For an ordered set W = {w1, w2, . . . , wk} of vertices and a vertex v in a connected graph G, the ordered k-vector r(v|W) := (d(v, w1), d(v, w2), . . . , d(v, wk)) is called the metric representation of v with respect to W, where d(x, y) is the distance between vertices x and y. A set W is called a resolving set for G if distinct vertices of G have distinct representations with respect to W. The minimum cardinality of a resolving set for G is its metric dimension. In this paper, we characterize all graphs of order n with metric dimension n - 3.
An information-theoretic approach was used to evaluate non-native freshwater fish species introduced to insular habitats of Hawaii and Guam comparing successful establishments vs. failures. Since the late 1800s, as many as 81 non-native freshwater fish species have been recorded as introduced to Hawaii and Guam (combined) and 50 (62%) of these are documented as having one or more established populations. We examined eleven independent variables to investigate establishment success by creating 21 a priori logistic regression models ranked using Akaike's Information Criterion adjusted for small sample size. An additional eight post-hoc models were included that comprised the best a priori model and various combinations of individual variables. The best overall model of establishment probability included effects of taxonomic affinity (family membership), prior establishment success on other tropical islands, and hypoxia tolerance. Establishment success in Hawaii and Guam was highest for those species established on many other islands, and according to our best model air-breathing fishes were more likely to become established. Six fish families, each with from three to 18 species introduced to Pacific islands, were highly successful at establishment: Cichlidae (16 established of 18 species introduced), Poeciliidae (seven of eight), Cyprinidae (four of seven), Centrarchidae (four of four), Clariidae (three of three), and Loricariidae (three of four). Those that successfully established include both small and moderately large-bodied taxa, while representing a diverse array of other morphological and life-history traits. Pathways and motives associated with fish introductions in the Pacific have been linked to desires to develop aquaculture, enhance wild stocks of food, sport, and bait fishes, for use as biological control agents, or are linked to the ornamental fish trade. We found that many established species were introduced via multiple pathways (up to eight) and our analyses suggest that the combination of prior establishment success on other tropical islands and presence of non-native fishes in multiple pathways was indicative of high propagule pressure. Our study results and conclusions on Pacific tropical island introductions are in general agreement with previous studies on non-native freshwater fishes in other regions of the world and similar to observations in continental ecosystems and temperate zones.
In this paper some infinitely based varieties of groups are constructed and these results are transferred to the associative algebras (or Lie algebras) over an infinite field of an arbitrary positive characteristic.
The global environment is faced with growing threats from anthropogenic disturbance, propelling the Earth into a 6th mass extinction. For the world's mammals, this is reflected in the fact that 25% of species are threatened with some risk of extinction. During this time of species loss and environmental alteration, the world's natural history museums (NHMs) are uniquely poised to provide novel insight into many aspects of conservation. This review seeks to provide evidence of the importance of NHMs to mammal conservation, how arguments against continued collecting of physical voucher specimens is counterproductive to these efforts, and to identify additional threats to collecting with a particular focus on small mammals across Africa. NHMs contribute unique data for assessing mammal species conservation status through the International Union for Conservation of Nature's (IUCN) Red List of Threatened species. However, NHMs' contributions to mammal conservation go well beyond supporting the IUCN Red List, with studies addressing topics such as human impacts, climate change, genetic diversity, disease, physiology, and biodiversity education. Increasing and diverse challenges, both domestic and international, highlight the growing threats facing NHMs, especially in regards to the issue of lethally sampling individuals for the purpose of creating voucher specimens. Such arguments are counterproductive to conservation efforts and tend to reflect the moral opposition of individual researchers than a true threat to conservation. The need for continued collecting of holistic specimens of all taxa across space and time could not be more urgent, especially for underexplored biodiversity hotspots facing extreme threats such as the Afrotropics.
Southern Africa is considered one of the world's 'hotspots' for the diversity of cartilaginous fishes (Chondrichthyes), with currently 204 reported species. Although numerous literature records and treatises on chondrichthyan fishes are available, a paucity of information exists on the biodiversity of their parasites. Chondrichthyan fishes are parasitised by several groups of protozoan and metazoan organisms that live either permanently or temporarily on and within their hosts. Reports of parasites infecting elasmobranchs and holocephalans in South Africa are sparse and information on most parasitic groups is fragmentary or entirely lacking. Parasitic copepods constitute the best-studied group with currently 70 described species (excluding undescribed species or nomina nuda) from chondrichthyans. Given the large number of chondrichthyan species present in southern Africa, it is expected that only a mere fraction of the parasite diversity has been discovered to date and numerous species await discovery and description. This review summarises information on all groups of parasites of chondrichthyan hosts and demonstrates the current knowledge of chondrichthyan parasites in South Africa. Checklists are provided displaying the host-parasite and parasite-host data known to date., Bjoern C. Schaeffner, Nico J. Smit., and Obsahuje bibliografii
Cílem studie je přispět k porozumění souvislostem mezi nesymbolickými numerickými schopnostmi a vývojovou dyskalkulií. Zabýváme se tedy početními funkcemi již na úrovni vrozených dispozic, předcházejících osvojení číselného aparátu, které jsou zajišťovány instancí tzv. aproximativního numerického systému (ANS) a projevují se v dovednosti odhadu kvantit. Pokud tento vztah existuje, bylo by jej zřejmě možné využít pro praktickou diagnostiku dyskalkulie již v raném věku dítěte před projevením případných obtíží v numerických dovednostech. Naše pilotní studie srovnává úroveň nesymbolických početních schopností (početního odhadu) u dětí s dyskalkulií a kontrolní skupiny. Kompletní výzkumný soubor tvořilo 75 žáků ve věkovém rozmezí 6,6 až 17,8 let (M = 12,03; SD = 2,68), přičemž 25 (33 %) z nich vykazovalo matematické obtíže, které jsou v 17 případech(23 %)vysvětleny diagnózou dyskalkulie. Sběr dat byl realizován s využitím elektronického „testu početního odhadu“ vlastní konstrukce, tvořeného tzv. aproximativními úlohami založenými na principu diferenciace množství. Výsledky naznačují, že kontrolní skupina diskriminuje množství lépe než děti s matematickými obtížemi. Po kontrole věku respondentů je však vztah dyskalkulie a výkonu v testu početního odhadu slabý a statisticky nevýznamný, beta = –0,232, p = 0,056. Zjištěné výsledky jsou diskutovány ve vztahu k možnostem jejich využití v praxi. and The aim of the study is to contribute to the understanding of the links between non-symbolic numerical abilities and developmental dyscalculia. Therefore, we deal with the numerical functions already at the level of innate dispositions preceding the acquiring of numerical apparatus, which are ensured by the instance of the so-called approximate number system (ANS) and are manifested in the quantitative estimation skill. If the relationship exists, it might be possible to use it for the practical diagnosis of dyscalculia at an early age before showing any difficulties in numerical skills. Our pilot study compares the level of non-symbolic numerical abilities (counting) in children with dyscalculia and control groups. The complete research group consisted of 75 pupils aged between 6.6 and 17.8 years (M = 12.03; SD = 2.68), with 25 (33%) showing mathematical difficulties in 17 cases (23%) explained by the diagnosis of dyscalculia. Data was collected using an electronic “numerical estimate test” of the own construction, constituted by the so-called approximation tasks based on the principle of differentiation of quantities. The results suggest that the control group discriminates the quantity better than children with mathematical difficulties. However, after checking the age of the respondents, the relationship between dyscalculia and numerical test output is weak and statistically insignificant, beta = -0.232, p = 0.056. The results are discussed in relation to the possibilities of their use in practice.
In the context of food self-sufficiency, the River Senegal Valley has been undergoing profound environmental changes for several decades. Rice production has increased due to the development of vast irrigated perimeters, which has been accompanied by recurrent proliferations of rodent populations that are crop pests and reservoirs of zoonoses. The aim of our study was to determine the factors underlying these phases of increased rodent abundance over a ten-year (2008 to 2019) sampling period during the hot dry season (February-May). A total of 1,867 rodents of four species were captured, among which Arvicanthis niloticus and Mastomys huberti dominated. Our results showed that, during this season, rodent abundance (i) increases significantly with rainfall from the previous year, (ii) is higher in cultivated than in uncultivated plots, (iii) increases with plant cover, (iv) increases, for M. huberti, with the presence of open water. We showed that in an area that was first sparsely cultivated and then impacted by hydro-agricultural rehabilitation of irrigation and drainage infrastructure, the abundance of A. niloticus changed following this program, reaching the level of a nearby area that has been intensively cultivated for decades. Moreover, we showed that the proportion of adults among the captured individuals was lower in rice plots than in vegetable gardening fields and uncultivated plots. The breeding pattern of adult individuals was also affected by land use. Results suggest that uncultivated areas and vegetable gardening fields constitute refuge and breeding ground hotspots and would thus form a starting point for the invasion of rice fields. Following these results, we advocate for regular monitoring of rodent breeding and abundance patterns, with a special focus on these refuge areas, particularly during the hot dry season. We recommend implementing effective and sustainable science-based control strategies at national and community levels to keep rodent populations within tolerable limits.