Buffel grass in Queensland's semi-arid woodlands: response to local and landscape scale variables, and relationship with grass, forb and reptile species.

Buffel grass [Pennisetum ciliare (L.) Link] has been widely introduced in the Australian rangelands as a consequence of its value for productive grazing, but tends to competitively establish in non-target areas such as remnant vegetation. In this study, we examined the influence landscape-scale and local-scale variables had upon the distribution of buffel grass in remnant poplar box (Eucalyptus populnea F. Muell.) dominant woodland fragments in the Brigalow Bioregion, Queensland. Buffel grass and variables thought to influence its distribution in the region were measured at 60 sites, which were selected based on the amount of native woodland retained in the landscape and patch size. An information-theoretic modelling approach and hierarchical partitioning revealed that the most influential variable was the percent of retained vegetation within a 1-km spatial extent. From this, we identified a critical threshold of similar to 30% retained vegetation in the landscape, above which the model predicted buffel grass was not likely to occur in a woodland fragment. Other explanatory variables in the model were site based, and included litter cover and long-term rainfall. Given the paucity of information on the effect of buffel grass upon biodiversity values, we undertook exploratory analyses to determine whether buffel grass cover influenced the distribution of grass, forb and reptile species. We detected some trends; hierarchical partitioning revealed that buffel grass cover was the most important explanatory variable describing habitat preferences of four reptile species. However, establishing causal links - particularly between native grass and forb species and buffel grass - was problematic owing to possible confounding with grazing pressure. We conclude with a set of management recommendations aimed at reducing the spread of buffel grass into remnant woodlands.

Transcriptional regulation of a pineapple polyphenol oxidase gene and its relationship to blackheart.

Two genes encoding polyphenol oxidase (PPO) were isolated from pineapple (Ananas comosus[L.] Merr. cv. Smooth Cayenne). Sequence analyses showed that both contained a single intron and encoded typical chloroplast-localized PPO proteins, the sequences of which corresponded to two pineapple PPO cDNAs, PINPPO1 and PINPPO2, recently described by Stewart et al. (2001). Southern blot analyses suggested that pineapple contained only two PPO genes. Analysis of expression of PINPPO1 promoter GUS fusion constructs showed this promoter had a low basal activity and was cold- and wound-inducible, consistent with known mRNA expression profiles. Striking homologies to gibberellin response complexes (GARC) were observed in sequences of both the PINPPO1 and PINPPO2 promoters. Transient assays in mature pineapple fruit and stable expression in transgenic tobacco showed that PINPPO1 promoter-GUS fusions were indeed gibberellin (GA) responsive. A role for the element within the putative GARCs in mediating GA-responsiveness of the PINPPO1 promoter was confirmed by mutational analysis. PINPPO2 was also shown to be GA-responsive by RT-PCR analysis. Mutant PINPPO1 promoter-GUS fusion constructs, which were no longer GA-inducible, showed a delayed response to cold induction in pineapple fruit in transient assays, suggesting a role for GA in blackheart development. This was supported by observations that exogenous GA3 treatment induced blackheart in the absence of chilling. Sequences showing homology to GARCs are also present in some PPO promoters in tomato, suggesting that GA regulates PPO expression in diverse species.

Scrotal Circumference at Puberty and its Relationship to Testes Mass in Three Genotypes of Beef Cattle

Scrotal circumference (SC) is a simple, non-invasive measurement commonly used to evaluate bull breeding potential although its validity as a predictor of fertility is questionable (Holroyd, 1998). SC is highly heritable but varies with breed and animal factors such as condition, live weight and age. As an indicator of fertility, recommended SC values range broadly from 30cm to 38cm (Miller, 1992). It is assumed that SC accurately reflects testes mass (TM) which may be related to direct measures of fertility such as spermatogenesis (Entwistle, 1992). The SC measurements made here test the assumption that SC, used to estimate testes volume (TV), is directly related to TM. Miller (1992) reported a value of 261mm as the SC threshold for puberty. We have studied serial SC measurements so as to devise a more accurate means of using SC to determine puberty.

Seasonal resource availability and use by an endangered tropical mycophagous marsupial

This study highlights the importance of considering how seasonality of rainfall affects availability of resources and consequently species distributions within tropical ecosystems. The endangered northern bettong, Bettongia tropica Wakefield is thought to be restricted to habitats where seasonal availability of hypogeous fungi, their principal food resource, remains high. To test this hypothesis fungal abundance was quantified in the early wet, late wet, early dry and late dry seasons within known bettong habitat. A relationship was found between precipitation and fungal availability, with the abundance of hypogeous fungi being significantly lower in the late dry season. Fungal availability correlated strongly with the seasonal rainfall pattern determined from 74-year monthly means. This contrasts with a previous study where mycophagy, measured by faecal analysis, remained high across seasons presumably because of aseasonal rainfall during that study period. Alloteropsis semialata R.Br. (cockatoo grass) use by bettongs increased significantly during the period of low fungal availability. This suggests that the importance of cockatoo grass as an alternative food resource during annual and extended dry periods has previously been underestimated. With the frequency and intensity of drought expected to increase with global climate change, these findings have significant implications for bettong management. The important and possibly equivalent dependence of B. tropica on both hypogeous fungi and A. semialata helps to explain their habitat preference and identifies this species as a true ecotonal specialist.

Patterns in tropical seagrass photosynthesis in relation to light, depth and habitat

Seagrass meadows across north-eastern Australia, survive a range of environmental conditions in coastal bays, reefs, estuarine and deepwater habitats through adaptation of a range of structural, morphological and physiological features. The aim of this study was to investigate the influence of spatial features (habitat type, site and depth) and photon flux on the photosynthetic performance of 11 tropical seagrass species. Pulse amplitude modulated (PAM) fluorometry was used to generate rapid light curves from which measures of maximal electron transport rate (ETRmax), photosynthetic efficiency (?), saturating irradiance (Ek) and effective quantum yield (?F/Fm?) were derived. The amount of light absorbed by leaves (absorption factor) was also determined for each population. In intertidal habitats many seagrass species exhibited typical sun-type responses with a close coupling of both ETRmax and Ek with photon flux. Photosynthetic performance ranged from minima in Thalassodendron ciliatum to maxima in Syringodium isoetifolium. The absence of a coupling between photosynthetic performance and photon flux in subtidal populations was most likely due to highly variable light climates and possible light attenuation, and hence the photo-biology of estuarine and deepwater seagrasses exhibited photosynthetic responses indicative of light limitation. In contrast seagrass species from shallow reef and coastal habitats for the most part exhibited light saturation characteristics. Of all the variables examined ETRmax, Ek and ?F/Fm? were most responsive to changing light climates and provide reliable physiological indicators of real-time photosynthetic performance of tropical seagrasses under different light conditions.

Assessing the relationship between shire winter crop yield and seasonal variability of the MODIS NDVI and EVI images

Australian researchers have been developing robust yield estimation models, based mainly on the crop growth response to water availability during the crop season. However, knowledge of spatial distribution of yields within and across the production regions can be improved by the use of remote sensing techniques. Images of Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation indices, available since 1999, have the potential to contribute to crop yield estimation. The objective of this study was to analyse the relationship between winter crop yields and the spectral information available in MODIS vegetation index images at the shire level. The study was carried out in the Jondaryan and Pittsworth shires, Queensland , Australia . Five years (2000 to 2004) of 250m resolution, 16-day composite of MODIS Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) images were used during the winter crop season (April to November). Seasonal variability of the profiles of the vegetation index images for each crop season using different regions of interest (cropping mask) were displayed and analysed. Correlation analysis between wheat and barley yield data and MODIS image values were also conducted. The results showed high seasonal variability in the NDVI and EVI profiles, and the EVI values were consistently lower than those of the NDVI. The highest image values were observed in 2003 (in contrast to 2004), and were associated with rainfall amount and distribution. The seasonal variability of the profiles was similar in both shires, with minimum values in June and maximum values at the end of August. NDVI and EVI images showed sensitivity to seasonal variability of the vegetation and exhibited good association (e.g. r = 0.84, r = 0.77) with winter crop yields.

Relationship Between Hardness Genes and Quality in Barley (Hordeum vulgare)

Barley (Hordeum vulgare) genotypes were sequenced for polymorphism in the hardness genes, these being the three hordoindoline (hin a, hin b1 and hin b2) genes. The variation in haplotype was determined by sequencing for single nucleotide polymorphisms (SNPs). Polymorphism between each gene was then compared to grain hardness (three methods), malt quality characteristics (hot water extract and friability) and cattle feed quality. Two haplotypes were found in a set of forty barley genotypes. For hin a, two alleles were present, namely hin a1 and hin a2. However, there was no specific hin a allele that was associated with grain hardness, malt and feed quality. Barley has two hin b genes, namely hin b1 and hin b2, and the genotypes tested here had one of two alleles for each gene. However, there were no obvious effects on hardness or quality from either of these hin b alleles. Unlike wheat, where a clear relationship has been demonstrated between a number of SNPs in the wheat hardness genes and quality (soft or hard wheat), there was no such relationship for barley. Despite the wide range in hardness, malt and feed quality, there were only two haplotypes for each of the hin a, hin b1 and hin b2 genes and there was no clear relationship between grain hardness, malt or feed quality. The genotypes used in this study demonstrated that there was a low level of polymorphism in hardness genes in current commercial varieties as well as breeding lines and these polymorphisms had no impact on quality.

Assessing the relationship between patch type and soil mites: A molecular approach

An urgent need exists for indicators of soil health and patch functionality in extensive rangelands that can be measured efficiently and at low cost. Soil mites are candidate indicators, but their identification and handling is so specialised and time-consuming that their inclusion in routine monitoring is unlikely. The aim of this study was to measure the relationship between patch type and mite assemblages using a conventional approach. An additional aim was to determine if a molecular approach traditionally used for soil microbes could be adapted for soil mites to overcome some of the bottlenecks associated with soil fauna diversity assessment. Soil mite species abundance and diversity were measured using conventional ecological methods in soil from patches with perennial grass and litter cover (PGL), and compared to soil from bare patches with annual grasses and/or litter cover (BAL). Soil mite assemblages were also assessed using a molecular method called terminal-restriction fragment length polymorphism (T-RFLP) analysis. The conventional data showed a relationship between patch type and mite assemblage. The Prostigmata and Oribatida were well represented in the PGL sites, particularly the Aphelacaridae (Oribatida). For T-RFLP analysis, the mite community was represented by a series of DNA fragment lengths that reflected mite sequence diversity. The T-RFLP data showed a distinct difference in the mite assemblage between the patch types. Where possible, T-RFLP peaks were matched to mite families using a reference 18S rDNA database, and the Aphelacaridae prevalent in the conventional samples at PGL sites were identified, as were prostigmatids and oribatids. We identified limits to the T-RFLP approach and this included an inability to distinguish some species whose DNA sequences were similar. Despite these limitations, the data still showed a clear difference between sites, and the molecular taxonomic inferences also compared well with the conventional ecological data. The results from this study indicated that the T-RFLP approach was effective in measuring mite assemblages in this system. The power of this technique lies in the fact that species diversity and abundance data can be obtained quickly because of the time taken to process hundreds of samples, from soil DNA extraction to data output on the gene analyser, can be as little as 4 days.

Effect of fragmentation, habitat loss and within-patch habitat characteristics on ant assemblages in semi-arid woodlands of eastern Australia.

The reliability of ants as bioindicators of ecosystem condition is dependent on the consistency of their response to localised habitat characteristics, which may be modified by larger-scale effects of habitat fragmentation and loss. We assessed the relative contribution of habitat fragmentation, habitat loss and within-patch habitat characteristics in determining ant assemblages in semi-arid woodland in Queensland, Australia. Species and functional group abundance were recorded using pitfall traps across 20 woodland patches in landscapes that exhibited a range of fragmentation states. Of fragmentation measures, changes in patch area and patch edge contrast exerted the greatest influence on species assemblages, after accounting for differences in habitat loss. However, 35% of fragmentation effects on species were confounded by the effects of habitat characteristics and habitat loss. Within-patch habitat characteristics explained more than twice the amount of species variation attributable to fragmentation and four times the variation explained by habitat loss. The study indicates that within-patch habitat characteristics are the predominant drivers of ant composition. We suggest that caution should be exercised in interpreting the independent effects of habitat fragmentation and loss on ant assemblages without jointly considering localised habitat attributes and associated joint effects.

An assessment of the genetic relationship between sweet and grain sorghums, within Sorghum bicolor ssp. bicolor (L.) Moench, using AFLP markers

Compared to grain sorghums, sweet sorghums typically have lower grain yield and thick, tall stalks which accumulate high levels of sugar (sucrose, fructose and glucose). Unlike commercial grain sorghum (S. bicolor ssp. bicolor) cultivars, which are usually F1 hybrids, commercial sweet sorghums were selected as wild accessions or have undergone limited plant breeding. Although all sweet sorghums are classified within S. bicolor ssp. bicolor, their genetic relationship with grain sorghums is yet to be investigated. Ninety-five genotypes, including 31 sweet sorghums and 64 grain sorghums, representing all five races within the subspecies bicolor, were screened with 277 polymorphic amplified fragment length polymorphism (AFLP) markers. Cluster analysis separated older sweet sorghum accessions (collected in mid 1800s) from those developed and released during the early to mid 1900s. These groups were emphasised in a principle component analysis of the results such that sweet sorghum lines were largely distinguished from the others, particularly by a group of markers located on sorghum chromosomes SBI-08 and SBI-10. Other studies have shown that QTL and ESTs for sugar-related traits, as well as for height and anthesis, map to SBI-10. Although the clusters obtained did not group clearly on the basis of racial classification, the sweet sorghum lines often cluster with grain sorghums of similar racial origin thus suggesting that sweet sorghum is of polyphyletic origin within S. bicolor ssp. bicolor.

Seagrass-Watch: Engaging Torres Strait Islanders in marine habitat monitoring

Involvement in scientifically structured habitat monitoring is a relatively new concept to the peoples of Torres Strait. The approach we used was to focus on awareness, and to build the capacity of groups to participate using Seagrass-Watch as the vehicle to provide education and training in monitoring marine ecosystems. The project successfully delivered quality scientifically rigorous baseline information on the seasonality of seagrasses in the Torres Strait-a first for this region. Eight seagrass species were identified across the monitoring sites. Seagrass cover varied within and between years. Preliminary evidence indicated that drivers for seagrass variability were climate related. Generally, seagrass abundance increased during the north-west monsoon (Kuki), possibly a consequence of elevated nutrients, lower tidal exposure times, less wind, and higher air temperatures. Low seagrass abundance coincided with the presence of greater winds and longer periods of exposure at low tides during the south-east trade wind season (Sager). No seasonal patterns were apparent when frequency of disturbance from high sedimentation and human impacts was high. Seagrass-Watch has been incorporated in to the Thursday Island High School's Marine Studies Unit ensuring continuity of monitoring. The students, teachers, and other interested individuals involved in Seagrass-Watch have mastered the necessary scientific procedures to monitor seagrass meadows, and developed skills in coordinating a monitoring program and skills in mentoring younger students. This has increased the participants' self-esteem and confidence, and given them an insight into how they may participate in the future management of their sea country.

The effect of habitat and environmental history on otolith chemistry of barramundi Lates calcarifer in estuarine populations of a regulated tropical river

We examine the microchemistry of otoliths of cohorts of a fished shed population of the large catadromous fish, barramundi Lates calcarifer from the estuary of a large tropical river. Barramundi from the estuary of the large, heavily regulated Fitzroy River, north eastern Australia were analysed by making transects of 87Sr/86Sr isotope and trace metal/Ca ratios from the core to the outer edge. Firstly, we examined the Sr/Ca, Ba/Ca, Mg/Ca and Mn/Ca and 87Sr/86Sr isotope ratios in otoliths of barramundi tagged in either freshwater or estuarine habitats that were caught by the commercial fishery in the estuary. We used 87Sr/86Sr isotope ratios to identify periods of freshwater residency and assess whether trace metal/Ca ratios varied between habitats. Only Sr/Ca consistently varied between known periods of estuarine or freshwater residency. The relationships between trace metal/Ca and river flow, salinity, temperature were examined in fish tagged and recaptured in the estuary. We found weak and inconsistent patterns in relationships between these variables in the majority of fish. These results suggest that both individual movement history within the estuary and the scale of environmental monitoring were reducing our ability to detect any patterns. Finally, we examined fish in the estuary from two dominant age cohorts (4 and 7 yr old) before and after a large flood in 2003 to ascertain if the flood had enabled fish from freshwater habitats to migrate to the estuary. There was no difference in the proportion of fish in the estuary that had accessed freshwater after the flood. Instead, we found that larger individuals with each age cohort were more likely to have spent a period in freshwater. This highlights the need to maintain freshwater flows in rivers. About half the fish examined had accessed freshwater habitats before capture. Of these, all had spent at least their first two months in marine salinity waters before entering freshwater and some did not enter freshwater until four years of age. This contrasts with the results of several previous studies in other parts of the range that found that access to freshwater swamps by larval barramundi was important for enhanced population productivity and recruitment.

Stocking density and artificial habitat influence stock structure and yield from intensive nursery systems for mud crabs Scylla serrata (Forsskål 1775)

Intensive nursery systems are designed to culture mud crab postlarvae through a critical phase in preparation for stocking into growout systems. This study investigated the influence of stocking density and provision of artificial habitat on the yield of a cage culture system. For each of three batches of postlarvae, survival, growth and claw loss were assessed after each of three nursery phases ending at crab instars C1/C2, C4/C5 and C7/C8. Survival through the first phase was highly variable among batches with a maximum survival of 80% from megalops to a mean crab instar of 1.5. Stocking density between 625 and 2300 m-2 did not influence survival or growth in this first phase. Stocking densities tested in phases 2 and 3 were 62.5, 125 and 250 m -2. At the end of phases 2 and 3, there were five instar stages present, representing a more than 20-fold size disparity within the populations. Survival became increasingly density-sensitive following the first phase, with higher densities resulting in significantly lower survival (phase 2: 63% vs. 79%; phase 3: 57% vs. 64%). The addition of artificial habitat in the form of pleated netting significantly improved survival at all densities. The mean instar attained by the end of phase 2 was significantly larger at a lower stocking density and without artificial habitat. No significant effect of density or habitat on harvest size was detected in phase 3. The highest incidence of claw loss was 36% but was reduced by lowering stocking densities and addition of habitat. For intensive commercial production, yield can be significantly increased by addition of a simple net structure but rapidly decreases the longer crablets remain in the nursery.

Habitat dynamics in the bed sediments of an intermittent upland stream

The effects of the hydrological regime on temporal changes to physical characteristics of substratum habitat, sediment texture of surface sediments (<10 cm), were investigated in a sub-tropical headwater stream over four years. Surface discharge was measured together with vertical hydraulic gradient and groundwater depth in order to explore features of sediment habitat that extend beyond the streambed surface. Whilst the typical discharge pattern was one of intermittent base flows and infrequent flow events associated with monsoonal rain patterns, the study period also encompassed a drought and a one-in-a-hundred-year flood. Rainfall and discharge did not necessarily reflect the actual conditions in the stream. Although surface waters were persistent long after discharge ceased, the streambed was completely dry on several occasions. Shallow groundwater was present at variable depths throughout the study period, being absent only at the height of the drought. The streambed sediments were mainly gravels, sand and clay. Finer sediment fractions showed a marked change in grain size over time, although bedload movement was limited to a single high discharge event. In response to a low discharge regimen (drought), sediments characteristically showed non-normal distributions and were dominated by finer materials. A high-energy discharge event produced a coarsening of sands and a diminished clay fraction in the streambed. Particulate organic matter from sediments showed trends of build-up and decline with the high and low discharge regimes, respectively. Within the surface sediment intersticies three potential categories of invertebrate habitat were recognised, each with dynamic spatial and temporal boundaries.

Dispersal and establishment of bird-dispersed weed and native species in early successional subtropical habitats

Eve White, Anna Barnes and Gabrielle Vivian-Smith recently published their paper 'Dispersal and establishment of bird-dispersed weed and native species in early successional subtropical habitats' in Proceedings of the 16th Australian Weeds Conference. Eve also presented this paper at the conference. They investigated patterns of dispersal and establishment of bird-dispersed weeds and native species in early successional habitats in northern New South Wales. Patterns varied among growth forms, between native species and weeds, and among vegetation types. Their results indicated that the number of seeds dropped by birds is not necessarily a good predictor of recruitment and that post-dispersal factors, such as microsite characteristics, may be more important influences on seedling recruitment. This knowledge will assist with designing management strategies for bird-dispersed weeds in natural areas.