Simon C. Barry

Are there any consistent predictors of invasion success

This article summarises the results of 49 studies that together test the significance of 115 characteristics in 7 biological groups: birds, finfish, insects, mammals, plants, reptiles/amphibians and shellfish. Climate/habitat match, history of invasive success and number of arriving/released individuals are associated with establishment success in at least four independent data sets, both within and across biological groups, and none are contraindicated by other studies. In the introduced-invasive control group, two species level characteristics—taxon and geographic range size—were significantly associated with establishment success across two biological groups. These characteristics, however, were not supported by independent data sets, or were contraindicated by these data sets, within the biological groups examined here. In the introduced-native control group, three species level characteristics—geographic range size, leaf surface area and fertilisation system (monoecious, hermaphroditic or dioecious)—were consistently supported within plants but were either not supported by independent data sets or contraindicated by datasets within or across other biological groups. Climate/habitat match is the only characteristic that is consistently significantly associated with invasive behaviour (in this case exotic range size) across biological groups. This finding, however, is not supported by two or more independent data sets within any of the biological groups examined here. Within plants there are a suite of characteristics, predominately associated with reproduction, that are significantly associated with a range of invasion metrics, predominately abundance in the invaded range. None of these characteristics, however, are supported across any other biological groups. We note the confounding effects of phylogeny, residence time and propagule pressure and suggest that site- and taxa-specific analysis will provide further useful insights.

Generalized additive modelling and zero inflated count data

This paper describes a flexible method for modelling zero inflated count data which are typically found when trying to model and predict species distributions. Zero inflated data are defined as data that has a larger proportion of zeros than expected from pure count (Poisson) data. The standard methodology is to model the data in two steps, first modelling the association between the presence and absence of a species and the available covariates and second, modelling the relationship between abundance and the covariates, conditional on the organism being present. The approach in this paper extends previous work to incorporate the use of Generalized Additive Models (GAM) in the modelling steps. The paper develops the link and variance functions needed for the use of GAM with zero inflated data. It then demonstrates the performance of the models using data on stem counts of Eucalyptus mannifera in a region of South East Australia.

Predicting establishment success for alien reptiles and amphibians: a role for climate matching

We examined data comprising 1,028 successful and 967 failed introduction records for 596 species of alien reptiles and amphibians around the world to test for factors influencing establishment success. We found significant variations between families and between genera. The number of jurisdictions where a species was introduced was a significant predictor of the probability the species had established in at least one jurisdiction. All species that had been introduced to more than 10 jurisdictions (34 species) had established at least one alien population. We also conducted more detailed quantitative comparisons for successful (69 species) and failed (116 species) introductions to three jurisdictions (Great Britain, California and Florida) to test for associations with climate match, geographic range size, and history of establishment success elsewhere. Relative to failed species, successful species had better climate matches between the jurisdiction where they were introduced and their geographic range elsewhere in the world. Successful species were also more likely to have high establishment success rates elsewhere in the world. Cross-validations indicated our full model correctly categorized establishment success with 78–80% accuracy. Our findings may guide risk assessments for the import of live alien reptiles and amphibians to reduce the rate new species establish in the wild.

Hollow selection by vertebrate fauna in forests of southeastern Australia and implications for forest management

Abstract We examined the types of hollows, and types of hollow-bearing trees, occupied by vertebrate fauna in temperate eucalypt forests in southeastern Australia. Hollow-bearing trees are selected for retention in wood production forests to mitigate the effects of logging on hole-nesting fauna. A total of 471 hollows was examined in 228 trees felled as part of routine logging operations. Fauna had occupied 43% of all hollows (⩾2cm minimum entrance width; ⩾5cm depth). Hollows with small (2–5cm), medium (6–10cm) and large (>10cm) minimum entrance widths had occupancy rates of 29, 44 and 62%, respectively. The internal dimensions of hollows, especially hollow depth, were the best predictors of hollow occupancy, even when variables measured at the tree and site levels were considered. Fauna occupied 57% of all hollow-bearing trees. In a Poisson regression model, the number of hollows in trees that contained evidence of occupancy was positively associated with: (1) the total number of hollows visible in the tree; (2) the proportion of the trees crown that contained dead branches; and (3) tree diameter. The number of different vertebrate species that occupied trees was positively associated with the same explanatory variables except tree diameter. Thus, our results suggest that trees with multiple hollows and dead branches in the crown should be preferentially selected for occupancy by hollow-using fauna. Our results suggest that trees with the largest diameter are not the most suitable for retention. Possibly because they contain proportionally fewer hollows with small entrances, which are favoured by some vertebrate species.

Extreme bias in sex allocation in Eclectus parrots

We investigated extraordinary patterns of sex allocation in captive eclectus parrots (Eclectus roratus). These birds are extremely unusual as they show reverse sexual dichromatism, they are the only cooperatively breeding parrot, and they are one of the few birds with nestlings that are easily sexed. They lay two eggs per clutch, but often only fledge one young, and the sex ratio of 209 fledglings did not differ significantly from parity. However, when two young are fledged together they are very likely to be of the same sex, and some females produce long unbroken runs of one sex (the maximum was 20 males) before switching to the other sex. Monte–Carlo simulations show that these runs of same–sex clutches defy expectation if we assume that the sex of chicks within each clutch is independent of the previous clutch. We use further simulations to show that the sex bias must occur at fertilization (i.e. the primary sex ratio), although the female may make further adjustments via infanticide. Control over sex allocation in eclectus parrots is one of the most extreme reported from birds.

Diversity and habitat relationships of hypogeous fungi. II. Factors influencing the occurrence and number of taxa

Fruit-bodies of hypogeous fungi were sampled over two seasons across 136 forested study sites representing a stratified sample of the climatic, geological and topographic features of far south-eastern mainland Australia. Two hundred and nine species, over three-quarters being undescribed, were recorded. Statistical models based on various environmental attributes measured for each site were developed for the occurrence of several common taxa. At a landscape scale, climatic factors such as mean minimum temperature of the coldest month and annual mean moisture index were important explanatory variables for most taxa examined, but the type of response varied. More locally, topographic position, soil fertility, time since last fire and micro-habitat structures such as the leaf litter layer and number of large fallen trees also influenced the distribution of taxa in different ways. A model was then developed for the number of fungal species occurring at each site. Important explanatory variables were type of substrate, topography and diversity of potential host eucalypt species. The utility of each model constructed needs evaluation by further sampling of hypogeous fungi. Possible implications of our findings for forest management are discussed. Further analyses of our existing data are also identified.

The Analysis of Ring-Recovery Data Using Random Effects

We show how random terms, describing both yearly variation and overdispersion, can easily be incorporated into models for mark-recovery data, through the use of Bayesian methods. For recovery data on lapwings, we show that the incorporation of the random terms greatly improves the goodness of fit. Omitting the random terms can lead to overestimation of the significance of weather on survival, and overoptimistic prediction intervals in simulations of future population behavior. Random effects models provide a natural way of modeling overdispersion-which is more satisfactory than the standard classical approach of scaling up all standard errors by a uniform inflation factor. We compare models by means of Bayesian p-values and the deviance information criterion (DIC).

Predicting establishment success for introduced freshwater fishes: a role for climate matching.

We modelled data comprising 1,189 successful and 489 failed introduction records for 280 species of freshwater fishes around the world. We found significant variations in establishment success between genera and families. The number of countries where introductions occurred was a significant predictor of the probability a species would establish in at least one country and all species that had been introduced to nine or more countries (46 species) had established at least one exotic population. We also conducted more detailed quantitative modelling for 135 species introduced to 10 countries to identify factors affecting establishment success. Relative to failed species, established species had better climate matches between the country where they were introduced and their geographic range elsewhere in the world. Established species were also more likely to have high establishment success rates elsewhere in the world. Neither the reason why fish were introduced nor the country where they were introduced was correlated with establishment success. Cross-validations indicated our model correctly categorised establishment success with 78% accuracy. Our findings may guide risk assessments for the import of live exotic fish to reduce the rate new species establish in the wild.

The effectiveness of air bags.

Previous research has shown that the installation of air bags in vehicles significantly reduces crash related deaths, but these analyses have used statistical techniques which have not been capable of controlling for other major determinants of crash survival. This study analysed data from the US FARS database of fatal crashes using conditional logistic regression which is simultaneously able to estimate occupant protection effects for a range of variables. Results of the analysis provided a comparative quantification of both the effect of the air bag as well as other well known determinants of occupant crash survival (age, seat belt use, and gender). When potentially confounding variables were controlled, both the driver and passenger side air bag devices were shown to significantly reduce the probability of death in direct frontal collisions, but the effect size calculated was small compared to the effect of the seat belt. The effect size may also be very small in absolute terms depending on the severity of the crash involved. Given the limited benefit of the air bag, efforts to promote air bags seem particularly difficult to justify in countries such as the United States where the vastly superior occupant protection of the seat belt is under-utilised.

Distance sampling methodology

We consider the method of distance sampling described by Buckland, Anderson, Burnham and Laake in 1993. We explore the properties of the methodology in simple cases chosen to allow direct and accessible comparisons of distance sampling in the design- and model-based frameworks. In particular, we obtain expressions for the bias and variance of the distance sampling estimator of object density and for the expected value of the recommended analytic variance estimator within each framework. These results enable us to clarify aspects of the performance of the methodology which may be of interest to users and potential users of distance sampling.