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1. Ant nest architecture is shaped by local adaptation and plastic response to temperature

   https://doi.org/10.1038/s41598-021-02491-w  

   Sankovitz, Madison ; Purcell, Jessica ( November 2021 , Scientific Reports)

   Social insects are among the most abundant arthropods in terrestrial ecosystems, where they provide ecosystem services. The effect of subterranean activity of ants on soil is well-studied, yet little is known about nest architecture due to the difficulty of observing belowground patterns. Furthermore, many species’ ranges span environmental gradients, and their nest architecture is likely shaped by the climatic and landscape features of their specific habitats. We investigated the effects of two temperature treatments on the shape and size of nests built byFormica podzolicaants collected from high and low elevations in the Colorado Rocky Mountains in a full factorial experiment. Ants nested in experimental chambers with soil surface temperatures matching the local temperatures of sample sites. We observed a plastic response of nest architecture to conditions experienced during excavation; workers experiencing a high temperature excavated deeper nests than those experiencing a cooler temperature. Further, we found evidence of local adaptation to temperature, with a significant interaction effect of natal elevation and temperature treatment on nest size and complexity. Specifically, workers from high elevation sites built larger nests with more tunnels when placed in the cool surface temperature treatment, and workers from low elevation sites exhibited the opposite pattern. Our results suggest that subterranean ant nest architecture is shaped by a combination of plastic and locally adapted building behaviors; we suggest that the flexibility of this ‘extended phenotype’ likely contributes to the widespread success of ants.

    

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2. Effects of Formica podzolica ant colonies on soil moisture, nitrogen, and plant communities near nests

   https://doi.org/10.1111/een.12677  

   Sankovitz, Madison A. ; Breed, Michael D. ; McCreery, Helen F. ( October 2018 , Ecological Entomology)

   1. Ants are widely regarded as ‘ecosystem engineers’ because their nest construction and contributions to nutrient cycling change the biological, chemical, and physical properties of the soil around their nests. Despite increasing attention to ant manipulation of soil ecosystems, the extent to which many common species influence soil properties, as well as nutrient uptake and community composition of plants near nests, is still unknown.

   2. This study tested hypotheses that activities of a common subalpine ant,Formica podzolica, alter soil moisture and pH, redistribute nitrogen around nests, and affect plant species abundance and ground cover.

   3. A combination of field sampling techniques showed that distance from a nest had a positive relationship with soil moisture and a negative relationship with plant abundance next to and downhill from nests. Slope aspect also affected plant communities, with downhill transects having higher plant cover and above‐ground biomass than uphill transects. A stable isotope analysis did not reveal that plants near nests had enriched¹⁵N, but there were substantial differences in¹⁵N among sites.

   4. Overall, this study uncovers significant impacts ofF. podzolicaon the subalpine microhabitats directly surrounding their nests.

    

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3. The Role of the Ecosystem Engineer, the Leaf‐Cutter Ant Atta cephalotes , on Soil CO 2 Dynamics in a Wet Tropical Rainforest

   https://doi.org/10.1029/2018JG004723  

   Fernandez‐Bou, A. S. ; Dierick, D. ; Swanson, A. C. ; Allen, M. F. ; Alvarado, A. G. F. ; Artavia‐León, A. ; Carrasquillo‐Quintana, O. ; Lachman, D. A. ; Oberbauer, S. ; Pinto‐Tomás, A. A. ; et al ( February 2019 , Journal of Geophysical Research: Biogeosciences)

   Leaf‐cutter ants are dominant herbivores that disturb the soil and create biogeochemical hot spots. We studied how leaf‐cutter antAtta cephalotesimpacts soil CO₂dynamics in a wet Neotropical forest. We measured soil CO₂concentration monthly over 2.5 years at multiple depths in nonnest and nest soils (some of which were abandoned during the study) and assessed CO₂production. We also measured nest and nonnest soil efflux, nest vent efflux, and vent concentration. Nest soils exhibited lower CO₂accumulation than nonnest soils for the same precipitation amounts. During wet periods, soil CO₂concentrations increased across all depths, but were significantly less in nest than in nonnest soils. Differences were nonsignificant during drier periods. Surface efflux was equal across nest and nonnest plots (5 μmol CO₂m⁻²s⁻¹), while vent efflux was substantially (10³to 10⁵times) greater, a finding attributed to free convection and sporadic forced convection. Vent CO₂concentrations were less than in soil, suggesting CO₂efflux from the soil matrix into the nest. Legacy effects in abandoned nests were still observable after more than two years. These findings indicate that leaf‐cutter ant nests provide alternative transport pathways to soil CO₂that increase total emissions and decrease soil CO₂concentrations, and have a lasting impact. Estimated total nest‐soil CO₂emissions were 15 to 60% more than in nonnest soils, contributing 0.2 to 0.7% to ecosystem‐scale soil emissions. The observed CO₂dynamics illuminate the significant carbon footprint of ecosystem engineerAtta cephalotesand have biogeochemical implications for rainforest ecosystems.

    

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4. Factors affecting the nesting success of Swainson's Thrush ( Catharus ustulatus ) along an elevational gradient

   https://doi.org/10.1002/ece3.10738  

   Deckel, Sarah C. ; DeLuca, William V. ; Gerson, Alexander R. ; King, David I. ( January 2024 , Ecology and Evolution)

   Montane birds experience a range of challenges that may limit their breeding success, including nest predation and severe climactic conditions. The continuing effects of climate change are causing shifts in biotic and abiotic factors that may compound these threats to montane bird species. In northeastern montane forests, many bird species are shifting downslope, potentially as the result of increased precipitation and temperature at higher elevations. Although lower elevations might be more favorable in terms of climactic conditions, nest predation is higher at lower elevations. Thus, montane birds might be faced with the opposing pressures of adverse climactic conditions at higher elevations and increased predation at lower elevations. We monitored nests of Swainson's Thrush (Catharus ustulatus) along an elevation gradient in the White Mountain National Forest in New Hampshire in 2016, 2018, 2019, and 2021 to examine the effect of biotic and abiotic factors on daily nest survival rate (DSR). Linear time explained the most variation of DSR in AICc model comparison, indicating that DSR decreases across the breeding season. Rain intensity (mm/h) had a weak negative effect on DSR, indicating that heavier rain per hour decreases Swainson's Thrush DSR. Moreover, we found some support for a negative interaction effect of elevation in conjunction with minimum daily temperature: DSR of Swainson's Thrush nests at low elevations (281 m) increased with increasing minimum daily temperatures and decreased at high elevations with increasing minimum daily temperatures. Our results suggest nesting survival of montane breeding birds may be at risk as heavier precipitation events become more frequent and intense due to the changing climate and raises the possibility that other passerine species could be at risk in this system.

    

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5. Environmental variation structures reproduction and recruitment in long‐lived mega‐herbivores: Galapagos giant tortoises

   https://doi.org/10.1002/ecm.1599  

   Blake, Stephen ; Cabrera, Freddy ; Cruz, Sebastian ; Ellis‐Soto, Diego ; Yackulic, Charles B. ; Bastille‐Rousseau, Guillaume ; Wikelski, Martin ; Kuemmeth, Franz ; Gibbs, James P. ; Deem, Sharon L. ( February 2024 , Ecological Monographs)

   Migratory, long‐lived animals are an important focus for life‐history theory because they manifest extreme trade‐offs in life‐history traits: delayed maturity, low fecundity, variable recruitment rates, long generation times, and vital rates that respond to variation across environments. Galapagos tortoises are an iconic example: they are long‐lived, migrate seasonally, face multiple anthropogenic threats, and have cryptic early life‐history stages for which vital rates are unknown. From 2012 to 2021, we studied the reproductive ecology of two species of Galapagos tortoises (Chelonoidis porteriandC. donfaustoi) along elevation gradients that coincided with substantial changes in climate and vegetation productivity. Specifically, we (1) measured the body and reproductive condition of 166 adult females, (2) tracked the movements of 33 adult females using global positioning system telemetry, and monitored their body condition seasonally, (3) recorded nest temperatures, clutch characteristics, and egg survival from 107 nests, and (4) used radiotelemetry to monitor growth, survival, and movements of 104 hatchlings. We also monitored temperature and rainfall from field sites, and remotely sensed primary productivity along the elevation gradient. Our study showed that environmental variability, mediated by elevation, influenced vital rates of giant tortoises, specifically egg production by adult females and juvenile recruitment. Adult females were either elevational migrants or year‐round lowland residents. Migrants had higher body condition than residents, and body condition was positively correlated with the probability of being gravid. Nests occurred in the hottest, driest parts of the tortoise's range, between 6 and 165 m elevation. Clutch size increased with elevation, whereas egg survival decreased. Hatchling survival and growth were highest at intermediate elevations. Hatchlings dispersed rapidly to 100–750 m from their nests before becoming sedentary (ranging over <0.2 ha). Predicted future climates may impact the relationships between elevation and vital rates of Galapagos tortoises and other species living across elevation gradients. Resilience will be maximized by ensuring the connectivity of foraging and reproductive areas within the current and possible future elevational ranges of these species.

    

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