Comparison Of Community Structure Research Articles

Stability in Pleistocene Mediterranean mammalian communities

The present paper evaluates the differences in community structure between nine mammalian paleocommunities from the late early Pleistocene to the late middle Pleistocene from Sierra de Atapuerca (Burgos, Spain). The magnitude of the differences inside this group of paleocommunities is compared with the heterogeneity observed in 43 recent Eurasian communities grouped by biome. A new method is used to compare community structure. Species are assigned to 1 of 23 possible ecological groups and a multidimensional “eco-space” is computed based on the abundance of these groups in each community using Principal Components Analysis (PCA). The dispersion of the communities in the “eco-space” is used as a measure of their differences in community structure. The group of paleocommunities from Atapuerca exhibits less heterogeneity than that observed inside groups of recent communities from a particular biome. Thus, it is concluded that a considerable constancy in community structure existed in the paleocommunities from Atapuerca along the Pleistocene. This stability contrasts with the existence of various climatic cycles and with the development of different plant communities at Atapuerca throughout this period. To explain the observed pattern, a theoretical model of community evolution is proposed. According to this model, only a limited number of community structures are possible in a given environment, although the exact configuration attained by a particular community depends upon historical and biogeographic factors. Once a community structure has been established, emergent mechanisms maintain it with minor changes (resilience) until a large perturbation disrupts the community and a new assembling process begins.

Comparison of community structure and species diversity of mixed forests of deciduous broad-leaved tree and Korean pine in Northeast China

Comparison of community structure and species diversity of mixed forests of deciduous broad-leaved tree and Korean pine in Northeast China

Assessment of effects of chromated copper arsenate (CCA)-treated timber on nontarget epibiota by investigation of fouling community development at seven European sites.

To assess the effect of the anti-marine-borer timber preservative CCA (a pressure-impregnated solution of copper, chromium, and arsenic compounds) on nontarget epibiota, fouling community development was investigated. Panels of Scots pine treated to target retentions of 12, 24, and 48 kg CCA per m3 of wood (covering the range of retentions recommended for marine use) plus untreated controls were submerged at seven coastal sites (Portsmouth, UK; La Tremblade [two sites], France; Ria Formosa, Portugal; Sagres, Portugal; Kristineberg, Sweden; Athens, Greece). The fouling community on the surfaces of the panels was assessed both qualitatively and quantitatively after 6, 12, and 18 months of exposure. Multivariate statistical methods were used to compare community structure between panel treatments. Panels treated to the three CCA loadings supported very similar fouling assemblages, which in most cases had higher numbers of taxa and individuals than assemblages on untreated panels. No detrimental effects on epibiota due to CCA preservatives were detected at any of the treatment levels at all seven exposure sites, suggesting that the range of environmental conditions at the sites had no bearing on preservative impact on fouling biota. Differences in community structure between CCA-treated and untreated panels may be due to enhanced larval settlement on CCA-treated timber by some species as a result of modifications to the surface properties of the timber by the preservative. Possible reasons for the higher numbers of certain species on the surface of CCA-treated panels are discussed.

Using Tree Shape

Although the primary purpose of phylogenies is to depict evolutionary relationships among taxa, they have other interesting properties. One of the most interesting is their shape, some quantifiable measure of how they look. Such measures come in two general flavors: diversity variation among contemporaneous clades (e.g., when averaged over the whole tree, this is tree balance) and distribution of splitting times (e.g., lineages-through-time plots). These measures represent variation in diversification rates among taxa at a given time and within a taxon through time, respectively. As such, tree shape is the signature of the forces that produce biodiversity, and its study informs one of the major areas in evolutionary biology. It has been over a decade since Craig Guyer and Joseph Slowinski (Slowinski and Guyer, 1989; Guyer and Slowinski, 1991, 1993) began the current era of tree shape work (for a history and general review, see Mooers and Heard, 1997). The concept was elegant: compare shapes of published trees with expectations from reasonable null models, deal with uninteresting technical confounds, and interpret what remains with an eye to explaining past and (perhaps) predicting future biodiversification (though we might not have called it that a decade ago). A decade on, it is well established that trees shapes contain interesting and important information about the evolutionary process (see, e.g., Gaston and Spicer, 1998; Schluter, 2000; Felsenstein, in press). For the 2001 joint SSB/SSE/ASN meeting, we were fortunate to be able to organize a symposium titled Developing uses for phylogenetic tree shape in the study of evolution, an opportunity to organize the decade's work and foster collaboration for the future. Collected here are papers representing many of the contributing authors and others who presented related material in other sessions of that 2001 meeting. We gratefully acknowledge the support of the Society of Systematic Biologists, which both sponsored the symposium and agreed to review these papers for publication. These papers are an excellent, if incomplete, update on the decade's work on tree shape. As expected, the descriptive aspect has become more sophisticated, with new software tools and ever better statistical power (contributions in this issue by Agapow and Purvis, and Chan and Moore; see also McKenzie and Steel, 2000; Stam, 2002). We are getting better at incorporating and analyzing branch length information (the latest update and extension is by Pybus et al., this issue). There are also some new observations: perhaps the most intriguing is the idea that species-level and higher level phylogenies might actually differ in shape (Purvis and Agapow, this issue). Along with these changes is a welcome expansion into new fields. Two sampled here are comparative methods (a potentially powerful way to summarize tree shapes is presented by Martins and Housworth, this issue) and community structure (Webb and Pitman, this issue). An important distinction between neontological and paleontological phylogenies has been recognized, and tools for dealing with the latter have been developed (Harcourt-Brown, this issue). Finally, Alan de Queiroz submits a provocative essay on the complexity of the question of why some taxonomic groups might diversify more than others. But we have still just begun. The patterns are certainly real and are becoming better documented (Purvis and Agapow, and Savolainen et al., this issue; Stam, 2002), and the evolutionary models are inching towards increased realism (Heard and Mooers, this issue). However, present explanations for nonrandom tree shapes are incomplete, and the application of tree-shape concepts in related disciplines is still in its infancy (see, e.g., Heard and Mooers, 2000; von Euler, 2001). We expect to see major advances made with

Community‐level responses by stream insects to neem products containing azadirachtin

AbstractOutdoors sream channels weret teated with a commercial neem formulation, Neemixx® 4.5, and a neem extract (no formulation ingredients) to determine the effects on aquatic insect communities. An exposure period of 5 h was chosen to simulate the transient nature of pesticide residues in streams and rivers after aerial applications. Multivariate analytic procedures based on Bray‐Curtis similarity matrices were used to compare community structure among the replicate channels 9 d after treatment. No significant differences in community structure were found among controls and channels treated with Neemix at an azadirachtin concentration of 0.28 mg/L, but a multivariate measure of community stress indicated an increase in variability among treated channels. Significant differences in community structure were found among controls and channels treated with Neemix at 0.84 and 2.54 mg/L, and this resulted from reductions in several key taxa. During subsequent experiments with a neem powder extract, the formulation ingredients of Neemix were at least partially responsible for the significant effects on community structure at 0.84 mg/L azadirachtin. No significant differences were found among controls and channels treated with the extract at 0.9 mg/L, whereas the community structure of aquatic insects in channels treated at 3.0 mg/L differed significantly from controls. In a Canadian forest pest‐management context, the expected environmental concentration in water bodies of areas sprayed with azadirachtin at 50 g/ha is 0.035 mg/L.

A Comparison of the Use of In Vitro-Transcribed and Native rRNA for the Quantification of Microorganisms in the Environment.

Abstract Nearly full-length, small subunit (SSU) rRNA was transcribed in vitro from clones of SSU rDNA genes. Comparing the use of in vitro-transcribed and native rRNA indicated that, when in vitro-transcribed rRNA was used as a standard for quantitative hybridizations with oligonucleotide probes, the population was consistently underestimated. The population abundance was expressed as a percentage of specific target SSU rRNA (determined with a specific oligonucleotide probe), relative to the total SSU rRNA (measured with a universal probe). Differences in hybridization signals could be related to specific probe target locations and rRNA denaturation conditions, suggesting that higher order structure is important in quantitative membrane hybridizations. Therefore, in vitro-transcribed rRNA cannot always be used for the absolute quantification of microbial populations, but can be employed as a standard to quantify shifts in population abundance over time, and to compare community structure in various environments.

Freshwater zooplankton in the Hawkesbury-Nepean River: comparison of community structure with other rivers

The Hawkesbury-Nepean River is a regulated coastal river in New South Wales, Australia. Between March 1992 and March 1993, the freshwater portion of the river was inhabited by a taxonomically rich (total: 116 taxa) and dense (annual mean community density: up to 1024 animals l-1) microzooplankton community, comparable to that in some of the large regulated temperate rivers in the Northern Hemisphere. The common zooplankton taxa in the river were similar to those observed in other rivers at the genus or species level, with a characteristic increase in protists ( Vorticella spp.) towards the downstream reaches of the river. Zooplankton community density in the Hawkesbury-Nepean River was, to some degree, predictable from river environmental variables: density was significantly negatively correlated with river flow rate but positively correlated with temperature, turbidity, conductivity, total phosphorus and chlorophyll a. The results of the present study generally conform to the hypothesis of similar structure of zooplankton communities in rivers, relative to that in lakes.

Functional groups and patterns of organization in North American ant communities: a comparison with Australia

Ant distribution and behavioural dominance is examined at nine sites along an elevational gradient (1400–2600 m) in south eastern Arizona, in order to classify North American species according to a functional group scheme used extensively in Australia. The functional groups are then used as a basis for determining patterns of community structure along the environmental gradient, and for comparing community structure between Australia and North America. Quantitative information on species com‐ position was obtained from pitfall traps, and patterns of ant abundance at tuna baits were used to determine relative behavioural dominance among taxa. A total of eighty‐three species from twenty‐eight genera was recorded along the elevational gradient, with site species richness ranging from four (high elevation Douglas fir forest) to thirty‐three (mid elevation oak–juniper woodland). There was a strong correlation between ant abundance and richness, which was not an artefact of sampling intensity. The most common ants were species of Forelius, Monomorium, Crematogaster and Pheidole at the three desert sites, species of Formica, Pheidole and Crematogaster at the three woodland sites, and species of Prenolepis and Formica at one forest site. No species were abundant at two other forest sites. The most common species in traps also tended to be the most common species at baits. In terms of behavioural dominance, highly competitive ants included species of Solenopsis, Forelius, Monomorium and Liometopum. Species of Pheidole and Crematogaster tended to be moderately competitive, whereas species of Dory‐ myrmex, Myrmica, Camponotus and Formica (fusca gp) had low competitive ability. On the basis of these results and on published records of other taxa, North American ants were assigned to functional groups as follows (major taxa only given here): Dominant Dolichoderinae—Forelius, Liome‐ topum; Subordinate Camponotini—Camponotus; Hot Climate Specialists—Pogonomyrmex, Myrmecocystus; Cold Climate Specialists—Formica (rufa, exsecta and microgyna groups), Leptothorax, Stenamma, Lasius, Prenolepis; Cryptic Species—Smithistruma, Solenopsis (subgenus Diplorhop‐ trum), Acanthomyops; Opportunists—Formica (fusca group), Myrmica, Paratrechina, Dorymyrmex; Generalized Myr‐ micinae—Pheidole, Crematogaster, Monomorium; Specialist Predators—no major taxa. Functional group composition varied systematically along the elevation gradient: Dominant Dolichoderinae, Generalized MyrÍmicinae and Hot Climate Specialists were predominant at desert sites; Generalized Myrmicinae and Opportunists were predominant at woodland sites; and Opportunists and Cold Climate Specialists were predominant at forest sites. These patterns are consistent with published studies from elsewhere in North America. Almost all North American taxa can be matched with what appear to be ecologically equivalent taxa in Australia, and biogeographic patterns of functional group composition are broadly similar across the two continents. The major differences are that Australian ant communities are far richer in species, and are almost always dominated by dolichoderines, particularly species of Iridomyrmex. Generalized myrmicines are subdominant to dolichoderines in Australia, but are the behaviourally dominant ants throughout the warmer parts of North America. In cool‐temperate North America, species of Formica (especially rufa and exsecta groups) are behaviourally dominant, as they are throughout the Palearctic. Some major features of the North American fauna can be linked to its poor representation of Dominant Dolichoderinae, including (1) the relatively low degree of physiological, morphological and behavioural specialization of Hot Climate Specialists; (2) behavioural dominance by formicines in cool‐temperate habitats; and (3) the susceptibility to invasion by behaviourally dominant species such as the imported fire ant Solenopsis invicta and the Argentine ant Linepithema humile.

Phylogenetic Perspectives on Community Ecology

Ecologists have long been interested in the differences that exist among communities. If species adapted rapidly and without constraint, and if any lineage could occur in any community, then we would expect differences in community structure to be indicative of environmental differences. Because lineages differ in their evolutionary potential and are geographically restricted, however, comparisons of community structure must take account of communities' histories. Phylogenetic information about the constituent lineages in a community can allow lineage effects to be factored out, thus allowing an assessment of environmental determinants of community structure. In addition, phylogenetic information permits understanding of how communities have evolved through time and suggests hypotheses that may be tested using extant communities. Methodological difficulties with the application of these methods to community ecological issues are also discussed.

Benthic macroinvertebrate community structure, function and production with respect to habitat type, reach and drainage basin in the southern Appalachians (U.S.A.)

SUMMARY1. Benthic macroinvertebrates were sampled for 1 year to assess functional and taxonomic differences in invertebrate biomass and production with respect to habitat types, reaches and catchments in Wine Spring Basin, western North Carolina. Quantitative samples were collected from depositional, cobble‐riffle and bedrock outcrop habitats at four stream reaches (two headwater sites, one second order, and one third order). Other measures included physical parameters, periphyton and organic matter standing crops. Invertebrate data from the Wine Spring catchment were also compared with data from another catchment (Ball Creek) within the same region.2. The three habitat types had different current velocities and mean substratum particle sizes; both measures were greatest in bedrock outcrop habitats and lowest in depositional habitats. Organic matter standing crops, invertebrate functional group productivity and biomass also differed significantly with respect to habitat type. Cobble‐riffle areas had the lowest standing crops of organic matter, invertebrate productivity and biomass.3. Both invertebrate communities and organic matter standing crops differed significantly between the two headwater reaches. First‐ to third‐order reaches differed in taxonomic composition at the genus level, yet had similar relative functional group productivity and biomass.4. Annual mean invertebrate biomass and secondary production were greater in the Wine Spring Basin than in Ball Creek. Sites in both the Wine Spring and Ball Creek catchments, however, exhibited similar functional group distributions per habitat type.5. Local geomorphology and related physical parameters influenced the structure of invertebrate functional group composition, and the distribution of organic matter standing crops. Furthermore, comparison of community structure in Wine Spring with that in Ball Creek suggested that taxonomic composition was more related to catchment‐specific parameters (e.g. thermal regime, evolutionary history) than stream size.

Comparisons of Community Structure Among Small Mammals of North-American and Australian Deserts

Data on the presence of small mammal species at 201 sites in North American deserts and 245 in arid Australia were used to quantify similarities and differences in community structure between the two continents. In all, 41 species of rodents were sampled in North America and 26 species, both rodents and marsupials, in Australia. On both continents, each species occurred throughout its geographic range with many other species and as a member of many different combinations. The number of species with which each species coexisted was positively correlated with its area of geographic range, although most species occurred at less than half the sites within their ranges. The median number of species at a site was three in North America and two in Australia, but the numbers of species per site on the two continents were not significantly different. Despite the relatively small numbers of species per site, numerous different combinations of species were observed (North America, 158; Australia, 108). Communities in North America were dominated by granivores and in Australia by omnivores; insectivores were also prominent in Australia. These results support conclusions of an earlier study of granivorous rodents in North America, in suggesting that there is substantial spatial variation in the composition of small mammal communities. The magnitude of this variation indicates that species and communities tend to be individualistic in spatial distribution, such that communities are not tightly restricted to particular specific combinations. There is evidence from North America that deterministic processes play a limited role in determining community structure; no such analyses have yet been undertaken for communities in arid Australia. Trophic structure of communities is markedly different on the two continents. Not all trophic differences can presently be explained, but they may be due to differences between the continents in temporal patterns of food supply.

Dynamics of a Small Mammal Community in a Fragmented Forest

-Community structure [species richness (S) and numbers of individuals captured] of a small mammal community were studied in July and August, 1987-1989, on a 1166-ha forested area in central Pennsylvania, which was divided into reference and treated sectors of comparable size. The reference sector was uncut, whereas the treated sector contained two areas with 50% and 75% fragmentation, respectively, resulting from forest clear-cutting in winter 1985-1986 and 1986-1987. I examined whether community structure of small mammals differed among years (1987-1989) or among forested areas that varied in extent of fragmentation. In addition, I compared community structure in 1987-1989 to that obtained on the same study site in 1982-1984 when extent of forest fragmentation was considerably less (25% and 50%) on the treated sector. Four-hundred nine individuals of seven species were captured during 4500 trap nights in 1987-1989, including white-footed mice (Peromyscus leucopus) (67.3% of total individuals), southern red-backed voles (Clethrionomys gapperi) (13.3%), and masked shrews (Sorex cinereus) (12.0%). Numbers of individuals captured of all species combined and of the three common species were significantly (P < 0.05) lower in 1988 than in 1987 and 1989, which I attributed to a drought in 1988 that presumably reduced the availability of terrestrial arthropods as a food resource. Although S was similar in 1987-1989 among areas of forest fragmentation and between 1982-1984 and 1987-1989, numbers of P. leucopus and C. gapperi captured were significantly (P < 0.05) higher in 1987-1989, especially in the area with 75% fragmentation. Numbers of P. leucopus were greater in 1987-1989 than in 1982-1984, perhaps because of a greater variety of microenvironments created by clear-cutting and increased availability of mast (acorns of oaks [Quercus] spp.) in 1987-1989. Numbers of C. gapperi likely were higher in 1987-1989 than in 1982-1984 because of moist microenvironments resulting from abundant low vegetation in clear-cut plots on the treated sector. I conclude that forests fragmented into small, even-aged plots can benefit P. leucopus and C. gapperi by increasing abundance of these two

Community Structure and Composition of Breeding and Wintering Birds in a Wastewater-Irrigated Oak Forest

We compared avian community structure and composition between 4 forested sites irrigated with wastewater (chlorinated sewage effluent) and 4 nonirrigated forested sites in central Pennsylvania during 1 breeding season and 2 winters. Compared to nonirrigated sites, irrigated sites had higher densities of all species combined and higher species richness (S) in the breeding season and in the winters. In the breeding season, 9 species were significantly (P < 0.05) more abundant on irrigated sites, whereas only 1 species was more abundant on nonirrigated sites. In winter, 4 species were more abundant on irrigated sites, but none was more abundant on nonirrigated sites. Because irrigation resulted in dense herbaceous growth, species that foraged or nested in vegetation near (<3 m) ground level were particularly abundant on irrigated sites. We conclude that community structure and composition of breeding and wintering avifauna were not negatively affected by wastewater irrigation, but breeding populations of species that forage or nest in leaf litter may be affected negatively by irrigation. J. WILDL. MANAGE. 54(3):493-500 Approximately 22 of 2,000 municipal sewage systems in the United States that apply treated wastewater directly on land do so in forests (W. E. Sopper, pers. commun.; Urie 1986). But this practice is expected to increase as small, localized facilities are needed in nonagricultural areas, on steeply sloping terrains, or where crop irrigation is not necessary (Nutter and Red 1986). Application of wastewater to land is attractive for several reasons (Sopper 1968); but irrigation of forest habitats, in particular, results in higher soil infiltration rates, less runoff and erosion, lower land acquisition costs, and fewer potential human health risks than irrigation of agricultural lands (U.S. Environ. Prot. Agency 1981, Burd 1986). Changes to forests irrigated with wastewater have been well-documented. Wastewater application alters the structure and species composition of forest understory plants, abundance of invertebrates, and occurrence of fruit-producing vegetation (Sopper and Kardos 1973, Lewis 1977, Mastrota et al. 1989). Thus, irrigation directly affects the resources (e.g., nesting sites, food, or cover) available to forest birds. Yet little is known about the effects of wastewater irrigation on community structure and omposition of forest birds (Rollfinke 1988). Three previous studies of breeding avian communities associated with wastewater irrigation (Savidge and Davis 1971, Snider 1974, Lewis and Samson 1981) were conducted on sma l forested plots within The Pennsylvania State University's (PSU) Wastewater Renovation System with irregular or partial-year irriga ion schedules (Rollfinke 1988). The PSU system was expanded from 40 to 200 ha and began using a year-round irrigation schedule in 1983. We compared community structure and composition of breeding and wintering birds on irrigated and nonirrigated forested sites after the expansion of this irrigation system. ' Present address: Friends School, 5114 N. Charles Street, Baltimore, MD 21210. This content downloaded from 207.46.13.120 on Wed, 14 Sep 2016 04:56:46 UTC All use subject to http://about.jstor.org/terms 494 IRRIGATED FORESTS * Rollfinke and Yahner J. Wildl. Manage. 54(3):1990 We thank E. D. Bellis and J. A. Kurland for comments on the manuscript. Our research was supported by the Pennsylvania Agriculture Experiment Station and the Max McGraw Wildlife Foundation.

Size and Shape of Sawfly Assemblages on Arroyo Willow

We present new techniques for the analysis of abundance data from multispecies communities. We partitioned variation in abundance into two components: variation in absolute abundance and variation in relative abundance. We examined patterns of absolute and relative abundance for multispecies assemblages from a multivariate morphometrics perspective. Multivariate morphometric analyses of abundance patterns have both heuristic and quantitative advantages over information theoretic approaches. We extended the concepts of isometry and allometry to community structure and illustrated these principles with density data from a group of five closely related tenthredinid sawflies that infest clones of arroyo willow (Salix lasiolepis). There were significant differences among willow clones in the size and shape of their sawfly assemblages. In fact, willow clones are virtually unique in terms of absolute and relative densities of sawflies. We used size and shape analysis to compare community structure of sawflies on male and female willows. Male clones differed from female clones in absolute densities of sawflies but not in relative densities.

Comparison of community structure among streams with different temporal flow regimes

A study was conducted in four streams in the same watershed in New York to determine whether the benthic invertebrate community structure varied among streams with different temporal flow regimes. Timed kick samples were taken from 13 riffles and 4 pools once a month from June to November 1982. Riffle sites were classified according to temporal flow regime as permanent, intermittent (dry for less than 3 months), or dry (dry for over 3 months), and varied in size as a function of discharge. Ordination analysis (detrended correspondence analysis) showed that the structure of the benthic invertebrate communities in these streams was related not only to riffle permanence, but also to other abiotic and biotic parameters. Differences in community structure were greater between adjacent pools and riffles than between temporary and permanent riffles. Stream size, seasonal changes in taxa, how recently the riffle had dried, and the length of the dry period contributed to differences in community structure among riffles. It appears that differences in community structure between permanent and temporary riffles are minimized by generalized adaptations of stream benthos, such as high rates of migration, drought-resistant eggs, and the tendency to take refuge in the hyporheic zone.

Resource partition among lacertid lizards in southern Europe

Twenty‐four species of lacertid lizards were examined at 31 sites in western Yugoslavia, Greece and Iberia. Comparative observations were made on over 4500 individual lizards, noting such features as times of activity, hunting methods, diet, micro‐ and macro‐habitat, refuges used and body temperature. These data are used as a basis for assessing resource partition in related sympatric species, for finding out whether different systematic groups have characteristic types of niche, and for comparing community structure in the three peninsulas of southern Europe.

Plant Megafossil Biostratigraphy and the Late Cretaceous Environment of the North Slope, Alaska: ABSTRACT

The Early Cretaceous evolution and subsequent geographic spread of flowering plants resulted in major global floristic changes. Studies of recently collected angiosperm fossil leaf-forms using analyses of comparative leaf architecture, facies associations, migrations, and community structure have resulted in a biostratigraphic tool for Alaskan Cretaceous nonmarine deposits, and a greater understanding of the Late Cretaceous terrestrial environment of the North Slope when substantial coal resources were being laid down. Angiosperms first arrived in northern Alaska, from the south, in latest Albian time. The Brooks Range apparently acted as a filter for some taxa and may have locally modified the climate. There is no evidence for major plant radiations at high paleolatitudes at this time. Putative evergreens form a large component of the pre-angiosperm floras. Throughout the Late Cretaceous, progressive loss of evergreen and thermophilic elements suggest a deteriorating climate. Paleoclimatic interpretations based on gymnosperm and angiosperm taxa are that: (1) there was no seasonal dark period on the North Slope in mid-Cretaceous times; (2) a mid-Cretaceous warm, mildly seasonal climate deteriorated to being cool temperate, with pronounced seasonality, by the Paleocene; and (3) vegetation may have been light- or cold-limited by latest Cretaceous times. The paleolatitude of greater than 70°N predicted for northern Alaska by paleogeographic reconstructions would appear to conflict with the interpretation that plants experienced no seasonal dark period. An obliquity of 15° could explain this conflict and a closer relative position to the rotational pole accounts for the apparent climatic deterioration. A detailed study of high-latitude terrestrial-plant ecosystems provides information critical to global climate models and therefore our understanding of the biosphere as a whole. End_of_Article - Last_Page 679------------

Changes in water and sediment bacterial community structure in a lake receiving acid mine drainage

Water and sediment bacterial communities in a freshwater impoundment were studied over a 13-month period for stress-related responses to a point source of acid mine drainage (AMD). Comparisons of community structure were made on collections taken at the mouth of the acid stream, at a point 2 km downstream, and at the mouth of an uncontaminated stream. Monthly measurements of pH and specific conductance indicated the expected decrease in the AMD pollution with increasing distance from the source. Acridine orange direct counts did not differ significantly among the sites; however significantly fewer viable heterotrophs were observed by plate counts at the acid impacted station relative to the uncontaminated site. The diversity of the communities was significantly lower at the sites receiving mine drainage as compared with the unaffected station, and comparisons of community similarity showed that collections from the impacted sites were more like each other than like the control site. The assemblage at the latter site contained many bacterial guilds not found at the contaminated sites. The guilds unique to the control site showed a reduced in vitro ability to tolerate heavy metals as compared with the general community.

Comparative community structure ofChamaecyparis thyoides bog forests: Canopy diversity

Chamaecyparisthyoides (L) BSP (Atlantic White Cedar), found only in acid wetlands of the eastern United States coast, dominates readily-recognized biotic assemblages that vary with latitude. This is the first of a four-part study of the literature on biota associated withC.thyoides throughout its range. The number of tree species found with cedar in each state ranges from 2 to 18. State regions with the highest canopy diversity are: east and west Florida, Massachusetts and Mississippi. States with the lowest number of associated tree species are: Alabama, Georgia and New York and Maryland. Fifty-five tree species are found growing withC.thyoides overall, with no single species in all the 17 state-regions of its range. Most trees co-occur in a narrow band: over 85% are found in 5 states or less. Species most frequently associated are:Acerrubrum,Nyssasylvatica andMagnoliavirginiana. Fire control, logging, road building, mosquito control and agricultural practices continue to alter and obliterateC.thyoides communities.

Effects of Logging on Macroinvertebrates in Streams With and Without Buffer Strips

The impact of logging with and without buffer strip protection on stream macroinvertebrates was examined through comparisons of community structure in commercially logged and control watersheds throughout northern California. A nonparametric test of community dissimilarities within matched blocks of two control and one or two treated stations showed significant (P &lt; 0.05) logging effects on unprotected streams when Euclidean distance and mutual information were used as dissimilarity indices, but not when chord distance was used. Shannon diversity in unprotected streams was lower (P &lt; 0.01) than in control (unlogged) streams; densities of total macroinvertebrate fauna and of Chironomidae, Baetis, and Nemoura were higher in unprotected streams than in controls (P &lt; 0.05). Streams with narrow buffer strips (&lt; 30 m) showed significant effects by the Euclidean distance test, but diversity varied widely and was not significantly different from that in either unprotected or control streams. Macroinvertebrate communities in streams with wide buffers (≥ 30 m) could not be distinguished from those of controls by either Euclidean distance or diversity; however, diversity in wide-buffered streams was significantly greater than in streams without buffer strips, indicating effective protection from logging effects.Key words: buffer strips, California, diversity, ecological dissimilarity, invertebrates, logging, streams