Statistical quantification of the effect of thermal stratification on patterns of dispersion in a freshwater zooplankton community

Seed dispersal is qualitatively effective when it increases recruitment probability. A poorly studied factor likely affecting recruitment is the spatial distribution of dispersed seeds. Seed-caching animals are thought to disperse seeds in a way that reduces clumping and density to impede cache pilfering. Furthermore, dispersal might differ depending on whether the seed is immediately consumed versus cached for later consumption, and might differ depending on the ecological context. The main objectives of this study were to determine: 1) the spatial pattern of seed dispersal by rodents in a heterogeneous environment; 2) whether the patterns differ among years and among acorn competitor exclosure treatments, and 3) whether rodents create different spatial patterns of dispersal for acorns that are cached versus consumed immediately following dispersal. We studied the degree of spatial aggregation of acorn dispersal by rodents using two different estimators derived from the Ripley K and the Diggle G functions. We also analyzed various metrics of dispersal distances. For both analyses we used observed acorn dispersal patterns in two years differing in crop size and inside versus outside exclosures restricting access to acorn-consuming ungulates. During 2003, a year with a larger crop size, maximum seed dispersal distances were less, and the pattern of dispersed seeds was more clumped, than in 2004, a year with a smaller crop size. Median dispersal distances did not differ between years. In the presence of ungulates, seed dispersal was marginally sparser than in their absence. Cached acorns were dispersed more sparsely than acorns eaten immediately. These results have important implications for the quality of seed dispersal for oak recruitment that are likely relevant to other systems as well.

According to environmental predictions, West Africa is becoming vulnerable to the adverse effects of climate change and land use dis- turbance. Herbaceous vegetation is the most sensitive to these effects. To assess the poten- tial of species to cope with these changes, this study investigated the dispersal potential of different herbaceous species. Data on her- baceous plant composition and environmen- tal parameters were collected along climate, land use and habitat gradients in West Afri- can savannah areas, as well as the diaspores of all herbaceous species encountered. Their traits were described in order to document the diversity of diaspore categories in herbaceous savannah vegetation. Based on an occurrence diagram, variations in dissemination patterns within families were identified. The dispersal potential of each species was determined on the basis of their patterns of dispersal. A hie- rarchical classification method was used to establish a dispersal typology, and principal component analysis was applied to identify the environmental conditions that account for their patterns of dispersal. The results show that the diaspores of herbaceous spe- cies can be classified according to fruit type, diaspore type, presence of heterodiaspory, exposure of diaspores, number of seeds per diaspore, diaspore morphology, shape of diaspores and pattern of dispersal. Poaceae, the most abundant family in savannah areas, have six patterns of dispersal. Most species have more than one pattern, and species with high dispersal potential (85.43%) dominate the herbaceous vegetation. Four groups of herbaceous species were identified according to their dispersal patterns. Potentially epizoo- chorous and anemochorous species (39.25% of the flora) were more related to village areas independently of climatic conditions and habi- tat types. Potentially endozoochorous and dysozoochorous species (31.06% of the flora) were more related to fresh and dry habitats in protected areas of the North and South Suda- nian zones. Potentially hydrochorous species (12.63% of the flora) were related to wet habi- tats but were more prominent in the Sahel, and potentially autochorous species (17.06% of the flora) were more related to bowé habi- tats in the southern Sudanian zone. Our study showed that all herbaceous species have good dispersal potential, which might enable them to persist in West African savannahs despite the severe climatic changes predicted.

The distribution of suitable habitat influences natal and breeding dispersal at small spatial scales, resulting in strong microgeographic genetic structure. Although environmental variation can promote interpopulation differences in dispersal behavior and local spatial patterns, the effects of distinct ecological conditions on within‐species variation in dispersal strategies and in fine‐scale genetic structure remain poorly understood. We studied local dispersal and fine‐scale genetic structure in the thorn‐tailed rayadito (Aphrastura spinicauda), a South American bird that breeds along a wide latitudinal gradient. We combine capture‐mark‐recapture data from eight breeding seasons and molecular genetics to compare two peripheral populations with contrasting environments in Chile: Navarino Island, a continuous and low density habitat, and Fray Jorge National Park, a fragmented, densely populated and more stressful environment. Natal dispersal showed no sex bias in Navarino but was female‐biased in the more dense population in Fray Jorge. In the latter, male movements were restricted, and some birds seemed to skip breeding in their first year, suggesting habitat saturation. Breeding dispersal was limited in both populations, with males being more philopatric than females. Spatial genetic autocorrelation analyzes using 13 polymorphic microsatellite loci confirmed the observed dispersal patterns: a fine‐scale genetic structure was only detectable for males in Fray Jorge for distances up to 450 m. Furthermore, two‐dimensional autocorrelation analyzes and estimates of genetic relatedness indicated that related males tended to be spatially clustered in this population. Our study shows evidence for context‐dependent variation in natal dispersal and corresponding local genetic structure in peripheral populations of this bird. It seems likely that the costs of dispersal are higher in the fragmented and higher density environment in Fray Jorge, particularly for males. The observed differences in microgeographic genetic structure for rayaditos might reflect the genetic consequences of population‐specific responses to contrasting environmental pressures near the range limits of its distribution.

Previously, American black bears (Ursus americanus) were thought to follow the pattern of female philopatry and male-biased dispersal. However, recent studies have identified deviations from this pattern. Such flexibility in dispersal patterns can allow individuals greater ability to acclimate to changing environments. We explored dispersal and spatial genetic relatedness patterns across ten black bear populations-including long established (historic), with known reproduction >50 years ago, and newly established (recent) populations, with reproduction recorded <50 years ago-in the Interior Highlands and Southern Appalachian Mountains, United States. We used spatially explicit, individual-based genetic simulations to model gene flow under scenarios with varying levels of population density, genetic diversity, and female philopatry. Using measures of genetic distance and spatial autocorrelation, we compared metrics between sexes, between population types (historic and recent), and among simulated scenarios which varied in density, genetic diversity, and sex-biased philopatry. In empirical populations, females in recent populations exhibited stronger patterns of isolation-by-distance (IBD) than females and males in historic populations. In simulated populations, low-density populations had a stronger indication of IBD than medium- to high-density populations; however, this effect varied in empirical populations. Condition-dependent dispersal strategies may permit species to cope with novel conditions and rapidly expand populations. Pattern-process modeling can provide qualitative and quantitative means to explore variable dispersal patterns, and could be employed in other species, particularly to anticipate range shifts in response to changing climate and habitat conditions.

Natal dispersal is a key process in ecology and evolution. Similarities of dispersal patterns between relatives can lead to small-scale kin structure within populations with consequences for population dynamics and genetics. Most studies have focused on birds, lizards, and small mammals. How family effects may shape sex-specific natal dispersal patterns in a large-sized social mammal remains unexplored. We fill this gap thanks to a 30-year-long monitoring of a wild boar population. This polytocous, polygynous, and size dimorphic species displays a matrilineal social organization. From the monitoring of individuals from early life to adulthood, we characterized natal dispersal patterns by investigating the propensity to disperse and the dispersal distance. As expected for a species subjected to strong sexual selection, offspring males dispersed more often and farther than females. Looking specifically at similarities of dispersal patterns among relatives within a group, we found that offspring females from the same family displayed more similar dispersal propensity and distance than females from different groups, highlighting family effects. However, this dispersal pattern did not hold for males. Family effects can thus shape natal dispersal patterns in a sex-specific way in social mammals and are key to understanding individual variation in dispersal patterns.

Seed dispersal is a key process that humans can influence in various ways. However, this type of interaction is less studied than dispersal by other animals. In addition, tracking seeds to determine dispersal pattern is a complicated task. We explored the effects of mowing machinery on seed dispersal in roadsides by testing two methods, (i) by marking fruits and diaspore of plants within the standing vegetation (ii) by making fake plants containing estimated quantities of marked seeds. We measured the pattern of dispersal by considering each seed and the centre of seed shadows of each species calculated by two means (i.e. the centroids and the gravity centres). We estimated the distance of dispersal from roadsides, and the deviation angle from the direction of the mowing. We then analysed the variation in dispersal patterns among species, seed mass and width/length ratio by using correlation tests. Seeds coloured within the standing vegetation were detected from 0.5 to 15.51 metres away from roadsides, with deviation angles from the mowing machinery ranging from –153.43° to 161.57°. With the other method we found a mean distance of dispersal ranging from 0.5 to 13.01 metres and deviation angle from –168.69° to 180°. We did not find strong variation in dispersal patterns among species and seed traits, but we demonstrated however that mowing machinery influenced both dispersal distance and deviation angles.

秦岭大熊猫种群扩散格局及研究方法

Variability in trail-following and aggregation in Nodilittorina unifasciata Gray

Las teleconexiones climáticas muestran relaciones remotas y a gran escala entre puntos distantes de la Tierra. Sus relaciones con la precipitación son importantes para monitorear y anticipar las anomalías que pueden producir en el clima local, como eventos de inundaciones y sequías que impactan la agricultura, la salud y la generación de energía hidroeléctrica. Las teleconexiones climáticas en relación con la precipitación se han estudiado ampliamente. Sin embargo, la asociación espacial de los patrones de teleconexión (es decir, la delimitación espacial de regiones con teleconexiones) ha sido desatendida. Dicha asociación espacial permite caracterizar cuán estable (heterogeneidad / dependiente y estadísticamente significativa) es el fenómeno espacial subyacente para un patrón dado. Por lo tanto, nuestro objetivo fue caracterizar la asociación espacial de los patrones de teleconexión climática relacionados con la precipitación utilizando un enfoque exploratorio de análisis de datos espaciales. Se utilizaron indicadores globales y locales de asociación espacial (I de Moran y LISA) para detectar patrones espaciales de teleconexiones basados ​​en imágenes de satélite de TRMM e índices climáticos. El I de Moran representó una asociación espacial positiva alta para diferentes índices climáticos, y LISA representó dos tipos de patrones de teleconexiones. Los patrones homogéneos se localizaron en las regiones de la Costa y Amazonas, mientras que los patrones dispersos tuvieron una mayor presencia en la Sierra. Los resultados también mostraron algunas áreas que, aunque con influencias de teleconexión moderadas a altas, tenían patrones espaciales aleatorios (es decir, asociación espacial no significativa). Otras áreas mostraron tanto teleconexiones como una asociación espacial significativa, pero con patrones dispersos. Esto señaló la necesidad de explorar las características subyacentes locales (topografía, orientación, viento y microclimas) que restringen (asociación espacial no significativa) o reafirman (patrones dispersos) los patrones de teleconexión.

Abstract. Climate teleconnections show remote and large-scale relationships between distant points on Earth. Their relations to precipitation are important to monitor and anticipate the anomalies that they can produce in the local climate, such as flood and drought events impacting agriculture, health, and hydropower generation. Climate teleconnections in relation to precipitation have been widely studied. Nevertheless, the spatial association of the teleconnection patterns (i.e. the spatial delineation of regions with teleconnections) has been unattended. Such spatial association allows to characterize how stable (heterogeneity/dependent and statistically significant) is the underlying spatial phenomena for a given pattern. Thus our objective was to characterize the spatial association of climate teleconnection patterns related to precipitation using an exploratory spatial data analysis approach. Global and local indicators of spatial association (Moran’s I and LISA) were used to detect spatial patterns of teleconnections based on TRMM satellite images and climate indices. Moran’s I depicted high positive spatial association for different climate indices, and LISA depicted two types of teleconnections patterns. The homogenous patterns were localized in the Coast and Amazonian regions, meanwhile the disperse patterns had a major presence in the Highlands. The results also showed some areas that, although with moderate to high teleconnection influences, had a random spatial patterns (i.e. non-significant spatial association). Other areas showed both teleconnections and significant spatial association, but with dispersed patterns. This pointed out the need to explore the local underlying features (topography, orientation, wind and micro-climates) that restrict (non-significant spatial association) or reaffirm (disperse patterns) the teleconnection patterns.

Isolation by distance (IBD) is a phenomenon characterized by increasing genetic divergence and decreasing gene flow with increasing geographic distance. IBD is often used in conservation biology to infer the extent of gene flow among populations. An assumption inherent to this approach is equilibrium between genetic drift and gene flow, which may take thousands of years to achieve. This implies that empirical IBD studies of recently colonized areas, such as postglacial systems, should be concerned with whether or not equilibrium has been reached. Short of equilibrium, IBD should increase with the length of time since a geographical area was colonized. We test the prediction that IBD increases with increasing time since colonization through a meta-analysis based on a diverse range of empirical systems. P and r 2 values from published IBD studies were analyzed with respect to time since colonization (in generations and years), taking into account variation in sample sizes, molecular markers, divergence metrics (genetic distance, F st, Nm), and dispersal patterns (one or two dimensional). Overall, we found weak evidence for associations between time since colonization and IBD. Sample sizes, molecular markers, divergence metrics, and dispersal patterns did not appreciably influence IBD. We propose that the expected relationship between IBD and time since colonization is obscured by the influence of other factors, such as dispersal ability, geographical barriers, and proximity to glacial refugia. The possible effects of time since colonization should continue to be evaluated in empirical studies, but other potential factors should also be thoroughly explored.

Recent studies have revealed that reef fish larvae have excellent sustained swimming capabilities and considerable potential for modifying their dispersal patterns by active swimming. However, these studies concentrate solely on the late pelagic phase. We examined the development of swimming abilities from hatching through to settlement in 3 reef fish species (Pomacentrus amboinensis, Sphaeramia nematoptera, Amphiprion melanopus). Larval rearing provided larvae at all stages of development. Experiments were conducted in flow chambers designed for measuring the critical and sustained swimming capability of young larvae. In all 3 species, critical swimming ability increased steadily with age, size, relative propulsive area and developmental stage of the larvae. In contrast, sustained swimming ability showed a marked inflection during development. Differences among species throughout development appear to reflect variations in the developmental patterns of the 3 species. Propulsive area was highly correlated with swimming ability and may prove useful for estimating swimming capabilities among species. The results suggest that some species have the potential to actively modify their dispersal patterns from an early age.

Although knowledge on dispersal patterns is essential for predicting long-term population dynamics, critical information on the modalities of passive dispersal and potential interactions between vectors is often missing. Here, we use mangrove propagules with a wide variety of morphologies to investigate the interaction between water and wind as a driver of passive dispersal. We imposed 16 combinations of wind and hydrodynamic conditions in a flume tank, using propagules of six important mangrove species (and genera), resulting in a set of dispersal morphologies that covers most variation present in mangrove propagules worldwide. Additionally, we discussed the broader implications of the outcome of this flume study on the potential of long distance dispersal for mangrove propagules in nature, applying a conceptual model to a natural mangrove system in Gazi Bay (Kenya). Overall, the effect of wind on dispersal depended on propagule density (g l-1). The low-density Heritiera littoralis propagules were most affected by wind, while the high-density vertically floating propagules of Ceriops tagal and Bruguiera gymnorrhiza were least affected. Avicennia marina, and horizontally floating Rhizophora mucronata and C. tagal propagules behaved similarly. Morphological propagule traits, such as the dorsal sail of H. littoralis, explained another part of the interspecific differences. Within species, differences in dispersal velocities can be explained by differences in density and for H. littoralis also by variations in the shape of the dorsal sail. Our conceptual model illustrates that different propagule types have a different likelihood of reaching the open ocean depending on prevailing water and wind currents. Results suggest that in open water, propagule traits (density, morphology, and floating orientation) appear to determine the effect of water and wind currents on dispersal dynamics. This has important implications for inter- and intraspecific variation in dispersal patterns and the likelihood of reaching suitable habitat patches within a propagule's viable period.

Elevated lake chloride concentration has been observed in many regions, due to human activities such as mining, agriculture, and urbanisation. Meanwhile, lakes are also experiencing increasing frequency and intensity of heatwaves. The combination of elevated salinity and heatwaves has not been thoroughly studied in freshwater communities, limiting our ability to predict outcomes of future disturbances. We conducted a mesocosm experiment to investigate the individual and interactive effects of increased salinity and heatwaves on a freshwater zooplankton community. The combined effects of the two stressors were examined in two scenarios: when they occurred simultaneously and when a heatwave was preceded by an 8‐week increase in salinity. We expected to see a synergistic effect when the two stressors were applied simultaneously, as organisms might experience energy deficiency due to physiological changes caused by salinity stress and be overwhelmed by the heat treatment. When the two stressors were applied sequentially, we expected them to act independently as the two stressors trigger different physiological responses and physiological homeostasis may have already recovered from previous salt exposure and not influence an organism's response to a subsequent stressor. Individually, increased salinity and heatwave conditions both impaired zooplankton communities with largest effects on copepod nauplii and cladocerans. Together, these stressors caused antagonistic effects on total zooplankton abundance and biomass in both the simultaneous and sequential scenarios, with the combined effects being similar to the salt‐only effects. Our experiment illustrates the potential for heatwaves to have hidden effects when they occur in lakes experiencing salinisation. The findings suggested that the two stressors negatively impacted some zooplankton taxonomic groups, and at the community level, they acted antagonistically such that the occurrence of a 3‐day heatwave did not cause any additional loss of abundance or biomass regardless of whether the community was exposed to the sequential or simultaneous scenario. Our findings also illustrated that even when the two stressors were decoupled in time, the community could still be influenced by a previous stressor.

A static broadband snapshot imaging spectrometer (BSIS) is proposed. This device consists of a telescope, four prisms, a focusing lens, and a detector. The first prism disperses sharply in the visible range along the vertical direction, and it is relatively nondispersive in the mid-wave infrared range. The second prism controls the beam deviation introduced by the first prism. The third prism is substantially more dispersive in the mid-wave infrared range than within the visible range along the horizontal direction. The fourth prism controls the beam deviation caused by the third prism. The BSIS will disperse the spectra of a target to form a V-shaped dispersion pattern (DP). The formulas and numerical simulation of the DP are given. The BSIS can locate multiple targets based only on one frame of data. The BSIS is suitable for detecting and measuring energetic targets in real time.