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

Seedling Establishment ◽

Ecosystem Engineer ◽

Environmental Gradients ◽

Dominant Role ◽

Canopy Cover ◽

Spatial Extent ◽

Related Factors ◽

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.

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

10.7287/peerj.preprints.1692v2 ◽

2016 ◽

Author(s):

Alan N Costa ◽

Emilio M Bruna ◽

Heraldo L Vasconcelos

Keyword(s):

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.

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

10.7287/peerj.preprints.1692v3 ◽

2016 ◽

Author(s):

Alan N Costa ◽

Emilio M Bruna ◽

Heraldo L Vasconcelos

Keyword(s):

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.

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

10.7287/peerj.preprints.1692v5 ◽

2018 ◽

Author(s):

Alan N Costa ◽

Emilio M Bruna ◽

Heraldo L Vasconcelos

Keyword(s):

Species Richness ◽

Plant Communities ◽

Ecosystem Engineer ◽

Dominant Role ◽

Canopy Cover ◽

Plant Establishment ◽

Related Factors ◽

Local Conditions ◽

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.

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

10.7287/peerj.preprints.1692 ◽

2018 ◽

Author(s):

Alan N Costa ◽

Emilio M Bruna ◽

Heraldo L Vasconcelos

Keyword(s):

Species Richness ◽

Plant Communities ◽

Ecosystem Engineer ◽

Dominant Role ◽

Canopy Cover ◽

Plant Establishment ◽

Related Factors ◽

Local Conditions ◽

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.

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 ◽

10.7717/peerj.5612 ◽

2018 ◽

Vol 6 ◽

pp. e5612 ◽

Cited By ~ 1

Author(s):

Alan N. Costa ◽

Emilio M. Bruna ◽

Heraldo L. Vasconcelos

Keyword(s):

Species Richness ◽

Plant Communities ◽

Ecosystem Engineer ◽

Dominant Role ◽

Canopy Cover ◽

Plant Establishment ◽

Related Factors ◽

Local Conditions ◽

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.

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

Scientific Reports ◽

10.1038/s41598-019-55917-x ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 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.

Isolated individuals and groups show opposite preferences toward humidity

10.1101/398651 ◽

2018 ◽

Author(s):

Mariano Calvo Martín ◽

Stamatios C. Nicolis ◽

Isaac Planas-Sitjà ◽

Jean-Christophe de Biseau ◽

Jean-Louis Deneubourg

Keyword(s):

Relative Humidity ◽

Group Level ◽

Individual Level ◽

Negative Effect ◽

Multi Level ◽

The Individual ◽

Shed Light ◽

Selection Of

AbstractCockroaches, like most social arthropods, are led to choose collectively among different alternative resting places. These decisions are modulated by different factors, such as environmental conditions (temperature, relative humidity) and sociality (groups size, nature of communications). The aim of this study is to establish the interplay between environmental conditions and the modulation of the interactions between individuals within a group leading to an inversion of preferences. We show that the preferences of isolated cockroaches and groups of 16 individuals, on the selection of the relative humidity of a shelter are inversed and shed light on the mechanisms involved. We suggest that the relative humidity has a multi-level influence on cockroaches, manifested as an attractant effect at the individual level and as a negative effect at the group level, modulating the interactions.

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

Journal of Experimental Biology ◽

10.1242/jeb.228031 ◽

2021 ◽

Vol 224 (Suppl 1) ◽

pp. jeb228031

Author(s):

Lauren B. Buckley ◽

Sean D. Schoville ◽

Caroline M. Williams

Keyword(s):

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.

Nitric oxide, an endogenous regulator of Dictyostelium discoideum differentiation

Development ◽

10.1242/dev.124.18.3587 ◽

1997 ◽

Vol 124 (18) ◽

pp. 3587-3595

Author(s):

Y.P. Tao ◽

T.P. Misko ◽

A.C. Howlett ◽

C. Klein

Keyword(s):

Nitric Oxide ◽

Cell Differentiation ◽

Dictyostelium Discoideum ◽

Initial Phase ◽

Cell Aggregation ◽

Developmental Cycle ◽

Cell Signal ◽

Constant Rate ◽

Negative Effect

We have previously demonstrated that nitric oxide (NO)-generating compounds inhibit D. discoideum differentiation by preventing the initiation of cAMP pulses (Tao, Y., Howlett, A. and Klein, C. (1996) Cell. Signal. 8, 37–43). In the present study, we demonstrate that cells produce NO at a relatively constant rate during the initial phase of their developmental cycle. The addition of oxyhemoglobin, an NO scavenger, stimulates cell aggregation, suggesting that NO has a negative effect on the development of aggregation competence. Starvation of cells in the presence of glucose, which has been shown to prevent the initiation of cAMP pulses (Darmon, M. and Klein, C. (1978) Dev. Biol. 63, 377–389), results in an increased production of NO. The inhibition of cell aggregation by glucose treatment can be reversed by oxyhemoglobin. These findings indicate that NO is a signaling molecule for D. discoideum cells and that physiological or environmental conditions that enhance external NO levels will delay the initiation of cAMP pulses, which are essential for cell differentiation.