A temporal dimension to the influence of pollen rewards on bee behaviour and fecundity in Aloe tenuior
- Duffy, Karl J, Johnson, Steven D, Peter, Craig I
- Authors: Duffy, Karl J , Johnson, Steven D , Peter, Craig I
- Date: 2014
- Language: English
- Type: Article
- Identifier: vital:6561 , http://hdl.handle.net/10962/d1011735 , http://dx.doi.org/10.1371/journal.pone.0094908
- Description: The net effect of pollen production on fecundity in plants can range from negative – when self-pollen interferes with fecundity due to incompatibility mechanisms, to positive – when pollen availability is associated with increased pollinator visitation and fecundity due to its utilization as a reward. We investigated the responses of bees to pollen and nectar rewards, and the effects of these rewards on pollen deposition and fecundity in the hermaphroditic succulent shrub Aloe tenuior. Self-pollinated plants failed to set fruit, but their ovules were regularly penetrated by self-pollen tubes, which uniformly failed to develop into seeds as expected from ovarian self-incompatibility (or strong early inbreeding depression). Bees consistently foraged for pollen during the morning and early afternoon, but switched to nectar in the late afternoon. As a consequence of this differential foraging, we were able to test the relative contribution to fecundity of pollen- versus nectar-collecting flower visitors. We exposed emasculated and intact flowers in either the morning or late afternoon to foraging bees and showed that emasculation reduced pollen deposition by insects in the morning, but had little effect in the afternoon. Despite the potential for self-pollination to result in ovule discounting due to late-acting self-sterility, fecundity was severely reduced in artificially emasculated plants. Although there were temporal fluctuations in reward preference, most bee visits were for pollen rewards. Therefore the benefit of providing pollen that is accessible to bee foragers outweighs any potential costs to fitness in terms of gender interference in this species.
- Full Text:
- Authors: Duffy, Karl J , Johnson, Steven D , Peter, Craig I
- Date: 2014
- Language: English
- Type: Article
- Identifier: vital:6561 , http://hdl.handle.net/10962/d1011735 , http://dx.doi.org/10.1371/journal.pone.0094908
- Description: The net effect of pollen production on fecundity in plants can range from negative – when self-pollen interferes with fecundity due to incompatibility mechanisms, to positive – when pollen availability is associated with increased pollinator visitation and fecundity due to its utilization as a reward. We investigated the responses of bees to pollen and nectar rewards, and the effects of these rewards on pollen deposition and fecundity in the hermaphroditic succulent shrub Aloe tenuior. Self-pollinated plants failed to set fruit, but their ovules were regularly penetrated by self-pollen tubes, which uniformly failed to develop into seeds as expected from ovarian self-incompatibility (or strong early inbreeding depression). Bees consistently foraged for pollen during the morning and early afternoon, but switched to nectar in the late afternoon. As a consequence of this differential foraging, we were able to test the relative contribution to fecundity of pollen- versus nectar-collecting flower visitors. We exposed emasculated and intact flowers in either the morning or late afternoon to foraging bees and showed that emasculation reduced pollen deposition by insects in the morning, but had little effect in the afternoon. Despite the potential for self-pollination to result in ovule discounting due to late-acting self-sterility, fecundity was severely reduced in artificially emasculated plants. Although there were temporal fluctuations in reward preference, most bee visits were for pollen rewards. Therefore the benefit of providing pollen that is accessible to bee foragers outweighs any potential costs to fitness in terms of gender interference in this species.
- Full Text:
Catching on to concatenation : evidence for prepollination intrasexual selection in plants
- Peter, Craig I, Shuttleworth, Adam
- Authors: Peter, Craig I , Shuttleworth, Adam
- Date: 2013
- Language: English
- Type: Article
- Identifier: vital:6560 , http://hdl.handle.net/10962/d1011615 , http://dx.doi.org/10.1111/nph.12838
- Description: [from introduction] Darwin (1871) proposed the mechanism of sexual selection to explain the extreme traits, secondary sex characters, seen primarily in male animals for either display or competition. These elaborate traits for attracting members of the opposite sex or competing for access to mates, inter- and intra-sexual selection, respectively, would increase the mating success of individuals but may reduce individual survival. Sexual selection has traditionally been associated with motile, dioecious animals that have well-developed sensory abilities and has long been viewed as absent as a mode of selection in plants (Grant, 1995). However, since the 1980s, several workers have argued that sexual selection is applicable to plants and should be considered as a factor in floral evolution (Skogsmyr & Lankinen, 2002). Opponents such as Grant (1995) point to incompatibility with Darwin’s usage, hermaphroditism, the absence of obvious secondary sex characters and the apparent absence of female choice in plants (Skogsmyr & Lankinen, 2002; Moore & Pannell, 2011). Proponents, however, argue that historical definitions should be expanded to explain modern evidence and that sexual selection can, in principle, occur in hermaphrodites and hence play a role in the evolution of floral traits. The latter view is supported by a recent study by Cocucci et al. (this issue of New Phytologist, pp. 280–286) which demonstrates intra-sexual selection in plants via direct male–male competition between the pollinaria of milkweeds for optimal attachment sites on pollinators to ensure subsequent pollinium deposition. This is the first example of male–male competition resulting in secondary sex characters in hermaphrodite plants, highlighting the possibility of overlooked mechanisms of sexual selection in plants.
- Full Text:
- Authors: Peter, Craig I , Shuttleworth, Adam
- Date: 2013
- Language: English
- Type: Article
- Identifier: vital:6560 , http://hdl.handle.net/10962/d1011615 , http://dx.doi.org/10.1111/nph.12838
- Description: [from introduction] Darwin (1871) proposed the mechanism of sexual selection to explain the extreme traits, secondary sex characters, seen primarily in male animals for either display or competition. These elaborate traits for attracting members of the opposite sex or competing for access to mates, inter- and intra-sexual selection, respectively, would increase the mating success of individuals but may reduce individual survival. Sexual selection has traditionally been associated with motile, dioecious animals that have well-developed sensory abilities and has long been viewed as absent as a mode of selection in plants (Grant, 1995). However, since the 1980s, several workers have argued that sexual selection is applicable to plants and should be considered as a factor in floral evolution (Skogsmyr & Lankinen, 2002). Opponents such as Grant (1995) point to incompatibility with Darwin’s usage, hermaphroditism, the absence of obvious secondary sex characters and the apparent absence of female choice in plants (Skogsmyr & Lankinen, 2002; Moore & Pannell, 2011). Proponents, however, argue that historical definitions should be expanded to explain modern evidence and that sexual selection can, in principle, occur in hermaphrodites and hence play a role in the evolution of floral traits. The latter view is supported by a recent study by Cocucci et al. (this issue of New Phytologist, pp. 280–286) which demonstrates intra-sexual selection in plants via direct male–male competition between the pollinaria of milkweeds for optimal attachment sites on pollinators to ensure subsequent pollinium deposition. This is the first example of male–male competition resulting in secondary sex characters in hermaphrodite plants, highlighting the possibility of overlooked mechanisms of sexual selection in plants.
- Full Text:
Large pollen loads of a South African asclepiad do not interfere with the foraging behaviour or efficiency of pollinating honey bees
- Coombs, Gareth, Dold, Anthony P, Brassine, Eleanor I, Peter, Craig I
- Authors: Coombs, Gareth , Dold, Anthony P , Brassine, Eleanor I , Peter, Craig I
- Date: 2012
- Language: English
- Type: Article
- Identifier: vital:6509 , http://hdl.handle.net/10962/d1005936
- Description: The pollen of asclepiads (Asclepiadoideae, Apocynaceae) and most orchids (Orchidaceae) are packaged as large aggregations known as pollinaria that are removed as entire units by pollinators. In some instances, individual pollinators may accumulate large loads of these pollinaria. We found that the primary pollinator of Cynanchum ellipticum (Apocynaceae-Asclepiadoideae), the honey bee Apis mellifera, accumulate very large agglomerations of pollinaria on their mouthparts when foraging on this species. We tested whether large pollinarium loads negatively affected the foraging behaviour and foraging efficiency of honey bees by slowing foraging speeds or causing honey bees to visit fewer flowers, and found no evidence to suggest that large pollinarium loads altered foraging behaviour. C. ellipticum displayed consistently high levels of pollination success and pollen transfer efficiency (PTE). This may be a consequence of efficiently loading large numbers of pollinaria onto pollinators even when primary points of attachment on pollinators are already occupied and doing so in a manner that does not impact the foraging behaviour of pollinating insects.
- Full Text:
- Authors: Coombs, Gareth , Dold, Anthony P , Brassine, Eleanor I , Peter, Craig I
- Date: 2012
- Language: English
- Type: Article
- Identifier: vital:6509 , http://hdl.handle.net/10962/d1005936
- Description: The pollen of asclepiads (Asclepiadoideae, Apocynaceae) and most orchids (Orchidaceae) are packaged as large aggregations known as pollinaria that are removed as entire units by pollinators. In some instances, individual pollinators may accumulate large loads of these pollinaria. We found that the primary pollinator of Cynanchum ellipticum (Apocynaceae-Asclepiadoideae), the honey bee Apis mellifera, accumulate very large agglomerations of pollinaria on their mouthparts when foraging on this species. We tested whether large pollinarium loads negatively affected the foraging behaviour and foraging efficiency of honey bees by slowing foraging speeds or causing honey bees to visit fewer flowers, and found no evidence to suggest that large pollinarium loads altered foraging behaviour. C. ellipticum displayed consistently high levels of pollination success and pollen transfer efficiency (PTE). This may be a consequence of efficiently loading large numbers of pollinaria onto pollinators even when primary points of attachment on pollinators are already occupied and doing so in a manner that does not impact the foraging behaviour of pollinating insects.
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The invasive ‘mothcatcher’ (Araujia sericifera Brot.; Asclepiadoideae) co-opts native honeybees as its primary pollinator in South Africa
- Coombs, Gareth, Peter, Craig I
- Authors: Coombs, Gareth , Peter, Craig I
- Date: 2010
- Language: English
- Type: Article
- Identifier: vital:6510 , http://hdl.handle.net/10962/d1005937
- Description: Background and aims: Successful invasive plants such as Araujia sericifera usually either are capable of automatic self-pollination or maintain pollinator services by having generalized pollination systems to make use of local pollinators in the invaded range. Alternatively, plants must co-opt new pollinators with similar morphology to native pollinators or reproduce asexually. We aimed to document the pollination biology of A. sericifera in South Africa. Given the success of this species as an invader, we predicted that sexual reproduction occurs either through self-pollination or because A. sericifera has successfully co-opted native insect pollinators. Methodology: We examined the pollination biology of the South American A. sericifera in South Africa. We documented the effective pollinators including a comparison of the efficacy of nocturnal versus diurnal pollinators as well as the breeding system and long-term natural levels of the pollination success of this species. Principal results: We found that native honeybees (Apis mellifera) were the main pollinators of A. sericifera in South Africa. Visiting moths are unimportant pollinators despite being attracted by the pale colour and nocturnal scent of the flowers. Plants from the Grahamstown population were incapable of autonomous self-pollination but pollinator-mediated self-pollination does occur. However, the highest fruit initiation resulted from out-crossed pollination treatments. The high pollen transfer efficiency of this species was comparable to other hymenopteranpollinated exotic and native milkweeds, suggesting that A. sericifera maintains pollinator services at levels experienced by indigenous asclepiad species. Conclusions: Araujia sericifera reproduces successfully in South Africa due to a combined ability of this species to attract and exploit native honeybees as its pollinators and of individual plants to set fruit from pollinator-mediated self-pollination.
- Full Text:
- Authors: Coombs, Gareth , Peter, Craig I
- Date: 2010
- Language: English
- Type: Article
- Identifier: vital:6510 , http://hdl.handle.net/10962/d1005937
- Description: Background and aims: Successful invasive plants such as Araujia sericifera usually either are capable of automatic self-pollination or maintain pollinator services by having generalized pollination systems to make use of local pollinators in the invaded range. Alternatively, plants must co-opt new pollinators with similar morphology to native pollinators or reproduce asexually. We aimed to document the pollination biology of A. sericifera in South Africa. Given the success of this species as an invader, we predicted that sexual reproduction occurs either through self-pollination or because A. sericifera has successfully co-opted native insect pollinators. Methodology: We examined the pollination biology of the South American A. sericifera in South Africa. We documented the effective pollinators including a comparison of the efficacy of nocturnal versus diurnal pollinators as well as the breeding system and long-term natural levels of the pollination success of this species. Principal results: We found that native honeybees (Apis mellifera) were the main pollinators of A. sericifera in South Africa. Visiting moths are unimportant pollinators despite being attracted by the pale colour and nocturnal scent of the flowers. Plants from the Grahamstown population were incapable of autonomous self-pollination but pollinator-mediated self-pollination does occur. However, the highest fruit initiation resulted from out-crossed pollination treatments. The high pollen transfer efficiency of this species was comparable to other hymenopteranpollinated exotic and native milkweeds, suggesting that A. sericifera maintains pollinator services at levels experienced by indigenous asclepiad species. Conclusions: Araujia sericifera reproduces successfully in South Africa due to a combined ability of this species to attract and exploit native honeybees as its pollinators and of individual plants to set fruit from pollinator-mediated self-pollination.
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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:
- 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.
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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:
- 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.
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Doing the twist: a test of Darwin's cross-pollination hypothesis for pollinarium reconfiguration
- Peter, Craig I, Johnson, Steven D
- Authors: Peter, Craig I , Johnson, Steven D
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6534 , http://hdl.handle.net/10962/d1005975
- Description: Mating success in plants depends largely on the efficiency of pollen dispersal. For hermaphrodite plants, self-pollination, either within or among flowers, can reduce mating opportunities because of pollen and ovule discounting and inbreeding depression. Self-pollination may be particularly detrimental in plants such as orchids and asclepiads that package each flower’s pollen into one or more pollinia which, together with accessory structures, comprise a pollinarium. Darwin proposed that physical reconfiguration of pollinaria serves as a mechanism for reducing the likelihood of self-pollination. To be effective, the time taken for pollinarium reconfiguration would need to exceed that spent by a pollinator on a plant. We investigated pollinarium reconfiguration (including pollinarium bending, pollinium shrinking and anther cap retention) in 19 species and found a strong positive relationship between reconfiguration time and the duration of pollinator visits. Reconfiguration times were also consistently longer than pollinator visit times. These results provide strong support for Darwin’s idea that this mechanism promotes cross-pollination. , Elsevier
- Full Text:
- Authors: Peter, Craig I , Johnson, Steven D
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6534 , http://hdl.handle.net/10962/d1005975
- Description: Mating success in plants depends largely on the efficiency of pollen dispersal. For hermaphrodite plants, self-pollination, either within or among flowers, can reduce mating opportunities because of pollen and ovule discounting and inbreeding depression. Self-pollination may be particularly detrimental in plants such as orchids and asclepiads that package each flower’s pollen into one or more pollinia which, together with accessory structures, comprise a pollinarium. Darwin proposed that physical reconfiguration of pollinaria serves as a mechanism for reducing the likelihood of self-pollination. To be effective, the time taken for pollinarium reconfiguration would need to exceed that spent by a pollinator on a plant. We investigated pollinarium reconfiguration (including pollinarium bending, pollinium shrinking and anther cap retention) in 19 species and found a strong positive relationship between reconfiguration time and the duration of pollinator visits. Reconfiguration times were also consistently longer than pollinator visit times. These results provide strong support for Darwin’s idea that this mechanism promotes cross-pollination. , Elsevier
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Pollination biology of Bergeranthus multiceps (Aizoaceae) with preliminary observations of repeated flower opening and closure
- Peter, Craig I, Dold, Anthony P, Barker, Nigel P, Ripley, Bradford S
- Authors: Peter, Craig I , Dold, Anthony P , Barker, Nigel P , Ripley, Bradford S
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6529 , http://hdl.handle.net/10962/d1005970
- Description: Little is known about pollination of the Aizoaceae (Mesembryanthemaceae). There are sparse reports of generalist pollination in the family by a variety of insects (predominantly bees). Furthermore, most species are self-incompatible in cultivation. In this study, observations were made on two populations of Bergeranthus multiceps (Salm-Dyck) Schwantes growing in the Eastern Cape province of South Africa. Insects visiting the flowers were collected and examined for pollen. While 79 individual insects (in 24 genera representing 14 families and four orders) were collected visiting the flowers, the majority (43 individuals) were female Allodapula variegata bees (Apidae, subfamily Xylocopinae, tribe Allodapini)collecting pollen. All other bee visitors were also female, suggesting pollen collection as the primary activity at the flowers. The protandrous flowers were found to be self-incompatible, pointing to the importance of bee-mediated xenogamy in this species. The flowers of B. multiceps are bright yellow in the human visual spectrum. In addition, the petals of this species reflect ultraviolet light. In contrast, the yellow anthers absorb UV. Flower opening and closing is common in the Aizoaceae. Interestingly, in B. multiceps flowers open at about 15:30 and remain open for approximately three hours before closing again in the late afternoon. These afternoon flower opening events were found to be closely correlated to ambient temperatures above 23°C, relative humidity lower than 50% and vapour pressure deficit below 1.05 kPa measured from as early as 09:00 on the days when flowers opened.
- Full Text:
- Authors: Peter, Craig I , Dold, Anthony P , Barker, Nigel P , Ripley, Bradford S
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6529 , http://hdl.handle.net/10962/d1005970
- Description: Little is known about pollination of the Aizoaceae (Mesembryanthemaceae). There are sparse reports of generalist pollination in the family by a variety of insects (predominantly bees). Furthermore, most species are self-incompatible in cultivation. In this study, observations were made on two populations of Bergeranthus multiceps (Salm-Dyck) Schwantes growing in the Eastern Cape province of South Africa. Insects visiting the flowers were collected and examined for pollen. While 79 individual insects (in 24 genera representing 14 families and four orders) were collected visiting the flowers, the majority (43 individuals) were female Allodapula variegata bees (Apidae, subfamily Xylocopinae, tribe Allodapini)collecting pollen. All other bee visitors were also female, suggesting pollen collection as the primary activity at the flowers. The protandrous flowers were found to be self-incompatible, pointing to the importance of bee-mediated xenogamy in this species. The flowers of B. multiceps are bright yellow in the human visual spectrum. In addition, the petals of this species reflect ultraviolet light. In contrast, the yellow anthers absorb UV. Flower opening and closing is common in the Aizoaceae. Interestingly, in B. multiceps flowers open at about 15:30 and remain open for approximately three hours before closing again in the late afternoon. These afternoon flower opening events were found to be closely correlated to ambient temperatures above 23°C, relative humidity lower than 50% and vapour pressure deficit below 1.05 kPa measured from as early as 09:00 on the days when flowers opened.
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Comparing models for predicting species' potential distributions : a case study using correlative and mechanistic predictive modelling techniques
- Robertson, Mark P, Peter, Craig I, Villet, Martin H, Ripley, Bradford S
- Authors: Robertson, Mark P , Peter, Craig I , Villet, Martin H , Ripley, Bradford S
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6539 , http://hdl.handle.net/10962/d1005980 , http://dx.doi.org/10.1016/S0304-3800(03)00028-0
- Description: Models used to predict species’ potential distributions have been described as either correlative or mechanistic. We attempted to determine whether correlative models could perform as well as mechanistic models for predicting species potential distributions, using a case study. We compared potential distribution predictions made for a coastal dune plant (Scaevola plumieri) along the coast of South Africa, using a mechanistic model based on summer water balance (SWB), and two correlative models (a profile and a group discrimination technique). The profile technique was based on principal components analysis (PCA) and the group-discrimination technique was based on multiple logistic regression (LR). Kappa (κ) statistics were used to objectively assess model performance and model agreement. Model performance was calculated by measuring the levels of agreement (using κ) between a set of testing localities (distribution records not used for model building) and each of the model predictions. Using published interpretive guidelines for the kappa statistic, model performance was “excellent” for the SWB model (κ=0.852), perfect for the LR model (κ=1.000), and “very good” for the PCA model (κ=0.721). Model agreement was calculated by measuring the level of agreement between the mechanistic model and the two correlative models. There was “good” model agreement between the SWB and PCA models (κ=0.679) and “very good” agreement between the SWB and LR models (κ=0.786). The results suggest that correlative models can perform as well as or better than simple mechanistic models. The predictions generated from these three modelling designs are likely to generate different insights into the potential distribution and biology of the target organism and may be appropriate in different situations. The choice of model is likely to be influenced by the aims of the study, the biology of the target organism, the level of knowledge the target organism’s biology, and data quality.
- Full Text:
- Authors: Robertson, Mark P , Peter, Craig I , Villet, Martin H , Ripley, Bradford S
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6539 , http://hdl.handle.net/10962/d1005980 , http://dx.doi.org/10.1016/S0304-3800(03)00028-0
- Description: Models used to predict species’ potential distributions have been described as either correlative or mechanistic. We attempted to determine whether correlative models could perform as well as mechanistic models for predicting species potential distributions, using a case study. We compared potential distribution predictions made for a coastal dune plant (Scaevola plumieri) along the coast of South Africa, using a mechanistic model based on summer water balance (SWB), and two correlative models (a profile and a group discrimination technique). The profile technique was based on principal components analysis (PCA) and the group-discrimination technique was based on multiple logistic regression (LR). Kappa (κ) statistics were used to objectively assess model performance and model agreement. Model performance was calculated by measuring the levels of agreement (using κ) between a set of testing localities (distribution records not used for model building) and each of the model predictions. Using published interpretive guidelines for the kappa statistic, model performance was “excellent” for the SWB model (κ=0.852), perfect for the LR model (κ=1.000), and “very good” for the PCA model (κ=0.721). Model agreement was calculated by measuring the level of agreement between the mechanistic model and the two correlative models. There was “good” model agreement between the SWB and PCA models (κ=0.679) and “very good” agreement between the SWB and LR models (κ=0.786). The results suggest that correlative models can perform as well as or better than simple mechanistic models. The predictions generated from these three modelling designs are likely to generate different insights into the potential distribution and biology of the target organism and may be appropriate in different situations. The choice of model is likely to be influenced by the aims of the study, the biology of the target organism, the level of knowledge the target organism’s biology, and data quality.
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Environmental limits to the distribution of Scaevola plumieri along the South African coast
- Peter, Craig I, Ripley, Bradford S, Robertson, Mark P
- Authors: Peter, Craig I , Ripley, Bradford S , Robertson, Mark P
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6872 , http://hdl.handle.net/10962/d1011617
- Description: Scaevola plumieri is an important pioneer on many tropical and subtropical sand dunes, forming a large perennial subterranean plant with only the tips of the branches emerging above accreting sand. In South Africa it is the dominant pioneer on sandy beaches along the east coast, less abundant on the south coast and absent from the southwest and west coasts. Transpiration rates (E) of S. plumieri are predictably related to atmospheric vapour pressure deficit under a wide range of conditions and can therefore be predicted from measurement of ambient temperature and relative humidity. Scaling measurements of E at the leaf level to the canopy level has been demonstrated previously. Using a geographic information system, digital maps of regional climatic variables were used to calculate digital maps of potential transpiration from mean monthly temperature and relative humidity values, effectively scaling canopy level transpiration rates to a regional level. Monthly potential transpiration was subtracted from the monthly median rainfall to produce a map of mean monthly water balance. Seasonal growth was correlated with seasonal water balance. Localities along the coast with water deficits in summer corresponded with the recorded absence of S. plumieri, which grows and reproduces most actively in the summer months. This suggests that reduced water availability during the summer growth period limits the distribution of S. plumieri along the southwest coast, where water deficits develop in summer. Temperature is also important in limiting the distribution of S. plumieri on the southwest coast of South Africa through its effects on the growth and phenology of the plant.
- Full Text:
- Authors: Peter, Craig I , Ripley, Bradford S , Robertson, Mark P
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6872 , http://hdl.handle.net/10962/d1011617
- Description: Scaevola plumieri is an important pioneer on many tropical and subtropical sand dunes, forming a large perennial subterranean plant with only the tips of the branches emerging above accreting sand. In South Africa it is the dominant pioneer on sandy beaches along the east coast, less abundant on the south coast and absent from the southwest and west coasts. Transpiration rates (E) of S. plumieri are predictably related to atmospheric vapour pressure deficit under a wide range of conditions and can therefore be predicted from measurement of ambient temperature and relative humidity. Scaling measurements of E at the leaf level to the canopy level has been demonstrated previously. Using a geographic information system, digital maps of regional climatic variables were used to calculate digital maps of potential transpiration from mean monthly temperature and relative humidity values, effectively scaling canopy level transpiration rates to a regional level. Monthly potential transpiration was subtracted from the monthly median rainfall to produce a map of mean monthly water balance. Seasonal growth was correlated with seasonal water balance. Localities along the coast with water deficits in summer corresponded with the recorded absence of S. plumieri, which grows and reproduces most actively in the summer months. This suggests that reduced water availability during the summer growth period limits the distribution of S. plumieri along the southwest coast, where water deficits develop in summer. Temperature is also important in limiting the distribution of S. plumieri on the southwest coast of South Africa through its effects on the growth and phenology of the plant.
- Full Text:
Pollination success in a deceptive orchid is enhanced by co-occurring rewarding magnet plants
- Johnson, Steven D, Peter, Craig I, Nilsson, L Anders, Agren, Jon
- Authors: Johnson, Steven D , Peter, Craig I , Nilsson, L Anders , Agren, Jon
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6520 , http://hdl.handle.net/10962/d1005949 , http://www.jstor.org/stable/3449962
- Description: It has been debated whether pollination success in nonrewarding plants that flower in association with nectar-producing plants will be diminished by competition for pollinator visits or, alternatively, enhanced through increased local abundance of pollinators (the magnet species effect). We experimentally evaluated these effects using the nonrewarding bumblebee-pollinated orchid Anacamptis morio and associated nectar-producing plants at a site in Sweden. Pollination success (estimated as pollen receipt and pollen removal) in A. morio was significantly greater for individuals translocated to patches of nectar-producing plants (Geum rivale and Allium schoenoprasum) than for individuals placed outside (similar to20 m away) such patches. These results provide support for the existence of a facilitative magnet species effect in the interaction between certain nectar plants and A. morio. To determine the spatial scale of these interactions, we correlated the visitation rate to flowers of A. morio with the density of sympatric nectar plants in 1-m(2) and 100-m(2) plots centered around groups of translocated plants, and at the level of whole meadows (similar to0.5-2 ha). Visitation rate to flowers of A. morio was not correlated with the 1-m(2) patch density of G. rivale and A. schoenoprasum, but showed a significant positive relationship with density of these nectar plants in 100-m(2) plots. In addition, visitation to flowers of A. morio was strongly and positively related to the density of A. schoenoprasum at the level of the meadow. Choice experiments showed that bees foraging on the purple flowers of A. schoenoprasum (a particularly effective magnet species) visit the purple flowers of A. morio more readily (47.6% of choices) than bees foraging on the yellow flowers of Lotus corniculatus (17% of choices). Overall similarity in flower color and shape may increase the probability that a pollinator will temporarily shift from a nectar-producing "magnet" plant to a nonrewarding plant. We discuss the possibility of a mimicry continuum between those orchids that exploit instinctive food-seeking behavior of pollinators and those that show an adaptive resemblance to nectar-producing plants.
- Full Text:
- Authors: Johnson, Steven D , Peter, Craig I , Nilsson, L Anders , Agren, Jon
- Date: 2003
- Language: English
- Type: Article
- Identifier: vital:6520 , http://hdl.handle.net/10962/d1005949 , http://www.jstor.org/stable/3449962
- Description: It has been debated whether pollination success in nonrewarding plants that flower in association with nectar-producing plants will be diminished by competition for pollinator visits or, alternatively, enhanced through increased local abundance of pollinators (the magnet species effect). We experimentally evaluated these effects using the nonrewarding bumblebee-pollinated orchid Anacamptis morio and associated nectar-producing plants at a site in Sweden. Pollination success (estimated as pollen receipt and pollen removal) in A. morio was significantly greater for individuals translocated to patches of nectar-producing plants (Geum rivale and Allium schoenoprasum) than for individuals placed outside (similar to20 m away) such patches. These results provide support for the existence of a facilitative magnet species effect in the interaction between certain nectar plants and A. morio. To determine the spatial scale of these interactions, we correlated the visitation rate to flowers of A. morio with the density of sympatric nectar plants in 1-m(2) and 100-m(2) plots centered around groups of translocated plants, and at the level of whole meadows (similar to0.5-2 ha). Visitation rate to flowers of A. morio was not correlated with the 1-m(2) patch density of G. rivale and A. schoenoprasum, but showed a significant positive relationship with density of these nectar plants in 100-m(2) plots. In addition, visitation to flowers of A. morio was strongly and positively related to the density of A. schoenoprasum at the level of the meadow. Choice experiments showed that bees foraging on the purple flowers of A. schoenoprasum (a particularly effective magnet species) visit the purple flowers of A. morio more readily (47.6% of choices) than bees foraging on the yellow flowers of Lotus corniculatus (17% of choices). Overall similarity in flower color and shape may increase the probability that a pollinator will temporarily shift from a nectar-producing "magnet" plant to a nonrewarding plant. We discuss the possibility of a mimicry continuum between those orchids that exploit instinctive food-seeking behavior of pollinators and those that show an adaptive resemblance to nectar-producing plants.
- Full Text:
An empirical formula for estimating the water use of Scaevola plumieri
- Peter, Craig I, Ripley, Bradford S
- Authors: Peter, Craig I , Ripley, Bradford S
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6530 , http://hdl.handle.net/10962/d1005971
- Description: Transpirational water loss of Scaevola plumieri (L) Vahl. (= Scaevola thunbergii Eckl. & Zeyh.) (Goodeniaceae), a dune pioneer plant along the eastern and southern coasts of South Africa, was measured over a wide range of atmospheric conditions and related to the atmospheric vapour pressure deficit (VPD). A plot of leaf transpiration rate (E) against VPD yielded a curvilinear relationship (r[sup 2] = 0.88, P = 0.000). As both leaf and canopy E were found to be closely coupled to atmospheric conditions, this correlation was used to calculate canopy E for entire days. The bulk volumes of water transpired per day were related to the mean daily temperature as recorded at a nearby weather station and were strongly related (r2 = 0.71, P = 0.0037). This correlation allowed the bulk volume of water transpired by one square metre of a S. plumieri-covered dune to be calculated on a daily basis for an entire year. Transpirational losses (566 litres) in 1997 were then compared with rainfall (539 litres), indicating that rainfall was perhaps insufficient to support the plants that year. Similar deficits were calculated for 1996, suggesting that plants were possibly reliant on water stored in the sand or taped ground water. This species showed an unusual positive response of increasing leaf conductance to increasing VPD over the range 0-3 kPa.
- Full Text: false
- Authors: Peter, Craig I , Ripley, Bradford S
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6530 , http://hdl.handle.net/10962/d1005971
- Description: Transpirational water loss of Scaevola plumieri (L) Vahl. (= Scaevola thunbergii Eckl. & Zeyh.) (Goodeniaceae), a dune pioneer plant along the eastern and southern coasts of South Africa, was measured over a wide range of atmospheric conditions and related to the atmospheric vapour pressure deficit (VPD). A plot of leaf transpiration rate (E) against VPD yielded a curvilinear relationship (r[sup 2] = 0.88, P = 0.000). As both leaf and canopy E were found to be closely coupled to atmospheric conditions, this correlation was used to calculate canopy E for entire days. The bulk volumes of water transpired per day were related to the mean daily temperature as recorded at a nearby weather station and were strongly related (r2 = 0.71, P = 0.0037). This correlation allowed the bulk volume of water transpired by one square metre of a S. plumieri-covered dune to be calculated on a daily basis for an entire year. Transpirational losses (566 litres) in 1997 were then compared with rainfall (539 litres), indicating that rainfall was perhaps insufficient to support the plants that year. Similar deficits were calculated for 1996, suggesting that plants were possibly reliant on water stored in the sand or taped ground water. This species showed an unusual positive response of increasing leaf conductance to increasing VPD over the range 0-3 kPa.
- Full Text: false
Phloem loading in the sucrose-export-defective (SXD-1) mutant maize is limited by callose deposition at plasmodesmata in bundle sheath-vascular parenchyma interface
- Botha, Christiaan E J, Cross, Robin H M, Van Bel, A J E, Peter, Craig I
- Authors: Botha, Christiaan E J , Cross, Robin H M , Van Bel, A J E , Peter, Craig I
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6503 , http://hdl.handle.net/10962/d1005926
- Description: Using Lucifer Yellow we have demonstrated that the phloem-loading pathway from the mesophyll to the bundle sheath-vascular parenchyma interface in Zea mays source leaves follows a symplasmic route in small and intermediate vascular bundles in control as well as in the green sections of mutant sucrose-export-defective (SXD-1) plants. In the anthocyanin-rich mutant leaf sections, Lucifer Yellow transport was prohibited along the same path, at the bundle sheath-vascular parenchyma interface in particular. Plasmodesmata at the latter interface in SXD-1 anthocyanin-rich leaf sections appear to be structurally altered through callose deposition at the plasmodesmal orifices. We suggest that a transport bottleneck at the bundle sheath-vascular parenchyma interface is thus orchestrated and regulated through callose formation, preventing symplasmic transport across this important loading interface.
- Full Text:
- Authors: Botha, Christiaan E J , Cross, Robin H M , Van Bel, A J E , Peter, Craig I
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6503 , http://hdl.handle.net/10962/d1005926
- Description: Using Lucifer Yellow we have demonstrated that the phloem-loading pathway from the mesophyll to the bundle sheath-vascular parenchyma interface in Zea mays source leaves follows a symplasmic route in small and intermediate vascular bundles in control as well as in the green sections of mutant sucrose-export-defective (SXD-1) plants. In the anthocyanin-rich mutant leaf sections, Lucifer Yellow transport was prohibited along the same path, at the bundle sheath-vascular parenchyma interface in particular. Plasmodesmata at the latter interface in SXD-1 anthocyanin-rich leaf sections appear to be structurally altered through callose deposition at the plasmodesmal orifices. We suggest that a transport bottleneck at the bundle sheath-vascular parenchyma interface is thus orchestrated and regulated through callose formation, preventing symplasmic transport across this important loading interface.
- Full Text:
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