread recovery of Tsuga in the Holocene after its seeming decimation, likely due to a pest outbreak.

Spatial–temporal scales of synchrony in marine zooplankton biomass and abundance patterns: A world-wide comparison

Large scale synchrony in the fluctuations of abundance or biomass of marine fish populations in regions on opposite sides of an ocean basin or in different oceans have been viewed as externally forced by correlated environmental stochasticity (e.g., common external forcing), most often as atmospheric teleconnections of basin-to-global scale atmospheric forcing, such as the Arctic Oscillation, North Atlantic Oscillation or the Pacific Decadal Oscillation. Specific causal mechanisms have been difficult to unequivocally discover, but possible mechanisms include influences on habitat temperatures, productivity operating through bottom-up (trophodynamic) mechanisms or direct climate influence on the fish populations (top-down mechanisms). For small pelagic fishes (sardines and anchovies) in widely separated large marine ecosystems that lack obvious ocean interconnectivity, it has been argued that the teleconnections may be atmospheric, acting on the fishes directly and propagating to the ecosystem from the middle out (wasp-waist species). Zooplankton biomass or abundance time series data from >100 sites world-wide are used to examine the spatial scales of coherent temporal synchrony. If spatially correlated environmental factors (like climate) are important for creating synchrony in fish populations via bottom-up effects (trophic interactions involving fish prey, e.g., zooplankton), then we would expect to observe synchrony in fluctuations of zooplankton biomass/numbers at spatial scales similar to those found for fish species. Zooplankton biomass/abundance have 50% spatial decorrelation scales of ca. 700–1400km and scales of significant coherence that extend to separation distances of ca. 3000km. These are also the spatial scales of environmental (sea surface temperature) synchrony from our global analysis. These scales are slightly greater than the 50% decorrelation scales of ca. 150–700km for recruitment synchrony in Atlantic marine fish and survival and recruitment synchrony of Northeast Pacific salmonids (150–1000km depending on species). However, the spatial scales of synchrony of annual zooplankton biomass anomalies in the Humboldt Current, California Current and Kuroshio ecosystems of the Pacific are much too small (ca. 2000km) to be directly causal of the basin-scale (7000–15,000km) synchrony exhibited by sardine and/or anchovy populations in those ecosystems.

Phase locking, the Moran effect and distance decay of synchrony: experimental tests in a model system

Spatially separated populations of many species fluctuate synchronously. Synchrony typically decays with increasing interpopulation distance. Spatial synchrony, and its distance decay, might reflect distance decay of environmental synchrony (the Moran effect), and/or short-distance dispersal. However, short-distance dispersal can synchronize entire metapopulations if within-patch dynamics are cyclic, a phenomenon known as phase locking. We manipulated the presence/absence of short-distance dispersal and spatially decaying environmental synchrony and examined their separate and interactive effects on the synchrony of the protist prey species Tetrahymena pyriformis growing in spatial arrays of patches (laboratory microcosms). The protist predator Euplotes patella consumed Tetrahymena and generated predator-prey cycles. Dispersal increased prey synchrony uniformly over both short and long distances, and did so by entraining the phases of the predator-prey cycles. The Moran effect also increased prey synchrony, but only over short distances where environmental synchrony was strongest, and did so by increasing the synchrony of stochastic fluctuations superimposed on the predator-prey cycle. Our results provide the first experimental demonstration of distance decay of synchrony due to distance decay of the Moran effect. Distance decay of the Moran effect likely explains distance decay of synchrony in many natural systems. Our results also provide an experimental demonstration of long-distance phase locking, and explain why cyclic populations provide many of the most dramatic examples of long-distance spatial synchrony in nature.

Tissue‐type plasminogen activator‐plasmin‐BDNF modulate glutamate‐induced phase‐shifts of the mouse suprachiasmatic circadian clock in vitro

The mammalian circadian clock in the suprachiasmatic nucleus (SCN) maintains environmental synchrony through light signals transmitted by glutamate released from retinal ganglion terminals. Brain-derived neurotrophic factor (BDNF) is required for light/glutamate to reset the clock. In the hippocampus, BDNF is activated by the extracellular protease, plasmin, which is produced from plasminogen by tissue-type plasminogen activator (tPA). We provide data showing expression of proteins from the plasminogen activation cascade in the SCN and their involvement in circadian clock phase-resetting. Early night glutamate application to SCN-containing brain slices resets the circadian clock. Plasminogen activator inhibitor-1 (PAI-1) blocked these shifts in slices from wild-type mice but not mice lacking its stabilizing protein, vitronectin (VN). Plasmin, but not plasminogen, prevented inhibition by PAI-1. Both plasmin and active BDNF reversed alpha(2)-antiplasmin inhibition of glutamate-induced shifts. alpha(2)-Antiplasmin decreased the conversion of inactive to active BDNF in the SCN. Finally, both tPA and BDNF allowed daytime glutamate-induced phase-resetting. Together, these data are the first to demonstrate expression of these proteases in the SCN, their involvement in modulating photic phase-shifts, and their activation of BDNF in the SCN, a potential 'gating' mechanism for photic phase-resetting. These data also demonstrate a functional interaction between PAI-1 and VN in adult brain. Given the usual association of these proteins with the extracellular matrix, these data suggest new lines of investigation into the locations and processes modulating mammalian circadian clock phase-resetting.

Not everything is everywhere: the distance decay of similarity in a marine host–parasite system

AbstractAim We test the similarity–distance decay hypothesis on a marine host–parasite system, inferring the relationships from abundance data gathered at the lowest scale of parasite community organization (i.e. that of the individual host).Location Twenty‐two seasonal samples of the bogueBoops boops(Teleostei: Sparidae) were collected at seven localities along a coastal positional gradient from the northern North‐East Atlantic to the northern Mediterranean coast of Spain.Methods We used our own, taxonomically consistent, data on parasite communities. The variations in parasite composition and structure with geographical and regional distance were examined at two spatial scales, namely local parasite faunas and component communities, using both presence–absence (neighbour joining distance) and abundance (Mahalanobis distance) data. The influence of geographical and regional distance on faunal/community divergence was assessed through the permutation of distance matrices.Results Our results revealed that: (1) geographical and regional distances do not affect the species composition in the system under study at the higher scales; (2) geographical distance between localities contributes significantly to the decay of similarity estimated from parasite abundance at the lowest scale (i.e. the individual host); (3) the structured spatial patterns are consistent in time but not across seasons; and (4) a restricted clade of species (the ‘core’ species of the bogue parasite fauna) contributes substantially to the observed patterns of both community homogenization and differentiation owing to the strong relationship between local abundance and regional distribution of species.Main conclusions The main factors that tend to homogenize the composition of parasite communities of bogue at higher regional scales are related to the dispersal of parasite colonizers across host populations, which we denote as horizontal neighbourhood colonization. In contrast, the spatial structure detectable in quantitative comparisons only, is related to a vertical neighbourhood colonization associated with larval dispersal on a local level. The stronger decline with distance in the spatial synchrony of the assemblages of the ‘core’ species indicates a close‐echoing environmental synchrony that declines with distance. Our results emphasize the importance of the parasite supracommunity (i.e. parasites that exploit all hosts in the ecosystem) to the decay of similarity with distance.