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 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 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 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 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.

scholarly journals Shifts in the relative fitness contributions of fecundity and survival in variable and changing environments

2021 ◽  
Vol 224 (Suppl 1) ◽  
pp. jeb228031
Author(s):  
Lauren B. Buckley ◽  
Sean D. Schoville ◽  
Caroline M. Williams
Keyword(s):  
Environmental Conditions ◽  
Energy Use ◽  
Environmental Gradients ◽  
Relative Fitness ◽  
Relative Importance ◽  
Fitness Components ◽  
Climate Variability And Change ◽  
Short Term ◽  
Climate Gradients ◽  
Recent Climate

ABSTRACTOrganisms respond to shifts in climate means and variability via distinct mechanisms. Accounting for these differential responses and appropriately aggregating them is central to understanding and predicting responses to climate variability and change. Separately considering fitness components can clarify organismal responses: fecundity is primarily an integrated, additive response to chronic environmental conditions over time via mechanisms such as energy use and acquisition, whereas survival can be strongly influenced by short-term, extreme environmental conditions. In many systems, the relative importance of fecundity and survival constraints changes systematically along climate gradients, with fecundity constraints dominating at high latitudes or altitudes (i.e. leading range edges as climate warms), and survival constraints dominating at trailing range edges. Incorporating these systematic differences in models may improve predictions of responses to recent climate change over models that assume similar processes along environmental gradients. We explore how detecting and predicting shifts in fitness constraints can improve our ability to forecast responses to climate gradients and change.

scholarly journals Change in the meiofauna community structure of sandy beaches of the Nuevo Gulf (Chubut, Argentina)

2012 ◽  
Vol 52 (34) ◽  
pp. 411-422 ◽  
Author(s):  
Carlos A. Harguinteguy ◽  
M. Noelia Cofré ◽  
Catalina T. Pastor de Ward
Keyword(s):  
Community Structure ◽  
Environmental Gradients ◽  
Sandy Beaches ◽  
Core Tube ◽  
Meiofauna Community ◽  
Diameter Core ◽  
Abiotic Variables ◽  
Abundance And Diversity ◽  
One Way Anova ◽  
Main Factor

The composition and distribution of the benthic meiofauna assemblages of the Nuevo Gulf (Chubut, Argentina) are described in relation to abiotic variables. The meiofauna and sediment samples were collected in the intertidal zone of four sandy beaches with different anthropic disturbances in June 2005. The samples were obtained at 20 sampling sites using a 2.5 cm diameter core tube at a depth of 10 cm. A total of 13 meiofauna taxa were identified, with the meiofauna being primarily represented by nematodes, gastrotrichs, ciliates and polychaetes and the meiofauna abundances ranging from 1.5 × 10³ to 6.5 × 10³ ind. 10 cm‑2. Univariate (one-way ANOVA test) and multivariate (ANOSIM/MDS test) analyses showed clear dissimilarities in community structures between sites with anthropic effects and those in pristine condition, revealed by the significant differences were found between beaches near to and far way from a city with port activity. The meiofaunal assemblage varied in abundance and diversity, and these changes in the community structure may have been related to environmental gradients on the shore. The BIO‑ENV analysis showed that the redox potential discontinuity depth might be the main factor in the spatial distribution of organisms.

scholarly journals Testing for consistency in the impacts of a burrowing ecosystem engineer on soil and vegetation characteristics across biomes

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
M. A. Louw ◽  
N. S. Haussmann ◽  
P. C. le Roux
Keyword(s):  
Species Composition ◽  
Ecosystem Engineer ◽  
Environmental Gradients ◽  
Plant Cover ◽  
Ecosystem Engineers ◽  
Conservation Strategies ◽  
Annual Rainfall ◽  
Mesic Grassland ◽  
Vegetation Characteristics ◽  
Semi Arid

AbstractThe impacts of ecosystem engineers may be expected to vary along environmental gradients. Due to some resources being more limited in arid than in mesic environments, disturbances created by burrowing mammals are expected to have a greater ameliorating effect in arid environments, with larger differences in microhabitat conditions expected between burrows and undisturbed areas. The aim of this study was to test if the impacts of a medium-sized burrowing mammal, the aardvark, on soil properties (soil temperature, moisture and compaction) and vegetation characteristics (plant cover, species richness and species composition) are consistent across three biomes that differ strongly in annual rainfall. Burrowing affected soil and vegetation attributes, but the direction and magnitude of these biogeomorphological impacts were not consistent across the different biomes. For example, plant species composition was altered by burrowing in the arid scrubland and in the mesic grassland, but not in the semi-arid savannah. Contrary to expectations, the difference in the impacts of burrowing between biomes were not related to rainfall, with burrowing having strong, albeit different, impacts in both the arid scrubland and the mesic grassland, but weaker effects in the semi-arid savannah. It appears, therefore, that the impacts of these biogeomorphic agents may be site-specific and that it may be difficult to predict variation in their biotic and abiotic effects across environmental gradients. As a result, forecasting the impacts of ecosystem engineers under different conditions remains a challenge to management, restoration and conservation strategies related to these types of species.

Distribution, abundance, and diversity of stream fishes under variable environmental conditions

2006 ◽  
Vol 63 (1) ◽  
pp. 43-54 ◽  
Author(s):  
Christopher M Taylor ◽  
Thomas L Holder ◽  
Riccardo A Fiorillo ◽  
Lance R Williams ◽  
R Brent Thomas ◽  
...  
Keyword(s):  
Species Richness ◽  
Environmental Conditions ◽  
Community Dynamics ◽  
Local Community ◽  
Fish Assemblages ◽  
Fish Distribution ◽  
Stream Fish ◽  
Spatial And Temporal Variability ◽  
Regional Patterns ◽  
Abundance And Diversity

The effects of stream size and flow regime on spatial and temporal variability of stream fish distribution, abundance, and diversity patterns were investigated. Assemblage variability and species richness were each significantly associated with a complex environmental gradient contrasting smaller, hydrologically variable stream localities with larger localities characterized by more stable flow regimes. Assemblages showing the least variability were the most species-rich and occurred in relatively large, stable environments. Theory suggests that species richness can be an important determinant of assemblage variability. Although this appears to be true in our system, we suggest that spatial and temporal heterogeneity in the environment largely determines both assemblage richness and variability, providing a more parsimonious explanation for the diversity–variability correlation. Changes in species richness of local assemblages across time were coordinated across the landscape, and assemblages formed spatially and temporally nested subset patterns. These results suggest an important link between local community dynamics and community-wide occurrence. At the species level, mean local persistence was significantly associated with regional occurrence. Thus, the more widespread a species was, the greater its local persistence. Our results illustrate how the integrity of local stream fish assemblages is dependent on local environmental conditions, regional patterns of species distribution, and landscape continuity.

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