Quantitative plant-wood nesting bee interaction networks sampled across four different post-fire ... more Quantitative plant-wood nesting bee interaction networks sampled across four different post-fire age categories (freshly-burnt, intermediate-burnt, old-burnt and unburnt) in an arid ecosystem (Monte Desert of Villavicencio Nature Reserve, Mendoza, Argentina). Plant-bee interaction weights were estimated as the proportion of pollen grains from each plant species found on the trap-nest cells. The .zip file contains: the interaction matrices of the 14 sites; the diversity of floral resources available at each site (‘floral_resources.csv’); and a file with species ids, their respective codes used in the interaction matrices, and the post-fire age category of each site (‘species_ids_and_postfire_categories.xls’)
1. The study of plant-pollinator interactions in a network context is receiving increasing attent... more 1. The study of plant-pollinator interactions in a network context is receiving increasing attention. This approach has helped to identify several emerging network patterns such as nestedness and modularity. However, most studies are based only on qualitative information, and some ecosystems, such as deserts and tropical forests, are underrepresented in these data sets. 2. We present an exhaustive analysis of the structure of a 4-year plant-pollinator network from the Monte desert in Argentina using qualitative and quantitative tools. We describe the structure of this network and evaluate sampling completeness using asymptotic species richness estimators. Our goal is to assess the extent to which the realized sampling effort allows for an accurate description of species interactions and to estimate the minimum number of additional censuses required to detect 90% of the interactions. We evaluated completeness of detection of the community-wide pollinator fauna, of the pollinator fauna associated with each plant species and of the plant-pollinator interactions. We also evaluated whether sampling completeness was influenced by plant characteristics, such as flower abundance, flower life span, number of interspecific links (degree) and selectiveness in the identity of their flower visitors, as well as sampling effort. 3. We found that this desert plant-pollinator network has a nested structure and that it exhibits modularity and high network-level generalization. 4. In spite of our high sampling effort, and although we sampled 80% of the pollinator fauna, we recorded only 55% of the interactions. Furthermore, although a 64% increase in sampling effort would suffice to detect 90% of the pollinator species, a fivefold increase in sampling effort would be necessary to detect 90% of the interactions. 5. Detection of interactions was incomplete for most plant species, particularly specialists with a long flowering season and high flower abundance, or generalists with short flowering span and scant flowers. Our results suggest that sampling of a network with the same effort for all plant species is inadequate to sample interactions. 6. Sampling the diversity of interactions is labour intensive, and most plant-pollinator networks published to date are likely to be undersampled. Our analysis allowed estimating the completeness of our sampling, the additional effort needed to detect most interactions and the plant traits that influence the detection of their interactions.
Recent studies of plant-animal mutualistic networks have assumed that interaction frequency betwe... more Recent studies of plant-animal mutualistic networks have assumed that interaction frequency between mutualists predicts species impacts (population-level effects), and that field estimates of interaction strength (per-interaction effects) are unnecessary. Although existing evidence supports this assumption for the effect of animals on plants, no studies have evaluated it for the reciprocal effect of plants on animals. We evaluate this assumption using data on the reproductive effects of pollinators on plants and the reciprocal reproductive effects of plants on pollinators. The magnitude of species impacts of plants on pollinators, the reciprocal impacts of pollinators on plants, and their asymmetry were well predicted by interaction frequency. However, interaction strength was a key determinant of the sign of species impacts. These results underscore the importance of quantifying interaction strength in studies of mutualistic networks. We also show that the distributions of interaction strengths and species impacts are highly skewed, with few strong and many weak interactions. This skewed distribution matches the pattern observed in food webs, suggesting that the community-wide organization of species interactions is fundamentally similar between mutualistic and antagonistic interactions. Our results have profound ecological implications, given the key role of interaction strength for community stability.
Most rare species appear to be specialists in plant-pollinator networks. This observation could r... more Most rare species appear to be specialists in plant-pollinator networks. This observation could result either from real ecological processes or from sampling artifacts. Several methods have been proposed to overcome these artifacts, but they have the limitation of being based on visitation data, causing interactions involving rare visitor species to remain undersampled. We propose the analysis of food composition in bee trap nests to assess the reliability of network specialization estimates. We compared data from a plant-pollinator network in the Monte Desert of Villavicencio Nature Reserve, Argentina, sampled by visit observation, and data from trap nests sampled at the same time and location. Our study shows that trap nest sampling was good for estimating rare species degree. The rare species in the networks appear to be more specialized than they really are, and the bias in the estimation of the species degree increases with the rareness. The low species degree of these rare species in the visitation networks results from insufficient sampling of the rare interactions, which could have important consequences for network structure.
Annals of the Entomological Society of America, 2005
Flea beetles of alligator weed, Alternanthera philoxeroides (Martius) Grisebach (Amaranthaceae), ... more Flea beetles of alligator weed, Alternanthera philoxeroides (Martius) Grisebach (Amaranthaceae), were collected in Argentina, Uruguay, Paraguay, and Brazil. Species in the genera Disonycha Chevrolat, Agasicles Jacoby, and Systena Chevrolat were frequently found on this weed. Systena nitentula Bechyné 1954 was the most abundant within Systena. This species is reported for the Þrst time from Argentina at north of 308 S. The male is described and holotype female is redescribed adding new diagnostic characters: mouthparts, hind wings, metendosternite, and male and female genitalia. S. nitentula is recognized by the combined characters of piceous elytra with J-shaped vittae, a small spermatheca pump, and internal median lobe sac with Þve sclerotized plates. Differences in color patterns between S. nitentula, S. tenuis Bechyné , and S. s-littera L. also are considered. S. nintentula presents three instars that can be separated through head width. New biological data based on laboratory rearing and Þeld observations shows that S. nintentula could be a monophagous species strongly associated to the alligator weed growing in terrestrial conditions. This information promotes S. nintentula as a potential biocontrol agent of this invasive weed.
Proceedings of the Royal Society B: Biological Sciences
Species respond idiosyncratically to environmental variation, which may generate phenological mis... more Species respond idiosyncratically to environmental variation, which may generate phenological mismatches. We assess the consequences of such mismatches for solitary bees. During 9 years, we studied flowering phenology and nesting phenology and demography of five wood-nesting solitary bee species representing a broad gradient of specialization/generalization in the use of floral resources. We found that the reproductive performance and population growth rate of bees tended to be lower with increasing nesting–flowering mismatches, except for the most generalized bee species. Our findings help elucidate the role of phenological mismatches for the demography of wild pollinators, which perform key ecosystem functions and provide important services for humanity. Furthermore, if climate change increases phenological mismatches in this system, we expect negative consequences of climate change for specialist bees.
... por LAURA MACHINANDIARENA1, DANIEL R. BROWN1, MARTÍN D. EHRLICH1, 2, MARCELO PÁJARO1, JIMENA ... more ... por LAURA MACHINANDIARENA1, DANIEL R. BROWN1, MARTÍN D. EHRLICH1, 2, MARCELO PÁJARO1, JIMENA DORADO2 y VALERIA TESO2 ... La distancia recorri-da necesaria para realizar el cálculo de área barrida se estimó por medio del GPS del barco, ...
Agricultural plastic waste can alter wildlife diversity and behavior. Species survival will depen... more Agricultural plastic waste can alter wildlife diversity and behavior. Species survival will depend on their ability to adapt to new environmental conditions. In a seed-producing farm, a Megachile sp. nest made fully with plastic was found in a trap nest. This record represents the first one worldwide on revealing the use of plastic in the total construction of a bee nest. solitary bees / plastic / adaptive flexibility
1. Fire represents a frequent disturbance in many ecosystems, which can affect plantpollinator as... more 1. Fire represents a frequent disturbance in many ecosystems, which can affect plantpollinator assemblages and hence the services they provide. Furthermore, fire events could affect the architecture of plant-pollinator interaction networks, modifying the structure and function of communities. 2. Some pollinators, such as wood-nesting bees, may be particularly affected by fire events due to damage to the nesting material and its long regeneration time. However, it remains unclear whether fire influences the structure of bee-plant interactions. 3. Here, we used quantitative plant-wood-nesting bee interaction networks sampled across four different post-fire age categories (from freshly-burnt to unburnt sites) in an arid ecosystem to test whether the abundance of wood-nesting bees, the breadth of resource use and the plant-bee community structure change along a post-fire age gradient. 4. We demonstrate that freshly-burnt sites present higher abundances of generalist than specialist wood-nesting bees and that this translates into lower network modularity than that of sites with greater post-fire ages. Bees do not seem to change their feeding behaviour across the post-fire age gradient despite changes in floral resource availability. 5. Despite the effects of fire on plant-bee interaction network structure, these mutualistic networks seem to be able to recover a few years after the fire event. This result suggests that these interactions might be highly resilient to this type of disturbance.
Diverse flower communities are more stable in floral resource production along the flowering seas... more Diverse flower communities are more stable in floral resource production along the flowering season, but the question about how the diversity and stability of resources affect pollinator reproduction remains open. High plant diversity could favor short foraging trips, which in turn would enhance bee fitness. In addition to plant diversity, greater temporal stability of floral resources in diverse communities could favor pollinator fitness because such communities are likely to occupy the phenological space more broadly, increasing floral availability for pollinators throughout the season. In addition, this potential effect of flower diversity on bee reproduction could be stronger for generalist pollinators because they can use a broader floral spectrum. Based on above arguments we predicted that pollinator reproduction would be positively correlated to flower diversity, and to temporal stability in flower production, and that this relationship would be stronger for the most generali...
The diversity-stability hypothesis posits that species diversity confers redundancy in function, ... more The diversity-stability hypothesis posits that species diversity confers redundancy in function, so that richer communities show higher temporal stability in ecosystem processes than poorer communities. The diversity-stability relationship has not been studied in terms of flower production before. A diverse flower community may stabilize the availability of floral resources along the floral season. Considering this type of stability is important because it could promote the stability and persistence of the pollination service. We evaluated 1) the diversity-stability relationship in floral production along a flowering season; 2) the effect of additional factors that could blur the diversity-stability relationship, such as flower abundance, elevation, and the time elapsed since the last fire, a common human disturbance in the study area; and 3) whether the most important plants for pollinators in terms of interspecific interactions contribute differentially to temporal stability. The most diverse communities were more stable in floral resource production along the flowering season. Stability of flower production was also influenced by a positive indirect effect of elevation. The plants that contributed the most to temporal stability were the most abundant and densely connected species, those at the core of the plant-pollinator network. Our study shows that species richness enhances the availability of floral resources for pollinators, providing a strong support for the diversity-stability hypothesis.
Clearance rates of Limnoperna fortunei (Bivalvia) were investigated in laboratory experiments usi... more Clearance rates of Limnoperna fortunei (Bivalvia) were investigated in laboratory experiments using monocultures of the alga Chlorella vulgaris. Experimental conditions included two mollusc sizes (15 and 23 mm), and three water temperatures (15, 20 and 25°C) covering the normal seasonal range in the lower Parana´river and Rı´o de la Plata estuary. Filtration rates obtained were, for the larger mussels: 9.9, 13.1 and 17.7 ml mg tissue dry weight À1 h À1 at 15, 20 and 25°C, respectively; and for the smaller ones: 17.7, 20.8 and 29.5 ml mg À1 h À1. Differences between sizes and between temperatures (except 15 vs. 20°C) were statistically significant. In absolute terms larger animals have higher clearance rates, but as a function of body mass smaller individuals feed more actively. Within the range of experimental values used, filtration rates were positively associated with water temperature. These clearance rates (125-350 ml individual À1 h À1) are among the highest reported for suspension feeding bivalves, including the invasive species Dreissena polymorpha, D. bugensis and Corbicula fluminea. High filtration rates, associated with the very high densities of this mollusc in the Parana´watershed (up to over 200,000 ind m À2) suggest that its environmental impact may be swiftly changing ecological conditions in the areas colonized.
... por LAURA MACHINANDIARENA1, DANIEL R. BROWN1, MARTÍN D. EHRLICH1, 2, MARCELO PÁJARO1, JIMENA ... more ... por LAURA MACHINANDIARENA1, DANIEL R. BROWN1, MARTÍN D. EHRLICH1, 2, MARCELO PÁJARO1, JIMENA DORADO2 y VALERIA TESO2 ... La distancia recorri-da necesaria para realizar el cálculo de área barrida se estimó por medio del GPS del barco, ...
The flea beetle Systena silvestrii Bechyné 1957 was studied in context with the evaluation of nat... more The flea beetle Systena silvestrii Bechyné 1957 was studied in context with the evaluation of natural enemies of the alligator weed, Alternanthera philoxeroides (Martius) Grisebach (Amaranthaceae). The female is described and the holotype male is redescribed adding ...
Résumé: Objectives: To analyse the dynamics of the Health SWAp in Mali. Methods: Questionnaire an... more Résumé: Objectives: To analyse the dynamics of the Health SWAp in Mali. Methods: Questionnaire and semi-structured interviews with various stakeholders (totalling 42 national health executives and donor representatives in 2005 and 27 in 2006) on the ...
1. The study of plant-pollinator interactions in a network context is receiving increasing attent... more 1. The study of plant-pollinator interactions in a network context is receiving increasing attention. This approach has helped to identify several emerging network patterns such as nestedness and modularity. However, most studies are based only on qualitative information, and some ecosystems, such as deserts and tropical forests, are underrepresented in these data sets. 2. We present an exhaustive analysis of the structure of a 4-year plant-pollinator network from the Monte desert in Argentina using qualitative and quantitative tools. We describe the structure of this network and evaluate sampling completeness using asymptotic species richness estimators. Our goal is to assess the extent to which the realized sampling effort allows for an accurate description of species interactions and to estimate the minimum number of additional censuses required to detect 90% of the interactions. We evaluated completeness of detection of the community-wide pollinator fauna, of the pollinator fauna associated with each plant species and of the plant-pollinator interactions. We also evaluated whether sampling completeness was influenced by plant characteristics, such as flower abundance, flower life span, number of interspecific links (degree) and selectiveness in the identity of their flower visitors, as well as sampling effort. 3. We found that this desert plant-pollinator network has a nested structure and that it exhibits modularity and high network-level generalization. 4. In spite of our high sampling effort, and although we sampled 80% of the pollinator fauna, we recorded only 55% of the interactions. Furthermore, although a 64% increase in sampling effort would suffice to detect 90% of the pollinator species, a fivefold increase in sampling effort would be necessary to detect 90% of the interactions. 5. Detection of interactions was incomplete for most plant species, particularly specialists with a long flowering season and high flower abundance, or generalists with short flowering span and scant flowers. Our results suggest that sampling of a network with the same effort for all plant species is inadequate to sample interactions. 6. Sampling the diversity of interactions is labour intensive, and most plant-pollinator networks published to date are likely to be undersampled. Our analysis allowed estimating the completeness of our sampling, the additional effort needed to detect most interactions and the plant traits that influence the detection of their interactions.
Most rare species appear to be specialists in plant-pollinator networks. This observation could r... more Most rare species appear to be specialists in plant-pollinator networks. This observation could result either from real ecological processes or from sampling artifacts. Several methods have been proposed to overcome these artifacts, but they have the limitation of being based on visitation data, causing interactions involving rare visitor species to remain undersampled. We propose the analysis of food composition in bee trap nests to assess the reliability of network specialization estimates. We compared data from a plant-pollinator network in the Monte Desert of Villavicencio Nature Reserve, Argentina, sampled by visit observation, and data from trap nests sampled at the same time and location. Our study shows that trap nest sampling was good for estimating rare species degree. The rare species in the networks appear to be more specialized than they really are, and the bias in the estimation of the species degree increases with the rareness. The low species degree of these rare species in the visitation networks results from insufficient sampling of the rare interactions, which could have important consequences for network structure.
Quantitative plant-wood nesting bee interaction networks sampled across four different post-fire ... more Quantitative plant-wood nesting bee interaction networks sampled across four different post-fire age categories (freshly-burnt, intermediate-burnt, old-burnt and unburnt) in an arid ecosystem (Monte Desert of Villavicencio Nature Reserve, Mendoza, Argentina). Plant-bee interaction weights were estimated as the proportion of pollen grains from each plant species found on the trap-nest cells. The .zip file contains: the interaction matrices of the 14 sites; the diversity of floral resources available at each site (‘floral_resources.csv’); and a file with species ids, their respective codes used in the interaction matrices, and the post-fire age category of each site (‘species_ids_and_postfire_categories.xls’)
1. The study of plant-pollinator interactions in a network context is receiving increasing attent... more 1. The study of plant-pollinator interactions in a network context is receiving increasing attention. This approach has helped to identify several emerging network patterns such as nestedness and modularity. However, most studies are based only on qualitative information, and some ecosystems, such as deserts and tropical forests, are underrepresented in these data sets. 2. We present an exhaustive analysis of the structure of a 4-year plant-pollinator network from the Monte desert in Argentina using qualitative and quantitative tools. We describe the structure of this network and evaluate sampling completeness using asymptotic species richness estimators. Our goal is to assess the extent to which the realized sampling effort allows for an accurate description of species interactions and to estimate the minimum number of additional censuses required to detect 90% of the interactions. We evaluated completeness of detection of the community-wide pollinator fauna, of the pollinator fauna associated with each plant species and of the plant-pollinator interactions. We also evaluated whether sampling completeness was influenced by plant characteristics, such as flower abundance, flower life span, number of interspecific links (degree) and selectiveness in the identity of their flower visitors, as well as sampling effort. 3. We found that this desert plant-pollinator network has a nested structure and that it exhibits modularity and high network-level generalization. 4. In spite of our high sampling effort, and although we sampled 80% of the pollinator fauna, we recorded only 55% of the interactions. Furthermore, although a 64% increase in sampling effort would suffice to detect 90% of the pollinator species, a fivefold increase in sampling effort would be necessary to detect 90% of the interactions. 5. Detection of interactions was incomplete for most plant species, particularly specialists with a long flowering season and high flower abundance, or generalists with short flowering span and scant flowers. Our results suggest that sampling of a network with the same effort for all plant species is inadequate to sample interactions. 6. Sampling the diversity of interactions is labour intensive, and most plant-pollinator networks published to date are likely to be undersampled. Our analysis allowed estimating the completeness of our sampling, the additional effort needed to detect most interactions and the plant traits that influence the detection of their interactions.
Recent studies of plant-animal mutualistic networks have assumed that interaction frequency betwe... more Recent studies of plant-animal mutualistic networks have assumed that interaction frequency between mutualists predicts species impacts (population-level effects), and that field estimates of interaction strength (per-interaction effects) are unnecessary. Although existing evidence supports this assumption for the effect of animals on plants, no studies have evaluated it for the reciprocal effect of plants on animals. We evaluate this assumption using data on the reproductive effects of pollinators on plants and the reciprocal reproductive effects of plants on pollinators. The magnitude of species impacts of plants on pollinators, the reciprocal impacts of pollinators on plants, and their asymmetry were well predicted by interaction frequency. However, interaction strength was a key determinant of the sign of species impacts. These results underscore the importance of quantifying interaction strength in studies of mutualistic networks. We also show that the distributions of interaction strengths and species impacts are highly skewed, with few strong and many weak interactions. This skewed distribution matches the pattern observed in food webs, suggesting that the community-wide organization of species interactions is fundamentally similar between mutualistic and antagonistic interactions. Our results have profound ecological implications, given the key role of interaction strength for community stability.
Most rare species appear to be specialists in plant-pollinator networks. This observation could r... more Most rare species appear to be specialists in plant-pollinator networks. This observation could result either from real ecological processes or from sampling artifacts. Several methods have been proposed to overcome these artifacts, but they have the limitation of being based on visitation data, causing interactions involving rare visitor species to remain undersampled. We propose the analysis of food composition in bee trap nests to assess the reliability of network specialization estimates. We compared data from a plant-pollinator network in the Monte Desert of Villavicencio Nature Reserve, Argentina, sampled by visit observation, and data from trap nests sampled at the same time and location. Our study shows that trap nest sampling was good for estimating rare species degree. The rare species in the networks appear to be more specialized than they really are, and the bias in the estimation of the species degree increases with the rareness. The low species degree of these rare species in the visitation networks results from insufficient sampling of the rare interactions, which could have important consequences for network structure.
Annals of the Entomological Society of America, 2005
Flea beetles of alligator weed, Alternanthera philoxeroides (Martius) Grisebach (Amaranthaceae), ... more Flea beetles of alligator weed, Alternanthera philoxeroides (Martius) Grisebach (Amaranthaceae), were collected in Argentina, Uruguay, Paraguay, and Brazil. Species in the genera Disonycha Chevrolat, Agasicles Jacoby, and Systena Chevrolat were frequently found on this weed. Systena nitentula Bechyné 1954 was the most abundant within Systena. This species is reported for the Þrst time from Argentina at north of 308 S. The male is described and holotype female is redescribed adding new diagnostic characters: mouthparts, hind wings, metendosternite, and male and female genitalia. S. nitentula is recognized by the combined characters of piceous elytra with J-shaped vittae, a small spermatheca pump, and internal median lobe sac with Þve sclerotized plates. Differences in color patterns between S. nitentula, S. tenuis Bechyné , and S. s-littera L. also are considered. S. nintentula presents three instars that can be separated through head width. New biological data based on laboratory rearing and Þeld observations shows that S. nintentula could be a monophagous species strongly associated to the alligator weed growing in terrestrial conditions. This information promotes S. nintentula as a potential biocontrol agent of this invasive weed.
Proceedings of the Royal Society B: Biological Sciences
Species respond idiosyncratically to environmental variation, which may generate phenological mis... more Species respond idiosyncratically to environmental variation, which may generate phenological mismatches. We assess the consequences of such mismatches for solitary bees. During 9 years, we studied flowering phenology and nesting phenology and demography of five wood-nesting solitary bee species representing a broad gradient of specialization/generalization in the use of floral resources. We found that the reproductive performance and population growth rate of bees tended to be lower with increasing nesting–flowering mismatches, except for the most generalized bee species. Our findings help elucidate the role of phenological mismatches for the demography of wild pollinators, which perform key ecosystem functions and provide important services for humanity. Furthermore, if climate change increases phenological mismatches in this system, we expect negative consequences of climate change for specialist bees.
... por LAURA MACHINANDIARENA1, DANIEL R. BROWN1, MARTÍN D. EHRLICH1, 2, MARCELO PÁJARO1, JIMENA ... more ... por LAURA MACHINANDIARENA1, DANIEL R. BROWN1, MARTÍN D. EHRLICH1, 2, MARCELO PÁJARO1, JIMENA DORADO2 y VALERIA TESO2 ... La distancia recorri-da necesaria para realizar el cálculo de área barrida se estimó por medio del GPS del barco, ...
Agricultural plastic waste can alter wildlife diversity and behavior. Species survival will depen... more Agricultural plastic waste can alter wildlife diversity and behavior. Species survival will depend on their ability to adapt to new environmental conditions. In a seed-producing farm, a Megachile sp. nest made fully with plastic was found in a trap nest. This record represents the first one worldwide on revealing the use of plastic in the total construction of a bee nest. solitary bees / plastic / adaptive flexibility
1. Fire represents a frequent disturbance in many ecosystems, which can affect plantpollinator as... more 1. Fire represents a frequent disturbance in many ecosystems, which can affect plantpollinator assemblages and hence the services they provide. Furthermore, fire events could affect the architecture of plant-pollinator interaction networks, modifying the structure and function of communities. 2. Some pollinators, such as wood-nesting bees, may be particularly affected by fire events due to damage to the nesting material and its long regeneration time. However, it remains unclear whether fire influences the structure of bee-plant interactions. 3. Here, we used quantitative plant-wood-nesting bee interaction networks sampled across four different post-fire age categories (from freshly-burnt to unburnt sites) in an arid ecosystem to test whether the abundance of wood-nesting bees, the breadth of resource use and the plant-bee community structure change along a post-fire age gradient. 4. We demonstrate that freshly-burnt sites present higher abundances of generalist than specialist wood-nesting bees and that this translates into lower network modularity than that of sites with greater post-fire ages. Bees do not seem to change their feeding behaviour across the post-fire age gradient despite changes in floral resource availability. 5. Despite the effects of fire on plant-bee interaction network structure, these mutualistic networks seem to be able to recover a few years after the fire event. This result suggests that these interactions might be highly resilient to this type of disturbance.
Diverse flower communities are more stable in floral resource production along the flowering seas... more Diverse flower communities are more stable in floral resource production along the flowering season, but the question about how the diversity and stability of resources affect pollinator reproduction remains open. High plant diversity could favor short foraging trips, which in turn would enhance bee fitness. In addition to plant diversity, greater temporal stability of floral resources in diverse communities could favor pollinator fitness because such communities are likely to occupy the phenological space more broadly, increasing floral availability for pollinators throughout the season. In addition, this potential effect of flower diversity on bee reproduction could be stronger for generalist pollinators because they can use a broader floral spectrum. Based on above arguments we predicted that pollinator reproduction would be positively correlated to flower diversity, and to temporal stability in flower production, and that this relationship would be stronger for the most generali...
The diversity-stability hypothesis posits that species diversity confers redundancy in function, ... more The diversity-stability hypothesis posits that species diversity confers redundancy in function, so that richer communities show higher temporal stability in ecosystem processes than poorer communities. The diversity-stability relationship has not been studied in terms of flower production before. A diverse flower community may stabilize the availability of floral resources along the floral season. Considering this type of stability is important because it could promote the stability and persistence of the pollination service. We evaluated 1) the diversity-stability relationship in floral production along a flowering season; 2) the effect of additional factors that could blur the diversity-stability relationship, such as flower abundance, elevation, and the time elapsed since the last fire, a common human disturbance in the study area; and 3) whether the most important plants for pollinators in terms of interspecific interactions contribute differentially to temporal stability. The most diverse communities were more stable in floral resource production along the flowering season. Stability of flower production was also influenced by a positive indirect effect of elevation. The plants that contributed the most to temporal stability were the most abundant and densely connected species, those at the core of the plant-pollinator network. Our study shows that species richness enhances the availability of floral resources for pollinators, providing a strong support for the diversity-stability hypothesis.
Clearance rates of Limnoperna fortunei (Bivalvia) were investigated in laboratory experiments usi... more Clearance rates of Limnoperna fortunei (Bivalvia) were investigated in laboratory experiments using monocultures of the alga Chlorella vulgaris. Experimental conditions included two mollusc sizes (15 and 23 mm), and three water temperatures (15, 20 and 25°C) covering the normal seasonal range in the lower Parana´river and Rı´o de la Plata estuary. Filtration rates obtained were, for the larger mussels: 9.9, 13.1 and 17.7 ml mg tissue dry weight À1 h À1 at 15, 20 and 25°C, respectively; and for the smaller ones: 17.7, 20.8 and 29.5 ml mg À1 h À1. Differences between sizes and between temperatures (except 15 vs. 20°C) were statistically significant. In absolute terms larger animals have higher clearance rates, but as a function of body mass smaller individuals feed more actively. Within the range of experimental values used, filtration rates were positively associated with water temperature. These clearance rates (125-350 ml individual À1 h À1) are among the highest reported for suspension feeding bivalves, including the invasive species Dreissena polymorpha, D. bugensis and Corbicula fluminea. High filtration rates, associated with the very high densities of this mollusc in the Parana´watershed (up to over 200,000 ind m À2) suggest that its environmental impact may be swiftly changing ecological conditions in the areas colonized.
... por LAURA MACHINANDIARENA1, DANIEL R. BROWN1, MARTÍN D. EHRLICH1, 2, MARCELO PÁJARO1, JIMENA ... more ... por LAURA MACHINANDIARENA1, DANIEL R. BROWN1, MARTÍN D. EHRLICH1, 2, MARCELO PÁJARO1, JIMENA DORADO2 y VALERIA TESO2 ... La distancia recorri-da necesaria para realizar el cálculo de área barrida se estimó por medio del GPS del barco, ...
The flea beetle Systena silvestrii Bechyné 1957 was studied in context with the evaluation of nat... more The flea beetle Systena silvestrii Bechyné 1957 was studied in context with the evaluation of natural enemies of the alligator weed, Alternanthera philoxeroides (Martius) Grisebach (Amaranthaceae). The female is described and the holotype male is redescribed adding ...
Résumé: Objectives: To analyse the dynamics of the Health SWAp in Mali. Methods: Questionnaire an... more Résumé: Objectives: To analyse the dynamics of the Health SWAp in Mali. Methods: Questionnaire and semi-structured interviews with various stakeholders (totalling 42 national health executives and donor representatives in 2005 and 27 in 2006) on the ...
1. The study of plant-pollinator interactions in a network context is receiving increasing attent... more 1. The study of plant-pollinator interactions in a network context is receiving increasing attention. This approach has helped to identify several emerging network patterns such as nestedness and modularity. However, most studies are based only on qualitative information, and some ecosystems, such as deserts and tropical forests, are underrepresented in these data sets. 2. We present an exhaustive analysis of the structure of a 4-year plant-pollinator network from the Monte desert in Argentina using qualitative and quantitative tools. We describe the structure of this network and evaluate sampling completeness using asymptotic species richness estimators. Our goal is to assess the extent to which the realized sampling effort allows for an accurate description of species interactions and to estimate the minimum number of additional censuses required to detect 90% of the interactions. We evaluated completeness of detection of the community-wide pollinator fauna, of the pollinator fauna associated with each plant species and of the plant-pollinator interactions. We also evaluated whether sampling completeness was influenced by plant characteristics, such as flower abundance, flower life span, number of interspecific links (degree) and selectiveness in the identity of their flower visitors, as well as sampling effort. 3. We found that this desert plant-pollinator network has a nested structure and that it exhibits modularity and high network-level generalization. 4. In spite of our high sampling effort, and although we sampled 80% of the pollinator fauna, we recorded only 55% of the interactions. Furthermore, although a 64% increase in sampling effort would suffice to detect 90% of the pollinator species, a fivefold increase in sampling effort would be necessary to detect 90% of the interactions. 5. Detection of interactions was incomplete for most plant species, particularly specialists with a long flowering season and high flower abundance, or generalists with short flowering span and scant flowers. Our results suggest that sampling of a network with the same effort for all plant species is inadequate to sample interactions. 6. Sampling the diversity of interactions is labour intensive, and most plant-pollinator networks published to date are likely to be undersampled. Our analysis allowed estimating the completeness of our sampling, the additional effort needed to detect most interactions and the plant traits that influence the detection of their interactions.
Most rare species appear to be specialists in plant-pollinator networks. This observation could r... more Most rare species appear to be specialists in plant-pollinator networks. This observation could result either from real ecological processes or from sampling artifacts. Several methods have been proposed to overcome these artifacts, but they have the limitation of being based on visitation data, causing interactions involving rare visitor species to remain undersampled. We propose the analysis of food composition in bee trap nests to assess the reliability of network specialization estimates. We compared data from a plant-pollinator network in the Monte Desert of Villavicencio Nature Reserve, Argentina, sampled by visit observation, and data from trap nests sampled at the same time and location. Our study shows that trap nest sampling was good for estimating rare species degree. The rare species in the networks appear to be more specialized than they really are, and the bias in the estimation of the species degree increases with the rareness. The low species degree of these rare species in the visitation networks results from insufficient sampling of the rare interactions, which could have important consequences for network structure.
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Papers by Jimena Dorado