Keywords: Invasive species Ecosystem function Insect pests Invasive plants Ecological restoration Biological control Natural ecosystems a b s t r a c tOf the 70 cases of classical biological control for the protection of nature found in our review, there were fewer projects against insect targets (21) than against invasive plants (49), in part, because many insect biological control projects were carried out against agricultural pests, while nearly all projects against plants targeted invasive plants in natural ecosystems. Of 21 insect projects, 81% (17) provided benefits to protection of biodiversity, while 48% (10) protected products harvested from natural systems, and 5% (1) preserved ecosystem services, with many projects contributing to more than one goal. In contrast, of the 49 projects against invasive plants, 98% (48) provided benefits to protection of biodiversity, while 47% (23) protected products, and 25% (12) preserved ecosystem services, again with many projects contributing to several goals. We classified projects into complete control (pest generally no longer important), partial control (control in some areas but not others), and ''in progress," for projects in development for which outcomes do not yet exist. For insects, of the 21 projects discussed, 62% (13) achieved complete control of the target pest, 19% (4) provided partial control, and 43% (9) are still in progress. By comparison, of the 49 invasive plant projects considered, 27% (13) achieved complete control, while 33% (16) provided partial control, and 49% (24) are still in progress. For both categories of pests, some projects' success ratings were scored twice when results varied by region. We found approximately twice as many projects directed against invasive plants than insects and that protection of biodiversity was the most frequent benefit of both insect and plant projects. Ecosystem service protection was provided in the fewest cases by either insect or plant biological control agents, but was more likely to be provided by projects directed against invasive plants, likely because of the strong effects plants exert on landscapes. Rates of complete success appeared to be higher for insect than plant targets (62% vs 27%), perhaps because most often herbivores gradually weaken, rather than outright kill, their hosts, which is not the case for natural enemies directed against pest insects. For both insect and plant biological control, nearly half of all projects reviewed were listed as currently in progress, suggesting that the use of biological control for the protection of wildlands is currently very active.

We explored the spatial structure of seed size variation and tested whether seed size differed between native and exotic populations in two invasive species. Seed of Cytisus scoparius (Scotch broom) is significantly heavier in its exotic range, whereas seed of Ulex europaeus (European gorse) is no different between ranges. This result suggests that seed size in C. scoparius is either adaptively or phenotypically responsive to conditions in its exotic range or that plants with large seeds were preferentially introduced. We found that modern ornamental broom seed was no bigger than seed from natural or naturalized populations, suggesting that large seed size in the exotic range is not due to preferential introduction of ornamental varieties with large seeds. Most previous studies of trait differences between native and exotic ranges in invasive species have not taken variation throughout the ranges into account. This is the most comprehensive survey of seed size variation in any species, and the first time that variation in a trait of an invasive species has been studied from individual plant level up to global ranges. Demographic rates can be affected by seed attributes making this study an important first step in understanding how population processes may differ between native and exotic ranges.

Gorse (Ulex europaeus L.) has become naturalized in at least 50 countries outside its native range, from the high elevation tropics to the subantarctic islands and Scandinavia. Its habit, adaptability and ability to colonize disturbed ground makes it one of the world's most invasive temperate weeds. It is 80 years since New Zealand first initiated research into biological control for gorse. This paper briefly reviews the progress made worldwide since then, and examines future opportunities for biological control of this weed. The range of available agents is now known, and this list is critically assessed. Ten organisms have been released variously in six countries and islands and their performance is reviewed. In most cases, agent populations have been regulated either from 'top-down' or 'bottomup', and there is no evidence anywhere of consistent outbreaks that could cause significant reduction in existing gorse populations in the medium term. Habitat disturbance and seedling competition are important drivers of gorse population dynamics. Existing agents may yet have long-term impact through sublethal effects on maximum plant age, another key factor in gorse population dynamics. Along with habitat manipulation, seed-feeding insects may yet play a long-term role in reducing seed banks below critical levels for replacement in some populations. In the short term, progress will rely on rational and integrated weed management practices, exploiting biological control where possible.

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