Response of American dippers (Cinclus mexicanus) to variation in stream water quality

1. Semi‐aquatic birds may be sensitive to altered water quality. While avian species are not used in the bioassessment of streams, they may complement the more common use of benthic macroinvertebrates and fish. We estimated the extent to which water quality can predict attributes of the populations of one common semi‐aquatic bird, the American dipper (Cinclus mexicanus). 2. First, we estimated dipper presence/absence in relation to water quality as measured by a multimetric assessment index and individual bioassessment metrics. Second, we estimated dipper territory area and reproductive success in response to variation in water quality. We studied the diet, territory area and fecundity of dippers and sampled benthic macroinvertebrates, water chemistry and physical variables at 32 sites with and 17 sites without nesting dippers. 3. Dipper presence was only weakly related to chemical, physical and commonly recorded bioassessment metrics such as per cent Ephemeroptera, Plecoptera and Trichoptera (%EPT). Dippers were strongly related to the abundance of their common prey, Drunella and Heptageniidae, which are only a small component of the commonly recorded bioassessment metrics. The variances in territory area and reproductive success were weakly predicted by water quality variables. 4. Dipper presence reflected disturbance as measured by their common prey, showing that lower abundance of these stream invertebrates affected this semi‐aquatic bird. We suggest dipper presence/absence might be used in multimetric indices of biotic integrity for the bioassessment of streams.     

Time-activity budgets and energetics of Dipper Cinclus cinclus are dictated by temporal variability of river flow

The white-throated Dipper (Cinclus cinclus) is unique among passerine birds by its reliance on diving to achieve energy gain in fast-flowing waters. Consequently, it should have evolved behavioural adaptations allowing responding directly to runoff patterns (one of the assumptions of the Natural Flow Regime Paradigm—NRFP). In this study (October 1998–August 2001), we investigated how behavioural and energy use strategies in Dippers might vary under the natural flow regime of snowmelt-dominated streams in The Pyrénées (France) where natural flow regime is highly seasonal and predictable. We recorded time spent in each of 5 behavioural activities of ringed birds to estimate time–activity budgets and derive time–energy budgets enabling the modelling of daily energy expenditure (DEE). Annual pattern in ‘foraging’ and ‘resting’ matched perfectly the annual pattern of the natural regime flow and there was a subtle relationship between water stage and time spent ‘diving’ the later increasing with rising discharge up to a point where it fell back. Thus, time–activity budgets meet the main prediction of the NRFP. For males and females Dippers, estimates of feeding rates (ratio E_obs/E_req = observed rate of energy gain / required foraging rate) and energy stress (M = DEE / Basal Metabolic Rate) also partly matched the NFRP. Maximum value for the ratio E_obs/E_req was registered in May whilst M peaked in spring. These ratios indicated that Pyrenean Dippers could face high energy stress during winter but paradoxically none during high snowmelt spates when food is expected to be difficult to obtain in the channel and when individual birds were observed spending ca 75% of the day ‘resting’. Annual pattern in DEE did not match the NFRP ; two phases were clearly identified, the first between January to June (with oscillating values 240–280 kJ d^− 1 ind^− 1) and the second between July and December (200–220 kJ d^− 1 ind^− 1). As total energy expenditure was higher during the most constraining season or life cycle, we suggest that energy management by Dippers in Pyrenean mountain streams may fit the ‘peak total demand’ hypothesis. At this step of the study, it is not possible to tell whether Dippers use an ‘energy-minimisation’ or an ‘energy-maximisation' strategy.     

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.     

Interactions of bacterial cytokinins and IAA in the rhizosphere may alter phytostimulatory efficiency of rhizobacteria

Phytohormones from rhizobacterial origin have been linked to their phytostimulation potential. However, while studying the efficacy of plant growth promoting bacteria, focus has always been on a single hormone. The role of plant hormones often overlay and they mutually modulate their effect. In current study focus was on the role of two hormones (cytokinins and indole acetic acid) in phytostimulation by rhizobacteria. Endogenous rhizosphere bacteria were isolated and screened for the presence of phytohormones. Bacterial strains from three different genera (Pseudomonas, Bacillus and Azospirillum) were screened positive for cytokinins and IAA. Phytohormones were simultaneously determined in SPE purified bacterial extract by ultra performance liquid chromatography (UPLC) coupled to a tandem mass spectrometer through electrospray interface. Cytokinins and IAA were determined in positive and negative mode, respectively with MRM scan. Zeatin, zeatin riboside and dihydrozeatin riboside were detected and quantified in the selected strains. Significant positive correlation between cytokinins and IAA in bacterial culture and plant endogenous hormones (r = 0.933 and r = 0.983; P = 0.01, respectively) was observed. However, strains with high IAA to cytokinins ratio could hardly enhance in-planta cytokinins, indicating antagonistic relation between the two hormones. Significant correlation of cytokinin with shoot length (r = 0.797; P = 0.01), fresh weight (r = 0.685; P = 0.01) and dry weight (r = 0.704; P = 0.01) was reported under axenic conditions. Bacterial IAA was correlated negatively to root length (r = 0.853; P = 0.01) and positively correlated to the number of roots (r = 0.964; P = 0.01). In natural conditions maximum increase in spike length (33%), number of tillers (71%) and weight of seeds (39%) was documented at final harvest in bacterially inoculated plants.     

Phytostimulation and biofertilization in wheat by cyanobacteria

Cyanobacteria are commonly used for the phytostimulation and biofertilization of agriculture crops due to their nitrogen-fixing ability. However, the contribution by their phytohormones has been neglected. This study focuses on the screening of rhizospheric and free-living cyanobacteria for in vitro phytohormones production and growth stimulation in wheat. Selected isolates were shown to release cytokinin and indole-3-acetic acid (IAA) by using UPLC coupled with MS/MS via an electrospray interface. The maximum cytokinin and IAA concentration was 22.7 pmol mg⁻¹ ch-a and 38 pmol mg⁻¹ ch-a, respectively, in the culture medium of Chroococcidiopsis sp. Ck4 and Anabaena sp. Ck1. The growth of wheat inoculated with cyanobacterial strains was stimulated under axenic as well as field conditions. Seed germination, shoot length, tillering, number of lateral roots, spike length, and grain weight were significantly enhanced in inoculated plants. The maximum increase in grain weight (43%) was demonstrated in wheat plants inoculated with Chroococcidiopsis sp. Ck4 under natural conditions. Positive linear correlation of cyanobacterial cytokinin with shoot length (r = 0.608; P = 0.01), spike length (r = 0.682; P = 0.01), and grain weight (r = 0.0.869; P = 0.01) was recorded. Similarly, cyanobacterial IAA was correlated with the root growth parameters shoot length (r = 0.588; P = 0.01), spike length (r = 0.0.689; P = 0.01), and weight of seeds (r = 0.480; P = 0.05). The endogenous phytohormones pool of the plant was enhanced significantly as a result of the plant–cyanobacteria association in the rhizosphere. It was concluded that cyanobacterial phytohormones are a major tool for improved growth and yield in wheat.     

Influence of Arbuscular Mycorrhizal (AM) Fungi and Salinity on Seedling Growth, Solute Accumulation, and Mycorrhizal Dependency of Jatropha curcas L.

Production of Jatropha curcas as a biodiesel feedstock on marginal lands is growing rapidly. Biomass production on these lands is limited. Hence, the objective of this study was to evaluate the effect of arbuscular mycorrhiza (AM) fungi and salinity (0.1, 0.2, 0.3, 0.4, and 0.5% NaCl) on (1) seedling growth, leaf relative water content (RWC), lipid peroxidation, solute accumulation (proline and sugars), and photosynthetic pigments (Chl a and b) of Jatropha; (2) mycorrhizal colonization (%) and mycorrhizal dependency (MD) of Jatropha; and (3) glomalin content (Bradford reactive soil protein) in soil. Increased soil salinity significantly (P < 0.05) decreased AM root colonization (r ² = 0.98) of AM-inoculated plants and decreased survival (r ² = 0.93) and growth (shoot length, r ² = 0.89; tap root length, r ² = 0.93; shoot diameter, r ² = 0.99; shoot dry weight, r ² = 0.92; and root dry weight, r ² = 0.92) of non-AM-inoculated Jatropha. Under salt stress, AM-inoculated Jatropha plants had greater dry weight of shoots and roots, better leaf water status, less leaf membrane damage (low lipid peroxidation activity), higher solute (proline and sugars), and higher leaf chlorophyll concentrations than non-AM-inoculated plants. The mycorrhizal dependency (MD) of Jatropha increased from 12.13 to 20.84% with salinity (0–0.4% NaCl). Root AM colonization (%) and glomalin content in soil were negatively correlated with salinity (P < 0.05, r = −0.95). We conclude that inoculation with AM fungi lessens the deleterious effect of salt stress on seedling growth parameters under salt levels up to 0.5% NaCl (electrical conductivity of 7.2 dS m⁻¹). Inoculation of Jatropha seedlings with AM fungi can promote the establishment of Jatropha under NaCl-induced stress.     

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.     

Iron plaque formation on wetland plants and its influence on phosphorus,calcium and metal uptake

We investigated Fe plaque formation and Ca, Cu, Mn, Zn, and P uptake capacities of fifteen kinds of wetland plants. The test plants were cultured in 3 l nutrient solutions for 8 days. Fe plaque was induced by adding 200 mg l⁻¹ Fe²⁺ as FeSO₄·7H₂O for 4 days in one set of experiment and 8 days in another. This plaque ranged from 2.38 to 8.67 mg g⁻¹ of plant root after 4 days and from 4.56 to 15.71 mg g⁻¹ of plant root after 8-day treatment. In both experimental durations, the plaque was significantly correlated with root surface area (r = 0.904 and 0.878, P < 0.01). Thus, Canna generalis, Typha latifolia and Thalia dealbata, with their larger root surface areas (>1,400 cm²), formed relatively greater Fe plaque amounts. The amounts of Ca, Cu, Zn and P in the Fe plaques were significantly correlated with Fe plaque amount, (r = 0.819, 0.742, 0.693, 0.917, respectively, for these four elements for the 4-day treatment; and r = 0.917, 0.768, 0.949, 0.872, respectively, for 8-day treatment, P < 0.01). Plants varied widely in accumulating Ca, Cu, Mn, Zn, and P in their tissues. The amounts accumulated on root were significantly correlated with Fe plaque amount in both for 4- and 8-day exposure treatments with Fe (r = 0.973, 0.847, 0.709, 0.837, 0.892, respectively, for 4-day treatment; and r = 0.943, 0.691, 0.843, 0.957, 0.983, respectively, for 8-day treatment, P < 0.01). No such significant correlations were found for the Fe plaque in shoot. Canna generalis, Typha latifolia and Thalia dealbata were superior in Ca, P and Zn uptake, while Canna generalis and Thalia dealbata accumulated Cu and Mn well in case of concentrated wastewater treatment.     

Reproductive traits of shovelnose sturgeon Scaphirhynchus platorynchus (Rafinesque, 1820) in the lower Platte River,Nebraska

We assessed reproductive status, fecundity, egg size, and spawning dynamics of shovelnose sturgeon Scaphirhynchus platorynchus in the lower Platte River. Shovelnose sturgeon were captured throughout each year during 2011 and 2012 using a multi‐gear approach designed to collect a variety of fish of varying sizes and ages. Fish were collected monthly for a laboratory assessment of reproductive condition. Female shovelnose sturgeon reached fork length at 50% maturity (FL₅₀) at 547 mm and at a minimum length of 449 mm. The average female spawning cycle was 3–5 years. Mean egg count for adult females was 16 098 ± 1103 (SE), and mean egg size was 2.401 ± 0.051 (SE) mm. Total fecundity was positively correlated with length (r² = 0.728; P < 0.001), mass (r² = 0.896; P < 0.001), and age (r² = 0.396; P = 0.029). However, fish size and age did not correlate to egg size (P > 0.05). Male shovelnose sturgeon reached FL₅₀ at 579 mm and at a minimum length of 453 mm. The average male spawning cycle was 1–2 years. Reproductively viable male and female sturgeon occurred during the spring (March–May) and autumn (September–October) in both years, indicating spring and potential autumn spawning events. Shovelnose sturgeon in the lower Platte River are maturing at a shorter length and younger age compared to populations elsewhere. Although it is unknown if the change is plastic or evolutionary, unfavorable environmental conditions or over‐harvest may lead to hastened declines compared to other systems.     

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.     

Impacts of cultivation of red algae Kappaphycus alvarezii on planktonic and benthic faunal density in relation to environmental and hydrobiological parameters in tropical coastal ecosystem

The experimental cultivation of Kappaphycus alvarezii was done to investigate its daily growth rates and biomass yields, and their impacts on planktonic and benthos population densities were evaluated by floating raft culture method. Biomass yields and daily growth rates of K. alvarezii were observed. The phytoplankton and zooplankton densities varied from 25,250 to 319,033 cells/m³ and 12,060 to 207,893 individuals/m³, respectively. Similarly, macrobenthos and meiobenthos densities varied from 11,105 to117061 nos/m² and 14,740 to 727,000 nos/m², respectively. The maximum values of plankton and benthos were recorded in the control site compared with the culture sites. Pearson correlation suggests that growth rate of K. alvarezii is negatively correlated with zooplankton density (r = ?0.9); macrobenthos (r = ?0.9) and meiobenthos density (r = ?0.8) at P < 0.01 level. The crop yield negatively correlated with macrobenthos density (r = ?0.7) at P < 0.01 level and with meiobenthos density (r = ?0.6) at P < 0.05 level for the two culture sites. One- way ANOVA revealed the differences in the growth rates and crop yields. Among the two culture sites, culture site 1 showed significant variation (P < 0.01), whereas culture site 2 showed statistically insignificant (P > 0.01). The conclusion suggests that water nutrient declined at both culture sites than control site. So, the plankton and benthic fauna were declined in the culture sites.     

Length‐weight relationships of three estuarine fish species from Bangladesh

The length‐weight relationships (LWRs) of three fish species; Toxotes chatareus (Hamilton, 1822), Datnioides polota (Hamilton, 1822), and Chela cachius (Hamilton, 1822) collected between September 2016 and August 2017 from Tentulia estuary of Bangladesh were analyzed. Fish were caught seasonally using set bag net and cast net with mesh size of 0.5 cm and < 0.5 cm, respectively. LWRs of Toxotes chatareus, Datnioides polota and Chela cachius were calculated as W = 0.0154L^2.926 (r² = .962), W = 0.0149L^3.106 (r² = .992) and W = 0.0109L^2.968 (r² = .981), respectively. The study provides a new maximum total length for Chela cachius.     

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.     

Pattern of leaf vein density and climate relationship of Quercus variabilis populations remains unchanged with environmental changes

The leaf vein traits of plants result partially from adaptations to environmental factors during the long-term evolution. However, no general conclusion on the variation trend of the vein density along a climate gradient or the response of such vein density–climate relationship pattern to climate changes has been made. We examined the variations in leaf vein density and other leaf traits of oriental oak (Quercus variabilis) in 10 in situ populations (in situ populations) across temperate-subtropical biomes and the response of the leaf vein density to environmental changes in 7 populations grown in a common garden (garden populations). The results show that the minor vein density of the in situ populations (≥3rd order) significantly decreased with increasing latitude (r ²  = 0.44 and P = 0.04). This pattern remained unchanged for the garden populations (r ²  = 0.67 and P = 0.02). The minor vein densities of both the garden and in situ populations were positively correlated to the mean annual temperature (MAT) of the origins (r ²  = 0.66 and P = 0.03 for the garden populations; r ²  = 0.37 and P = 0.06 for the in situ populations), but their correlation to the mean annual precipitation (MAP) of the origins was not significant. Compared with the MAT and MAP, the vein density displayed a significantly lower correlation to climate variables in the current year or the current-year growing seasons. For the garden populations, the minor vein density significantly increased with leaf dry mass per area and decreased with petiole length and leaf length. These results imply that leaf vein density is genotypically fixed and is therefore not responsive to temporal changes in the growing conditions.     

Successional changes in soil nitrogen availability,non-symbiotic nitrogen fixation and carbon/nitrogen ratios in southern Chilean forest ecosystems

Vast areas of southern Chile are now covered by second-growth forests because of fire and logging. To study successional patterns after moderate-intensity, anthropogenic fire disturbance, we assessed differences in soil properties and N fluxes across a chronosequence of seven successional stands (2–130 years old). We examined current predictions of successional theory concerning changes in the N cycle in forest ecosystems. Seasonal fluctuations of net N mineralization (N_min) in surface soil and N availability (N_a; N_a=NH ₄ ⁺ –N+NO ₃ ^– –N) in upper and deep soil horizons were positively correlated with monthly precipitation. In accordance with theoretical predictions, stand age was positively, but weakly related to both N_a (r ²=0.282, P<0.001) and total N (N_tot; r ²=0.192, P<0.01), and negatively related to soil C/N ratios (r ²=0.187, P<0.01) in surface soils. A weak linear increase in soil N_min (upper plus deep soil horizons) was found across the chronosequence (r ²=0.124, P<0.022). N_min occurred at modest rates in early successional stands, suggesting that soil disturbance did not impair microbial processes. The relationship between N fixation (N_fix) in the litter layer and stand age best fitted a quadratic model (r ²=0.228, P<0.01). In contrast to documented successional trends for most temperate, tropical and Mediterranean forests, non-symbiotic N_fix in the litter layer is a steady N input to unpolluted southern temperate forests during mid and late succession, which may compensate for hydrological losses of organic N from old-growth ecosystems.     

Maternal behaviours may explain riffle‐scale variations in some stream insect populations

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Gonad maturation and spawning of cobia,Rachycentron canadum (Linnaeus, 1766) off the Dungun coast,Malaysia

The reproductive biology of cobia, Rachycentron canadum, from the coastal waters of Dungun, Malaysia was studied from June 2014 to May 2015. From commercial trawls, a total of 201 samples (combined sexes) were collected (fork lengths [FL] 37.5–124.0 cm; body weights 0.5–20.4 g). The overall sex ratio of females to males was 1:0.9, which was not significantly different (χ² = 2.12, df = 1; p < .05). Estimations of length at 50% maturity (L₅₀) showed that both sexes matured at approximately 75 cm FL; estimated spawning frequency was 6 days. Mean batch fecundity (BF) ranged from 0.55 to 4.32 million eggs. The average number of eggs per gram of ovary was from 2,100 to 5,400 eggs, and relative fecundity 147 eggs/g. There was a weak positive correlation (r² = .48) between BF and female FL as well as BF with an ovary‐free body weight (r² = .56), possibly due to females being in a continuous spawning condition and some possibly half‐spent, based on the histological examination of the female gonads. Despite cobia being asynchronous spawners, the gonadosomatic index in both males and females showed peaks in June, November, and particularly March. Based on histological examination, spawning‐capable males were encountered throughout the study period, whereas spawning‐capable females in the late developing subphase were found mostly in March and April. This is the first study on the reproductive aspects of cobia in Malaysian waters.     

Big boys get big girls: Factors influencing pupping site and territory location in Australian fur seals

To examine the factors influencing birth site selection and territory location in Australian fur seals (Arctocephalus pusillus doriferus), habitat variables (slope, substrate, and elevation) were quantified in seven zones within a breeding colony on Kanowna Island (39º15′S, 146º18′E), southeastern Australia. Distribution across the colony was not uniform with zones at low elevations (i.e., close to water) being preferred areas, having earlier occupancies and greater female densities. Body length of females and territorial adult males was assessed using laser‐metrics. Average female length increased throughout the breeding season, within zones and across the colony, with larger females arriving to give birth later. Larger females also occupied areas of lower elevation close to water. Adult male body length had no influence on territory size, but was positively correlated with the number of females in harems (r² = 0.70, P < 0.05) and female length (r² = 0.87, P < 0.01) within harems. By monopolizing larger females, adult males may enhance their reproductive success as these individuals are more likely to give birth and have greater weaning success.     

Age and growth of early-life-stage Atlantic tarpon (Megalops atlanticus) from the northcentral Gulf of Mexico

Age and growth of early-life-stage Atlantic tarpon Megalops atlanticus collected from Mississippi coastal waters in the northcentral Gulf of Mexico (GOM) are described using otolith microstructure analysis. Tarpon leptocephali (n = 95, 16.0—27.8 mm standard length, L_S) collected from June throughOctober 2013—2018, ranged in age from 22 to 43 days (mean = 30.9 ± 0.5 days). Leptocephalus somatic growth rates ranged 0.46—1.24 mm day⁻¹ (mean = 0.76 ± 0.02 mm day⁻¹), and leptocephalus otolith growth rates ranged 1.78—3.97 μm day⁻¹ (mean = 2.58 ± 0.04 μm day⁻¹). Growth rates were inversely correlated to leptocephalus age, indicating the shrinkage phase associated with leptocephalus metamorphosis. Juvenile tarpon (n = 358, 50—359 mm fork length, L_F) were collected from August through December 2007—2018. Juveniles exhibited a positive allometric relationship (adjusted R² = 0.99, P < 0.001) between length and mass. The age of 100 juveniles (71—277 mm L_F) ranged from 76 to 174 days. Juvenile growth rate was estimated as 1.56 ± 0.11 mm day⁻¹. Significant (P < 0.001) linear relationships were found between juvenile age and otolith metrics, including otolith mass (R² = 0.81) and radius (R² = 0.68). Evaluation of the backcalculated hatch dates suggests that specimens in the collection hatched from late May through mid-September with slight peaks during July and August. A Rao's Spacing Test of Uniformity indicates the presence of significant lunar periodicity in leptocephalus hatch dates (n = 95, U = 250.1, P < 0.05), with 50% of the leptocephali hatched within 5 days (before or after) of the full moon. This study fills critical gaps in the scientific knowledge of tarpon and provides estimates of early-life-history metrics for an iconic game fish at the northernmost extent of its GOM range.     

Two lowland stream riffles – linkages between physical habitats and macroinvertebrates across multiple spatial scales

The physical structure of two riffles in a lowland Danish stream was studied and its importance for the composition and density of the macroinvertebrate communities was evaluated. The two riffles were visually assessed to be very similar, but measurements revealed that they differed in overall hydraulic conditions, stability, substratum composition and consolidation. Differences affected abundance of both burrowing and surface dwelling macroinvertebrates. The unstable unconsolidated riffle had higher total macroinvertebrate abundance (4137 m⁻² vs. 1698 m⁻²), diptera abundance (2329 m⁻² vs. 386 m⁻²) and total estimated species richness (31.7 vs. 28.8) as well as lower evenness (0.77 vs. 0.83) than the compact riffle. Among samples within the unconsolidated riffle, variations in macroinvertebrate communities were related to differences in mean substratum particle size. Here a linear log–log relationship existed between macroinvertebrate abundance, the abundance of EPT taxa and the median particle size (r ² _total = 0.46, p = 0.002; r ² _EPT = 0.73, p < 0.001). No similar relationships were evident on the consolidated riffle. Moreover, macroinvertebrate communities on the unconsolidated riffle were dominated by species with a high colonising potential. Despite being assessed to the same morphological unit, physical variation between riffles was surprisingly high as the riffles differed substantially with respect to consolidation, substratum heterogeneity and overall hydraulic structure. Macroinvertebrate community structure and composition also differed between riffles despite being drawn from the same species pool. The findings address the question if we use the correct methods and parameters when assessing the macroinvertebrate communities at the scale of the morphological unit.