Patch distribution and dispersal limitation of four plant species in Swedish semi-natural grasslands

This study examined whether the patch distribution of four plant species Agrimonia eupatoria, Carlina vulgaris, Hypochoeris maculata and Plantago media were affected by dispersal limitation. Analysis of the patch size/isolation relationship was combined with a seed sowing experiment examining the recruitment of the species. Patch size was negatively correlated to isolation in Carlina, Hypochoeris and indicating that dispersal processes might affect the distribution pattern. Patch size of Agrimonia was not correlated, or in one case positively correlated, to isolation. Agrimonia was also the only species among the four where the recruitment not was affected by disturbance treatment or locality. The recruitment of Carlina, Hypochoeris and Plantago was higher in disturbed plots compared to undisturbed, and the latter two species were also affected by locality. This suggests that Agrimonia is less sensitive to isolation (and the ongoing fragmentation of the landscape) compared to the other three species, probably due to better dispersal and recruitment ability. We conclude in a discussion how different management strategies could serve to maintain viable populations of these species. This revised version was published online in August 2006 with corrections to the Cover Date.     

Seasonal variation in the lateral distribution of mayfly nymphs in a boreal river

Seasonal variations in the lateral distribution of mayfly nymphs were investigated in the North Swedish river Vindelälven; a river with large seasonal differences in water level, current velocity and ice conditions, A total of 22 mayfly species about equally divided between summer and winter species were found along a single transect. At low water level in late summer and autumn most species were distributed over the whole transect. In winter the populations occupying the littoral moved into deeper water, so avoiding the ice. Only very small mortalities were detected in the ice. Prior to the spring flood most characteristically still water species moved to the shallow uppermost littoral while lotic species and the burrowing Ephemera vulgata L. did not show the same aggregation near the shore. It is suggested that these lateral movements allow the nymphs to avoid adverse environmental conditions and to exploit food resources over the whole transect.     

Plant species occurrences in a rural hemiboreal landscape: effects of remnant habitats, site history, topography and soil

Changes in land use during the last century have caused fragmentation and a reduction in area of many species-rich habitats in the hemiboreal region. We examined abundances of plant species and their occurrence in different habitats in south-east Sweden. We found 361 plant species in 146 sample sites, which represented 14 different types of habitat. Most species were rare and occurred only in a few habitats. Almost half of all species (49%) were found in one or two habitats. Of these, 99 species occurred in one habitat only. The habitats with largest number of restricted species, i.e. habitat specialists, were dry to mesic semi-natural grasslands and remnant habitats such as road verges and mid field islets. The occurrence of 52 species was analysed with respect to topography, top- and subsoil and land use history. Few of the 52 species were affected by aspect or type of topsoil. Subsoil affected nearly half of the species and habitats with a convex landform influenced occurrence of > 90% of the species. Seventeen species were positively associated with a long continuity of grassland management, whereas two species were associated with lack of management. Open grasslands that are encroached by trees and shrubs show a decline in species number. Deciduous forests, especially wet deciduous forests, have a potential for restoring moist to mesic grassland habitats. Small remnant habitats are important for many of the species restricted to semi-natural grasslands. These habitats may function as "rescue sites" for the species, which in turn may promote dispersal and increase likelihood of restoration success. Therefore, remnant habitats are important for maintaining and restoring species richness in rural landscapes.     

Colony connectivity of Pacific Coast double-crested cormorants based on post-breeding dispersal from the region's largest colony

To reduce conflicts with fish resources, other colonial waterbirds, and damage to habitats, double-crested cormorants (Phalacrocorax auritus) are currently controlled (lethally and non-lethally) throughout much of their range. Concerns are growing over the Pacific Coast's largest double-crested cormorant colony at East Sand Island (ESI), Oregon near the mouth of the Columbia River, where cormorants forage on juvenile salmonids, many of which are listed under the United States Endangered Species Act. Management of this colony is currently under consideration and may call for a redistribution of a portion of this colony numbering more than 12,000 breeding pairs in 2009. We investigated regional and site-specific connectivity of ESI cormorants using satellite-telemetry to track post-breeding dispersal. Cormorants dispersed widely west of the Cascade-Sierra Nevada Mountains from British Columbia, Canada to northern Mexico. Tracking data demonstrated direct connectivity between the double-crested cormorant colony at ESI and nesting sites throughout the dispersal area. Results of this study indicate that some cormorants from ESI could disperse to prospect for nesting sites throughout much of the western portion of the range of the Western Population; however, regional variation in connectivity with the ESI population, distance from ESI, and site-specific nesting history will likely result in variable prospecting rates among regions and sub-regions. Management efforts aimed at redistributing ESI cormorants across western North America (e.g., social attraction or dissuasion techniques) might be best allocated to areas or sites known to be used by tagged cormorants, particularly those sites with an established nesting history. © 2012 The Wildlife Society.     

Asymmetric competition between distant taxa: poecilid fishes and water striders

Summary Competition for water surface prey between fish (Priapichtus annectens: Poeciliidae) and water striders (Potamobates unidentatus: Gerridae) was studied in the laboratory and in pools in a small tropical stream. Laboratory experiments showed that fish depressed activity and foraging success of water striders. Large fish (4–5 cm) had a greater effect than small fish (2–3 cm). The field experiment showed that competition was highly asymmetric. Presence of fish decreased water strider foraging success while the reverse interaction was insignificant. It is suggested that the higher individual foraging success of the fish, harassment of water striders by fish and the use of an exclusive resource, benthic invertebrates, by the fish, contribute to this pattern. Habitat use differed between the two species. Fish used the deeper parts of stream pools and water striders used the shallower parts of the pools. Asymmetric interference and exploitation competition may force water striders to use shallow edge habitats.     

Long‐standing environmental conditions,geographic isolation and host–symbiont specificity influence the relative ecological dominance and genetic diversification of coral endosymbionts in the genus Symbiodinium

Aim This study examines the importance of geographic proximity, host life history and regional and local differences in environment (temperature and water clarity) in driving the ecological and evolutionary processes underpinning the global patterns of diversity and distribution of symbiotic dinoflagellates. By comparing and contrasting coral–algal symbioses from isolated regions with differing environmental conditions, we may assess the potential of coral communities to respond to significant changes in climate. Location Indian Ocean. Methods Community assemblages of obligate symbiotic invertebrates were sampled at numerous sites from two regions, the north‐eastern Indian Ocean (Andaman Sea, western Thailand) and the western Indian Ocean (Zanzibar, Tanzania). Molecular genetic methods, including denaturing gradient gel electrophoresis analysis of the ribosomal internal transcribed spacers, DNA sequencing and microsatellite genotyping, were used to characterize the ‘species’ diversity and evolutionary relationships of symbiotic dinoflagellates (genus Symbiodinium). Host–symbiont specificity, geographic isolation and local and regional environmental factors were evaluated in terms of their importance in governing the distribution and prevalence of certain symbiont taxa. Results Host‐generalist symbionts (C3u and D1‐4, formerly D1a now designated Symbiodinium trenchi) frequently occurred alone and sometimes together in hosts with horizontal modes of symbiont acquisition. However, the majority of Symbiodinium diversity consisted of apparently host‐specific ‘species’. Clade C Symbiodinium were diverse and dominated host assemblages from sites sampled in the western Indian Ocean, a pattern analogous to symbiont communities on the Great Barrier Reef with similar environmental conditions. Clade D Symbiodinium were diverse and occurred frequently in hosts from the north‐eastern Indian Ocean, especially at inshore locations, where temperatures are warmer, water turbidity is high and large tidal exchanges commonly expose coral populations to aerial desiccation. Main conclusions Regional and local differences in cnidarian–algal combinations indicate that these symbioses are ecologically and evolutionarily responsive and can thrive under various environmental conditions. The high temperatures and turbid conditions of the north‐eastern Indian Ocean partly explain the ecological success of Clade D Symbiodinium relative to Clade C. Phylogenetic, ecological and population genetic data further indicate that Clade D has undergone an adaptive radiation, especially in regions around Southeast Asia, during the Pleistocene.