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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

Duckweed, a growing concern: are populations driven by bottom-up or top-down mechanisms in two Eastern Cape rivers

Duckweed, a growing concern: are populations driven by bottom-up or top-down mechanisms in two Eastern Cape rivers
Phillippa C. Muskett, Jackie M. Hill, Philip S.R. Weyl
Department of Zoology and Entomology, Rhodes University, Grahamstown

Lemna spp., Spirodela spp. and Wolffia spp. (referred to as duckweed) are considered native and ubiquitous plants in South Africa that are becoming a growing concern in slow moving water bodies due to their extremely rapid growth. Duckweed populations often dominate water bodies, in some cases with 100% cover, resulting in trickle down effects in the ecosystem. These are very similar problems to those commonly associated with other invasive plants such as water hyacinth, Kariba weed and water lettuce. An understanding of the drivers of duckweed population growth and associated increases in biomass is a key to the development of management strategies for these systems. Several physicochemical as well as biological aspects of the Bushmans (33˚18’45 S, 26˚ 04’

45 E) and the Bloukrans (33˚19’25 S, 26˚ 36’ 00 E) river systems in the Eastern Cape were studied. These included macroinvertebrate diversity, abundance and functional feeding groups as well as basic water parameters and nutrient analysis to gain an understanding of whether the populations are bottom-up (nutrients) or top-down (herbivory) driven. Preliminary results   indicating a lack of macroinvertebrate  herbivores  and  herbivory  in  conjunction  with    relatively  high  nutrient  levels suggests that populations of duckweed in these two river systems are likely to be driven by bottom -up mechanisms rather than top-down herbivory. Management of this nuisance plant may then require a reduction in available nutrients in problematic areas.

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General News Updates

2019 National Symposium on Biological Invasio…

26-02-2019

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

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28-02-2018

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