Andrew L. Sheldon

Species Diversity and Longitudinal Succession in Stream Fishes

A quantitative survey was made of the distribution and abundance of fishes in Owego Creek, New York. Four of the five headwaters species occurred throughout the area and two of these species dominated the fauna in all areas. Thirty-one species were found in the area. Succession took the form of additions to the headwaters assemblage and replacement was of minor importance. Regression analyses show that the number of species in any area was correlated most strongly with stream depth although an effect of position was also sig- nificant. Species diversity (information theoretic) was independent of position and depended on depth alone. Behavioral observations support the importance of the depth factor. The distribution of fishes in small streams is characterized by large faunal changes within rela- tively short distances (Shelford 1911) and pro- vides a convenient situation for the study of gradients in species composition and diversity. This paper presents the results of a quantitative survey of fish distributions in a New York stream from 1961 to 1963.

Equitability Indices: Dependence on the Species Count

Three measures of equitability or relative diversity are shown to be dependent on the species count component of total diversity. This dependence limits the use of equitability indices as comparative statistics. See full-text article at JSTOR

POST-DEFAUNATION RECOVERY OF FISH ASSEMBLAGES IN SOUTHEASTERN BLACKWATER STREAMS'

The authors analyzed fish assemblage structure at 37 sites in South Carolina streams before and nearly one year after experimental defaunation to test assemblage resiliency. Decreases in stream depth and width in the second year reflected an intervening drought, but habitat structure remained highly correlated between years. Fish assemblages recovered well over four scales of analysis. Total fishes sampled, collective assemblage properties (species richness, density, biomass, and mean mass of fish), local assemblage structure, and single-species attributes generally did not significantly differ after defaunation, as determined by species- and individual-abundance correlations, detrended correspondence analysis, and a proportional similarity index. These assemblages were not randomly structured units, but were largely deterministic systems highly predictable from local habitat structure.

Short-Term Recolonization by Fishes of Experimentally Defaunated Pools of a Coastal Plain Stream

Fishes were removed from pools in a South Carolina stream to observe subsequent recolonization patterns and development of community structure. Recolonization, measured between two and 32 days, was rapid; and downstream sites attained preexperimental density, richness, and proportional composition by day 32. However, recovery of upstream sites was incomplete in that time. Species colonized in proportion to abundance, and rare species returned later; both of these results are interpreted as simple proportional sampling of a mobile fauna. In a longer experiment, defaunated pools did not differ from controls; and density, richness, and composition showed no temporal trend over 31-63 days. Movement, measured by directional trapping, was dominated by spawning yellowfin shiners (Notropis lutipinnis), but 16 of 26 species present were trapped, demonstrating active movement by much of the fauna. Rapid recolonization of defaunated areas is plausibly explained by a combination of high mobility and equilibrium with source populations.

Blackfly (Diptera: Simuliidae) abundance in a lake outlet: test of a predictive model

A mathematical model based on assumptions of proportionality of filter-feeding insect larvae and their food supply and of the ability of the larvae to substantially reduce the sestonic food supply was developed. The predictions of the model were tested by censusing simuliid blackfly larvae in the outlet stream of a mesotrophic lake. Observed trends in simuliid density agree closely with the predictions. Two seston components (diatoms, detritus) increase downstream contrary to prediction. Potential predators of simuliids were censumed. Isoperla spp. decreased with increasing distance below the lake while the perlid stoneflies Calineuria and Hesperoperla seemed to be excluded from the outfall region.

Multivariate analysis of feeding relationships of fishes in blackwater streams

SynopsisThe autumnal diets of 23 fish species in 9 families from South Carolina blackwater streams were characterized by rank order statistics and analyzed by detrended correspondence analysis (DCA). DCA ordinations of fishes and their food items indicate two primary gradients. The first axis contrasts fine particle feeders and omnivores (Catostomidae, some cyprinids) eating algae, detritus, microcrustacea and bivalves, with predators(Anguilla, Esox, largeAmeiurus) on decapods and vertebrates. The second is a gradient from benthic feeders (percid darters,Noturus catfishes) with varied invertebrate diets, to taxa (Gambusia, some cyprinids and centrarchids) feeding at the surface. With increasing size, fishes shift to larger prey and increased surface feeding. Much of the trophic differentiation within the assemblage reflects diversification at generic and family levels. DCA is an effective method for summarizing trophic relations in diverse assemblages.

Effects of exported seston on aquatic insect faunal similarity and species richness in lake outlet streams in Montana, USA

The quantity of seston exported from a lake affected the qualitative composition and species richness of aquatic insects in 13 lake outlet streams in northwestern Montana. Mean values for chlorophyll and particulate organic carbon in lake effluent waters ranged from 0.5 to 2.7 and 80 to 601 mg m-3, respectively. Correlations between a detrended correspondence analysis of faunal similarities in outlet streams and measures of organic export from the lake indicated that distributional patterns were primarily dependent upon the general trophic status of the lakes. A comparison of faunal assemblages at stream stations located at the outlet and 100 m downstream demonstrated that species composition at the two stations was more similar in productive systems.

Cost and precision in a stream sampling program

Nomograms relating fixed, variable and total costs (time) to sample size and precision are presented for use in research planning. Time costs for a survey of a Montana, U.S.A., stream were dominated by fixed costs and the laboratory component of variable costs while variable field costs were small. Reductions in both fixed and variable costs influence precision of low-budget survey sampling while reduction of variable costs in large budget research sampling has more effect on total cost than on precision.

Resource division by perlid stoneflies (Plecoptera) in a lake outlet ecosystem

In a stream draining a productive lake, two abundant (250/m2) stoneflies Calineuria californica and Hesperoperla pacifica differed in population size structure, habitat use and food although overlap in resource use was extensive. Life cycles of two (Calineuria) and three years (Hesperoperla) were indicated. A multivariate analysis of habitat use demonstrated size dependent habitat selection in both species and between species habitat differences. Feeding habits differed although only the largest Hesperoperla had a food refuge. Diets of individual nymphs represented an interaction of species, size and habitat.

Phylogeography and species biogeography of montane Great Basin stoneflies

Sky islands are ideal systems for determining the effects of climatic oscillations on species distributions and genetic structure. Our study focused on montane stonefly populations in the Great Basin of western North America. We used niche‐based distribution modelling, phylogeography and traditional species‐based biogeography to test several hypotheses as follows: (i) genetic differentiation among Doroneuria baumanni populations will be independent of hydrologic connectivity (headwater model); (ii) Sky islands were colonized when habitat was more continuous and populations likely experienced multiple expansions and contractions; (iii) Colonization events were coincident with the late Pleistocene and Holocene; and (iv) Shared topography and climate history will result in concordant patterns of genetic differentiation in D. baumanni and occurrences of 32 stonefly species across the region. Overall, ΦST’s and coalescent‐based estimates of migration were consistent with the headwater model. Maximum likelihood and Bayesian gene trees identified three major nonoverlapping east‐west clades. Distribution modelling indicated more suitable habitat in the Great Basin during the Last Glacial Maximum than at present, but none during the last interglacial period. Demographic analyses showed evidence of population expansion in one of the three major east–west clades. Intra‐clade divergence times (60 000–183 000 ybp) were well within the late Pleistocene while among‐clade divergence times (499 000–719 000 ybp) were deeper. Genetic differentiation in D. baumanni and distributions of stonefly species were significantly concordant. These results imply that climatic oscillations have played major roles in shaping the genetic structure and distributions of Great Basin stoneflies, but that divergence among clades occurred much earlier than our late Pleistocence/early Holocene predictions.