Discontinuous Distribution Patterns Research Articles

An effective way to monitor the population of juvenile horseshoe crabs in the Beibu Gulf of China

Population conservation of horseshoe crab is urgently required in China as their population is declining dramatically. However, conservation efforts are severely constrained by the lack of information on the population dynamics of the species. Here, a citizen science-based investigation was conducted to continuously monitor the population dynamics of juvenile Tachypleus tridentatus and Carcinoscorpius rotundicauda in the Beibu Gulf of China over five years. A low abundance of horseshoe crabs was observed at all stations. T. tridentatus was primarily observed in the eastern of Beibu Gulf, with an abundance (0.179 ind/100 m2) larger than that of C. rotundicauda (0.007 ind/100 m2). The prosomal width range of T. tridentatus was between 9.0 and 138.0 mm while that of C. rotundicauda was between 20.0 and 111.0 mm, representing their different age distribution patterns. A continuous distribution pattern from 3rd to 14th instar was observed in the T. tridentatus population, whereas a discontinuous distribution pattern from 6th to 16th instars was observed in the C. rotundicauda population. This instar distribution pattern implies that these areas are crucial nursery habitats for the two species. No horseshoe crab within the 1st to 2nd instars (for T. tridentatus) or before 6th instar (for C. rotundicauda) were observed within five years, indicating a declining age structure with few natural births. It was concluded that the declining population would exacerbate the risk of endangered horseshoe crab. There is an urgent need to strengthen the protection of horseshoe crab in the Beibu Gulf, particularly to protect their nursery habitats. The value of long-term citizen science based-monitoring was highlighted, which greatly increased public awareness of horseshoe crab protection.

Floristic diversity of mangroves and mangrove associate species of Kali River Estuary, Karwar, Karnataka, India

This study assessed the mangrove flora of the Kali River estuary, Uttara Kannada district, Karnataka. Fourteen true mangrove species belonging to eight families and 11 genera were documented from four locations: Devbagh, Mavinhole, Kalimatha Island, and Halgejoog. The mangrove species show a discontinuous distribution pattern in the Kali River estuary. The highest IVI in true mangroves was recorded for Avicennia officinalis at Devbagh, Acanthus ilicifolius at Mavinhole, Sonneratia caseolaris (after Oryza coarctata) at Kalimatha Island, and S. caseolaris (after Derris trifoliata) at Halgejoog. Of the four sites, Devbagh has the highest Shannon-Wiener diversity index, and with regard to species composition, Devbagh and Kalimatha Island are the most similar sites. Kalimatha island has the most well-preserved mangrove community.

New insights into infrageneric relationships of Lonicera (Caprifoliaceae) as revealed by nuclear ribosomal DNA cistron data and plastid phylogenomics

AbstractThe discontinuous geographic distribution pattern of plants in the north temperate zone has been a focus of biogeographic research, especially concerning the mechanisms behind the formation of such a pattern and the spatial and temporal evolution of this intermittent distribution pattern. Hypotheses of boreotropical origin, land bridge migration, and out‐of‐Tibet have been proposed to explain the formation of the discontinuous distribution pattern. The distribution of Lonicera shows a typical Europe–Asia–North America discontinuous distribution, which makes for a good case study to investigate the above three hypotheses. In this study, we inferred the phylogeny based on plastid genomes and a nuclear data set with broad taxon sampling, covering 83 species representing two subgenera and four sections. Both nuclear and plastid phylogenetic analyses found section Isika polyphyletic, while sections Nintooa, Isoxylosteum, and Coelxylosteum were monophyletic in subgenus Chamaecerasus. Based on the nuclear and chloroplast phylogeny, we suggest transferring Lonicera maximowiczii and Lonicera tangutica into section Nintooa. Reconstruction of ancestral areas suggests that Lonicera originated in the Qinghai–Tibetan Plateau (QTP) and/or Asia, and subsequently dispersed to other regions. The aridification of the Asian interior may have facilitated the rapid radiation of Lonicera in the region. At the same time, the uplifts of the Tibetan Plateau appear to have triggered the spread and recent rapid diversification of the genus on the QTP and adjacent areas. Overall, our results deepen the understanding of the evolutionary diversification history of Lonicera.

Expansion of non-native plant Flaveria bidentis (L.) Kuntze driven by a range of factors leading to patchy distribution patterns.

Given the growing concern over the ecological impacts of non‐native species, exploring these species' expansion edge and distribution patterns and their driving factors is important for developing suitable management measures. Flaveria bidentis (L.) Kuntze, a non‐native plant that was introduced to China in the 1990s, has spread from southern Hebei Province, where it first took root, to the surrounding regions and has become one of the most notorious invasive weeds in northern China. Based on 15 years (2006–2021) of extensive field investigations, the spatial distribution of sampling and occurrence points were mapped in the recently expanded region of F. bidentis' population. Then, nearest neighbor analysis is used to characterize the spatial pattern differences between samplings and occurrences. An exponential decay function was used to elucidate the driving factors contributing to the presence and absence of F. bidentis. Our results demonstrated an effective random sampling setup, a heterogeneous spatial distribution of F. bidentis, and a multi‐regional independent aggregation distribution pattern (p < .01). There were significant spatial correlations between the aggregation areas of plant occurrence points and the locations of roads and construction sand distribution centers. These findings suggest that human activities involving major roads and construction sand distribution centers were driving factors contributing to this long‐distance dispersal and spatially discontinuous distribution patterns. The presence of these patchy distribution patterns has important implications for ongoing efforts to manage populations of non‐native species.

An analytically derived delineation of the West African Coastal Province based on bivalves

AbstractAimTo assess the pattern of biotic regions (BR) and their boundaries, to detect chorotypes and to relate these patterns to key environmental factors.LocationEastern Atlantic Ocean.Time periodRecent.Taxon studiedBivalvia.MethodsDistributions were scored for 595 species. Operational geographical units are classified hierarchically using Baroni‐Urbani &amp; Buser similarity index, clusters were assessed for statistical significance with the ‘RMacoqui 1.0’ software using G tests of independence, and chorotypes were inferred likewise from similarity between species distributions.ResultsThree strong biotic boundaries delimit four BR: (1) European Atlantic and Mediterranean; (2) West African, from western Sahara to southern Angola; (3) Baia dos Tigres/Namibia; and (4) Saint Helena/Ascension. The West African BR is subdivided by two weak boundaries into three subordinate BR: the tropical region proper, the north‐western African transition zone and the cluster (southern Angola/São Tomé/Cape Verde Islands). Of the 429 species present in West Africa, 261 (60.7%) are endemic, and 19 genera (7.2%) are endemic. Sixteen chorotypes were identified; the European BR is correlated with chorotypes C5 (149 species mostly European and Mediterranean) and C3 (38 species mostly in northern Europe), whereas the West African BR is mainly characterized by chorotype C6 (221 species). Some discontinuous distribution patterns of tropical West African species were identified as chorotypes, but subordinate to chorotype C6. The West African BR is mainly characterized by sea surface temperature and chlorophyll; characterization without the islands also involved the extensive sandy coast. The north‐western African transition region is characterized by an arid climate and few rivers and influenced by seasonal upwelling. The cluster of southern Angola, Sao Tomé and Cape Verdes contrasts with the remainder of West Africa in having a predominantly rocky shore.Main conclusionsThe present analyses provide an objective regionalization based on species occurrences, which supports the traditional recognition of West Africa as a major biotic region with a high level of endemism. Attention is called on that the unique endemic component is insufficiently represented in current marine protected areas.

Refugia in Glacial Ages Led to the Current Discontinuous Distribution Patterns of the Dark Red-backed VoleMyodes rexon Hokkaido, Japan

The terrestrial mammalian fauna of the North Japanese island, Hokkaido, is more similar to that of Southern Siberia than to the main island of Japan, Honshu. Three species of the genus Myodes (Muridae, Rodentia) are found on Hokkaido, but not on Honshu. While Myodes rufocanus and M. rutilus are widely distributed across Hokkaido as well as the Eurasian continent, M. rex, which is endemic to Hokkaido and its adjacent islands, shows a discontinuous distribution pattern. We analyzed the phylogeographic history of M. rex using the mitochondrial DNA control region in order to interpret their discontinuous distribution pattern. Phylogenetic relationships among 54 distinct haplotypes showed that M. rex can be divided into four clades that occur on the northern, central, and southern regions of the Hokkaido mainland and on Rishiri Island, respectively. The phylogroups in the northern and central regions were largely separated in space, although several areas of sympatry were found. The phylogroup in the southern region, which was clearly separated from other phylogroups, showed markedly low genetic variability. All analyzed individuals from the population on Rishiri belonged to a separate lineage. Across a range of divergence rate estimates, we dated the basal divergence of all phylogroups to the mid to late Pleistocene, with subsequent signals of population expansion within lineages. We conclude that current phylogeographic structure in M. rex likely reflects Pleistocene survival in several separate refugia in situ. Past glacial ages have thus played an important role in shaping the current distribution patterns of mammalian species on Hokkaido.

Study on the Flora in Xarxili Nature Reserve in Xinjiang

The Xarxili Nature Reserve (45°07'43″-45°23'15″N,81°43'09″-82°33'18″E) is located in the southern piedmont of the Alataw Mountain in Xinjiang,its western part borders on the Republic of Kazakhstan,and its area is 314 km2. Since the ancient times,this area has been the territory of China. It was forcibly occupied by the former Soviet Union before the 1960s,and it was a disputed area between China and the former Soviet Union due to a series of unfair treaties imposed by tsarist Russia. After the disintegration of the former Soviet Union,the area became as a disputed area between China and the Republic of Kazakhstan. A series of agreements and joint communiques were signed after carrying out the equal and friendly consultations between the two countries in the 1990s,and then the new national boundaries and boundary lines in the disputed area were delimited. As a result,the Xarxili Nature Reserve returned to China in 1999. After carrying out on-the-spot investigations,it has been found that there are 1 680 species of vascular plants (including the subspecies and variants) in 517 genera and 81 families,among which there are 23 species in 14 genera and 9 families of fern,9 species in 3 genera and 3 families of gymnosperm,and 1 648 species in 500 genera and 69 families of angiosperm. Analysis of distribution patterns of the genera and species reveals that the proportions of the north-temperate-zone distribution pattern and its variants,temperate distribution pattern of the Old World and its variants are the highest because of the geographical location and the temperate features of the flora in this area. The proportions of the Mediterranean and West Asian-Central Asian distribution patterns and their variants are the second highest,and the proportions of the temperate Asian and tropical distribution patterns are the third highest. The proportions of East-Asian distribution pattern and its variants and the North-American discontinuous distribution pattern are the lowest. These reveal that there are the most interflows between the flora in this area and that in the Old World temperate zone,Mediterranean and Western Asia-Central Asia,there are also certain interflows with the temperate Asian and tropical flora,and the interflows with the East Asian and North American flora are the lowest.

Cactus species turnover and diversity along a latitudinal transect in the Chihuahuan Desert Region

A standardized sampling method was used to evaluate turnover (β diversity) among cactus species assemblages along a 798 km long latitudinal megatransect across the Chihuahuan Desert Region, from north-central Mexico to southern Texas. A total of 71 cactus species were found along the megatransect, 66.2% of which appeared at low frequencies, mostly as a consequence of their highly discontinuous distribution pattern. At the scale the study was conducted, there was always species turnover among cactus assemblages. The rate of turnover among contiguous sites primarily fluctuated from low to medium, but when all site combinations were considered (contiguous and non-contiguous), medium β diversity values were predominant (β = 0.331–0.66); however, 25.4% of the site pair combinations registered high values (β = 0.661–1.0). Our results showed that turnover among cactus species assemblages in the CDR does not consist for the most part of a process of species succession in the geographic space. Instead, we concluded that the continuous spatial changes in cactus species composition are primarily explained by the commonly intermittent distribution patterns of the species, by the presence in the megatransect of species at the margin of their distribution range, and, to a lesser extent, by the existence of narrowly endemic species.

Adaptation of Nitraria sphaerocarpa to wind-blown sand environments at the edge of a desert oasis

This study addresses the adaptation of Nitraria sphaerocarpa to blown sand at the edge of a desert oasis with regard to the aspects of soil seed banks seedlings and population. Horizontally the total number of seeds per unit area decreased from the shrub canopy center to intershrub areas and most seeds were found under shrub canopies. Vertically the highest proportion of seeds was found at depths of 5–10 cm. The emergence percentage seedling mass and seedling height which were significantly affected by both burial depth and seed size were highest at the optimal burial depth of 2 cm and decreased with increasing burial depth in each seed size-class. Although seedling mass was usually greatest for large seeds and least for small seeds at each burial depth little difference was observed in seedling height at shallow burial depths of 0–3 cm. The population shows a patchy and discontinuous distribution pattern. Population height increases with increasing sand depth. Also the density increases with increasing depth of sand in the desert; however there is a steady decrease when the depth of sand is more than 100 cm. This result indicates that the depth of sand that is most suitable for the growth of Nitraria sphaerocarpa is 100 cm. The size of the population is significantly correlated with the sand depth which increases with increasing depth in the desert.

Comparative development of aseptate and septate anthers of Annonaceae

We compared anther development in 13 genera and 15 species of Annonaceae to document the nature and development of anther septa. In aseptate anthers, all sporogenous initials proceed to sporogenesis and meiosis. In septate anthers, a small number of sporogenous initials, in a discontinuous distribution pattern, differentiate into sporogenous cells; the remaining initials become sterile and form cellular septa that partition each anther lobe into multiple sporangial chambers. In species where the septum is 1-2 cell layers thick, the entire septum becomes tapetal (T-type septa) and breaks down before anther dehiscence. In species in which the septum is three or more cell layers thick, only the layer in direct contact with the sporogenous cells becomes tapetal, and the remaining cells become parenchymatous (P-type septa). These thicker P-type septa are sometimes visible in dehisced anthers. Both types are homologous in ontogeny and are highly associated with the production of compound pollen. We propose that the evolution of anther septation in Annonaceae was mainly driven by the requirement for highly efficient nutrient and physical support to the development of large, compound pollen units.

Millennial-scale glacial variability versus Holocene stability: changes in planktic and benthic foraminifera faunas and ocean circulation in the North Atlantic during the last 60 000 years

Two piston cores, DS97-2P from the Reykjanes Ridge in the central North Atlantic Ocean (1685 m water depth) and ENAM33 from southwest of the Faeroe Islands in the NE Atlantic (1217 m water depth), have been investigated for their planktic and benthic foraminiferal content. DS97-2P is situated near the Subarctic Front and productivity measured by accumulation rates of benthic and planktic foraminifera has been generally high during the Holocene. The productivity shows a clear decrease from an early Holocene maximum to a late Holocene minimum. Coeval changes in the benthic faunas indicate that the food supply changed from large, irregular pulses during the early Holocene to a more sustained flux during the late Holocene. Presumably in concert with decreasing bottom current activity oxygen conditions in the bottom water became poorer. Another feature of the late Holocene is an increasing instability of the North Atlantic thermohaline circulation regime. Nevertheless, the changes in faunal composition and productivity during the Holocene were gradual as compared to the discontinuous distribution patterns and abrupt productivity shifts during the glacial. The glacial shifts were on a millennial time scale and correlate with the interstadial–stadial phases of the Dansgaard–Oeschger cycles in the Greenland ice cores. The faunas of the warm interstadial phases resembled the Holocene faunas, and both surface and bottom productivity was high. The faunas suggest that the interstadial circulation pattern was very similar to the modern system with convection in the Nordic seas and generation of North Atlantic Deep Water. The planktic faunas during the cold stadials and Heinrich events were completely dominated by the polar species Neogloboquadrina pachyderma s, and surface conditions were cold and the productivity low. The benthic faunas were dominated by species that presently thrive in areas with a low amount of food and reduced oxygen content. The water column was probably stratified with low saline, cold surface water overlying poorly aerated, intermediate water masses.

&amp;lt;i&amp;gt;Loculicytheretta morkhoveni&amp;lt;/i&amp;gt; sp. nov. (Ostracoda) from West Africa and its relevance to the history of the Mediterranean Seaway

Abstract. Loculicytheretta morkhoveni sp. nov., of which the females have six loculi per valve, was found in Recent beachsand samples from Senegal and The Gambia (West Africa). A displaced specimen of the same species was present in a sample from deeper water off Guinea, where it occurred with L. aff. L. pavonia (having four loculi per valve). The presence of the Mediterranean species L. pavonia (with three loculi) in deep samples West of Gibralter is interpreted as a result of transportation by outflowing currents.The discontinuous distribution pattern of the genus Loculicytheretta is tentatively related to a reversal of the flow regime in the Mediterranean basin during the Pliocene.