Mean Species Diversity Research Articles

Effects of Depth and Marine Reserve Fishing Restrictions on the Structure of a Rocky Reef Fish Assemblage in the North-Western Mediterranean Sea

SUMMARY (1) A visual scuba diving census, in which abundance and size class structure of conspicuous fish species were determined, was used to assess the effects of depth and marine reserve fishing restrictions on the structure of a Mediterranean rocky reef fish assemblage by comparing communities at sites from two depth ranges inside and outside a marine reserve. (2) The total assemblage had thirty-five conspicuous species and was dominated by Labridae (thirteen spp.) and Sparidae (nine spp.). (3) Mean species richness (number of species) and diversity (Shannon) did not differ significantly between sites. (4) Ordination of abundance data showed that occurrence and relative abundance of species was affected by depth (deep samples separated completely from shallow samples) and marine reserve status (samples from the marine reserve were significantly separated from those taken at the same depth outside the reserve). (5) Samples from the same depth were similar, because the majority of species showed a preference for either deep or shallow areas. The known biology of several species indicated that feeding requirements may be responsible for depth preferences. (6) Samples from reserve sites had signficantly higher densities of fish species sought after and/or vulnerable to local fishing methods, than those from non-reserve sites of similar depth. (7) Size frequency distributions of vulnerable species at reserve sites generally had a larger modal size class than distributions from non-reserve sites. (8) The data suggest that reduced fishing pressure in the reserve has provided effective protection for species vulnerable to fishing.

Structure and Productivity of Grassland Small Mammal Communities Related to Grazing-Induced Changes in Vegetative Cover

Effect of grazing on the structure and productivity of small mammal communities in four types of North American grasslands is examined quantitatively using data collected during a 4-year period. Small mammal communities in tallgrass and montane grasslands appear more affected by grazing and the subsequent reduction in vegetative cover (=total above-ground standing crop of plants) than do small mammal communities in shortgrass and bunchgrass grasslands. This trend is evident when small mammals in grazed versus ungrazed habitats are compared with regard to mean community biomass, annual community respiration, production, and consumption, mean species diversity and evenness, proportional species and functional group composition, seasonal dynamics of community biomass, and temporal variation in proportional species composition. These results lend further support to the hypothesis that the general composition of grassland small mammal communities is determined primarily by structural attributes of the habitat.

Benthic fauna species diversity in six central Florida lakes in summer

The summer macroinvertebrate fauna was studied in six central Florida monomictic lakes during July, 1973. No direct relationships were found between physiochemical conditions and species diversity. Of the 22 species of benthic organisms recorded, only four species were found in all the lakes. Mean species diversity (d) values for the lakes ranged from 0.735 to 1.731.

Distributional Patterns in Assemblages of Attached Diatoms from Yaquina Estuary, Oregon

Summer and winter distributional patterns of attached diatoms were investigated in Yaquina Bay and estuary, Oregon. Differences in species composition and diversity of diatom assemblages at selected stations from fresh water just below Elk City, Oregon, to the marine waters of lower Yaquina Bay were released to environmental gradients. A total of 16,475 diatoms from 30 samples was separated into 256 species and varieties, of which 97 were found in only one sample, and 72 were represented by a single individual. The most abundant diatoms in the August samples were Fragilaria striatual var. californica, Melosira moniliformis, M. nummuloides, Navicula mutica, and Synedra fasciculata, while in the February samples Achnanthes no.2 and no.4, Navicula diserta, N. mutica, and Nitzschia frustulum var. perpusilla were dominant. Of the most abundant taxa, Navicula no. 2, N. diserta, N. gregaria, Nitzschia frustulum var. perpusilla, Synedra fasciculata and Thalassionema nitzschioides were the most evely distributed among the stations. The mean species diversity for diatom assemblages sampled in February was slightly higher than for assemblages collected in August. In February the mean specific diversity within a genus was higher and the mean generic diversity slightly lower than in August. In general, differences in assemblages were closely related horizontally to the salinity gradient and vertically to the desiccation and insolation gradients. However, biological factors were more important in accounting for differences among assemblages in the summer than in the winter and these factors were primarily species interactions between diatoms and macro—algae.

Environmental Complexity and Species Diversity in the Gastropod Genus Conus on Indo-West Pacific Reef Platforms

Species diversity of assemblages of the gastropod genus Conus occurring on tropical Indo-West Pacific reef platforms increases in the following order of habitat types: (1) extensive regions of sand substrate (mean number of species N = 3.0; mean species diversity H = 0.5); (2) intertidal smooth limestone plantforms (mean N = 7.6; mean H = 1.3); (3) topographically complex subtidal coral reefs (mean N = 13.7; mean H = 2.1). The census data show a close correlation between N and H (Spearman r = 0.93). The absence of a longitudinal gradient of species number and diversity in the uniform Type II habitats over 160⚬ of longitude, despite reports of larger total numbers of species near the "faunistic center" of the Indo- West Pacific region, also supports the conclusion that habitat complexity is an important determinant of species diversity. Type III habitats near the "faunistic center" have more diverse assemblages than those of outlying areas east and west, but it has not been possible to distinguish the roles of habitat complexity and other possible determinants of species diversity gradients.