Showing papers on "Species richness published in 1975"

Plant Species Diversity in Old-Field Successional Ecosystems in Southern Illinois

Abstract: In old—field ecosystems in the deciduous forest, plant species diversity generally increases with succession and reaches a maximum during the forest stage when structural diversity is highest and at the time when both shade—tolerant and shade—intolerant species are present together. Species diversity may be exceptionally high in succesional communities when there is a high degree of vertical and horizontal heterogeneity. Diversity may be exceptionally low in old—field ecosystems when there is strong dominance by species with alleolopathic chemicals or other effective interference methods. Species distribution curves are geometric during the first few years of succession and gradually change to lognormal as more species are added to the community, the process resulting in a high degree of evenness.

Equilibrium plant species associations on badger disturbances in a tall-grass prairie'

Abstract: Badger disturbances in a tall-grass prairie were used to study colonization patterns and the formation of equilibrium plant species associations in a complex mainland community. Colonization processes were described from field observations over a 4-yr period. A qualitative colonization model was developed to predict noninteractive species equilibria. Predicted colonization rates were based upon relative immigration rates determined by interactions among propagule production rates, dispersal capacities, and the source-site distances of the species involved. The immigration rates both between groups with different life history characteristics (mature prairie, prairie fugitive, and ruderal species) and within groups (K-type, intermediate, and r-type fugitive species) were predicted. Manipulation of important variables enabled different conditions affecting relative immigration rates to be simulated. Species with intermediate life history characteristics (propagule production and dispersal capacity) and located at intermediate distances from the colonization site were predicted to have the highest immigration rates. Thus, prairie fugitive forbs were predicted to have higher rates than either mature prairie or ruderal species. Immigration rates of different fugitive species onto a site were predicted to depend upon the frequency and distribution of previously colonized disturbances in the vicinity of the colonization site. In general, model predictions were consistent with field observations. The model predicted the noninteractive species equilibrium among seedlings of mature prairie, fugitive, and ruderal forbs, but not the interactive species equilibrium among these groups of forbs. Within the fugitive species, both noninteractive and interactive species equilibria were predicted. The noninteractive colonization model was constructed for prediction of colonization patterns on local disturbances in complex plant communities, but since it utilized general life history characteristics to predict immigration rates it should also be applicable to other colonization processes. Equilibrium plant species associations were studied on badger disturbances in virgin prairie and in a less complex tract of overgrazed prairie. Peak standing crop biomass was not different on and off disturbances in either community, but biomass production occurred earlier in the year on disturbances. Although the species present differed, species diversity, equitability, and the distribution of biomass among species were similar on and off disturbances in virgin prairie and on disturbances in overgrazed prairie. The dominant species comprised 20%-26% of the biomass. In contrast, off disturbances in overgrazed prairie were different. The species diversity and equitability were low, and the biomass was concentrated in the dominant species (60% ). Thus, in overgrazed prairie local disturbances depressed dominance and resulted in increased complexity of the plant species association formed. In virgin prairie alternate states of equivalent complexity resulted from local disturbances, and thus spatial heterogeneity was increased. The fugitive species comprise a guild using a common resource (disturbance sites). Direct competition among the species is reduced by spatial and temporal separation of the species. Overlap of species persistent on badger disturbances is reduced because of colonization specificity, site contingencies that determine germination and growth, and suppression of later colonists. The species guild of fugitive plants thus is characterized by diffuse competitive interactions. The reduction of direct competition enhances the formation of persistent species associations on badger disturbances, enhances coexistence, and enables species packing to occur within fugitive species guild.

The Colonization and Formation of Equilibrium Plant Species Associations on Badger Disturbances in a Tall-Grass Prairie

Abstract: Badger disturbances in a tall-grass prairie were used to study colonization patterns and the formation of equilibrium plant species associations in a complex mainland community. Colonization processes were described from field observations over a 4-yr period. A qualitative colonization model was developed to predict noninteractive species equilibria. Predicted colonization rates were based upon relative immigration rates determined by interactions among propagule production rates, dispersal capacities, and the source-site distances of the species involved. The immigration rates both between groups with different life history characteristics (mature prairie, prairie fugitive, and ruderal species) and within groups (K-type, intermediate, and r-type fugitive species) were predicted. Manipulation of important variables enabled different conditions affecting relative immigration rates to be simulated. Species with intermediate life history characteristics (propagule production and dispersal capacity) and located at intermediate distances from the colonization site were predicted to have the highest immigration rates. Thus, prairie fugitive forbs were predicted to have higher rates than either mature prairie or ruderal species. Immigration rates of different fugitive species onto a site were predicted to depend upon the frequency and distribution of previously colonized disturbances in the vicinity of the colonization site. In general, model predictions were consistent with field observations. The model predicted the noninteractive species equilibrium among seedlings of mature prairie, fugitive, and ruderal forbs, but not the interactive species equilibrium among these groups of forbs. Within the fugitive species, both noninteractive and interactive species equilibria were predicted. The noninteractive colonization model was constructed for prediction of colonization patterns on local disturbances in complex plant communities, but since it utilized general life history characteristics to predict immigration rates it should also be applicable to other colonization processes. Equilibrium plant species associations were studied on badger disturbances in virgin prairie and in a less complex tract of overgrazed prairie. Peak standing crop biomass was not different on and off disturbances in either community, but biomass production occurred earlier in the year on disturbances. Although the species present differed, species diversity, equitability, and the distribution of biomass among species were similar on and off disturbances in virgin prairie and on disturbances in overgrazed prairie. The dominant species comprised 20%-26% of the biomass. In contrast, off disturbances in overgrazed prairie were different. The species diversity and equitability were low, and the biomass was concentrated in the dominant species (60% ). Thus, in overgrazed prairie local disturbances depressed dominance and resulted in increased complexity of the plant species association formed. In virgin prairie alternate states of equivalent complexity resulted from local disturbances, and thus spatial heterogeneity was increased. The fugitive species comprise a guild using a common resource (disturbance sites). Direct competition among the species is reduced by spatial and temporal separation of the species. Overlap of species persistent on badger disturbances is reduced because of colonization specificity, site contingencies that determine germination and growth, and suppression of later colonists. The species guild of fugitive plants thus is characterized by diffuse competitive interactions. The reduction of direct competition enhances the formation of persistent species associations on badger disturbances, enhances coexistence, and enables species packing to occur within fugitive species guild.

Taxonomic diversity estimation using rarefaction

Abstract: Benthic ecologists have successfully applied rarefaction techniques to the problem of compensating for the effect of sample size on apparent species diversity (= species richness). The same method can be used in studies of diversity at higher taxonomic levels (families and orders) in the fossil record where samples represent world-wide distributions of species or genera over long periods of geologic time. Application of rarefaction to several large samples of post-Paleozoic echinoids (totaling 7,911 species) confirms the utility of the method. Rarefaction shows that the observed increase in the number of echinoid families since the Paleozoic is real in the sense that it cannot be explained solely by the increase in numbers of preserved species. There has been no statistically significant increase in the number of families since mid-Cretaceous, however. At the order level, echinoid diversity may have been nearly constant since late Triassic or early Jurassic.

The Distributional Ecology and Diversity of Benthic Insects in Cement Creek, Colorado

Abstract: A bstract. Distributional patterns and species diversity of benthic insects in an alpine stream in Gunnison County, Colorado, USA were investigated on several levels of spatial scale, from faunal replacement over 1,000 vertical m to microdistribuLtion within the stony substratum. Ecotones including zonation in terrestrial vegetation and in trout distribution did not appear to affect faunal replacement. Competition among congeners accounted for 7-30% of the cases, while in the majority of species, faunal replacement appeared to be associated with gradual changes in the physical gradient. Trout zonation may affect total numbers of insects, however, as the trotut-free headwaters had two to six times higher insect densities. Microdistribution was investigated by measures of species and substratunm patterning in a series of microhabitats (0.093 mi) at a series of sites (separated by 75-150 vertical m), and by field colonization experiments with various substratum choices. I hypothesize that increased suibstratum complexity leads to greater species richness based on several lines of evidence: (I ) different species showed different substratum preferences, (2) colonization of mixed stubstrata generally resulted in greater mean species richness than did colonization of a single substr-atum type, and (3 ) both species diversity and substratum complexity were greatest at the within-microhabitat level. However, substratum composition showed little variation along the elevational gradient and did not appear to be a cause of faunal replacement. The several scales of investigation were complementary, as congeners exhibiting sharp mutuLal exclusion in vertical distribution had similar microhabitat preferences, while othercongeners showed less exclusion and differed in microhabitat preferences. Most of species diversity as measured by H' was found within habitats rather than between habitats while species richness depended equally upon within-habitat variation (owing to rare species) and between-habitat variation (owing to faunal replacement).

A comparison of three diversity indices based on their components of richness and evenness

Abstract: Species diversity was calculated using three different indices on sets of real and artificial data. Each index was analyzed to determine its relationship to the two component parts of diversity, richness and evenness. Shannon's information formula, H' = C~pi log2 pi, is found to be linearly related to evenness and to the log2 of the number of species. Simpson's Index, D = 1 n(n 1) and __ zg~~~~N(N -1) N V/ni2 McIntosh's Index, D' = N , when expressed in probits are found to

Comparison of Species Richness for Stream-Inhabiting Insects in Tropical and Mid-Latitude Streams

Abstract: A quantitative comparison based on statistically smooth species-sample curves between tropical and mid-latitude species richness for rheophile insects from seven mid-latitude and nine tropical stream samples is presented. Actual data in the form of accumulated numbers of species compared with numbers of rocks taken from riffle sites are applied to a mathematical model in order to estimate numbers of species that should be present in a given area. Species-sample curves show that species richness of rheophile insects is significantly higher at a theoretical sample size of 100 rocks for tropical streams than it is for mid-latitude streams. This trend is not obvious until 20 or 25 rocks have been sampled. The results suggest to us that earlier studies indicating no differences in species richness between the two latitudinal regimes were based on inadequate sampling. Altitudinal trends exist between lowland and mid-elevation tropical sites. Seasonal differences were also observed for a tropical stream sampled ...

Factors determining the distribution patterns of mud snails (Hydrobiidae).

Abstract: The distribution patterns of four species of mud snails (Hydrobiidae) in a complex, estuarine environment are described. The species show habitat selection with respect to salinity but the tolerance ranges of the species overlap and it is shown that this factor alone cannot predict the distribution in the field. The found patterns show that the species are subdivided into many, more or less isolated sub-populations. It is conjectured that the distribution of the species results from the interaction of habitat selection, dispersal rates, colonizations, interspecific competition and extinctions. This interpretation explains features of the distribution patterns; e.g., the boundaries between two species in salinity gradients occur at different salinities in different areas, the species with an intermediate position with respect to salinity preference is the least frequent one, and that coexistence between two, and sometimes three species may occur under certain conditions. The possibility that the species may sustain populations within some areas as “fugitive” species is also discussed.

Aspect diversity in moths: a temperate-tropical comparison.

Abstract: This analysis attempts to answer, for assemblages of adult moths, whether the increased number of species in a tropical sample compared to two temperate samples represents an increase in the density of species packing in the community or an increase in the total ecological space occupied by the community as a whole. We view a species as occupying a niche defined by the interactions of that species with its environment, especially by its utilization of limiting resources. The increased species richness in some tropical habitats compared to temperate habitats can be related to either (a) an increase in the total niche space occupied by all species, (b) a decrease in the average size of the niche of each species, (c) an increase in the degree of niche overlap between species, or any combination of these factors. In this paper we approach the problem of species richness by assuming that the interactions of a species with the environment, which define its niche, are reflected in the morphological adaptations of the species. By placing species in an abstract multidimensional space ordinated by morphological characteristics, we can indirectly assess the relative roles of community niche size and species packing in variation in species number. We cannot, however, estimate niche overlap by this technique. We have analyzed the appearance of adult moths in two temperate communities and one tropical community. We assume that the cryptic appearance of most species (Fig. 1) is an adaptation to match the

Temporal and Spatial Variation in Species Diversity of Wandering Spiders (Araneae) in Deciduous Forest Litter

Abstract: A guild of wandering spiders was studied in an oak-tuliptree-maple forest in northern Delaware. Specimens were collected by pitfall trapping and weather data recorded at weekly intervals over the summer season (3 months). A seasonal peak in species diversity ( H' ) and species richness in midsummer was significantly correlated with prey abundance but not with seasonal temperature, humidity, or rainfall. Annual patterns of detritivore productivity in temperate forests and their influence on niche partitioning and seasonal abundance of species are discussed as a possible explanation. Spatial differences in species diversity were significantly correlated with the amount of litter and a measure of habitat space, but not with microclimatic moisture and temperature, vegetative diversity, or prey abundance. Physical aspects of the litter habitat, either as structural microhabitats or refuges from predation, are suggested as being important in regulating within-habitat species diversity. Interaction of diversity-regulating environmental factors in space and time are discussed.

The relation of foliage complexity to ecological diversity of three amazonian bird communities

Abstract: The relation between foliage complexity and bird species diversity has been studied by several investigators. Some (MacArthur and MacArthur 1961, MacArthur et al., 1962, Recher 1969, Karr 1971, Karr and Roth 1971) found that the complexity of the vertical distribution of leaves, as measured by foliage height diversity ( FHD ) , was a good predictor of bird species diversity (BSD). Other investigators (Terborgh 1967, Balda 1969, Lovejoy 1972) have found little correlation between FHD and BSD. BSD, as measured by a statistic derived from information theory, necessitates knowledge of the number of individuals of each species as well as number of species. In mature tropical forests, estimates of population size are difficult because such a large proportion of the bird species do not typically occur in low strata where they can be readily netted and marked. Orians ( 1969) avoided this problem in Costa Rican forests by comparing only the number of bird species (bird species richness, BSR) to FHD. He suggested that the range of resource types permanently above threshold values in tropical forests was the major factor determining bird species richness. However, in all these relations between foliage complexity and the number of bird species inhabiting the foliage, the assumption is made that the community is in an equilibrium or saturated state, that is, new species can enter the community only if they exclude a species already present. The Amazon Basin presents a distinct difficulty in applying FHD-BSD (BSR) correlations. Due to numerous historical changes in climate, continuous forest apparently alternated with forest islands (refugia) surrounded by non-forest vegetation throughout the Pleistocene and post-Pleistocene (Haffer 1969, Vanzolini 1973). It is now generally recognized that islands with similar habitat harbor different numbers of species depending on the area and distance of the island from the mainland species pool (MacArthur and Wilson 1967). Island-like effects are also recognized for continental habitats that occur in patches

Ecology of Conus on eastern Indian Ocean fringing reefs: Diversity of species and resource utilization

Abstract: The most diverse assemblages of the genus Conus known occur on fringing coral reefs in Thailand and Indonesia. As many as 27 congeneric species of these gastropods inhabit a single reef; in all, we examined 1,350 individuals of 48 species. Several attributes of the populations we observed conform to expectations of a model of ecological characteristics of bench and reef Conus proposed by Kohn (1971a). Number of species (S) averaged 15, and species diversity (H″) averaged 2.3 in the most heterogeneous habitat type — topographically complex, subtidal reef platforms (Type III habitat). Both species richness and evenness of distribution of individuals among species contribute strongly to H″. Fewer congeners and greater numerical dominance by single species characterize more homogeneous habitats. On subtidal reef platforms with large areas of sand substrate and less coral limestone (Type I–III habitat), mean values were S=10, and H″=1.6. In the one intensively studied, truncated reef-limestone platform (Type II–III intermediate habitat), S=13 and H″=1.4. Summed population density of all Conus species in Type III and I–III habitats is similar (0.02 to 0.05 individuals /m2) and comparable to estimates from similar habitats elsewhere in the Indo-West Pacific region. Mean density (0.7/m2) and other population attributes in Type II–III habitat more closely resemble those of Type II than Type III habitats in general. We combined analysis of species diversity and other attributes of assemblages in habitats of different environmental complexity with analysis of microhabitat and food-resource utilization, in order to demonstrate the extent to which specialization on different resources occurs in assemblages differing in diversity and habitat type. In the habitats studied, co-occurring species of Conus specialized to a greater extent on different prey species than on different microhabitat patches, but degree of microhabitat specialization was greater than in similarly complex habitats with assemblages of lower diversity elsewhere in the Indo-West Pacific region. While most Conus species preyed primarily on a different species or higher taxon of polychaetes, diets are not more specialized or dissimilar than in similar habitats elsewhere. Degree of specialization on different prey is not correlated with Conus species diversity in the different types of habitats studied. The data lead to the conclusion that differential predation is as important — and differential microhabitat utilization is more important — in permitting coexistence of potentially competing congeners, compared with conditions in habitats of comparable heterogeneity that support fewer congeners farther from the center of the Indo-West Pacific region. Pairwise comparisons of congeners indicate that many species pairs have low or no overlap in both microhabitat and food utilization. Members of species pairs with high overlap in microhabitat utilization typically eat different prey organisms, and those with similar diets typically occupy different habitats or microhabitats. This applies to molluscivorous as well as vermivorous species. Information on the diets of 11 species is reported here for the first time. Of 48 Indo-West Pacific Conus species whose food is now known, 35 prey on polychaetes, 2 on enteropneusts, 6 on gastropods, and 5 on fishes. Vermivorous Conus prey on relatively few of the polychaete species present in the environments. Species eaten represent only 12% of a total estimated polychaete population density of 27,000 individuals /m2. Certain very abundant polychaetes may be protected from predation by Conus by their small size, others by their long tubes. Two new aspects of size-selective predation by Conus are reported: (1) Although comparisons of predation rate with prey standing-crop suggest that food is plentiful, selective predation on the largest prey individuals present suggests that only small proportions of prey-species populations may have large enough body size to repay foraging effort by the Conus present; (2) composition of the diet changes qualitatively with increase in body size in several vermivorous Conus species; shifting by larger individuals to larger prey species could be documented in C. ebraeus.

Convergence in Vegetation Structure along Analogous Climatic Gradients in California and Chile

Abstract: A series of plant communities along analogous climatic gradients in southern California and central Chile has been analyzed to determine the extent of convergence in a variety of ecologically significant characters. Results show that, despite distinct genetic his- tories, the structure of the vegetations of these areas has converged under similar climatic constraints. Such characters as species richness, growth form, leaf duration, leaf size, and spines are quantitatively more similar between floristically distinct yet climatically analogous sites on the two continents than between floristically similar but climatically distinct sites a short distance apart on the same continent. Such findings, which hold true for both the native woody vegetation and the partially exotic herbaceous understory, provide quantitative support for the general hypothesis that plant form and community structure are highly determined, regardless of genetic constraints, by environmental parameters.

Diversity and Organization of the Ground Foraging Ant Faunas of Forest, Grassland and Tree Crops in Papua New Guinea

Abstract: Thirty samples of ants were taken in each of seven habitats: primary forest, rubber plantation, coffee plantation, oilpalm plantation, kunai grassland, eucalypt savannah and urban grassland. Sixty samples were taken in cocoa plantations. A total of 156 species was taken, and the frequency of occurrence of each in each habitat is given. Eight stenoecious species are suggested as habitat indicators. Habitats fell into a series according to the similarity of their ant faunas: forest, rubber and coffee, cocoa and oilpalm, kunai and savannah, urban. This series represents an artificial, discontinuous succession from a complex stable ecosystem to a simple unstable one. Availability of species suitably preadapted to occupy habitats did not appear to limit species richness. Habitat heterogeneity and stability as affected by human interference did seem to account for inter-habitat variability in species richness. Species diversity was compared between habitats using four indices: Fisher et al.; Margalef; Shannon; Brillouin. Correlation of diversity index with habitat hetero- geneity plus stability was good for the first two, moderate for Shannon, and poor for Brillouin. Greatest diversity was found in rubber, the penultimate in the series of habitats according to hetero- geneity plus stability ('maturity'). Equitability exceeded the presumed maximum in rubber, and was close to the maximum in all habitats. The mosaic dispersion pattern found among ants elsewhere also appeared to be present in each habitat. The mean maximum number of territories possible to be overlapping is about 4.6; the number in a particular case probably being a function of the specialization of the dominant ant present. Ecological isolating mechanisms among ants are probably similar to those among birds; size and structure of mouthparts in ant communities warrant further study.

Species richness of the parasitic fungi of british trees.

Abstract: The species richness of fungi associated with British trees is described by a significant species/area curve (r = 0.53, 0.01 > P > 0.001). Introduced tree species cannot be shown to have fewer fungal species than natives, per unit distributional range about Britain. Also, among natives and among introductions, older host taxa do not have more fungal species than do younger ones. This indicates the species richness of fungi to rapidly reach the limit set by host range, within ecological time. The slope of the species/area relationship for fungi is one-fourth that for insects; we propose that this is due to the inherently greater dispersability of fungi. Finally, the species/area regression residuals for fungi are correlated with those for insects (r = 0.65, 0.001 > P), suggesting plant defense mechanisms may be generally effective to plant parasites, be they insects or fungi.

Geographical variation of diversity in Argentine passerine birds

Abstract: The number of species, genera, and families of passerine birds is presented in the form of isoline maps, using a 100 x 100 km grid. The main features of these maps are discussed according to the biogeographic background. A similar procedure is performed for entropy (information content) of species per genera, species per family and genera per family. Simple linear and multiple correlations between taxa richness and entropy with precipitation, temperatures (mean annual, mean July, and mean January), minimum altitude, maximum altitude, and slope were performed, calculating also the beta coefficients weighing the importance of independent variables. Comparisons are given for the whole country as well as for four selected transects. Latitudinal variation of species' richness is also analysed. According to a phytogeographical map, a strata index was calculated for each quadrat according to proportions of different biomes and the number of contacts or ecotones which they have. The strata index, at a macrogeographical scale, accounts fairly wellfor the richness of taxa.

Methods for Measurement of Community Structure in Deep-Sea Macrobenthos*

Abstract: Methods are compiled and developed for the analysis of community structure in the deep-sea benthos. These methods are tailored to the conditions of high species diversity and low standing crop. A new modification of the 0.25-m2 box corer is described. Fisher's index of dispersion is adapted by using each species as a replicate. When the resultant summary statistic is partitioned in the illustrated manner, it is possible to determine whether species indeed behave as homegeneous replicates of a single dispersion pattern, or, alternatively, whether habitat partitioning is indicated. Species are also used as replicates in a modification of Pielou's “joins” technique of determining whether high-density and low-density areas of given species are randomly mingled. An indirect analytical approach is developed which proposes that, if an environmental grain of relatively small dimensions has been important in structuring the community, species which have smaller ambits will be more diverse than species having larger ambits.

Edaphic Climax Pattern of the Pygmy Forest Region of California

Abstract: The dwarfed conifer forests occurring on the coastal terraces of Mendocino County, California, are oligotrophic communities containing edaphic endemics as dominants. Species distributions and community characteristics are traced along a gradient in podzolization of the soils from these pygmy conifer stands on highly weathered terrace spodosols, to redwood stands on weakly developed slope spodsols. Vegetation stature, canopy closure, species richness, litter biomass and pH generally decrease along the gradient as podzolization and nutrient impoverishment increase, whereas soil organic matter and available water capacity tend to be highest at the gradient extremes. Analyses of pygmy forest soils show low levels of macro— and micro—nutrients, and high levels of exchangeable aluminum. When ordinations of stands based on vegetational data are compared with rankings based on environmental data, changes in pH of the soil A horizon are found to correlate most highly with vegetation changes. Nutrient loss and acidification, initiated by varying rates of soil weathering in the pygmy forest region, may be aggravated, in the case of pygmy forest soils, by a series of feedback effects, including solubilization of possibly toxic amounts of aluminum by low pH, which may contribute to the observed plant stunting and shrinking pools of nutrients in the biomass. A ranking of stands along a soil nutrient gradient, based on field observations and presence data for species, correlated successively less strongly with ordinations computed by similarity—projection, Bray—Curtis method, importance—projection, principal components analysis, and factor analysis. Although these ordinations were expected to produce distortions in the interstand relations due to the modal and even polymodal nature of species response curves and to the presence of species not spanning the range of the data set, additional distortions due to variability in sample data were also highlighted.

Clumps of Heliconia Inflorescences as Ecological Islands

Abstract: A bstract. Previous theoretical and field studies have identified quantifiable relationships between migration, extinction, island size, and distance to mainland with species richness on islands. Some of these relationships hold for insects living in spatially and temporally separated Heliconia inflorescences. Analysis of 45 clumps of Heliconia wagneriana and 77 clumps of Heliconia imbricata using MacArthur and Wilson's (1967) island biogeography theory indicates that area-species richness curves are more similar to those of true islands than to those of mainland areas. Other island relationships such as distance influences could not be found. It is postulated that beta diversity (the diversity due to the number of habitats available) is more important in increasing species richness of animals in Heliconia clumps than is alpha diversity (the diversity due to the number of species using a given resource). The reduction of evenness as area size increases indicates that increasing ecological island size increases populations of common insects more rapidly than new species can invade these ecological islands.

On the influence of sewage pollution on inshore benthic communities in the South of Kiel Bay

Abstract: 1. The influence of organic sewage pollution on the macrobenthic community structure of a shallow inshore region was studied in the South of Kiel Bay (Baltic Sea). 2. The sandy bottom bears three associations within the pollution gradient. They can be characterized by: (a)Capitella capitata and Oligochaeta (50–100 m distance from the sewage outlet), (b)Pygospio elegans (200-ca. 700 m) and (c)Bathyporeia sarsi (>700 m). They have no distinct borders but resemble rather a continuum. 3. In the less affected reaches the influence of biological substrate structure becomes more evident. Distinct associations can be distinguished. 4. The combination of life forms, number of species, diversity and other community features depend on the degree of the substrate's spatial heterogenity in a characteristic way. They are also strongly influenced by the extent of pollution. 5. The inshore benthic macrofauna provides an important contribution to the self purification of the whole ecosystem by transforming particulate organic matter to available fish food. Abundance and biomass are multiplied due to sewage sedimentation. This process creates the danger of accumulation of poisonous substances in addition to the eutrophication problem. 6. More highly diverse systems (e. g. mussel beds) resist better those factors which directly influence the evenness of the community. The ecological buffer consists of many specialized competitors and predators. Systems low in diversity (e. g. sand) react much more strongly to disturbances of this type. 7. Faunal composition, evenness, species richness, population density and biomass of the communities are suitable parameters of an ecological method for the early recognition of environmental stress.

Impact of kraft pulp-mill effluents on estuarine and coastal fishes in Apalachee Bay, Florida, USA

Abstract: A 2-year field study was carried out to determine the impact of kraft pulp-mill effluents on the fish fauna of a shallow-bay system in north Florida (Apalachee Bay, USA). Offshore areas that received kraft-mill effluents (KME) displayed significant increases in color and turbidity and reductions in (benthic) dissolved oxygen compared to a nearby control area. Estuarine and marsh fish assemblages in areas of acute impact were severely reduced in terms of numbers of individuals (N) and species (S). Offshore areas exposed to varying (chronic) levels of KME were characterized by complex interactions that included seasonal variations of impact. A broad offshore area showed reductions in numbers of individuals and species taken per month. However, the cumulative (annual) number of species taken was the same for polluted and unpolluted (control) areas due to a recruitment of relatively rare species in the areas of impact. Such polluted areas showed decreased dominance as well as qualitative differences in species composition compared to control areas. Inshore bay stations that were most severely affected by KME were dominated by the bay anchovy, Anchoa mitchilli. While species richness and species diversity were lower at the highly stressed stations, in other outlying areas of moderate impact (reduced N and S) there were no reductions of such parameters compared to control areas. Thus, species diversity was not an indicator of pollution per se, and was useful only when taken in conjunction with various other parameters. Transition areas (between polluted and unpolluted portions of the bay) showed substantial (although periodic) increases in N, S, and species diversity. Equitability indices were unchanged in polluted portions of the bay. In general, the effects of KME on offshore fish assemblages appeared to be due to a complex combination of habitat alteration, reduced benthic productivity, and individual behavioral reactions. The alterations of fish assemblages were compared to other studies in this area on benthic macrophytes and invertebrates in an effort to assess the usefulness of various indices in studies on the long-term effects of pollution on estuarine and coastal systems. It was found that kraft pulp-mill effluents had a pronounced effect on the benthic standing crop of plants and animals, but that intensive sampling over prolonged periods of time was necessary for an adequate assessment of the problem. Overall, there were some significant changes in the biota such as reduced dominance and productivity in polluted areas that were similar for the various types of organisms sampled.

Terrestrial Vertebrates of the New Hebrides: Origin and Distribution

Abstract: The known terrestrial vertebrate fauna of the New Hebrides consists of 16 species of mammals (excluding feral domestic stock), 61 species of resident land- and fresh-water birds, 20 species of reptiles and one amphibian. Of these, three, five, four and one species respectively have apparently been introduced by man. The non-introduced fauna is clearly Indo-Australian in origin, but some species have an exclusively Pacific island distribution and others (two bats, seven birds, and four lizards) are endemic. On the six islands visited 95 out of the possible 98 vertebrate species occur. Santo, the largest and most northerly island, supports the richest fauna. The comparative impoverishment of more southerly islands is not directly attributable to the progressive increase in isolation and distance from presumptive source area, nor to decrease in island area or maximum height. Most of the native vertebrates, including all endemic species, occur in mature seral or climax forest; relatively few species, all of which are cosmopolitan or wide-ranging in the Indo-Pacific region, are restricted to open habitats. Of introduced vertebrates only the feral pig, Rattus exulans and Gallus gallus occur in forest; the remainder are commensal with man or confined to disturbed or open habitats. Forest faunas show altitudinal zonation and vertical stratification under the canopy. The ranges of three large skinks are mutually exclusive, and may be complementary. No bats or birds have comparable complementary distributions, but among four closely related pairs of birds the niche of species widespread in the archipelago is reduced in the presence of a less widely distributed relative. The diversity of the netted avifauna was constant despite marked variation in the diversity of canopy trees in the netting plots. Vegetational characteristics also failed to correlate with the presence or absence of bird species irregularly distributed throughout the archipelago. There have been suggestions that some forest-adapted species (pigeons, lorikeets) may move from island to island but direct observations are lacking. Among Halcyon chloris and many passerines interrupted distributions, differences in habitat preference and/or taxonomically significant differences in size or colour indicate limited exchange between adjacent islands, implying that populations are sedentary. The distribution of certain bird species indicates that active colonization of the New Hebrides is not yet complete. Artamus leucorhynchus has apparently invaded Aneityum in recent years. The present distribution of Lichmera incana is also interpreted in terms of current invasion, and suggests that a preliminary period of selection is necessary before an invader can advance from the coastal strip into the forested interior.

Relationship between sediment texture, species richness and volume of sediment sampled by a grab

Abstract: This paper discusses the problems involved in obtaining grab samples for direct comparison of the respective benthic fauna, using information from a survey conducted across the South African Continental Shelf below the Benguela Current. Many factors influence the depth of grab penetration into the sediment and, hence, the grab sample volume. One of the most important of these factors is sediment texture. While this fact has been long recognised, most workers have attached little significance to it. It is shown here that an exponential relationship exists between the grab sample volume and sediment texture, until the minimum percentage of silt plus clay that will give a maximum grab sample volume is reached. This relationship only extends to a certain depth, in this case to 280 m. There are more species per unit number of specimens (“species richness”) in association with sand or muddy-sand than with mud. A linear relationship is given between the grab sample volume and species richness between the depths of 280 and 440 m, inclusive.

Species Richness on the Nondisturbed Northwestern Hawaiian Islands

Abstract: An examination of selected ecological variables on the 18 low, sandy, non—disturbed islands of the northwestern Hawaiian Islands, and the vascular plants and birds, primarily seabirds, occurring there shows that species richness on low, sandy, oceanic islands is influenced by ecological diversity and is affected by variables similar to those on high, rocky islands. Species richness of vascular plants on these islands can be predicted by means of stepwise regression on the basis of area of vegetation, and to a lesser extent, elevation. In turn, variation in numbers of breeding species of seabirds, total species of seabirds, and total species of birds on these same islands can be predicted on the basis of number of species of vascular plants, and to a lesser extent, area of the island. Ecological diversity, although poor in quality, is of prime importance in regulating use of low, sandy, oceanic islands by any seabird. Although terrestrial bird use islands for obtaining food and for nesting whereas seabird use islands only as a nesting and roosting place, species of terrestrial birds and seabirds on islands are associated with similar ecological variables.

The Plecoptera community of a small stream in Oregon, U.S.A. *

Abstract: Summary The Plecoptera community of a small woodland stream in Oregon was studied by examining density and species composition. Four sites were studied using benthos sampling for larvae and emergence trap collections for adults. Sixteen genera and forty-three species were identified with most species occurring in relatively low numbers. A comparison with the species list from an earlier study suggested that the species composition has not changed markedly in 40 years but there were several changes in relative abundance. Species diversity of stoneflies decreased with distance from the headwaters. These changes were correlated with decrease in habitat complexity, decrease in stability of the substrate, and increase in water depth. Examples of longitudinal succession are given as a method enabling the large number of species to partition the habitat. Concurrent benthos and emergence sampling demonstrated differences in emergence success that were correlated with habitat suitability.

A survey of the invertebrates of four streams in The Moor House National Nature Reserve in Northern England

Abstract: Summary The Moor House Nature Reserve, Westmorland, is situated in typical north Pennine moorland and experiences a rigorous climate. Three of the streams arise between 700 and 750 m O.D. and the fourth at 590 m O.D. The sampling sites lie between 570 and 540 m O.D. and conditions in the streams range from slow-flowing peaty-bottomed reaches to typical fast-flowing stony streams. Samples were taken in riffles and pools in May, August and October using the kick method. 111 taxa were recorded from the four streams, 90 of which were identified to the species level. The most abundant and widespread taxa were Leuctra inermis, L. fusca, Rhithrogena semicolorata, Elmis aenea and Chironomidae. Seasonal and annual variation in abundance of several species was marked with L. inermis most numerous in May, E. aenea and Chironomidae in August and R. semicolorata most abundant in October. The total number of animals caught was generally higher in riffles than in pools and the mean number per 60-sec kick for riffles and pools, based on May, August and October samples between 1967 and 1970, ranged from 110 to 128 in the four streams. Capnia bifrons, Paraleptophlebia submarginata, P. cincta, Leptophlebia marginata, Centroptilum pennulatum, Plectrocnemia geniculata, Cyrnus trimaculatus, Lepidostoma hirtum, Hydropsychidae (larvae indet.) and Philopotamidae (larvae indet.), are all additions to the lists of previously studied groups on the Reserve. All the species of Tricladida, Annelida, Coleoptera, Hydrachnellae and Pisidium are here recorded for the first time for the Reserve. Great Dodgen Pot Sike supported the largest number of species and species groups (88) and was characterized by having water with the lowest pH (6.75) of all the streams and by having the most gentle gradient and a relatively stable bottom. The fauna is discussed and compared with that of the adjacent Cow Green area. Some of the differences between these areas may be attributable to the slightly greater variation in flow-conditions and water chemistry in the Cow Green basin. Comparison with other areas in the British Isles are made briefly and it is suggested that habitat diversity may account for the species richness of the Moor House streams.

Foliage arthropod communities of crop and fallow fields.

Abstract: Two crop fields (alfalfa and orchard grass) and two fallow fields (bluegrass and old field) were compared on the basis of plant and foliage arthropod complexity. Plant species richness and foliage height diversity increased substantially from crop to fallow: bluegrass to fallow: old field. The trend in arthropod complexity paralleled this trend in plant complexity but dit not appear to be as striking. Fallow fields typically possessed more species, fever individuals, higher evenness in relative abundance patterns and proportionally more predators. However, crop fields had quite diverse foliage arthropod faunas, and we suggest that high primary productivity of crop fields may somewhat offset lowered plant habitat complexity.