Aim (a) To characterize the riparian bird assemblage, and its variation, in a large area of northern Australia; (b) to examine the distinctiveness of this assemblage in relation to the broader landscape; (c) to consider the influence of disturbance on this assemblage; (d) to examine temporal variability in the riparian assemblage, and especially evidence for seasonal movements between riparian and non-riparian areas.Location c. 620,000 km 2 of the seasonal tropics of the Northern Territory, Australia.Methods (a) Synchronous sampling of birds in riparian and adjacent non-riparian areas at 100 sites stratified across 13 catchments and an extensive rainfall gradient. (b) Repeat visits to 13 of these sites at contrasting seasons. (c) Analysis of a larger distributional database to assess the relative occurrence of records in riparian areas relative to nonriparian areas.Results Species richness and the total abundance of birds was significantly greater in riparian zones than in matched non-riparian areas, especially where the riparian zones contained extensive cover of rain forest plants and Melaleuca . Similarity in bird species composition between riparian zones and adjacent non-riparian areas was generally low, and this distinction was greatest in lower reaches of the rivers and where the riparian zone contained no eucalypts. Bird species composition varied gradationally from riparian zones in high rainfall areas, through riparian zones in low rainfall areas and non-riparian zones in high rainfall areas, to non-riparian zones in low rainfall areas. Many species occurred widely across the riparian sites sampled. Of ninety-four species recorded from more than five sites, forty-five species were significantly more abundant in riparian zones than in matched non-riparian zones, whereas this pattern was reversed for only twelve species. There was little association between foraging group and preference for riparian zones. Species had highly idiosyncratic distributions across the riparian samples, with the most common trend being an association with mean annual rainfall. Many species were significantly more closely associated with riparian zones in lower rainfall areas than in higher rainfall areas. Indeed, many species typical of higher rainfall areas extended into lower rainfall areas only, or mainly, along riparian strips. There was some temporal fluidity in bird species composition of riparian zones, suggesting seasonal movements between riparian zones and the surrounding landscape. There was little evidence that disturbance was a major factor influencing the distribution of riparian birds, probably because other major geographical and environmental gradients probably dwarfed the influence of the relatively minor variation between samples in disturbance. Main conclusionsThe bird fauna of riparian areas is distinct from that of the surrounding savannas, and especially so in lower rainfall areas. Riparian vegetation allows many species to extend their distributions into lower rainfall areas. The riparian assemblage is l...

The distributions of the 567 plant species considered to be endemic to the Northern Territory, Australia, were collated from a distributional database comprising about 600 000 records. Endemic species comprise a non-random taxonomic subset of all plants known from the Northern Territory. Because of substantial geographic disparity in collecting effort, we analysed geographic patterning of these endemic species by using both (1) actual records only and (2) interpolated ranges (minimum convex polygons). The geographic distribution of the number of Northern Territory endemic plant species was well predicted by a measure of topographic complexity and climate (particularly rainfall). The observed distributional patterning of endemic species was also influenced by survey effort, but this latter influence was substantially reduced by the use of minimum convex polygons. Both analyses revealed that there was a clear aggregation of endemic species in the 32 000 km2 of the sandstone plateau of western Arnhem Land. This ‘hotspot’ has been previously recognised in coarser-scale assessments of national and international centres of plant biodiversity. Our analysis concluded that 172 species are restricted to this plateau, and that the plateau comprised at least 90% of the distribution of a further 25 species. More broadly, 438 plant species are endemic to the northern part of the Northern Territory (the 316 000 km2 north of 16°S), a level of endemism that may match that of Cape York Peninsula and surpasses that of the Kimberley. The core area for Northern Territory endemic plants, the plateau of western Arnhem Land, is currently threatened, particularly by unfavourable fire regimes.

Eighteen non-marine mammal species (including seven species of bats) were recorded from a total of 49 islands in the Wessel and English Company island chains off north-eastern Arnhem Land, Northern Territory. Most individual species were restricted to, or had higher incidence on, larger islands, and species richness as a whole increased as island size increased. The most notable exception was the semi-aquatic Hydromys chrysogaster, which occurred relatively equitably across island sizes; this species, two bat species and the macropod Petrogale brachyotis were recorded from islands smaller than 10 ha. However, the variation between islands in the number of native terrestrial mammal species was not best predicted by island size, but rather by a combination of sampling effort and altitude (which explained 64% of the deviance in species richness), or altitude and distance to larger land mass (explaining 63% of deviance). Richness–area patterns for individual islands in these chains were reasonably consistent with those of other islands sampled in northern Australia. However, the fauna of the Wessel and English Company groups as a whole was less rich than that of the Pellew and Kimberley islands, and individual islands appeared to have lower species richness than comparable mainland areas. Species that were notably absent or that were recorded from relatively few islands include large macropods, Tachyglossus aculeatus, Antechinus bellus, Phascogale tapoatafa, Sminthopsis spp., Mesembriomys gouldii, Rattus colletti, Leggadina lakedownensis and Pseudomys calabyi. Some of these species may be absent through lack of suitable habitat; others have presumably disappeared since isolation, possibly due to Aboriginal hunting. Richness at the quadrat (50 × 50 m) scale was generally very low. Habitat relationships are described for the 7 species recorded from more than 5 quadrats. At a quadrat-scale, the richness of native mammals was greater on islands larger than 1000 ha than on islands smaller than 1000 ha. Quadrat-scale species richness varied significantly among the islands sampled by the most quadrats (even when the comparison was restricted to either of the two most extensive vegetation types), but this variation was not closely related to either area or altitude. The two most frequently recorded species, the rodents Melomys burtoni and Zyzomys argurus, showed distinct habitat segregation on islands where both were present, but tended to expand their habitat range on islands where only one of the species occurred. The most notable conservation feature of the mammal fauna of the Wessel and English Company Islands is the occurrence of the golden bandicoot, Isoodon auratus, a vulnerable species apparently now extinct on the Northern Territory mainland. Four feral animal species (Rattus rattus, Canis familiaris, Bubalus bubalis and Capra hircus) were recorded from a total of 6 islands.

Aim To describe the habitat characteristics and status of the brush-tailed rabbitrat, Conilurus penicillatus Gould, 1842, on the Tiwi Islands, northern Australia, as part of a broader programme aimed at the conservation management of this species. In addition, comparable environmental modelling is undertaken for other co-occurring small native mammals, including the black-footed tree-rat, Mesembriomys gouldii Gray, 1843, a taxonomically and ecologically related species. These objectives relate to the significance for mammal conservation of islands generally in Australia, and the recent intensification of plantation forestry on these previously little-disturbed islands.Location Melville and Bathurst islands (Tiwi Islands), respectively, Australia's second and fifth largest islands.Methods A systematic survey was conducted for mammals across Bathurst (115 sampled quadrats) and Melville Island (236 quadrats). A broad range of environmental variables was recorded for every quadrat. All quadrats were classified by their woody plant species composition. The relative occurrence of individual mammal species across the resulting vegetation groups was examined using Kruskal-Wallis anova. The habitat relationships of C. penicillatus and the most commonly recorded mammal species were described by generalized linear modelling, with separate models for each island, for both islands combined, for all habitats and for only those sites dominated by eucalypts.Results Twelve small mammal species (excluding bats, macropods and feral animals) were recorded in this study. The most notable feature of this survey was the lack of records of M. gouldii from Bathurst Island. In contrast, the proportion of quadrats with C. penicillatus was not significantly different between the two islands. There was no significant tendency for these two species to co-occur in quadrats on Melville Island more or less commonly than by chance. Conilurus penicillatus was most abundant in eucalypt forest while M. gouldii showed a weak association with eucalypt forests and woodlands and shrub land. The five most commonly recorded species showed highly idiosyncratic relationships with environmental variables, with this relationship showing some variation between the two islands. None showed any significant association with floristic variation within the extensive eucalypt forests, but most showed significant associations with tree height, basal area (especially of large trees), landscape position (distance to watercourse) and fire history.Main conclusions Conilurus penicillatus was most likely to occur in tall eucalypt forest away from watercourses. This habitat is now being targeted for clearance for the development of plantations of the exotic Acacia mangium. Seven of the 12 mammal species examined in this study (C. penicillatus, M. gouldii, Rattus tunneyi

Forty‐four species of terrestrial reptiles and eight species of frogs were recorded from 60 continental islands of the Wessel and English Company groups off northeastern Arnhem Land, Northern Territory. Two gecko species, Oedura rhombifer and Heteronotia binoei, were present on the most islands (34 and 31, respectively), and occurred on islands < 5 ha. In contrast, agamids, pygopodids and varanids were absent from islands < 18 ha, and snakes and frogs were not reported from islands < 240 ha. Island size explained 82% of the variation in species richness for terrestrial reptiles, and 84% of that for lizards. The relationship was less good for (i) groups with generally uncommon species (notably snakes), for which sampling effort explained more variation, and (ii) groups with species which had relatively specific habitat requirements (notably frogs), for which island size and isolation factors were not especially relevant. For most taxonomic groups considered, isolation factors added little to the relationship between species richness and island size. Across all reptiles, larger species were found on fewer islands, and had larger island size thresholds. This relationship broke down with analysis restricted to the single most species‐rich family, Scincidae. Only 6 of the 20 most frequently recorded species showed significant variation in abundance among 8 vegetation types sampled by 226 quadrats across 40 islands. The number of species (alpha‐diversity) and total abundance of herpetofauna within quadrats was generally unrelated to island size; however, (with analysis restricted to islands on which they occurred) six individual species were significantly more abundant on smaller islands than on larger islands, with no species showing the opposite pattern. The islands’ herpetofauna is largely a relatively depauperate subset of that of the far more complex sandstone massif and escarpment of western Arnhem Land, especially missing species associated with rugged sandstone gorges, riparian areas, open forests, swamps and clay soils. Patterns in species richness and composition are explained by greater range of environments on larger islands allowing better retention of species since isolation and/or richer tallies at the time of isolation. The evidence suggests that there has been relatively little colonization, although at least two gecko species and one varanid may have moved reasonably frequently.