Showing papers on "Species richness published in 1972"

Competition among Fugitive Species in a Harlequin Environment

Abstract: We examine the qualitative behavior of differential equations for the proportion of insular patches of each of two kinds of habitat occupied by each of two species with characteristics rates of migration between patches and of local extinction within a habitat. Certain migration and extinction rates result in stable coexistence, even of closely similar species; others lead to competitive exclusion, even when each species is competitively superior in one kind of habitat. For a community of many species in many habitats, we surmise qualitative limits to the subdivision of resources, and alternative stable communities. Our results extend to species that live in successional or ephemeral habitats. We therefore conjecture equilibrial theories for the number of patches of habitat occupied by insular species, fugitive plants and invertebrates, or infesting parasites.

Species densities of predators and their prey

Abstract: Any given species of snake tends to eat one or a very few basic prey types, and sympatric snake species tend to concentrate on different prey species. When correlations between numbers of sympatric prey species and snake species densities in various feeding guilds are examined by the method of path coefficients, distinct patterns emerge. Much of the variance in numbers of sympatric snake species is related to prey species densities. This effect is not due to common correlation with latitude. Correlations between the number of sympatric snake species in particular feeding guilds and the number of sympatric species of nonprey are, in nearly all cases, due to common correlation with latitude. These observations support the view that where there are more species of prey, more species of predators can coexist because there are more ways to avoid competition for food. This relationship is very nearly all that is required to explain observed latitudinal gradients in number of sympatric species of snakes in some ...

Bird Species Diversity: The Effect of Species Richness and Equitability on the Diversity Index

Abstract: A study of bird species diversity (BSD) on three seral stages characteristic of secondary succession on the New Jersey Piedmont was done during the winter of 1968—69, the spring of 1969, and the summer of 1969. The seral studies were a 2— to 33—year—old field (the herbaceous field), a 30—year—old field (the cedar field), and a climax oak—hickory forest (the oak forest). Two study plots, each with an area of 2 hectares, were chosen within each seral stage. Diversity indices were calculated using the Shannon—Weaver information formula, H'=—-Σpilogepi. The species count (species richness) was found to account for many of the differences in BSD between the seral stages. The evenness with which species were numerically distributed (equitability) was found to be lowest and to be lowest and to have its greatest influence on the diversity index in the herbaceous field, due to the presence of large flocks of non—nesting species. Equitability was higher and more constant in the cedar field and oak forest. Territoriality was thought to account for the higher equitabilities observed in summer. In winter, the more rigorous environment was thought to be a factor in lowering the equitability at least in the cedar field.Equitability was not lowered as much in the oak forest, possibly due to aggregations of birds into mixed species flocks. The cedar field and oak forest were qui te different in the seasonal patterns of equitability. Both species richness and equitability were concluded to be important parameters in ecological study.

Species diversity of marine macrobenthos in the Virginia area

Abstract: Species diversity of benthic macro-organisms as measured by Shannon’s formula was highest on the outer continental shelf. Benthic diversity was higher in polyhaline zones of estuaries than on the shallow shelf and decreased sharply into the mesohaline zone, declining to the lowest in oligohaline zones. In addition to environmental stability and salinity regime, sediment grain size and pollution also affect species diversity. Analysis of the components of informational diversity, species richness and equitability indicates that the richness component accounts for most of the observed pattern, although both components are important to within-habitat differences.

Temporal Changes in Populations and Species Diversity in a California Rodent Community

Abstract: Population trends and their proximate effects on the species diversity of a rodent community were examined on a stand of coastal sage scrub in southern California, from the summer of 1968 to the autumn of 1969. The rodents comprising the fauna were Dipodomys agilis agilis, Perognathus fallax fallax, P. longimembris pacificus, Peromyscus eremicus fraterculus, P. maniculatus gambellii, P. californicns insignis, Reithrodontomys megalotis longicaudus, Neotoma lepida intermedia , and Neotoma fuscipes macrotis . Live-trapping was done at monthly intervals for a period of 15 months. Individuals collected were examined for reproductive condition, marked and released. Periods of population increase, decrease, or stability were accompanied by variable patterns of survivorship and addition of residents and transients. During periods of population decrease the rodents exhibited reduced survival with the exception of P. maniculatus , which showed increased survival. For the increase phase of the rodent populations, survival was equal to, or greater than, mean survival for the entire period of study; however, the addition of new residents and transients was often high ( P. maniculatus and N. lepida ). The temporal changes in these population components led to asynchronous fluctuations in population densities of the rodents, which yielded the major changes in species diversity. This is further emphasized by examining the correlation of population numbers between the six commonest species. Only six of the 15 pair-wise correlations were significant. Rodent species diversity was measured by employing Brillouin's information formula. Of the three components of diversity—relative abundance, species number, and sample size—a significant relationship was found between species richness and diversity ( r = +0.910), and sample size and diversity ( r = +0.566). Although uncorrelated with diversity, evenness was important, as some of the diversity changes between months were due to shifts in evenness and not changes in species numbers. The fluctuations in the relative abundance of species and the variable presence of the rarer species led to the temporal fluctuations in species diversity.

Feature, patch and refuge area: some influences on diversity of bird species

Abstract: Censuscs of birds (individuals and species) were made in northern Queensland in woodland habitats that were near special features (streams, swamps, rocky outcrops) and in habitats representative of the features themselves. Those features whose habitat was more varied than the surrounding woodland supported a higher diversity of bird species than did the woodland. This was not, primarily, because the features supported a distinct and discrete avifauna, but rather it seemed because some specific need of a particular species was provided by the feature and that species could now use the area adjacent to the feature or because the feature concentrated certain resources relevant to several species common to the general area. The features studied, therefore, importantly influenced the diversity of bird species in contiguous woodland. Influences of this kind upon local diversity of bird species may be common in Australia and would call in question the value here of census techniques developed for northern temperate avifaunas and environments.

Studies on the arthropod fauna of alfalfa: ii. arthropod–fungus associations

Abstract: Observations were made during 1967 to 1969 at Ithaca, N.Y., supplemented by collections at New Cumberland and Carlisle, Pa., on arthropods associated with fungi occurring on alfalfa, Medicago saliva L. Five species of Coleoptera, two species of Diptera, one species each of Collembola and Psocoptera, and nine species of Acari were reared or collected consistently from fungus-covered alfalfa leaves, stems, and seed pods. Attraction to fungi on the plants, principally Alternaria sp., accounted for the presence on alfalfa of arthropod species that normally might be considered as accidentals or visitors. The mycetophagous species thus contributed to the richness of the alfalfa fauna. Immature stages of several species were collected only in late fall or on 3- or 4-year-old plants. The possible role of the fungus-feeding species in seasonal changes in the alfalfa fauna and changes in the fauna in successive years is discussed.