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1. Competition shapes individual foraging and survival in a desert rodent ensemble

   https://doi.org/10.1111/1365-2656.13583  

   Manlick, Philip J. ; Maldonado, Karin ; Newsome, Seth D. ( September 2021 , Journal of Animal Ecology)

   Intraspecific variation, including individual diet variation, can structure populations and communities, but the causes and consequences of individual foraging strategies are often unclear.

   Interactions between competition and resources are thought to dictate foraging strategies (e.g. specialization vs. generalization), but classical paradigms such as optimal foraging and niche theory offer contrasting predictions for individual consumers. Furthermore, both paradigms assume that individual foraging strategies maximize fitness, yet this prediction is rarely tested.

   We used repeated stable isotope measurements (δ¹³C, δ¹⁵N;N = 3,509) and 6 years of capture–mark–recapture data to quantify the relationship between environmental variation, individual foraging and consumer fitness among four species of desert rodents. We tested the relative effects of intraspecific competition, interspecific competition, resource abundance and resource diversity on the foraging strategies of 349 individual animals, and then quantified apparent survival as function of individual foraging strategies.

   Consistent with niche theory, individuals contracted their trophic niches and increased foraging specialization in response to both intraspecific and interspecific competition, but this effect was offset by resource availability and individuals generalized when plant biomass was high. Nevertheless, individual specialists obtained no apparent fitness benefit from trophic niche contractions as the most specialized individuals exhibited a 10% reduction in monthly survival compared to the most generalized individuals. Ultimately, this resulted in annual survival probabilities nearly 4× higher for generalists compared to specialists.

   These results indicate that competition is the proximate driver of individual foraging strategies, and that diet‐mediated fitness variation regulates population and community dynamics in stochastic resource environments. Furthermore, our findings show dietary generalism is a fitness maximizing strategy, suggesting that plastic foraging strategies may play a key role in species' ability to cope with environmental change.

    

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2. Plant community response to Artemisia rothrockii (sagebrush) encroachment and removal along an arid elevational gradient

   https://doi.org/10.1111/jvs.12669  

   Kopp, Christopher W. ; Cleland, Elsa E. ; Kikvidze, ed., Zaal ( August 2018 , Journal of Vegetation Science)

   Shrub expansion into alpine ecosystems worldwide raises important questions regarding the influence of shrub encroachment on alpine species diversity. The stress gradient hypothesis (SGH) predicts interactions will be competitive when resources are plentiful and the environment is benign, but that facilitative interactions will dominate when conditions are stressful. We asked howArtemisia rothrockii(sagebrush) encroachment in an arid mountain range is affecting alpine plant species there and how the plant community responds to the experimental removal of sagebrush at three sites along an elevational gradient.

   The White Mountains, California,USA(37°30′N, 118°10′W).

   A shrub removal experiment was established at three elevations (2,900, 3,100 and 3,750 m) to evaluate how sagebrush interacts with alpine and sub‐alpine plant communities.

   The study sites experienced a strong drought over the 4 yrs of the experiment and plant cover declined overall. However, in the sagebrush removal treatment, cover of co‐occurring species increased at both the high‐elevation and low‐elevation sites, with no differences observed at the mid‐elevation site.

   We observed the greatest inhibitory effects of sagebrush at high and low elevations, where plants experience the largest temperature and moisture stress, respectively, and no evidence of facilitation anywhere along the elevational gradient. These results demonstrate that while sagebrush has important influences on herbaceous species composition in the White Mountains, they are inconsistent with the classic predictions of theSGH.

    

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3. Community Response to Extreme Drought ( CRED ): a framework for drought‐induced shifts in plant–plant interactions

   https://doi.org/10.1111/nph.15595  

   Ploughe, Laura W. ; Jacobs, Elin M. ; Frank, Graham S. ; Greenler, Skye M. ; Smith, Melinda D. ; Dukes, Jeffrey S. ( January 2019 , New Phytologist)

   Contents
   	Summary	52
   I.	Introduction	52
   II.	The Community Response to Extreme Drought (CRED) framework	55
   III.	Post‐drought rewetting rates: system and community recovery	61
   IV.	Site‐specific characteristics influencing community resistance and resilience	63
   V.	Conclusions	64
   	Acknowledgements	65
   	References	66

   As climate changes, many regions of the world are projected to experience more intense droughts, which can drive changes in plant community composition through a variety of mechanisms. During drought, community composition can respond directly to resource limitation, but biotic interactions modify the availability of these resources. Here, we develop the Community Response to Extreme Drought framework (CRED), which organizes the temporal progression of mechanisms and plant–plant interactions that may lead to community changes during and after a drought. TheCREDframework applies some principles of the stress gradient hypothesis (SGH), which proposes that the balance between competition and facilitation changes with increasing stress. TheCREDframework suggests that net biotic interactions (NBI), the relative frequency and intensity of facilitative (+) and competitive (−) interactions between plants, will change temporally, becoming more positive under increasing drought stress and more negative as drought stress decreases. Furthermore, we suggest that rewetting rates affect the rate of resource amelioration, specifically water and nitrogen, altering productivity responses and the intensity and importance ofNBI, all of which will influence drought‐induced compositional changes. System‐specific variables and the intensity of drought influence the strength of these interactions, and ultimately the system's resistance and resilience to drought.

    

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4. Positive interactions between corals and damselfish increase coral resistance to temperature stress

   https://doi.org/10.1111/gcb.16480  

   Shantz, Andrew A. ; Ladd, Mark C. ; Ezzat, Leila ; Schmitt, Russell J. ; Holbrook, Sally J. ; Schmeltzer, Emily ; Vega Thurber, Rebecca ; Burkepile, Deron E. ( October 2022 , Global Change Biology)

   By the century's end, many tropical seas will reach temperatures exceeding most coral species' thermal tolerance on an annual basis. The persistence of corals in these regions will, therefore, depend on their abilities to tolerate recurrent thermal stress. Although ecologists have long recognized that positive interspecific interactions can ameliorate environmental stress to expand the realized niche of plants and animals, coral bleaching studies have largely overlooked how interactions with community members outside of the coral holobiont shape the bleaching response. Here, we subjected a common coral,Pocillopora grandis, to 10 days of thermal stress in aquaria with and without the damselfishDascyllus flavicaudus(yellowtail dascyllus), which commonly shelter within these corals, to examine how interactions with damselfish impacted coral thermal tolerance. Corals often benefit from nutrients excreted by animals they interact with and prior to thermal stress, corals grown with damselfish showed improved photophysiology (F_v/F_m) and developed larger endosymbiont populations. When exposed to thermal stress, corals with fish performed as well as control corals maintained at ambient temperatures without fish. In contrast, corals exposed to thermal stress without fish experienced photophysiological impairment, a more than 50% decline in endosymbiont density, and a 36% decrease in tissue protein content. At the end of the experiment, thermal stress caused average calcification rates to decrease by over 80% when damselfish were absent but increase nearly 25% when damselfish were present. Our study indicates that damselfish‐derived nutrients can increase coral thermal tolerance and are consistent with the Stress Gradient Hypothesis, which predicts that positive interactions become increasingly important for structuring communities as environmental stress increases. Because warming of just a few degrees can exceed corals' temperature tolerance to trigger bleaching and mortality, positive interactions could play a critical role in maintaining some coral species in warming regions until climate change is aggressively addressed.

    

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5. Plant–hummingbird pollination networks exhibit limited rewiring after experimental removal of a locally abundant plant species

   https://doi.org/10.1111/1365-2656.13935  

   Leimberger, Kara G. ; Hadley, Adam S. ; Betts, Matthew G. ( May 2023 , Journal of Animal Ecology)

   Mutualistic relationships, such as those between plants and pollinators, may be vulnerable to the local extinctions predicted under global environmental change. However, network theory predicts that plant–pollinator networks can withstand species loss if pollinators switch to alternative floral resources (rewiring). Whether rewiring occurs following species loss in natural communities is poorly known because replicated species exclusions are difficult to implement at appropriate spatial scales.

   We experimentally removed a hummingbird‐pollinated plant,Heliconia tortuosa, from within tropical forest fragments to investigate how hummingbirds respond to temporary loss of an abundant resource. Under therewiring hypothesis, we expected that behavioural flexibility would allow hummingbirds to use alternative resources, leading to decreased ecological specialization and reorganization of the network structure (i.e. pairwise interactions). Alternatively, morphological or behavioural constraints—such as trait‐matching or interspecific competition—might limit the extent to which hummingbirds alter their foraging behaviour.

   We employed a replicated Before‐After‐Control‐Impact experimental design and quantified plant–hummingbird interactions using two parallel sampling methods: pollen collected from individual hummingbirds (‘pollen networks’, created from >300 pollen samples) and observations of hummingbirds visiting focal plants (‘camera networks’, created from >19,000 observation hours). To assess the extent of rewiring, we quantified ecological specialization at the individual, species and network levels and examined interaction turnover (i.e. gain/loss of pairwise interactions).

   H. tortuosaremoval caused some reorganization of pairwise interactions but did not prompt large changes in specialization, despite the large magnitude of our manipulation (on average, >100 inflorescences removed in exclusion areas of >1 ha). Although some individual hummingbirds sampled through time showed modest increases in niche breadth followingHeliconiaremoval (relative to birds that did not experience resource loss), these changes were not reflected in species‐ and network‐level specialization metrics.

   Our results suggest that, at least over short time‐scales, animals may not necessarily shift to alternative resources after losing an abundant food resource—even in species thought to be highly opportunistic foragers, such as hummingbirds. Given that rewiring contributes to theoretical predictions of network stability, future studies should investigate why pollinators might not expand their diets after a local resource extinction.

    

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