Summary 1. RIVPACS‐type predictive models were developed at a relatively large spatial scale for the Australian state called New South Wales (NSW, 801 428 km2). Aquatic macroinvertebrate samples and physical and chemical data were collected from 250 reference sites (little affected by human activities) and 23 test sites (with known human impacts) throughout NSW in autumn and spring 1995 and identified mostly to family level. Reference sites were grouped based on their macroinvertebrate data using classification (UPGMA) and ordination techniques. Relationships between macroinvertebrate and environmental data were established using principal axis correlations and stepwise multiple discriminant function analysis. models for predicting invertebrate assemblages were developed separately for edge and riffle habitats for autumn and spring data sets and for combined autumn and spring data sets. 2. Sites in the lowland sections of the western flowing rivers were characterized by low taxonomic richness and were distinct from the sites in the eastern part of the state. Sites on the western slopes of the Great Dividing Range in southern and northern NSW mostly fell into separate groups. In eastern NSW, site groups did not represent a north, central and south division. Sites on highland streams, coastal fringe streams and large rivers mostly formed distinct groups, but most of the sites on east‐flowing rivers fell into large site groups that did not have clear geographic boundaries. 3. Environmental variables that were strongly correlated with ordinations of macroinvertebrate presence/absence at sites were water temperature, altitude, longitude and maximum distance from source. The predictor variables determined by DFA for the six models created included alkalinity, altitude, location (longitude and/or latitude), stream size and substratum composition. These are generally in common with the variables determined for other large geographic areas in Australia and the United Kingdom. 4. Model outputs from reference sites suggest that, among the six models, the riffle model combining autumn and spring is likely to give the most reliable predictions. The combined edge model also performed well but refinements are needed for single season models to provide reliable outputs. 5. Combined season models both for riffles and for edges detected biological impairment at all but one of the test sites. Single season riffle models also detected impairment while single season edge models characterized sites as unimpaired despite other models’ indications of impaired fauna. Riffle models may be more sensitive than edge models but the sampling of riffles is often limited by flow. Edge habitats are available at most sites but there may be few riffles in floodplain rivers. Available resources, desired model sensitivity, and river type should be considered jointly to determine the most useful habitat to sample.

Mexican palo-verde is a serious woody weed in tropical parts of the world. Like many such leguminous species, it has relatively large seeds with hard-seeded (physical) dormancy. It therefore has the potential for long-lived seed banks that are difficult to manage. The physiology of hard-seeded dormancy is still relatively poorly understood but has important implications for weed management. We propose that wet heat is a potentially important dormancy release mechanism for summer rainfall tropical regions. We described the relationships between wet heat and dormancy release (in water; three seed sources) and germination (near saturation; single seed source) by testing seeds at constant temperatures between 10 and 60 C. The logistic transformation of the temperature–dormancy relationship was best described by a quadratic equation below a threshold of ∼ 33.6 C and a linear equation above that threshold. The relationship was the same for all seed sources other than a phase shift of up to 6.6 C, which is likely to be of biological significance. Germination occurred between 15 and 40 C and was limited by cold stress at ≤ 20 C and heat stress > 35 C. The sensitivity of dormancy to naturally encountered temperature ranges suggests that wet heat is an important dormancy release mechanism and one that can be exploited when developing management strategies for invasive populations.

Beneficial exotic trees and shrubs have been widely spread throughout semiarid and arid regions of the world. These trees and shrubs can however cause severe negative impacts. Mesquite (Prosopis species), native to the New World, is one example which continues to be promoted despite causing serious impacts both in its native and introduced ranges. We describe the population structure of the largest population of fire-tolerant hybrid mesquite (P. velutina  P. glandulosa var. glandulosa  P. pallida) in Australia, which was intentionally established in the 1930s. We compare it with invasive populations within its native range, and consider the implications for managing exotic mesquite invasions. We found relatively high juvenile densities at all levels of canopy cover (<30% to 90-100%), and low mortality rates for both juveniles and adults (<2%/y), which suggests that populations are still in an early phase of invasion. Exotic populations differed from native range populations in being more dense (average 4,859 adults/ha), having a sizable sapling (seedling and juvenile) bank that can remain quiescent under canopy cover (average 10,914 seedlings and juveniles/ha), failing to act as nurse plants for native shrubs (<8 native shrubs/ha), and almost totally excluding the herbaceous (grass) layer (average 0.3% cover). Our results suggest that ecosystem impacts in the introduced range are likely to be even worse, and management even more difficult, than has already been reported for invasions within its native range. The lack of feasible means for managing highly invasive, broad-scale mesquite populations need to be addressed, and needs to be considered explicitly when promoting mesquite as a beneficial plant.

These results demonstrate that wet heat is the principal dormancy release mechanism for P. aculeata when conditions are hot and wet. They also highlight the potential importance of microclimate in driving the population dynamics of such species.

Summary1. Specialist seed-feeders are widely used in weed biological control, but seed predation rates are frequently insufficient to cause the required impacts. Understanding the underlying reasons is prerequisite to predicting efficacy. 2. We conducted continental-scale surveys of an introduced, multi-voltine seed-feeder [Bruchidae: Penthobruchus germaini (Pic.)] on an invasive legume (Caesalpinaceae: Parkinsonia aculeata L.). We tested three hypotheses as to what limits seed predation; namely, seed escape through egg aggregation, mortality of immature beetle stages, and failure to track temporal fluctuations in resource availability. We also tested how these factors interacted with the environment and each other. 3. Mean seed predation was relatively low (2-30%), despite mean egg densities of between 0·55 and 3·2 eggs per seed. Eggs were slightly aggregated (negative binomial, k = 1·87). Unexplained egg mortality (6-44%), egg parasitism (10-70%) and larval/pupal mortality (62%) were high, but egg parasitism was the only mortality factor that was density-dependent and that varied across climatic regions. Egg densities responded poorly to rapid within-season increases in seed availability. 4. All examined factors dampened seed predation rates. However, we developed a deterministic mathematical model which showed that seed predation would still have been relatively low (5-56%) at the observed egg densities, even without direct effects of immature beetle mortality. Also, to achieve a benchmark seed predation rate of 80%, egg densities would need to be over 8·5 eggs per seed with no parasitism, and an unrealistically high 27·8 at 70% parasitism. Available data suggest that seed predation by specialist seed-feeders will often be constrained by one or more of the factors we identified. 5. Synthesis and applications . Selecting effective biological control agents is an important challenge for weed biocontrol. Our results suggest that many seed-feeders will not regulate plant populations, but that predictions of their efficacy can be greatly improved by quantifying the way eggs are distributed across seeds and the various mortality factors that affect immature beetle stages. The ability of seed-feeders to track resource fluctuations may also be predictable. For example, multivoltine insects appear better at tracking between-season and between-site variation in resource availability than sharp changes in within-season availability.