Variation In Number Of Species Research Articles

Variation in environmental conditions, understorey species number, abundance and composition among natural and managed Picea abies forest stands

We studied four south-facing and three north-facing boreal spruce forest stands (ca . 0.1 ha each) in SE Norway with the aim of testing the hypothesis that former logging has long-term effects on boreal forest-floor vegetation. The stand series comprised unlogged natural forests and forests that were selectively or clear cut 60–70 years prior to our study. Each stand was described with respect to history of forestry impact and tree-stand structure. Environmental, species number, species abundance and species composition (vegetation gradients obtained as ordination axes) variables obtained for 25 m×1 m plots in each stand were tested for among-stand differences. Significant among-stand differences were found, partly related to former forest management and partly due to among-stand differences in topography. Differences among stands related to management were found for tree stand density, highest in managed stands, and for Dryopteris expansa agg. and Luzula pilosa abundances, peaking in formerly clear-cut stands. Species number (at plot or stand scales) was weakly related to former management. On southerly as well as northerly aspects, gradients in species composition were found that separated plots according to former management. Differences among stand conditioned on topography resulted in opposite patterns in the two series of stands because among southerly stands the clear cut was the least while among northerly the clear cut was the most strongly sloping. Low-inclination sites tended more strongly to be paludified and to have high Sphagnum cover, and to have low abundance of specific microsites with small mosses and hepatics. Vegetation gradients related to soil moisture and microtopography were found for both aspects. A strong gradient in species composition related to tree influence at within-stand scales was found, with variation in species number. Existence of such a gradient should provide for significant biotic effects (of short or long duration) of the environmental changes that take place during forest re-growth: (1) the immediate creation of small or large tree-layer gaps by tree felling; and (2) the closing of the tree layer during the regeneration phase. Most notably, the phases at which the tree layer reaches minimum and maximum cover, respectively, may act as ‘bottlenecks’ for survival of forest-floor species. We conclude that forestry impacts understorey vegetation by way of changes in tree-layer structure and, to a lesser extent, substrate availability and the local environment, during forest regrowth. The extent and duration of this impact will depend on a complex set of factors. Our results are consistent with the view that if maintenance of species diversity is aimed at, environmental considerations should be built into forest management practices, preferably by mimicking the natural structural dynamics of the tree layer.

Species richness and seasonality of forest avifauna in three South African Afromontane forests

Presence data were recorded and analysed for avian bird species in a study of three separate Afromontane Forests in the KwaZulu-Natal Midlands, South Africa. Levels of endemism for South Africa and forest-specificity were investigated. In total, 136 species were identified utilizing forest, yet not all species occurred in all three forests. Slight differences in species composition are attributable to latitudinal and altitudinal differences as well as differences in disturbance regime. However, the respective subsets of forest-specific, frugivorous or migrant birds were similar between forests. Almost all forest-specific species were found at all three study sites and the absence of particular species may be attributable to extinction or rarity. Subsets of endemic frugivores and endemic forest-specific species were also similar between forests. Relatively high levels, for South Africa, of forest-specificity (about 24%) and endemicity (about 17%) were recorded, showing little seasonal variation in species numbers whereas frugivorous and migrant species showed seasonality in their presence. The importance of these forests in conserving avifaunal biodiversity in the region is highlighted. Bird ringing was conducted at two forests to supplement observational data, and assisted in detecting rare and cryptic species. Recommendations are made for the conservation of the larger forest patches, within a naturally fragmented biome.

Palaeoceanographic and palaeoclimatic inferences from Late Cretaceous planktonic foraminiferal assemblages from the Exmouth Plateau (ODP Sites 762 and 763, eastern Indian Ocean)

The evolution of planktonic foraminifera during the Late Cretaceous is marked in the Santonian by the disappearance of complex morphotypes (the marginotruncanids), and the contemporary increasing importance and diversification of another group of complex taxa, the globotruncanids. Upper Turonian to lower Campanian planktonic foraminiferal assemblages from Holes 762C and 763B (Ocean Drilling Program, Leg 122, Exmouth Plateau, 47°S palaeolatitude) were studied in detail to evaluate the compositional variations at the genus and species level based on the assumption that, in the Cretaceous oceans as in the modern, any faunal change was associated with changes in the characteristics and the degree of stability of the oceanic surface waters. Three major groups were recognised based on gross morphology, and following the assumption that Cretaceous planktonic foraminifera, although extinct, had life-history strategies comparable to those of modern planktonics: 1 – r-selected opportunists; 2 – k-selected specialists; 3 – r/k intermediate morphotypes which include all genera that display a range of trophic strategies in-between opportunist and specialist taxa. Although planktonic foraminiferal assemblages are characterised by a progressive appearance of complex taxa, this trend is discontinuous. Variation in number of species and specimens within genera has allowed recognition of five discrete intervals each of them reflecting different oceanic conditions based on fluctuations in diversity and abundance of the major morphotypes. Planktonic forms show cyclical fluctuations in diversity and abundance of cold (r-strategists) and warm taxa (k-strategists), perhaps representing alternating phases of unstable conditions (suggesting a weakly stratified upper water column in a mesotrophic environment), and well-stratified surface and near-surface waters (indicating a more oligotrophic environment). Interval 1, middle Turonian to early Coniacian in age, is dominated by the r/k intermediate morphotypes which alternate with r-strategists. These cyclical alternations are used to identify three additional sub-intervals. Interval 2, aged middle to late Coniacian, is characterised by the increasing number of species and relative abundance of k-strategists. After this maximum diversification the k-strategists show a progressive decrease reaching a minimum value in Interval 3 (early to late Santonian), which corresponds to the extinction of the genus Marginotruncana. In the Interval 4, latest Santonian in age, the k-strategists, represented mainly by the genera Globotruncana, increase again in diversity and abundance. The last Interval 5 (early Campanian) is dominated by juvenile globotruncanids and r-strategists which fluctuate in opposite phase. The positive peak (Interval 2) related to the maximum diversification of warm taxa (k-strategists) in the Coniacian seems to correspond to a warmer episode. It is followed by a marked decrease in the relative abundance of warm taxa (k-strategists crisis) with a minimum in the late Santonian (Interval 3), reflecting a decrease in temperature. Detailed analysis of faunal variations allows the Santonian faunal turnover to be ascribed to a cooling event strong enough to cause the extinction of the marginotruncanids.

Substrate heterogeneity and number of plant species in Everglades savannas (Florida, USA)

Environmental heterogeneity, especially that related to topography, has been proposed to influence numbers of plant species in different sized areas. Despite little variation in elevation, large numbers of vascular plant species occur in some habitats. This study explored possible relationships between number of plant species and substrateheterogeneity in two species-rich habitats, subtropical pine savannas and short-hydroperiod prairies, in the Long Pine Key region of Everglades National Park (Florida, U.S.A.). We examined relationships between numbers of vascular plant species and topographic heterogeneity by measuring numbers of species and elevations in differ-ent sizes of nested plots that spanned five orders of magnitude (0.1 m2 to 1000 m2 ) and that were located along two transects extending from pine savannas into short-hydroperiod prairies in different areas of Long Pine Key. We also classified substrates and soil depths in 1 m 2 sized submodules within the nested plots. Pine savannas occurred at higher elevations than adjacent short-hydroperiod prairies. Although differences occurred in substrate types and distribution within 1 m 2 plots, numbers of species were not associated with these differences. Vari-ances in elevations were similar in the smallest plots, but increased with area more rapidly in pine savannas than in short-hydroperiod prairies. Plot size explained about 85% of the variation in species numbers, which increased from 20‐40 per 1 m 2 to 80‐120 per 1000 m2 . An interaction between habitat and scale explained 5% of the variation; more species occurred in short‐hydroperiod prairies than pine savannas at scales 10 m2. The number of species in pine savannas at scales of 1 m2and 10 m2was positively associated with variation in elevations; no significant relationships were obtained in short-hydroperiod prairies, which lack the fine-scale topographic variation of pine savannas. Our data indicate that substrate het-erogeneity, measured as variation in elevations, is not likely to be involved in the co-occurrence of many species within small areas of these savannas, but may influence numbers of species at larger scales of observation, es-pecially in pine savannas. Why many plant species occur within very small areas in these savannas remains un-answered.

A comparative analysis of the avifaunas of different zoogeographical regions

AbstractThis paper provides a comparison of the landbirds of all main zoogeographical regions, based on the most recent (Sibley–Monroe) listing and classification of the world's birds. This classification arranges 9416 landbird species (i.e. excluding seabirds) into 2002 genera, 140 families and 23 orders. On this basis, the Neotropical region holds 36% of all known landbird species and 45% of genera, the Afrotropical region holds 21% of species and 24% of genera, the Indomalayan region 18% of species and 22% of genera, the Australasian region 17% of species and 23% of genera, the Palaearctic region 10% of species and 14% of genera and the Nearctic region 8% of species and 15% of genera. These major continental regions thus show 4.6‐fold variation in species numbers or 9.1‐fold variation in species numbers per unit area. The region of Oceania, comprising many Pacific Islands, holds only 2% of the world's bird species and 4% of genera. About 92% of all bird species on the continental parts of the Neotropical, Afrotropical and Australasian regions are endemic to those regions, compared to 64% of the Indomalayan, 54% of the Nearctic and 46% of the Palaearctic species. The Oceania region has the smallest number of endemics, but these form 87% of all species occurring naturally in this region. About 91% of all landbird species breed in only one zoogeographic region, another 8% in two regions, with the remaining 1% in three to seven regions. Only four species breed in all seven regions. Similarities in the species composition of different regions were compared using Jaccard and Simpson indices. As expected, each region shares the greatest number of species with the closest other region and the fewest species with the most remote region. As in previous analyses, the Neotropical and Australasian regions emerged as having the most distinctive avifaunas. Regions that hold large numbers of landbird species also hold large numbers of genera and families, as well as high species‐per‐genus and species‐per‐family ratios. Comparable levels of diversity thus extend through all these taxonomic categories. This implies that, whatever factors have promoted particular levels of avian diversity in the different regions, they are of long standing. As found in previous studies, species‐per‐genus and species‐per‐family ratios are lower in island than in continental avifaunas. No relationship is apparent between the size of each zoogeographical region and the numbers of species, genera and families found there; rather those regions with tropical forest have many more bird taxa overall than those without.

The effect of 50 years of landscape change on species richness and community composition

AbstractWe analysed a 50‐year dataset of avian species observations to determine how richness and community composition varied over a period of landscape‐scale environmental change. Our study area, northern lower Michigan, has experienced substantial land‐use and land‐cover change over time. Like much of the northern Midwest, it has shifted from a largely unpopulated, post‐logging shrubland to a moderately populated closed‐canopy forest. Such changes are generally expected to influence overall richness and community composition. We found that regional richness per year remained virtually unchanged over the study period. Year‐to‐year variation in species number was surprisingly low. Richness totals included vastly different species groups as the composition of the regional bird community changed substantially over time. Changes in the types of species present appear to reflect deterministic changes in habitat. The number of grassland and open‐habitat species decreased, for example, while species associated with older forests and urban habitats increased. Our results suggest that habitat changes at the landscape scale do not necessarily lead to changes in the number of species a region can support. Such changes, however, do appear to influence the types of species that will occupy a region, and can lead to substantial changes in community composition.

The species-pool hypothesis from a bryological perspective

Bryophytes form one-layered communities, which provide good opportunities to test predictions of the species pool hypothesis. The prediction that competitive exclusion occurs rarely, if at all, in established communities seems to hold for many types of bryophyte vegetation, but the drastic effects on local diversity of some invading exotic species suggests, that this may be partly due to the "ghost of competition past". In a survey of bryophyte communities on earth banks, variation in species number per stand was rather larger than predicted by the species-pool hypothesis. Large differences in accessibility of the stands may have played an important role in this respect. Small-scale repeated chartings and permanent grid studies suggest, that competitive exclusion hardly ever occurs in a range of terrestrial bryophyte communities. Evidence for interspecific competition (as derived from small-scale association between behaviour - increase or decrease in grid cells - of species pairs) was equally rare, but this may have been due to interaction with positively density-dependent facilitation effects. However, a rigorous proof of the hypothesis that facilitation may prevent competitive exclusion is still lacking.

Cloning and Localization of a Human Diphthamide Biosynthesis-like Protein-2 Gene,DPH2L2

Sequence analysis of the candidate tumor suppressor OVCA1 revealed extensive sequence identity and similarity to proteins from a diverse number of species, including the yeast diphthamide biosynthesis protein-2, dph2, which suggested thatOVCA1may be the human homologue to this yeast gene. However, searches of the translated EST database for sequences in common with dph2 and OVCA1 uncovered an EST, h52976, with significant amino acid conservation with dph2. Isolation of a cDNA clone encompassing the EST by RACE methodologies and sequence analysis indicate the identification of a previously unidentified gene that is ubiquitously expressed and maps to chromosome 1p34. Based on amino acid sequence analysis, the 489-amino-acid protein encoded by this novel gene is distinct from OVCA1 and is more closely related to the yeastdph2gene product. Therefore, we refer to this novel gene asDPH2L2,which constitutes one member of a novel gene family that may be involved in diphthamide biosynthesis in humans.

Influence of Drainage Connectivity, Drainage Area and Regional Species Richness on Fishes of the Interior Highlands in Arkansas

There has been strong recent interest in the “macroecological” approach of explaining local community phenomena as a consequence of patterns at larger geographic scales. Various authors have suggested that if local observations can be explained by the larger-scale patterns in which they are embedded, there is less need to invoke local (within-site) processes (like competition, habitat structure, etc.) to explain community structure. We used a large database on local stream fish assemblages and species distributions in the Interior Highlands of Arkansas to test three macroecological hypotheses: (1) faunal similarities among upland river basins can be predicted from the hierarchical geographical connectivities of those streams in the larger Mississippi River Basin drainage network; (2) faunal richness of drainages up to the size of small rivers (ca. 4000 km2) increases with drainage area; and (3) local (within-site) species richness increases in proportion to regional (basin) richness. These hypotheses were tested at the level of “all species”, and within the families Cyprinidae (minnows) and Percidae (darters). For the first hypothesis, Mantel tests comparing matrices of faunal similarities and basin connectivity (based on number of nodes separating these smaller basins within the Mississippi River Basin) showed that similarities in composition of fish faunas among the upland basins were predictable from the pattern of drainage connectivity. This pattern existed at the levels of “all species”, minnows, and darters. Upland basins separated by the fewest nodes had fish faunas that were most similar, with all basins in the more northern White-Arkansas river basin separating (across all taxa and within families) from the southern Ouachita river basin drainages; and lesser rivers within these basins also showed similarity generally related to their connectivity. In tests of the second hypothesis, drainages up to small rivers in size exhibited positive, species-areas slopes at all taxonomic levels. Species-area regression slopes (z) were 0.30 for “all species”, and 0.36 for darters, both differing significantly from a slope of zero. However, minnows had a species-area regression slope of z = 0.20, which did not differ statistically (P = 0.16) from a slope of zero. For the third hypothesis, regional (basin) species richness explained little of the variation in species richness at individual local sites, with the relationship significant at P = 0.054 for mean local number of “all species”, and nonsignificant within the minnow and darter families. Within all levels of regional (basin) species richness, there was great variation in number of species found at individual sites. Overall, we conclude that extrinsic macroecological hypotheses, based on patterns at large spatial scales, differed in explaining composition of the faunas or assemblages at smaller spatial scales, leaving much variation in local assemblage structure to be explained by local intrinsic factors.

The Insular Biogeography of Small Bahamian Cays

1 The species occurring on 128 small cays in the central Exumas and 54 small cays near Andros, Bahamas, were surveyed. 2 Step-wise multiple linear regressions selected the log transformations of vegetated area or total area as the variables explaining the most variation in species number at Andros. In the Exumas, the ratio of vegetated area to total area, which is an expression of both insular area and exposure, was the most frequent first-selected variable. 3 In both archipelagoes, cays with vegetation were significantly larger, higher and closer to a mainland island than cays naturally devoid of vegetation. 4 High degrees of nestedness were observed in both archipelagoes, both at the level of the entire species assemblage and at the level of individual species. Ninety per cent of the species that did not display significant nested patterns were rare species, occurring on 7500 for all but one species. 6 Species turnover was measured for 77 cays in the Exumas, which were surveyed annually over a 4-year period. Turnover was very low, and most of the observed turnover was due to immigrants that never became, established. Contributing factors to the observed low turnover included the absence of annuals and the physical stability of these predominantly rocky cays. 7 Propagules of Sesuvium portulacastrum were introduced to 10 cays naturally lacking vegetation. After 40 months, S. portulacastrum was still present on nine of 10 cays and had increased in vegetated area from approximately 1 m2 up to 650 m2, indicating that non-vegetated cays were physically able to support plant life, at least in the short term. 8 A 'small island effect' (i.e. a weak species-area relationship on very small islands) was apparent at Andros and probably resulted from smaller cays being washed over by waves.

Factors Associated with Artificial-Reef Fish Assemblages

Visual census (5-min point-count, 100 m2) was used to estimate fish assemblage parameters associated with artificial reef variables from 64 reefs over a 3-yr period in the northern Gulf of Mexico. Dependent variables, recorded by divers [i.e., number of species, number of individuals, length (TL in cm), and species diversity (H')], were analyzed for their associations with potentially underlying environmental attributes using stepwise regression, TWINSPAN, and canonical correspondence analyses (CCA). The fish assemblages (dominated by haemulids, labrids, and serranids) were qualitatively and quantitatively similar to the assemblages described by others from the same general area. Pelagic fishes (carangids and scombrids) associated with the reefs were among the most numerous and were the largest predators in the assemblage. The stepwise regression analysis was able to account for fairly high percentages of the variation in number of species (37%), number of red snapper (43%), and size of red snapper (52%). TWINSPAN allowed the recognition of fish assemblages based on their inshore-offshore biotopes. Vermilion snapper was identified as a key indicator species. The CCA helped identify species groups and factors associated with them. The affinity of pinfish and spottail pinfish with rock jetty was evident, as was the association of triggerfish with vertical steel structure. Although the axis loadings using CCA did not identify a clear species/factor relationship, this analytical method should prove useful in recognizing environmental factors that can be controlled to optimize species-specific artificial reef construction.

Local and Regional Species Richness in North American Lacustrine Fish

1. Species-area and local-regional species richness patterns in lacustrine fish in North America were investigated by reduced major axis regression, using a database of 651 lakes. 2. Small lakes (area < 1.5 km(2)) had steeper species-area slopes than large lakes. In one area open water species declined in frequency in small lakes, suggesting that within-lake habitat diversity is partly responsible for the species-area slope. Local lake characteristics (area, mean depth and altitude) explained only about one-third of the variation in species numbers. 3. Species-area slopes were not significantly different across regions but there were considerable differences between regions in local richness for standardized lake sizes. Local richness was linearly related to regional richness when the regional pool consisted only of native species. 4. Pseudosaturation, the detection of curvilinearity when the true relation is linear, was found when introduced species were included in the regional species pool. Introduced species tend to have more localized distributions than native species, and their inclusion over-estimated regional pool sizes but had little effect on local richness estimates. Additionally, undersampling of small species, coupled with an increase in the relative importance of small species in southern regions, led to pseudosaturation by underestimating local richness in species-rich regions. 5. Turnover diversity was not correlated with regional pool size. However, comparison of three eastern regions showed that the percentage of the region occupied per species was less in the more speciose, southern regions, consistent with increased turnover diversity and pseudosaturation. 6. These results support the notion that regional-scale processes play a major role in determining the number of species in North American lacustrine fish communities.

Factors Influencing Bird Species Numbers in Small Woods in South-East England

151 woods, ranging in size from 0.02 to 30 ha and with differing degrees of isolation, were surveyed to determine the numbers of breeding bird species present in each of three consecutive years. Woodland and edge species were analysed separately. Numbers of woodland species showed a strong relationship with woodland area which explained c. 70% of the variation in breeding species numbers. Several other features of the woods and of the surrounding landscape also had small additional influences on species numbers. Numbers of edge species showed a poor relationship with woodland area, but length of perimeter explained 30-40% of the variation in species numbers. The number of structural features within a wood and isolation from other woodland also had small additional positive influences on edge species numbers. Small woods held more edge species than equivalent areas of large woods, but tended to hold fewer woodland species than equivalent areas of large woods.

Variability in species richness and guild structure in two species-rich grasslands

It has been suggested that variation in the proportion of species in guilds (=guild proportionality) indicates community structuring by guilds in biotic communities. This hypothesis was tested on a subthermophilous grassland and a mesotrophic meadow at a scale of 0.09 m2 based on a five-year data set. Further, variation in the total number of species, variation in the number of species belonging to a guild and non-randomness in species composition of guilds were studied. A number of criteria for guild definition were used, such as life form, Grime's C-S-R strategy, phenology, plant height, pollination and dispersal syndromes, leaf shape and anatomy and taxonomy at the family level.

Phylogenetic conservation and physical mapping of members of the H6 homeobox gene family.

Homeobox genes represent a class of transcription factors that play key roles in the regulation of embryogenesis and development. Here we report the identification of a homeobox-containing gene family that is highly conserved at both the nucleotide and amino acid levels in a diverse number of species. These species encompass both vertebrate and invertebrate phylogenies, ranging from Homo sapiens to Drosophila melanogaster. In humans, at least two homeobox sequences from this family were identified representing a previously reported member of this family as well as a novel homeobox sequence that we physically mapped to the 10q25.2-q26.3 region of human Chromosome (Chr) 10. Multiple members of this family were also detected in three additional vertebrate species including Equus caballus (horse), Gallus gallus (Chicken), and Mus musculus (mouse), whereas only single members were detected in Tripneustes gratilla (sea urchin), Petromyzon marinus (lamprey), Salmo salar (salmon), Ovis aries (sheep), and D. melanogaster (fruit fly).

Prediction of neotropical tree and liana species richness from soil and climatic data

We present an analysis of local species richness in neotropical forests, based on a number of 0.1 ha samples of woody plants collected by the late Alwyn Gentry. For each of 69 forests, soils were analysed and climatic data were collated. Using transformed independent variables and interaction terms, multiple regression equations were developed that explained the greatest possible amount of variation in species richness, and the best equations were selected on the basis of regression diagnostics. The best models are presented for (a) all neotropical forests, (b) forests west of the Andes (transandean) and (c) east of the Andes (cisandean), and for various subsets based on elevation and annual rainfall. For the whole dataset, and for most subsets, annual rainfall and rainfall seasonality were the most important variables for explaining species richness. Soil variables were correlated with precipitation — drier forests have more nutrient-rich soils. After the inclusion of rainfall variables, available soil nutrient concentrations contributed little to explaining or accounting for additional variation in species numbers, indicating that tropical forest species richness is surprisingly independent of soil quality. The results are consistent with the hypothesis that plants in mature tropical forests may obtain nutrients through the process of direct cycling, in which mineral nutrients are extracted from litterfall before they enter the soil. The strong relationship between community species richness and rainfall patterns has implications for biodiversity conservation. Wet forests with an ample year-round moisture supply harbour the greatest number of woody plant species and should be a focus of conservation efforts.

Effects of isolation, logging and dispersal on woody-species richness of islands

Isolation effects on species richness of woody plants were investigated in a system of islands that were created by the filling of the Clarks Hill Reservoir, Georgia. This reservoir was built between 1946–1954. Some islands were logged and cleared of woody plants prior to the filling of the reservoir and others were not logged. The presence of logged versus unlogged islands in the same system allowed us to test whether and how geographical isolation interacts with island history and species-specific dispersal properties in determining patterns of among-island variation in species number. Thirty-six years after the islands were created, logged islands had significantly fewer species of woody plants than unlogged ones. On logged islands, total number of woody species was negatively correlated with distance to the closest mainland (r=−0.95). On unlogged islands, variation in species number was very low (CV=4.9%) and was not correlated with distance to the mainland. These results indicate that the studied system as a whole has not yet reached equilibrium. However, the mean number of species on unlogged islands was very close to the intercept of the regression obtained for logged islands, suggesting that islands close to the mainland have already reached their equilibrium species richness. This conclusion is consistent with predictions of island biogeography theory. When species representing different dispersal properties were analyzed separately, statistically significant distance effects were obtained for bird-dispersed species (r=0.88) and for species with no adaptations to bird or wind dispersal (r=0.81). Wind-dispersed species did not show a decrease in species number with increasing isolation, but their relative frequency was positively and significantly correlated with distance to the mainland (r=0.94). Historical factors, as well as differences among species in dispersal properties, are important in explaining patterns of among-island variation in species number.

An analysis of the distribution of fish species in a large prairie lake

The distribution of fishes in Dauphin Lake, a large, shallow, turbid, prairie lake in west‐central Manitoba, was examined using gillnets. Catch per unit effort was used to assess differences in distribution thai may be attributed lo year, season, lake zone (inshore, offshore), substratum, water depth, water temperature, turbidity and presence of other fish species. Although 13 species were caught, only the distributions of the six most abundant was analysed. Variation in number of species caught was attributed mainly to lake zone, water depth and water temperature. White sucker (Catastomus commersoni) distribution can be explained by zone and temperature. Shorthead redhorse (Moxostoma macrolepidotum) catches were related to depth and temperature. Cisco (Coregonus artedii) catches varied with year, zone and temperature. Variances in northern pike (Esox Indus) distribution reflected year and zone. Walleye (Stizostedkm vitreum) varied with year, depth and temperature and differences in the catches of yellow perch (Pertaflurescens) were attributed to year, depth, temperature and turbidity. They were also positively correlated to the numbers of northern pike caught.

An analysis of the distribution of fish species in a large prairie lake

The distribution of fishes in Dauphin Lake, a large, shallow, turbid, prairie lake in west-central Manitoba, was examined using gillnets. Catch per unit effort was used to assess differences in distribution thai may be attributed lo year, season, lake zone (inshore, offshore), substratum, water depth, water temperature, turbidity and presence of other fish species. Although 13 species were caught, only the distributions of the six most abundant was analysed. Variation in number of species caught was attributed mainly to lake zone, water depth and water temperature. White sucker (Catastomus commersoni) distribution can be explained by zone and temperature. Shorthead redhorse (Moxostoma macrolepidotum) catches were related to depth and temperature. Cisco (Coregonus artedii) catches varied with year, zone and temperature. Variances in northern pike (Esox Indus) distribution reflected year and zone. Walleye (Stizostedkm vitreum) varied with year, depth and temperature and differences in the catches of yellow perch (Pertaflurescens) were attributed to year, depth, temperature and turbidity. They were also positively correlated to the numbers of northern pike caught.

Fruit Characteristics, Life Forms, and Species Richness in the Plant Family Rubiaceae

We investigated how fruit types, or combinations of fruit types and life forms, affect species number in the large, mostly tropical plant family Rubiaceae. The aim was to test the hypothesis that animal dispersal promotes species diversification in plants. Information was compiled for 427 of the 630 genera in the family. Analyses were based on genera and on groups of taxa derived from a cladistic study of chloroplast DNA variation in the family. The results demonstrated that no single trait explains variation in species number. Instead, certain combinations of dispersal modes and life forms promote species richness. Genera consisting of (1) herbs with abiotic dispersal, (2) shrubs with animal dispersal, and (3) shrubs and trees with winged seeds were all characterized by comparatively large species numbers. These results imply an association between seed dispersibility and rate of species diversification.