Conceptual Frameworks and Methods for Advancing Invasion Ecology

Invasion ecology has much advanced since its early beginnings. Nevertheless, explanation, prediction, and management of biological invasions remain difficult. We argue that progress in invasion research can be accelerated by, first, pointing out difficulties this field is currently facing and, second, looking for measures to overcome them. We see basic and applied research in invasion ecology confronted with difficulties arising from (A) societal issues, e.g., disparate perceptions of invasive species; (B) the peculiarity of the invasion process, e.g., its complexity and context dependency; and (C) the scientific methodology, e.g., imprecise hypotheses. To overcome these difficulties, we propose three key measures: (1) a checklist for definitions to encourage explicit definitions; (2) implementation of a hierarchy of hypotheses (HoH), where general hypotheses branch into specific and precisely testable hypotheses; and (3) platforms for improved communication. These measures may significantly increase conceptual clarity and enhance communication, thus advancing invasion ecology

Predicting dispersal and recruitment of Miconia calvescens (Melastomataceae) in Australian tropical rainforests

Miconia calvescens (Melastomataceae) is a serious invader in the tropical Pacific, including the Hawaiian and Tahitian Islands, and currently poses a major threat to native biodiversity in the Wet Tropics of Australia. The species is fleshy-fruited, small-seeded and shade tolerant, and thus has the potential to be dispersed widely and recruit in relatively intact rainforest habitats, displacing native species. Understanding and predicting the rate of spread is critical for the design and implementation of effective management actions. We used an individual-based model incorporating a dispersal function derived from dispersal curves for similar berry-fruited native species, and life-history parameters of fecundity and mortality to predict the spatial structure of a Miconia population after a 30 year time period. We compared the modelled population spatial structure to that of an actual infestation in the rainforests of north Queensland. Our goal was to assess how well the model predicts actual dispersion and to identify potential barriers and conduits to seed movement and seedling establishment. The model overpredicts overall population size and the spatial extent of the actual infestation, predicting individuals to occur at a maximum 1,750 m from the source compared with the maximum distance of any detected individual in the actual infestation of 1,191 m. We identify several characteristic features of managed invasive populations that make comparisons between modelled outcomes and actual infestations difficult. Our results suggest that the model’s ability to predict both spatial structure and spread of the population will be improved by incorporating a spatially explicit element, with dispersal and recruitment probabilities that reflect the relative suitability of different parts of the landscape for these processes

Understanding and managing the introduction pathways of alien taxa: South Africa as a case study

For the effective prevention of biological invasions, the pathways responsible for introductions must be understood and managed. However introduction pathways, particularly for developing nations, have been understudied. Using the Hulme et al. (2008) pathway classification, we assessed the South African introduction pathways in terms of the number of introductions, the invasion success of introduced taxa, how the pathways have changed over time, and how these factors vary for vertebrates, invertebrates and plants. Pathway and date of introduction, region of origin, distribution and invasion status data for 2111 alien taxa were extracted from databases. Most alien and invasive taxa were deliberately introduced and subsequently escaped captivity or cultivation. Pathway prominence also varied temporally and across organism types. Vertebrates and plants were largely escapes and although most plant escapes have become invasive, this is not the case for vertebrates. However the number of new plant and vertebrate escapes has increased over time. Invertebrates have been deliberately released or unintentionally introduced as contaminants or stowaways. For invertebrates the number of release, contaminant and stowaway introductions has increased, and most contaminants and stowaways have become invasive. As effective screening procedures are in place for invertebrates released for biological control, the major threats for South Africa are from vertebrate and plant escapes and invertebrate contaminants and stowaways. We recommend improvements to risk assessment and education to prevent escapes, and prioritised inspection strategies to reduce stowaway and contaminant introductions. Finally, as introduction pathways and introduced taxa change temporally, biosecurity decisions need to be informed by information on current and future pathways.South African National Department of Environment Affairs through its funding of the South African National Biodiversity Institute‟s Invasive Species Programme. Additional funding was provided by the DST-NRF Centre for Invasion Biology, the South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation of South Africa.http://link.springer.com/journal/105302017-01-30hb201

Population collapses in introduced non-indigenous crayfish

Invasive species often have instable population dynamics and are known to collapse or oscillate heavily after passing through the initial lag/growth phases. Long-term data-series documenting these fluctuations are however rare. We use long-term (starting in the early 1960s), semi-quantitative data on the invasive signal crayfish (Pacifastacus leniusculus), capturing its population development after introduction in 44 Swedish lakes. In total 18 (41 %) of these populations had experienced a collapse. A stepwise discriminant function analysis including 20 different ecological or physicochemical characteristics identified three variables explaining collapses in the following order: stocking year, population age and mean air temperature. Populations stocked in the 1980s were more likely to collapse than populations stocked in the 1970s. Lakes with collapses were located in areas with 0.4 A degrees C higher yearly mean air temperatures than the still viable populations. Collapses also depended on the time phase of the population and started to occur 12 years after stocking and were most frequent in the interval 16-20 years after stocking and after 11-15 years duration of the established phase with harvestable densities. An analysis of prevalence and pathogen load of Aphanomyces astaci was conducted in eight of the studied populations. A. astaci was present in all populations but neither the level of prevalence nor the pathogen load in infested specimens differed significantly between lakes with collapses and lakes without. Our results highlight the potential sensitivity and instability of introduced crayfish. The importance of density-dependence and temperature suggest that both climate variability and/or fisheries can influence these processes