Nematode assemblages from Avicennia marina leaf litter in a temperate mangrove forest in south-eastern Australia

Meiofauna from Avicennia marina leaf litter in a temperate mangrove forest was enumerated, and the nematode assemblages compared on the bases of leaf colour (used as a guide to leaf age) and shore horizon where samples were collected. Twenty-one putative nematode species were collected from 48 leaf litter samples. Univariate analyses indicated that neither the colour of the leaf nor the shore horizon significantly affected abundance of nematodes. However, of the four (222) treatment groups, rarefaction curves revealed highest diversity on brown leaves from under the shade of the tree canopy (H'=0.751-0.126 SE, n=17). Species diversity of leaf litter nematodes was lower in this temperate mangrove system than reported from tropical mangrove studies. ANOSIM tests confirmed a significant effect of shore horizon on nematode assemblages. The dominant feeding group among nematodes was non-selective deposit feeders (7/21 species, but 77% of all nematodes). Epigrowth grazers were represented by 8/21 species of nematodes, but only 19% of the total number. Excised leaves became skeletonised by about 15 weeks. Shorter temporal scales of life cycles of nematodes compared with leaf degradation, and the dynamic nature of epibiontic assemblages, probably explain the similar assemblage structure on yellow and brown leaves.

An integrated study of the temporal and spatial variation in the supply of propagules, recruitment and assemblages of intertidal macroalgae on a wave-exposed rocky coast, Victoria, Australia

Recruitment is known to influence distributions and abundances of benthic marine organisms. It is therefore important to document patterns of variability in recruitment and how these relate to patterns in established assemblages. This study provides an integrated assessment of the temporal and spatial variation in supply and recruitment of propagules and established populations of several macroalgae. Propagules in water samples from two stages of the incoming tide, recruitment to artificial substrata and percentage cover of species established on the shore were recorded every 2 months from December 1994 to October 1995, in two zones of an intertidal, wave-exposed rocky shore. Variability in recruitment was measured at three spatial scales: 10s cm, 100s cm and 100s m. Availability and recruitment of most taxa were greatest between April and August, although many species had available propagules and recruited throughout the year. Temporal variation in the established assemblages was, however, more species-specific. Differences in established assemblages between zones were reflected in differences in availability and recruitment of propagules between zones. Recruitment could not be predicted directly from supply of propagules, but the two processes were linked. For most species, the greatest variation in recruitment occurred at the smallest spatial scale of 10s cm, although there was also considerable large-scale (between site) variation in recruitment of several species. Results indicate that while pre-and post-settlement mortality are likely to influence macroalgal distribution and abundance, the temporal and spatial variability in supply and recruitment of propagules can explain much of the patchiness in macroalgal assemblages.

Non-uniform bird assemblages in urban environments : the influence of streetscape vegetation

The urban landscape encompasses a broad spectrum of variable environments ranging from remnant patches to highly modified streetscapes. Despite the expansion of urban environments, few studies have examined the influence of urbanization on faunal diversity, particularly in the Southern Hemisphere. In this study, four broad habitat types were recognized in the urban environment, representing a continuum of modification ranging from parks with remnant vegetation to streetscapes dominated by native vegetation and those dominated by exotic vegetation to recently developed streetscapes. Bird censuses were conducted at 36 sites throughout urban Melbourne, with nine sites surveyed in each habitat type. The four habitat types supported significantly different bird communities based on species richness, abundance and composition suggesting that bird assemblages of urban environments are non-uniform. Parks and native streetscapes generally supported fewer introduced species than exotic and recently developed streetscapes. Overall abundance and richness of species were lower in the exotic and recently developed streetscapes than in parks and native streetscapes. Significant differences were also observed in foraging guilds within the four habitat types, with parks having the most foraging guilds and recently developed streetscapes having the fewest. The transition from native to exotic streetscapes saw the progressive loss of insectivorous and nectarivorous species reflecting a reliance by these species on structurally diverse and/or native vegetation for both shelter and food resources. The implementation of effective strategies and incentives which encourage the planting of structurally diverse native vegetation in streetscapes and gardens should be paramount if avian biodiversity is to be retained and enhanced in urban environments. It is also critical to encourage the maintenance of the existing remnant vegetation in the urban environment.

Urban amphibian assemblages as metacommunities

1. Urban ecosystems are expanding throughout the world, and urban ecology is attracting increasing research interest. Some authors have questioned the value of existing ecological theories for understanding the processes and consequences of urbanization.
2. In order to assess the applicability of metacommunity theory to urban systems, I evaluated three assumptions that underlie the theory – the effect of patch area, the effect of patch isolation, and species–environment relations – using data on assemblages of pond-breeding amphibians in the Greater Melbourne area of Australia. I also assessed the relative impact of habitat fragmentation, habitat isolation, and changes to habitat quality on these assemblages.
3. Poisson regression modelling provided support for an important increase in species richness with patch area (pond size) and a decrease in species richness with increasing patch isolation, as measured by surrounding road cover. Holding all other variables constant, species richness was predicted to be 2·8–5·5 times higher at the largest pond than at the smallest, while the most isolated pond was predicted to have 12–19% of the species richness of the least isolated pond. Thus, the data were consistent with the first two assumptions of metacommunity theory evaluated.
4. The quality of habitat at a pond was also important, with a predicted 44–56% decrease in the number of species detected at ponds with a surrounding vertical wall compared with those with a gently sloping bank. This demonstrates that environmental differences between habitat patches were also influencing amphibian assemblages, providing support for the species-sorting and/or mass-effect perspectives of metacommunity theory.
5. Without management intervention, urbanization may lead to a reduction in the number of amphibian species persisting in urban ponds, particularly where increasing isolation of ponds by roads and associated infrastructure reduces the probability of re-colonization following local extinction.

The influence of reduced flow during a drought on patterns of variation in macroinvertebrate assemblages across a spatial hierarchy in two lowland rivers

1. With the aim of determining whether patterns of variation in macroinvertebrate assemblage composition across the hierarchy of spatial units in two lowland rivers changed during a supra-seasonal drought (1997–2000), patterns during a reduced flow season (1999–2000) were compared with those during two preceding higher flow seasons (1997–98 and 1998–99) using samples from the Glenelg and Wimmera Rivers, two lowland regulated rivers in western Victoria, Australia.

2. We hypothesised that (i) differences between reaches would increase during the reduced flow season owing to decreased hydrological connectivity, (ii) differences between the habitats would decrease because the cessation of flow in run habitats should cause them to become more similar to pool habitats and (iii) differences between microhabitats would also decrease because of reduced scour of inorganic substrata and large woody debris.

3. During each season, macroinvertebrates were sampled from three microhabitats (sand/silt substratum, large woody debris and macrophytes) that were hierarchically nested within a run or pool habitat and within one of three reaches within each river. A range of physico-chemical variables was also sampled.

4. Analysis of similarity showed that assemblage composition in both rivers during the higher flow seasons differed more among microhabitats than other spatial units. However, during the reduced flow season, assemblage composition in the Wimmera River differed most among reaches. This change in pattern was associated with the combined effects of decreased flow and longitudinal increases in salinity. In contrast, the fauna of the Glenelg River appeared to be resistant to the effects of the reduced flow season, owing to limited decline in water quality despite lower river discharge.

5. As salinisation and poor water quality in the Wimmera River result from human activities in the catchment, these results support the idea that human impacts on rivers can change macroinvertebrate scaling patterns and exacerbate the effects of drought beyond the tolerance of many riverine macroinvertebrates.

Temporal changes in macroinvertebrate assemblages following experimental flooding in permanent and temporary wetlands in an Australian floodplain forest

The River Murray, Australia, is a highly regulated river from which almost 80% of mean annual flow is removed for human use, primarily irrigated agriculture. Consequent changes to the pattern and volume of river flow are reflected in floodplain hydrology and, therefore, the wetting/drying patterns of floodplain wetlands. To explore the significance of these changes, macroinvertebrate samples were compared between permanent and temporary wetlands following experimental flooding in a forested floodplain of the River Murray. Weekly samples from two permanent wetlands and four associated temporary sites were used to track changes in macroinvertebrate assemblage composition. Non-metric multidimensional scaling was used to ordinate the macroinvertebrate data, indicating consistent differences between the biota of permanent and temporary wetlands and between the initial and later assemblages in the temporary sites. There were marked changes over time, but little sign that the permanent and temporary assemblages were becoming more alike over the 25-week observation period. The apparent heterogeneity of these systems is of particular importance in developing river management plans which are likely to change flooding patterns. Such plans need to maintain a mosaic of wetland habitats if floodplain biodiversity is to be supported.

Hydrological regime and macrophyte assemblages in temporary floodplain wetlands: implications for detecting responses to environmental water allocations

This study describes the macrophyte assemblages of temporary floodplain wetlands situated on the floodplain of the Murray River, southeast Australia. Wetlands in the study are subject to flooding, the frequency, duration, and magnitude of which are dictated by the current, regulated river-flow regime. Our aim was to examine the influence of the existing flooding regime on macrophyte assemblages and to trial a monitoring program, based on a multiple before-after-control-impact (MBACI) design, to detect the impact of proposed environmental water allocations (EWAs) on the wetlands. Two categories of flooding regime were identified based on the flow magnitudes required for flooding to occur (flooding thresholds). In this scheme, wetlands with relatively low flooding thresholds are classed as ‘impact’ and those with higher thresholds are classed as ‘control.’ The wetlands were surveyed over a two-year period that incorporated at least one wetting-drying cycle at all wetlands. Results showed significant differences between survey times (season and year), but differences between flooding regime categories were significant only for some components of macrophyte assemblages. Differences between survey dates appear to reflect largely short-term responses to the most recent flood events. However, macrophyte differences observed between control and impact wetlands reflected the cumulative effect of flood events over several years. Differences between control and impact wetlands were strongest for post-flooding surveys based on full assemblages (using ANOSIM) and among specific taxa and functional groups (using ANOVA). Power to detect differences between control and impact wetlands was greatest for species richness and total abundance, but taxa with low variability among wetlands, and hence good power, were actually less sensitive to hydrologic change. We conclude that the MBACI design used in this study will be most effective in detecting wetland ecosystem responses to the implementation of EWAs if response variables are carefully chosen based on their sensitivity to hydrologic change.

Differing responses to landscape change : implications for small mammal assemblages in forest fragments

Human modification of landscapes typically results in many species being confined to small, isolated and degraded habitat fragments. While fragment size and isolation underpin many studies of modified landscapes, vegetation characteristics are less frequently incorporated. The relative influence of biogeographic (e.g. size, isolation) and vegetation parameters on assemblages is poorly understood, but critical for conservation management. In this study, a multiple hypothesis testing framework was used to determine the relative importance of biogeographic and vegetation parameters in explaining the occurrence of an assemblage of small mammals in 48 forest fragments in an agricultural landscape in south-eastern Australia. Fragment size and vegetation characteristics were consistently important predictors of occurrence across species. In contrast, fragment isolation was important for just one native species. Differing abilities of species to move through the landscape provide a reasonable explanation for these results. We conclude that for effective conservation of assemblages, it is important to: (1) consider differing responses of species to landscape change, and (2) move beyond a focus primarily on spatial attributes (size, isolation) to recognise that landscape change also has profound effects on habitat composition and quality.

Riverine macroinvertebrate assemblages up to 8 years

Willow removal followed by riparian revegetation is a widespread river restoration practice in Australia, but the ecological response to this has rarely been evaluated. We sampled river macroinvertebrates from six sites each of three riparian vegetation types: revegetated (treatment), willow-dominated (control) and native forest (reference) in the Gellibrand River catchment during austral spring 2007 and autumn 2008, and measured temperature and light intensity. Revegetated sites varied in age from 1 to 8 years since restoration. Abundances of invertebrates were similar across vegetation types, but were higher during autumn. Macroinvertebrate assemblages at revegetated sites (regardless of age) and at willow-dominated sites showed little among-site variation compared with native forest sites,which showed high site-to-site variability. Water temperatures and light intensity were higher at revegetated sites where works had recently been completed and cooler in native forest sites and long-established revegetated sites. The reduced variability in macroinvertebrate communities among revegetated sites may result from their history as willow-dominated sites or from the disturbance created by willow removal. Either way, these results suggest that longer than 8 years is required before macroinvertebrate assemblages in restored stretches of stream show the variation that appears characteristic of natural sites.