Do vegetation patch spatial patterns disrupt the spatial organization of plant species?

The mechanisms that structure plant diversity and generate long-range correlated spatial patterns have important implications for the conservation of fragmented landscapes. The ability to disperse and persist influences a plant species’ capacity for spatial organization, which can play a critical role in structuring plant diversity in metacommunities. This study examined the spatial patterns of species diversity within a network of patches in Cabo de Gata Natural Park, southeastern Spain. The objectives were to understand how the spatial heterogeneity of species composition (beta diversity) varies in a structured landscape, and how the long-range spatial autocorrelation of plant species is affected by the spatial configuration of patches.The mechanisms underlying the spatial distribution of plants acted at two scales. Between patches, spatial variation in species distributions was greater than that expected based on spatial randomization, which indicated that movement among patches was restricted. Within patches, diffusion processes reduced spatial variability in species distributions, and the effect was more prominent in large patches. Small patch size negatively influenced the long-range spatial autocorrelation of characteristic species, whereas inter-patch distance had a stronger effect on species frequency than it had on the disruption of spatial organized patterns.The long-range spatial autocorrelation was evaluated based on the dispersal abilities of the species. Among the 106 species evaluated, 39% of the woody species, 17% of the forbs, and 12% of the grasses exhibited disrupted long-range spatial autocorrelation where patches were small. The species that are more vulnerable to the effects of fragmentation tended to be those that have restricted dispersal, such as those that have short-range dispersal (atelechoric), e.g., Phlomis purpurea, Cistus albidus, Teucrium pseudochamaepytis, Brachypodium retusum, and the ballistic species, Genista spartioides. Helianthemum almeriense is another vulnerable species that has actively restricted dispersal (antitelechory), which is common in arid regions. Wind dispersers such as Launaea lanifera were less vulnerable to the effects of fragmentation. Long-distance dispersers whose persistence depends on facilitative interactions with other individuals, e.g., allogamous species such as Thymus hyemalis, Ballota hirsuta, and Anthyllis cytisoides, exhibit disrupted long-range spatial autocorrelation when patch size is reduced.     

Effect of the spatial context along the invasion process: “Hierarchical spatial” or “Host-switching spatial” hypotheses?

Very little is known about how spatial effects influence invasive species throughout the invasion sequence. We propose here two mechanisms to explain the changes in spatial effects throughout the stages of invasion, using the soybean aphid (Aphis glycines) as a model. First, the “hierarchical spatial effect” hypothesis, based on a change in the relative importance of the spatial scales throughout the invasion process, with main effect at broad scale during the first years of invasion, and main effect at local scale during the subsequent years. Second, the “host-switching spatial effect” hypothesis, stating that the spatial effect is driven by a switch in the effect of the host/habitat throughout the invasion process, from effect of main summer host/habitat during the first years of invasion to effect of overwintering host/habitat during the subsequent years. Data from governmental archives and field samplings enabled to investigate the spatial effects on aphid density at three scales (regional, landscape, local) during a 7 year period (2006–2012). Our results demonstrate that the hierarchical spatial effect hypothesis is not an adequate model for the soybean aphid, aphid density being more affected by landscape-scale factors irrespective of years. In contrast, our results are in accordance with the host-switching spatial hypothesis, with positive effect of the main summer host/habitat (soybean) during the first steps of invasion (2006–2008), followed by a positive effect of overwintering habitats (buckthorn, woodland) during the subsequent years (2010–2012). Overall, investigating these hypotheses in other systems would determine whether the same tendency is observed for other invasive species.     

Dispersal of fleshy-fruited species: a matter of spatial scale?

The processes associated with the dispersal of fleshy-fruited species have been an important focus of ecological research during the last two decades. These processes include fruit removal, seed rain, seed predation, seed bank dynamics, germination and establishment. Some of them interfere with the mutualistic interaction of frugivorous birds and fleshy-fruited plants. We might expect such interference to be most pronounced where the intensity of the different processes has a spatial distribution similar to that of the original seed shadow. The central theme of this review is that the main processes associated with dispersal and recruitment act at different spatial scales. To investigate this idea, about 140 publications on dispersal of fleshy-fruited species from 1980 to 2000 were screened for the spatial scaling of these processes. Microhabitat, habitat, landscape, region and biome were the five spatial scales most commonly used. However, the representation of the different scales was not fully balanced; large-scale studies were scarce and most publications considered only one scale.The review reveals some trends in scaling of the main processes of plant dispersal and recruitment. Seed dispersal by birds and seed predation by rodents are strongly determined at the habitat level, and several studies report negative results for contrasts between microhabitats. Germination and seedling establishment, on the other hand, appear to be mainly influenced by differences between microhabitats, though information on larger scales is scarce. Genetic differentiation and phenology of fruiting have mostly been investigated at the habitat, landscape and regional scale, whereas information on the abundance of frugivorous birds and patterns in plant distribution results are available across the full range of scales from the level of the microhabitat to the region and biome. Future research should be directed to the major gaps in our knowledge, i.e. regional and zonal comparisons of the processes associated with dispersal. They should also be more sensitive to scale issues and ideally should have a multi-scaled design.     

Divide and conquer? Persistence of infectious agents in spatial metapopulations of hosts

Persistence of an infectious agent in a population is an important issue in epidemiology. It is assumed that spatially fragmenting a population of hosts increases the probability of persistence of an infectious agent and that movement of hosts between the patches is vital for that. The influence of migration on persistence is however often studied in mean-field models, whereas in reality the actual distance travelled can be limited and influence the movement dynamics. We use a stochastic model, where within- and between-patch dynamics are coupled and movement is modelled explicitly, to show that explicit consideration of movement distance makes the relation between persistence of infectious agents and the metapopulation structure of its hosts less straightforward than previously thought. We show that the probability of persistence is largest at an intermediate movement distance of the host and that spatially fragmenting a population of hosts is not necessarily beneficial for persistence.     

Is spatial autocorrelation an intrinsic property of territory size?

In animals, competition for space and resources often results in territorial behaviour. The size of a territory is an important correlate of fitness and is primarily determined by the spatial distribution of resources and by interactions between competing individuals. Both of these determinants, alone or in interaction, could lead to spatial non-independence of territory size (i.e. spatial autocorrelation). We investigated the presence and magnitude of spatial autocorrelation (SAC) in territory size using Monte Carlo simulations of the most widely used territory measures. We found significant positive SAC in a wide array of competition-simulated conditions. A meta-analysis of territory size data showed that SAC is also a feature of territories mapped based on behavioural observations. Our results strongly suggest that SAC is an intrinsic trait of any territory measure. Hence, we recommend that appropriate statistical methods should be employed for the analysis of data sets where territory size is either a dependent or an explanatory variable.     

Does spatial distribution of tree size account for spatial variation in soil respiration in a tropical forest?

We explored the relationship between soil processes, estimated through soil respiration (R _soil ), and the spatial variation in forest structure, assessed through the distribution of tree size, in order to understand the determinism of spatial variations in R _soil in a tropical forest. The influence of tree size was examined using an index (I _c ) calculated for each tree as a function of (1) the trunk cross section area and (2) the distance from the measurement point. We investigated the relationships between I _c and litterfall, root mass and R _soil , respectively. Strong significant relationships were found between I _c and both litterfall and root mass. R _soil showed a large range of variations over the 1-ha experimental plot, from 1.5 to 12.6 g_C m^?2 d^?1. The best relationship between I _c and R _soil only explained 17% of the spatial variation in R _soil . These results support the assumption that local spatial patterns in litter production and root mass depend on tree distribution in tropical forests. Our study also emphasizes the modest contribution of tree size distribution–which is mainly influenced by the presence of the biggest trees (among the large range size of the inventoried trees greater than 10 cm diameter at 1.30 m above ground level or at 0.5 m above the buttresses)–in explaining spatial variations in R _soil .     

Do spatial effects play a role in the spatial distribution of desert‐dwelling Acacia raddiana?

Abstract. We investigated the spatial pattern of A. raddiana in the Negev desert of Israel in order to gain insights into the factors and processes driving the dynamics of this species. Using a scale‐dependent measure, the ring statistic, we analysed both patterns observed in the field and time series of spatial tree distributions produced by a simulation model. In the field, random spacing was the predominant pattern observed. However seedlings were clumped on small scales. We ran the model under two contrasting scenarios representing hypotheses that explain the clumping of seedlings and the random distribution of trees. One hypothesis is that there is spatial heterogeneity in seed distribution, germination and seedling mortality, but that these heterogeneities are not correlated with each other in space. The second hypothesis assumes a correlation between these heterogeneities leading to areas suitable for establishment. However, the suitability of the sites is temporally variable. Furthermore, the second hypothesis assumes density‐dependent tree mortality due to competition. Both hypotheses lead to spatial distributions that are in qualitative agreement with the patterns observed in the field. Therefore, the classical view that a clumped seedling distribution and a random pattern of older trees is due to clumped regeneration and density‐dependent mortality may not hold for Acacia trees in the Negev.     

Patterns of richness and endemism of the Mexican herpetofauna,a matter of spatial scale?

The goal of this study was to compare the richness and endemism patterns of Mexican species of amphibians and reptiles at different spatial scales. We used the best available dataset of distributional ranges generated from ecological niche models and employed geographically weighted regressions (GWRs) to test whether richness and endemism were related. Patterns were found to vary with the scale used for richness and endemism, and these patterns were not coincident. The results showed that: (1) only relatively coarse spatial scales can address latitudinal patterns in amphibians and reptiles, and, in fine scales, they are related to topographic formations; (2) areas of greatest endemism for amphibians and reptiles are located in the highlands of the central or southern part of the country, although not necessarily in the same specific highlands for both groups; (3) there is a strong average correlation between richness and endemism for both groups, indicating that the same factors contribute to both patterns, but these factors act differentially in terms of regions among amphibians and reptiles; and (4) the scale at which the analysis is conducted is important, and we believe that careful consideration of spatial scale must be undertaken to avoid false conclusions. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 305–316.     

Robustness of Taylor’s law under spatial hierarchical groupings of forest tree samples

Testing how well Taylor's law (TL) describes spatial variation of the population density of a species requires grouping sampling areas (patches of habitat) into blocks so that a mean and a variance of the population density can be calculated over the patches in each block. The relationship between specific groupings and TL remains largely unknown. Here, using tree counts from a deciduous forest, we studied the effect of four biological methods of grouping sampling areas into blocks on the form and parameters of TL. Regardless of the method of grouping, the species-specific basal area densities obeyed TL, and the estimated slopes were not significantly different from one grouping method to another. Surprisingly, TL remained valid when four kinds of randomizations were performed to the biological groupings and tree census. These randomizations randomly assigned sampling areas to blocks, and/or randomized the species composition within or across sampling areas. We found that the form of TL was robust to different grouping methods and species randomizations, but its parameter values depended significantly on species compositions at sampling areas.     

Isolation, properties and spatial site analysis of γ subunits of B-phycoerythrin and R-phycoerythrin

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Effects of spates on interstitial assemblages of the Rhône River. Importance of spatial heterogeneity

The dynamics of interstitial assemblages, after a spate and during low discharge, was studied in a regulated channel (Miribel Canal) of the Upper Rhône River, France. Using a Bou-Rouch pump, three stations were samples: 1) Station IIA, a site fed by superficial water infiltrations, 2) Station IIC, a site fed by riparian phreatic water, and 3) Station IA, a site fed by both surface and phreatic waters. The spate greatly influenced the interstitial assemblages, their dynamics were different according to the hydrology of the given site. At Station IIA, the spate had a wash-out effect on the assemblages (reduction in abundance and diversity), whereas during low discharge the interstitial layer received a continuous influx of epigean organisms (benthic and limnophilous). At Stations IIC and IA, the spate introduced numerous limnophilous and benthic invertebrates into the interstices, which function as an organismic trap. However, these sites appear to be more isolated from surface waters during low discharge. Stygobites decreased or disappeared after the spate. They appear highly sensitive to hydrologic perturbations in the surface waters.     

Efficiency of paramagnetism-based constraints to determine the spatial arrangement of α-helical secondary structure elements

A computational approach has been developed to assess the power of paramagnetism-based backbone constraints with respect to the determination of the tertiary structure, once the secondary structure elements are known. This is part of the general assessment of paramagnetism-based constraints which are known to be relevant when used in conjunction with all classical constraints. The paramagnetism-based constraints here investigated are the pseudocontact shifts, the residual dipolar couplings due to self-orientation of the metalloprotein in high magnetic fields, and the cross correlation between dipolar relaxation and Curie relaxation. The relative constraints are generated by back-calculation from a known structure. The elements of secondary structure are supposed to be obtained from chemical shift index. The problem of the reciprocal orientation of the helices is addressed. It is shown that the correct fold can be obtained depending on the length of the -helical stretches with respect to the length of the non helical segments connecting the -helices. For example, the correct fold is straightforwardly obtained for the four-helix bundle protein cytochrome b ₅₆₂, while the double EF-hand motif of calbindin D_9k is hardly obtained without ambiguity. In cases like calbindin D_9k, the availability of datasets from different metal ions is helpful, whereas less important is the location of the metal ion with respect to the secondary structure elements.     

Does spatial aggregation of total nectar production lead to genetic structure?

Spatial aggregation of plants of high nectar production, receiving an enhanced pollinator service is known to occur in Echium vulgare. Moreover, an emanating effect of nectar production on pollinator visits may occur, i.e. many pollinator visits may be observed around high nectar patches. Consequently, gene flow within patches of plants of high nectar production and their close neighbours may result in genetic structure. In this study, we investigated whether aggregation of total nectar production (nectar production per flower×number of flowers) and its emanating effect resulted in genetic structure in a natural E. vulgare population. We compared the spatial structure of total nectar production, pollinator visits and microsatellite markers using spatial autocorrelation analysis. Increased geitonogamy, caused by longer boutlengths in plants of high nectar production may generate genetic structure. We estimated selfing rates of plants of the highest and lowest total nectar production. Spatial aggregation of total nectar production occurred on a relatively small scale up to 2.83 m. A significant emanating correlation between total nectar production and pollinator visits was observed on a relatively large scale up to a 4.24 m. Thus, around patches of high nectar production numbers of pollinator visits were relatively high, while few visits were observed around patches of low nectar production. Weak genetic structure was present on a small scale up to 2.20 m. This corresponded with the scale of aggregation of total nectar production. High gene flow around the patches of high nectar production seems to weaken genetic structure. This is supported by the relatively low selfing rates. The average selfing rate of the plants of highest nectar production was 8.8% and that of the plants of lowest nectar production 5.0%. Low gene flow within and around low nectar patches sustain a weak genetic structure or, conversely, may have caused it in the first instance. Results indicate the importance of spatial structure of nectar production for pollinator movement.     

Temporal and spatial variations in macrofouling of silicone fouling‐release coatings

Nontoxic, low surface free energy silicone coatings having reduced biofouling adhesion strength have been developed as an alternative to antifouling paints. Silicone coatings permit macrofouling to adhere; however, fouling can be removed easily by water pressure or light scrubbing. One of the current methods used to evaluate the performance of non‐toxic silicone fouling‐release coatings relies heavily on fouling coverage. The organismal community structure as well as total coverage can affect the ease of fouling removal from these coatings. This paper explores fouling coverage and organismal adhesion over time. Long‐term fouling coverage data were collected at four sites (in Massachusetts, Hawaii and Florida) using static immersion panels coated with silicone and oil‐amended silicone systems. Inter‐site differences in fouling coverage and community structure were observed for each coating. Intra‐site variation and temporal change in coverage of fouling was minimal, regardless of coating formulation. The extent of coverage was affected by the duration of immersion and the local environmental conditions; these factors may also have an impact on the foul‐release capability of the silicone coatings. Organismal adhesion data was collected in Hawaii and Florida. These adhesion measurements were used as a tool to discriminate and rank fouling release coatings.     

Experimental determination of the spatial scale of a prey patch from the predator’s perspective

Foraging theory predicts that predators should prefer foraging in habitat patches with higher prey densities. However, density depends on the spatial scale at which a “patch” is defined by an observer. Ecologists strive to measure prey densities at the same scale that predators do, but many natural landscapes lack obvious, well-defined prey patches. Thus one must determine the scale at which predators define patches of prey. We estimated the scale at which guppies, Poecilia reticulata, selected patches of zooplankton prey using a behavioral assay. Guppies could choose between two prey arrays, each manipulated to have a density that depended on the spatial scale at which density was calculated. We estimated the scale of guppy foraging by comparing guppy preferences across a series of trials in which we systematically varied the scale associated with “high” prey density. This approach enables the application of foraging theory to non-discrete habitats and prey landscapes.     

Are there genetically controlled habitat-specific differences in spatial aggregation of drosophilids?

Variation in spatial patterns of competing organisms is of fundamental importance for community and population processes. Yet the mechanisms controlling subjects like the degree of spatial aggregation in competing insect larvae across fragmented resources have rarely been addressed. In the present study, we tested for systematic differences in the spatial distribution patterns of Drosophila subobscura in natural fly communities, and found significant differences in two habitats that differ in the availability of breeding substrate types (decaying fruits). Assuming that the spatial egg-laying behaviour of drosophilids is under genetic control, and that different breeding substrates mediate different density-dependent larval fitness consequences, we tested whether adaptive genotypic variability is involved in the local variation of egg distribution patterns. We extracted isofemale lines from both habitats and analysed the spatial distribution of eggs achieved by single female flies under controlled laboratory conditions. This is a reasonable first test, because spatial patterns at the fly population level can be attributed to individual egg-laying behaviour. The degree of individual egg aggregation significantly depended on fly line identity, which indicates the existence of behavioural variants in natural populations. Based on habitat-dependent differences in the degree of spatial aggregation, we discuss to what extent our findings may reflect a behavioural adaptation to local breeding conditions.     

When is connectivity important? A case study of the spatial pattern of sudden oak death

Although connectivity has been examined from many different angles and in many ecological disciplines, few studies have tested in which systems and under what conditions connectivity is important in determining ecological dynamics. Identifying general rules governing when connectivity is important is crucial not only for basic ecology, but also for our ability to manage natural systems, particularly as increasing fragmentation may change the degree to which connectivity influences ecological dynamics. In this study, we used statistical regression, least‐cost path analysis, and model selection techniques to test the relative importance of potential connectivity in determining the spatial pattern of sudden oak death, a tree disease that is killing millions of oak and tanoak trees along coastal forests of California and Oregon. We hypothesized that potential connectivity, in addition to environmental conditions, is important in determining the spatial distribution of sudden oak death, the importance of connectivity is more apparent when measured using biologically meaningful metrics that account for the effects of landscape structure on disease spread, and the relative importance of environmental variables and connectivity is approximately equal. Results demonstrate that potential connectivity was important in determining the spatial pattern of sudden oak death, though it was relatively less important than environmental variables. Moreover, connectivity was important only when using biologically meaningful metrics as opposed to simple distance‐based metrics that ignore landscape structure. These results demonstrate that connectivity can be important in systems not typically considered in connectivity studies – highlighting the importance of examining connectivity in a variety of different systems – and demonstrate that the manner in which connectivity is measured may govern our ability to detect its importance.     

Effect of livestock grazing in the partitions of a semiarid plant–plant spatial signed network

In recent times, network theory has become a useful tool to study the structure of the interactions in ecological communities. However, typically, these approaches focus on a particular kind of interaction while neglecting other possible interactions present in the ecosystem. Here, we present an ecological network for plant communities that consider simultaneously positive and negative interactions, which were derived from the spatial association and segregation between plant species. We employed this network to study the structure and the association strategies in a semiarid plant community of Cabo de Gata-Níjar Natural Park, SE Spain, and how they changed in 4 sites that differed in stocking rate. Association strategies were obtained from the partitions of the network, built based on a relaxed structural balance criterion. We found that grazing simplified the structure of the plant community. With increasing stocking rate species with no significant associations became dominant and the number of partitions decreased in the plant community. Independently of stocking rate, many species presented an associative strategy in the plant community because they benefit from the association to certain ‘nurse’ plants. These ‘nurses’ together with species that developed a segregating strategy, intervened in most of the interactions in the community. Ecological networks that combine links with different signs provide a new insight to analyze the structure of natural communities and identify the species which play a central role in them.