Do wild dogs exclude foxes? Evidence for competition from dietary and spatial overlaps

Abstract The management of wild canids (wild dogs/dingoes and foxes) presents a conservation dilemma for land managers across Australia. These canids are predators of wildlife and domestic stock but dingoes are considered native and anecdotal reports suggest that they may suppress foxes such that dingo/dog conservation may have a net benefit to wildlife. This study examines dietary and spatial interactions between wild dogs and foxes in the Greater Blue Mountains region of NSW to address the possibility of suppression through competitive exclusion by dogs on foxes. Predator diets were compared using faecal analysis as well as an analysis of 19 dietary studies from similar forest habitats in eastern Australia. Spatial relationships were examined using data from an extensive canid control programme. Diets of wild dogs and foxes showed a high degree of overlap in species taken, indicating potential for competition. But there was also evidence of resource partitioning with the size and arboreality of mammalian prey differing between the two predators. Wild dogs and foxes responded to different landscape‐scale variation in the physical environment, but there was no clear evidence of large‐scale differences in their distribution. At the fine scale there was a negative association between these predators that indicated possible temporal avoidance or localized habitat shifts. Therefore, there is evidence for dietary competition and fine‐scale exclusion, but no support for landscape‐scale exclusion of foxes by wild dogs in the Blue Mountains.     

Distribution of Oriental and German cockroaches, Blatta orientalis and Blattella germanica (Dictyoptera), in the United Kingdom

Results are presented of a survey carried out by Rentokil Ltd on the distribution of the Oriental cockroach Blatta orientalis L. and the German cockroach Blattella germanica L. in the United Kingdom. The known ranges of both species are increased considerably by the findings of the survey, with several new vice-county records for Scotland (including the Western Isles), England and Wales. The frequency at which Blatta orientalis was observed in outdoor habitats may indicate that this species sometimes spreads to new areas without human assistance.     

Production of benthic macroinvertebrate communities along a southern Appalachian river continuum

1. Annual production was estimated for macroinvertebrate communities of principle habitats along a first- to seventh-order river continuum in the southern Appalachian Mountains (U.S.A.). Annual production was relatively low in depositional habitats, pebble/gravel substrata, and on cobble devoid of plant biomass (mosses and hydrophytes). Production was greater in bedrock habitats and greatest on hydrophyte-covered cobble, with estimates reaching 364 g AFDM (ash-free dry mass)m^–2 yr^–1 in a sixth-order river reach. Annual production in depositional habitats was correlated to standing crops of benthic organic material (BOM) in low-order stream reaches but not in higher-order reaches, indicating differences in BOM availability with stream size. In cobble, pebble/gravel and bedrock habitats production was significantly correlated to standing crops of aquatic plants, which can stabilize substrata and enhance access of collector-filtering invertebrates to entrained food resources. 2. By accounting for proportional availability of habitats along the continuum, estimates of total production ranged from 5 to 154 g AFDM m^–2 yr^–1, and increased significantly with stream size. Annual production estimated for sixth- and seventh-order reaches of the continuum were amongst the highest reported thus far for lotic systems. Organization of the benthic community along the continuum, based on production estimates for individual functional feeding-groups, generally supported predictions of the River Continuum Concept (RCC): shredder contributions were greatest in low-order reaches and declined downstream; scraper percentages were greatest in the middle of the continuum; collector-filterer contributions increased with increasing stream size. Longitudinal trends for collector-gatherers and predators did not support RCC predictions; these groups appeared to be influenced by localized changes in habitat availability and occurrence of vertebrate predators along the continuum.     

Decomposition of litter produced under elevated CO2: Dependence on plant species and nutrient supply

We investigated the effect of CO₂ concentration and soilnutrient availability during growth on the subsequent decomposition andnitrogen (N) release from litter of four annual grasses that differ inresource requirements and native habitat. Vulpia microstachys isa native grass found on California serpentine soils, whereas Avenafatua, Bromus hordaceus, and Lolium multiflorum areintroduced grasses restricted to more fertile sandstone soils (Hobbs & Mooney 1991). Growth in elevated CO₂ altered litter C:N ratio,decomposition, and N release, but the direction and magnitude of thechanges differed among plant species and nutrient treatments. ElevatedCO₂ had relatively modest effects on C:N ratio of litter,increasing this ratio in Lolium roots (and shoots at high nutrients),but decreasing C:N ratio in Avena shoots. Growth of plants underelevated CO₂ decreased the decomposition rate of Vulpialitter, but increased decomposition of Avena litter from the high-nutrient treatment. The impact of elevated CO₂ on N loss fromlitter also differed among species, with Vulpia litter from high-CO₂ plants releasing N more slowly than ambient-CO₂litter, whereas growth under elevated CO₂ caused increased Nloss from Avena litter. CO₂ effects on N release in Lolium and Bromus depended on the nutrient regime in whichplants were grown. There was no overall relationship between litter C:Nratio and decomposition rate or N release across species and treatments.Based on our study and the literature, we conclude that the effects ofelevated CO₂ on decomposition and N release from litter arehighly species-specific. These results do not support the hypothesis thatCO₂ effects on litter quality consistently lead to decreasednutrient availability in nutrient-limited ecosystems exposed to elevatedCO₂.     

A long-term record of carbon exchange in a boreal black spruce forest: means, responses to interannual variability, and decadal trends

We present a decadal (1994–2004) record of carbon dioxide flux in a 160‐year‐old black spruce forest/veneer bog complex in central Manitoba, Canada. The ecosystem shifted from a source (+41 g C m⁻², 1995) to a sink (−21 g C m⁻², 2004) of CO₂ over the decade, with an average net carbon balance near zero. Annual mean temperatures increased 1–2° during the period, consistent with the decadal trend across the North American boreal biome. We found that ecosystem carbon exchange responded strongly to air temperature, moisture status, potential evapotranspiration, and summertime solar radiation. The seasonal cycle of ecosystem respiration significantly lagged that of photosynthesis, limited by the rate of soil thaw and the slow drainage of the soil column. Factors acting over long time scales, especially water table depth, strongly influenced the carbon budget on annual time scales. Net uptake was enhanced and respiration inhibited by multiple years of rainfall in excess of evaporative demand. Contrary to expectations, we observed no correlation between longer growing seasons and net uptake, possibly because of offsetting increases in ecosystem respiration. The results indicate that the interactions between soil thaw and water table depth provide critical controls on carbon exchange in boreal forests underlain by peat, on seasonal to decadal time scales, and these factors must be simulated in terrestrial biosphere models to predict response of these regions to future climate.     

Direct Inhibition of <Emphasis Type="Italic">Col</Emphasis> E<Subscript>1</Subscript> Plasmid DNA Replication in <Emphasis Type="Italic">Escherichia coli</Emphasis> by Rifampicin

COLICINOGENIC factor E₁ (Col E₁) is a small bacterial plasmid (4.2×10⁶ daltons) present in colicinogenic strains of Escherichia coli¹ to the extent of about twenty-four copies per cell (Clewell and Helinski, unpublished results), which continues to replicate in the presence of high levels of chloramphenicol, a specific inhibitor of protein synthesis, although the chromosome only completes current rounds of replication and ceases (Clewell and Helinski, unpublished results). The average rate of Col E₁ semiconservative replication in the absence of protein synthesis is, in certain conditions, faster than (as much as eight times) the normal rate of synthesis (Clewell, unpublished results). Replication continues for 10–15 h after the addition of chloramphenicol, resulting in nearly 3,000 copies of Col E¹ DNA per cell. We are taking advantage of this system to study the effects of a number of antibiotics on DNA replication and now report evidence that rifampicin (an active semisynthetic derivative of rifamycin B)², an antibiotic known specifically to inhibit bacterial DNA dependent RNA polymerase^3–6, has a dramatic inhibitory effect on Col E¹ DNA replication.     

Nitrite reductase in Dunaliella tertiolecta: Isolation and properties

1. A soluble nitrite reductase has been isolated from cell-freepreparations of Dunaliella tertiolecta and purified fifty fold. 2. The enzyme resembles nitrite reductases isolated from higherplants in that it is a ferredoxin-nitrite reductase, but differsin that it will not accept electrons from either NADH or NADPHeven if exogenous diaphorase is added. 3. The Km value for nitrite is 1.1 x 10^–4 M and the molecularweight as determined by chromatography on G-200 Sephadex is70,000. 4. The rates of nitrite reduction obtained in vitro, using thedithionite-viologen electron donor system are sufficient toaccount for the in vivo rates of nitrate and nitrite assimilationobserved in this species. (Received July 4, 1969; )     

Studies in the Principles of Phytotoxicity: V. INTERRELATIONSHIPS BETWEEN SPECIFIC DIFFERENCES IN SPRAY RETENTION AND SELECTIVE TOXICITY

In a detailed study of the factors which control spray retentionby the shoot, five species with markedly different morphologicalcharacteristics have been examined (Helianthus annuus, Brassicaatha, Linum usitatisrnnwn, Hordeum vulgare, and Pisum sativum).The amount of spray retained, expressed as volume per unit weightof shoot or unit leaf area, is dependent on the stage of developmentof each species, the volume of spray applied, and the surfacetension of the spray solution. The interrelationships betweenthese factors are complex for all the second-order interactionsproved to be highly significant. Under one set of condi tionsthere may be a tenfold difference in retention between two specieswhile under another set the corresponding difference may beas little as twofold. Between a spray output of 14 and 143 ml./m.³ the level of retentionby P. sativum and H. vulgare is linearly related to output butfor H. annuus and B. alba the relationship is curvilinear. Whenthe surface tension is reduced below 40 dynes/cm. retentionby P. sativum and H. vulgare is increased, but for B. alba andH. annuus retention is decreased if the output exceeds 50 ml./m.For a given output, a reduction in the mean droplet size augmentsretention by H. vulgare but not by H. annuus. Differences in retention either between species or between stagesof develop ment are linked with the ratio of leaf area to shootweight, the nature of the leaf surfaces, the angle of incidenceat which the droplets strike the leaf, and localized accumulation.Retention is maximal when the leaf-area ratio is high, the surfacescompletely wetted, and the laminae set in a horizontal plane:once this maximum value is reached any additional spray receivedruns off the shoot. The relationship between retention and the concentration ofthe spray solution required to bring about some standard biologicalresponse has been examined for two groups of compounds—thosewhich are freely translocated (triethanolarnine salts of 2:4-dichloro-,2:4:5-trichloro-, and z-methyl-4-chloro-phenoxyacetic acids)and those which are not (arnrnonium 2:4-dinitro-6-sec-butylphenate).For the first group the equi-effective concentration is inverselyand linearly related to retention since the total amount receivedis of primary importance in determining the inhibition of growth,though the position of the droplets must be taken into account.Placing micro-drops containing the growth regulator on the cotyledonsof L. usitatimmwn inhibits the growth of the shoot less thana spray application of the same amount over the whole shoot:for H. annuus placing the growth regulator on either the firstor second pair of leaves or on the first internode induces moreinhibition of growth than application to the cotyledons. With ammonium dinitro-sec-butylphenate the relationship betweenretention and concentration is also inverse but approximatelylogarithmic for L. usitatisrimum. For some other species thechanges in retention consequent upon a reduction in the surfacetension are not matched by comparable changes in the equi-effectiveconcentration. For B. alba and H. annuus though lowering thesurface tension may decrease retention it may also Himiniahthe concentration because the fall in retention is more thanoffset by a greater penetration of the compound into the shoot. It is concluded that differences in spray retention betweenspecies can play a major role in determining selective actionand the conditions under which this factor may operate mosteffectively are discussed.