Summary 1.With continued globalization, species are being transported and introduced into novel habitats at an accelerating rate. Interactions between invasive species may provide important mechanisms that moderate their impacts on native species. 2. The European green crab Carcinus maenas is an aggressive predator that was introduced to the east coast of North America in the mid-1800s and is capable of rapid consumption of bivalve prey. A newer invasive predator, the Asian shore crab Hemigrapsus sanguineus , was first discovered on the Atlantic coast in the 1980s, and now inhabits many of the same regions as C. maenas within the Gulf of Maine. Using a series of field and laboratory investigations, we examined the consequences of interactions between these predators. 3. Density patterns of these two species at different spatial scales are consistent with negative interactions. As a result of these interactions, C. maenas alters its diet to consume fewer mussels, its preferred prey, in the presence of H. sanguineus . Decreased mussel consumption in turn leads to lower growth rates for C. maenas , with potential detrimental effects on C. maenas populations. 4. Rather than an invasional meltdown, this study demonstrates that, within the Gulf of Maine, this new invasive predator can moderate the impacts of the older invasive predator.

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Cascading effects of high trophic levels onto lower trophic levels have been documented in many ecosystems. Some studies also show evidence of extended trophic cascades, in which guilds dependent on lower trophic levels, but uninvolved in the trophic cascade themselves, are affected by the trophic cascade due to their dependence on lower trophic levels. Top-down effects of large mammals on plants could lead to a variety of extended trophic cascades on the many guilds dependent on plants, such as pollinators. In this study, floral-visitor and floral abundances and assemblages were quantified within a series of 1-ha manipulations of large-mammalian herbivore density in an African savanna. Top-down effects of large mammals on the composition of flowers available for floral visitors are first shown, using regressions of herbivore activity on metrics of floral and floral-visitor assemblages. An extended trophic cascade is also shown: the floral assemblage further altered the assemblage of floral visitors, according to a variety of approaches, including a structural equation modelling approach (model with an extended trophic cascade was supported over a model without, AICc weight = 0.984). Our study provides support for extended trophic cascades affecting floral visitors, suggesting that trophic cascades can have impacts throughout entire communities.

Three new species of the Afrotropical braconine wasp genus Bacuma are described, and biological observations (nectar feeding) by one of them are noted. The new species are: B. kayserae Quicke & Butcher sp. nov. from Kenya, B. madiensis Quicke & Butcher sp. nov. from Uganda and B. darfurensis Quicke & Butcher sp. nov. from Sudan. A group of four large nominal species with red metasomas and finely sculptured tergites (B. granulatus, B. maculipennis, B. rufa and B. whitei) may represent a single widespread species or a pair of species separated by mesoscutum colour, or four separate but morphologically very similar species. However, given the small number of specimens available for study and the poor condition of some of these, including the types, they are not formally synonymised here. A partial key to the species of Bacuma is presented, which recognizes those species that are clearly distinct, including three new species. Interactive Lucid dichotomous and matrix keys are available on www.waspweb.org.

Coastal environments, not directly transformed by urbanisation but within an urban matrix, can be transformed by changes in climate, invasive species and plantings. We assess changes in vegetation structure since European settlement and changes in native species abundance since 2003 on the cuspate dune complex at Lower Sandy Bay, Tasmania. The pre-European vegetation of the cuspate forehead seems likely to have been grassland dominated by Spinifex sericeus and Austrofestuca littoralis on the foredunes and Eucalyptus viminalis open-forest with a shrubby to grassy understorey on the older dunes. Some trees of E. viminalis still occur on the dune system, together with many elements of the original understorey. The foredune native vegetation had been replaced by Ammophila arenaria closed-grassland by 2003. Much of this grassland was invaded by the native shrub, Acacia longifolia, by 2017. Between 2003 and 2017 almost all native shrub species increased in abundance. Succulent, grass and herb species suffered decline. Increased competition with exotic species, changes in disturbance regimes and decreases in fire frequency in the coastal area are most likely to have influenced the changes in native species distributions.