Thermal constraints on foraging of tropical canopy ants

Spicer, Michelle Elise; Stark, Alyssa Y.; Adams, Benjamin J.; Kneale, Riley; Kaspari, Michael; Yanoviak, Stephen P.

doi:10.1007/s00442-017-3825-4

Cited by 53 publications

(43 citation statements)

References 52 publications

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“…Vials were randomly arranged in a tray and placed into a drying oven (Lab Line Model 100) at 50°C (a temperature commonly experienced by tropical ants within the boundary layer on unshaded branches: Spicer et al. ) for 70 min. We removed vials at 10‐min intervals to check for ant mortality before placing them back into the oven.…”

Section: Methodsmentioning

confidence: 99%

Influence of neighboring plants on the dynamics of an ant–acacia protection mutualism

Palmer

Riginos

Damiani

et al. 2017

Ecology

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Ant-plant protection symbioses, in which plants provide food and/or shelter for ants in exchange for protection from herbivory, are model systems for understanding the ecology of mutualism. While interactions between ants, host plants, and herbivores have been intensively studied, we know little about how plant-plant interactions influence the dynamics of these mutualisms, despite strong evidence that plants compete for resources, that hosting ants can be costly, and that host-plant provisioning to ants can therefore be constrained by resource availability. We used field experiments in a semiarid Kenyan savanna to examine interactions between the ant-plant Acacia drepanolobium, neighboring grasses, and two species of symbiotic acacia-ants with divergent behaviors: Crematogaster mimosae, an aggressive symbiont that imposes high costs to host trees via consumption of extrafloral nectar, and Tetraponera penzigi, a less-protective symbiont that imposes lower costs because it does not consume nectar. We hypothesized that by competing with acacias for resources, neighboring grasses (1) reduce hosts' ability to support costly C. mimosae, while having little or no effect on the ability of hosts to support low-cost T. penzigi, and (2) reduce sapling growth rates irrespective of ant occupant. We factorially manipulated the presence/absence of grasses and the identity of ant occupants on saplings and evaluated effects on colony survivorship and sapling growth rates over 40 weeks. Contrary to prediction, the high-cost/high-reward nectar-dependent mutualist C. mimosae had higher colony-survival rates on saplings with grass neighbors present. Grasses appear to have indirectly facilitated the survival of C. mimosae by reducing water stress on host plants; soils under saplings shaded by grasses had higher moisture content, and these saplings produced more active nectaries than grass-removal saplings. Consistent with prediction, survival of low-cost/low-reward T. penzigi did not differ significantly between grass-removal treatments. Saplings occupied by low-cost/low-reward T. penzigi grew 100% more on average than saplings occupied by high-cost/high-reward C. mimosae, demonstrating that mutualist-partner identity strongly and differentially influences demographic rates of young plants. In contrast, contrary to prediction, grass neighbors had no significant net impact on sapling growth rates. Our results suggest that neighboring plants can exert strong and counterintuitive effects on ant-plant protection symbioses, highlighting the need to integrate plant-plant interactions into our understanding of these mutualisms.

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Section: Methodsmentioning

confidence: 99%

Influence of neighboring plants on the dynamics of an ant–acacia protection mutualism

Palmer

Riginos

Damiani

et al. 2017

Ecology

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“…However, we did not find a curvilinear relationship, as predicted, suggesting that there are additional factors that could be usefully incorporated into our model. For example, arboreality will expose species to different thermal conditions from ground level to the canopy (Bakken, ; Scheffers et al, ; Spicer et al, ). Although we attempted to account for the major temperature differences between ground‐dwelling and arboreal lizards, more precise data on perch height and type could improve predictions of T b in treed environments.…”

Section: Discussionmentioning

confidence: 99%

“…suggesting that there are additional factors that could be usefully incorporated into our model. For example, arboreality will expose species to different thermal conditions from ground level to the canopy (Bakken, 1989;Scheffers et al, 2013;Spicer et al, 2017).…”

Section: Discussionmentioning

confidence: 99%

Remote sensing restores predictability of ectotherm body temperature in the world’s forests

Algar

Morley

Boyd

2018

Global Ecol Biogeogr

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Aim Rising global temperatures are predicted to increase ectotherms’ body temperatures, benefitting some species but threatening others. Biophysical models predict a key role for shade in buffering these effects, but the difficulty of measuring shade across broad spatial extents limits predictions of ectotherms’ thermal futures at the global scale. Here, we extend biophysical models of ectotherm body temperature to include effects of forest canopy shade, via leaf area index, and test whether considering remotely‐sensed canopy density improves predictions of body temperature variation in heavily shaded habitats. Location Worldwide. Time period 1990–2010. Major taxa studied Lizards. Methods We test predictions from biophysical ecological theory for how body temperature should vary with microclimate for 269 lizard populations across open, semi‐open and closed habitats worldwide. We extend existing biophysical models to incorporate canopy shade effects via leaf area index, test whether body temperature varies with canopy density as predicted by theory, and evaluate the extent to which incorporating canopy density improves model performance in heavily shaded areas. Results We find that body temperatures in open habitats, like deserts, vary with air temperature and incident solar radiation as predicted by biophysical equations, but these relationships break down in forests, where body temperatures become unpredictable. Incorporating leaf area index into our models revealed lower body temperatures in more heavily shaded environments, restoring the predictability of body temperature in forests. Conclusions Although biophysical ecological theory can predict ectotherm body temperature in open habitats, like deserts, these relationships decay in closed forests. Models incorporating remotely‐sensed data on canopy density improved predictability of body temperatures in these habitats, providing an avenue to incorporate canopy shade effects into predictions of animals’ vulnerability to climate change. These results highlight the thermal threat of changes in canopy structure and loss of forest cover for the world's ectotherms.

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“…Surface dwelling ants exposed to shade have CTmax values that are 3.5-5 °C lower than those of canopy ants (Kaspari et al 2015), while resistance to desiccation is also affected by these habitat differences (Bujan et al 2016). Microhabitat features that are used differently by species can further modify temperature responses, such as the extent to which ants are exposed to sun flecks through the forest canopy (Spicer et al 2017) and spiders are exposed to shading from rocks (van den Berg et al 2015). Stress exposure is also influenced by diel patterns of activity of a species (Verble-Pearson et al 2015).…”

Section: Environmental Controlmentioning

confidence: 99%

“…Other criteria can also be used, depending on the species. In ants, it is possible to monitor behavioral responses to hot areas and to determine at what temperature these areas are abandoned (Spicer et al 2017). It is also possible to measure body temperature directly in live and dead individuals to see if thermal limits are exceeded (Hemmings & Andrew 2017).…”

Section: Relevant Vulnerability Endpointsmentioning

confidence: 99%

Comparative studies of critical physiological limits and vulnerability to environmental extremes in small ectotherms: How much environmental control is needed?

Hoffmann

Sgrò

2018

Integrative Zoology

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Researchers and practitioners are increasingly using comparative assessments of critical thermal and physiological limits to assess the relative vulnerability of ectothermic species to extreme thermal and aridity conditions occurring under climate change. In most assessments of vulnerability, critical limits are compared across taxa exposed to different environmental and developmental conditions. However, many aspects of vulnerability should ideally be compared when species are exposed to the same environmental conditions, allowing a partitioning of sources of variation such as used in quantitative genetics. This is particularly important when assessing the importance of different types of plasticity to critical limits, using phylogenetic analyses to test for evolutionary constraints, isolating genetic variants that contribute to limits, characterizing evolutionary interactions among traits limiting adaptive responses, and when assessing the role of cross generation effects. However, vulnerability assessments based on critical thermal/physiological limits also need to take place within a context that is relevant to field conditions, which is not easily provided under controlled environmental conditions where behavior, microhabitat, stress exposure rates and other factors will differ from field conditions. There are ways of reconciling these requirements, such as by taking organisms from controlled environments and then testing their performance under field conditions (or vice versa). While comparisons under controlled environments are challenging for many taxa, assessments of critical thermal limits and vulnerability will always be incomplete unless environmental effects within and across generations are considered, and where the ecological relevance of assays measuring critical limits can be established.

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Thermal constraints on foraging of tropical canopy ants

Cited by 53 publications

References 52 publications

Influence of neighboring plants on the dynamics of an ant–acacia protection mutualism

Influence of neighboring plants on the dynamics of an ant–acacia protection mutualism

Remote sensing restores predictability of ectotherm body temperature in the world’s forests

Comparative studies of critical physiological limits and vulnerability to environmental extremes in small ectotherms: How much environmental control is needed?

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