A comparison of success rates of introduced passeriform birds in New Zealand, Australia and the United States

In this study, we compiled lists of successful and unsuccessful passeriform introductions to nine sites in New Zealand, Australia and the United States. We limited our analysis to introductions during the 19th century to minimize potential variation in transport modes and habitat quality changes, such as those due to increasing urbanization. We compared introduction success rates at three levels. First we included all passeriforms introduced to any of the sites in the three locations, then we compared the fates of just those species with a European origin and finally we compared success rates of just the 13 species released into all three locations. We found that the pattern of success or failure differed significantly across the three locations: Passeriforms introduced by acclimatization organizations to the United States were significantly more likely to fail than those introduced to New Zealand or Australia. Several species that succeeded in either New Zealand or Australia failed in the United States, even after the introduction of seemingly sufficient numbers

Linking complex forest fuel structure and fire behaviour at fine scales

Abstract. Improved fire management of savannas and open woodlands requires better understanding of the fundamental connection between fuel heterogeneity, variation in fire behaviour and the influence of fire variation on vegetation feedbacks. In this study, we introduce a novel approach to predicting fire behaviour at the submetre scale, including measurements of forest understorey fuels using ground-based LIDAR (light detection and ranging) coupled with infrared thermography for recording precise fire temperatures. We used ensemble classification and regression trees to examine the relationships between fuel characteristics and fire temperature dynamics. Fire behaviour was best predicted by characterising fuelbed heterogeneity and continuity across multiple plots of similar fire intensity, where impacts from plot-to-plot variation in fuel, fire and weather did not overwhelm the effects of fuels. The individual plot-level results revealed the significance of specific fuel types (e.g. bare soil, pine leaf litter) as well as the spatial configuration of fire. This was the first known study to link the importance of fuelbed continuity and the heterogeneity associated with fuel types to fire behaviour at metre to submetre scales and provides the next step in understanding the complex responses of vegetation to fire behaviour

Variability in the carbon isotopic composition of foliage carbon pools (soluble carbohydrates, waxes) and respiration fluxes in southeastern U.S. pine forests

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): G02009, doi:10.1029/2011JG001867.We measured the δ13C of assimilated carbon (foliage organic matter (δCOM), soluble carbohydrates (δCSC), and waxes (δCW)) and respiratory carbon (foliage (δCFR), soil (δCSR) and ecosystem 13CO2 (δCER)) for two years at adjacent ecosystems in the southeastern U.S.: a regenerated 32 m tall mature Pinus palustris forest, and a mid-rotation 13 m tall Pinus elliottii stand. Carbon pools and foliage respiration in P. palustris were isotopically enriched by 2‰ relative to P. elliottii. Despite this enrichment, mean δCER values of the two sites were nearly identical. No temporal trends were apparent in δCSC, δCFR, δCSR and δCER. In contrast, δCOM and δCW at both sites declined by approximately 2‰ over the study. This appears to reflect the adjustment in the δ13C of carbon storage reserves used for biosynthesis as the trees recovered from a severe drought prior to our study. Unexpectedly, the rate of δ13C decrease in the secondary C32–36 n-alkanoic acid wax molecular cluster was twice that observed for δCOM and the predominant C22–26 compound cluster, and provides new evidence for parallel but separate wax chain elongation systems utilizing different carbon precursor pools in these species. δCFR and δCER were consistently enriched relative to assimilated carbon but, in contrast to previous studies, showed limited variations in response to changes in vapor pressure deficit (D). This limited variability in respiratory fluxes and δCSC may be due to the shallow water table as well as the deep taproots of pines, which limit fluctuations in photosynthetic discrimination arising from changes in D.This work was supported by a NSF grants DEB-0343604, DEB-0344562 and DEB-0552202, and DOE grant DE-FC02-06ER64156/06-SC-NICCR-1063.2012-10-1

Is propagule size the critical factor in predicting introduction outcomes in passeriform birds?

Influential analyses of the propagule pressure hypothesis have been based on multiple bird species introduced to one region (e.g. New Zealand). These analyses implicitly assume that species-level and site-level characteristics are less important than the number of individuals released. In this study we compared records of passerine introductions with propagule size information across multiple regions (New Zealand, Australia, and North America). We excluded species introduced to just one of the three regions or with significant uncertainty in the historical record, as well as species that succeeded or failed in all regions. Because it is often impossible to attribute success to any single event or combination of events, our analysis compared randomly selected propagule sizes of unsuccessful introductions with those of successful introductions. Using Monte Carlo repeated sampling we found no statistical support for the propagule pressure hypothesis, even when using assumptions biased toward showing an effect

Simulation of a Biscayne Bay, Florida commercial sponge population: effects of harvesting after Hurricane Andrew

The hardbottom communities of Biscayne Bay, Florida include populations of several commercial sponge species. These sponges have been subjected to harvesting, a major hurricane, trawling damage, and other stressors during the past 10 years. We developed a size-based matrix population model of the dominant commercial sponge species ( Spongia graminea) as a tool to aid in assessing sponge population viability and potentially managing the sponge harvest. Repeated measurements of tagged sponges allowed estimation of growth, survival and fragmentation probabilities. Fecundity was estimated by solving for values of the reproductive size classes that matched the observed population growth when coupled with the observed transition probabilities. Three fecundity functions were applied to the sponge model: constant, a linear function of size class, and a function of sponge volume. All three models indicated a long-term decline in the sponge population ( λ<1), attributed to poor recruitment, and significant vulnerability to harvesting. The responses were similar when either 7 or 2 size classes were assumed to be reproductively functional, and when using different methods and different assumptions of size-class distributions to fit the fecundity values. Models fit with the assumption of an open population (recruitment from outside the population) and with fecundity values increased to achieve a λ of 1 were less sensitive to harvest, but did not match the observed population dynamics

A reassessment of the role of propagule pressure in influencing fates of passerine introductions to New Zealand

Several studies have argued that principal factor in determining the fate of bird introductions is introduction effort. In large part, these studies have emerged from analyses of historical records from a single place—New Zealand. Here we raise two concerns about these conclusions. First, we argue that although many bird species were introduced repeatedly to New Zealand, in many cases the introductions apparently occurred only after the species were already successfully naturalized. The inclusion of such seemingly superfluous introductions may exaggerate the importance of propagule pressure. And second, we question the reliability of the records themselves. In many cases these records are equivocal, as inconsistencies appear in separate studies of the same records. Our analysis indicates that species were successful not because they were introduced frequently and in high numbers, but rather it is likely that they were introduced frequently and in high numbers because the initial releases were successful

Propagule size and patterns of success in early introductions of Chukar Partridges (Alectoris chukar) to Nevada

ABSTRACT Background: In an effort to combine the well-known evolutionary phenomenon of increased extinction probability in small populations with invasion biology models, some studies have concluded that propagule size is the primary determinant of establishment success in introduced birds. Question: Is establishment success in Chukar Partridges (Alectoris chukar) introduced to the state of Nevada predicted by propagule size, by location of release, or by the source (game farm or wild-caught)? Methods: We compared propagule sizes of successful and unsuccessful introductions of Chukar Partridges in Nevada, using logistic regression. We included tests for possible differences across introduction sites (i.e. counties) and between birds that originated from game farms or were wild-caught. Findings: Propagule size was not a significant predictor of introduction success. Moreover, we found no significant differences across 17 sites, or between wild birds and those from game farms. Conclusions: It appears most likely that site-level factors such as the availability of habitat are more important to the success of introductions than is propagule size