Synchrony In Population Dynamics Research Articles

Spatially correlated environmental factors drive synchronisation in populations of the Dalmatian Pelican

AbstractSpatial synchrony in population dynamics has been documented recently across a range of taxa, and a number of hypotheses about the mechanisms driving spatial synchrony and the consequences of this phenomenon for the persistence of populations have emerged. Spatial environmental covariance is one of the principal factors influencing this synchrony on a large scale. However, most studies focus on population abundances, and little evidence exists on the spatial synchrony of demographic parameters. We used a 15‐year dataset from two populations of a vulnerable bird species, the Dalmatian Pelican (Pelecanus crispus), to identify local and global environmental factors that cause population synchrony. We show that survival rates were temporally synchronised between the studied populations and that a large part (>50 % for both populations) of this covariation was driven by local environmental conditions. Several components of the North Atlantic Oscillation index were correlated with local climatic conditions, but not all of these components can be used as informative proxies for future variation in survival. We also present evidence that an individual's future survival can be strongly influenced by the conditions occurring during the early period of its life. Environmental factors such as water level and food availability had similar influences on breeding success and juvenile survival. Juvenile survival was lower during dry years and years of low food availability. This finding indicated that intra‐specific competition may act as a limiting factor for species demography, especially in large populations. Estimating the strength of synchrony is important and should be considered in population and metapopulation analyses and in relationship to conservation measures.

Spatial synchrony of recruitment in mountain‐dwelling woodland caribou

AbstractSpatial synchrony in population dynamics is a ubiquitous feature across a range of taxa. Understanding factors influencing this synchrony may shed light on important drivers of population dynamics. Three mechanisms influence the degree of spatial synchrony between populations: dispersal, shared predators, and spatial environmental covariance (the Moran effect). We assessed demographic spatial synchrony in recruitment (calf:cow ratio) of 10 northern mountain caribou herds in the Yukon Territory, Canada (1982–2008). Shared predators and dispersal were ruled out as causal mechanisms of spatial recruitment synchrony in these herds and therefore any spatial synchrony should be due to the Moran effect. We also assessed the degree of spatial synchrony in April snow depth to represent environmental variability. The regional average spatial synchrony in detrended residuals of April snow depth was 0.46 (95% CI 0.37 to 0.55). Spatial synchrony in caribou recruitment was weak at 0.13 (95% CI −0.06 to 0.32). The spatial scale of synchrony in April snow depth and caribou recruitment was 330.2 km (95% CI 236.3 to 370.0 km) and 170.0 km (95% CI 69.5 to 282.8 km), respectively. We also investigated how the similarity in terrain features between herds influenced the degree of spatial synchrony using exponential decay models. Only the difference in elevation variability between herds during calving was supported by the data. Herds with more similar elevation variability may track snowmelt ablation patterns in a more similar fashion, which would subsequently result in more synchronized predation rates on calves and/or nutritional effects impacting juvenile survival. Interspecific interactions with predators and alternate prey may also influence spatial synchrony of recruitment in these herds.

Geographical variation in the population dynamics of Thecodiplosis japonensis: causes and effects on spatial synchrony

AbstractGeographical variation in population dynamics of a species offers an opportunity to understand the factors determining observed patterns of spatial dynamics. We evaluated the spatial variation in the population dynamics of the pine needle gall midge (PNGM), Thecodiplosis japonensis, which is a severe insect pest in pine forests in Korea, and studied the influences of weather factors that could affect its population dynamics. Results revealed that PNGM population dynamics were classified into five clusters based on the analysis of autocorrelation function and self‐organizing map, which is an artificial neural network. We also quantified spatial synchrony in the population dynamics of PNGM using the nonparametric covariance function. Variation in spatial synchrony was strongly related to differences in maximum temperature and precipitation in Random Forest analysis, suggesting that the synchrony in PNGM population dynamics is largely the result of the Moran effect. In addition, spatial differences in population dynamics could be influenced by transient process of synchronization following invasion. Finally, the present results indicate that differences in population dynamics can be induced by interactions among several factors such as maximum temperature, precipitation, and invasion history of species.

Synchrony of spatial populations induced by colored environmental noise and dispersal

Spatial synchrony of oscillating populations has been observed in many ecological systems, and its influences and causes have attracted the interest of ecologists. Spatially correlated environmental noises, dispersal, and trophic interactions have been considered as the causes of spatial synchrony. In this study, we develop a spatially structured population model, which is described by coupled-map lattices and incorporates both dispersal and colored environmental noise. A method for generating time series with desired spatial correlation and color is introduced. Then, we use these generated time series to analyze the influence of noise color on synchrony in population dynamics. The noise color refers to the temporal correlation in the time series data of the noise, and is expressed as the degree of (first-order) autocorrelation for autoregressive noise. Patterns of spatial synchrony are considered for stable, periodic and chaotic population dynamics. Numerical simulations verify that environmental noise color has a major influence on the level of synchrony, which depends strongly on how noise is introduced into the model. Furthermore, the influence of noise color also depends on patterns of dispersal between local populations. In addition, the desynchronizing effect of reddened noise is always weaker than that of white noise. From our results, we notice that the role of reddened environmental noise on spatial synchrony should be treated carefully and cautiously, especially for the spatially structured populations linked by dispersal.

Climate mediated exogenous forcing and synchrony in populations of the oak aphid in the UK

Contemporary population dynamics theory suggests that animal fluctuations in nature are the result of the combined forces of intrinsic and exogenous factors. Weather is the iconic example of an exogenous force. The common approach for analyzing the relationship between population size and climatic variables is by simple correlation or using the climate as an additive covariable in statistical models. Here, we evaluated different functional forms in which climatic variables could influence population dynamics of the oak aphid Tuberculatus annulatus both in each locality and in relation to synchrony between localities. Results indicate that in at least four of eight aphid populations, climate influences population dynamics by modifying the carrying capacity of the system (lateral effect mediated by winter precipitation). Additionally, path analysis showed that synchrony in population dynamics is highly correlated with synchrony in winter precipitation regime, and the spatial scale of both processes is similar, which suggests that this is an example of the Moran effect. Our results show the key effects of precipitation on intra and inter population processes of this aphid. The methods used, mixing population dynamics modelling and test of synchrony, allowed us to connect the direct and indirect effects of exogenous variables into each population with patterns of synchrony inter populations.

Spatial (a)synchrony in population fluctuations of five plant species in fragmented habitats

Abstract The spatial scale at which populations show synchronous temporal fluctuations in abundance, relative to the spatial scale over which they can disperse, may influence the persistence of local and regional populations. There have been frequent demonstrations of spatial synchrony in population dynamics of animal populations. But few studies have investigated the degree of spatial synchrony in less mobile taxa, e.g. plants, where life history, dispersal and interaction with the environment would be different due to a sessile phase. This study has during three years investigated the synchrony in local population size changes in four short-lived species, and during a nine-year period for one long-lived species, in a semi-natural grassland landscape in southern Sweden. The spatial scale of this study was less than 15 km, which is quite small in comparison with other studies, but the temporal scale was of similar magnitude as the few studies on plant abundances and synchrony. When using detrended estimates of population size change, a significant pattern of decreasing synchrony with increasing distance was found for the two short-lived species that were most confined to manage semi-natural grasslands. Spatial synchrony was detected up to a few km. However, the species displayed synchrony in different years. The degree of synchrony can thus vary considerably across years and among species. Spatially autocorrelated weather conditions could partly explain the spatial scale of synchrony found during certain time intervals. However, the prevailing asynchrony suggests that local factors dominate the dynamics of the populations at the investigated scale.

Dispersal, colored environmental noise, and spatial synchrony in population dynamics: analyzing a discrete host–parasitoid population model

AbstractSpatial synchrony is common, and its influences and causes have attracted the interest of ecologists. Spatially correlated environmental noise, dispersal, and trophic interactions have been considered as the causes of spatial synchrony. In this study, we developed a spatially structured population model, which is described by coupled‐map lattices. Our recent investigation showed that trophic correlation of environmental noise was another important factor that affects spatial synchrony. As a supplement, we considered the influence of the color of the environmental noise on the spatial synchrony in this study. The noise color refers to the temporal correlation in the time series data of the noise, and is expressed as the degree of (first‐order) autocorrelation for autoregressive noise. Patterns of spatial synchrony were considered for stable, periodic (quasi‐periodic), and chaotic population dynamics. Numerical simulations verified that the color of the environmental noise is another mechanism that causes spatial synchrony. Generally, the effect of the color of the noise on the synchrony is dependent on the type of dynamics (stable, cyclic, chaotic) present in the population. For cyclic dynamics, simulation results clearly demonstrate that reddened noise has higher synchrony than white noise. The importance of our research is that it enriches the theory of potential causes of spatial synchrony.

Regional Synchrony of Brown Trout and Brook Trout Population Dynamics among Michigan Rivers

AbstractThe ability to describe regional patterns in trout density would be useful for biologists concerned with population status across large regions as well as managers of rivers at the local scale. Noting the importance of flow conditions at the time of emergence to trout year‐class strength in Michigan streams and the influence of age‐0 trout abundance on subsequent abundance of older age‐classes, we assessed the potential for regional synchrony in the population dynamics of brown trout Salmo trutta and brook trout Salvelinus fontinalis among Michigan rivers. We used correlation analyses to look for regional synchrony in May stream discharge (approximating the time of brown trout fry emergence) and fall trout density among many Michigan trout streams. We found a high degree of synchrony in average May discharge among streams, particularly those in the northern portion of Michigan's Lower Peninsula. There were significant correlations in the long‐term densities of brown trout and brook trout year‐classes among several rivers in this area, including sites up to 140 km apart and rivers draining into different Great Lakes. Predicted numbers of days to 50% swim‐up of brown trout fry were similar among four streams and synchronous, further supporting the hypothesis of synchrony in trout population dynamics in Michigan streams at the regional scale. Long‐term trout population estimates and streamflow data collected from a network of long‐term index (fixed) sites throughout Michigan will aid in further description of the spatial extent of synchrony in trout populations.

Life history strategies affect climate based spatial synchrony in population dynamics of West African freshwater fishes

Spatial synchrony in species abundance is a general phenomenon that has been found in populations representing virtually all major taxa. Dispersal among populations and synchronous stochastic effects (the so called effect) are the mechanisms most likely to explain such synchrony patterns. Very few studies have related the degree of spatial synchrony to the biological characteristics of species. Here we present a case where specific predictions can be made to relate river fish species characteristics and synchrony determined exclusively by a Moran effect through the expected sensitivity of species to the regional component of environmental stochasticity. By analyzing 23-year time series of abundance estimates in two isolated localities we show that species associated with synchronized reproduction during the wet season, high fecundity, small egg size and high gonado-somatic index (the so called strategy) have a higher degree of spatial synchrony in population dynamics than species associated with the opposite traits (the so called strategy). This is supported by significant relationships (P values <0.01) between species traits and the levels of synchrony after removing taxonomical relatedness. Spatial synchrony computed from summed annual total catches by groups of species, separated into strategy types also showed a significantly higher degree of synchrony for the periodic (r =0.83) than the equilibrium (r=0.46) group. Regional hydrological variability is likely to be partly responsible for the observed synchrony pattern and a regional discharge index showed better relationships with the periodic group, supporting the expected differential effect of regional environmental correlation on population dynamics.

Population Dynamics of Songbirds in the Boreal Mixedwood Forests of Alberta, Canada: Estimating Minimum and Maximum Extents of Spatial Population Synchrony

Ecological phenomena vary over space and time and interpretation of these processes also varies depending on the measurement scale. As the spatial scale of observation increases and decreases, changes in population abundance will likely exhibit alternating patterns of asynchrony and synchrony. While the study of how and why population dynamics change with spatial scale of measurement is intrinsically interesting, most population ecologists seek to study mechanisms of population change on a discrete study area. Our study develops methods that population ecologists can use to determine spatially appropriate sampling designs, and demonstrates how such spatial scales can be determined for 25 species of songbirds using longterm data from the boreal mixedwood forest of Alberta, Canada. To determine minimum scales of synchrony in population dynamics, we calculated the average correlation of changes in population abundance over time across different numbers of fixed-radius point-count samples. We then used a randomization test to remove the effect of number of replicates from the determination of appropriate spatial scale. The maximum extent of synchrony was estimated as the distance where population dynamics were no longer correlated. Estimates of the minimum scale of synchrony differed between species, ranging from 3.1 to 18.6 ha. The maximum scale of synchrony was estimated to be greater than or equal to 8 km for 14 of the 25 species examined, and to be greater than or equal to 70 km for Tennessee Warbler (Vermivora peregrina). Maximum spatial extents were significantly correlated with body mass and territory size.

SamplingAphis glycines(Homoptera: Aphididae) in Soybean Fields in Illinois

The aphid Aphis glycines Matsumura, which was first observed in North America in 2000, is a pest of soybean, Glycine max L., in the United States and southern Canada. This study focused on the distribution and sampling of this aphid at two spatial scales: field and township. We sampled 14 soybean fields in each of two townships in Kendall and Champaign counties in Illinois on four sampling dates during the summers of 2001–2003. Generally, there was little synchrony of population dynamics (increases or decreases) across the fields in either township during the middle of the summers. There was significant field-to-field variability in mean number of aphids per plant. Thus, multiple fields must be sampled to accurately understand the infestation levels in a township. For Kendall Township in all years, drilled soybean fields always had the highest mean density at the second and third sampling dates, but fields with wide rows (0.61–0.76-m widths) had the highest mean density at the fourth date. However, row spacing had no significant influence on the mean density in most of the other analyses of variance. The probability of finding an infested field by mid-July when mean density in the township is less than two aphids per plant is 50% for Kendall County and 11% for Champaign County. Thus, at least two and 14 fields in Kendall and Champaign counties, respectively, must be sampled (50 plants per field) to have at least a 75% chance of finding a new invader in at least one infested field in a township during that period. Variance was related to mean number of aphids per plant, M, in a field by S2 = 6.39911 × M1.71779. This specific form of Taylor’s power law allowed us to calculate the appropriate sample sizes (plants/field) needed to obtain different levels of precision. Regression analysis showed no relationship between aphid density and distance from the field edge over the 50-m transects used in sampling. The relationship between the proportion of infested plants in a field, P, and mean aphid density, M, is represented by P = 1 − exp(−0.195764M). The proportion exceeds 0.99 for mean densities exceeding 24 aphids per plant in a field. Thus, our results suggest that aphids should be counted on 50 plants per field to obtain a reliable estimate of the population.

Spatial synchrony in population dynamics of West African fishes: a demonstration of an intraspecific and interspecific Moran effect

Summary Synchronous fluctuations of the abundance of several populations at a regional scale can be a sign of a climatic effect on their dynamics (Moran effect). However, the interpretation of spatial synchrony is often complicated by the interaction between climatic disturbances and migrations between the studied populations. We addressed this question by studying 24‐year time‐series of abundance estimates for four populations of four fish species in three different catchment basins in Côte d’Ivoire (West Africa). As localities from two different basins cannot exchange individuals, dispersal cannot be considered a synchronizing factor in this system. A sign test performed on the four site × site correlation matrices rejected the null hypothesis of no spatial synchrony. No relation was detected in relating the level of synchrony in species dynamics (r = 0·58 on average) to the geographical distances between the four sites (176–367 km). A more detailed analysis taking account of sampling error was carried out between two sites, and confirmed the above results. When corrected for sampling noise, high values of spatial synchrony were obtained (r = 0·88 on average). Interspecific spatial synchronies (r = 0·57 on average) were almost as high as intraspecific values, suggesting that the four species are reacting in the same way to the same Moran effect. A good correlation (r = 0·54) between a regional river discharge index and the total catch of the four species 1 year later was observed, suggesting that hydrological variability is one of the main synchronizing factors. Moreover, as expected on theoretical grounds, spatial synchrony in river discharge (r = 0·84 and 0·88 on a log scale) is similar to spatial synchrony in population dynamics (r = 0·88 on average and corrected for sampling error).

ASYNCHRONOUS SPATIOTEMPORAL DEMOGRAPHY OF A HOUSE SPARROW METAPOPULATION IN A CORRELATED ENVIRONMENT

One important question in ecology is how large-scale regional phenomena affect the demography and dynamics of local populations. The purpose of the present study was to examine how climate affected spatial and temporal variation in demography within an insular metapopulation of House Sparrows (Passer domesticus). Daily weather conditions during the breeding season were highly correlated within the study region, and because the onset of breeding differed significantly among the five study islands, fledgling success was also affected. Thus, local recruitment was reduced by the occurrence of bad weather during the nestling period, and the asynchronous breeding phenology among the islands led to a significant island × year interaction in recruitment rate. Interaction between climate and the local environment provides a mechanism by which spatial synchrony in population dynamics can be reduced even in strongly spatially autocorrelated environments.

Asynchronous Spatiotemporal Demography of a House Sparrow Metapopulation in a Correlated Environment

One important question in ecology is how large-scale regional phenomena affect the demography and dynamics of local populations. The purpose of the present study was to examine how climate affected spatial and temporal variation in demography within an insular metapopulation of House Sparrows (Passer domesticus). Daily weather conditions during the breeding season were highly correlated within the study region, and because the onset of breeding differed significantly among the five study islands, fledgling success was also affected. Thus, local recruitment was reduced by the occurrence of bad weather during the nestling period, and the asynchronous breeding phenology among the islands led to a significant island × year interaction in recruitment rate. Interaction between climate and the local environment provides a mechanism by which spatial synchrony in population dynamics can be reduced even in strongly spatially autocorrelated environments.

Dispersal, Environmental Correlation, and Spatial Synchrony in Population Dynamics.

Many species exhibit widespread spatial synchrony in population fluctuations. This pattern is of great ecological interest and can be a source of concern when the species is rare or endangered. Both dispersal and spatial correlations in the environment have been implicated as possible causes of this pattern, but these two factors have rarely been studied in combination. We develop a spatially structured population model, simple enough to obtain analytic solutions for the population correlation, that incorporates both dispersal and environmental correlation. We ask whether these two synchronizing factors contribute additively to the total spatial population covariance. We find that there is always an interaction between these two factors and that this interaction is small only when one or both of the environmental correlation and the dispersal rate are small. The interaction is opposite in sign to the environmental correlation; so, in the normal case of positive environmental correlation across sites, the population synchrony will be lower than predicted by simply adding the effects of dispersal and environmental correlation. We also find that population synchrony declines as the strength of population regulation increases. These results indicate that dispersal and environmental correlation need to be considered in combination as explanations for observed patterns of population synchrony.

Dispersal, Environmental Correlation, and Spatial Synchrony in Population Dynamics

Dispersal, Environmental Correlation, and Spatial Synchrony in Population Dynamics

Distinguishing Causes of Intraspecific Synchrony in Population Dynamics

We examined the degree and cause of intraspecific synchrony in population dynamics between 29-42 populations for each of seven mammalian species. Regions containing multiple populations with similar dynamics were identified using cluster analysis. Two explanations for the observed synchrony were evaluated, dispersal and the Moran effect, a spatially correlated density independent perturbation, such as weather, which occurs across populations. Populations synchronized by dispersal are expected to exhibit a negative relationship between synchrony and distance, while populations synchronized by a Moran effect must have a similar density-dependent structure (DDS). To distinguish between these hypotheses we used autoregressive modeling to determine the DDS of each population, and cross-correlation to estimate the degree of synchrony between populations. Dispersal alone was assumed to be responsible for synchrony in populations with a significant negative synchrony-distance (S-D) relationship and heterogeneous DDS. We assumed that a Moran effect ould have produced synchrony in populations with homogeneous DDS and non-significant S-D relationship. It was not possible to assign synchrony to a single factor in regions with a homogeneous DDS and a significant S-D relationship, and we excluded the possibility of a Moran effect in regions with heterogeneous DDS and a non-significant S-D relationship. Using these criteria, we identified dispersal as synchronizing populations within one region each of ermine, lynx, mink and red fox and in two regions of muskrat. A Moran effect may have synchronized one region of ermine, fisher, lynx, and mink, although we were unable to identify a causative factor. One lynx and one mink region showed characteristics of both dispersal and Moran-based synchrony, and 9 regions of synchrony could not be assigned to either factor. These results show that by examining the DDS and the S-D relationship we were able to determine the factors most likely responsible for synchronized population dynamics in 10 of 21 cases. Possible cases of Moran-based synchrony do not appear to be common, occurring in only 18.2% of these regions. It should also be noted that just as correlation does not imply causation, presence of homogeneous DDS does not indicate a Moran effect, only its possible occurrence.

Noise Colour, Synchrony and Extinctions in Spatially Structured Populations

I analyse the importance and influence of noise with positive autocorrelation ('red noise') to extinction risk in spatially structured populations using a set of simple population dynamical simulation models. Noise colour has a major influence on both local and global extinction risk, level of synchrony in population dynamics, and spatial patterns of the synchrony. Generally, the stronger the autocorrelation in the noise is, the higher is the global extinction risk even though local extinction risk may decrease. Populations with high intrinsic growth rate are more prone to global extinction than populations with low growth rate. The influence of autocorrelated noise on population synchrony depends strongly on the way in which environmental noise is introduced into the model.

The Moran Effect and Synchrony in Population Dynamics

Our approach is twofold. First, with 1964-1983 data on red squirrel (Sciurus vulgaris) in 11 provinces in Finland we show that population fluctuations in different parts of the country are largely synchronous. Second, using two differing model types for producing the dynamics of populations we set up to examine the synchronizing effect of an extrinsic disturbing factor, the Moran effect. We show that in a spatially structured population system a randomly occurring stochastic perturbation reducing reproduction success is indeed capable of synchronizing subpopulations. The synchronizing effect is achievable with a wide range of probabilities of occurrence and strengths. However, when the Moran effect occurs in most years its synchronizing power wanes, despite the strength of the effect. Allowing regionality in the variance of the strength of the Moran effect reduces the synchronizing capacity of the perturbation. The Moran effect is also capable of producing a wide range of population dynamics from very simple premises.

Spatial and Temporal Patterns of Small‐Rodent Population Dynamics at a Regional Scale

Many species exhibit regional synchrony in population dynamics, and different influential biotic and abiotic factors can be indicated by the observed scale of spatial synchrony. Here, we present analyses of spatial patterns of bank vole Clethrionomys glareolus population fluctuations, based on a 5—yr (1990—1994) trapping series obtained from 31 trap stations regularly spaced along a 256—km transect in the boreal forest in southeastern Norway. The bank vole was known to exhibit typically cyclic population dynamics in this region prior to this study. Bank vole fall densities exhibited fluctuations with little year—to—year variation; all $s$—indices (a measure of temporal variability) were below 0.5. There was a large scale trend in the temporal variability of the populations, with highest variability at the south end and lowest in the middle of the transect. Analysis (Mantel correlogram) of the year—to—year rate of change of local populations showed that the opposite ends of the transect appeared to be most out of phase. At a smaller spatial scale (up to 30—40 km), local populations exhibited statistically significant synchrony in growth patterns. Spatiotemporal patterns in the dynamics of local populations were not related to habitat quality. We suggest that the scale domain of population synchrony is related to intrinsic population scaling properties such as dispersal capacity.