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1. Dynamic energy landscapes of predators and the implications for modifying prey risk

   https://doi.org/10.1111/1365-2435.14478  

   Papastamatiou, Yannis P. ; Binder, Benjamin M. ; Boswell, Kevin M. ; Malone, Margaret A. ; Heithaus, Michael R. ; Huveneers, Charlie ; Mourier, Johann ; Harborne, Alastair R. ( December 2023 , Functional Ecology)

   Landscapes of fear describe a spatial representation of an animal's perceived risk of predation and the associated foraging costs, while energy landscapes describe the spatial representation of their energetic cost of moving and foraging. Fear landscapes are often dynamic and change based on predator presence and behaviour, and variation in abiotic conditions that modify risk. Energy landscapes are also dynamic and can change across diel, seasonal, and climatic timescales based on variability in temperature, snowfall, wind/current speeds, etc.

   Recently, it was suggested that fear and energy landscapes should be integrated. In this paradigm, the interaction between landscapes relates to prey being forced to use areas of the energy landscape they would avoid if risk were not a factor. However, dynamic energy landscapes experienced by predators must also be considered since they can affect their ability to forage, irrespective of variation in prey behaviour. We propose an additional component to the fear and dynamic energy landscape paradigm that integrates landscapes of both prey and predators, where predator foraging behaviour is modulated by changes in their energyscape.

   Specifically, we integrate the predator's energy landscape into foraging theory that predicts prey patch‐leaving decisions under the threat of predation. We predict that as a predator's energetic cost of foraging increases in a habitat, then the prey's foraging cost of predation and patch quitting harvest rate, will decrease. Prey may also decrease their vigilance in response to increased energetic foraging costs for predators, which will lower giving‐up densities of prey.

   We then provide examples in terrestrial, aerial, and marine ecosystems where we might expect to see these effects. These include birds and sharks which use updrafts that vary based on wind and current speeds, tidal state, or temperature, and terrestrial predators (e.g. wolves) whose landscapes vary seasonally with snow depth or ice cover which may influence their foraging success and even diet selection.

   A predator perspective is critical to considering the combination of these landscapes and their ecological consequences. Dynamic predator energy landscapes could add an additional spatiotemporal component to risk effects, which may cascade through food webs.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

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2. Seagrass ecosystem metabolic carbon capture in response to green turtle grazing across Caribbean meadows

   https://doi.org/10.1111/1365-2745.13306  

   Johnson, Robert A. ; Gulick, Alexandra G. ; Constant, Nerine ; Bolten, Alan B. ; Smulders, Fee O. H. ; Christianen, Marjolijn J. A. ; Nava, Mabel I. ; Kolasa, Keith ; Bjorndal, Karen A. ; Randall Hughes, ed., A. ( November 2019 , Journal of Ecology)

   Increasing green turtle abundance will lead to increased grazing within seagrass habitats—ecosystems that are important for carbon sequestration and storage. However, it is not well understood how carbon dynamics in these ecosystems respond to grazing and whether a response differs among meadows or locations.

   We measured seagrass ecosystem metabolism in grazed and ungrazed areas ofThalassia testudinummeadows with established green turtle foraging areas across the Greater Caribbean and Gulf of Mexico. We sampled meadows from five locations that differed in seagrass and environmental characteristics. Established meadows of the invasive seagrassHalophila stipulaceawere also present at two of these locations, and we measured ecosystem metabolism in these meadows for comparison to grazed and ungrazed areas of the nativeT. testudinum.

   Across all individual sites, rates of net ecosystem production (NEP) ranged from 56% to 96% lower in grazed areas than ungrazed areas ofT. testudinummeadows. Rates of NEP were also strongly, positively correlated with above‐ground seagrass biomass across sites. While metabolic carbon capture rates were lower in grazed areas, heterotrophic respiration was not stimulated, and grazing therefore did not result in significant metabolic remineralization of carbon in these meadows. NEP inH. stipulaceameadows was similar to rates inT. testudinummeadows at all three sites, suggesting that metabolic carbon capture may remain similar in Caribbean meadows where this invasive seagrass is replacing native species.

   Synthesis. Our results show that there is a consistent response in metabolic carbon dynamics to green turtle grazing inT. testudinummeadows across the Greater Caribbean region. An increase in grazing will not likely stimulate remineralization of carbon as these important habitats are returned to a natural grazed state.

    

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3. Wild and domestic savanna herbivores increase smaller vertebrate diversity, but less than additively

   https://doi.org/10.1111/1365-2664.13843  

   Wells, Harry B. M. ; Kimuyu, Duncan M. ; Odadi, Wilfred O. ; Dougill, Andrew J. ; Stringer, Lindsay C. ; Young, Truman P. ; du Toit, ed., Johan ( February 2021 , Journal of Applied Ecology)

   Cattle and other livestock graze more than a quarter of the world's terrestrial area and are widely regarded to be drivers of global biodiversity declines. Studies often compare the effects of livestock presence/absence but, to our knowledge, no studies have tested for interactive effects between large wild herbivores and livestock at varying stocking rates on small‐bodied wild vertebrates.

   We investigated the effects of cattle stocking rates (none/moderate/high) on the diversity of wildlife 0.05–1,000 kg using camera traps at a long‐term exclosure experiment within a semi‐arid savanna ecosystem in central Kenya. In addition, by selectively excluding wild ‘mesoherbivores’ (50–1,000 kg) and ‘megaherbivores’ (>1,000 kg; elephant and giraffe), we tested whether the presence of these two wild herbivore guilds (collectively, ‘larger wild herbivores’) mediates the effect of cattle stocking rate on habitat use and diversity of ‘smaller wildlife’ (mammals ranging between 10 and 70 cm shoulder height and birds).

   Our results show that cattle enhance alpha diversity of smaller wildlife (with or without larger wild herbivore presence) and of all wildlife 0.05–1,000 kg (with or without megaherbivore presence), by altering vegetation structure. However, for smaller wildlife, this effect is less pronounced in the presence of larger wild herbivores, which also shorten grass. In the absence of cattle, mesoherbivore‐accessible sites showed higher alpha diversity of smaller wildlife than sites excluding mesoherbivores.

   Smaller wildlife habitat use was increased by high cattle stocking rates and wild mesoherbivores more in the presence of the other.

   Synthesis and applications. Our findings imply that grazing, whether by livestock or wildlife, can enhance local savanna wildlife diversity. The biodiversity benefits of localised increases in herbivory are likely to be due to shortened grass and associated visibility improvements (for predator avoidance/foraging). This suggests that land managers can increase local biodiversity by shortening grass, with wild or domestic herbivores (or both), at least in patches within a taller grass matrix.

    

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4. The past, present, and future of herbivore impacts on savanna vegetation

   https://doi.org/10.1111/1365-2745.13685  

   Staver, A. Carla ; Abraham, Joel O. ; Hempson, Gareth P. ; Karp, Allison T. ; Faith, J. Tyler ( June 2021 , Journal of Ecology)

   Herbivory is a key process structuring vegetation in savannas, especially in Africa where large mammal herbivore communities remain intact. Exclusion experiments consistently show that herbivores impact savanna vegetation, but effect size variation has resisted explanation, limiting our understanding of the past, present and future roles of herbivory in savanna ecosystems.

   Synthesis of vegetation responses to herbivore exclusion shows that herbivory decreased grass abundance by 57.0% and tree abundance by 30.6% across African savannas.

   The magnitude of herbivore exclusion effects scaled with herbivore abundance: more grazing herbivores resulted in larger grass responses and more browsing herbivores in larger tree responses. However, existing experiments are concentrated in semi‐arid savannas (400–800‐mm rainfall) and soils data are mostly lacking, which makes disentangling environmental constraints a challenge and priority for future research.

   Observed herbivore impacts were ~2.1× larger than existing estimates modelled based on consumption. Wildlife metabolic rates may be higher than are usually used for estimating consumption, which offers one clear avenue for reconciling estimated herbivore consumption with observed herbivore impacts. Plant‐soil feedbacks, plant community composition, and the phenological or demographic timing of herbivory may also influence vegetation productivity, thereby magnifying herbivore impacts.

   Because herbivore abundance so closely predicts vegetation impact, changes in herbivore abundance through time are likely predictive of the past and future of their impacts. Grazer diversity in Africa has declined from its peak 1 million years ago and wild grazer abundance has declined historically, suggesting that grazing likely had larger impacts in the past than it does today.

   Current wildlife impacts are dominated by small‐bodied mixed feeders, which will likely continue into the future, but the magnitude of top‐down control may also depend on changing climate, fire and atmospheric CO₂.

   Synthesis. Herbivore biomass determines the magnitude of their impacts on savanna vegetation, with effect sizes based on direct observation that outstrip existing modelled estimates across African savannas. Findings suggest substantial ecosystem impacts of herbivory and allow us to generate evidence‐based hypotheses of the past and future impacts of herbivores on savanna vegetation.

    

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5. Contrasting patterns of risk from human and non‐human predators shape temporal activity of prey

   https://doi.org/10.1111/1365-2656.13621  

   Gaynor, Kaitlyn M. ; McInturff, Alex ; Brashares, Justin S. ( November 2021 , Journal of Animal Ecology)

   Spatiotemporal variation in predation risk arises from interactions between landscape heterogeneity, predator densities and predator hunting mode, generating landscapes of fear for prey species that can have important effects on prey behaviour and ecosystem dynamics.

   As widespread apex predators, humans present a significant source of risk for hunted animal populations. Spatiotemporal patterns of risk from hunters can overlap or contrast with patterns of risk from other predators. Human infrastructure can also reshape spatial patterns of risk by facilitating or impeding hunter or predator movement, or deterring predators that are themselves wary of humans.

   We examined how anthropogenic and natural landscape features interact with hunting modes of rifle hunters and mountain lionsPuma concolorto generate spatiotemporal patterns of risk for their primary prey. We explored the implications of human‐modified landscapes of fear for Columbian black‐tailed deerOdocoileus hemionus columbianusin Mendocino County, California. We used historical harvest records, hunter GPS trackers and camera trap records of mountain lions to model patterns of risk for deer. We then used camera traps to examine deer spatial and temporal activity patterns in response to this variation in risk.

   Hunters and mountain lions exhibited distinct, contrasting patterns of spatiotemporal activity. Risk from rifle hunters, who rely on long lines of sight, was highest in open grasslands and near roads and was confined to the daytime. Risk from mountain lions, an ambush predator, was highest in dense shrubland habitat, farther from developed areas, and during the night and crepuscular periods. Areas of human settlement provided a refuge from both hunters and mountain lions. We found no evidence that deer avoided risk in space at the scale of our observations, but deer adjusted their temporal activity patterns to reduce the risk of encounters with humans and mountain lions in areas of higher risk.

   Our study demonstrates that interactions between human infrastructure, habitat cover and predator hunting mode can result in distinct spatial patterns of predation risk from hunters and other predators that may lead to trade‐offs for prey species. However, distinct diel activity patterns of predators may create vacant hunting domains that reduce costly trade‐offs for prey. Our study highlights the importance of temporal partitioning as a mechanism of predation risk avoidance.

    

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