Aim Reproductive traits are important mediators of establishment and spread of introduced species, both directly and through interactions with other life-history traits and extrinsic factors. We identify features of the reproductive biology of Australian acacias associated with invasiveness.Location Global.Methods We reviewed the pollination biology, seed biology and alternative modes of reproduction of Australian acacias using primary literature, online searches and unpublished data. We used comparative analyses incorporating an Acacia phylogeny to test for associations between invasiveness and eight reproductive traits in a group of introduced and invasive (23) and non-invasive (129) species. We also explore the distribution of groups of trait 'syndromes' between invasive and non-invasive species.Results Reproductive trait data were only available for 126 of 152 introduced species in our data set, representing 23/23 invasive and 103/129 non-invasive species. These data suggest that invasives reach reproductive maturity earlier (10/ 13 within 2 years vs. 7/26 for non-invasives) and are more commonly able to resprout (11/21 vs. 13/54), although only time to reproductive maturity was significant when phylogenetic relationships were controlled for. Our qualitative survey of the literature suggests that invasive species in general tend to have generalist pollination systems, prolific seed production, efficient seed dispersal and the accumulation of large and persistent seed banks that often have fire-, heat-or disturbance-triggered germination cues.Conclusions Invasive species respond quicker to disturbance than non-invasive taxa. Traits found to be significant in our study require more in-depth analysis involving data for a broader array of species given how little is known of the reproductive biology of so many taxa in this species-rich genus. Sets of reproductive traits characteristic of invasive species and a general ability to reproduce effectively in new locations are widespread in Australian acacias. Unless there is substantial evidence to the contrary, care should be taken with all introductions.

Hybrid elements containing optical power with both diffractive (holographic) and refractive components are shown to be useful for obtaining arbitrary or, in special cases, achromatic dispersive characteristics. In one configuration a volume holographic element is coated on the surface of a crown glass lens, and by varying the power distributions among the refractive and holographic components while maintaining constant overall optical power the effective Abbe V numbers of the resultant hybrid element are shown to span all real numbers excepting a narrow interval around zero. In the achromat case (V number = infinity), both refractive and diffractive components are of the same sign resulting in much smaller glass curvatures than in all-refractive achromat doublets or apochromat triplets. The large separation between holographic partial dispersions and available glass partial dispersions is shown to lead to hybrid three-color achromats with greatly reduced glass curvatures. Applications are expected to include broadband achromatic objectives and chromatic aberration corrector plates in high performance optical systems. Such corrector plates may have any net power (including zero) while exhibiting effective V numbers that are positive or negative and that span a wide range, e.g., +/-1 or +/-1000. Further advantages include reducing the need for choosing high dispersion glasses, which may be costly and difficult to grind or polish. High diffraction efficiency and broad spectral bandwidths (in excess of 3000 A) are obtained in the holographic optical elements using single-element central-stop and cascaded element designs.

Transmission functions are derived that are valid in the nonparaxial case for a class of lenses that will image a continuum of points along an optical axis to a single image point. This lens, which we call a logarithmic asphere, is then used in a digital camera. The resolution of the camera is limited by the pixel size of the CCD; i.e., it is not diffraction limited. Digital processing is used to recover the image, and image-plane processing is used for speed. We find a tenfold increase in the depth of field over that for the diffraction-limited case.

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