scholarly journals Do an ecosystem engineer and environmental gradient act independently or in concert to shape juvenile plant communities? Tests with the leaf-cutter ant Atta laevigata in a Neotropical savanna

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e5612 ◽  
Author(s):  
Alan N. Costa ◽  
Emilio M. Bruna ◽  
Heraldo L. Vasconcelos
Keyword(s):  
Species Richness ◽  
Plant Communities ◽  
Environmental Conditions ◽  
Ecosystem Engineer ◽  
Dominant Role ◽  
Canopy Cover ◽  
Plant Establishment ◽  
Related Factors ◽  
Local Conditions ◽  
Atta Laevigata

Background Ecosystem engineers are species that transform habitats in ways that influence other species.While the impacts of many engineers have been well described, our understanding of how their impact varies along environmental gradients remains limited. Although disentangling the effects of gradients and engineers on biodiversity is complicated—the gradients themselves can be altered by engineers—doing so is necessary to advance conceptual and mathematical models of ecosystem engineering. We used leaf-cutter ants (Atta spp.) to investigate the relative influence of gradients and environmental engineers on the abundance and species richness of woody plants. Methods We conducted our research in South America’s Cerrado. With a survey of plant recruits along a canopy cover gradient, and data on environmental conditions that influence plant recruitment, we fit statistical models that addressed the following questions: (1) Does A. laevigata modify the gradient in canopy cover found in our Cerrado site? (2) Do environmental conditions that influence woody plant establishment in the Cerrado vary with canopy cover or proximity to A. laevigata nests? (3) Do A. laevigata and canopy cover act independently or in concert to influence recruit abundance and species richness? Results We found that environmental conditions previously shown to influence plant establishment in the Cerrado varied in concert with canopy cover, but that ants are not modifying the cover gradient or cover over nests. However, ants are modifying other local environmental conditions, and the magnitude and spatial extent of these changes are consistent across the gradient. In contrast to prior studies, we found that ant-related factors (e.g., proximity to nests, ant changes in surface conditions), rather than canopy cover, had the strongest effect on the abundance of plant recruits. However, the diversity of plants was influenced by both the engineer and the canopy cover gradient. Discussion Atta laevigata in the Cerrado modify local conditions in ways that have strong but spatially restricted consequences for plant communities. We hypothesize that ants indirectly reduce seedling establishment by clearing litter and reducing soil moisture, which leads to seed and seedling desiccation. Altering soil nutrients could also reduce juvenile growth and survivorship; if so these indirect negative effects of engineering could exacerbate their direct effects of harvesting plants. The effects of Atta appear restricted to nest mounds, but they could be long-lasting because mounds persist long after a colony has died or migrated. Our results support the hypothesis that leaf-cutter ants play a dominant role in Cerrado plant demography. We suggest the ecological and economic footprint of these engineers may increase dramatically in coming decades due to the transformation of the Cerrado by human activities.

scholarly journals Do an ecosystem engineer and environmental gradient act independently or in concert to shape juvenile plant communities? Tests with the leaf-cutter ant Atta laevigata in a Neotropical savanna

2018 ◽  
Author(s):  
Alan N Costa ◽  
Emilio M Bruna ◽  
Heraldo L Vasconcelos
Keyword(s):  
Species Richness ◽  
Plant Communities ◽  
Environmental Conditions ◽  
Ecosystem Engineer ◽  
Dominant Role ◽  
Canopy Cover ◽  
Plant Establishment ◽  
Related Factors ◽  
Local Conditions ◽  
Atta Laevigata

Background. Ecosystem Engineers are species that transform habitats in ways that influence other species. While the impacts of many engineers have been well described, our understanding of how their impact varies along environmental gradients remains limited. Although disentangling the effects of gradients and engineers on biodiversity is complicated – the gradients themselves can be altered by engineers – doing so is necessary to advance conceptual and mathematical models of ecosystem engineering. We used leaf-cutter ants (Atta spp.) to investigate the relative influence of gradients and environmental engineers on the abundance and species richness of woody plants. Methods. We conducted our research in South America's Cerrado. With a survey of plant recruits along a canopy cover gradient, and data on environmental conditions that influence plant recruitment, we fit statistical models that addressed the following questions: (1) Does A. laevigata modify the gradient in canopy cover found in our Cerrado site? (2) Do environmental conditions that influence woody plant establishment in the Cerrado vary with canopy cover or proximity to A. laevigata nests? (3) DoA. laevigata and canopy cover act independently or in concert to influence recruit abundance and species richness? Results. We found that environmental conditions previously shown to influence plant establishment in theCerradovaried in concert with canopy cover, but that ants are not modifying the cover gradient or cover over nests. However, ants are modifying other local environmental conditions, and the magnitude and spatial extent of these changes is consistent across the gradient. In contrast to prior studies, we found that ant-related factors (e.g., proximity to nests, ant changes in surface conditions), rather than canopy cover, had the strongest effect on the abundance of plant recruits. However, the diversity of plants was influenced by both the engineer and the canopy cover gradient. Discussion. Atta laevigata in the Cerrado modify local conditions in ways that have strong but spatially restricted consequences for plant communities. We hypothesize that ants indirectly reduce seedling establishment by clearing litter and reducing soil moisture, which leads to seed and seedling desiccation. Altering soil nutrients could also reduce juvenile growth and survivorship; if so these indirect negative effects of engineering could exacerbate their direct effects of harvesting plants. The effects ofAttaappear restricted to nest mounds, but they could be long-lasting because mounds persist long after a colony has died or migrated. Our results support the hypothesis that leaf-cutter ants play a dominant role in Cerrado plant demography. We suggest the ecological and economic footprint of these engineers may increase dramatically in coming decades due to the transformation of the Cerrado by human activities.

scholarly journals Do an ecosystem engineer and environmental gradient act independently or in concert to shape juvenile plant communities? Tests with the leaf-cutter ant Atta laevigata in a Neotropical savanna

2018 ◽  
Author(s):  
Alan N Costa ◽  
Emilio M Bruna ◽  
Heraldo L Vasconcelos
Keyword(s):  
Species Richness ◽  
Plant Communities ◽  
Environmental Conditions ◽  
Ecosystem Engineer ◽  
Dominant Role ◽  
Canopy Cover ◽  
Plant Establishment ◽  
Related Factors ◽  
Local Conditions ◽  
Atta Laevigata

Background. Ecosystem Engineers are species that transform habitats in ways that influence other species. While the impacts of many engineers have been well described, our understanding of how their impact varies along environmental gradients remains limited. Although disentangling the effects of gradients and engineers on biodiversity is complicated – the gradients themselves can be altered by engineers – doing so is necessary to advance conceptual and mathematical models of ecosystem engineering. We used leaf-cutter ants (Atta spp.) to investigate the relative influence of gradients and environmental engineers on the abundance and species richness of woody plants. Methods. We conducted our research in South America's Cerrado. With a survey of plant recruits along a canopy cover gradient, and data on environmental conditions that influence plant recruitment, we fit statistical models that addressed the following questions: (1) Does A. laevigata modify the gradient in canopy cover found in our Cerrado site? (2) Do environmental conditions that influence woody plant establishment in the Cerrado vary with canopy cover or proximity to A. laevigata nests? (3) DoA. laevigata and canopy cover act independently or in concert to influence recruit abundance and species richness? Results. We found that environmental conditions previously shown to influence plant establishment in theCerradovaried in concert with canopy cover, but that ants are not modifying the cover gradient or cover over nests. However, ants are modifying other local environmental conditions, and the magnitude and spatial extent of these changes is consistent across the gradient. In contrast to prior studies, we found that ant-related factors (e.g., proximity to nests, ant changes in surface conditions), rather than canopy cover, had the strongest effect on the abundance of plant recruits. However, the diversity of plants was influenced by both the engineer and the canopy cover gradient. Discussion. Atta laevigata in the Cerrado modify local conditions in ways that have strong but spatially restricted consequences for plant communities. We hypothesize that ants indirectly reduce seedling establishment by clearing litter and reducing soil moisture, which leads to seed and seedling desiccation. Altering soil nutrients could also reduce juvenile growth and survivorship; if so these indirect negative effects of engineering could exacerbate their direct effects of harvesting plants. The effects ofAttaappear restricted to nest mounds, but they could be long-lasting because mounds persist long after a colony has died or migrated. Our results support the hypothesis that leaf-cutter ants play a dominant role in Cerrado plant demography. We suggest the ecological and economic footprint of these engineers may increase dramatically in coming decades due to the transformation of the Cerrado by human activities.

scholarly journals Are the effects of an ecosystem engineer and environmental gradient on plant biodiversity independent, additive, or synergistic? Tests with the leaf-cutter ant Atta laevigata in a Neotropical savanna

2017 ◽  
Author(s):  
Alan N Costa ◽  
Emilio M Bruna ◽  
Heraldo L Vasconcelos
Keyword(s):  
Species Richness ◽  
Environmental Conditions ◽  
Seedling Establishment ◽  
Ecosystem Engineer ◽  
Environmental Gradients ◽  
Dominant Role ◽  
Canopy Cover ◽  
Spatial Extent ◽  
Related Factors ◽  
Atta Laevigata

Background. Species that transform habitats in ways that influence other species are known as Ecosystem Engineers. While the impacts of many engineers have been well described, how the impacts of engineers vary along or even alter environmental gradients remains limited. While complicated – the gradients themselves can be altered by engineers – doing so is necessary to advance models of ecosystem engineering. We used leaf-cutter ants (Atta spp.) as a model system with which to investigate the relative influence of gradients and environmental engineers on the abundance and species richness of woody plant seedlings. Methods. We conducted our research in South American savanna woodlands (Cerrado). We surveyed seedlings along a canopy cover gradient and collected data on environmental conditions at different distances from ant colonies and fit statistical models that addressed the following questions (1) Do the environmental conditions previously shown to influence Cerrado seedling establishment vary with canopy cover? (2) Does A. laevigata alter the canopy cover gradient and the related environmental conditions influencing seedling establishment? (3) If so, what is the spatial extent of Atta impact on the gradient and environmental conditions, and how does this vary along the canopy cover-cover gradient? (4) Do A. laevigata and canopy cover act independently or in synergy to influence seedling abundance and species richness? Results. Environmental conditions that influence seedling establishment varied with canopy cover, but ants are not modifying the canopy cover gradient or canopy cover around nests. However, ants are modifying other environmental factors, and the magnitude and spatial extent of these changes is consistent across the gradient. In contrast to prior studies, we found both seedling abundance and diversity were independent of canopy cover; ant-related factors (e.g., proximity to nests) had the strongest effect on both abundance and richness. Discussion. Atta laevigata in the Cerrado modify environmental conditions in ways that have strong but spatially restricted consequences for seedling communities. We hypothesize that by clearing litter and reducing soil moisture ants indirectly reduce seedling establishment. The alteration of soil nutrients could also reduce seedling growth and survivorship; if so these indirect negative effects of engineering could exacerbate the direct effects of their herbivory. The effects of Atta on environmental conditions and seedling communities appear restricted to the nest mound, but they could be long-lasting because Atta mounds persist long after a colony has died or migrated. These results underscore the hypothesis that leaf-cutter ants play a dominant role in Cerrado plant demography, and that the ecological and economic footprint of these engineers may increase dramatically in coming decades due to ongoing transformations of the Cerrado by human activities.

scholarly journals Do the impacts of an ecosystem engineer vary along an environmental gradient? Tests with the leaf-cutter ant Atta laevigata in a Neotropical savanna

2016 ◽  
Author(s):  
Alan N Costa ◽  
Emilio M Bruna ◽  
Heraldo L Vasconcelos
Keyword(s):  
Environmental Conditions ◽  
Seedling Establishment ◽  
Ecosystem Engineer ◽  
Environmental Gradients ◽  
Dominant Role ◽  
Direct Reduction ◽  
Canopy Cover ◽  
Spatial Extent ◽  
Atta Laevigata ◽  
Abundance And Diversity

Background. Species that transform habitats in ways that influence other species are known as Ecosystem Engineers. While the impacts of many engineers have been well described, our understanding of how these impacts vary along or alter environmental gradients remains limited. While disentangling the effects of gradients and engineers on biodiversity is complicated – the gradients themselves can be altered by engineers – doing so is necessary to advance models of ecosystem engineering. We used leaf-cutter ants (Atta spp.), a major engineer in the Neotropics, as a model system with which to investigate the relative influence of gradients and engineers on the abundance and diversity of seedlings. Methods. We conducted our research South Americas Cerrado (savanna woodlands). We used a survey of seedlings along a canopy cover gradient and data on environmental conditions previously shown to influence seedling establishment that were collected at different distances from ant colonies to fit statistical models addressing the following questions: Do the environmental conditions previously shown to influence seedling establishment vary with canopy cover? Does A. laevigata alter canopy cover and related environmental conditions influencing seedling establishment? What is the spatial extent of Atta impact on the gradient and environmental conditions, and how does this vary along the canopy cover gradient? Do A. laevigata and canopy cover act independently or in synergy to influence seedling abundance and species richness? Results. We found that the environmental conditions varied in concert with canopy cover, but that ants are not modifying canopy cover. However, ants are modifying environmental conditions, with the magnitude and spatial extent of changes consistent across the gradient. In contrast to prior studies, we found that seedling abundance and diversity were independent of canopy-related environmental conditions. Proximity to leaf-cutter nests had the strongest effect on diversity and richness. Discussion. Atta laevigata engineers environmental conditions in the Cerrado, with strong but spatially restricted consequences for seedling communities. We hypothesize that ants indirectly reduce seedling establishment by increasing rates of seed dessication and reduce seedling growth and survivorship. As such the indirect reduction of seedling abundance due to engineering could exacerbate the direct reduction due to herbivory. The effects of Atta appear restricted to the nest mound, but they could be long-lasting because mounds persist long after a colony has died or migrated. These results underscore the hypothesis that Atta plays a dominant role in Cerrado plant demography, and that its footprint may increase dramatically in coming decades due to ongoing transformations of the Cerrado.

scholarly journals Do the impacts of an ecosystem engineer vary along an environmental gradient? Tests with the leaf-cutter ant Atta laevigata in a Neotropical savanna

2016 ◽  
Author(s):  
Alan N Costa ◽  
Emilio M Bruna ◽  
Heraldo L Vasconcelos
Keyword(s):  
Environmental Conditions ◽  
Seedling Establishment ◽  
Ecosystem Engineer ◽  
Environmental Gradients ◽  
Dominant Role ◽  
Direct Reduction ◽  
Canopy Cover ◽  
Spatial Extent ◽  
Atta Laevigata ◽  
Abundance And Diversity

Background. Species that transform habitats in ways that influence other species are known as Ecosystem Engineers. While the impacts of many engineers have been well described, our understanding of how these impacts vary along or alter environmental gradients remains limited. While disentangling the effects of gradients and engineers on biodiversity is complicated – the gradients themselves can be altered by engineers – doing so is necessary to advance models of ecosystem engineering. We used leaf-cutter ants (Atta spp.), a major engineer in the Neotropics, as a model system with which to investigate the relative influence of gradients and engineers on the abundance and diversity of seedlings. Methods. We conducted our research South Americas Cerrado (savanna woodlands). We used a survey of seedlings along a canopy cover gradient and data on environmental conditions previously shown to influence seedling establishment that were collected at different distances from ant colonies to fit statistical models addressing the following questions: Do the environmental conditions previously shown to influence seedling establishment vary with canopy cover? Does A. laevigata alter canopy cover and related environmental conditions influencing seedling establishment? What is the spatial extent of Atta impact on the gradient and environmental conditions, and how does this vary along the canopy cover gradient? Do A. laevigata and canopy cover act independently or in synergy to influence seedling abundance and species richness? Results. We found that the environmental conditions varied in concert with canopy cover, but that ants are not modifying canopy cover. However, ants are modifying environmental conditions, with the magnitude and spatial extent of changes consistent across the gradient. In contrast to prior studies, we found that seedling abundance and diversity were independent of canopy-related environmental conditions. Proximity to leaf-cutter nests had the strongest effect on diversity and richness. Discussion. Atta laevigata engineers environmental conditions in the Cerrado, with strong but spatially restricted consequences for seedling communities. We hypothesize that ants indirectly reduce seedling establishment by increasing rates of seed dessication and reduce seedling growth and survivorship. As such the indirect reduction of seedling abundance due to engineering could exacerbate the direct reduction due to herbivory. The effects of Atta appear restricted to the nest mound, but they could be long-lasting because mounds persist long after a colony has died or migrated. These results underscore the hypothesis that Atta plays a dominant role in Cerrado plant demography, and that its footprint may increase dramatically in coming decades due to ongoing transformations of the Cerrado.

scholarly journals Are the impacts of an ecosystem engineer context-dependent? Tests with the leaf-cutter ant Atta laevigata in a Neotropical savanna

2016 ◽  
Author(s):  
Alan N Costa ◽  
Emilio M Bruna ◽  
Heraldo L Vasconcelos
Keyword(s):  
Environmental Conditions ◽  
Ecosystem Engineer ◽  
Environmental Gradients ◽  
Canopy Cover ◽  
Ecosystem Engineers ◽  
Neotropical Savanna ◽  
Atta Laevigata ◽  
Beneficial Impact ◽  
Negative Effect ◽  
Context Dependent

Species that transform habitats or create new ones are known as Ecosystem Engineers. It has been posited that ecosystem engineers benefit other species by ameliorating conditions at the stressful end of environmental gradients, but that this beneficial impact diminishes as conditions along the gradient become more benign. We tested this hypothesis along a canopy-cover gradient in Brazil’s Cerrado with a widespread engineer of Neotropical ecosystems – the leaf-cutter ant Atta laevigata. We tested for changes in environmental conditions influencing seedling establishment, seedling abundance, and seedling diversity at different distances from ant nests. Local environmental conditions are influenced by both canopy cover and proximity to nests. Furthermore, the negative effect of Atta on seedlings overwhelms that of the gradient, but these impacts restricted to the area covered by nest mounds. The results demonstrate that some engineers amplify rather than reduce stress along environmental gradients, but that these impacts can be context-dependent and spatially-complex.

Eucalyptus plantations in temperate grasslands: responses of taxonomic and functional diversity of plant communities to environmental changes

2020 ◽  
Author(s):  
Pamela E. Pairo ◽  
Estela E. Rodriguez ◽  
M. Isabel Bellocq ◽  
Pablo G. Aceñolaza
Keyword(s):  
Species Richness ◽  
Leaf Litter ◽  
Plant Species ◽  
Functional Diversity ◽  
Plant Communities ◽  
Environmental Variables ◽  
Canopy Cover ◽  
Land Uses ◽  
Eucalypt Plantations ◽  
Plantation Age

ABSTRACTUnderstanding how human land-uses impact on local communities is required to implement management and conservational policies and practices. Tree plantations have become one of the fastest-growing land uses in recent decades and their impact on biodiversity was evaluated mainly at the taxonomic level. Our aim was to analyze the effects of changes in environmental drivers along the 12 years eucalypt plantations chronosequence on alfa, beta, taxonomic and functional diversity of understory plant communities. We selected nine plantation ages with three replicates per age and three protected grasslands as reference habitat. At each replicate, we established three plots to measure plant species cover and environmental variables, which are expected to change with plantation age. Results showed that species richness and all diversity indices significantly declined with increasing plantation age. Canopy cover, soil pH, and leaf litter were the most important drivers that explained the decline in taxonomic and functional diversity of plants through the forest plantation. Based on the Path analyses results, canopy cover had an indirect relationship with plant functional diversity mediated by leaf litter, soil pH and plant species richness. The results of the association between functional traits and environmental variables have revealed that high dispersal potential, annual, barochorous, and zoochorous plant species were the functional traits more affected by the eucalypt plantations. Given that leaf litter was negatively associated with all diversity facets, we recommend reducing their accumulation within eucalypt plantation to enhance biodiversity conservation and the provision of pampean grassland ecosystem functions.

Importance of regional diversity and environmental conditions on local species richness of aquatic macro-invertebrates in tropical forested streams

2014 ◽  
Vol 30 (4) ◽  
pp. 335-346 ◽  
Author(s):  
Salman Abdo Al-Shami ◽  
Che Salmah Md Rawi ◽  
Abu Hassan Ahmad ◽  
Madziatul Rosemahanie Madrus ◽  
Khalid AL Mutairi
Keyword(s):  
Species Richness ◽  
Environmental Conditions ◽  
Variation Partitioning ◽  
Regional Scale ◽  
Canopy Cover ◽  
Peninsular Malaysia ◽  
Stream Invertebrates ◽  
Regional Diversity ◽  
Local Species Richness ◽  
Local Species

Abstract:We used aquatic macro-invertebrates as a model to investigate the relationship between the regional species richness (RSR) and local species richness (LSR) in Peninsular Malaysia. A total of 38 streams (local scale) in seven catchments (regional scale), were sampled for aquatic macro-invertebrates. Eleven environmental variables (i.e. pH, DO, velocity, temperature, width, depth, TSS, BOD, COD, ammonia and canopy cover) were measured to assess their importance for local species richness. The average species richness was 34.9 species per region and the average abundance was 1380 individual per region. The highest number of species was 41, while the lowest species richness was 31. We applied local-regional richness regression models to explore the nature of the RSR–LSR relationship and then used variation partitioning to determine the relative importance of RSR and environmental conditions on LSR. We found a linear RSR–LSR relationship, which indicates unsaturated communities for macro-invertebrates in Malaysian streams and absence of local control with strong effects of regional processes. Variation in LSR explained by RSR was 43%, while the variation fraction in LSR explained by environmental conditions was low (2%) and not significant. We conclude that the variation in LSR is mainly controlled by the regional diversity pool (i.e. RSR) for aquatic macro-invertebrates in Peninsular Malaysia. However, weak effects of environmental conditions may reflect relatively low variability in the habitat among investigated streams. Further studies at larger scales, and involving different regions in this area, will be useful to draw comprehensive conclusions about determinants of local species diversity for stream invertebrates.

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