The increased demographic performance of biological invaders may often depend on their escape from specifically adapted enemies. Here we report that native taxa in colonized regions may swiftly evolve to exploit such emancipated exotic species because of selection caused by invaders. A native Australian true bug has expanded it host range to include a vine imported from tropical America that has become a serious environmental weed. Based on field comparisons and historical museum specimens, we show that over the past 30-40 years, seed feeding soapberry bugs have evolved 5-10% longer mouthparts, better suited to attack the forest-invading balloon vines, which have large fruits. Laboratory experiments show that these differences are genetically based, and result in a near-doubling of the rate at which seeds are attacked. Thus a native biota that initially permits invasion may rapidly respond in ways that ultimately facilitate control.

Aim  Thresholds often exist in the relationship between species richness and the area of remaining habitat in human‐modified landscapes, prompting debate about the mechanisms responsible. We hypothesize that if species–area relationships differ with underlying factors such as landscape productivity, and such factors correlate with patterns of habitat clearance, then spurious thresholds can arise where the separate species–area relationships intersect. We assessed whether this phenomenon could explain landscape‐level species–area relationships for birds occupying 31 landscapes of 100 km2 in eastern Australia. Location  Eastern Australia. Methods  Landscape‐level species richness estimates were modelled as a function of the percentage of native vegetation remaining in the study landscapes. The performance of traditional species–area curves and continuous and discontinuous piecewise models was compared using an information theoretic approach. Separate models for high‐ and low‐productivity and high‐ and low‐fragmentation landscapes were examined to determine whether they implied different species–area relationships. Results  The species–area relationship exhibited a rapid change‐point at approximately 40% vegetation cover, but this was most parsimoniously explained by two disjunct slopes rather than a continuous threshold model or a classic species–area curve. Exploration of models fitted separately to high‐ and low‐productivity landscapes suggested that such landscapes may differ in their characteristic species–area relationships. Main conclusions  The observed pattern is consistent with the spurious threshold hypothesis, and opens a new avenue of enquiry into the processes behind apparent ecological thresholds. This hypothesis may be valid in other regions where clearing history is confounded by underlying factors such as landscape productivity, and demands further research. In such systems, real thresholds for different landscape types may occur at different levels of cover, or might not exist at all. If so, a simple space‐for‐time substitution may not be valid, and management prescriptions based on threshold values (e.g. 40%) will be flawed.

Greater gliders, Petauroides volans, were radio-tracked within a large tract of forest in the dry inland of southern Queensland. This forest has been commercially logged for timber for more than 100 years. Home-range estimates ranged from 1.4 ha (female) to 19.3 ha (male). Minimum convex polygon (MCP) estimates were larger for males (average, 11.5 ha) than females (average, 3.3 ha) and combined (6.8 ha, sexes pooled) were larger than estimates from other Australian populations. Gliders were located foraging in myrtaceous tree species only, using mostly Eucalyptus moluccana, E. fibrosa and Corymbia citriodora. E. moluccana was used for foraging more frequently than would be expected on the basis of its availability in the forest. E. fibrosa and C. citriodora were used in proportion to their availability in the forest. Gliders were not seen foraging in non-myrtaceous species or myrtaceous trees <20 cm diameter at breast height (dbh), preferring trees in 30–70-cm dbh classes and as ‘mature’ and ‘over-mature’ classified according to growth-stage characteristics. Den tree species included the same species used for foraging as well as dead trees (16% of den trees). E. fibrosa and E. tereticornis were preferred significantly more than expected by their availability in the forest. Non-myrtaceous species were not used as live den trees. Large (dbh >50 cm) and old living trees (in deteriorating and senescent condition: ‘late mature’ and ‘over-mature’ categories) were primarily used as den trees. Individual gliders utilised 4–20 den trees. Females utilised more den trees per unit area of home range (3.8 den trees ha–1, maximum) than males (0.9 den trees ha–1, maximum). Fewer den trees were used per unit area of home range than by gliders at a coastal location with approximately the same latitude. The density of live stems containing hollows suitable as dens is currently lower than 1 tree ha–1 in some parts of the study forest. Gliders were two and half times less likely to be observed during standardised spotlighting surveys in the study area than elsewhere in southern Queensland. It is likely that low availability of den trees is contributing to large home ranges and the apparent low population density observed in this study.

The impact of forest management on diurnal bird assemblages and abundance was investigated in contiguous tracts of eucalypt forest in the Brigalow Belt Bioregion, south central Queensland. Sites were located across three levels of livestock grazing intensity and three levels of selective logging intensity within the most extensive habitat type, Corymbia citriodora-dominant forest.We recorded a high rate of incidence and large numbers of the hyper-aggressive noisy miner Manorina melanocephala (Passeriformes: Meliphagidae) at the majority of our survey sites, a phenomenon rarely reported in non-cleared landscapes. As shown by numerous studies in fragmented landscapes, the distribution of this species in our study had a substantial negative effect upon the distribution of small passerine species. Noisy miners exerted the strongest influence upon small passerine abundance, and masked any forest management effects. However, key habitat features important for small passerines were identified, including a relatively high density of large trees and stems in the midstorey. Selective logging appeared to exert a minimal effect upon noisy miner abundance, whereas grazing intensity had a profound, positive influence. Noisy miners were most abundant in intensively grazed forest with minimal midstorey and a low volume of coarse woody debris. Higher road density in the forest landscape also corresponded with increased numbers of noisy miners. Reduction in grazing pressure in Brigalow Belt forests has the potential to benefit small passerine assemblages across large areas through moderating noisy miner abundance. The strong relationship between noisy miners and small passerines suggests that noisy miner abundance could act as an easily measured indicator of forest condition, potentially contributing to monitoring of forest management outcomes.

Aim We explored whether one native bird (the yellow-throated miner Manorina flavigula) greatly affected the composition of avifaunas in > 500,000 km 2 in northern Australia. Location Rangelands of north-eastern AustraliaMethods Repeated avian surveys were conducted in 368 locations, for which in-site vegetation and landscape-contextual measurements were made. Hierarchical Bayesian models were used to determine whether avian assemblages were affected by variation in abundances of the yellow-throated miner.Results Variation in the abundances of the yellow-throated miner appeared to be governed largely by vegetation cover in surrounding landscapes. Summed abundances and richness of birds less massive than the yellow-throated miner (< 53 g) were negatively associated with abundances of the yellow-throated miner. Variation in other widely distributed species with larger body masses than the yellow-throated miner (> 53 g) bird could not explain the patterns of variation in small-bodied species as well as the yellow-throated miner. There were no relationships between abundances and richness of larger species and abundances of the yellow-throated miner. Main conclusionsThe genus Manorina appears to be a competitive despot insofar as species smaller than it are concerned. There now is strong evidence that the local composition of avifaunas over much of a continent is controlled by the indiscriminate aggression of a colonial genus. Many of the existing ideas in community ecology that have been proffered for explaining the composition of vertebrate assemblages are inadequate for these assemblages given the profound influence of species of the genus Manorina. The mooted agricultural expansion of development in northern Australia almost certainly would favour the spread of the yellow-throated miner and probably will depress the occurrence and abundances of small-bodied bird species.