Weeds and Pests: eradicating the invasive threat
A 2003 position paper published by the World Wildlife Foundation Australia branch. [pdf 204.0 kb]
Total annual seed loss on a perennial legume through predation by insects: The importance of within-season seed and seed feeder dynamics
Determining total annual seed loss from seed predators is an important step in quantifying the role they have in modifying plant populations. Total seed loss is typically estimated with a single, well-timed survey. However, this overlooks the potential importance of within-season patterns of seed availability and insect activity, particularly where seed gain and loss are not synchronous and where insects are multivoltine. In Australia the introduced legume weed, Parkinsonia aculeata L. (Caesalpinaceae) is one such example. A replicated survey was conducted throughout a single cropping season in two contrasting habitats (uplands and wetland) to estimate total annual seed loss from seed predation and to test the relative importance of seed availability, seed feeder abundance, seed feeder behaviour and parasitism in determining total seed loss. Two seed feeders were present, the introduced biological control agent Penthobruchus germaini (Pic) (Bruchidae) and the moth, Mesophleps palpigera (Walsingham) (Gelechiidae). Seed availability patterns differed with habitat, with a greater proportion of seeds being available for longer in uplands, and resulted in total seed consumption by the beetle being twice as high in the uplands (5.2%) and no difference between habitats for the moth. Total seed loss from beetle predation was restricted by the egg parasitoid Uscana sp. (Trichogrammatidae), which was abundant throughout the season, and also by unexplained larval mortalities. This study highlights the potential importance of within-season interactions between plant, seed feeder, natural enemies and environment in determining total seed loss through predation. The possible population and evolutionary consequences of such interactions for both the plant and the seed feeder require further consideration. [pdf 330.4 kb]
Ecological restoration, cultural preferences and the negotiation of ‘nativeness’ in Australia
The paper addresses cultural assumptions about ‘nativeness’ and ‘belonging’ to place as they are implicated in notions of ‘ecological restoration’. Given the centrality of complex notions of ‘indigeneity’ to the issue of what ecological ‘restoration’ means in Australia, this is a rich area for cultural and historical analysis. Case materials illustrate the negotiated and ambiguous nature of Australian ideas about what ‘belongs’ ecologically and culturally across the broad continent of this relatively young post-Settler nation. We seek to foreground these issues through consideration of what ‘restoring’ nature might mean in the context of debates about native plants, the re-introduction of an iconic species of ground dwelling bird, the removal of cane toads that are demonised as highly ‘alien’, and the multiple ways in which the dingo is regarded ambiguously as both native and a ‘pest’ that needs to be controlled and culled. By showing how ‘restoration’ can be understood and mobilised in a variety of ways – in terms of the ‘re-naturing’, ‘re-valuing’ and/or ‘repatriating’ of indigenous species, as well as impassioned rejection of ‘exotics’ – we emphasise the importance of social science for building a well-grounded sense of how environmental management priorities and approaches are informed by a wider set of cultural assumptions. [pdf 314.8 kb]
Optimal eradication: when to stop looking for an invasive plant
The notion of being sure that you have completely eradicated an invasive species is
fanciful because of imperfect detection and persistent seed banks. Eradication is
commonly declared either on an ad hoc basis, on notions of seed bank longevity, or on
setting arbitrary thresholds of 1% or 5% confidence that the species is not present.
Rather than declaring eradication at some arbitrary level of confidence, we take an
economic approach in which we stop looking when the expected costs outweigh the
expected benefits. We develop theory that determines the number of years of absent
surveys required to minimize the net expected cost. Given detection of a species is
imperfect, the optimal stopping time is a trade-off between the cost of continued
surveying and the cost of escape and damage if eradication is declared too soon. A
simple rule of thumb compares well to the exact optimal solution using stochastic
dynamic programming. Application of the approach to the eradication programme of
Helenium amarum reveals that the actual stopping time was a precautionary one given the ranges for each parameter. [pdf 208.7 kb]
Understanding the Ghost of Cactoblastis Past: Historical Clarifications on a Poster Child of Classical Biological Control
The applied ecological discipline of classical biological control (CBC) has a long history, bolstered by some spectacular successes in the management of pest insect and plant species. A major poster child of CBC is the control of prickly pear (Opuntia spp.) in Australia by the moth Cactoblastis cactorum. In this article we investigate the idiosyncrasies of this CBC program and relate it to contemporary CBC, highlighting the intensive rearing and spatially extensive distribution effort critical to the rapid success of this project. We also emphasize the importance of the sociopolitical and economic context of the Opuntia CBC program and its role in its success. We use these historical clarifications to temper the expectations of equivalent successes in future CBC projects. Cactoblastis cactorum has recently invaded North America, and its threat to native cacti is of concern.We examine the global use of this moth as a biocontrol agent to clarify the nature of the hazard that it may pose as an invader in North
and Central America. [pdf 471.8 kb]
GRASS RESPONSE TO SHRUB REMOVAL IN TWO SEMI-ARID VEGETATION COMMUNITIES
The control of woody weeds in the mulga lands of south-west Queensland is commonly regarded as essential for restoration of degraded systems. However, these shrubs have become a dominant and stable component of many mulga land ecosystems, and their removal may have unknown ecosystem impacts. This paper reports an experiment to determine the effect of woody weeds and grazing pressure on grass recruitment, cover and diversity in two vegetation communities in Queensland's mulga lands. Both factors influence grass recruitment, cover and diversity, but the response differs between the two vegetation communities investigated. The overall grass cover is consistently greater in sites where woody weeds were removed, and where grazing pressure was lowest. However, in the Dunefields community the cover and frequency of grass plants responded more to the removal of woody weeds than in the Mulga Sandplain community. In contrast, in the Mulga Sandplain community the grasses responded more to reducing or removing grazing pressure. Results suggest that subtle differences between systems influence grass dynamics, highlighting the need for community-specific research and management. [pdf 1.5 Mb]
THE IMPACT OF BIOLOGICAL CONTROL ON THE DEVELOPMENT OF THE PACIFIC
The roots of development of any country are complex and many-sided. It is ambitious
to attempt to assess the role of our small discipline in the development of the Pacific. Yet, benefits from biological control in this region have been substantial and reflected as economic and cultural improvements for several programs. Impacts are seen most clearly during periods of early development, when agriculture was a major component of a region's economy. Hence, we focus on the very early or broadly significant programs. Early programs axe centered in Hawaii, Australia, California, Fiji, Mexico and Peru; other examples involved various Pacific countries or islands. Australia has benefitted most, as a result of the successful control of prickly pear
and other weeds, rabbits and other pests in vast agricultural areas. California continued her threatened development, when control of the cottony cushion scale and St. Johnswort was achieved. Similarly Hawaii (sugarcane), Fiji (coconut and pastures), Peru (cotton), Mexico (citrus), and New Zealand (forests) have all seen their economies boosted when biological control of pests of the commodities indicated and others, was successfully achieved. [pdf 810.0 kb]
