Summary1. Predictions of the identities and ecological impacts of invasive alien species are critical for risk assessment, but presently we lack universal and standardized metrics that reliably predict the likelihood and degree of impact of such invaders (i.e. measurable changes in populations of affected species). This need is especially pressing for emerging and potential future invaders that have no invasion history. Such a metric would also ideally apply across diverse taxonomic and trophic groups. 2. We derive a new metric of invader ecological impact that blends: (i) the classic Functional Response (FR; consumer per capita effect) and Numerical Response (NR; consumer population response) approaches to determining consumer impact, that is, the Total Response (TR = FR 9 NR), with; (ii) the 'Parker-Lonsdale equation' for invader impact, where Impact = Range 9 Abundance 9 Effect (per capita effect), into; (iii) a new metric, Relative Impact Potential (RIP), where RIP = FR 9 Abundance. The RIP metric is an invader/native ratio, where values >1 predict that invader ecological impact will occur, and increasing values above 1 indicate increasing impact. In addition, the invader/invader RIP ratio allows comparisons of the ecological impacts of different invaders. 2017, 54, 1259-1267 doi: 10.1111/1365-2664.12849 3. Across a diverse range of trophic and taxonomic groups, including predators, herbivores, animals and plants (22 invader/native systems with 47 individual comparisons), high-impact invaders were significantly associated with higher FRs compared to native trophic analogues. However, the RIP metric substantially improves this association, with 100% predictive power of high-impact invaders. 4. Further, RIP scores were significantly and positively correlated with two independent ecological impact scores for invaders, allowing prediction of the degree of impact of invasive alien species with the RIP metric. Finally, invader/invader RIP scores were also successful in identifying and associating with higher impacting invasive alien species. 5. Synthesis and applications. The Relative Impact Potential metric combines the per capita effects of invaders with their abundances, relative to trophically analogous natives, and is successful in predicting the likelihood and degree of ecological impact caused by invasive alien species. As the metric constitutes readily measurable features of individuals, populations and species across abiotic and biotic context-dependencies, even emerging and potential future invasive alien species can be assessed. The Relative Impact Potential metric can be rapidly utilized by scientists and practitioners and could inform policy and management of invasive alien species across diverse taxonomic and trophic groups. Journal of Applied Ecology

The introduction and spread of non-native species is one of the least reversible human-induced global changes. In South Africa, non-native fish introductions have occurred over the last two and a half centuries. Resultant invasions have been cited as a primary threat to imperilled South African fishes and other aquatic fauna. Addressing a problem of this magnitude requires an organised approach. The aim of this paper is to summarise the current knowledge, risk and ecological impacts associated with non-native freshwater fish introductions in South Africa. A total of 55 fishes have been introduced into novel environments in South Africa. Of these, 27 were alien and 28 were extralimital introductions. Only 11 introduced species failed to establish and of the 44 species that have established, 37% are considered fully invasive. Introductions for angling were responsible for the highest proportion (55%) of fully invasive species with the remainder linked to inter-basin water transfers (15%), bio-control (15%), ornamental fish trade (10%) and aquaculture (5%). There was a general paucity of published literature on the introduction, establishment and spread of non-native fishes, and recent research has largely focused on impacts on native biota. While documented impacts spanned multiple levels of biological organisation, most papers focused on individual and population level impacts. Large taxonomic biases were also observed, and invasive impacts were estimated for less than 50% of fully invasive fishes. There is also an extensive knowledge gap on the impacts of associated parasites and diseases introduced with non-native fishes. These knowledge gaps constrain effective management of non-native fishes in South Africa and research at all invasion stages (introduction, establishment, spread and impact) is necessary to guide conservation practitioners and managers with information to manage current invasions and curb future introductions.

1. Mediterranean climate regions are globally recognized as hotspots of endemism in fishes; however, these unique assemblages are increasingly threatened by human mediated impacts including water abstraction, damming and non-native species introductions.2. The Cape Fold aquatic ecoregion (CFR) of South Africa supports an assemblage of range-restricted endemic freshwater fishes, the majority of which are conservation priorities because they are under severe threat of extinction. Effective conservation and management are constrained by the lack of readily available information on this imperilled group of fishes because research efforts over the last century have been temporally disjointed and relatively uncoordinated.3. This review provides an exhaustive appraisal of published literature on the taxonomy, biogeography, life history, ecology and physiology of freshwater fishes in the CFR, and the human impacts that affect them. Its aim is to direct future research needs for effective management and conservation of this imperilled group. 4. Only 103 peer-reviewed articles on CFR fishes were recorded and the majority of available research is on taxonomy and biogeography (40.8%), followed by ecological investigations (22.3%), conservation (19.4%) and human impacts (17.5%). 5.Despite a plethora of studies on taxonomy and biogeography, recent genetic evidence suggests that fish diversity in the CFR has been severely underestimated and requires urgent attention. Human impacts severely threaten the existence of many native CFR fishes and require further study. Information on the biology and ecology of CFR fishes is limited to studies on selected species; of particular note is the lack of physiological information which is particularly pertinent given projected climate change scenarios.

Summary Predator diversity alterations have been observed in most ecosystems as a result of the loss and/ or addition of species. This has implications for predator–prey dynamics as non‐trophic interactions among predators, so‐called multiple predator effects (MPE), are known to influence predation success. In addition, there is often a density‐dependent relationship between prey availability and prey consumption (functional response). While MPE investigations are common in the literature, functional responses have rarely been incorporated into this field of predation ecology. Here, we outline an experimental procedure that incorporates functional responses into multiple predator effect studies. Using three fish species with different functional traits as model predators (bluegill Lepomis macrochirus, southern mouthbrooder Pseudocrenilabrus philander and banded tilapia Tilapia sparrmanii), we assess intra‐ and interspecific predator interaction outcomes on predator–prey dynamics. This was done by contrasting observed functional responses of heterospecific and conspecific combinations of predators with expected responses based on those of individual predators. Multipredator combinations produced variable results. Bluegill were the only species in which observed conspecific multipredator functional responses matched those of expected based on individual performance (prey risk neutral effects). In contrast, prey risk reduction was observed for both mouthbrooder and tilapia conspecific multipredator trials. Heterospecific combinations revealed strong prey risk reduction effects for mouthbrooder–tilapia and bluegill–tilapia trials, while mouthbrooder–bluegill multipredator functional responses combined additively. These results are discussed within the context of behavioural traits of the species and the development of a trait‐based predictive framework. Using a functional response approach allowed for the assessment of multiple predator effects across a range of prey densities. We propose that the incorporation of within‐guild predator combinations into classic functional response investigations will enhance predictive capacity development in competition and predation ecology. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12682/suppinfo is available for this article.

The contribution of inland fisheries to food security, livelihood provision, poverty alleviation, and economic development in developing African countries is well documented, but there is surprisingly little literature on the history, current status and potential of South Africa's inland fishery resources. This presents a constraint to the management and sustainable development of inland fisheries. A literature review of peer-reviewed and grey literature was thus undertaken which is presented as a synthesis of knowledge on inland fisheries in South Africa. We track the chronology of literary themes on inland fisheries from the colonial era to the present, provide an overview of the recreational, subsistence and commercial sub-sectors, the production potential of inland waters, interventions to promote fishery development, and attempts to value inland fisheries. The review summarises the current state of knowledge on fisheries resources, outlines potential sources of data, highlights relevant and important information, and identifies knowledge gaps. The literature survey reveals an urgent need for research covering the biological, social, economic and governance aspects, if inland fisheries are to be developed in a rational and sustainable manner which promotes South Africa's national policy goals.

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ABSTRACT1. Traditionally headwater streams are surveyed using electrofishing, a potentially harmful sampling method. Increasingly scientists are seeking out the least destructive stream sampling methods, especially when sampling imperilled fishes. It is therefore imperative that the efficacy of alternative, non-destructive sampling methods be investigated.2. This study investigated the potential for using underwater video analysis (UWVA) as an alternative to electrofishing for assessing the diversity and relative abundance of imperilled fishes in clear, relatively shallow (<1.5 m) headwater streams.3. Detection rates using UWVA were higher than with electrofishing, relative abundance estimates between the two methods were significantly correlated, the attractive effect of the camera was negligible and UWVA was logistically feasible for sampling small headwater streams.4. These results have clear conservation implications as it was demonstrated that UWVA is a suitable sampling method for estimating relative abundance of fishes in small, clear headwater streams.

Southern Africa has a long history of non-native fish introductions for the enhancement of recreational and commercial fisheries, due to a perceived lack of suitable native species. This has resulted in some important inland fisheries being based on non-native fishes. Regionally, these introductions are predominantly not benign, and non-native fishes are considered one of the main threats to aquatic biodiversity because they affect native biota through predation, competition, habitat alteration, disease transfer and hybridization. To achieve national policy objectives of economic development, food security and poverty eradication, countries are increasingly looking towards inland fisheries as vehicles for development. As a result, conflicts have developed between economic and conservation objectives. In South Africa, as is the case for other invasive biota, the control and management of non-native fishes is included in the National Environmental Management: Biodiversity Act. Implementation measures include import and movement controls and, more recently, non-native fish eradication in conservation priority areas. Management actions are, however, complicated because many non-native fishes are important components in recreational and subsistence fisheries that contribute towards regional economies and food security. In other southern African countries, little attention has focussed on issues and management of non-native fishes, and this is cause for concern. This paper provides an overview of introductions, impacts and fisheries in southern Africa with emphasis on existing and evolving legislation, conflicts, implementation strategies and the sometimes innovative approaches that have been used to prioritize conservation areas and manage non-native fishes.