Community assembly time and the relationship between local and regional species richness

Many previous studies have assumed that a linear relationship between local and regional species richness indicates that communities are limited by regional processes, while a saturating relationship suggests that species interactions restrict local richness. We show theoretically that the relationship between local and regional richness changes in a consistent fashion with assembly time in interacting communities. Communities show saturation in their early assembly stages because only a subset of the regional pool may colonize a locality. At intermediate assembly times, communities will appear unsaturated until significant competitive exclusion occurs. Finally, when communities reach equilibrium, we found saturation as a result of resource competition resulting in the dominance of a limited number of species. We show that habitat size and species fecundity are important in determining the time needed for the community to reach equilibrium and thus affect the relationship between local and regional species richness. Our results suggest the number of coexisting species is a function of local and regional processes whose relative influences might vary over time and that research using the relationship between local and regional species richness to infer mechanisms limiting species richness must have knowledge of the assembly time of the community.     

Hybridization and regional variation in Pacific Northwestern Impatiens (Balsaminaceae)

Variation patterns ofImpatiens species in the Pacific Northwest are discussed. Much of the variability there is attributed to widespread interspecific hybridization. Taxonomy of the genus is briefly reviewed, and it is suggested that four species should be recognized for the region. An account of natural hybridization betweenI. capensis andI. ecalcarata is given in detail, and it is postulated that the effects of this hybridization may extend beyond the immediate area in which it is detectable on the basis of morphological patterns. It is suggested thatI. aurella may be of hybrid origin since it combines characters of two species in the Pacific Northwest. Although natural hybridization is occurring at the present time, geographical distribution of variant populations of the species suggests that extensive hybridization may have been initiated in late Pleistocene as a result of the ecological disturbances prevalent at that time.     

Variation in plant responses to neighbors at local and regional scales

Differences in the responses of plant species to neighbors may determine their distribution among contrasting environments, but no studies have compared variation in competitive or facilitative abilities both within and among environments. We determined whether the responses of plants to interspecific interactions varied at large scales (between environments) and small scales (among sites within an environment) across a tree line. We separated the effects of above- and belowground interactions on seedlings of grasses and trees grown in prairie or forest using vegetation removals at several sites. Species interactions generally had no significant effect on transplant survival. Competition reduced seedling growth by about 33%-89% in both prairie and forest environments. Despite the strong suppression of growth by neighbors, environment and species effects contributed more to variation in transplant performance than did neighbor removals. Responses to neighbors varied among transplant species but generally did not vary significantly between environments or among sites. With vegetation removed, grasses grew significantly faster in prairie and trees grew faster in forest. Thus, in the absence of neighbors, species showed distinct preferences for the environment in which they are most abundant. In summary, the responses of grasses and woody species to neighbors did not vary significantly at either large (between environments) or small (among sites) scales. These results suggest that species responses to interspecific interactions do not vary strongly with environment or smaller-scale site effects.     

Behaviour and local distribution of the freshwater oligochaete Nais pardalis Piguet (Fam. Naididae)

1. Nais pardalis Piguet, a small freshwater oligochaete, lives in the surface few cm of sandy sediments in Loch Leven, County of Kinross, Scotland. 2. It forms branching passageways or tubes in the sediment not by any active constructional behaviour, but by the secretion of a material which sticks the sand grains together. 3. The sand grains making up the tubes are exactly the same size as those in the surrounding sediment. 4. Animals select the smallest grains in their environment for ingestion. 5 In the laboratory, rates of ingestion of sand grains measured on different animals vary from 5 to 60 grains/hour and rates of excretion from 3 to 6/hour, but these figures should be viewed with caution. 6. Analysis of the rate of ingestion of sand grains indicates that grains are not ingested randomly in time. Having eaten one grain, an animal is less likely to eat another within the next 10 seconds.     

Subcellular and regional distribution of 125I-labeled alpha-bungarotoxin binding in rat brain and its relationship to acetylcholinesterase and choline acetyltransferase.

1. The subcellular distribution of binding sites for 125I-labeled alpha-bungarotoxin was studied in rat cerebral cortex. Primary fractions showing higher specific activity than homogenate were P2 (crude mitochondria and nerve endings) and P3-P2 was subfractionated on a Ficoll gradient with the P2B (nerve ending) subfraction exhibiting the greatest recovery (65%) and enrichment of toxin binding. Toxin binding showed a distribution similar to that of acetylcholinesterase, choline acetyltransferase, and sodium and potassium ion-activated ATPase. 2. P2B and P3 were subfractionated on five-step discontinuous sucrose gradients. The highest specific activity of toxin binding and acetylcholinesterase was associated with fractions of relatively low buoyant density, while choline acetyltransferase activity was associated with fractions of higher density. 3. Toxin binding, acetylcholinesterase, and choline acetyltransferase activities were relatively high in olfactory lobes, cerebral cortex, thalamic region, caudate nucleus, and brain stem; intermediate in hippocampus; low in cerebellum. 4. The relationship of toxin binding to the putative acetylcholine receptor in brain is discussed.     

Radiocarbon Dating and Wood Density Chronologies of Mangrove Trees in Arid Western Australia

Mangrove trees tend to be larger and mangrove communities more diverse in tropical latitudes, particularly where there is high rainfall. Variation in the structure, growth and productivity of mangrove forests over climatic gradients suggests they are sensitive to variations in climate, but evidence of changes in the structure and growth of mangrove trees in response to climatic variation is scarce. Bomb-pulse radiocarbon dating provides accurate dates of recent wood formation and tree age of tropical and subtropical tree species. Here, we used radiocarbon techniques combined with X-ray densitometry to develop a wood density chronology for the mangrove Avicennia marina in the Exmouth Gulf, Western Australia (WA). We tested whether wood density chronologies of A. marina were sensitive to variation in the Pacific Decadal Oscillation Index, which reflects temperature fluctuations in the Pacific Ocean and is linked to the instrumental rainfall record in north WA. We also determined growth rates in mangrove trees from the Exmouth Gulf, WA. We found that seaward fringing A. marina trees (∼10 cm diameter) were 48±1 to 89±23 years old (mean ± 1σ) and that their growth rates ranged from 4.08±2.36 to 5.30±3.33 mm/yr (mean ±1σ). The wood density of our studied mangrove trees decreased with increases in the Pacific Decadal Oscillation Index. Future predicted drying of the region will likely lead to further reductions in wood density and their associated growth rates in mangrove forests in the region.     

The relationship between local and regional diversity of indigenous forest fauna in KwaZulu-Natal Province, South Africa

The relationship between local and regional diversity was tested by regressing local community richness against regional species diversity for three taxa, birds, butterflies and mammals, in subtropical forest. The quadratic model best fits the relationship between local and regional diversity for birds. Local bird species richness is theoretically independent of the size of the regional pool of species and may represent saturated communities. A linear model best describes the relationship for mammals and butterflies. For mammals, the slope is shallow (0.264) and regional richness overestimates local species richness, suggesting communities are undersaturated. Extinction filtering may explain this pattern. Past climatic changes have filtered out many mammalian species, these changes have been too recent for autochthanous speciation, and the relatively low vagility of mammals has prevented extensive recolonisation. Differences in the nature of the diversity relationship between taxa are as much due to independent evolutionary histories as to differences in vagility and colonising potential. A pervasive role is suggested for regional biogeographic processes in the development of faunal assemblage structure. Large-scale processes are not considered in current conservation plans. We encourage the shift of conservation emphasis from local ecological processes and species interactions, to whole communities and consideration of regional processes.     

Free-living heterotrophic euglenids from freshwater sites in mainland Australia

This paper presents new data on free-living heterotrophic euglenids (Euglenozoa, Protista) that were found at several freshwater sites in New South Wales, Northern Territory, and Queensland, Australia. Thirty-six species are described with uninterpreted records based on light-microscopy. The records include accounts of two new taxa: Heteronema pterbicanov. spec., Sphenomonas alburiae nov. spec., and of six new combinations: Dinema dimorphum (Skuja, 1932) nov. comb., Notosolenus mediocanellatus(Stein, 1878) nov. comb., Notosolenus steini (Klebs, 1893) nov. comb., Ploeotia obliqua(Klebs, 1893) nov. comb., Ploeotia plana(Christen, 1959) nov. comb., and Rhabdomonas mirabilis (Playfair, 1921) nov. comb. We also introduce the following: Astasia skvortzovi nom. nov., Heteronema hexagonum var. elegans (Playfair, 1921) nov. comb., Petalomonas compressa (Schewiakoff, 1893) nov. comb., and Jenningsia deflexumvar dextrum (Shi, 1975) nov. comb. All records of heterotrophic euglenids in Australia are reviewed. The majority of species reported here have also been found at other locations worldwide, and we find little or no evidence that there is endemism in this group.     

Abundance and distribution within a guild of benthic stream fishes: local processes and regional patterns

1. Spatial patterns at regional and local scales were examined for evidence that species interactions can influence distribution and abundance within a guild of benthic fishes in upland streams of Oklahoma, U.S.A. Three groups of community patterns were examined: the species–area relationship, species–habitat associations, and interspecific associations.
2. The species–area relationship for riffle habitats was compared to a null species–area model based on random placement. The observed species–area curve was steeper resulting in less species per unit area in small streams than predicted by the null model.
3. Small, species-poor streams had summed fish densities at least as high as larger, species-rich streams, suggesting density compensation.
4. Several significant patterns of negative covariation were found among species at the regional scale, before and after statistically accounting for effects due to measured habitat variables.
5. For two of these negatively covarying taxa ( Cottus carolinae and Etheostoma spectabile ), the influence of each species on the distribution of the other was evaluated experimentally in field enclosures varying in depth and current velocity. The sculpin C . carolinae caused a shift in habitat use by the darter E . spectabile , but no reciprocal shift was found.
6. These results indicate an agreement between local and regional patterns of distribution for C . carolinae and E . spectabile and suggest that biotic interactions can influence regional patterns of distribution for species within this guild.     

Abundance and distribution within a guild of benthic stream fishes: local processes and regional patterns

1. Spatial patterns at regional and local scales were examined for evidence that species interactions can influence distribution and abundance within a guild of benthic fishes in upland streams of Oklahoma, U.S.A. Three groups of community patterns were examined: the species–area relationship, species–habitat associations, and interspecific associations.
2. The species–area relationship for riffle habitats was compared to a null species–area model based on random placement. The observed species–area curve was steeper resulting in less species per unit area in small streams than predicted by the null model.
3. Small, species-poor streams had summed fish densities at least as high as larger, species-rich streams, suggesting density compensation.
4. Several significant patterns of negative covariation were found among species at the regional scale, before and after statistically accounting for effects due to measured habitat variables.
5. For two of these negatively covarying taxa ( Cottus carolinae and Etheostoma spectabile ), the influence of each species on the distribution of the other was evaluated experimentally in field enclosures varying in depth and current velocity. The sculpin C . carolinae caused a shift in habitat use by the darter E . spectabile , but no reciprocal shift was found.
6. These results indicate an agreement between local and regional patterns of distribution for C . carolinae and E . spectabile and suggest that biotic interactions can influence regional patterns of distribution for species within this guild.     

Extra-pair paternity in relation to regional and local climate in an Arctic-breeding passerine

Reproductive processes are affected by local and regional climate variation. Birds breeding in the Arctic may experience strong energetic constraints, which will affect their reproductive output. Recent research has emphasized the importance of extra-pair copulation as a means of improving reproductive output. In this paper, we explore ecological and climatic determinants that may explain variation in extra-pair paternity (EPP) in an arctic-breeding passerine, the snow bunting Plectrophenax nivalis. EPP occurred in 10.8 % of the young and 20.9 % of the broods sampled from 1999 to 2003. We found that the proportion of extra-pair young in a nest was positively related to the body size and age of the social male and weakly negatively related to the local average minimum temperature prior to the onset of egg laying. These results suggest that older and larger males lost a larger share of paternity than smaller and younger males, and that the relative loss of paternity decreased with cold weather during the female’s fertile period. Large and old males spend less time mate guarding compared to small and young males and may allocate more time towards extra-pair forays, and thus lose more paternity in their own nest. Climatic conditions most likely constrain the total energy budget with less energy available for extra-pair activity in cold weather.     

Patterns of local wood use and cutting of Philippine Mangrove Forests

Small-scale wood harvesting from mangrove forests is a commonplace yet barely studied phenomenon. This paper integrates bio-ecological and ethnographic methods to examine local wood use and cutting of mangrove forests in two areas of the Philippines. Findings reveal considerable site variation in cutting intensity, with heavier cutting typically closer to settlements and in forest stands that are not effectively regulated by government or private interests. Overall, cutting is responsible for almost 90% of stem mortality in both natural and plantation forests. Field measurements confirm ethnographic evidence indicating that harvesting for construction wood, but not fuelwood, is both species- and size-selective. Mangrove management and conservation efforts can be made more effective by better understanding how local people are harvesting wood resources from these forests.     

Saline seepage and vertical distribution of oxygen in a brackish ditch

Summary Seepage caused salinity gradients in a 120 cm deep ditch adjacent to Lake Veere in the Dutch Delta area. The water was mixed by strong horizontal currents, forced by a pumping engine. The restoration of vertical chloride and oxygen gradients was studied.During summer when the level of Lake Veere was raised by 70 cm, a rapid seepage into the ditch was observed, ranging from 6 to 10 mm.h^–1. This caused an anoxic saline layer. At the anaerobic-aerobic interface 1.4 to 2.4 mg O₂.l^–1.h^–1 of the oxygen present in the upper water column was taken up. Sulfide oxidation required one quarter of this amount of oxygen.During winter the level of Lake Veere was lowered again. Normally seepage was absent then, and chloride entered the water column by diffusion; the mud chlorinity decreased from 15 to 3 Cl^– on its way to the ditch. Only after maximum discharge of polder water a moderate seepage of less than 4.4 mm.h^–1 restored a chloride gradient; about 1.6 mg O₂.l^–1.h^–1, produced by benthic diatoms, had to be supplied to the reducing materials in the seepage water in less than 12 hours.A saline seepage was simulated in the laboratory. These simulation tests showed that seepage below 1 mm.h^–1, as well as benthic respiration only, had a small impact on the vertical oxygen profile in the water column. Bottom oxygen demand increased with seepage velocity. At a strong seepage the water column could become entirely anaerobic.Communication no. 226.     

Surface Elevation Dynamics in a Regenerating Mangrove Forest at Homebush Bay,Australia

Following the dieback of an interior portion of a mangrove forest at Homebush Bay, Australia, surface elevation tables and feldspar marker horizons were installed in the impacted, intermediate and control forest to measure vertical accretion, elevation change, and shallow subsidence. The objectives of the study were to determine current vertical accretion and elevation change rates as a guide to understanding mangrove dieback, ascertain the factors controlling surface elevation change, and investigate the sustainability of the mangrove forest under estimated sea-level rise conditions. The study demonstrates that the influences on surface dynamics are more complex than soil accretion and soil autocompaction alone. During strong vegetative regrowth in the impacted forest, surface elevation increase exceeded vertical accretion apparently as a result of belowground biomass production. In addition, surface elevation in all forest zones was correlated with total monthly rainfall during a severe El Niño event, highlighting the importance of rainfall to groundwater recharge and surface elevation. Surface elevation increase for all zones exceeded the 85-year sea level trend for Sydney Harbour. Since mean sea-level also decreased during the El Niño event, the decrease in surface elevation did not translate to an increase in inundation frequency or influence the sustainability of the mangrove forest. These findings indicate that subsurface soil processes such as organic matter accumulation and groundwater flux can significantly influence mangrove surface elevation, and contribute to the long-term sustainability of mangrove systems under a scenario of rising sea levels.     

Patterns in the distribution of Arctic freshwater zooplankton related to glaciation history

We analysed circumpolar samples from 68 lakes within the 10°C-July isotherm from Arctic Canada, Nunavut, Greenland, Svalbard, Eastern Siberia, the Beringia region, and Alaska. In total, we found 3 species of Anostraca, 17 of Diplostraca, 1 species of cyclopoid and 14 species of calanoid copepods. Our study identifies a wider distribution for some copepods—e.g. Eurytemora pacifica, Leptodiaptomus sicilis, Arctodiaptomus novosibiricus, Cyclops abyssorum—than previously known. Moreover, one anostracan species, Artemiopsis bungei, was recorded in North America for the first time; and one chydoriid, Chydorus gibbus, is a new species for Greenland. We observed that species richness of crustaceans is lower in lakes that were glaciated during the Quaternary period, compared to those not glaciated (e.g. Chukotski Peninsula, Siberia; Point Barrow, Alaska; and Disko Island, Greenland). This confirms the findings of classic studies: glaciation has strongly affected the biogeography of freshwater crustaceans in circumpolar areas. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.