Biotic and abiotic drivers of macroinvertebrate assemblages in a South African river
- Authors: Bellingan, Terence Andrew
- Date: 2018
- Subjects: Aquatic insects -- South Africa -- Eastern Cape , Stream ecology -- South Africa -- Eastern Cape , Freshwater ecology -- South Africa -- Eastern Cape , Riparian areas -- Management , Ecosystem management -- South Africa -- Eastern Cape , Mayflies -- South Africa -- Eastern Cape , Stoneflies -- South Africa -- Eastern Cape , Keiskamma River
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/61839 , vital:28067
- Description: Aquatic insects are the most numerically abundant and diverse group of organisms found in lotic ecosystems in South Africa and the world over. They play vital roles in freshwater ecosystem functioning, processing nutrients and in turn forming integral links in stream food-webs. This thesis focussed on examining the macroinvertebrate fauna within three reaches of headwater streams of the Keiskamma River system: reaches that were considered to be fishless; reaches that were invaded by non-native salmonid species; and reaches that were dominated by native fish. I described the effects of predatory fish presence through detailed examination of macroinvertebrate assemblage composition; macroinvertebrate drift timing and density; and through niche utilisation determined from stable isotope data. Patterns in the macroinvertebrate assemblages of the headwaters of the Keiskamma River appear to be driven more strongly by flow rate and seasonal influences, but fish presence and biotope availability were also significant drivers. Niche shifts due to predator presence were not easy to detect and, while patterns of influence may have been evident, they were not found to be significant. However, I demonstrated that salmonids selectively feed on native fish species when the opportunity is presented, occupying significantly higher trophic levels when co-occurring with native fish than in invaded reaches where native fish are absent. Drift timing and density were demonstrated to be significantly different between reach for specific macroinvertebrate species from the Ephemeroptera and Plecoptera, under differing fish predation regimes, in agreement with what has been observed from studies in rivers elsewhere. In freshwater ecosystems of South Africa and worldwide, mitigation of negative effects of alien fishes through their removal using piscicides may also affect non-target organisms. To better understand the effects of just such a removal operation, employed for the first time in the history of freshwater conservation in South Africa, macroinvertebrate communities were assessed for non-target effects of rotenone. The fish eradication operations were demonstrated to have a short-term negative effect on the macroinvertebrate assemblage, through water quality index measurements and alteration of densities of macroinvertebrate taxa collected from stone surfaces. However, no long-term detrimental impact was observed as macroinvertebrate faunas returned to a comparable pre-treatment state within a year of each rotenone application.
- Full Text:
- Date Issued: 2018
- Authors: Bellingan, Terence Andrew
- Date: 2018
- Subjects: Aquatic insects -- South Africa -- Eastern Cape , Stream ecology -- South Africa -- Eastern Cape , Freshwater ecology -- South Africa -- Eastern Cape , Riparian areas -- Management , Ecosystem management -- South Africa -- Eastern Cape , Mayflies -- South Africa -- Eastern Cape , Stoneflies -- South Africa -- Eastern Cape , Keiskamma River
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/61839 , vital:28067
- Description: Aquatic insects are the most numerically abundant and diverse group of organisms found in lotic ecosystems in South Africa and the world over. They play vital roles in freshwater ecosystem functioning, processing nutrients and in turn forming integral links in stream food-webs. This thesis focussed on examining the macroinvertebrate fauna within three reaches of headwater streams of the Keiskamma River system: reaches that were considered to be fishless; reaches that were invaded by non-native salmonid species; and reaches that were dominated by native fish. I described the effects of predatory fish presence through detailed examination of macroinvertebrate assemblage composition; macroinvertebrate drift timing and density; and through niche utilisation determined from stable isotope data. Patterns in the macroinvertebrate assemblages of the headwaters of the Keiskamma River appear to be driven more strongly by flow rate and seasonal influences, but fish presence and biotope availability were also significant drivers. Niche shifts due to predator presence were not easy to detect and, while patterns of influence may have been evident, they were not found to be significant. However, I demonstrated that salmonids selectively feed on native fish species when the opportunity is presented, occupying significantly higher trophic levels when co-occurring with native fish than in invaded reaches where native fish are absent. Drift timing and density were demonstrated to be significantly different between reach for specific macroinvertebrate species from the Ephemeroptera and Plecoptera, under differing fish predation regimes, in agreement with what has been observed from studies in rivers elsewhere. In freshwater ecosystems of South Africa and worldwide, mitigation of negative effects of alien fishes through their removal using piscicides may also affect non-target organisms. To better understand the effects of just such a removal operation, employed for the first time in the history of freshwater conservation in South Africa, macroinvertebrate communities were assessed for non-target effects of rotenone. The fish eradication operations were demonstrated to have a short-term negative effect on the macroinvertebrate assemblage, through water quality index measurements and alteration of densities of macroinvertebrate taxa collected from stone surfaces. However, no long-term detrimental impact was observed as macroinvertebrate faunas returned to a comparable pre-treatment state within a year of each rotenone application.
- Full Text:
- Date Issued: 2018
The potential significance of refugia in safeguarding Non-Timber Forest products under Harvesting
- Authors: Mjoli, Nwabisa
- Date: 2018
- Subjects: Non-timber forest products -- South Africa -- Eastern Cape , Nature conservation -- South Africa -- Eastern Cape , Ecosystem management -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/60596 , vital:27801
- Description: Many rural households living in and adjacent to forests in South Africa harvest a variety of NonTimber Forest Products (NTFPs) such as wild fruits, fibre, fuelwood, seeds, medicine and bush meat for domestic use, sale and maintaining cultural values. To promote the continued availability of these NTFPs it is important that NTFPs are well maintained and that harvest offtake is sustainable, because if it is not, then the important livelihood function that they fulfil will be jeopardized over time. The role of refugia in conserving pockets of threatened species from overharvesting has rarely been considered. Building on Shackleton et al. (2015), six applications of the concept are considered: size refugia, spatial refugia, cultural/spiritual refugia and physical/habitat refugia. I examined the prevalence and type of refugia for NTFPs at three coastal sites in the Eastern Cape province of South Africa. This was done via several community focus group discussions at each site. Here I report on the role of refugia in offering some safeguard to NTFPs by assessing harvested and non-harvested sites of refugia as well as individual plant species by measuring population density, harvest damage and size class profile. Respondents from the focus group discussions perceived a general decline in the abundance of common, widely used species over the past five decades. Decreasing rainfall and distant farming activities was reported consistently by the majority of the respondents. The most common form of refugia was spatial refugia, followed by cultural/spiritual refugia and physical/habitat refugia. Only six species were identified to be in refugia, namely Cyperus congestus, Cyperus textillis, Millettia grandis, Olea europaea subsp. africana, Phoenix reclinata, and Ptaeroxylon obliquum. Population inventories revealed that regeneration and population densities of some NTFP species in the non-refuge site were adversely affected by harvesting. Populations in refuge sites generally had the largest size classes indicating a regeneration potential but likely to impact regeneration over time if pressures are maintained. Therefore, if refuge sites keep larger individuals, NTFP populations can be maintained. Few studies have critically analyzed the concept of refugia in relation to how NTFPs can be safeguarded and the practical implication of the refuge concept needs to be considered in conservation and strategies and population models.
- Full Text:
- Date Issued: 2018
- Authors: Mjoli, Nwabisa
- Date: 2018
- Subjects: Non-timber forest products -- South Africa -- Eastern Cape , Nature conservation -- South Africa -- Eastern Cape , Ecosystem management -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/60596 , vital:27801
- Description: Many rural households living in and adjacent to forests in South Africa harvest a variety of NonTimber Forest Products (NTFPs) such as wild fruits, fibre, fuelwood, seeds, medicine and bush meat for domestic use, sale and maintaining cultural values. To promote the continued availability of these NTFPs it is important that NTFPs are well maintained and that harvest offtake is sustainable, because if it is not, then the important livelihood function that they fulfil will be jeopardized over time. The role of refugia in conserving pockets of threatened species from overharvesting has rarely been considered. Building on Shackleton et al. (2015), six applications of the concept are considered: size refugia, spatial refugia, cultural/spiritual refugia and physical/habitat refugia. I examined the prevalence and type of refugia for NTFPs at three coastal sites in the Eastern Cape province of South Africa. This was done via several community focus group discussions at each site. Here I report on the role of refugia in offering some safeguard to NTFPs by assessing harvested and non-harvested sites of refugia as well as individual plant species by measuring population density, harvest damage and size class profile. Respondents from the focus group discussions perceived a general decline in the abundance of common, widely used species over the past five decades. Decreasing rainfall and distant farming activities was reported consistently by the majority of the respondents. The most common form of refugia was spatial refugia, followed by cultural/spiritual refugia and physical/habitat refugia. Only six species were identified to be in refugia, namely Cyperus congestus, Cyperus textillis, Millettia grandis, Olea europaea subsp. africana, Phoenix reclinata, and Ptaeroxylon obliquum. Population inventories revealed that regeneration and population densities of some NTFP species in the non-refuge site were adversely affected by harvesting. Populations in refuge sites generally had the largest size classes indicating a regeneration potential but likely to impact regeneration over time if pressures are maintained. Therefore, if refuge sites keep larger individuals, NTFP populations can be maintained. Few studies have critically analyzed the concept of refugia in relation to how NTFPs can be safeguarded and the practical implication of the refuge concept needs to be considered in conservation and strategies and population models.
- Full Text:
- Date Issued: 2018
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