Interactive effects of land use, temperature, and predators determine native and invasive mosquito distributions

1. Land-use and climate change could alter the distribution of both native and exotic mosquitoes by changing abiotic and biotic characteristics of freshwater habitats. We initially studied the influence of land use on standing water habitats, and the subsequent effects on native and exotic mosquito and mosquito-predator presence. 2. Associated with abiotic habitat characteristics, mosquito predator richness was highest in aquatic habitats of natural land uses (forest and grassland), and lowest in human-modified land uses (pastoral and urban), and the opposite relationship was true for mosquito presence. 3. Based on the outcome of the field survey we investigated the potential effects of climate-induced habitat warming and drying on interactions between invasive Aedes notoscriptus and native Culex pervigilans mosquitoes and native invertebrate predators affected by the land-use gradient. 4. Predator presence, which is directly affected by both climate and land-use change, influenced both mosquito survivorship and behaviour. We found predation rates increased with temperature, but the magnitude of changes depended on both predator and prey identity. In general, higher temperatures increased mosquito pupation rates, but also made mosquitoes more susceptible to predation. Although invasive Ae. notoscriptus were more susceptible to predation, increased temperature resulted in shorter life cycles, thereby reducing the net effect of increased predation caused by higher temperatures. 5. Overall, our results suggest interactions between temperature, land use and predator identity will be important in determining mosquito distributions, and will likely differ between mosquito species. Such interactions and species-specific responses will be particularly important if environmental changes facilitate range expansion of invasive mosquito species that vector disease

Biological Invasions and Ecological Restoration in South Africa

This chapter provides an overview of the researchers and research initiatives relevant to invasion science in South Africa over the past 130 years, profiling some of the more recent personalities, particularly those who are today regarded as international leaders in the field. A number of key points arise from this review. Since 1913, South Africa has been one of a few countries that have investigated and implemented alien plant biological control on a large scale, and is regarded as a leader in this field. South Africa was also prominent in the conceptualisation and execution of the international SCOPE project on the ecology of biological invasions in the 1980s, during which South African scientists established themselves as valuable contributors to the field. The development of invasion science benefitted from a deliberate strategy to promote multi-organisational, interdisciplinary research in the 1980s. Since 1995, the Working for Water programme has provided funding for research and a host of practical questions that required research solutions. Finally, the establishment of a national centre of excellence with a focus on biological invasions has made a considerable contribution to building human capacity in the field, resulting in advances in all aspects of invasion science—primarily in terms of biology and ecology, but also in history, sociology, economics and management. South Africa has punched well above its weight in developing the field of invasion science, possibly because of the remarkable biodiversity that provided a rich template on which to carry out research, and a small, well-connected research community that was encouraged to operate in a collaborative manner

Phragmites australis: How do genotypes of different phylogeographic origins differ from their invasive genotypes in growth, nitrogen allocation and gas exchange?

It has been suggested that in plant invasions, species may develop intrinsically higher gas exchange and growth rates, and greater nitrogen uptake and allocation to shoots, in their invasive range than in their native habitat under excess nutrients. In this study, native populations of two old world Phragmitesaustralis phylogeographic groups (EU and MED) were compared with their invasive populations in North America [NAint (M) and NAint (Delta)] under unlimited nutrient availability and identical environmental conditions in a common garden. We expected that both introduced groups would have higher growth, nitrogen uptake and allocation, and gas exchange rates than their native groups, but that these enhanced traits would have evolved in different ways in the two introduced ranges, because of different evolutionary histories. Biomass, leaf area, leaf nitrogen concentrations (NH4+ and NO3−) and transpiration rates increased in introduced versus native groups, whereas differences in SLA, leaf pigment concentrations and assimilation rates were due to phylogeographic origins. Despite intrinsic differences in the allocation of C and N in leaves, shoots and rhizome due to phylogeographic origin, the introduced groups invested more biomass in above-ground tissues than roots and rhizomes. Our results support the concept that invasive populations develop enhanced morphological, physiological and biomass traits in their new ranges that may assist their competiveness under nutrient-enriched conditions, however the ecophysiological processes leading to these changes can be different and depend on the evolutionary history of the genotypes

Regional differences in the abundance of native, introduced, and hybrid Typha spp. in northeastern North America influence wetland invasions

In northeastern North America, an important wetland invader is the cattail Typha × glauca, a hybrid of native Typha latifolia and introduced Typha angustifolia. Although intensively studied in localized wetlands around the Great Lakes, the distributions of the hybrid and its parental species across broad spatial scales are poorly known. We obtained genotypes from plants collected from 61 sites spanning two geographical regions. The first region, near the Great Lakes and St. Lawrence Seaway (GLSL), has experienced substantial Typha increases over the last century, whereas more modest increases have occurred in the second region across Nova Scotia, New Brunswick, and Maine (NSNB). We found that hybrids predominate in the GLSL region, thriving in both disturbed and undisturbed habitats, and are expanding at the expense of both parental species. In contrast, the native T. latifolia is by far the most common of the three taxa across all habitat types in the NSNB region. We found no evidence that the formation of backcrossed and advanced-generation hybrids is limited by the reproductive barriers that are evident in F1 hybrids. However, although backcrossed individuals arise in both regions, they are much less common than F1 hybrids, which may explain why the parental species boundary remains. We conclude that F1 hybrids are playing a key role in the invasion of wetlands in the GLSL region, whereas their low frequency in the NSNB region may explain why Typha appears to be much less invasive further east. An improved understanding of these contrasting patterns of distribution is necessary before we can accurately predict future wetland invasions