Showing papers on "Diversity index published in 1973"

Diversity and Evenness: A Unifying Notation and Its Consequences

Abstract: Three commonly used measures of diversity, Simpson's index, Shannon's entropy, and the total number of species, are related to Renyi's definition of a generalized entropy. A unified concept of diversity is presented, according to which there is a continuum of possible diversity measures. In a sense which becomes apparent, these measures provide estimates of the effective number of species present, and differ only in their tendency to include or to ignore the relatively rarer species. The notion of the diversity of a community as opposed to that of a sample is examined, and is related to the asymptotic form of the species—abundance curve. A new and plausible definition of evenness is derived.

Diversity in Fresh-water Phytoplankton

Abstract: Seasonal changes and mean values of diversity, calculated by the Shannon formula, are given for the phytoplankton communities of three freshwater bodies. Particularly in the more eutrophic bodies, diversity increased in summer but was low in winter. Diversity decreased with increased fertility of the water. The data confirm predictions made in the literature, but existing explanations of the phenomena are considered unnecessarily complex. An explanation based on the balance of cell numbers between overlapping populations of several species is given, supported by a simple mathematical model. The pigment diversity index and the nature of succession (periodicity) in freshwater phytoplankton are discussed. INTRODUCTION Diversity, though variously and precisely defined in several different formulae, is a concept to which it is difficult to give concrete meaning. Tendencies for numbers of organisms to become equally distributed among increasing numbers of species present are included in the recognition of progressively more diverse communities. However, different formulae, empirically or intuitively derived, may give different rankings to members of a series of communities. Similar discrepancies might be expected if standing crop or, better, individual annual production rather than numbers of individuals were used for calculation. Although Margalef (1968, p. 52) believes that diversity of a whole ecosystem is reflected accurately by the usually measured diversity of restricted taxonomic or trophic groups, this correspondence has yet to be tested. This paper takes one widely used diversity index, considers what it means practically, and examines two propositions: (1) diversity increases with time during the spring and summer development of phytoplankton populations in temperate waters (Margalef, 1958 ); (2) phytoplankton communities in infertile waters are more diverse than those in fertile waters (Margalef, 1964; 1968, p. 56). Analogies between seasonal development in phytoplankton communities and succession of vegetation types on land are also discussed. CHOICE OF DIVERSITY INDEX Phytoplankton communities contain cells of some species that from time to time divide and produce populations in the open water. Also present are many species which are not truly planktonic and do not reproduce in the open water, but are resuspended from algal comContribution number 236 from the W. K. Kellogg Biological Station.

Summer Bird Species Diversity in Relation to Secondary Succession on the New Jersey Piedmont

Abstract: Bird species diversity was studied in three seral stages characteristic of secondary succession on the New Jersey Piedmont during the summers of 1968 and 1969. The seral stages studied were a 2to 3year-old field (the herbaceous field), a 30-year-old field (the cedar field), and a near climax oak-hickory forest (the oak forest). Two study plots each with an area of 2 ha were chosen within each seral stage. Diversity indices were calculated using the Shannon-Weaver information formula, H-' -pi loge Pi. Bird species diversity (BSD) and age of the seral stage were positively correlated, and the greatest increase in the diversity index occurred between the herbaceous field and the cedar field. BSD in the oak forest was consistently higher than in the cedar field, although the mean values were not greatly different. BSD variability decreased with the age of the seral stage. The highest variability estimates were for the herbaceous field. Much of the variability in the herbaceous field was due to the importance of nonnesting birds which fed in the field. The importance of nonnesting birds decreased with the age of the seral stage. The suggestion is made that variability is an important parameter and should be examined more closely in future species-diversity studies. Although no cause-effect mechanism between species diversity and habitat stability was found, the trends observed suggest that low species diversity and high variability characterize unstable habitats. INTRODUCTION Species diversity is an attribute of all biological communities. Ecologists have long recognized that the number of species which characterizes a community differs from one community to another. Why one community should contain more or fewer species than another is as yet poorly understood, and numerous hypotheses regarding the functional role of species diversity have been proposed (Elton, 1958; Hutchinson, 1959; Connell and Orias, 1964; MacArthur, 1965; Pianka, 1966). Species diversity changes in relation to succession have been studied by Margalef (1963, 1968). Many of Margalef's conclusions are now considered to be characteristic of autotrophic succession in general (Odum, 1963, 1969). Karr (1968) has recently described species diversity and avian succession in Illinois. Prior to that, studies on avian succession have not specifically considered species diversity (Odum, 1950; Johnston and Odum, 1956). Evaluation of many previous studies of species diversity is difficult for several reasons. Often, studies are restricted to only a single ecosystem. Those that are not often fail to supply such information as sample size per ecosystem and sample number per ecosystem, making 1 Research conducted while at Department of Zoology, Rutgers University, New Brunswick, New Jersey.

Species Diversity of Periphyton Communities in the Littoral of a Temperate Lake

Abstract: Species diversity of littoral periphyton sampled from Elk Lake (B. C., Canada) was dependent on station location and period of substrate exposure. Site differences were not statistically related to physico-chemical variables. However, diversity was negatively correlated with age of the communities and standing crop, and appeared to be associated with biological interaction or competition for available substrate surface. Further investigation revealed that the Shannon-Weaver index, as commonly applied, was inappropriate for data summarization since it reflected only the changes in evenness of the most abundant species. Components of the diversity index, as illustrated by the periphyton, were discussed.

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.