Exotic vascular plant invasiveness and forest invasibility in urban boreal forest types

The riverine forests of the northern city of Edmonton, Alberta, Canada display strong resilience to disturbance and are similar in species composition to southern boreal mixedwood forest types. This study addressed questions such as, how easily do exotic species become established in urban boreal forests (species invasiveness) and do urban boreal forest structural characteristics such as, native species richness, abundance, and vertical vegetation layers, confer resistance to exotic species establishment and spread (community invasibility)? Eighty-four forest stands were sampled and species composition and mean percent cover analyzed using ordination methods. Results showed that exotic tree/shrub types were of the most concern for invasion to urban boreal forests and that exotic species type, native habitat and propagule supply may be good indicators of invasive potential. Native forest structure appeared to confer a level of resistance to exotic species and medium to high disturbance intensity was associated with exotic species growth and spread without a corresponding loss in native species richness. Results provided large-scale evidence that diverse communities are less vulnerable to exotic species invasion, and that intermediate disturbance intensity supports species coexistence. From a management perspective, the retention of native species and native forest structure in urban forests is favored to minimize the impact of exotic species introductions, protect natural succession patterns, and minimize the spread of exotic species.     

Host Plant and Biotype Density Interactions – Their Role in the Establishment of the Invasive B Biotype of Bemisia tabaci

Bemisia tabaciis a complex of closely related genetic types of whiteflies, few of which are invasive. One of these, B biotype, has proven to be particularly adapted to invading new areas, but the underlying reasons as to why it has a well-developed capacity to invade is not known. To develop an understanding of factors that may be contributing to B’s invasive capacity, inter-biotype mating interactions and host plant suitability for the exotic B (B. tabaci Mediterranean/Asia Minor/Africa) and the indigenous Australian (AN) biotype (B. tabaci Australia) were examined. The results suggest that when confined to a mutually acceptable host, B cannot establish when the ratio of AN : B exceeds 20 : 1. However, when simultaneously provided with a host that only it prefers, B is able to establish even at 50 : 1 (AN : B). Further, when both biotypes occur together the number of progeny per female increases (relative to the number produced when only one biotype is present). The response is observed for both biotypes, but is considerably greater in the case of B. In addition, B performs better in the presence of the AN biotype B. tabaci Australia while AN perform worse in coexistence with B, but only if the demographics allow B to mate without significant interference. This leads to the prediction that B will invade in circumstances where its unique hosts are of sufficient number to escape the full negative impact of inter-biotype mating interactions and reduced competitiveness in terms of reproductive rate, while exposing the indigenous biotype to the full effects of the interaction.     

Role of exotic tree stands on the current distribution and social behaviour of Swainson's hawk, Buteo swainsoni in the Argentine Pampas

Aim The Argentine Pampas was extensively and abruptly altered by European colonization. Between 1880 and 1885 the indigenous human inhabitants were completely displaced, and native grasslands were replaced by exotic pasture plants and crops. One of the most important ecological changes in the Pampas landscape, the introduction of tall exotic tree species, has received little attention, and its effect on wildlife has never been assessed. We have made an intensive survey of habitat use of Swainson's hawk, Buteo swainsoni in its most important non‐breeding quarters, the Pampas of Argentina, aiming to characterize the sites used by hawks for communal roosting. Location Pampas grasslands, Argentina. Methods We surveyed 30,000 km of roads by car during the austral summer from 2001 to 2004, covering the main non‐breeding area occupied by Swainson's hawks. Their roost sites were located by direct observation of birds roosting in tree stands close to the roads, by surveying potential roost sites around places where groups of pre‐ and post‐roosting hawks were recorded, and by gathering information from local farmers. Results Swainson's hawks exclusively used stands of exotic tree species for roosting. Eucalyptus viminalis was present in all 34 roosts surveyed, and in 59% of them it was the only species present. The remaining exotic tree species were the Siberian elm, Ulmus pumila, pines (Pinus spp.) and cypress (Cupressus spp.). Flock sizes at roost sites were unusually high for a raptor, with an average of 658 individuals (range 8–5000 hawks, n = 27 flocks). Main conclusions The introduction of exotic trees may have resulted in the expansion of the suitable habitat for Swainson's hawks, permitting a recent colonization of the Argentine Pampas. Tree stands may have also changed the communal roosting behaviour of this raptor, by virtue of their providing new structural elements in a region that almost completely lacked trees prior to European occupation.     

Pollen germination and pollen tube growth in Fraxinus pennsylvanica

With regard to adaptation of green ash (Fraxinus pennsylvanica Marshall) to ecological conditions in Croatia, pollen germination and pollen tube length after 2, 4 and 6 hours were examined in vitro at 10, 15, 20 and 25°C during two years 2001 and 2002. Narrow leaved ash (F. angustifolia Vahl) pollen served as a control in 2002. The year, time and temperature, and the interaction between time and temperature were significant for both germination percentage and pollen tube length. Interactions year × temperature and year × time were significant for pollen tube length only. The highest germination percentage (17.86% in 2001 and 19.40% in 2002) of green ash pollen was at 15°C after 6 hours. The pollen tube length was greatest at 20°C (393.46 μm) in 2001 and 25°C (899.50 μm) in 2002 after 6 hours. Narrow leaved ash pollen had the highest germination percentage (19.22%) at 20°C after 6 hours and was significantly reduced at 25°C. The pollen tube length was greatest at 25°C (518.90 μm) after 6 hours. It can be concluded that green ash pollen has satisfactory germination in ecological conditions in Croatia and that the optimum temperature for pollen germination is higher than 20°C.     

Species specificity of barnacle settlement-inducing proteins

We previously isolated a larval settlement-inducing protein complex (SIPC) from adult extracts of the barnacle, Balanus amphitrite using a nitrocellulose membrane settlement assay. In the present study, we found that the extracts of other adult barnacles, Megabalanus rosa and Balanus eburneus, also induced the settlement of B. amphitrite cyprids although the inductive activity was slightly lower than that of conspecific extracts. Furthermore, we examined reactivity to anti-SIPC antibody in adult extracts from six species of Japanese barnacles other than B. amphitrite, brine shrimp and eight marine sessile organisms besides barnacles. The results showed that all barnacles examined contained SIPC-like proteins with slightly different molecular weight, while the other animals did not react to the antibody by immunoblot analysis. These findings suggest that species specificity in settlement-inducing proteins of barnacles is not so strict, but these proteins are characteristic to barnacle species.     

Sexing of mid‐incubation avian embryos as a management tool for zoological breeding programs

Skewed sex ratios in zoo breeding programs may require housing single birds of an overrepresented gender, increasing demands on limited resources that could otherwise be diverted to breeding pairs or other important species. The ability to selectively incubate and hatch eggs of a desired sex represents a significant improvement in the long‐term management of avian species. This study describes a successful method for in ovo sexing of embryos from stage 30 through 42 of incubation (Hamburger and Hamilton [1951] J Morphol 88:49–92). A 0.01–1 µl blood sample was collected from either the vitelline vessel (VV) or the blood vessels of the chorio–allantoic membrane (CAM) of embryos at stages 14–18 or 30–42, respectively. DNA was isolated from whole blood using the Chelex method (Walsh et al. [1991] Biotechniques 10:506–513; Jensen et al., [2003] Zoo Biol 22:561–571). Sex was determined by PCR amplification using the previously described P2/P8 (Griffiths et al. [1998] Mol Ecol 7:1071–1075) and 1237L/1272H (Kahn et al. [1998] Auk 115:1074–1078) primers or by commercial vendor. Success rate was calculated as the percent of sampled embryos surviving to hatch. Embryos of the undesired sex were not incubated, thus not included in the calculation. There was a considerable difference in success rate when blood was collected from the stage 14–18 VV (0–25%, average 12%) vs. stage 30–42 CAM (33–100%, average 76%). In conclusion, in ovo sexing of embryos between stages 30 and 42 yields acceptable embryo survival rates while providing enough blood for genetic testing. Zoo Biol 31:694‐704, 2012. © 2011 Wiley Periodicals, Inc.     

Using space‐for‐time substitution and time sequence approaches in invasion ecology

1. Invasion biologists use two main approaches to evaluate the effects of non‐native species (NNS) on diversity of native species (DNS), namely space‐for‐time and time approaches. These approaches have pitfalls related to lack of controls: the former lacks pre‐invasion data, while the latter often lacks data from non‐invaded sites. 2. We propose a framework that combines space‐for‐time and time approaches and which should result in more focused mechanistic hypotheses and experiments to test the causes of invasibility and the effects of NNS on DNS. We illustrate the usefulness of our framework using two case studies: one with the submersed macrophyte, Hydrilla verticillata, in reservoir and the other with the fish, Geophagus proximus, in a large river–floodplain system. 3. Hydrilla verticillata invaded sites with DNS similar to that found in non‐invaded sites, indicating that biotic and/or abiotic factors did not influence invasion success; however, DNS increased over time in invaded sites compared with non‐invaded sites, suggesting that H. verticillata facilitated natives. In contrast, G. proximus invaded sites with higher DNS than non‐invaded sites, suggesting that biotic and/or abiotic factors favouring natives were important for invasion success, but DNS increased in invaded and non‐invaded sites over time, indicating that an independent factor contributed to DNS increases. 4. Conclusions from both studies would have been inaccurate or incomplete if the space‐for‐time and time approaches had not been used in combination as proposed in our framework.