Juvenile proportion as a predictor of freshwater turtle population change

The extreme longevity of turtles and tortoises can make it difficult to determine the conservation status of their populations because high annual adult survival may mask gradual attrition due to low levels of recruitment. When long-term demographic trends are unknown and available data are insufficient for population modelling, it may be assumed that a scarcity of juveniles indicates low recruitment that will result in population ageing and numerical decline. However, the reliability with which the proportion of juveniles foreshadows demographic change is uncertain. We tested the hypothesis that a low proportion of juveniles in a turtle population presages its ageing by analysing over 20 years of survey data for five discrete populations of the Australian western saw-shelled turtle (Myuchelys bellii: Chelidae), a listed threatened species. The analysis tested whether the initial proportion of juvenile turtles in each population was related to its temporal trend in average body size. The five populations had varied structure and trends, with the initial proportion of juvenile turtles ranging from 10% to 39% and average body size increasing over time in some populations and decreasing in others. Contrary to expectation, the initial proportion of juveniles was unrelated to the trend in average body size and, by inference, average age, indicating that effective trend forecasting requires more detailed demographic information than merely population structure.     

Rapid assessment of rivers using macroinvertebrates: the role of experience, and comparisons with quantitative methods

We assessed rapid biological assessment (RBA) of macroinvertebrate communities in comparison with quantitative sampling at 18 pairs of river sites in south-eastern Australia. One member of each pair served as a reference site and the other was affected by mild to moderate human disturbance from a point or diffuse source (fish farm effluents, small municipal sewage discharges, a dam, agriculture and grazing). Samples were taken from riffles, stream edges and rocks in pools, mostly using hand nets (RBA) and Hess samplers (quantitative). Macroinvertebrates in RBA samples were always subsampled by live-picking by eye on site for 30 min. Comparisons were made between novice operators (university undergraduates) and experienced river biologists in the application of RBA, including sample identification. Quantitative samples were collected only by experienced river biologists, preserved and picked under stereomicroscopes in the laboratory, either in their entirety or after mechanical subsampling. Specimens were identified to family level for both methods. Novices recorded slightly fewer families than experts and misidentified some specimens, and expert data for the same site and habitat were on average more consistent than novice data. Nevertheless, Procrustes analysis of ordinations showed that differences between RBA and quantitative data did not depend on the type of RBA operator. And regardless of the operator, RBA data were better than quantitative data at discriminating between reference and disturbed sites for all three habitat types. We conclude that this type of RBA is sensitive and cost-effective, and we recommend improvements to inter-operator consistency.     

Trophic linkages between periphyton and grazing macroinvertebrates in rivers with different levels of catchment development

Stable isotope signatures (δ¹³C and δ¹⁵N) were used to compare trophic linkages between epilithic periphyton and three families of macroinvertebrates (Baetidae, Leptophlebiidae and Gripopterygidae) in riffles of two rivers with developed catchments (including agriculture, urbanization, impoundment and flow regulation) and two with undeveloped catchments (native forest with no major impoundments) in the Murrumbidgee River system, New South Wales, Australia. Periphyton had much higher average δ¹⁵N values and lower average C:N ratios in the developed rivers than in the undeveloped rivers, probably because of the combined effects of nutrient enrichment, upstream impoundment and alteration of riparian vegetation. The invertebrates were generally slightly depleted in ¹³C and ¹⁵N relative to expected values if they were assimilating whole periphyton alone, which suggests that they were assimilating periphyton components selectively or also consuming other foods. The match in isotope signatures between periphyton and invertebrates was only slightly weaker in the developed than in the undeveloped rivers, suggesting that development did not greatly disrupt trophic linkages between periphyton and these invertebrates. Handling editor: M. Power     

Differing effects of catchment land use on water chemistry explain contrasting behaviour of a diatom index in tropical northern and temperate southern Australia

The DSIAR biotic index for freshwater diatoms, regarded as a potential indicator of impact from agricultural and urban land use on rivers in temperate south-eastern Australia, did not correlate significantly with an index of catchment condition in a tropical region of northern Australia. However, the relationships between the index and water chemistry, especially pH, salinity and concentrations of nitrogen and phosphorus, were consistent in both regions. The variable relationship between the index and catchment conditions can be explained by differing effects of catchment land use on stream-water chemistry in northern and southern Australia. In the south, land use has commonly resulted in increases in stream pH, salinity and nutrients, whereas in the north its impact on pH and salinity appears weak. These findings emphasise the need to interpret biological and ecological indices in the context of the varying causal pathways by which human activities affect stream ecosystems in different circumstances.     

Biological traits predict shifts in geographical ranges of freshwater invertebrates during climatic warming and drying

Aim To test the ability of biological traits to predict climate‐related changes in geographical ranges of running‐water invertebrates. Location The Australian state of New South Wales and the Australian Capital Territory. Methods I analysed data from 8928 biomonitoring samples collected during a 16‐year period of generally rising air temperatures and declining precipitation. I used quantile regression to test for expansions and contractions on the climatically cooler, warmer, drier and wetter edges of the ranges of 120 invertebrate taxa, and correlated these shifts with the traits of thermophily (degree of preference for high versus low temperature) and rheophily (preference for flowing versus still water). Results The most commonly inferred range shifts were cool‐edge expansion plus warm‐edge contraction (71 taxa) and wet‐edge expansion plus dry‐edge contraction (71), but contractions from both cool and warm extremes (36) and from both dry and wet extremes (28) were also frequent. High‐temperature preference was associated with cool‐edge expansion and low‐temperature preference with wet‐edge expansion and contraction from all other extremes. A preference for flow was associated with wet‐edge expansion and dry‐edge contraction. Main conclusions Trait analysis has potential for predicting which species will expand their ranges and which will contract, but needs to be coupled with assessment of how the landscape provides each species with opportunities to track or avoid climate change. Improved quantification of climatically relevant traits and integration of trait analysis with species distribution modelling are likely to be beneficial.     

Responses of the Fructose-1,6-bisphosphatase and Glutamate Dehydrogenase Activities of Alfalfa to Boron,Gypsum, and Limestone Amendments of Soil

Plants cultivated on acid soils that contain toxic levels of Al³⁺ usually produce low yields. A multi-factorial treatment of gypsum (G), boron (B), and limestone (Lm) was applied to such soil in order to determine the biochemical basis of the best management plan for ameliorating the soil acidity for sustainable growth of alfalfa. The alfalfa shoots were subjected to analysis for hexose, protein, nucleotide, and chlorophyll (Chl) contents, fructose 1,6-bisphosphatase (FBPase) activity, and the RNA synthetic activity of glutamate dehydrogenase (GDH). Hexose and protein contents of control alfalfa without B and G, but with Lm (672 g m^–2) amendment were 0.87 and 38.30 g, respectively, per kg shoot. Increasing the G doses at fixed moderate doses of 0.15 and 0.30 g m^–2 B decreased the FBPase activity by 53 and 31 %, respectively. However, increasing the B doses at higher fixed G (1 kg m^–2= G_1.0) increased the FBPase activity by 91 % thus indicating that G₁ optimized the saccharide metabolism by neutralizing the soil acidity. In the absence of B, increasing the G doses also maximized the hexose and Chl contents, but minimized the nucleotide amount. In the absence of G, increasing the B doses maximized the RNA synthetic activity of GDH, but lowered the hexose and Chl contents as well as the FBPase activity without affecting the protein contents, thereby permitting the selection of B (0.45 g m^–2) with Lm as the best amendment for the sustainable growth of alfalfa. Treatment with 0.45 g B and 0.5 kg G (= G_0.5) induced the strongest B-Ca antagonism by maximizing the hexose and Chl contents but severely suppressing the FBPase activity and the RNA synthetic activity of GDH. Therefore, the coordinate optimization of saccharide metabolism through the G-dependent neutralization of soil acidity, and of RNA metabolism through the B-dependent detoxification of Al³⁺ are the biochemical options for the mitigation of the adverse effects of soil acidity for the optimization of sustainable alfalfa production.     

Use of cloned populations of mouse lymphocytes to analyze cellular differentiation

We describe a method for generation of homogeneous cell populations that each arise from clonal expansion of cells at a discrete stage of differentiation within a single lineage. We have used this to produce continuously propagatable lymphocyte clones. Each clone represents a cell at a progressive stage of thymus-dependent cellular differentiation. These cloned cells bear stable surface membrane glycoproteins characteristic of precursor cells and mature progeny; conditions allowing maximal cloning efficiencies for each cell type (10–85%) have been established. Mature lymphocyte clones continue to express specialized function and provide material for biochemical analysis of T lymphocyte functions; one fully differentiated clone from the “inducer” lymphocyte set synthesizes a molecule that activates other lymphocytes to secrete immunoglobulin. This activity is associated with a highly purified molecule having a molecular weight of 45,000 daltons and an isoelectric point of approximately 6.0. This molecule, together with clones of precursor and mature T lymphocytes, may provide a system to further study the mechanisms of gene activation during cellular differentiation.     

Limitations of trait‐based approaches for stressor assessment: The case of freshwater invertebrates and climate drivers

The appeal of trait‐based approaches for assessing environmental vulnerabilities arises from the potential insight they provide into the mechanisms underlying the changes in populations and community structure. Traits can provide ecologically based explanations for observed responses to environmental changes, along with predictive power gained by developing relationships between traits and environmental variables. Despite these potential benefits, questions remain regarding the utility and limitations of these approaches, which we explore focusing on the following questions: (a) How reliable are predictions of biotic responses to changing conditions based on single trait–environment relationships? (b) What factors constrain detection of single trait–environment relationships, and how can they be addressed? (c) Can we use information on meta‐community processes to reveal conditions when assumptions underlying trait‐based studies are not met? We address these questions by reviewing published literature on aquatic invertebrate communities from stream ecosystems. Our findings help to define factors that influence the successful application of trait‐based approaches in addressing the complex, multifaceted effects of changing climate conditions on hydrologic and thermal regimes in stream ecosystems. Key conclusions are that observed relationships between traits and environmental stressors are often inconsistent with predefined hypotheses derived from current trait‐based thinking, particularly related to single trait–environment relationships. Factors that can influence findings of trait‐based assessments include intercorrelations of among traits and among environmental variables, spatial scale, strength of biotic interactions, intensity of habitat disturbance, degree of abiotic stress, and methods of trait characterization. Several recommendations are made for practice and further study to address these concerns, including using phylogenetic relatedness to address intercorrelation. With proper consideration of these issues, trait‐based assessment of organismal vulnerability to environmental changes can become a useful tool to conserve threatened populations into the future.     

Relationships between lotic macroinvertebrate traits and responses to extreme drought

相似文献   

Occurrence of the mayfly family Teloganodidae in northern New South Wales

Teloganodid mayfly nymphs, previously known in Australia only from south-eastern Queensland, have now been recorded from numerous localities in the coastal drainages of northern New South Wales (NSW) from the Barrington Tops district to the Richmond River system. The nymphs seem to be restricted to riffles in forest streams and occur over a wide altitudinal range with records up to 940 m. They appear identical to those of Austremerella picta Riek, but rearing to the adult is needed to be certain that they represent the same species. The apparent restriction of Australian Teloganodidae to southern Queensland and northern NSW poses a biogeographical puzzle.