Showing papers on "Species richness published in 1973"

Organization of a Plant-Arthropod Association in Simple and Diverse Habitats: The Fauna of Collards (Brassica Oleracea)

Abstract: Collards were grown at Ithaca, New York, in two experimental habitats: pure stands and single rows that were bounded on each side by diverse, meadow vegetation. The arthropods associated with these plants were sampled on 20 dates over a 3—year period. The status of the herbivore species was measured by their rank in biomass in each sample. The two most prominent species, Phyllotreta cruciferae and Pieris rapae, maintained high status throughout the investigation, but another important species, Brevicoryne brassicae, was absent for an entire season. Pit feeders usually formed the most important herbivore guild. Nevertheless, the guild spectrum, which describes the functional structure of the fauna, varied widely in time and space. The size distributions of species and of individuals were both highly skewed toward the smaller sizes. Herbivore loads, the mean biomass of herbivores per 100 g of consumable foliage, were consistently higher in the pure stands. Moreover, herbivore loads varied significantly with season in each experimental habitat. Both the number of herbivore species and the diversity of the herbivore load were greater in the diverse habitat. Biomass was more heavily concentrated among the prominent herbivores in the pure stands; increased dominance, rather than differences in species richness, appeared to be the major cause for the lower herbivore diversity in this habitat. The diversity of predators and parasitoids was higher in the pure stands. Most of the abundant species found on collards shared a similar narrow range of hosts. As a result the species in this core group of herbivores and parasitoids were regularly associated with each other. Predators and the less abundant herbivores tended to be less specialized and served to link the collard association with the surrounding community. Plant—arthropod associations are representative of component communities, well—integrated systems that form portions of larger compound communities. This distinction facilitates the analysis of community structure. Microclimates and the effectiveness of "enemies" did not appear to differ sufficiently in the two experimental habitats to account for the observed differences in the herbivore load. The results suggest a new proposition, the resource concentration hypothesis, which states that herbivores are more likely to find and remain on hosts that are growing in dense or nearly pure stands; that the most specialized species frequently attain higher relative densities in simple environments; and that, as a result, biomass tends to become concentrated in a few species, causing a decrease in the diversity of herbivores in pure stands.

Resource Utilization and Coexistence of Seed-Eating Desert Rodents in Sand Dune Habitats

Abstract: As many as five species of seed—eating rodents coexist in sand dune habitats in the North American deserts. Among species occuring together the ratio of body weights of adjacent species pairs is usually greater than 1.5. The seed resources of the habitats appear to be apportioned among species chiefly in two ways: (1) rodents differentially harvest seeds of different sizes, and seed size selection is positively correlated with body size: (2) species forage in different areas relative to the cover of perennial shrubs. The species also differ in their annual activity (some are active all year, others may go torpid for short periods or hibernate for several months), but is difficult to evaluate how these differences affect the utilization of seeds. Our estimates of total overlap in resource utilization between species indicate that competition for seeds have an important influence on community structure in desert rodents. In productive habitats species that are quite similar (overlap values greater than 80%) in resource utilization are able to coexist and species diversity is high, but in less productive habitats ecologically similar species are excluded, resulting in decreased species diversity.

Classification and community structure of macrobenthos in the Hampton Roads area, Virginia

Abstract: Benthic macrofauna was sampled by grab at 16 stations in Hampton Roads and the adjacent Elizabeth River, Virginia, USA. Samples were taken in February, May and August. Sampling sites and species were grouped by a classification strategy which basically consisted of the Canberra metric dissimilarity-measure and flexible and group average clustering. Following reallocations, 8 site groups and 16 species groups instructively classified the 47 sites and 93 species considered in the analysis. The sites were grouped into “associations” on mud, muddy-sand and sand-bottom, and those in the Elizabeth River. Species groupings distinguished a few species most frequent at Elizabeth River or mud and muddy-sand sites, larger numbers of species restricted to muddy-sand and sand or solely to sand sites, ubiquitous species, epifaunal species which were microhabitat-restricted, and seasonal species. An analysis of numerically dominant species in the different associations indicated the relative importance of ubiquitous species and seasonally abundant species. Community-structure statistics (species diversity, species richness and evenness) showed definite spatial and temporal patterns. Diversity was high at sand and muddy-sand sites and low at mud and Elizabeth River sites. This spatial pattern was predominantly one of species richness. At Elizabeth River and mud stations, diversity increased from February to August because of increased evenness, while at sand and muddy-sand stations, diversity peaked in May in response to both high species richness and high evenness. The applicability of “community concepts”, the causes of substrate specificity, seasonality and species diversity, and the effects of pollution on community structure are discussed.

Numbers of Mammal Species in North and Central American Forest Communities

Abstract: Latitudinal trends in the species diversity of North and Central American Mammalian communities are documented by examining seven habitats ranging from the tundra of central Alaska to the moist tropical forest of central Panama. The communities are compared with respect to the numbers and kinds of species in each habitat and their size, spatial, and trophic relationships. Fifteen to 16 species occur in the two Alaskan habitats examined, 31—35 species in three forests in the eastern United States, and 70 species in two Panamanian forests, Observed latitudinal changes in species diversity, ecological diversity, and community structure are primarily a result of a southward increase in the number of bat species. The greater variety and year—round availaility of food resources such as fleshy fruits and insects, rather than increased spatial heterogeneity, appear to account for the greater diversity of mammals in the tropical habitats. The structure of Old and New World tropical mammalian communities appears to be very similar. One major difference is that among the bats there are relatively more fruit—and/or pollen—eating species and fewer insect—eating species in the Panamanian community than in Malaya.

Diversity, Floristic Richness, and Species Evenness During a Secondary (Post-Fire) Succession

Abstract: Diversity, species richness, and species evenness were analyzed in II boreal forest areas that had been burned from 0 to 44 years previously. The values of the information measure of diversity, H'. and Hurlbert's probability of interspecific encounter. Delta_1, obtained here are highly correlated. Both show a long—term declining successional trend, but exhibit relatively high values for the period 4 to 11 years after burning. Fluctuations in both appear to be attributable to variations in richness rather than evenness, supporting Pielou and Hurlbert's contentions that the two components of diversity should be analyzed separately. Delta_1 is preferred to H' because, if used in conjunction with a knowledge of spatial heterogeneity, it can provide information about the levels of competition in a community. The results indicate a slight increase in the amount of intraspecific competition during the course of succession, contrary to what might be expected as the outcome of evolution. It is argued that the species present are adapted to the occurrence of frequent catastrophes, particularly fires, so that prevailing evolutionary pressures and their outcome differ from those in more stable environments.

On the Correlations between Certain Diversity Indices

Abstract: Positive correlations are expected between a number of widely used diversity indices. The correlations arise from definitions of the indices, and make it difficult to interpret calculated correlation coefficients between them. The value of these expected correlations depends on the probability distributions assumed to describe the distributions of values of the several indices over samples from different communities. The only indication, in published data, of a biological phenomenon that may possibly influence values these indices take is a decrease in variance of species evenness as species richness increases.

Species and Diversity of Arthropods in the Alfalfa Community

Abstract: The kinds and numbers of arthropods associated with an alfalfa community in New York State were studied. For the whole alfalfa community (591 species), 72 percent of species represented a single species per genus. Single-species-per-genus percentages were not consistently higher for primary members of the alfalfa community comparcd with incidental members. Interspecific competition should have been more intense between primary than incidental members. The calculated species equatability index H' was observed to vary 3- to 4-fold during a season. A new equatability index (Ec) which has many advantages, was employed. The variability of the indices indicates that evenness is not buffered and that it varies in time and probably in space. The conclusion, however, was that neither the species-per-genus nor the species-equatability indices were adequate to describe the species and abundance relationships within the alfalfa community.

Molluscs in Mangrove Swamps: Physiognomy, Diversity, and Regional Differences

Abstract: Vermeij, G. J. (Department of Zoology, University of Maryland, College Park, Maryland 20742) 1974. Molluscs in Mangrove Swamps: Physiognomy, Diversity, and Regional Differences. Syst. Zool. 22:609-624.-This paper on mangrove-associated molluscs is designed to provide comparative data on physiognomy, diversity, geographic distribution of species, and similarities and differences between parallel assemblages in various geographic regions. In Singapore, both the absolute range and the upper limit of the range of maximum adult size and three other parameters of shell shape are smaller in the littoral-fringe tree-associated gastropod assemblage than in either the intertidal tree-associated or sediment-associated groups. Shells in three of the four families in the littoral-fringe exhibit either intemal whorl resorption or apical decollation, possibly resulting from acidic conditions during anaerobic respiration while the animals are exposed to air. Intertidal tree-associated gastropods are morphologically diverse, but there is a tendency toward squatness related to the need for maintaining gravitational stability on hard substrata. In soft sediments, this requirement is obviated, and the diversity of form is even greater. Aside from a number of taxonomic differences between the mangrove assemblages in different provinces, most within-habitat differences in physiognomy and width of geographic distribution are related to species richness. The absolute range, upper limit of the range, and number of categories for all parameters are greater in assemblages of many species than in those with few species. Maximum adult size exhibits a similar correlation with species richness. Physiognomic diversity within a habitat or region is largely independent of taxonomic composition. The high proportion of narrowly distributed species among Singapore littoral-fringe molluscs and the rapid decrease in maximum adult size and number of species in this habitat from Singapore to more peripheral parts of the Indo-West-Pacific suggest that regional differences among littoral-fringe assemblages are greater than those of other mangrove habitats.

Diversity, richness, and evenness during a primary sand dune succession at Grand Bend, Ontario

Abstract: Asymptotic increases in diversity, richness, and evenness are reported from a primary sand dune succession. Rapid increases in diversity and evenness were observed in the first 1000 years of the 48...

Species richness and stand diversity in relation to site and succession of forests in Sarawak and Brunei (Borneo)

Abstract: The combined effects of a strong tendency to endemism and of a variable and diverse, but climatically continually favourable environment provided the extraordinarily large niche hyperspace which has become occupied by the great multitude of tree species, each with an apparently narrow ecological range. These many tree species form communities on the various site types (BRtNIG, in print) which differ distinctly with respgct to species composition, stand structure and physiognomy. These differences seem to correlate with site conditions. In some cases this is clearly obvious. In others, close scrutiny is needed to detect it. The existence of narrowly defined but not clearþ delimited types and the consistent occurrence ofspecies and forest types on certain site types suggest that the environment and the interaction between species produces a vaçt niche hyperspace in the equatorial lowland forest with individually narrow niches for which a species probability of occurrence is greater than for other regions of the niche space.

Observations on the distribution of surface-living land arthropods on the Subantarctic Île de la Possession, Îles Crozet

Abstract: Summary Collecting by various methods in Jan.–April, 1968, of surface-living arthropods on Ile de la Possession, Iles Crozet most of which were already known from the efforts of previous collectors, were made in order to determine to what extent the 46 species are confined to the three main land habitat types distinguished. The results were as follows: The sea-edge habitat is relatively rich, with 10 species, 8 apparently confined to it. Peat-clothed moorland and bog occupying lower ground (about 25–40 km2 in area) has 26 species, including 6 species of Diptera, while the fell-field habitat above about 100 m altitude (120–135 km2 area) with very scanty vegetation, has 24 species. The relatively species-rich fell-field was surprisingly rich in individuals, particularly ectemnorrhine weevils totalling 7 species (some rare), of carabid beetles (3 spp.). About 8 species showed wide distribution in both moorland and fell-field. The existence in the depauperate fauna of the island of at least 5 pairs or triplet...

Food Habits of the Mountain Whitefish, Prosopium williamsoni (Girard)

Abstract: Quantitative and qualitative analyses of organisms eaten by mountain whitefish in the Snake River were undertaken. Abundance of an organism in a whitefish stomach appears to be dependent upon the organism's overall availability. The stomach contents of all size classes differed in taxonomic composition. Overlap in the taxonomic categories of food organisms eaten by fish of size classes II and III was about 50%. Larger fish were more generalized feeders and could utilize a greater size range of prey organisms than could smaller fish. This was reflected in the increase of food length diversity (FLD) and food taxa diversity (FTD) with increasing fish size. FTD was correlated most closely with the taxonomic richness of stomach contents rather than relative abundance of items in each taxonomic category. Hence, merely counting the taxa in stomachs gave some measure of FTD. This suggests that choices concerning the type of food eaten (species richness component of diversity) are most important in affect...

Citrus halimii: A New Species from Malaya and Peninsular Thailand

Abstract: A hitherto undescribed species of Citrus (Rutaceae), indigenous to the Malayan Peninsula and the adjacent peninsular region of Thailand, is identified, named C. halimii, and characterized by data from vegetative, floral, fruit and embryo morphology, chromosome number, ecology, and phytochemical analysis of the fruits, leaves, and stem. ALTHOUGH THE genus Citrus has been studied as intensively as almost any other plant genus, the prevalence of several peculiar features has made species classification singularly difficult. These features are the comparative ease of hybridization, the production of spurious embryos and nucellar polyembryony, the obliteration of many original habitats, the presence of numerous cultivars, including spontaneous mutants, and the often inadequate original descriptions and specimens. A plethora of species names exists: 870 at last count, according to Carpenter and Reece (1969). There are two extremely different schemes of classification. That of Tanaka (1954) recognizes 159 species, while that of Swingle (1943) admits but 16 species. Tanaka clearly has conferred species status on many purely horticultural forms and does not subscribe to a modern biological species concept. On the other hand, Swingle probably recognized too few species. Another investigator (Hodgson 1961) recognized 36 species, which is no doubt closer to the truth, but numerous problems remain. Among these is our poor understanding of the wild tropical taxa. For some of these nothing is known apart from the general data obtainable from herbarium specimens. While extensive breeding and other research programs have been carried out in the past in the U.S.A., Europe, and Japan, the primary emphasis has naturally been on temperate and subtropical taxa. The cultivars of tropical Southeast Asia are much less well known, and agricultural knowledge of their behavior is insufficient. In this context, the recognition of a previously unknown wild Citrus species assumes considerable importance. It is now realised that the great majority of taxa which bear species names are in fact cultivars of various kinds, although they may "breed true" from seed. Nevertheless it may appear that, owing to the rather chaotic state of Citrus classification and the vast number of available names in the genus, the proposal of a new species would be ipso facto rather suspect. On the other hand it must be pointed out that several other new Citrus species have been discovered in the period since 1930, and have been accepted as natural taxa of species rank even when evaluated on the extremely conservative basis of Swingle (Bhattacharya and Dutta 1956, Corner 1952, Hodgson 1961). Historically, plant exploration and systematic analysis has lagged in Southeast Asia, and parts of this region and the adjacent archipelagoes are poorly or quite unexplored botanically. In most genera, the discovery of new species from Malaya, Thailand, or Indonesia is almost a routine occurrence when revisions are made (van Steenis 1954). Equally relevant is the richness of these regions, in which numerous species are endemic (van Steenis 1954). Citrus is undoubtedly a native here, and several species most probably originated in the Malesian tropics, e.g., limes (C. aarantifolia) and pomelos (C. grandis). It is reasonable to suppose that in Citrus, as in other genera, undiscovered species still exist. Because of this background of unsettled classification, peculiar and taxonomically confusing breeding systems, hybrids, and reproductive behavior, an overabundance of names (sometimes ill-defined), and some reluctance to admit that species remain to be discovered, we have been careful to attempt evaluation of as many characters as possible, including macroand micro-morphological characters, ecological data, and phytochemical analysis of fruits, leaves, and stems. 102 BIOTROPICA 5(2): 102-11

Trophic Level Effects on Species Diversity in Arthropod Communities of Forest Canopies

Abstract: Species diversity for arthropod communities inhabiting white pine and coppice canopies was measured using the Shannon Wiener information theory index, H(s), the Margalef index, D, and the Pielou evenness index, J'. The 2 insect orders Coleoptera and Hymenoptera were investigated. The general index H(s) was significantly higher for the more diverse coppice stand than for the white pine monoculture, and was significantly higher for Hymenoptera than for Coleoptera. The other 2 indices demonstrated that differences in diversity between watersheds were due to greater species richness in the coppice, while differences between insect orders were due to greater evenness of individuals in the Hymenoptera. Since the Coleoptera were principally herbivores and the Hymenoptera predator-parasites, results can be interpreted in a trophic level context. It is suggested that, in a plant monoculture, low diversity is not propagated along food chains but rather is recovered at higher trophic levels.

An analysis of the Flora of Natal

Abstract: The recently completed Flora of Natal (Ross, Mem. Bot. Surv. S.Afr. No. 39, 1973) is analysed numerically and a brief comparison is made with the total number of families, genera and species recorded by Bews in his Flora of Natal and Zululand (1921). A number of diagrams illustrating the proportional representation of certain elements of the Flora are provided. The families whose species constitute more than 0 ,5% of the total number of species in Natal, and those genera containing 15 or more species, are tabulated. The marked inverse relationship between numbers of genera and families is illustrated. Brief mention is made of some of the elements contributing to the richness of the flora.

Pattern Diversity in a Eucalyptus Forest

Abstract: Pattern diversity is a measure of the degree of spatial intermingling of species in a community of sessile organisms, combining the effects of species richness and equitability with those due to spatial patterning. The pattern diversity index was computed for an Australian Eucalyptus forest and the results interpreted in the light of an earlier analysis of the pattern of component species. The pattern diversity index was found to be sensitive to the number of individuals sampled at each point, reflecting a dependence of the index on the scale of species pattern, and hence on the scale of sampling. Limitations of the method in relation to low sample sizes and to particularly diverse samples are also discussed.