Fine Spatial Scales (fine + spatial_scale)

Distribution by Scientific Domains


Selected Abstracts


Spatial patterns of kangaroo density across the South Australian pastoral zone over 26 years: aggregation during drought and suggestions of long distance movement

JOURNAL OF APPLIED ECOLOGY, Issue 5 2007
ANTHONY R. POPLE
Summary 1Wildlife surveys usually focus on estimating population size, and management actions such as commercial harvesting, culling and poison baiting are referenced commonly to population size alone, without taking into account the way in which those animals are distributed. This paper outlines how point-based aerial survey data can be converted to continuous density surfaces using spatial analysis techniques. Using this approach, we describe and explore the spatial patterns of density of two species of kangaroos in an area exceeding 200 000 km2 in South Australia over a 26-year period. 2Densities of red and western grey kangaroos were estimated in 2 km2 segments along aerial survey transect lines, yielding point density estimates. Universal kriging provided an unbiased interpolation of these data using the spatial autocorrelation structure described by the semi-variogram. The Getis statistic identified clusters of high and low kangaroo density. 3Considerable year-to-year variation in the spatial patterns of kangaroo density was observed. In many cases, annual rates of increase over large areas were too high to be explained by vital rates alone, implying immigration from surrounding areas. These large shifts in distribution were occasionally to areas that had received better rainfall than the surrounding areas. For both species, there was no obvious local spatial autocorrelation pattern or clustering of kangaroo density beyond that described by average density and the present set of management regions, suggesting the latter are appropriate divisions for harvest management. 4Data for both species fitted the power law relationship extremely well. During dry times, red kangaroos, but not western grey kangaroos, were more aggregated, supporting past ground observations at a fine spatial scale. 5Synthesis and applications. Kriged density surfaces enable estimation of kangaroo density on individual properties, which are the management units at which harvest quotas or culling approvals are allocated. These estimates will be marked improvements over systematic sampling estimates when sampling intensity is low. Predictions of shifts in kangaroo distribution using rainfall or satellite imagery will allow more accurate allocation of harvest quotas. Similarly, predictions of more even kangaroo dispersion following high rainfall will allow managers to anticipate downturns in harvest rate. [source]


Arctiid moth ensembles along a successional gradient in the Ecuadorian montane rain forest zone: how different are subfamilies and tribes?

JOURNAL OF BIOGEOGRAPHY, Issue 1 2006
Nadine Hilt
Abstract Aim, We examined changes in the species diversity and faunal composition of arctiid moths along a successional gradient at a fine spatial scale in one of the world's hot spots for moths, the Andean montane rain forest zone. We specifically aimed to discover whether moth groups with divergent life histories respond differentially to forest recovery. Location, Southern Ecuador (province Zamora-Chinchipe) along a gradient from early successional stages to mature forest understorey at elevations of 1800,2005 m a.s.l. Methods, Moths were sampled with weak light traps at 21 sites representing three habitat categories (early and late succession, mature forest understorey), and were analysed at species level. Relative proportions were calculated from species numbers as well as from specimen numbers. Fisher's , was used as a measure of local diversity, and for ordination analyses non-metric multidimensional scaling (NMDS) was carried out. Results, Proportions of higher arctiid taxa changed distinctly along the successional gradient. Ctenuchini (wasp moths) contributed more strongly to ensembles in natural forest, whereas Lithosiinae (lichen moths) decreased numerically with forest recovery. Arctiid species diversity (measured as Fisher's ,) was high in all habitats sampled. The three larger subordinated taxa contributed differentially to richness: Phaegopterini (tiger moths) were always the most diverse clade, followed by Ctenuchini and Lithosiinae. Local species diversity was higher in successional habitats than in forest understorey, and this was most pronounced for the Phaegopterini. Dominance of a few common species was higher, and the proportion of species represented as singletons was lower, than reported for many other tropical arthropod communities. NMDS revealed a significant segregation between ensembles from successional sites and from forest understorey for all larger subordinated taxa (Phaegopterini, Ctenuchini, Lithosiinae). Abandoned pastures held an impoverished, distinct fauna. Faunal segregation was more pronounced for rare species. Ordination axes reflected primarily the degree of habitat disturbance (openness of vegetation, distance of sites from mature forest) and, to a lesser extent, altitude, but not distance between sampling sites. Main conclusions, Despite the geographical proximity of the 21 sites and the pronounced dispersal abilities of adult arctiid moths, local ecological processes were strong enough to allow differentiation between ensembles from mature forest and disturbed sites, even at the level of subfamilies and tribes. Differences in morphology and life-history characteristics of higher arctiid taxa were reflected in their differential representation (proportions of species and individuals) at the sites, whereas patterns of alpha and beta diversity were concordant. However, concordance was too low to allow for reliable extrapolation, in terms of biodiversity indication, from one tribe or subfamily to the entire family Arctiidae. Phaegopterini (comprising more putative generalist feeders during the larval stages) benefited from habitat disturbance, whereas Ctenuchini (with host-specialist larvae) were more strongly affiliated with forest habitats. [source]


Conservation planning and viability: problems associated with identifying priority sites in Swaziland using species list data

AFRICAN JOURNAL OF ECOLOGY, Issue 3 2010
Robert J. Smith
Abstract Conservation planning assessments based on species atlas data are known to select planning units containing ecotones because these areas are relatively species-rich. However, this richness is often dependent on the presence of adjoining core habitat, so populations within these ecotones might not be viable. This suggests that atlas data may also fail to distinguish between planning units that are highly transformed by agriculture or urbanization with those from neighbouring untransformed units. These highly transformed units could also be identified as priority sites, based solely on the presence of species that require adjoining habitat patches to persist. This potential problem was investigated using bird and mammal atlas data from Swaziland and a landcover map and found that: (i) there was no correlation between planning unit species richness and proportion of natural landcover for both taxa; (ii) the priority areas that were identified for both birds and mammals were no less transformed than if the units had been chosen at random and (iii) an approach that aimed to meet conservation targets and minimize transformation levels failed to identify more viable priority areas. This third result probably arose because 4.8% of the bird species and 22% of the mammal species were recorded in only one planning unit, reducing the opportunity to choose between units when aiming to represent each species. Therefore, it is suggested that using species lists to design protected area networks at a fine spatial scale may not conserve species effectively unless population viability data are explicitly included in the analysis. Résumé On sait que les évaluations de planifications de la conservation qui se basent sur les données d'atlas des espèces choisissent des unités de planification qui contiennent des écotones parce que ces zones sont relativement riches en espèces. Cependant, cette richesse dépend souvent de la présence proche d'un habitat principal, de sorte que les populations de ces écotones pourraient en fait ne pas être viables. Cela signifie que les données des atlas pourraient aussi ne pas faire la distinction entre les unités de planification qui sont fortement modifiées par l'agriculture ou l'urbanization et celles, voisines, qui ne sont pas modifiées. Des unités profondément modifiées pourraient aussi être identifiées comme sites prioritaires, si l'on se base seulement sur la présence d'espèces qui ont besoin des îlots d'habitats voisins pour subsister. Ce problème potentiel fut étudié en utilisant les données d'atlas sur des oiseaux et des mammifères du Swaziland et une carte de la couverture du terrain, et on a découvert que (i) il n'y avait pas de corrélation entre la richesse en espèces des unités de planification et la proportion de couverture naturelle pour les deux taxons; (ii) les zones prioritaires qui avaient été identifiées pour les oiseaux et pour les mammifères n'étaient pas moins transformées que si les unités avaient été choisies au hasard et (iii) une approche qui visait à atteindre des cibles de conservation et à minimizer le taux de transformation n'avait pas réussi à identifier les zones prioritaires les plus viables. Ce troisième résultat vient peut-être du fait que 4.8% des espèces d'oiseaux et 22% des espèces de mammifères avaient été rapportés pour une seule unité de planification, ce qui a réduit la possibilité de choisir entre les unités lorsque l'on a cherchéà représenter chaque espèce. C'est pourquoi on attire l'attention sur le fait que l'utilization des listes d'espèces pour concevoir les réseaux d'AP à petite échelle spatiale risque de ne pas préserver efficacement les espèces à moins que les données sur la viabilité de leur population ne soient explicitement incluses dans l'analyzse. [source]


Recurrent nuclear DNA introgression accompanies chloroplast DNA exchange between two eucalypt species

MOLECULAR ECOLOGY, Issue 7 2010
G. E. MCKINNON
Abstract Numerous studies within plant genera have found geographically structured sharing of chloroplast (cp) DNA among sympatric species, consistent with introgressive hybridization. Current research is aimed at understanding the extent, direction and significance of nuclear (nr) DNA exchange that accompanies putative cpDNA exchange. Eucalyptus is a complex tree genus for which cpDNA sharing has been established between multiple species. Prior phylogeographic analysis has indicated cpDNA introgression into the widespread forest species Eucalyptus globulus from its rare congener E. cordata. In this study, we use AFLP markers to characterize corresponding nrDNA introgression, on both a broad and fine spatial scale. Using 388 samples we examine (i) the fine-scale spatial structure of cp and nrDNA introgression from E. cordata into E. globulus at a site in natural forest and (ii) broad-scale patterns of AFLP marker introgression at six additional mixed populations. We show that while E. globulus and E. cordata retain strongly differentiated nuclear gene pools overall, leakage of nrDNA occurs at mixed populations, with some AFLP markers being transferred to E. globulus recurrently at different sites. On the fine scale, different AFLP fragments show varying distances of introgression into E. globulus, while introgression of cpDNA is extensive. The frequency of E. cordata markers in E. globulus is correlated with spatial proximity to E. cordata, but departs from expectations based on AFLP marker frequency in E. cordata, indicating that selection may be governing the persistence of introgressed fragments in E. globulus. [source]


Intimately linked or hardly speaking?

MOLECULAR ECOLOGY, Issue 3 2001
The relationship between genotype, environmental gradients in a Louisiana Iris hybrid population
Abstract Several models of hybrid zone evolution predict the same spatial patterns of genotypic distribution whether or not structuring is due to environment-dependent or -independent selection. In this study, we tested for evidence of environment-dependent selection in an Iris fulva×Iris brevicaulis hybrid population by examining the distribution of genotypes in relation to environmental gradients. We selected 201 Louisiana Iris plants from within a known hybrid population (80 m × 80 m) and placed them in four different genotypic classes (I. fulva, I. fulva -like hybrid, I. brevicaulis -like hybrid and I. brevicaulis) based on seven species-specific random amplified polymorphic DNA (RAPD) markers and two chloroplast DNA haplotypes. Environmental variables were then measured. These variables included percentage cover by tree canopy, elevation from the high water mark, soil pH and percentage soil organic matter. Each variable was sampled for all 201 plants. Canonical discriminant analysis (CDA) was used to infer the environmental factors most strongly associated with the different genotypic groups. Slight differences in elevation (,0.5 m to +0.4 m) were important for distinguishing habitat distributions described by CDA, even though there were no statistical differences between mean elevations alone. I. brevicaulis occurred in a broad range of habitats, while I. fulva had a narrower distribution. Of all the possible combinations, I. fulva -like hybrids and I. brevicaulis -like hybrids occurred in the most distinct habitat types relative to one another. Each hybrid class was not significantly different from its closest parent with regard to habitat occupied, but was statistically unique from its more distant parental species. Within the hybrid genotypes, most, but not all, RAPD loci were individually correlated with environmental variables. This study suggests that, at a very fine spatial scale, environment-dependent selection contributed to the genetic structuring of this hybrid zone. [source]


DIVERSIFICATION OF THE AFRICAN GENUS PROTEA (PROTEACEAE) IN THE CAPE BIODIVERSITY HOTSPOT AND BEYOND: EQUAL RATES IN DIFFERENT BIOMES

EVOLUTION, Issue 3 2010
Luis M. Valente
The Cape region of South Africa is a hotspot of flowering plant biodiversity. However, the reasons why levels of diversity and endemism are so high remain obscure. Here, we reconstructed phylogenetic relationships among species in the genus Protea, which has its center of species richness and endemism in the Cape, but also extends through tropical Africa as far as Eritrea and Angola. Contrary to previous views, the Cape is identified as the ancestral area for the radiation of the extant lineages: most species in subtropical and tropical Africa are derived from a single invasion of that region. Moreover, diversification rates have been similar within and outside the Cape region. Migration out of the Cape has opened up vast areas, but those lineages have not diversified as extensively at fine spatial scales as lineages in the Cape. Therefore, higher net rates of diversification do not explain the high diversity and endemism of Protea in the Cape. Instead, understanding why the Cape is so diverse requires an explanation for how Cape species are able to diverge and persist at such small spatial scales. [source]


Effects of an exotic invasive macrophyte (tropical signalgrass) on native plant community composition, species richness and functional diversity

FRESHWATER BIOLOGY, Issue 6 2010
THAÍSA SALA MICHELAN
Summary 1.,The issue of freshwater species being threatened by invasion has become central in conservation biology because inland waters exhibit the highest species richness per unit area, but apparently have the highest extinctions rates on the planet. 2.,In this article, we evaluated the effects of an exotic, invasive aquatic grass (Urochloa subquadripara, tropical signalgrass) on the diversity and assemblage composition of native macrophytes in four Neotropical water bodies (two reservoirs and two lakes). Species cover was assessed in quadrats, and plant biomass was measured in further quadrats, located in sites where tropical signalgrass dominated (D quadrats) and sites where it was not dominant or entirely absent (ND quadrats). The effects of tropical signalgrass on macrophyte species richness, Shannon diversity and number of macrophyte life forms (a surrogate of functional richness) were assessed through regressions, and composition was assessed with a DCA. The effects of tropical signalgrass biomass on the likelihood of occurrence of specific macrophyte life forms were assessed through logistic regression. 3.,Tropical signalgrass had a negative effect on macrophyte richness and Shannon and functional diversity, and also influenced assemblage composition. Emergent, rooted with floating stems and rooted submersed species were negatively affected by tropical signalgrass, while the occurrence of free-floating species was positively affected. 4.,Our results suggest that competition with emergent species and reduction of underwater radiation, which reduces the number of submersed species, counteract facilitation of free-floating species, contributing to a decrease in plant diversity. In addition, homogenisation of plant assemblages shows that tropical signalgrass reduces the beta diversity in the macrophyte community. 5.,Although our results were obtained at fine spatial scales, they are cause for concern because macrophytes are an important part of freshwater diversity. [source]


A resource-based conceptual model of plant diversity that reassesses causality in the productivity,diversity relationship

GLOBAL ECOLOGY, Issue 3 2006
Chris Lavers
ABSTRACT Biogeographical studies frequently reveal positive correlations between species richness and estimates of environmental water and/or energy. A popular interpretation of this relationship relates the supply of water and energy to productivity, and then, in turn, to richness. Productivity,diversity theories are now legion, yet none has proved sufficiently intuitive to gain broad acceptance. Like productivity, heterogeneity is known to influence diversity at fine spatial scales, yet the possibility that richness might relate to water,energy dynamics at coarse spatial scales via a heterogeneity-generating mechanism has received little attention. In this paper we outline such a conceptual model for plants that is internally consistent and testable. We believe it may help to explain the capacity of environments receiving different inputs of water and energy to support variable numbers of species at a range of spatial scales, the pervasive correlation between productivity and richness, some exceptions to the productivity,diversity relationship, the form of productivity,diversity curves and the link between richness and environmental ,harshness'. The model may also provide an answer to one of the most venerable puzzles in the field of diversity studies: why high inputs of water and energy correspond to more species rather than simply more individuals. [source]


Fine-scale heterogeneity in beetle assemblages under co-occurring Eucalyptus in the same subgenus

JOURNAL OF BIOGEOGRAPHY, Issue 10 2010
Philip S. Barton
Abstract Aim, Insect biodiversity is often positively associated with habitat heterogeneity. However, this relationship depends on spatial scale, with most studies focused on differences between habitats at large scales with a variety of forest tree species. We examined fine-scale heterogeneity in ground-dwelling beetle assemblages under co-occurring trees in the same subgenus: Eucalyptus melliodora A. Cunn. ex Schauer and E. blakelyi Maiden (Myrtaceae). Location, Critically endangered grassy woodland near Canberra, south-eastern Australia. Methods, We used pitfall traps and Tullgren funnels to sample ground-dwelling beetles from the litter environment under 47 trees, and examined differences in diversity and composition at spatial scales ranging from 100 to 1000 m. Results, Beetle assemblages under the two tree species had distinctive differences in diversity and composition. We found that E. melliodora supported a higher richness and abundance of beetles, but had higher compositional similarity among samples. In contrast, E. blakelyi had a lower abundance and species richness of beetles, but more variability in species composition among samples. Main conclusions, Our study shows that heterogeneity in litter habitat under co-occurring and closely related eucalypt species can influence beetle assemblages at spatial scales of just hundreds of metres. The differential contribution to fine-scale alpha and beta diversity by each eucalypt can be exploited for conservation purposes by ensuring an appropriate mix of the two species in the temperate woodlands where they co-occur. This would help not only to maximize biodiversity at landscape scales, but also to maintain heterogeneity in species richness, trophic function and biomass at fine spatial scales. [source]


Genetic identity of interspecific neighbours mediates plant responses to competition and environmental variation in a species-rich grassland

JOURNAL OF ECOLOGY, Issue 5 2007
JASON D. FRIDLEY
Summary 1Although outbreeding populations of many grassland plants exhibit substantial genetic and phenotypic variation at fine spatial scales (< 100 m2), the implications of local genetic diversity for community structure are poorly understood. Genetic diversity could contribute to local species diversity by mediating the effects of competition between species and by enhancing species persistence in the face of environmental variation. 2We assayed the performance of three genotypes each of a dominant tussock grass (Koeleria macrantha [Ledeb.] J.A. Schultes) and dominant sedge (Carex caryophyllea Lat.) derived from a single 10 × 10 m quadrat within a limestone grassland in Derbyshire, UK. Genotypes were grown in monoculture and grass,sedge mixtures of different genetic composition in two environments of contrasting fertility. Species mixtures also included one genotype of the subordinate forb Campanula rotundifolia L. 3When grown without neighbours, intraspecific genotypes responded similarly to environmental treatments. One genotype of the sedge performed worse in both environments than the other two sedge genotypes. 4When grown in species mixtures, genotype performance was significantly influenced by the genetic identity of the neighbouring species for both the sedge and the grass. At high fertility, differential genotype performance was not sufficient to alter the expectation of competitive exclusion of the sedge by the grass. However, at low fertility, the competitive dominant depended on the genetic identity of both the grass and the sedge. In addition, each genotype of the grass performed best next to a different genotype of the sedge, and the identity of the best genotype pairings switched with environment. 5Performance of a single genotype of the subordinate Campanula was not predictable by fertility alone, but by how fertility interacted with different neighbouring genotypes of both the grass and the sedge. 6Results support the hypothesis that the genetic identity of interspecific neighbours influences plant performance in multispecies assemblages and mediates species' responses to environmental variation. Such interactions could be a key factor in the contribution of local intraspecific genetic diversity to species diversity. [source]


Exploring spatiotemporal patterns in early stages of primary succession on former lignite mining sites

JOURNAL OF VEGETATION SCIENCE, Issue 2 2008
Birgit Felinks
Abstract Questions: 1. Does random colonization predominate in early stages of primary succession? 2. Do pioneer species facilitate the establishment of later arriving species? 3. Does an initially random distribution change to an aggregated pattern with ongoing succession? Location: Lignite mining region of Lower Lusatia, eastern Germany. Methods: Individual plants were mapped along a 2 m × 28 m transect during three successive years and classified into two groups (1) the pioneer Corynephorus canescens and (2),all other species'. Using the pair-correlation function, univariate point pattern analysis was carried out by applying a heterogeneous Poisson process as null model. Bivariate analysis and a toroidal shift null model were applied to test for independence between the spatial patterns of the two groups separately for each year, as well by exploring spatiotemporal patterns from different years. Results: In the first year Corynephorus and ,all other species' showed an aggregated pattern on a spatial scale > 40 cm and in the second and third years a significant attraction for distances between 4 and 12 cm, with an increasing radius in the third year. The analyses of interspecific spatiotemporal dynamics revealed a change from independence to attraction between distances of 4 cm and 16 cm when using Corynephorus as focal species. However, applying ,all other species' as focal points results in a significant attraction at distances up to 60 cm in the first year and a diminishing attraction in the second and third years with distances , 6 cm. Conclusions: Facilitative species-species interactions are present in early stages of primary succession, resulting mainly from pioneer species acting as physical barriers and their ability to capture diaspores being drifted by secondary dispersal along the substrate surface. However, due to gradual establishment of perennial species and their ability of lateral extension by vegetative dispersal, facilitation may influence spatial pattern formation predominantly on short temporal and fine spatial scales. [source]


Negative native,exotic diversity relationship in oak savannas explained by human influence and climate

OIKOS, Issue 9 2009
Patrick L. Lilley
Recent research has proposed a scale-dependence to relationships between native diversity and exotic invasions. At fine spatial scales, native,exotic richness relationships should be negative as higher native richness confers resistance to invasion. At broad scales, relationships should be positive if natives and exotics respond similarly to extrinsic factors. Yet few studies have examined both native and exotic richness patterns across gradients of human influence, where impacts could affect native and exotic species differently. We examined native,exotic richness relationships and extrinsic drivers of plant species richness and distributions across an urban development gradient in remnant oak savanna patches. In sharp contrast to most reported results, we found a negative relationship at the regional scale, and no relationship at the local scale. The negative regional-scale relationship was best explained by extrinsic factors, surrounding road density and climate, affecting natives and exotics in opposite ways, rather than a direct effect of native on exotic richness, or vice versa. Models of individual species distributions also support the result that road density and climate have largely opposite effects on native and exotic species, although simple life history traits (life form, dispersal mode) do not predict which habitat characteristics are important for particular species. Roads likely influence distributions and species richness by increasing both exotic propagule pressure and disturbance to native species. Climate may partially explain the negative relationship due to differing climatic preferences within the native and exotic species pools. As gradients of human influence are increasingly common, negative broad-scale native,exotic richness relationships may be frequent in such landscapes. [source]