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Ecological Relationships (ecological + relationships)
Selected AbstractsEcological relationships between stream communities and spatial scale: implications for designing catchment-level monitoring programmesFRESHWATER BIOLOGY, Issue 5 2007RICHARD K. JOHNSON Summary 1. Stream communities are structured by factors acting over multiple spatial and temporal scales. Identifying what factors are driving spatial patterns in stream communities is a central aim of ecology. 2. Here we used two large European data sets of fish, invertebrates, macrophytes, benthic diatoms and environmental data in two stream groups (lowland and mountain) to determine the importance of variables at different spatial scales (geographical, regional, local) on community structure. 3. Both geographical position and ecoregion were selected first in canonical correspondence analysis (CCA), clearly showing the broad spatial gradients covered in the data set. Secondary predictors (after accounting for spatial and/or ecoregion effects) were similar between stream groups and among the four organism groups. In particular, conductivity and N concentration were strong predictors reflecting catchment land use. 4. Using partial CCA, we assessed the individual importance of the three spatial scales on the community structure of the four organism groups in the two stream groups. The majority of among-site variability (22,29%) was accounted for by local scale variables (e.g. water chemistry and substratum type), with regional and spatial variables accounting 11,13% and 5,6%, respectively. Our findings indicate that the four organism groups are responding similarly to the different levels of spatial scale, implying much redundancy which should be consider when implementing studies of bioassessment. [source] Prior encounters modulate subsequent choices in host acceptance behavior by the bark beetle Ips piniENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 3 2002Kimberly F. Wallin Abstract Laboratory bioassays indicate that the bark beetle Ips pini employs flexible, rather than absolute, responses to phytochemicals in its host acceptance behavior. Each beetle's decision to enter substrate was influenced by the types and concentrations of monoterpenes present. However, previous rejection of a simulated host containing a moderate concentration of monoterpenes increased the likelihood that the same concentration would be accepted upon a second or third encounter. This flexibility more than offsets any loss of vigor due to starvation and age that accompanies a process of trial and error. Starvation decreased beetles' total lipid content, but beetles can recover some energetic losses by a small amount of feeding during each trial. In addition to its adaptive value, a flexible host acceptance strategy may yield population level consequences. That is, bark beetles preferentially enter trees having low concentrations of monoterpenes, but may modify their acceptance thresholds when cues associated with stressed trees are not available. This could partially explain how some tree-killing bark beetles colonize a broader physiological range of trees during outbreaks. The adaptive value of relating individual decisions to population density may arise from two ecological relationships: first, as populations rise, the pool of stressed trees is rapidly depleted; secondly, healthy trees are attainable through pheromone , mediated mass attacks when adequate numbers of beetles are present. Flexible host acceptance behaviors may also reduce the advantage of relying exclusively on pre-landing cues to distinguish between susceptible and non-susceptible trees. [source] Assessing the reliability of biodiversity databases: identifying evenly inventoried island parasitoid faunas (Hymenoptera: Ichneumonoidea) worldwideINSECT CONSERVATION AND DIVERSITY, Issue 2 2010ANA M. C. SANTOS Abstract., 1.,Taxonomic and geographic biases are common in biodiversity inventories, especially in hyperdiverse taxa, such as the Ichneumonoidea. Despite these problems, biodiversity databases could be a valuable source of information if their reliability is carefully assessed. 2.,One major problem of using these data for large-scale analyses is the unevenness of data quality from different areas, which makes them difficult to compare. One way of surpassing such problem would be to identify sets of areas that are evenly inventoried. 3.,Here, we propose a scoring protocol for the identification of sets of evenly inventoried areas from taxonomic databases, based on three criteria: (i) completeness at high taxonomic levels, (ii) congruence with well-established ecological relationships (such as species,area relationship), and (iii) publication effort received. We apply this protocol to the selection of a set of evenly inventoried islands worldwide for two Ichneumonoidea families (Braconidae and Ichneumonidae) from the data gathered in Taxapad database. 4.,From the 118 islands included in Taxapad, 53 and 70 can be considered sufficiently inventoried for Braconidae and Ichneumonidae, respectively. The publication effort criterion was more restrictive than the other two criteria. The Indomalayan, Nearctic and Palearctic regions had more than half of their islands identified as evenly inventoried, for both families. 5.,We discuss the generality of the biases and incompleteness of most biodiversity data, and also how the basic principles of the protocol proposed here can be applied to taxonomic databases devoted to other taxa. Also, the islands identified here can serve as the basis for large-scale analyses of the poorly known biogeography of the Ichneumonoidea. [source] GUEST EDITORIAL: The interplay of pollinator diversity, pollination services and landscape changeJOURNAL OF APPLIED ECOLOGY, Issue 3 2008Ingolf Steffan-Dewenter Summary 1Pollinators are a functional group with high relevance for ensuring cross-pollination in wild plant populations and yields in major crops. Both pollinator declines and losses of pollination services have been identified in the context of habitat destruction and land use intensification. 2This editorial synthesizes and links the findings presented in seven papers in this Special Profile, focusing on pollinator diversity and plant,pollinator interactions in natural habitats and agricultural landscapes. 3The results contribute to our understanding of local and landscape scale effects of land use intensification on pollinator densities and diversity, and pollination functions in wild plant communities and crops. 4Synthesis and applications. We emphasize the exceptional coverage in pollination ecology ranging from basic ecological relationships to applied aspects of ecosystem services and ecosystem management, and conclude with identifying gaps in current knowledge and challenging research areas for the future. [source] Rodent assemblage in a habitat mosaic within the Valley Thicket vegetation of the Eastern Cape Province, South AfricaAFRICAN JOURNAL OF ECOLOGY, Issue 1 2008Boris Kry, tufek Abstract We sampled small mammal assemblage in a mosaic of Valley Thicket vegetation in the Great Fish River Reserve during the summers of 2001 and 2002. Assemblage was dominated by seven rodent species with a single nonrodent species (Elephantulus edwardii) in the 357 trapped specimens. Rhabdomys dilectus was the most abundant in both years, followed by Mus minutoides (ranking 2nd in 2001) and Mastomys coucha (2nd in 2002). These three species, which are widespread generalists, made up 85.0% of the total rodent catch in 2001 and 74.3% in 2002. Individual species were captured on 2,14 sites of a total of 17 and M. minutoides was the most widespread. The majority of samples consisted of two (ten sites in a pooled sample for 2 years) or three species (ten sites). Significant morphological structuring was found only in two-species samples. Species turnover was high both among sites and between the 2 years. We found no evidence of significant nested structure which would suggest hierarchical sets of ecological relationships among the species. Vegetation structure explained better than species interactions, the population variables in the rodent assemblage. Résumé Nous avons échantillonné l'assemblage de petits mammifères dans une mosaïque végétale de Valley Thicket dans la Great Fish River Reserve au cours des étés de 2001 et 2002. L'assemblage des 357 spécimens attrapés était dominé par sept espèces de rongeurs et une autre espèce (Elephantulus edwardii). Rhabdomys dilectusétait l'espèce la plus abondante les deux années, suivie par Mus minutoides (classé 2ème en 2001) et par Mastomys coucha (2ème en 2002). Ces trois espèces, qui sont des espèces généralistes très répandues, représentaient 85,0% des prises totales de rongeurs en 2001 et 74,3% en 2002. Les espèces individuelles furent capturées sur deux à 14 sites sur un total de 17, et Mus minutoidesétait la plus répandue. La majorité des échantillons se composaient de deux (10 sites sur un échantillonnage groupé de deux ans) ou trois espèces (dix sites). On n'a découvert de structure morphologique significative que dans des échantillons de deux espèces. Le turnover des espèces était élevé entre les différents sites et entre les années. Nous n'avons trouvé aucune preuve d'une structure significative qui puisse suggérer l'existence de relations hiérarchiques écologiques entre les espèces. La structure de la végétation expliquait mieux que les interactions interspécifiques les variables des populations de l'assemblage des rongeurs. [source] Biofilms in the Edentulous Oral CavityJOURNAL OF PROSTHODONTICS, Issue 5 2008Amit Sachdeo BDS, DMSc Abstract Purpose: The oral cavity presents numerous surfaces for microbial colonization. These surfaces produce biofilms of differing complexities unique to each individual. Several studies have looked at biofilms in dentate patients. There has been limited research regarding biofilms on dentures or soft tissues of edentulous patients. The purpose of the present investigation was to provide meaningful data describing microbial ecological relationships in the oral cavity of edentulous patients and to evaluate the microbiota on hard and soft tissue surfaces and saliva in edentulous patients wearing complete dentures. Materials and Methods: Sixty-one edentulous subjects with complete maxillary and mandibular dentures were recruited. "Supragingival" biofilm samples were taken from 28 denture teeth for each subject. Biofilm samples were also taken from the dorsal, lateral, and ventral surfaces of the tongue, floor of mouth, buccal mucosa, hard palate, vestibule/lip, "attached gingiva," and saliva. Samples were individually analyzed for their content of 41 bacterial species using checkerboard DNA,DNA hybridization. Levels and proportions of each species were determined for every sample location. Results: Periodontal pathogens such as Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis were clearly present in the samples from the edentulous subjects. Microbial profiles in samples from the soft tissue surfaces differed among site locations. Samples from the dorsum of the tongue exhibited the highest bacterial counts followed by the "attached gingiva" and the lateral surfaces of the tongue, while the lowest mean counts were found in samples from the buccal mucosa and labial vestibules. Using cluster analysis of the proportions of the test species, three clusters were formed. The first cluster comprised saliva, supragingival plaque, and the lateral and dorsal surfaces of the tongue. The second cluster comprised the other six soft tissue surfaces. Species on the denture palate formed a third cluster. Conclusions: One of the major findings in this study was the detection of periodontal pathogens, A. actinomycetemcomitans and P. gingivalis, in the edentulous subjects, as these species were thought to disappear after removal of all natural teeth. This finding has implications regarding future dental treatment and the general health of individuals. Distinct patterns of microbial colonization were seen on the different soft tissue surfaces. Thus, this investigation provided the first step in defining the organisms that are associated with edentulous patients on both soft (mucosa) and hard surfaces (denture). The study also provided meaningful data that described microbial ecological relationships in the oral cavity of edentulous subjects. The authors believe that this study is the first comprehensive assessment of the microbiota in the complete denture-wearing subject. [source] Disentangling complex fine-scale ecological patterns by path modelling using GLMM and GISJOURNAL OF VEGETATION SCIENCE, Issue 5 2009Vegar Bakkestuen Abstract Question: How can statistical modelling tools (GLMM) and GIS be used as an aid in understanding complex ecological patterns? This general question was approached by using bryophyte demography data as an example. More specifically, we asked what is the contribution of terrain shape to explaining the performance and fate of plant individuals, controlling for all other known relationships? Location: Norway. Methods: Information on demography was obtained for 140 populations of the perennial clonal bryophyte Hylocomium splendens in Norway spruce forests during an 11-year period (1992-2002). Performance (size and branching pattern) was recorded for mature segments and fate was recorded for growing points. Positions of each of the more than 30 000 recorded bryophyte ramets were coupled with (micro-) topographic characteristics (slope and convexity) derived from fine-scale digital elevation models in a GIS framework. Carefully planned sequences of generalised linear mixed models (GLMM) were performed to test predictions from a conceptual path model. Results: We demonstrate strong dependence of size on branching, fate and on vertical position in the bryophyte carpet, and an effect of vertical position on branching pattern. Micro-topography contributed to explaining plant performance by four different mechanisms: (1) a direct effect of slope on the segment's vertical position in the carpet; (2-3) direct effects of both slope and convexity on fates of individuals via controls on risk of burial; and (4) an indirect effect of convexity on branching pattern via a direct effect on size. No indication of a direct effect of terrain on branching was found. Conclusions: Our study exemplifies the usefulness of GLMM for disentangling complex ecological relationships. Specifically, we recognise micro-topography as a potentially important factor for plant demography in general and for performance and fate of individuals in particular. [source] Do introduced North American beavers Castor canadensis engineer differently in southern South America?MAMMAL REVIEW, Issue 1 2009An overview with implications for restoration ABSTRACT 1Twenty-five pairs of North American beavers Castor canadensis Kuhl were introduced to Tierra del Fuego Island in 1946. The population has expanded across the archipelago, arriving at the Chilean mainland by the mid-1990s. Densities range principally between 0.5,2.05 colonies/km. They have an impact on between 30,50% of stream length and occupy 2,15% of landscape area with impoundments and meadows. Beaver impacts constitute the largest landscape-level alteration in subantarctic forests since the last ice age. 2The colonization pattern, colony densities and impacted area indicate that habitat in the austral archipelago is optimal for beaver invasion, due to low predator pressure and suitable food resources. Nothofagus pumilio forests are particularly appropriate habitat, but a more recent invasion is occurring in adjacent steppe ecosystems. Nonetheless, Nothofagus reproductive strategies are not well adapted to sustain high beaver population levels. 3Our assessment shows that at the patch-scale in stream and riparian ecosystems, the direction and magnitude of exotic beaver impacts are predictable from expectations derived from North American studies, relating ecosystem engineering with underlying ecological mechanisms such as the relationships of habitat heterogeneity and productivity on species richness and ecosystem function. 4Based on data from the species' native and exotic range, our ability to predict the effects of beavers is based on: (i) understanding the ecological relationships of its engineering effects on habitat, trophic dynamics and disturbance regimes, and (ii) having an adequate comprehension of the landscape context and natural history of the ecosystem being engineered. 5We conclude that beaver eradication strategies and subsequent ecosystem restoration efforts, currently being considered in southern Chile and Argentina, should focus on the ecology of native ecosystems rather than the biology of this invasive species per se. Furthermore, given the nature of the subantarctic landscape, streams will probably respond to restoration efforts more quickly than riparian ecosystems. [source] Assessment of intraradicular bacterial composition by terminal restriction fragment length polymorphism analysisMOLECULAR ORAL MICROBIOLOGY, Issue 5 2009D. Saito Background:, The aim of the study was to assess the bacterial community structures associated with endodontic infections using terminal restriction fragment length polymorphism (T-RFLP), and to investigate the correlation of whole community profiles with the manifestation of particular clinical features. Methods:, Intraradicular samples were collected from 34 subjects and classified into three study groups based on the observed clinical symptoms: acute (n = 16), sub-acute (n = 8), and asymptomatic (n = 10). Genomic DNA was extracted from each sample, submitted to polymerase chain reaction using a fluorescently labeled 16S ribosomal DNA forward primer, and digested with two tetrameric endonucleases (HhaI and MspI). The terminal restriction fragments (T-RFs) were subsequently discriminated in an automated DNA sequencer, and the results were filtered using a statistics-based criterion. Results:, Totals of 138 (HhaI) and 145 (MspI) unique T-RFs were detected (means 13.1 and 11.9) and there was high inter-subject variability in the bacterial assemblages. Odds-ratio analysis unveiled the existence of higher order groups of positively associated T-RFs, restating the concept that intricate ecological relationships may take place in the root canal space. A significantly greater T-RF prevalence was detected in acute cases, suggesting a straight correlation between species richness and spontaneous pain. Conclusion:, Overall, no T-RFLP profile representing a specific bacterial consortium could be associated with the manifestation of symptoms of endodontic origin. [source] Effectiveness of the river environment classification in the Auckland RegionNEW ZEALAND GEOGRAPHER, Issue 3 2008Liza Inglis Abstract:, The River Environment Classification (REC) provides a GIS-based tool to differentiate between biophysical attributes of river systems. This study tests the effectiveness of the REC as a tool to differentiate physical habitat and macroinvertebrate assemblages between four classes of stream in the Auckland region. Results indicate significant within-class variability in physical habitat and macroinvertebrate assemblages, with considerable overlap among the four classes. Biophysically meaningful stream classes cannot be identified from GIS-derived data applied in this research. Field analyses of physical habitat (i.e. geomorphic river condition) are required as a supplementary tool to interpret ecological relationships for differing stream types. [source] Evaluating the role of the dingo as a trophic regulator in Australian ecosystemsAUSTRAL ECOLOGY, Issue 5 2007A. S. GLEN Abstract The importance of strongly interactive predators has been demonstrated in many ecosystems, and the maintenance or restoration of species interactions is a major priority in the global conservation of biodiversity. By limiting populations of prey and/or competitors, apex predators can increase the diversity of systems, often exerting influences that cascade through several trophic levels. In Australia, emerging evidence points increasingly towards the dingo (Canis lupus dingo) as a strongly interactive species that has profound effects on ecosystem function. Through predatory and competitive effects, dingoes can alter the abundance and function of mesopredators including the introduced red fox (Vulpes vulpes) and feral cat (Felis catus), and herbivores including the European rabbit (Oryctolagus cuniculus). These effects often benefit populations of native prey, and diversity and biomass of vegetation, but may not occur under all circumstances. For example, the social structure of dingoes is of great importance; a pack subject to minimal human interference regulates its own numbers, and such packs appear to have fewer undesirable impacts such as predation on livestock. Despite abundant observational evidence that the dingo is a strong interactor, there have been few attempts to test its ecological role experimentally. Given the well-recognized importance of species interactions to ecosystem function, it is imperative that such experiments be carried out. To do this, we propose three broad questions: (i) do dingoes limit the abundance of other predators or prey? (ii) do dingoes affect the ecological relationships of other predators or prey (e.g. by altering their spatial or temporal activity patterns)? and (iii) does the removal or reintroduction of dingoes entrain ecological cascades? Finally, we discuss the design of appropriate experiments, using principles that may also be applied to investigate species interactions on other continents. Research might seek to clarify not only the impacts of dingoes at all trophic levels, but also the mechanisms by which these impacts occur. [source] Speciation mirrors geomorphology and palaeoclimatic history in African laminate-toothed rats (Muridae: Otomyini) of the Otomys denti and Otomys lacustris species-complexes in the ,Montane Circle' of East AfricaBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2009PETER J. TAYLOR We adopted an integrated systematic approach to delimit evolutionary species and describe phylogeographic, morphometric and ecological relationships in Otomys denti (from the Albertine Rift, Southern Rift in Malawi and the northern Eastern Arc Mountains) and Otomys lacustris (from the Southern Rift in Tanzania and Zambia, and the southern Eastern Arc Mountains). Molecular [cytochrome (cyt) b sequences, 1143 bp, N = 18], craniometric (classical, N = 100 and geometric, N = 60) and ecological (Partial Least Squares regression of shape and ecogeographic variables) approaches show a profound, parallel disjunction between two groups: (1) Eastern Arc and Southern Rift (including the Malawi Rift) (O. lacustris and Otomys denti sungae) and (2) Albertine Rift (Otomys denti denti and Otomys denti kempi) taxa. Within both groups, cyt b sequences or craniometric analysis provided evidence for the differentiation of both southern and northern Eastern Arc from Southern Rift lineages (across the so-called Makambako Gap). Within the Albertine Rift (denti,kempi) lineage, populations from individual mountain ranges differed significantly in skull shape (but not size), but were similar genetically. Over-reliance in the past on very few morphological characters (e.g. number of molar laminae) and a polytypic species concept has obscured phylogenetic relationships and species discrimination in this group. We recognize at least three species in this group, and distinct lineages within two of these species. Each species or lineage was endemic to one of three regions: the Albertine Rift, the Malawi Rift or the Eastern Arc. Our result echo conclusions of recent studies of other mammalian and bird taxa and reflect the geomorphology and palaeoclimatic history of the region. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 913,941. [source] Critical thresholds associated with habitat loss: a review of the concepts, evidence, and applicationsBIOLOGICAL REVIEWS, Issue 1 2010Trisha L. Swift A major conservation concern is whether population size and other ecological variables change linearly with habitat loss, or whether they suddenly decline more rapidly below a "critical threshold" level of habitat. The most commonly discussed explanation for critical threshold responses to habitat loss focus on habitat configuration. As habitat loss progresses, the remaining habitat is increasingly fragmented or the fragments are increasingly isolated, which may compound the effects of habitat loss. In this review we also explore other possible explanations for apparently nonlinear relationships between habitat loss and ecological responses, including Allee effects and time lags, and point out that some ecological variables will inherently respond nonlinearly to habitat loss even in the absence of compounding factors. In the literature, both linear and nonlinear ecological responses to habitat loss are evident among simulation and empirical studies, although the presence and value of critical thresholds is influenced by characteristics of the species (e.g. dispersal, reproduction, area/edge sensitivity) and landscape (e.g. fragmentation, matrix quality, rate of change). With enough empirical support, such trends could be useful for making important predictions about species' responses to habitat loss, to guide future research on the underlying causes of critical thresholds, and to make better informed management decisions. Some have seen critical thresholds as a means of identifying conservation targets for habitat retention. We argue that in many cases this may be misguided, and that the meaning (and utility) of a critical threshold must be interpreted carefully and in relation to the response variable and management goal. Despite recent interest in critical threshold responses to habitat loss, most studies have not used any formal statistical methods to identify their presence or value. Methods that have been used include model comparisons using Akaike information criterion (AIC) or t -tests, and significance testing for changes in slope or for polynomial effects. The judicious use of statistics to help determine the shape of ecological relationships would permit greater objectivity and more comparability among studies. [source] Landscape Patterns of Tropical Forest Recovery in the Republic of Palau,BIOTROPICA, Issue 4 2001Bryan A. Endress ABSTRACT A GIS (geographic information systems) database was constructed from aerial photographs, a vegetation map, and topographic map data of the Ngeremeduu Bay Drainage Area (NBDA), Palau, to examine relationships between upland land cover dynamics, environmental variables, and past land use. In 1992, 82.9 percent of the NBDA was forest, 16.6 percent was grassland, and 0.5 percent consisted of village areas. Between 1947 and 1992, there was a 11.2 percent reduction of grassland area primarily due to a 10.9 percent increase in forest cover. These land cover changes led to larger, more continuous stretches of forest and numerous, highly fragmented grassland patches. Significant relationships (P 0.001) were found between the spatial distribution of forest and grassland cover and slope, elevation, soil pH, and percent soil organic matter. These patterns, however, may have resulted from past farm site selection rather than from ecological relationships. Our results indicate that areas of forest expansion were significantly (P 0.001) associated with the location of abandoned agricultural communities. In addition, over 92 percent of areas of forest expansion occurred within 100 m of established forest. These results suggest that the proximity of established forest facilitate forest recovery following human disturbance. [source] | |||||||||||||||||||||||||