Showing papers on "Species richness published in 1976"
TL;DR: A heterogeneity index, D, derived from the point—quarter technique was significantly correlated with bird species diversity (BSD) for several shrub and forest areas and predicted BSD for a series of similar brushlands where other indices had failed.
Abstract: A heterogeneity index, D, derived from the point—quarter technique was significantly correlated with bird species diversity (BSD) for several shrub and forest areas. It predicted BSD for a series of similar brushlands where other indices had failed. Species richness increased faster than species overlap in a series of increasing complex habitats up to the forest stage. Species overlap was negatively correlated with patchiness. Additional species may be accommodated in preforest habitats primarily by horizontal spatial segregation facilitate by the presence of additional patches. New patches result from the addition of layers of vegetation. In late shrub or forest stages other kinds of segregation such as vertical segregation become important to species packing. Patchiness, as measured here, has a proximate effect on avian diversity. The extent or existence of latitudinal gradients in habitat patchiness and the effect on bird species diversity is unknown. The need remains for a universal simple, yet meaningful, heterogeneity index which incorporates both horizontal and vertical variability of vegetation.
417 citations
TL;DR: It is concluded that adverse abiotic conditions, rather than primary production or food density, limit the occurrence of species and in that way biomass in most of the Wadden Sea.
287 citations
TL;DR: Sweep samples of insects at 200, 1600, 3550, and 3600 m elevation in secondary vegetation in the Venezuelan Andes near Merida show that the greatest number of insect species and dry weight occurs at the intermediate elevation and that large insects are much less abundant at high than low elevations.
Abstract: Sweep samples of insects at 200, 1600, 3550, and 3600 m elevation in secondary vegetation in the Venezuelan Andes near Merida show that the greatest number of insect species and dry weight occurs at the intermediate elevation, that the species richness of Diptera and parasitic Hymenoptera is not as proportionately reduced by elevation as is the species richness of other insect groups, that at higher elevations there are a reduced number of species and an increasingly unequal distribution of the individuals among the species, and that large insects are much less abundant at high than low elevations. These results confirm trends first indicated in an earlier elevational transect of Costa Rican insects. WE REPORT the results of sweep sampling the insect community at 3600 m, 3550 m, 1600 m, and 200 m elevation in the Venezuelan Andes near Merida, and at 3380 m in Costa Rica. The study is a continuation of the examination of large scale heterogeneity in tropical insect community structure that was initiated by Janzen (1973a,b). Here, we ask how sweep samples of low secondary vegetation differ at elevations characterized by paramo, mid-elevation evergreen forest which is generally converted to coffee and sugar cane plantations in Venezuela, and lowland ("tierra caliente") evergreen forest, which is generally converted to cattle pasture and sugar cane in Venezuela.
203 citations
TL;DR: Three diversity indices were used to assess the community structure: Shannon's formula, its measurement of evenness, and Sanders' rarefaction technique and the measure of species richness were more satisfactory for this kind of assessment.
Abstract: took about eight years. By then the composition of the community was similar to that recorded forty years earlier. The successional changes in number of species, individuals and biomass are illustrated for the total fauna as well as for dominating groups. The sequential changes of some numerically dominant populations showed a bell-shaped curve pattern. During the first years after pollution abatement, when polychaetes dominated, these population changes were drastic but evened out in later seral stages. The role of larval recruitment in succession is discussed. Three diversity indices were used to assess the community structure: Shannon's formula, its measurement of evenness, and Sanders' rarefaction technique. As tools for assessing pollution or recovery, the two former had to be used with care, as the highest values were recorded at the beginning of the recovery process when the individuals found were few but evenly distributed among the few species present. The rarefaction technique and the measure of species richness were more satisfactory for this kind of assessment.
196 citations
TL;DR: This guild demonstrates that overlap values may not equal competition coefficients and that high overlap may exist because competition is rare and that herbivorous insects may be among the least likely groups to exhibit the patterns predicted by competition theory.
Abstract: Resource exploitation and competition were measured for 13 herbivorous stem—boring insects inhabiting a climax prairie in Illinois. Nine species overlapped > 70% in their exploitation of plant species, stem sizes, and locations within stems, but competition was detected between only two species. In this case the competition resulted from aggression rather than exploitation for limited resources, and exclusion may be delayed or prevented by specific behaviors or refuges. To quantify how closely the guild members were packed upon the available resources, probabilities of coccurrences between species were calculated using resource abundances, population sizes, and overlaps in resource exploitation. The species packing averaged over the entire guild was 30%, but some species had several potential competitors and probabilities of cooccurrences were > 60%. This species structure offers the conditions for diffuse competition, but competition seldom occurred because stems could support several individuals and resources were generally nonlimiting. Although the potential for competition is high and species probably compete occasionally, the high resource overlap and species richness that competition has not been a major organizing force within this guild. When factors known to influence competition are considered, it seems possible that competition has been too infrequent, mild, or nondirectional to cause strong selection for competitive avoidance or displacement. This guild demonstrates that overlap values may not equal competition coefficients and that high overlap may exist because competition is rare. This guild is probably not unique in lacking competitive organization; herbivorous insects may be among the least likely groups to exhibit the patterns predicted by competition theory.
161 citations
TL;DR: Seasonal fluctuation of water level is the most critical environmental factor affecting the fish community of the Everglades marshes, and during a 27—mo period of water—level stability, fish density decreased but biomass, average size of fish, species richness, and species diversity increased.
Abstract: Seasonal fluctuation of water level is the most critical environmental factor affecting the fish community of the Everglades marshes. During a 27—mo period of water—level stability, fish density decreased but biomass, average size of fish, species richness, and species diversity increased. These changes were accompanied by a functional shift from the dominance of small sized omnivorous species to the dominance of larger sized carnivorous fish. The changes resulted from immigration of large carnivorous species poorly adapted for survival in fluctuating marshes. Increased predation assumed the determining role in restructuring the community under environmentally stable conditions. The fish community of Everglades marshes oscillates between opposing tendencies of species domination, which depend on the degree of water level stability.
157 citations
TL;DR: This is the first demonstration of how specific environmental factors affect population density and species diversity of benthic invertebrates in a coral reef-associated habitat.
Abstract: Structural complexity of the habitat significantly increases population density and number of species in assemblages of predatory gastropod molluscs (families Conidae, Muricidae, Mitridae and Vasidae) on intertidal, generally smooth, horizontal limestone platforms fringing tropical Pacific islands. The important topographic features are physical (depressions partly filled with coral rubble) and biotic (thick algal turf binding sand). Higher population density and species richness in areas with than without such natural refuges, and following experimental addition of artificial refuges on portions of habitat lacking them support this hypothesis. Two species of Drupa differ from the other species present in not utilizing refuges during times of physical stress; this is attributed to their depressed shell and broad, tenacious foot. Highest gastropod densities occur in steep-sided depressions and those containing much coral rubble and sand, suggesting that these are important qualities of refuges. We believe this is the first demonstration of how specific environmental factors affect population density and species diversity of benthic invertebrates in a coral reef-associated habitat.
137 citations
TL;DR: A multiple regression equation including flood frequency and litter depth as variables was used to predict the impact of altered flooding regimes (due to reservoir construction downstream) on spider diversity.
Abstract: Species composition and diversity of a guild of wandering spiders was studied by pitfall trapping over an elevational gradient in an Illinois streamside forest. Differences in flooding frequency and their effect on the litter habitat (removal and/or compression) account for a majority of the variation in the number of species between elevations. Changes in spider communities with elevation over the flooding gradient are indicative of a transition from a harsh to a moderate environment: (1) increased abundance and species diversity; (2) decreased dominance of flood tolerant species accompanied by increased dominance of species with specialized microhabitats found in complex litter; (3) greater similarity in species composition between sites; and, (4) a change in species-abundance curves from a geometric series to a lognormal distribution. The influence of the flooding regime in regulating community structure of spiders is discussed. A multiple regression equation including flood frequency and litter depth as variables was used to predict the impact of altered flooding regimes (due to reservoir construction downstream) on spider diversity.
105 citations
TL;DR: The effects of area, environmental heterogeneity, and site favorability on plant species diversity and slope of the species—area curves were evaluated at thirty study sites in shrub—dominated communities within the pinyon—juniper zones of central Utah and northern New Mexico.
Abstract: The effects of area, environmental heterogeneity, and site favorability on plant species diversity and slope of the species—area curves were evaluated at thirty study sites in shrub—dominated communities within the pinyon—juniper zones of central Utah and northern New Mexico. Species diversity, as measured by total number of species per site, varies widely (24—87 species per hectare). Plant species diversity is highly correlated with increasing size of the area at each site (average r2 = .92). Environmental heterogeneity is also strongly positively heterogeneity account for > 98% of the variation in species number. Overall site heterogeneity and favorability combine to account for 74% of the observed variation in species number at Utah sites and 84% among New Mexico sites. Species diversity within these communities is largely controlled by two abiotic variables: (1) the amount of available moisture and (2) the number of different soil types within the site. Slope of the species—area curve (z—value) varies widely among the several study sites (.09—0.28). The observed values overlap expected z—values for continental communities. Environmental heterogeneity is shown to be positively associated with z—value. At Utah sites, heterogeneity of site solar irradiation, potential soil moisture, and soil depth explain 66% of the variation in z—values. At New Mexico sites, heterogeneity of solar irradiation, soil depth, and surface rock cover account for 90% of the variation in observed z—values.
104 citations
TL;DR: It was postulated that there was a constantly changing series of interactions of the various community components that precluded a single mechanism for the observed phenomena, and a general pattern of an annual double peak of fish and invertebrate richness and diversity was noted.
101 citations
TL;DR: Breeding birds were censused along four elevational gradients in the Adirondack Mountains, New York, and the Green Mountains, Vermont and found no convincing cases of altitudinal competitive exclusion between species.
Abstract: Breeding birds were censused along four elevational gradients in the Adirondack Mountains, New York, and the Green Mountains, Vermont. The bird communities of the four gradients were basically similar in species composition, richness and amplitude patterns. Three measures of species diversity decreased with increasing elevation. Low-elevation communities contained higher proportions of rare species and the relative abundances conformed to the broken-stick distribution. At higher elevations the communities showed greater dominance and the dominance-diversity curves approached geometric series. The species characteristic of high-elevation communities had the broadest altitudinal distributions. The upper and lower distributional limits of most species were independent of one another except at “ecotones” where marked changes in vegetation structure occurred. On each mountain, slightly more than half of the species’ limits coincided with ecotones. This is a significantly greater proportion than has been found in similar studies of tropical forest bird communities. In further contrast to tropical communities, we found no convincing cases of altitudinal competitive exclusion between species. Interspecific competition in the past seems to have been translated primarily into differences in habitat selection by temperate forest birds. Many of the differences between temperate forest breeding bird communities and tropical ones can be understood in terms of the migratory nature of most of the temperate species and the lower species richness in temperature forests.
TL;DR: There are more species associated with corals in the fluctuating environment than in the constant environment, supporting the hypothesis that species equilibrium within habitats is maintained by measurable ecological factors—in this case, the effects of a natural physical disturbance.
Abstract: The number of decapod species associated with the coral Pocillopora damicornis is compared between two regions on the Pacific coast of Panama which are of the same geologic age but differ in environmental characteristics. The relationship between number of species and coral head size does not differ between the two regions but species composition among coral heads is more variable in the fluctuating environment. Thus there are more species (55 compared to 37) associated with corals in the fluctuating environment than in the constant environment. These data impugn the concept that environmental constancy increases species richness. They support the hypothesis that species equilibrium within habitats is maintained by measurable ecological factors—in this case, the effects of a natural physical disturbance .
TL;DR: In this paper, the authors identified 209 species of free-living marine nematodes in four sedimentary environments off North Carolina, and 106 were restricted to one of four habitats.
TL;DR: Four species of ciliate protozoans isolated from a small pond were grown monoxenically on eight species of bacteria, suggesting that the wild bacteria possessed mechanisms to discourage predation.
Abstract: Four species of ciliate protozoans isolated from a small pond were grown monoxenically on eight species of bacteria. Four of the bacterial species were common "laboratory" species, the others were isolated from the same pond as the ciliates. The ciliates showed different growth responses to the wild bacteria, confirming the hypothesis that they were specialized with respect to the bacterial species on which they could grow. The laboratory bacteria all permitted good growth of all ciliates, suggesting that the wild bacteria possessed mechanisms to discourage predation. The results are interpreted as supporting the concept that food specialization may be part of a niche partitioning that accounts for the high species richness observed in protozoan communities.
TL;DR: Thirty-four beaches, located between central Washington and the Mexican border, were sampled for cover by replicate strip transects, and the results summarized by composite profile diagrams showed that beach vegetation seems less well correlated with macroclimate than inland vegetation.
Abstract: Thirty-four beaches, located between central Washington and the Mexican border (approximately 47-33? N), were sampled for cover by replicate strip transects, and the results summarized by composite profile diagrams. The zonation patterns of twenty species revealed that the majority could be found in the leading (seaward) edge of vegetation, but most taxa increased in cover with increasing distance from mean tide line; that is, few species exhibited an ecological optimum in the most severe part of the vegetated beach. Even in the most inland portion of the beach plant cover and species richness were typically low (about five species, 2000 cover). Cluster analysis revealed five grouips of stands. The groups were poorly correlated with latitude, except for a major break at 370 N in central California. Regressions showed, as a first approximation, that community composition correlated with factors that reflect protection from disturbance by waves, man, or introduced taxa. Beach vegetation seems less well correlated with macroclimate than inland vegetation. However, the distribution limits of some species did correlate well with macro-climate.
TL;DR: The numbers of grasshopper species in North and South American deserts are compared and Recruitment of species through immigration and colonization may be greater in North America where the deserts have richer source areas.
Abstract: The numbers of grasshopper species in North and South American deserts are compared. The Sonoran Desert of Arizona has a significantly richer fauna than the floristically similar Monte Desert of Argentina. Recruitment of species through immigration and colonization may be greater in North America where the deserts have richer source areas. Niche space differentes do not adequately account for the different diversities. South American deserts may also have fewer species because they were more strongly affected by Pleistocene events than their North American counterparts. Evidence that North American deserts are older is also discussed.
TL;DR: The effects of sheep stocking intensity on the species richness, evenness, diversity, relative abundance and spatial distribution of Collembola are reported for sown perennial pastures at Armidale, New South Wales, Australia.
Abstract: The Collembola are an important component of the invertebrate fauna of temperate grasslands and their abundance is influenced by domestic herbivore numbers (King & Hutchinson 1976). High stocking intensity modifies substantially the environment for invertebrates in sown pastures and this may affect their species richness, composition and spatial distribution. Changes in species diversity of grassland invertebrates have been associated with grazing (Morris 1971) and mowing and burning (Bulan & Barrett 1971). In this present paper the effects of sheep stocking intensity on the species richness, evenness, diversity, relative abundance and spatial distribution of Collembola are reported for sown perennial pastures at Armidale, New South Wales, Australia. The Collembola are a convenient group for studying the impact of management on grassland communities since they are abundant, are distributed throughout the herbage, litter and soil layers and their taxonomy has been well studied. The stocking treatments started in 1963 and the Collembola were collected in 1971-72 by which time it was assumed that the populations reflected the effects of the range of grazing intensities applied.
01 Jan 1976
TL;DR: In this article, King I LANDS ON MARS is described as a triumph of space technology, but not philosophically significant, but then we should not look for philosophy in material objects other than human brains, for there is philosophy in every piece of human knowledge and in or behind every step of rational action.
Abstract: Headline, 20th July, 1976: VIKING I LANDS ON MARS. Certainly a triumph of space technology. But philosophically significant? Doubtful, but then we should not look for philosophy in material objects other than human brains. If we look for philosophy at the right spots in the technological process we are bound to find some, for there is philosophy in or behind every piece of human knowledge and in or behind every step of rational action.
TL;DR: The familiar dynamic equilibrium theory of island biogeography predicts that the equilibrial number of species on an island is a function of rates of immigration and extinction, which in turn are dependent on area and distance from a source of colonizers.
Abstract: The familiar dynamic equilibrium theory of island biogeography (MacArthur and Wilson 1967) predicts that the equilibrial number of species on an island is a function of rates of immigration and extinction, which in turn are dependent on area and distance from a source of colonizers. A large island would tend to have greater habitat diversity supporting more species and would tend to have larger populations less prone to extinction than would a small island. Likewise, an island that is farther from a source of propagules is likely to have a reduced immigration rate of new species and hence a lower equilibrial species number than an island close to a source of colonizers.
TL;DR: Findings support the concept of birds representing an "equilibrium" taxon in terms of the evenness component of species diversity and suggest that resident bird populations be considered as "indicator taxa" when attempting to measure and evaluate the impact of man-made stress on total ecosystems.
Abstract: Two beech-maple forests, one virgin (control) and one selectively cut (experimental), were analyzed in detail for man-made stress effects upon tree-avian community structural relationships. Vegetation analyses revealed that Hueston Woods, a virgin beech-maple forest in southwestern Ohio, was stratified into two distinct canopy layers, whereas Lewis Woods, a previously thinned beech-maple forest in Ecentral Indiana, contained four distinct canopy strata. Although sugar maple (Acer saccharum) and American beech (Fagus grandifolia) were most abundant in both community types, they were truly dominant in terms of importance values in Hueston Woods. Lewis Woods had a more heterogeneous vegetational structure and greater absolute density, species diversity (H'), species richness (D) and species evenness (e) values than Hueston Woods. Lewis Woods resembled an earlier seral stage of ecological succession. This supports the hypothesis that species diversity is less in a climax community than in preclimax conditions. Avian analyses revealed significant differences (p < .05) for the resident evenness (apportionment) values between the two study areas. This difference was consistent through the 10-week (25 April-3 July 1973) observation period. Although Hueston Woods contained 38 resident species within a 15-acre (6.1 ha) study plot as compared to 32 species for Lewis Woods, evenness values were slightly greater for Lewis Woods. These findings support the concept of birds representing an "equilibrium" taxon in terms of the evenness component of species diversity. This study presents strong evidence that birds do tend to depict and to respond to the overall structure of a major plant community. It is suggested that resident bird populations be considered as "indicator taxa" when attempting to measure and evaluate the impact of man-made stress on total ecosystems.
TL;DR: In this article, a quantitative index of decrements in species richness from one biogeographic province to another is proposed to test the effects of plate tectonics on the distribution of cypraeid species.
Abstract: The distribution of living species of the Cypraeidae (Mollusca: Gastropoda) features two centres of species richness, one in the Western Pacific and the other in the west central Indian Ocean. Species richness declines from these two areas. By formulating a quantitative index of decrements in species richness from one biogeographic province to another, it is possible to test the effects of plate tectonics on the distribution of cypraeid species. Using a model developed by Valentine (1971), the data reveal significantly different biogeographic consequences of plate tectonic elements (ridges and subduction zones; F= 16 04, P < 0 005). The distribution of regional endemics and widespread species are consistent with this result. These data can also be used to infer the direction of migration from region to region. The distribution of higher levels of organization (tribes and sub-families) suggests that earlier lineages of the Cypraeidae dispersed through the Tethys corridor while more recent ones radiated widely in the IndoPacific after the suturing of Africa and Eurasia. Thus, the effects ofplate tectonics appear to be a major influence on the biogeography of the Cypraeidae. These data are compared to others in the literature, and some implications of them are discussed.
01 Jan 1976
TL;DR: The faunal Optimum is explained by the favourable combination of a suite of factors, such as relatively stable temperatures and increased salinity, sufficient aeration, and a strong “rain” of larvae and nutrition where the upper water mass is barred by the pycnocline.
Abstract: Great Belt, Vejsnas Rinne and Boknis Rinne form a major interconnected channel System of approximately 80 km length and 30 m depth on the Kiel Bay sea floor, which generally is only some 10 to 20 m deep. 1971 to 1973, 32 transects were sampled across the channel slopes using narrow Station distances and systematically adding data (T°, S°/oo) from 5 hydrographic cross sections over a one and a half year period. A quantitative, combined study of the molluscan fauna, dead shells and Sediments yielded the following results. 30 species of bivalves and 19 of gastropods were sampled as livingspecimens. According to their long life span, Cypritta islandica is dominant in the deep and the Astarte species on the upper part of the channel slope. Macoma baltica is dominantin a third, more shallow Zone, which is actually outside of the channels. Abra alba is the most persistent species of the channels being present in 86% of all samples. Except for Hydrobia, gastropods display low numbers of presence and abundance and are almost never dominant.
The bottom level of the thermohaline pycnocline impinges on the channel slope as a rule between (15-)18 and 22 (-25) m depth. This boundary layer is clearly reflected by the fauna, i.e. by maximum numbers of species and species richness, of species presence and abundance, as well as of the biomass of total molluscs and of most of the single mollusc species. The faunal Optimum is explained by the favourable combination of a suite of factors, such as relatively stable temperatures and increased salinity, sufficient aeration, and a strong “rain” of larvae and nutrition where the upper water mass is barred by the pycnocline. Substrate conditions (± 50 % of Sediment < 63 p) might be favourable as well.
The deeper water mass of the channel System is increasingly plumbed by the pycnocline and correspondingly poor in oxygen concentration towards the inner end of the bay. The oxygen deficiency more and more confines the Optimum beit of the molluscs from below, and causes a distinct elevation of the maximum numbers of species, species richness, species dominance and biomass from the entrance towards the inner part of the bay from 20-24 to 15 -20 m depth. Increasing distance from the bay ’s entrance , (the Great Belt) does not exert any other influence on the molluscan fauna. Averaging the whole transects, the mean numbers of species, species richness, species presence and biomass stay constant in line with constant T-S conditions. The molluscan Optimum belt is widened on the slope towards the deep and partly doubled at current and water exposed parts of the slope, where it also achieves its absolute maximum numbers. No molluscan species is bound to a specific type of Sediment, though eventually certain Sediments may be preferred. Mud forms an exception in showing a clear decrease of the number of specimens (by an overlap with the factor oxygen deficiency). Except for the well known general reduction of species in the Kiel Bay, the distribution pattern of temp erature and salinity exerts only minor influences on the fauna. The dead-shell species as semblage generally reflects the living one. On the whole, they correspond with their composition of species, the zonation of dominant species (middle, emergent Astarte beit) and the distribution and elevation pattern of the maxima of species, species richness and dead-shell quantities.
A downslope transport of shells is inferred, among other things, from a stronger presence of (dead-shell) species in the deeper part of the channel. As measured by the lateral displacement of the mollusc maximum belts, the transport amounts 1 to 3 m in vertical distance, rarely up to 7 m at current exposed slopes. These numbers correspond to 30-75 m horizontal distance. Besides currents, extreme wave action is a possible cause.
Current induced long-distance transport of dead shells generates increased numbers of species, species presence and dead-shell quantities at the channel bottom, especially behind narrow passes. Hotvever, taking into account the undisturbed distribution of dominant species, the quantity of reworked shells must be insignificant.
First indications of the shell production can be derived from the living-dead ratio of shell samples — notwithstanding the varying amounts of carbonate dissolution. For instance, the production of Astarte species is some 13 times smaller than the one of Abra alba and 7 times smaller than that of Cyprina islandica. — A general strong change from living to dead-shell dominance occurs below the pycnocline at 20 to 24 m depth. In the case of a fossil analogue of a Baltic Sea channel, marked shell horizons with a broad species spectrum most probably correspond to a molluscan zone at the
level of the mean pycnocline Position.
TL;DR: Two measures of 'effective species richness' (MacArthur 1965; Hill 1973) have been borrowed from information theory to adjust this simple measure of diversity for relative abundance differences.
Abstract: One commonly measured property of a collection or commonly estimated property for a community (an 'infinite collection') is its species diversity. The most simple measure of diversity, species richness (total number of species in the collection or community), ignores relative abundance differences between species. To adjust this simple measure of diversity for relative abundance differences, two measures of 'effective species richness' (MacArthur 1965; Hill 1973) have been borrowed from information theory: (1) the Brillouin H (Brillouin 1962) appropriate for collections (Pielou 1966b)
TL;DR: Bimonthly trawl catches at seven stations in the Piankatank River, Virginia, for the period July 1970 to May 1971 included 3417 specimens representing 41 species as mentioned in this paper.
Abstract: Bimonthly trawl catches at seven stations in the Piankatank River, Virginia, for the period July 1970 to May 1971 included 3417 specimens representing 41 species. Numeric and species abundance in the river reflected a seasonal pattern of species specific migrations with peak numerical abundance in September and a decline in marine fishes during winter.
TL;DR: The results of this study confirmed that temephos and chlorpyrifos were selective mosquito larvicides, controlling bloodsucking Nematocera without significantly changing the species richness and diversity of the nontarget salt marsh aquatic insect community or altering the densities of the dominant insects.
Abstract: The effects of 4 biweekly applications of recommended dosages of the mosquito larvicides temephos and chlorpyrifos on the community structure and seasonal succession of aquatic insects inhabiting salt marsh potholes were examined. Using an open-ended cylinder, benthic, neustonic and nectonic organisms were sampled at weekly intervals in treated and untreated potholes from May 29 through Aug. 15, 1974. Twenty species of aquatic insects were recovered, including both larval and adult life stages. One corixid, Trichocorixa verticalis (Fieber), dominated the pothole community. Effects of the larvicides on insect community structure were tested by monitoring species richness, species diversity, and densities of dominant, subdominant and predatory insects before and after pesticide applications. The results of this study confirmed that temephos and chlorpyrifos were selective mosquito larvicides, controlling bloodsucking Nematocera without significantly changing the species richness and diversity of the nontarget salt marsh aquatic insect community or altering the densities of the dominant insects.
TL;DR: Mist-netted samples of forest understory birds in neotropical (Costa Rica) and temperate (Illinois) forests (during spring migration) supported certain earlier observations: the neotropic understory sample contained more species, more rare species, and more species that use resources not sufficiently available in temperate forest.
Abstract: Mist-netted samples of forest understory birds in neotropical (Costa Rica) and temperate (Illinois) forests (during spring migration) supported certain earlier observations: the neotropical understory sample contained more species, more rare species, and more species that use resources not sufficiently available in temperate forest.During spring migration in Illinois, the number of bird species in a mist-netted sample of the community approaches (albeit temporarily) that of neotropical forests and is sometimes even equivalent. But the constitution of these samples seems to be quite different in different regions. Costa Rican samples showed greater within-habitat variability and individual recapture distances were shorter, implying a greater local patchiness of bird distributions than in Illinois in spring.
TL;DR: Neither trapping method should be used alone in studies concerning the entire tabanid community, but can be used effectively together.
Abstract: A comparison was made of the effectiveness of malaise trapping and aerial netting for sampling a community of 50 species of Tabanidae collected near Deer Lake, Boonton, NJ during 1974. Five sites in the study area were sampled by malaise traps and by netting about the head with an insect net. Comparisons were made of 4 community and 4 population parameters. No significant difference existed between the species richness of the community of flies sampled by each method, but malaise traps sampled the tabanid community with greater diversity and evenness than did netting. The species composition of the community trapped by each method differed substantially. Hybomitra and Tabanus were sampled in significantly greater numbers by malaise traps while netting favored the dominant Chrysops species. Seasonal niche breadths, seasonal ranges and seasonal distributions were measured concordantly by each sampling method. Neither trapping method should be used alone in studies concerning the entire tabanid community, but can be used effectively together.
TL;DR: The reaction of the three species to density at various stages of the life-cycle was studied, and the influence of soil surface heterogeneity on interference between species was examined.
Abstract: species. The life-span and the timing of the life-cycle of the three species are similar. They flower and germinate throughout the year and large numbers of their seedlings often emerge in mixed clusters. The three species occur together and are likely to compete for limited available resources. Pattern analysis has shown that the distribution of the three weeds is related to soil surface microtopography (M. A. Pemadasa, unpublished); Bidens chinensis is relatively more abundant in 'hollows' than on 'hummocks', while the converse is true for the other two species. Soil surface heterogeneity, therefore, appears to play an important role in controlling the size of the populations of the three species. Harper, Williams & Sagar (1965) argued that the relative abundance and cohabitation of different species in nature may be determined by the availability of 'welcoming microsites' on soil surfaces, but information regarding the effect of soil microtopography on interference between species is still scanty. Two aspects of the ecology of the three weed species were studied in the present investigation. Firstly, the reaction of the three species to density at various stages of the life-cycle was studied, and secondly the influence of soil surface heterogeneity on interference between species was examined.
01 Jan 1976
TL;DR: The relations and seasonal variations of some diversity indices of the phyto plankton were studied in different types of lakes to study their correlation with each other and with the species richness and biomass.
Abstract: The relations and seasonal variations of some diversity indices of the phyto plankton were studied in different types of lakes. The indices compared were the species richness index (d = S—1/ln N),_Shannon and Wiener's index (H = £ pi In pi), the evenness index (e = H/ln S) and the index of the concen tration of dominance (c = 2 (ni/N)2. The indices were correlated with each other and with the species richness and biomass, but the slopes of the correlation lines varied between the seasons and the different lake types.
TL;DR: 56 main areas are discussed which are in urgent need of protection from commercial speculation and the threat of irreparable damage and the authors hope that national and international public opinion will encourage the Italian Government to establish many more protected territories and to provide the resources for realistic management.