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German wasp | Vespula germanica

German wasp

Vespula germanica

Coral bush | Ardisia crenata

Coral bush

Ardisia crenata

Purple loosestrife | Lythrum salicaria

Purple loosestrife

Lythrum salicaria

Pom pom weed | Campuloclinium macrocephalum

Pom pom weed

Campuloclinium macrocephalum

Canarybird bush | Crotalaria agatiflora

Canarybird bush

Crotalaria agatiflora

Peanut butter cassia | Senna didymobotrya

Peanut butter cassia

Senna didymobotrya

Rubber vine | Cryptostegia grandiflora

Rubber vine

Cryptostegia grandiflora

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Environmental Programmes

In order to tackle our country’s socio-economic challenges, the government adopted the Outcomes based approach to improve government performance and providing focus on service delivery. find out more

The functional response of aquatic plant invaders

The functional response of aquatic plant invaders
Philip S.R. Weyl1, Mhairi E. Alexander2, Julie A. Coetzee3, Jaclyn M. HILL1
1Department of Zoology & Entomology, Rhodes University, Grahamstown, SA
2School of Science & Sport, University of West Scotland, Scotland
3Department of Botany, Rhodes University, Grahamstown, SA

Refining the protocols for risk assessment is one of the major challenges in invasive species management. Invasive species impacts are often highly speculative and as a consequence, developing robust predictions about the potential impacts of invasive species can be challenging. Invaders are regularly associated with rapid and efficient resource allocation; accordingly, comparing the functional response (defined as resource uptake as a function of resource density) of invasive and native species may help predict impacts of emerging invaders. The functional responses of three South African native (Lagarosiphon muscoides, Myriophyllum spicatum and Lagarosiphon major) and one invasive (Egeria densa) submerged macrophyte species were compared under two temperature regimes; 20⁰C and 30⁰C. Functional response was defined as nitrogen uptake rates (as a function of nitrogen concentration) of ammonia (NH3) over 4 hours under full light. All plants demonstrated a clear type II functional response characterized by a decelerating intake rate, where plants were likely limited by their capacity to take up nitrogen. Functional response curves and maximum uptake rates (Vmax) were similar between species at 20⁰C, but L. major showed a significantly reduced Vmax at 30⁰C. Nitrogen affinity (1/Ks) was slightly higher in both temperature regimes for all native species, with L. major showing the highest affinity for nitrogen at 30⁰C. Overall, despite the clear type II curves, functional response was a poor predictor of invasion potential. However, nitrogen affinity appears to be marginally higher in the native species, suggesting some potential for native plants to outperform their invasive counterparts.

Read 3041 times Last modified on Tuesday, 03 May 2016 12:13

General News Updates

2019 National Symposium on Biological Invasio…


This is your invitation to South Africa's 2019 National Symposium on Biological Invasions. The convention is hosted by the Centre for Invasion Biology (CIB), University of Stellenbosch, and the Biolo... Read more

2019 Invasive Species Training


During the past five years (2014-2018), ISSA invasive species trainers have trained 4 000 in the identification of invasive species and laws pertaining to invasive species across South Africa.  ... Read more

Alien Grass Working Group


Who are we? The South African National Alien Grass Working Group was jointly initiated by the South African Biodiversity Institute (SANBI) and the Centre for Excellence in Invasion Biology (C·I·B) in... Read more

Permits for planting indigenous Cynodon?


On 16 February, 2018, South Africa's Department of Environmental Affairs issued amendments to the regulations and lists relating to the National List of Invasive Species.  Updates to the draft&n... Read more

Invasive species training 2018 dates released


Interested in invasive species?  How much do you know about NEMBA invasive species compliance for landowners and organs of state? The South African Green Industries Council (SAGIC) have released... Read more

Communications post for Africa advertised


The Nature Conservancy has advertised a brand new post:  Communications Manager, Africa Region. Knowledge of invasive species and water would be an asset in this post. See details below:    Job Titl... Read more