Refining the stress gradient hypothesis for mixed species groups of African mammals

Kiffner, Christian; Boyle, Diana M.; Denninger-Snyder, Kristen; Kissui, Bernard M.; Waltert, Matthias; Krause, Stefan

doi:10.1038/s41598-022-22593-3

Cited by 4 publications

(9 citation statements)

References 73 publications

(98 reference statements)

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“…Collectively, our findings add to the growing body of evidence supporting the stress-gradient hypothesis (i.e. that the propensity of facilitative interactions should increase with increasing levels of environmental stress; [22][23][24]) as a mechanism driving network structure in mobile animals that have much greater freedom of choice in species interactions that sessile plants [26,92], while suggesting that activity matching plays an important role structuring flocking networks at lower elevations and latitudes. Besides climatic stability, we hypothesized that habitat characteristics at a local scale, represented by forest cover and human disturbance, would also affect flock properties.…”

Section: Discussionsupporting

confidence: 61%

Network structure of avian mixed-species flocks decays with elevation and latitude across the Andes

Montaño‐Centellas

Muñoz

Mangini

et al. 2023

Phil. Trans. R. Soc. B

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Birds in mixed-species flocks benefit from greater foraging efficiency and reduced predation, but also face costs related to competition and activity matching. Because this cost–benefit trade-off is context-dependent (e.g. abiotic conditions and habitat quality), the structure of flocks is expected to vary along elevational, latitudinal and disturbance gradients. Specifically, we predicted that the connectivity and cohesion of flocking networks would (i) decline towards tropical latitudes and lower elevations, where competition and activity matching costs are higher, and (ii) increase with lower forest cover and greater human disturbance. We analysed the structure of 84 flock networks across the Andes and assessed the effect of elevation, latitude, forest cover and human disturbance on network characteristics. We found that Andean flocks are overall open-membership systems (unstructured), though the extent of network structure varied across gradients. Elevation was the main predictor of structure, with more connected and less modular flocks upslope. As expected, flocks in areas with higher forest cover were less cohesive, with better defined flock subtypes. Flocks also varied across latitude and disturbance gradients as predicted, but effect sizes were small. Our findings indicate that the unstructured nature of Andean flocks might arise as a strategy to cope with harsh environmental conditions. This article is part of the theme issue ‘Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes’.

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Section: Discussionsupporting

confidence: 61%

Network structure of avian mixed-species flocks decays with elevation and latitude across the Andes

Montaño‐Centellas

Muñoz

Mangini

et al. 2023

Phil. Trans. R. Soc. B

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“…However, while buffalo, hartebeest and topi were most likely to be nearby heterospecifics under low NDVI, gazelle and zebra (and in wildebeest, but the relationship was non-significant) were most likely to be nearby heterospecifics under high NDVI. This finding may shed light on another recent finding from the Serengeti: that mixed-species groups were rarest under medium NDVI [68]. A key distinction between the species with negative versus positive effects of NDVI on heterospecific availability is that the species with strictly resident speciesbuffalo, hartebeest and topiwere more likely to occur near heterospecifics when NDVI was low.…”

Section: Discussionsupporting

confidence: 59%

“…Given the parameters of the cameras, animals in the same photo could be up to 14 m away from each other, if one individual was immediately in front of the camera and the other was at the maximum typical detection distance (see above). This distance, which corresponds to approximately 4–14 body lengths, falls within the range of nearest neighbour distances for group members in prior studies of these and similar species [16,65,68,69]. Although the precise social spacing of animals across the entire landscape is currently unknown, applying a standardized and biologically validated metric to classifying social interactions is needed to appropriately compare individuals or species [70].…”

Section: Methodsmentioning

confidence: 85%

“…In particular, one limitation of our analysis is that we did not distinguish potential partner species from one another, instead lumping them into a single category (heterospecifics). Other recent studies of mixed-species groups have found that dyadic patterns of social associations among species may be reshaped by environmental variation [68,91], suggesting that this may be a fruitful avenue for further research.…”

Section: Discussionmentioning

confidence: 99%

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Identifying the social context of single- and mixed-species group formation in large African herbivores

Saltz

Palmer

Beaudrot

2023

Phil. Trans. R. Soc. B

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Despite continued interest in mixed-species groups, we still lack a unified understanding of how ecological and social processes work across scales to influence group formation. Recent work has revealed ecological correlates of mixed-species group formation, but the mechanisms by which concomitant social dynamics produce these patterns, if at all, is unknown. Here, we use camera trap data for six mammalian grazer species in Serengeti National Park. Building on previous work, we found that ecological variables, and especially forage quality, influenced the chances of species overlap over small spatio-temporal scales (i.e. on the scales of several metres and hours). Migratory species (gazelle, wildebeest and zebra) were more likely to have heterospecific partners available in sites with higher forage quality, but the opposite was true for resident species (buffalo, hartebeest and topi). These findings illuminate the circumstances under which mixed-species group formation is even possible. Next, we found that greater heterospecific availability was associated with an increased probability of mixed-species group formation in gazelle, hartebeest, wildebeest and zebra, but ecological variables did not further shape these patterns. Overall, our results are consistent with a model whereby ecological and social drivers of group formation are species-specific and operate on different spatio-temporal scales. This article is part of the theme issue ‘Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes’.

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“…This is because harsh environments may restrict plants from acquiring resources, and any amelioration of these conditions due to the presence of a neighboring plant will favor growth to the extent that it outweighs the negative, competitive impact of growing in close association. Although originally proposed for plants, the stress gradient hypothesis has been tested and extended to animals [ 38 – 40 ] and, more recently, to bacteria [ 41 , 42 ]. Considering that vegetation is restricted by extremely low temperatures, strong wind, and snowfall at the upper limit of the TLT, whereas at the lower limit of this transect the onset of the absolute desert is marked by almost no precipitation [ 30 , 34 ], we have a unique and complex gradient of environmental severity where different patterns of ecological interactions can be tested.…”

Section: Introductionmentioning

confidence: 99%

Testing the stress gradient hypothesis in soil bacterial communities associated with vegetation belts in the Andean Atacama Desert

Mandaković

Aguado-Norese

García-Jiménez

et al. 2023

Environmental Microbiome

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Background Soil microorganisms are in constant interaction with plants, and these interactions shape the composition of soil bacterial communities by modifying their environment. However, little is known about the relationship between microorganisms and native plants present in extreme environments that are not affected by human intervention. Using high-throughput sequencing in combination with random forest and co-occurrence network analyses, we compared soil bacterial communities inhabiting the rhizosphere surrounding soil (RSS) and the corresponding bulk soil (BS) of 21 native plant species organized into three vegetation belts along the altitudinal gradient (2400–4500 m a.s.l.) of the Talabre–Lejía transect (TLT) in the slopes of the Andes in the Atacama Desert. We assessed how each plant community influenced the taxa, potential functions, and ecological interactions of the soil bacterial communities in this extreme natural ecosystem. We tested the ability of the stress gradient hypothesis, which predicts that positive species interactions become increasingly important as stressful conditions increase, to explain the interactions among members of TLT soil microbial communities. Results Our comparison of RSS and BS compartments along the TLT provided evidence of plant-specific microbial community composition in the RSS and showed that bacterial communities modify their ecological interactions, in particular, their positive:negative connection ratios in the presence of plant roots at each vegetation belt. We also identified the taxa driving the transition of the BS to the RSS, which appear to be indicators of key host-microbial relationships in the rhizosphere of plants in response to different abiotic conditions. Finally, the potential functions of the bacterial communities also diverge between the BS and the RSS compartments, particularly in the extreme and harshest belts of the TLT. Conclusions In this study, we identified taxa of bacterial communities that establish species-specific relationships with native plants and showed that over a gradient of changing abiotic conditions, these relationships may also be plant community specific. These findings also reveal that the interactions among members of the soil microbial communities do not support the stress gradient hypothesis. However, through the RSS compartment, each plant community appears to moderate the abiotic stress gradient and increase the efficiency of the soil microbial community, suggesting that positive interactions may be context dependent.

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Refining the stress gradient hypothesis for mixed species groups of African mammals

Cited by 4 publications

References 73 publications

Network structure of avian mixed-species flocks decays with elevation and latitude across the Andes

Network structure of avian mixed-species flocks decays with elevation and latitude across the Andes

Identifying the social context of single- and mixed-species group formation in large African herbivores

Testing the stress gradient hypothesis in soil bacterial communities associated with vegetation belts in the Andean Atacama Desert

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