Application and evaluation of classification trees for screening unwanted plants

Abstract Risk assessment systems for introduced species are being developed and applied globally, but methods for rigorously evaluating them are still in their infancy. We explore classification and regression tree models as an alternative to the current Australian Weed Risk Assessment system, and demonstrate how the performance of screening tests for unwanted alien species may be quantitatively compared using receiver operating characteristic (ROC) curve analysis. The optimal classification tree model for predicting weediness included just four out of a possible 44 attributes of introduced plants examined, namely: (i) intentional human dispersal of propagules; (ii) evidence of naturalization beyond native range; (iii) evidence of being a weed elsewhere; and (iv) a high level of domestication. Intentional human dispersal of propagules in combination with evidence of naturalization beyond a plants native range led to the strongest prediction of weediness. A high level of domestication in combination with no evidence of naturalization mitigated the likelihood of an introduced plant becoming a weed resulting from intentional human dispersal of propagules. Unlikely intentional human dispersal of propagules combined with no evidence of being a weed elsewhere led to the lowest predicted probability of weediness. The failure to include intrinsic plant attributes in the model suggests that either these attributes are not useful general predictors of weediness, or data and analysis were inadequate to elucidate the underlying relationship(s). This concurs with the historical pessimism that we will ever be able to accurately predict invasive plants. Given the apparent importance of propagule pressure (the number of individuals of an species released), future attempts at evaluating screening model performance for identifying unwanted plants need to account for propagule pressure when collating and/or analysing datasets. The classification tree had a cross‐validated sensitivity of 93.6% and specificity of 36.7%. Based on the area under the ROC curve, the performance of the classification tree in correctly classifying plants as weeds or non‐weeds was slightly inferior (Area under ROC curve = 0.83 ± 0.021 (±SE)) to that of the current risk assessment system in use (Area under ROC curve = 0.89 ± 0.018 (±SE)), although requires many fewer questions to be answered.     

Introduced mammals in Australian rangelands: Future threats and the role of monitoring programmes in management strategies

Abstract In the present paper, we have provided an initial assessment of the current and future threats to biodiversity posed by introduced mammals (predators and herbivores) inhabiting the Australian rangelands, exploring trends in populations and options for management. Notably, rabbits have declined in recent years in the wake of rabbit haemorrhagic disease, populations of feral camels have increased dramatically and foxes appear to have moved northwards, thereby threatening native fauna within an expanded range. Following on, we developed a framework for monitoring the impacts of introduced mammals in the Australian rangelands. In doing so, we considered the key issues that needed to be considered in designing a monitoring programme for this purpose and critically evaluated the role of monitoring in pest animal management. Finally we have provided a brief inventory of current best‐practice methods of estimating the abundance of introduced mammal populations in the Australian rangelands with some comments on new approaches and their potential applications.     

Towards an understanding of resilience in isolated coral reefs

In 1998, seawater temperature anomalies led to unprecedented levels of coral bleaching on reefs worldwide. We studied the direct effects of this thermal event on benthic communities and its indirect effects on their associated coral reef fish communities at a group of remote reefs off NW Australia. Long‐term monitoring of benthic and fish assemblages on these reefs allowed us to compare the responses of these communities to coral bleaching using a data series that included 4 years before, and 6 years following, this bleaching event. While bleaching mortality was evident to >30 m depth, it was patchy among the shallower survey sites with decreases in live coral cover ranging from 30% to 90% across seven surveyed locations Within 2 years of the bleaching, hard coral recovery had begun at all sites and by 2003 reef‐wide coral cover had increased to ～39% of its preimpact levels. We exploited this pattern of differential survival of corals among sites, the associated changes in these benthic communities, and their patterns of recovery, to better understand links between benthic community dynamics and their associated fish communities. Temporal changes in the resident fish communities strongly reflected the differential shifts in the benthic communities, but were lagged by 12–18 months. Five years after the bleaching event, the fish communities on five of the seven surveyed locations showed evidence of recovery, however, none had regained their preimpact structures. Analyses of these communities by taxonomic family revealed a range of responses to the disturbance reflective of their life‐histories and trophic and habitat affiliations. The slow but recognizable recovery of this isolated reef system has parallels with other relatively isolated systems that displayed resilience to the 1998 bleaching event, e.g. the Chagos archipelago, but it also contrasts sharply with low levels of resilience documented in other isolated reef systems subject to the same disturbance, e.g. the Seychelles. In this context, our results highlight the significant knowledge gaps remaining in understanding the resilience of these ecosystems to disturbance.     

Photosynthesis in the Pericarp of Developing Wheat Grains

Oxygen exchange in grains of wheat was measured in both lightand dark over the period of grain development. Between 10 dand 30 d after anthesis, the rate of photosynthesis exceededthe rate of respiration. Peak photosynthetic activity was observedat 20 d after anthesis, coinciding with maximum chlorophyllcontent in the pericarp green layer. Removal of the pericarptransparent layer increased rates of oxygen exchange in boththe light and the dark. Attempts to inhibit photosynthesis withDCMU were only successful with the pericarp transparent layerremoved. Key words: Wheat, pericarp, photosynthesis     

Age-specific mortality rates in reef fishes: Evidence and implications

Abstract Mortality is a fundamental demographic rate, the nature of which has profound consequences for both the dynamics of populations and the life-history evolution of species. For example, if per capita mortality rates are age- or stage-specific, life-history traits should evolve in response to age- and stage-specific differences in selection arising from these temporally variable rates. Similarly, variation in the average mortality rate across ages and/or stages can also select for shifts in life history. Mortality rates of recently settled reef fishes can be very high and per capita mortality is commonly assumed to decrease with increasing age. A review of evidence for age-specific per capita mortality rates in reef fishes from early postsettlement up to 13 months postsettlement suggests that during this period these rates are often age invariant. The data on which these interpretations are based, however, are extremely limited both in terms of the proportion of the life cycle over which mortality rates have been sampled and the quality of these data. Nonetheless, these data do suggest that selective pressures associated with patterns of mortality may vary among species of reef fishes and that these species therefore could be more effectively used in the study of life-history evolution. At present, reef fishes are under-represented in the study of life-history evolution compared with other vertebrate taxa.