Maximum sustainable swimming speeds of late-stage larvae of nine species of reef fishes

We examined the maximum sustainable swimming speed of late-stage larvae of nine species of tropical reef fishes from around Lizard Island, Great Barrier Reef, Australia. Larvae were captured in light traps and were swum in flumes at different experimental swimming speeds (of 5 cm s⁻¹ intervals) continuously for 24 h. Logistic regression was used to determine the speed at which 90% of larvae were able to maintain swimming, and this was used to indicate the maximum sustainable swimming speed for each species. Maximum sustainable swimming speeds varied among the species examined, with the lethrinid maintaining the fastest sustainable swimming speed (24 cm s⁻¹), followed by the Pomacentridae (10-20 cm s⁻¹) and the Apogonidae (8-12 cm s⁻¹). U-crit (maximum speed) explained 64% of the variation in sustainable speed among species, whereas total length only explained 33% of the variation in sustained swimming. A regression fitted across species suggests that 50% U-crit is a good approximation of the speed able to be maintained by these larvae for 24 h. A model based on a cubic relationship between sustained swimming time and speed was found to be more successful than either length or U-crit as a method of estimating sustainable swimming speed for most of the species examined. Overall, we found that swimming speed is an important factor when considering the potential for active swimming behaviour to influence dispersal patterns, recruitment success and levels of self-recruitment in reef fish larvae and needs to be carefully considered in models of larval dispersal.     

Species richness of Protozoa in Japanese lakes

The protozoan fauna and species richness in the pelagic zone of 15 Japanese lakes were investigated in 1996 using polyurethane foam (PF) substrates. The most common species were flagellates, such as Cryptomonas erosa, Oikomonas termo, and Pleuromonas jaculans. Cinetochilum margaritaceum and Actinophrys sol were the most common species of the Ciliata and Sarcodina, respectively. The similarity of species occurrence was calculated from presence/absence data, but this revealed no clear trend with respect to the influence of lake properties such as trophic state, surface area, or mean depth. The occurrence pattern of Protozoa was most similar in L. Chuzenji and L. Biwa (north basin), two oligomesotrophic natural lakes. Log species richness was positively correlated with log total phosphorus (r = 0.54, P < 0.05) and negatively with log mean depth (r = −0.58, P < 0.05). The diversity index (Margalef's formula), highly correlated with the total species number (r = 0.85, P < 0.01), was negatively correlated with log lake area (r = −0.71, P < 0.01). The logarithm of Phytomastigophora number was positively correlated with log total nitrogen (r = 0.53, P < 0.05), and the logarithm of Ciliata number was negatively correlated with log lake area (r = −0.55, P < 0.05). The species richness of Protozoa on PF substrates was determined by both the nutrient status of the lake and the distance from the location of the suspended PF substrate to the lake bottom or shore. Received: September 25, 1999 / Accepted: January 6, 2000     

Metabolic rates in an anadromous clupeid, the American shad (Alosa sapidissima)

To assess the energetics of migration in an anadromous fish, adult American shad (Alosa sapidissima) were swum in a large respirometer at a range of speeds (1.0–2.3 body lengths (BL) s⁻¹, 13–24 °C). Metabolic rate (M_O2) was logarithmically related to swimming speed (Bl s⁻¹; r ² = 0.41, slope = 0.23 ± 0.037) and tailbeat frequency (beats × min⁻¹; r ² = 0.52, slope = 0.003 ± 0.0003). Temperature had a significant effect on metabolic rate (r ² = 0.41) with a Q₁₀ of 2.2. Standard metabolic rate (SMR), determined directly after immobilization with the neuroblocker gallamine triethiodide, ranged from 2.2–6.2 mmolO₂ kg⁻¹ h⁻¹ and scaled with mass (W) such that SMR = 4.0 (±0.03)W^{0.695(±0.15)}. Comparison of directly determined and extrapolated SMR suggests that swimming respirometry provides a good estimate of SMR in this species, given the differences in basal activity monitored by the two methods. Overall, American shad metabolic rates (M_O2 and SMR) were intermediate between salmonids and fast-swimming perciforms, including tunas, and may be a result of evolutionary adaptation to their active pelagic, schooling life history. This study demonstrates variability in metabolic strategy among anadromous fishes that may be important to understanding the relative success of different migratory species under varying environmental conditions. Accepted: 3 March 1999     

Plant communities and landscape diversity along a Canadian Arctic river

Abstract. We analysed the structure and diversity of the vegetation along an Arctic river to determine the relationship between species richness and plant community structure. We examined whether variation in species richness along the corridor is structured as (1) an increase in the number of communities due to increasing landscape heterogeneity, (2) an increase in the floristic distinctiveness (β-diversity) of communities, or (3) an increase in within-community richness (α-diversity) as species-poor communities are replaced by species-rich communities. We described 24 community types and analysed the relationship between site vascular species richness (γ-diversity) and β-diversity, α-diversity, site environmental heterogeneity, and the number of distinct plant communities. We also measured diversity patterns of vascular, bryophyte, and lichen species within communities and examined their relationship to community-level estimates of environmental factors. We found that an increase in site species richness correlated with an increase in the number of communities (r²= 0.323, P= 0.0173) and β-diversity (r²= 0.388, P= 0.0075), rather than an increase in the α-diversity of individual communities. Moisture and pH controlled most of the differences in composition between communities. Measures of species richness and correlations with moisture and pH within communities differed among vascular, bryophyte, and lichen species. Bryophyte richness was positively correlated with moisture (r²= 0.862, P= 0.0010) and lichen richness was negatively correlated with moisture (r²= 0.809, P= 0.0031). Vascular plants had a peak in richness at pH 6.5 (r²= 0.214, P < 0.0001). We conclude that site variation in vascular richness in this region is controlled by landscape heterogeneity, and structured as variation in the number and distinctiveness of recognizable plant communities.     

Reproductive biology of Pethia ticto (Cyprinidae) from the Gorai River (SW Bangladesh)

Some aspects of reproductive biology of Pethia ticto (Hamilton, 1822) from the Gorai River of southwestern (SW) Bangladesh were investigated by regular monthly samples for a period of one year during July 2010 to June 2011. A sum of 1200 specimens (male = 454 and female = 746) were collected using cast net, lift net and conical trap. Total length (TL) and Body weight (BW) were measured with slide caliper and digital balance, respectively for each individual. Based on gonadosomatic index (GSI), modified gonadosomatic index (MGSI) and Dobriyal index (DI) first sexual maturity was 4.30 cm TL for male and 4.80 cm TL for female. Also, on the basis of higher values of GSI, MGSI and DI spawning season was ranged from April to September for P. ticto in the Gorai River ecosystem. The fecundity was ranged from 2230–8450 with a mean value of 4779 ± 1578. In addition, there was a significant relationship between total length and fecundity (r² = .931, p < .001); body weight and fecundity (r² = .943, p < .001). Therefore, the findings of this study would be very effective for sustainable management of this threatened species in the Gorai River and surrounding ecosystem.     

Relationships between butterflyfish (Chaetodontidae) feeding rates and coral consumption on the Great Barrier Reef

This study explored differences in the feeding rate among 20 species of coral reef butterflyfishes (Chaetodontidae) from Lizard Island, Great Barrier Reef. Feeding rate, measured as bites per minute (b.p.m.), varied between 2.98 ± 0.65 and 12.29 ± 0.27 (mean ± SE) according to species and was positively related to the proportional consumption of coral (r ² = 0.40, n = 20, P < 0.01), independent of phylogeny (standardised independent contrasts r ² = 0.29, n = 19, P < 0.05). All species fed actively throughout the day, with obligate corallivores having a higher feeding rate at all times than either facultative corallivores or non-corallivores. The feeding rate of the obligate corallivores was also highest during the middle of the day. For eight of the species for which data was available, there was a positive correlation between bite rate and competitive dominance (r = 0.71, P < 0.05). Chaetodon ephippium was the only species for which the feeding rate of pairs was higher than for solitary individuals.     

Swimming patterns and behaviour of upriver-migrating adult pink (Oncorhynchus gorbuscha) and sockeye (O. nerka) salmon as assessed by EMG telemetry in the Fraser River,British Columbia,Canada

Little is known about the behaviour patterns and swimming speed strategies of anadromous upriver migrating fish. We used electromyogram telemetry to estimate instantaneous swimming speeds for individual sockeye (Oncorhynchus nerka) and pink salmon (O. gorbuscha) during their spawning migrations through reaches which spanned a gradient in river hydraulic features in the Fraser River, British Columbia. Our main objectives were to describe patterns of individual-specific swim speeds and behaviours, identify swimming speed strategies and contrast these between sexes, species and reaches. Although mean swimming speeds did not differ between pink salmon (2.21 BL s^–1) and sockeye salmon (1.60 BL s^–1), sockeye salmon were over twice as variable (mean CV; 54.78) in swimming speeds as pink salmon (mean CV; 22.54). Using laboratory-derived criteria, we classified swimming speeds as sustained (<2.5 BL s^–1), prolonged (2.5–3.2 BL s^–1), or burst (>3.2 BL s^–1). We found no differences between sexes or species in the proportion of total time swimming in these categories – sustained (0.76), prolonged (0.18), burst (0.06); numbers are based on species and sexes combined. Reaches with relatively complex hydraulics and fast surface currents had migrants with relatively high levels of swimming speed variation (e.g., high swimming speed CV, reduced proportions of sustained speeds, elevated proportions of burst speeds, and high rates of bursts) and high frequency of river crossings. We speculate that complex current patterns generated by river constrictions created confusing migration cues, which impeded a salmon's ability to locate appropriate pathways.     

Validation of a physical activity questionnaire in the elderly

The purpose of this study was to validate a physical activity (PA) questionnaire, Questionnaire d'Activité Physique Saint-Etienne (QAPSE), in an homogenous population of elderly subjects and to estimate its potential for application in routine PA assessments in that age group. A group of 65 (31 men and 34 women) community dwelling, healthy people aged 65–84 years volunteered to participate in a validation substudy comparing maximal oxygen uptake ( ) and anthropometric data. correlated positively with mean habitual daily energy expenditure (MHDEE) (r=0.56,P<0.0001), greater than 3MET (metabolic equivalent) daily energy expenditure (DEE) activity (r=0.371,P=0.002), leisure activity (r=0.368,P=0.003), sports activity (r=0.461,P<0.0001), basic daily activity (r=0.325,P=0.008) and moving DEE activity (r=0.273,P=0.028) in both sexes, with MHDEE (r=0.366,P=0.043) and moving DEE activity (r=0.388,P=0.031) in the men and with MHDEE (r=0.624;P<0.001), greater than 3MET DEE activity (r=0.513,P=0.002), leisure activity (r=0.388,P=0.024) and sports activity (r=0.683,P<0.001) in the women. The MHDEE was positively correlated with body mass (r=0.464) and with fat free mass (r=0.639) and negatively correlated with percentage body fat (r=−0.501). In a reproducibility substudy (n=44) a paired Student'st-test, based on mean differences between the two administrations of the questionnaire did not reach statistical significance for any of the QAPSE activity scores studied. Test-retest correlation coefficients ranged from 0.648 for moving score to 0.967 for MHDEE with correlation coefficientP values being less than 0.001 for all of the QAPSE activity scores. We concluded that QAPSE demonstrated excellent repeatability and good validity in relation to physical fitness and anthropometric data in the population of these healthy elderly volunteers.     

Diversity and geographic distribution of <Emphasis Type="Italic">Chlorococcales</Emphasis> (<Emphasis Type="Italic">Chlorophyceae</Emphasis>) in contrasting lakes along a latitudinal transect in Argentinean Patagonia

The present study focuses on the geographic distribution and biodiversity of the Chlorococcales in Patagonian lakes, covering a latitudinal transect. Two different approaches are considered (a) a review of the historical records of Chlorococcales in Patagonia and (b) the analysis of the morphology-based species diversity, ecological remarks, and geographic distribution of the chlorococcalean species recorded in 33 aquatic environments during surveys 2007 and 2008. A total of 308 chlorococcalean species were recorded throughout a 60-year period in Patagonian freshwater systems, encountering the highest chlorococcalean richness in lakes and shallow lakes located in the more intensively sampled areas. In our surveys 2007–2008, 72 chlorococcalean taxa were registered, among which 80% are worldwide distributed, about 19% are restricted to cold temperate areas in both hemispheres and one species (Pediastrum patagonicum) is one of the taxa probably endemic for Patagonia. The chlorococcalean richness in relation to the environmental factors, revealed that it is directly correlated with the trophic status of the water bodies (chl a: r = 0.52 and DIN: r = 0.47; P < 0.05). The latitude was inversely correlated with the species richness (r = −0.40; P < 0.05), and the chlorococcalean biodiversity of the Andean lakes (mean value: 3.64) was significantly lower (P = 0.0022) than that of the lakes from the Patagonian Plateau (mean value: 9.62). In this study we observed a decreasing trend in the biodiversity of Chlorococcales with increasing latitude, which fits in the existing ecological pattern described for different groups of organisms.     

富营养化对白洋淀底栖-浮游耦合食物网结构和功能的影响

国际湖沼学的长期研究发现,一个完整的湖泊生态系统应包括底栖食物网和浮游食物网,而营养条件变化会显著改变浅水湖泊中底栖-浮游食物网的结构和功能。为了明晰富营养化对浅水湖泊底栖-浮游耦合食物网结构和功能的影响,以浅水草型湖泊——白洋淀为研究区,运用野外监测和ECOSIM与ECOPATH(Ew E)模型相结合方法,构建白洋淀底栖-浮游耦合食物网的概念模型,模拟1982—2011年间富营养化对白洋淀底栖路径和浮游路径的结构和功能影响:(1)野外监测的结果表明,从1999年至今白洋淀一直处于富营养化状态;(2)Ew E模型模拟结果表明1982—2006年,总生物量呈下降趋势,下降比例达66.38%;能流路径从以底栖路径为主转变为以浮游路径为主;(3)运用Pearson相关分析,结果表明:浮游植物与TN(r=0.67,P0.01)和TP(r=0.37,P0.05)呈显著正相关,而底栖藻类和大型沉水植物与TN(r=0.77,P0.01;r=0.67,P0.01)和TP(r=0.54,P0.01;r=0.36,P0.05)呈显著负相关。富营养化是白洋淀底栖初级和次级生产力向浮游初级和次级生产力转变的主要驱动力。采用科学的方法准确评估富营养化对湖泊底栖-浮游耦合食物网结构和功能的影响,可为湖泊生态系统管理提供技术和方法支持。     

Morphometric relationships for some species of elasmobranch from tropical eastern Pacific

This study proposes length relationship equations to determine total length of four species of sharks (Carcharhinus falciformis, Mustelus lunulatus, Sphyrna lewini and Carcharhinus limbatus) based on trunk lengths (TrL) and interdorsal lengths (IL) caught in Colombia and Central America Pacific Ocean. In Central American Pacific, data were recorded for C. falciformis, C. limbatus and S. lewini between 2006 and 2012. In the Colombian Pacific, data was recorded in 1994–1995 and from 2006 to 2012 for C. falciformis, S. lewini and M. lunulatus. In the Central American Pacific the IL – TL relationship was acceptable for C. falciformis (r² = .69) and C. limbatus which presented a good relationship (r² = .81) where most specimens were juveniles; the same trend was found for S. lewini (r² = .96). The TL‐TrL relationship estimated for species caught in the Colombian Pacific was significant for C. falciformis (r² = .98) and for M. lunulatus (r² = .84); however, for S. lewini this relationship was low (r² = .55). Results indicate this is a useful tool for fishery statistics and fishery management for elasmobranch species of the Eastern Tropical Pacific.     

Biological,chemical and physical factors influencing the seasonal change of polysaccharide concentration in irrigation-channel sediment

Variation of polysaccharide concentration in irrigation-channel sediment was determined concurrently with biological, chemical and physical factors influencing the benthic algal community. Phenol-sulphuric acid method was used to measure polysaccharide concentration. Polysaccharide concentration, biomass of benthic algae, and species composition changed spatially and temporally. Fluctuations of total suspended solid (TSS) concentration and exposure of channel bed to direct sunlight had major effects on algal growth and polysaccharide production. Polysaccharide concentration was correlated to chlorophyll a concentration (r=0.73, P<0.001) and algal biomass (r=0.57, P<0.001). Fragilaria construens and Aulacoseira (Melosira) italica were the most common diatoms in the benthic flora. Chlorophyll a concentration in the sediment showed a strong negative correlation (r=-0.99, P<0.001) with the seasonal variation of TSS concentration in channel water. The polysaccharides produced by benthic microorganisms play a major role in clogging channel bed and thereby reducing seepage from earthen irrigation channels. Correlations between polysaccharide concentration and chlorophyll a (and algal biomass) further indicate the importance of benthic algae for polysaccharide production. Since availability of light to the algal flora is critical for the production of polysaccharides, the effect of clogging can be maximized by exposing the channel bed to direct sunlight during non-irrigation period (winter).     

Genetic diversity of fragmented populations of<Emphasis Type="Italic"> Polygala reinii</Emphasis> (Polygalaceae), a perennial herb endemic to Japan

Genetic variation at 10 allozyme loci was analyzed in 14 populations of Polygala reinii (Polygalaceae), a perennial herb endemic to central Honshu, Japan, with a fragmented geographical distribution. The levels of genetic variation within species (P=80.0, A=3.10, H_E=0.303) and within populations (P=42.1, A=1.61, H_E=0.163) were considerably higher than the mean for other endemic plants or short-lived perennial herbs. Genetic differentiation among populations was also high (G_ST=0.404). The genetic distance phenogram tended to show a clustering of the populations reflecting the fragmentation of the species range. A principal component analysis revealed the same tendency, as well as three groupings of populations in the Tokai district, on the Kii Peninsula and in the northern Kinki district. A negative correlation was obtained between the levels of gene flow and geographical distance among the populations (r=–0.745, P<0.0001). These results indicated limited gene flow among populations in P. reinii, presumably due to the geographical isolation accompanying the fragmented distribution. On the other hand, the geographical differentiation between the Japan Sea and Pacific Ocean sides was found in P. reinii, suggesting the influence of postglacial migration on the establishment of the genetic structure of this species.     

Understanding ploidy complex and geographic origin of the Buchloe dactyloides genome using cytoplasmic and nuclear marker systems

Characterizing and inferring the buffalograss [Buchloe dactyloides (Nutt.) Engelm.] genome organization and its relationship to geographic distribution are among the purposes of the buffalograss breeding and genetics program. This buffalograss study was initiated to: (1) better understand the buffalograss ploidy complex using various marker systems representing nuclear and organelle genomes; (2) determine whether the geographic distribution was related to nuclear and organelle genome variation; and (3) compare the genetic structure of accessions with different ploidy levels. The 20 buffalograss genotypes (15 individuals from each genotype) that were studied included diploid, tetraploid, pentaploid, and hexaploid using nuclear (intersimple sequence repeat (ISSRs), simple sequence repeat (SSRs), sequence related amplified polymorphism (SRAPs), and random amplified polymorphic DNA (RAPDs)) and cytoplasmic markers (mtDNA and cpDNA). There was a significant correlation between the ploidy levels and number of alleles detected using nuclear DNA (ISSR, SSR, and SRAP, r=0.39, 0.39, and 0.41, P<0.05, respectively), but no significant correlation was detected when mitochondrial (r=0.17, P<0.05) and chloroplast (r=0.11, P<0.05) DNA data sets were used. The geographic distribution of buffalograss was not correlated with nuclear and organelle genome variation for the genotypes studied. Among the total populations sampled, regression analysis indicated that geographic distance could not explain genetic differences between accessions. However, genetic distances of those populations from the southern portion of buffalograss adaptation were significantly correlated with geographic distance (r= 0.48, P<0.05). This result supports the hypothesis that genetic relationship among buffalograss populations cannot be estimated based only on geographic proximity.     

A note on alarm cues in juvenile African catfish, Clarias gariepinus Burchell: Indications for opposing behavioural strategies

Following exposure of African catfish to alarm cues, a relationship (r_p = 0.60, N = 10, P = 0.07) between feed efficiency (measured as residual feed intake) and the change in percentage of time spent swimming in response to damage-released alarm cues was observed. Feed-efficient animals responded with a decrease in percentage of time spent swimming (P < 0.05) whereas feed-inefficient animals responded with an increase in percentage of time spent swimming (P < 0.05). This study shows opposing behavioural strategies in African catfish in response to damage-released alarm cues being related to feeding efficiency.     

Changes of weight and size of European bison testes during postnatal development

The material for this study was obtained from culled European bison (Linnaeus, 1758) originating from both captive breeding and free-ranging populations in Białowieża and Borecka Forests (north-east Poland), and was mostly collected from November until April. Mass difference between the right and left testis of the same individual up to 30% was considered to be physiological asymmetry, which proved typical of the species. Hypoplasia or atrophy of the testes exceeding 30% in size, were found in 37 males (13.6% of the examined animals;n=272). Cryptorchidism was recorded in 20 bison culled in Białowieża Forest at the age over 1 year (10.6% of individuals at the same age;n=188). We registered the weight of testes of 259 males aged 2 months to 20 years. In the examined males, no distinct predominance in size and weight between the right and left testes was observed. The weight of testes was significantly correlated with age (r=0.85,p < 0.0001) and body weight (r=0.93,p < 0.0001). The heaviest testicles belonged to older and sexually mature bulls aged 6–12 years (mean 216 g) and to old ones over 13 years (mean 242 g). Two testis measurements (length and width) were taken from 136 culled males, while two additional measurements (total length with the cauda of epididymis and circumference) from 65 males. The length and width of the testes were moderately correlated with age (r=0.31 andr=0.20,p < 0.01) and highly significantly correlated with testis (r=0.79,p < 0.001) and body weight (r=0.92,p < 0.001).     

Forest Canopy Properties and Variation in Aboveground Net Primary Production over Upper Great Lakes Landscapes

Relationships among aboveground net primary production (ANPP) and forest canopy properties were investigated in secondary successional forests of similar age and disturbance history in northern Lower Michigan, USA. Aboveground biomass, ANPP, canopy leaf area index (LAI), and several canopy nitrogen (N) measures were estimated from 12 stands representing major landform-level ecosystems and vegetation associations. Stand single-date and growing season average normalized difference vegetation indices (NDVI) were derived from Landsat TM. ANPP correlated most strongly with total canopy N content (r ² = 0.81, P < 0.001), followed by LAI (r ² = 0.73, P < 0.001) and area-based canopy-average leaf N concentration (r ² = 0.37, P < 0.05). No significant relationship was detected between ANPP and mass-based canopy-average leaf N concentration. Stand ANPP correlated positively with both total canopy N content (r ² = 0.62, P < 0.05) and mass-based leaf N concentration (r ² = 0.53, P < 0.05) of commonly dominant Populus spp. Relatively higher ANPP, total canopy N content and LAI corresponded to simultaneous presence of shade-intolerant P. grandidentata with shade-tolerant species. Both forms of NDVI were significantly related to ANPP, and more strongly to total canopy N content and LAI; relationships were stronger for seasonally averaged (r ² ≥ 0.75, P < 0.001) than for single-date NDVI (r ² ≥ 0.52, P < 0.01). Results indicate that on the transitioning study landscapes, ANPP was more closely related to canopy N content than to LAI, seasonally averaged NDVI was a more reliable predictor of ANPP and canopy properties than the single-date index, whereas measured canopy characteristics varied significantly between major landform-level ecosystems. The ongoing decline of P. grandidentata is likely to alter aboveground carbon and pools and fluxes in the course of succession.     

Relationships between stream habitat and breeding territory length of the Brown Dipper (Cinclus pallasii) in Taiwan

Dippers from the genus Cinclus are highly specialised predators on aquatic invertebrates, and occupy linear territories along rivers where measurements of variations in quality are relatively straightforward. For these reasons, they are ideal model species in which to examine factors affecting territory size. In this paper, we investigated the influence of stream habitats on the territory length of the Brown Dipper (Cinclus pallasii) in Taiwan. The biomass of aquatic insects and other stream habitat variables were analyzed to determine their relationships with the territory length of Brown Dippers from November 1988 to May 1989. Compared with slow-moving waters, riffle areas contained significantly greater insect biomass (paired t test, t ₁₁ = 3.49, P < 0.01), of which trichopteran larvae contributed about 70%. Dippers spent more time foraging in riffles than in slow-moving waters. In addition, dippers preferred foraging in shallow riffles, but avoided deep, slow-moving waters (G = 62.53, df = 3, P < 0.001). Territory length (1,045 ± 165 m [SE], n = 14) was negatively related to proportion of riffles (r ² = 0.5715, P < 0.01), total aquatic insect biomass (r ² = 0.5840, P < 0.01), and altitude (r ² = 0.7176, P < 0.001). In factor analysis, four factors were extracted from the 14 stream variables. However, only factor 1 was significantly related to territory length (r ² = 0.5207, P < 0.01). Factor 1 explained 42.8% of the total variance and collectively revealed the importance of high food abundance. In other words, Brown Dipper territories were the shortest along high-altitude streams with abundant riffles, fewer pools and abundant aquatic insects. These results indicate that abundant supply of accessible invertebrate prey is the most important factor affecting the territory length of Brown Dippers. This is consistent with Cinclus species elsewhere, and reveals the importance of clean, productive river ecosystems.     

Role of species identity in plant invasions: experimental test using Imperata cylindrica

The role of species richness, functional diversity and species identity of native Florida sandhill understory species were tested with Imperata cylindrica, an exotic rhizomatous grass, in mesocosms. I. cylindrica was introduced 1 year after the following treatments were established: a control with no native species, five monocultures, a grass mix treatment, a forb mix treatment, and a 3-species treatment and a 5-species treatment. Monthly cover, final biomass, root length, root length density (RLD) and specific root length (SRL) of all species were determined for one full growing season. There was a significant negative linear relationship between the cover of native species and I. cylindrica (r ² = 0.59, P = 0.01) and a negative logarithmic relationship between the biomass of native species and I. cylindrica (r ² = 0.70, P = 0.003). There was no diversity–invasibility relationship. Grasses proved to be the most resistant functional group providing resistance alone and in mixed functional communities. Repeated measures analysis demonstrated that treatments including Andropogon virginicus were the most resistant to invasion over time (P < 0.001). Significantly greater root length (P = 0.002), RLD (P = 0.011) and SRL (P < 0.001) than all of the native species and I. cylindrica in monocultures and in mixed communities made A. virginicus successful. The root morphology characteristics allowed it to be a great competitor belowground where I. cylindrica was most aggressive. The results suggest that species identity could be more important than species or functional richness in determining community resistance to invasion.     

Reactivity of isolated toad aortic rings to angiotension II: the role of nitric oxide

Little is known about the vascular actions of angiotensin II (Ang II) and nitric oxide (NO) in Amphibia. This study investigated (1) Ang II contractility, (2) NO concentrations, and (3) correlations between Ang II contractility, NO concentration and mean arterial pressure (MAP) in isolated Bufo arenarum toad aortic rings. Contractility was measured in isometric conditions, NO concentrations were determined by the Griess reaction, and MAP was determined by a direct method. In isolated toad aortic rings, Ang II produced a contractile response (292.7 ± 89.2 mg; n = 20). Furthermore, a contractile response to norepinephrine (NE) was also obtained. A significant correlation between both the Ang II and NE contractile responses was found (r = 0.89; n = 11; P < 0.01). Administration of Ang II increased MAP values (Basal 16.8 ± 1.7; n = 19 vs. Ang II 28.4 ± 1.8 mmHg; n = 19; P < 0.001), and the increase of MAP by Ang II was positively correlated with the Ang II contractile response (P < 0.01). Administration of L-NAME also increased MAP values, and this effect was higher in those toads that presented a lower pressure response to Ang II (Pearson r = −0.68; P < 0.05). NO was present in all aortic rings, and its concentrations were negatively related to the Ang II contractile response (P < 0.036) and pressure response (Pearson r = −7.08; P < 0.001). These findings suggest that, in the B. arenarum toad, the NO system contra-regulates both the contractile and pressure Ang II responses, although its action could be different in each specimen.