Environmental niche patterns of native and non‐native fishes within an invaded African river system

Abstract

To test ecological niche theory, this study investigated the spatial patterns and the environmental niches of native and non-native fishes within the invaded Great Fish River system, South Africa. For the native fishes, there were contrasting environmental niche breadths that varied from being small to being large and overlapped for most species, except minnows that were restricted to headwater tributaries. In addition, there was high niche overlap in habitat association among fishes with similar distribution. It was therefore inferred that habitat filtering-driven spatial organisation was important in explaining native species distribution patterns. In comparison, most non-native fishes were found to have broad environmental niches and these fishes showed high tolerance to environmental conditions, which generally supported the niche opportunity hypothesis. The proliferation of multiple non-native fishes in the mainstem section suggest that they form a functional assemblage that is probably facilitated by the anthropogenic modification of flow regimes through inter-basin water transfer. Based on the distribution patterns observed in the study, it was inferred that there was a likelihood of negative interactions between native and nonnative fishes. Such effects are likely to be exacerbated by altered flow regime that was likely to have negative implications for native ichthyofauna. K E Y W O R D S distribution patterns, environmental niche, invasions, native fishes, niche segregation, spatial organisation

Functional diversity does not explain the co‐occurrence of non‐native species within a flow‐modified African river system

“…Consistent with previous research and studies elsewhere (e.g. Kadye & Booth, 2020;Schmidt et al, 2019), it is likely that the anthropogenic modification of this river system, particularly through altered flow, may have resulted in a functional assemblage that has acclimatized to these conditions. This assemblage appears to largely reflect ichthyofauna groups with shared functional traits in different invaded sections, including the tributaries where non-native T. sparrmanii co-occurs with native species and the upper and lower mainstem sections where most non-native species co-occur with native species.…”

“…This is because, in addition to altering the physico‐chemical conditions of the recipient ecosystems, mainly through changing their natural flow regime, IBWTs may inadvertently facilitate species translocations and successful establishments of non‐native taxa into new environments (Ellender & Weyl, 2014; Laurenson & Hocutt, 1985). Often, IBWTs facilitate translocations of more than one species, thereby promoting co‐occurrences of multiple non‐native species, which raises concern over their potential impact within the invaded systems (e.g., Kadye & Booth, 2020; Laurenson & Hocutt, 1985; Nagelkerke et al, 2018).…”

“…The Great Fish River in the Eastern Cape, South Africa, is characterized by multiple non‐native fish species, mainly in the mainstem habitats (Kadye & Booth, 2020; Laurenson & Hocutt, 1985). Their co‐occurrences with native species in these habitats raise questions on mechanisms facilitating these relationships.…”

Distribution patterns and habitat associations ofSandelia bainsii(Teleostei:Anabantidae), a highly threatened narrow‐range endemic freshwater fish

“…Instream habitats and flow have been variously altered because of construction of weirs and dams, agricultural activities and invasion of the catchments by non‐native plants, particularly black wattle Acacia mearnsii De Wild. Non‐native fishes have also been introduced into the Kat River Dam located in the upper section of the Kat River and the lower sections of the Kat and Koonap rivers (Kadye & Booth, 2020; Laurenson & Hocutt, 1986).…”

Journal of Fish Biology special issue on The Biology and Ecology of African Freshwater Fishes

“…(2020) described upstream movements of up to 397 km by tigerfish Hydrocynus vittatus Castelnau 1861 and used information on their movement ecology to assess the feasibility of freshwater protected areas as a conservation tool. Kadye and Booth (2020) examined the degree of environmental niche overlap between native and non‐native fish species in the invaded Great Fish River system in South Africa. These authors concluded that environmental alterations are likely to create conditions that are favourable to the establishment and proliferation of introduced species, which in turn increases the risk of negative interactions with native species.…”