7 research outputs found
Niche expansion by indigenous fish species following the introduction of rainbow trout (Oncorhynchus mykiss) in a subtropical river system, upper Blyde River, South Africa
SUPPLEMENTARY TABLE S1
Frequency of occurrence (%) of prey items in the diets of indigenous and
alien invasive fish species in the catchments of the Blyde and Treur rivers,
Mpumalanga Province, South Africa.SUPPLEMENTARY TABLE S2
Trophic position (TP), corrected Carbon (Ccorr) and values of isotopic
niche (SEAc) for indigenous and alien invasive (bold) fish species sampled
in uninvaded and invaded catchments of the Blyde and Treur rivers,
Mpumalanga Province, South Africa.SUPPLEMENTARY TABLE S3
Isotopic niche overlap among fish species in river sections invaded by
rainbow trout (Oncorhynchus mykiss) on the Blyde River, South Africa.
Extent of overlap was classified as low (< 40%), intermediate (40 to 60%)
and high (> 60%) (Langton, 1982).SUPPLEMENTARY TABLE S4
Isotopic niche overlap among fish species in the Treur River, South Africa
that is free of rainbow trout (Oncorhynchus mykiss) invasion. Extent of
overlap was classified as low (< 40%), intermediate (40 to 60%) and high
(> 60%) (Langton, 1982).SUPPLEMENTARY TABLE S5
Isotopic matrices of food webs of fish communities sampled in sites
invaded by rainbow trout and sites free of invasion on the Blyde and
Treur rivers, Mpumalanga Province, South Africa.DATA AVAILABILITY STATEMENT : The original contributions presented in the study are
included in the article/Supplementary Material, further
inquiries can be directed to the corresponding author.The introduction of alien predatory fish such as rainbow trout (Oncorhynchus
mykiss) can have a significant effect on indigenous fish communities such as
altering the structure and dynamics of food webs. Quantifying the trophic niche
utilised by the alien fish species is therefore important to aid our understanding
of how their feeding strategies might aid establishment, define their functional
role and inform on potential impacts. This study assessed food web interactions
between fish communities in river reaches that are invaded by O. mykiss and
sections that are free of invasions in the upper Blyde River catchment, South
Africa. It specifically evaluated the hypothesis that O. mykiss invasion is likely to
lead to a decrease in the trophic functional diversity through predation and that
indigenous fish will shift their trophic niche to either minimise competition with,
or avoid predation, by O. mykiss. Gut content and stable isotope analyses were
used to determine trophic interactions. Fish communities in uninvaded areas
utilised fewer and similar food sources and occupied lower trophic levels, than
fish communities in invaded areas. Oncorhynchus mykiss fed mainly on
invertebrates and at trophic levels similar to and or lower than indigenous
fishes. This suggests that their current impact on indigenous fish communities is
mainly through competition for resources. We posit that O. mykiss invasions
reduced the abundance of indigenous fishes and thereby reduced predation
pressure on aquatic invertebrates, with a knock-on effect on the trophic interrelationships among fish assemblages. Our findings are consistent with
other studies in South Africa that have shown that the impacts of O. mykiss
invasion can lead to a decline and fragmentation of indigenous species
populations and niche shifts.The DSI-NRF Centre of Excellence for Invasion Biology, the South African Department of Forestry, Fisheries, and the Environment (DFFE) and the National Research Foundation.https://www.frontiersin.org/journals/environmental-scienceam2023Mammal Research InstituteZoology and Entomolog
Trophic ecology and persistence of invasive silver carp Hypophthalmichthys molitrix in an oligotrophic South African impoundment
The alien invasive silver carp Hypophthalmichthys molitrix established a self-sustaining feral population in an
oligotrophic impoundment, Flag Boshielo Dam, in South Africa. The ability of this population to persist in a dam with
low algal biomass (median annual suspended chlorophyll a = 0.08 ”g lâ1), and limited access to rivers considered
large enough for successful spawning, has implications for their invasive potential in other systems. Stomach content
and stable isotope analysis were used to assess the trophic ecology of H. molitrix, which was then compared with
indigenous Mozambique tilapia Oreochromis mossambicus, on a seasonal basis during 2011. Hypophthalmichthys
molitrix are generalist filter feeders, with a diet consisting primarily of sediment, vegetative detritus, dinoflagellates
and diatoms. The dominance of sediments in their stomachs suggests occasional benthic scavenging. However,
H. molitrix occupied a higher trophic level (TL = 2.8) than expected, suggesting that this population subsidised
their diet with an unidentified dietary constituent, characterised by enriched nitrogen values. Although the stomach
contents indicated dietary overlap between H. molitrix and O. mossambicus, stable isotopes revealed fine-scale
resource partitioning, despite both species occupying the same trophic level. Nonetheless, the persistence of this
feral H. molitrix population in an oligotrophic impoundment highlights their phenotypic plasticity.The Olifants River Forum, the DST-NRF Centre of Invasion Biology, University of Pretoria and the National Research Foundation (NRF).http://www.tandfonline.com/loi/taas202017-12-31hb2016Zoology and Entomolog
Invasive Nile tilapia Oreochromis niloticus (Linnaeus, 1758) in the Limpopo River system, South Africa : conservation implications
In most tropical river systems there has been a lack of integrated ecological research to
investigate the dynamics and impacts of invasive species on recipient river systems. This is in
sharp contrast to temperate river systems. This thesis investigated the nature, extent, and impact
of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758), on indigenous congenerics within the
Limpopo River basin in northern South Africa. An integrated approach was adopted to gain a
better understanding of factors that allow Nile tilapia to be a successful invader and also to gain
an insight into its invasion rate and conservation implications within South Africa.
Morphometric and genetic variation between Nile tilapia, indigenous congenerics and
their associated hybrids were determined. Intermediate meristic characters obscured the
identification of hybrid specimens from pure morpho-specimens and species identity was only
confirmed through mtDNA analysis. Preliminary evidence points to unidirectional hybridization
among Oreochromis congeners in the Limpopo River system. The hypothesis that bigger Nile
tilapia males may have a competitive advantage over spawning grounds and in female mate
choice is proposed.
The trophic ecology of Nile tilapia was investigated using both stomach contents and
stable isotope analysis. A high similarity in stomach contents was observed but interspecific
differences were revealed in the isotopic composition of diets that suggest fine scale patterns of
resource partitioning that could be achieved by the ability of fish to selectively feed on what is
immediately available and the ability to perceive the dynamics that determine food resource
availability. Ecological niche models were used to determine the potential invasive range of Nile
tilapia and revealed broad invasive potential over most river systems in southern Africa that
overlapped the natural range of endemic congenerics. It was noted that model performance and
the degree of niche conservatism varied significantly with variable selection and spatial extent of
study area. This implied that the spatial distribution of suitable and unsuitable environmental
variables varied between the native and introduced ranges of Nile tilapia and also indicated the
ability of Nile tilapia to survive in conditions incongruent with its native range. The extreme
hardiness and adaptive life history characteristics of Nile tilapia have probably predisposed it to
be a successful invader in novel systems within southern Africa.
Lastly, a qualitative risk assessment method was developed as a potential application to
determine the risk of establishment and spread of the invasive Nile tilapia. Results showed that in
the absence of quantitative data on ecosystem structure and functioning, habitat suitability
analysis in terms of known physiological tolerance limits to minimum water temperature,
presence or absence of dams, seasonality of river flows and the presence of indigenous fish
species of concern could be adequate for identifying vulnerable river systems. The model
developed also provides an objective method that is easy to implement, modify and improve on
as new data become available. Furthermore, the model can be applied to highlight areas of
uncertainty where future research should be directed.Thesis (PhD)--University of Pretoria, 2012.Zoology and EntomologyUnrestricte
Ecological niche modeling of the invasive potential of Nile tilapia, Oreochromis niloticus in African river systems : concerns and implications for the conservation of Oreochromis species
This study applied ecological niche models to determine the potential invasive range of Nile tilapia, Oreochromis niloticus, with a particular focus on river systems in southern Africa where it is now established and spreading. Computational tools such as niche models are useful in predicting the potential range of invasive species, but there are limitations to their application. In particular, models trained on native records may fail to predict the full extent of an invasion. This failure is often attributed to changes in either the niche of the invading species or the variables used to develop the models. In this study, we therefore evaluated the differences in the predictive power of models trained with different environmental variables, the effect of species range (native vs introduced) on model performance and assessed whether or not there is evidence suggestive of a niche shift in Nile tilapia following its introduction. Niche models were constructed using Maxent and the degree of niche similarity was assessed using Schoener`s index. Null models were used to test for significance. Model performance and niche conservatism varied significantly with variable selection and species range. This indicates that the environmental conditions available to Nile tilapia in its native and introduced ranges are not congruent. Nile tilapia exhibited broad invasive potential over most of southern Africa that overlaps the natural range of endemic congenerics. Of particular concern are areas which are free of exotic species but are now vulnerable due to the promotion of fish introductions mainly for aquaculture and sport fishing.The South African Working for Water (WfW) Programme through the DST-NRF Centre of Excellence for Invasion Biology (CIB), University of Pretoria, South Africa.http://www.springerlink.com/content/103794/hb2013ab201
Frameworks used in invasion science : progress and prospects
Our understanding and management of biological invasions relies on our ability to classify and conceptualise
the phenomenon. This need has stimulated the development of a plethora of frameworks, ranging in nature
from conceptual to applied. However, most of these frameworks have not been widely tested and their
general applicability is unknown. In order to critically evaluate frameworks in invasion science, we held
a workshop on âFrameworks used in Invasion Scienceâ hosted by the DSI-NRF Centre of Excellence for
Invasion Biology in Stellenbosch, South Africa, in November 2019, which led to this special issue. For the
purpose of the workshop we defined a framework as âa way of organising things that can be easily communicated
to allow for shared understanding or that can be implemented to allow for generalisations useful for
research, policy or managementâ. Further, we developed the Stellenbosch Challenge for Invasion Science:
âCan invasion science develop and improve frameworks that are useful for research, policy or management,
and that are clear as to the contexts in which the frameworks do and do not apply?â. Particular considerations
identified among meeting participants included the need to identify the limitations of a framework,
specify how frameworks link to each other and broader issues, and to improve how frameworks can facilitate
communication. We believe that the 24 papers in this special issue do much to meet this challenge. The
papers apply existing frameworks to new data and contexts, review how the frameworks have been adopted and used, develop useable protocols and guidelines for applying frameworks to different contexts, refine the
frameworks in light of experience, integrate frameworks for new purposes, identify gaps, and develop new
frameworks to address issues that are currently not adequately dealt with. Frameworks in invasion science
must continue to be developed, tested as broadly as possible, revised, and retired as contexts and needs
change. However, frameworks dealing with pathways of introduction, progress along the introductionnaturalisation-
invasion continuum, and the assessment of impacts are being increasingly formalised and
set as standards. This, we argue, is an important step as invasion science starts to mature as a discipline.This article emerged from the workshop âFrameworks used in Invasion Scienceâ hosted by the DSI-NRF Centre of Excellence for Invasion Biology in Stellenbosch, South Africa, 11â13 November 2019.Oppenheimer Memorial Trust, the South African Department of Forestry, Fisheries, and the Environment (DFFtE), the Belgian Science Policy Office's Brain program (BelSPO BR/165/A1/TrIAS), the visiting fellowship programme of the DSI-NRF Centre of Excellence for Invasion Biology and the University of Fribourg.http://www.pensoft.net/journals/neobiotaZoology and Entomolog
Is invasion science moving towards agreed standards? The influence of selected frameworks
The need to understand and manage biological invasions has driven the development of frameworks to circumscribe,
classify, and elucidate aspects of the phenomenon. But how influential have these frameworks really
been? To test this, we evaluated the impact of a pathway classification framework, a framework focussing
on the introduction-naturalisation-invasion continuum, and two papers that outline an impact classification
framework. We analysed how these framework papers are cited and by whom, conducted a survey to determine
why people have cited the frameworks, and explored the degree to which the frameworks are implemented.
The four papers outlining these frameworks are amongst the most-cited in their respective journals,
are highly regarded in the field, and are already seen as citation classics (although citations are overwhelmingly
within the field of invasion science). The number of citations to the frameworks has increased over time, and,
while a significant proportion of these are self-citations (20â40%), this rate is decreasing. The frameworks
were cited by studies conducted and authored by researchers from across the world. However, relative to a
previous citation analysis of invasion science as a whole, the frameworks are particularly used in Europe and
South Africa and less so in North America. There is an increasing number of examples of uptake into invasion
policy and management (e.g., the pathway classification framework has been adapted and adopted into
EU legislation and CBD targets, and the impact classification framework has been adopted by the IUCN).
However, we found that few of the citing papers (6â8%) specifically implemented or interrogated the frameworks;
roughly half of all citations might be viewed as frivolous (âcitation fluffâ); there were several clear cases
of erroneous citation; and some survey respondents felt that they have not been rigorously tested yet.
Although our analyses suggest that invasion science is moving towards a more systematic and standardised
approach to recording invasions and their impacts, it appears that the proposed standards are still not
applied consistently. For this to be achieved, we argue that frameworks in invasion science need to be
revised or adapted to particular contexts in response to the needs and experiences of users (e.g., so they
are relevant to pathologists, plant ecologists, and practitioners), the standards should be easier to apply in
practice (e.g., through the development of guidelines for management), and there should be incentives for
their usage (e.g., recognition for completing an EICAT assessment).This paper emerged from a workshop on âFrameworks used in Invasion Scienceâ hosted by the DSI-NRF Centre of Excellence for Invasion Biology in Stellenbosch, South Africa, 11â13 November 2019, that was supported by the National Research Foundation of South Africa and Stellenbosch University.The South African Department of Forestry, Fisheries and the Environment, (DFFtE); Czech Science Foundation; Czech Academy of Sciences; the Oppenheimer Memorial Trust; the DSI-NRF Centre of Excellence for Invasion Biology (CIB) and National Research Foundation.http://www.pensoft.net/journals/neobiotaam2021Zoology and Entomolog