A phytosociological study of weed communities on the southwestern Coastal Plain of North Carolina

Summary The vegetation of cultivated, fallow and ‘old’ fields of Scotland County, N.C. was both randomly and subjectively sampled throughout the growing season of 1973. Relevés were placed in each of the above management units, and the data collected in this relevé analysis were sorted into phytosociological charts, with the aid of the digital computer. Weed associations delimited in the charts reflected the importance of edaphic factors, time (aspect), and man's agricultural activities as causal factors in the determination of characteristic assemblages of weeds. Several character and differential species were denoted, in a tentative classification of the weed associations. The cultivated and fallow stands in the spring aspect were noted to be dominated by a group of spring annuals. Summer annuals were more prevalent in homologous situations in the summer. It was determined that perennials, appearing mainly as seedlings in cultivated and fallow fields, attained dominance in ‘old’ fields, one to five years in age. Within each of the major spheres of management, and in each season, associations of weeds mainly reflected differences in edaphic factors. Many character species were noted to maintain affinities to an assortment of soil types that ranged from moist loams to xeric, sterile sands. A study of roadsides, hedgerows, field margins and other ecotonal areas inhabited by weeds was carried throughout the growing season of 1973, also. Species presence was documented in each of these habitat types and reported in Sharp (1974). The weed flora of Scotland County was found to be rich in species. A total of 506 species representing 248 genera and 80 families were encountered throughout the study. Of the total number of species listed, approximately 25 percent were of foreign origin, and 28 percent represented additions to the flora of Scotland County. This paper is the short version of a masters thesis for the Department of Botany, University of North Carolina at Chapel Hill. The author would like to extend his appreciation and gratitude to Professors H. Lieth, A. E. Radford and J. Hardin for their generous advice and encouragement extended through the duration of the study.     

Testing for deterministic succession in metazoan parasite communities of marine fish

Parasite communities are similar to free‐living communities; decay of similarity over geographic distance, theory of island biogeography, species–area relationships and nestedness have been documented in both communities. Ecological succession has been studied in free‐living communities but has rarely been examined in parasite communities. We use seriation with replication to test the hypothesis that succession of parasite community structure is deterministic, thus developing throughout consecutive changes along the fish ontogeny, via a seriated pattern. 12 306 marine fishes (95 species) were studied. In 40 species, a seriated pattern was detected; 25 had a tendency towards a seriated pattern, and for 31 species, succession was at random. Age‐classes for each host species explained deterministic successional patterns for whole parasite communities and ectoparasites. Richness and number of age‐classes explained this pattern for endoparasites. Seriated successional pattern was evident for parasite communities of long‐lived marine fish, indicating that parasite communities follow sequential changes over time, like many free‐living communities.     

Spatial synchrony in the response of a long range migratory species (Salmo salar) to climate change in the North Atlantic Ocean

A major challenge in understanding the response of populations to climate change is to separate the effects of local drivers acting independently on specific populations, from the effects of global drivers that impact multiple populations simultaneously and thereby synchronize their dynamics. We investigated the environmental drivers and the demographic mechanisms of the widespread decline in marine survival rates of Atlantic salmon (Salmo salar) over the last four decades. We developed a hierarchical Bayesian life cycle model to quantify the spatial synchrony in the marine survival of 13 large groups of populations (called stock units, SU) from two continental stock groups (CSG) in North America (NA) and Southern Europe (SE) over the period 1971–2014. We found strong coherence in the temporal variation in postsmolt marine survival among the 13 SU of NA and SE. A common North Atlantic trend explains 37% of the temporal variability of the survivals for the 13 SU and declines by a factor of 1.8 over the 1971–2014 time series. Synchrony in survival trends is stronger between SU within each CSG. The common trends at the scale of NA and SE capture 60% and 42% of the total variance of temporal variations, respectively. Temporal variations of the postsmolt survival are best explained by the temporal variations of sea surface temperature (SST, negative correlation) and net primary production indices (PP, positive correlation) encountered by salmon in common domains during their marine migration. Specifically, in the Labrador Sea/Grand Banks for populations from NA, 26% and 24% of variance is captured by SST and PP, respectively and in the Norwegian Sea for populations from SE, 21% and 12% of variance is captured by SST and PP, respectively. The findings support the hypothesis of a response of salmon populations to large climate‐induced changes in the North Atlantic simultaneously impacting populations from distant continental habitats.     

Exploring movement patterns and changing distributions of baleen whales in the western North Atlantic using a decade of passive acoustic data

Six baleen whale species are found in the temperate western North Atlantic Ocean, with limited information existing on the distribution and movement patterns for most. There is mounting evidence of distributional shifts in many species, including marine mammals, likely because of climate‐driven changes in ocean temperature and circulation. Previous acoustic studies examined the occurrence of minke (Balaenoptera acutorostrata) and North Atlantic right whales (NARW; Eubalaena glacialis). This study assesses the acoustic presence of humpback (Megaptera novaeangliae), sei (B. borealis), fin (B. physalus), and blue whales (B. musculus) over a decade, based on daily detections of their vocalizations. Data collected from 2004 to 2014 on 281 bottom‐mounted recorders, totaling 35,033 days, were processed using automated detection software and screened for each species' presence. A published study on NARW acoustics revealed significant changes in occurrence patterns between the periods of 2004–2010 and 2011–2014; therefore, these same time periods were examined here. All four species were present from the Southeast United States to Greenland; humpback whales were also present in the Caribbean. All species occurred throughout all regions in the winter, suggesting that baleen whales are widely distributed during these months. Each of the species showed significant changes in acoustic occurrence after 2010. Similar to NARWs, sei whales had higher acoustic occurrence in mid‐Atlantic regions after 2010. Fin, blue, and sei whales were more frequently detected in the northern latitudes of the study area after 2010. Despite this general northward shift, all four species were detected less on the Scotian Shelf area after 2010, matching documented shifts in prey availability in this region. A decade of acoustic observations have shown important distributional changes over the range of baleen whales, mirroring known climatic shifts and identifying new habitats that will require further protection from anthropogenic threats like fixed fishing gear, shipping, and noise pollution.     

Length–weight relationships of five selected demersal fishes from the Cabo Verde Islands (eastern-central Atlantic)

The length–weight relationships (LWR) were estimated for five selected demersal marine fishes from the relatively undisturbed shelves and slopes of the Cabo Verde Islands. Most of them were of ecological and/or commercial interest. Occasional sampling was carried out during different fisheries research projects. LWRs were taken for the following bycatch species for which no such estimates exists in the science literature: Myroconger compressus, Synaphobranchus affinis, Physiculus cyanostrophus, Physiculus caboverdensis and Canthidermis maculata. Total length and fork length (to the nearest 0.1 cm) and total weight (to the nearest 0.1 g) were determined. The resulting length–weight equations are characterized by a high accompanying coefficient of correlation. The present data help improving the knowledge base needed for further fish biology studies and fisheries management.     

Movement of sturgeons (Acipenser oxyrinchus oxyrinchus and A. fulvescens) in the St. Lawrence Estuary: A 35-year tagging study

Movement of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) and lake sturgeon (A. fulvescens) in the St. Lawrence Estuary (Québec, Canada) are not fully understood. To assess the movement extent of both species, a mark–recapture study was conducted in collaboration with commercial fishermen operating in the St. Lawrence Estuary. Between 1981 and 2015, 3,367 Atlantic sturgeon (fork length 21.8–199.5 cm) and 3,180 lake sturgeon (fork length 17.8–190.8 cm) were tagged and released. Of these, 673 Atlantic sturgeon and 42 lake sturgeon were recaptured. The maximum distances traveled between capture and recapture locations were 1,307 km for Atlantic sturgeon (8 years after initial capture) and 252 km for lake sturgeon (less than 1 year after initial capture). Statistical analyses identified differences in the dispersal distance of both species as revealed by a first component characterized by individuals with short dispersal distances (98% and <35 km for Atlantic sturgeon; 58% and <1 km for lake sturgeon) and a second component characterized by individuals with longer dispersal distances (2% and >600 km for Atlantic sturgeon; 42% and >190 km for lake sturgeon). We suggest that the short dispersal distances detected in the vast majority of Atlantic sturgeon recaptures likely reflect strong site fidelity, highlighting the importance of the St. Lawrence Estuary as a preferred habitat for juveniles and subadults. Although recaptures were low for lake sturgeon because this species is only marginally targeted by commercial fishermen in the St. Lawrence Estuary, our results also showed that this species uses estuarine habitats and that half of the population seems to exhibit strong site fidelity (67% of individuals were recaptured within 2 km).     

The pollination seesaw of Rhynchospora cephalotes (L.) Vahl (Cyperaceae): Influence of plant location on the role of wind and insects as pollen vectors

Ambophily (wind and insect pollination) has been reported for some genera of the typically wind-pollinated family Cyperaceae, including the genus Rhynchospora. The significance of wind and insect pollination can vary, depending on local microclimatic conditions. Rhynchospora cephalotes is an ambophilous species that can grow under different environmental conditions, either along forest edges or inside forest fragments. This study, therefore, tests the hypothesis that (a) there is greater contribution by wind than insects to fruit set of the individuals at the forest edge and (b) there is greater contribution by insects than wind to fruit set of the individuals inside the forest. Field work was carried out in a fragment of Atlantic Forest in northeastern Brazil. We quantified the number of visits by insects, wind velocity and the reproductive success (fruit set) of R. cephalotes provided by wind and insects through exclusion experiments performed at the edge of and inside the forest. We observed a greater number of visits per day by pollinating bees to individuals inside the forest (36.83 ± 7.46) than to individuals at the edge (16.66 ± 6.53). The wind speed was significantly higher at the edge (1.71 ± 0.46 m/s) than inside the forest (0.97 ± 0.18 m/s). Bees and wind are both pollen vectors of R. cephalotes, but bees were the pollen vector that contributed most to fruit set (63.3%) for individuals inside the forest, whereas wind was the primary vector for individuals at the forest edge (76.6%). This seesaw in importance of each pollen vector in the two different environments guarantees high fruit set in R. cephalotes under different microclimatic conditions.