A test for Allee effects in the self-incompatible wasp-pollinated milkweed Gomphocarpus physocarpus
- Coombs, Gareth, Peter, Craig I, Johnson, Steven D
- Authors: Coombs, Gareth , Peter, Craig I , Johnson, Steven D
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6511 , http://hdl.handle.net/10962/d1005938 , http://dx.doi.org/10.1111/j.1442-9993.2009.01976.x
- Description: It has been suggested that plants which are good colonizers will generally have either an ability to self-fertilize or a generalist pollination system. This prediction is based on the idea that these reproductive traits should confer resistance to Allee effects in founder populations and was tested using Gomphocarpus physocarpus (Asclepiadoideae; Apocynaceae), a species native to South Africa that is invasive in other parts of the world. We found no significant relationships between the size of G. physocarpus populations and various measures of pollination success (pollen deposition, pollen removal, and pollen transfer efficiency) and fruit set. A breeding system experiment showed that plants in a South African population are genetically self-incompatible and thus obligate outcrossers. Out-crossing is further enhanced by mechanical reconfiguration of removed pollinaria before the pollinia can be deposited. Selfpollination is reduced when such reconfiguration exceeds the average duration of pollinator visits to a plant. Observations suggest that a wide variety of wasp species in the genera Belonogaster and Polistes (Vespidae) are the primary pollinators. We conclude that efficient pollination of plants in small founding populations, resulting from their generalist wasp-pollination system, contributes in part to the colonizing success of G. physocarpus. The presence of similar wasps in other parts of the world has evidently facilitated the expansion of the range of this milkweed.
- Full Text:
- Date Issued: 2009
- Authors: Coombs, Gareth , Peter, Craig I , Johnson, Steven D
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6511 , http://hdl.handle.net/10962/d1005938 , http://dx.doi.org/10.1111/j.1442-9993.2009.01976.x
- Description: It has been suggested that plants which are good colonizers will generally have either an ability to self-fertilize or a generalist pollination system. This prediction is based on the idea that these reproductive traits should confer resistance to Allee effects in founder populations and was tested using Gomphocarpus physocarpus (Asclepiadoideae; Apocynaceae), a species native to South Africa that is invasive in other parts of the world. We found no significant relationships between the size of G. physocarpus populations and various measures of pollination success (pollen deposition, pollen removal, and pollen transfer efficiency) and fruit set. A breeding system experiment showed that plants in a South African population are genetically self-incompatible and thus obligate outcrossers. Out-crossing is further enhanced by mechanical reconfiguration of removed pollinaria before the pollinia can be deposited. Selfpollination is reduced when such reconfiguration exceeds the average duration of pollinator visits to a plant. Observations suggest that a wide variety of wasp species in the genera Belonogaster and Polistes (Vespidae) are the primary pollinators. We conclude that efficient pollination of plants in small founding populations, resulting from their generalist wasp-pollination system, contributes in part to the colonizing success of G. physocarpus. The presence of similar wasps in other parts of the world has evidently facilitated the expansion of the range of this milkweed.
- Full Text:
- Date Issued: 2009
Is HIV/AIDS jeopardizing biodiversity?
- McGarry, Dylan K, Shackleton, Charlie M
- Authors: McGarry, Dylan K , Shackleton, Charlie M
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6642 , http://hdl.handle.net/10962/d1006871
- Description: The scourge of HIV/AIDS (human immunodeficiency virus/acquired immune deficiency syndrome) is most prevalent in southern Africa. South Africa has the highest number of people in the world living with HIV/AIDS and a prevalence rate of over 30 % for females presenting at antenatal clinics. There are now almost five million orphans within southern Africa, as a result of AIDS deaths of one or more or their parents. AIDS-related mortality and morbidity of care-givers may lead to increased reliance on wild sources of animal protein by surviving children. This increase in hunting pressure has unknown, but potentially important impacts on local animal populations.
- Full Text:
- Date Issued: 2009
- Authors: McGarry, Dylan K , Shackleton, Charlie M
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6642 , http://hdl.handle.net/10962/d1006871
- Description: The scourge of HIV/AIDS (human immunodeficiency virus/acquired immune deficiency syndrome) is most prevalent in southern Africa. South Africa has the highest number of people in the world living with HIV/AIDS and a prevalence rate of over 30 % for females presenting at antenatal clinics. There are now almost five million orphans within southern Africa, as a result of AIDS deaths of one or more or their parents. AIDS-related mortality and morbidity of care-givers may lead to increased reliance on wild sources of animal protein by surviving children. This increase in hunting pressure has unknown, but potentially important impacts on local animal populations.
- Full Text:
- Date Issued: 2009
Pollinators, “mustard oil” volatiles, and fruit production in flowers of the dioecious tree Drypetes natalensis (Putranjivaceae)
- Johnson, Steven D, Griffiths, Megan E, Peter, Craig I, Lawes, Michael J
- Authors: Johnson, Steven D , Griffiths, Megan E , Peter, Craig I , Lawes, Michael J
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6519 , http://hdl.handle.net/10962/d1005948
- Description: The Putranjivaceae is an enigmatic family, notable for being the only lineage outside the Capparales to possess the glucosinolate biochemical pathway, which forms the basis of an induced chemical defense system against herbivores (the “ mustard oil bomb ” ). We investigated the pollination biology and fl oral scent chemistry of Drypetes natalensis (Putranjivaceae), a dioecious subcanopy tree with fl owers borne on the stem (caulifl ory). Flowering male trees were more abundant than female ones and produced about 10-fold more fl owers. Flowers of both sexes produce copious amounts of nectar on disc-like nectaries accessible to short-tongued insects. The main fl ower visitors observed were cetoniid beetles, bees, and vespid wasps. Pollen load analysis indicated that these insects exhibit a high degree of fi delity to D. natalensis fl owers. Insects effectively transfer pollen from male to female plants resulting in about 31% of female fl owers developing fruits with viable seeds. Cetoniid beetles showed signifi cant orientation toward the scent of D. natalensis fl owers in a Y-maze olfactometer. The scents of male and female fl owers are similar in chemical composition and dominated by fatty acid derivatives and isothiocyanates from the glucosinolate pathway. The apparent constitutive emission of isothiocyanates raises interesting new questions about their functional role in flowers.
- Full Text:
- Date Issued: 2009
- Authors: Johnson, Steven D , Griffiths, Megan E , Peter, Craig I , Lawes, Michael J
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6519 , http://hdl.handle.net/10962/d1005948
- Description: The Putranjivaceae is an enigmatic family, notable for being the only lineage outside the Capparales to possess the glucosinolate biochemical pathway, which forms the basis of an induced chemical defense system against herbivores (the “ mustard oil bomb ” ). We investigated the pollination biology and fl oral scent chemistry of Drypetes natalensis (Putranjivaceae), a dioecious subcanopy tree with fl owers borne on the stem (caulifl ory). Flowering male trees were more abundant than female ones and produced about 10-fold more fl owers. Flowers of both sexes produce copious amounts of nectar on disc-like nectaries accessible to short-tongued insects. The main fl ower visitors observed were cetoniid beetles, bees, and vespid wasps. Pollen load analysis indicated that these insects exhibit a high degree of fi delity to D. natalensis fl owers. Insects effectively transfer pollen from male to female plants resulting in about 31% of female fl owers developing fruits with viable seeds. Cetoniid beetles showed signifi cant orientation toward the scent of D. natalensis fl owers in a Y-maze olfactometer. The scents of male and female fl owers are similar in chemical composition and dominated by fatty acid derivatives and isothiocyanates from the glucosinolate pathway. The apparent constitutive emission of isothiocyanates raises interesting new questions about their functional role in flowers.
- Full Text:
- Date Issued: 2009
Quantity and significance of wild meat off-take by a rural community in the Eastern Cape, South Africa
- Kaschula, Sarah A H, Shackleton, Charlie M
- Authors: Kaschula, Sarah A H , Shackleton, Charlie M
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6638 , http://hdl.handle.net/10962/d1006864
- Description: When compared to tropical forest zones in west and central Africa, off-take of wild meat from savannah and grassland biomes by local rural communities has not been well assessed. This case study of wild meat collection activities within a rural community in the Mount Frere region of the Eastern Cape (South Africa) uses last-catch records derived from 50 wild meat gatherers to calculate average off-take of taxa, species and fresh mass of wild meat per collection event. When per-event off take is overlaid onto household hunting frequency data, annual off-take would be 268.6 kg km−2 yr−1 or 3 kg person−1 yr−1 presuming constant off-take over an annual period. Monetary value of off-take would be South African R 307 (US$ 39) per household annually. For some species, off-take weight per km2 shows similar values to data from tropical forest zones, but high human population densities tend to dilute off-takes to less nutritionally significant amounts at the per person scale. However, unlike many tropical zones, none of the species harvested can be considered high-priority conservation species. Even densely populated and heavily harvested communal lands appear to offer high wild meat off-takes from low conservation priority species.
- Full Text:
- Date Issued: 2009
- Authors: Kaschula, Sarah A H , Shackleton, Charlie M
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6638 , http://hdl.handle.net/10962/d1006864
- Description: When compared to tropical forest zones in west and central Africa, off-take of wild meat from savannah and grassland biomes by local rural communities has not been well assessed. This case study of wild meat collection activities within a rural community in the Mount Frere region of the Eastern Cape (South Africa) uses last-catch records derived from 50 wild meat gatherers to calculate average off-take of taxa, species and fresh mass of wild meat per collection event. When per-event off take is overlaid onto household hunting frequency data, annual off-take would be 268.6 kg km−2 yr−1 or 3 kg person−1 yr−1 presuming constant off-take over an annual period. Monetary value of off-take would be South African R 307 (US$ 39) per household annually. For some species, off-take weight per km2 shows similar values to data from tropical forest zones, but high human population densities tend to dilute off-takes to less nutritionally significant amounts at the per person scale. However, unlike many tropical zones, none of the species harvested can be considered high-priority conservation species. Even densely populated and heavily harvested communal lands appear to offer high wild meat off-takes from low conservation priority species.
- Full Text:
- Date Issued: 2009
Stronger induction of callose deposition in barley by Russian wheat aphid than bird cherry-oat aphid is not associated with differences in callose synthase or ≤-1,3-glucanase expression
- Saheed, Sefiu A, Cierlik, Izabela, Larsson, Kristina A E, Delp, Gabriele, Bradley, Graeme, Jonsson, Lisbeth M V, Botha, Christiaan E J
- Authors: Saheed, Sefiu A , Cierlik, Izabela , Larsson, Kristina A E , Delp, Gabriele , Bradley, Graeme , Jonsson, Lisbeth M V , Botha, Christiaan E J
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6542 , http://hdl.handle.net/10962/d1005984
- Description: The effects of infestation by the bird cherry-oat aphid (BCA), (Rhopalosiphum padi L) and the Russian wheat aphid (RWA) (Diuraphis noxia Mordvilko) on callose deposition and gene expression related to callose accumulation were investigated in barley (Hordeum vulgare L. cv. Clipper). The BCA, which gives no visible symptoms, induced very limited callose deposition, even after 14 days of infestation. In contrast, RWA, which causes chlorosis, white and yellow streaking and leaf rolling, induced callose accumulation already after 24h in longitudinal leaf veins. The deposition was pronounced after 72 h, progressing during 7 and 14 days of infestation. In RWA-infested source leaves, callose was also induced in longitudinal veins basipetal to the aphid-infested tissue, whereas in sink leaves, more callose deposition was found above the feeding sites. Nine putative callose synthase genes were identified in a data base search, of which eight were expressed in the leaves, but with similar level of expression in control and aphid-infested tissue. Four out of 12 examined β-1,3-glucanases were expressed in the leaves, and three of them were up-regulated in aphid-infested tissue. They were all more strongly induced by RWA than BCA. The results suggest that callose accumulation may be partly responsible for the symptoms resulting from RWA feeding and that a callose-inducing signal may be transported in the phloem. Furthermore it is concluded that the absence of callose deposition in BCA-infested leaves is not due to a stronger induction of callose-degrading β-1,3-glucanases in this tissue, as compared to RWA-infested leaves.
- Full Text:
- Date Issued: 2009
- Authors: Saheed, Sefiu A , Cierlik, Izabela , Larsson, Kristina A E , Delp, Gabriele , Bradley, Graeme , Jonsson, Lisbeth M V , Botha, Christiaan E J
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6542 , http://hdl.handle.net/10962/d1005984
- Description: The effects of infestation by the bird cherry-oat aphid (BCA), (Rhopalosiphum padi L) and the Russian wheat aphid (RWA) (Diuraphis noxia Mordvilko) on callose deposition and gene expression related to callose accumulation were investigated in barley (Hordeum vulgare L. cv. Clipper). The BCA, which gives no visible symptoms, induced very limited callose deposition, even after 14 days of infestation. In contrast, RWA, which causes chlorosis, white and yellow streaking and leaf rolling, induced callose accumulation already after 24h in longitudinal leaf veins. The deposition was pronounced after 72 h, progressing during 7 and 14 days of infestation. In RWA-infested source leaves, callose was also induced in longitudinal veins basipetal to the aphid-infested tissue, whereas in sink leaves, more callose deposition was found above the feeding sites. Nine putative callose synthase genes were identified in a data base search, of which eight were expressed in the leaves, but with similar level of expression in control and aphid-infested tissue. Four out of 12 examined β-1,3-glucanases were expressed in the leaves, and three of them were up-regulated in aphid-infested tissue. They were all more strongly induced by RWA than BCA. The results suggest that callose accumulation may be partly responsible for the symptoms resulting from RWA feeding and that a callose-inducing signal may be transported in the phloem. Furthermore it is concluded that the absence of callose deposition in BCA-infested leaves is not due to a stronger induction of callose-degrading β-1,3-glucanases in this tissue, as compared to RWA-infested leaves.
- Full Text:
- Date Issued: 2009
Wealth differentiation in household use and trade in non-timber forest products in South Africa
- Paumgarten, Fiona, Shackleton, Charlie M
- Authors: Paumgarten, Fiona , Shackleton, Charlie M
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6646 , http://hdl.handle.net/10962/d1006892
- Description: Findings from southern Africa and internationally indicate the local use and trade of NTFPs to be significant however most present a composite picture, failing to account for intra-community socio-economic differences. These differences may have implications for policy and practice related to poverty alleviation and sustainable use. This paper reports on a study in South Africa which explored the relationship between household wealth and the use, procurement and sale of NTFPs in two villages. There was no influence of wealth on the proportion of households using or purchasing most of the NTFPs, or the number used. However, wealthier households bought significantly more resources per household, and poor households (at one village) sold significantly more. These results are discussed within the context of local conditions and poverty alleviation debates.
- Full Text:
- Date Issued: 2009
- Authors: Paumgarten, Fiona , Shackleton, Charlie M
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6646 , http://hdl.handle.net/10962/d1006892
- Description: Findings from southern Africa and internationally indicate the local use and trade of NTFPs to be significant however most present a composite picture, failing to account for intra-community socio-economic differences. These differences may have implications for policy and practice related to poverty alleviation and sustainable use. This paper reports on a study in South Africa which explored the relationship between household wealth and the use, procurement and sale of NTFPs in two villages. There was no influence of wealth on the proportion of households using or purchasing most of the NTFPs, or the number used. However, wealthier households bought significantly more resources per household, and poor households (at one village) sold significantly more. These results are discussed within the context of local conditions and poverty alleviation debates.
- Full Text:
- Date Issued: 2009
Will the real custodian of natural resource management please stand up
- Authors: Shackleton, Charlie M
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6657 , http://hdl.handle.net/10962/d1007076
- Description: South Africa is the custodian of an immense wealth of biodiversity resources, and is estimated to be the third most biodiverse country in the world. At the ecosystem level this biodiversity supports the production of goods and services used by us all; water, air, soil fertility, wood, food, etc. At a more local level the harvesting of numerous natural resources provides consumptive products for millions of poor South Africans, as well as income for equally significant numbers.Consumption of and trade in these resources is the very mainstay of their well-being, and crucial in preventing deeper poverty levels. For example, despite massive improvements in the provision of electricity, most rural and a significant proportion of urban South Africans continue to use fuelwood as a key energy source for cooking (e.g. 65% of electrified households in the urban areas of Makana municipality, and 92% of households in the rural areas of Bushbuckridge); approximately 75% of the population use medicinal plants for medicinal or cultural reasons; and millions of urban and rural households make use of wild edible herbs. With such high demand for these resources, it is not unsurprising that there are large and established trade networks spanning local, regional, national and, for some resources (e.g. specific medicinal plants, mopane worms), international boundaries. The total value of this trade is unknown, and unrecorded in local or national economic or GDP statistics. It certainly equates to billions of rands per year. The direct-use and trade values are substantial and provide a cost saving to the State. Where biodiversity resources are overused or exhausted, people have to purchase alternatives, which reduces their scarce cash resources, thereby increasing their likely dependency on State welfare grants.
- Full Text:
- Date Issued: 2009
- Authors: Shackleton, Charlie M
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6657 , http://hdl.handle.net/10962/d1007076
- Description: South Africa is the custodian of an immense wealth of biodiversity resources, and is estimated to be the third most biodiverse country in the world. At the ecosystem level this biodiversity supports the production of goods and services used by us all; water, air, soil fertility, wood, food, etc. At a more local level the harvesting of numerous natural resources provides consumptive products for millions of poor South Africans, as well as income for equally significant numbers.Consumption of and trade in these resources is the very mainstay of their well-being, and crucial in preventing deeper poverty levels. For example, despite massive improvements in the provision of electricity, most rural and a significant proportion of urban South Africans continue to use fuelwood as a key energy source for cooking (e.g. 65% of electrified households in the urban areas of Makana municipality, and 92% of households in the rural areas of Bushbuckridge); approximately 75% of the population use medicinal plants for medicinal or cultural reasons; and millions of urban and rural households make use of wild edible herbs. With such high demand for these resources, it is not unsurprising that there are large and established trade networks spanning local, regional, national and, for some resources (e.g. specific medicinal plants, mopane worms), international boundaries. The total value of this trade is unknown, and unrecorded in local or national economic or GDP statistics. It certainly equates to billions of rands per year. The direct-use and trade values are substantial and provide a cost saving to the State. Where biodiversity resources are overused or exhausted, people have to purchase alternatives, which reduces their scarce cash resources, thereby increasing their likely dependency on State welfare grants.
- Full Text:
- Date Issued: 2009
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