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Environment, Ecology & Earth's biodiversity
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Mechanistic insights into the role of large carnivores for ecosystem structure and functioning
Abstract: Large carnivores can exert top–down effects in ecosystems, but the size of these effects are largely unknown. Empirical investigation on the importance of large carnivores for ecosystem structure and functioning presents a number of challenges due to the large spatio‐temporal scale and the complexity of such dynamics. Here, we applied a mechanistic global ecosystem model to investigate the influence of large‐carnivore removal from undisturbed ecosystems. First, we simulated large‐carnivore removal on the global scale to inspect the geographic pattern of top–down control and to disentangle the functional role of large carnivores in top–down control in different environmental contexts. Second, we conducted four small‐scale ecosystem simulation experiments to understand direct and indirect changes in food‐web structure under different environmental conditions. We found that the removal of top–down control exerted by large carnivores (> 21 kg) can trigger large trophic cascades, leading to an overall decrease in autotroph biomass globally. Furthermore, the loss of large carnivores resulted in an increase of mesopredators. The magnitude of these changes was positively related to primary productivity (NPP), in line with the ‘exploitation ecosystem hypothesis’. In addition, we found that seasonality in NPP dampened the magnitude of change following the removal of large carnivores. Our results reinforce the idea that large carnivores play a fundamental role in shaping ecosystems, and further declines and extinctions can trigger substantial ecosystem responses. Our findings also support previous studies suggesting that natural ecosystem dynamics have been severely modified and are still changing as a result of the widespread decline and extinction of large carnivores.
This study is a very interesting one in understanding behavioural dynamics for the many cat enthusiasts on the forum. Male cheetah's are more influenced by resource distribution and females by resource abundance.
Resource pulses influence the spatio‐temporal dynamics of a large carnivore population Abstract: Resource availability is a key component in animal ecology, yet the manner in which carnivore populations respond to spatial and temporal fluctuations of resources remains unclear. We take a population‐level approach to determine how resource pulses, in this case a temporary hyper‐abundance of prey, influence the densities and space‐use of cheetahs Acinonyx jubatus. The Maasai Mara in Kenya experiences an annual migration of > 1.4 million wildebeest Connochaetes taurinus and large numbers of zebras Equus quagga and Thomson's gazelle Eudorcas thomsonii thereby providing a natural experiment to examine the influence of resource pulses on carnivore movement and densities. To draw inferences on fluctuating cheetah densities and space‐use, we collected unstructured search‐encounter data during eight sampling sessions, four during and four out of the migration, and analysed these using Bayesian spatially‐explicit capture–recapture (SECR) models with sex‐specific detection function parameters. Both densities and space‐use fluctuated seasonally but this varied according to sex. Local cheetah densities increased in areas and during times when prey abundance was highest but this was more pronounced for females than males. In terms of space‐use, movements were larger during the migration than out of the migration but this was more pronounced for males than females. These results suggest that males are influenced more by resource distribution whereas females by resource abundance. Overall densities did vary but there was no clear pattern in relation to resource pulses. Understanding the behavioural drivers of population dynamics in relation to resource pulses can provide important insights into ecological processes at multiple ecological levels. Here is a good graphic explaining the findings  *This image is copyright of its original author
I posted this in another thread before this one was made. A fascinating find:
Predation risk constrains herbivores’ adaptive capacity to warming Abstract Global warming compels larger endothermic animals to adapt either physiologically or behaviourally to avoid thermal stress, especially in tropical ecosystems. Their adaptive responses may however be compromised by other constraints, such as predation risk or starvation. Using an exceptional camera-trap dataset spanning 32 protected areas across southern Africa, we find that intermediate-sized herbivores (100–550 kg) switch activity to hotter times of the day when exposed to predation by lions. These herbivores face a tight window for foraging activity being exposed to nocturnal predation and to heat during the day, suggesting a trade-off between predation risk and thermoregulation mediated by body size. These findings stress the importance of incorporating trophic interactions into climate change predictions.
From: Fearing cougars more than wolves, Yellowstone elk manage threats from both predators
"Cougars hunted mainly in forested, rugged areas at night, whereas wolves hunted mainly in grassy, flat areas during morning and at dusk" said Kohl, lead author of the paper and now an assistant professor at the Warnell School of Forestry and Natural Resources at the University of Georgia in Athens. "Elk sidestepped both cougars and wolves by selecting for areas outside these high-risk domains, namely forested, rugged areas during daylight when cougars were resting, and grassy, flat areas at night when wolves were snoozing". Recognizing that cougars and wolves hunted in different places and at different times allowed the researchers to see how elk could simultaneously minimize threats from both predators. "Had we ignored the fact that these predators were on different schedules, we would have concluded, incorrectly, that avoiding one predator necessarily increased exposure to the other," said MacNulty, who is an associate professor in USU's Department of Wildland Resources and Ecology Center. "Movement out of the grassy, flat areas and into the forested, rugged areas to avoid wolves did not result in greater risk from cougars and vice versa because these predators were active at different times of the day". Full study: Do prey select for vacant hunting domains to minimize a multi‐predator threat?
A few interesting slides from: [color=var(--ytd-video-primary-info-renderer-title-color, var(--yt-spec-text-primary))]Connecting Rewilding Science and Practice 05 Restoring the role of megafauna in European ecosystems[/color]
 *This image is copyright of its original author  *This image is copyright of its original author  *This image is copyright of its original author Given the lack of predation on bison from wolves, does this represent an area lions could act as pleistocene surrogates for the cave lions before them as proposed by some?
Ensemble ecosystem modeling for predicting ecosystem response to predator reintroduction
Abstract: Introducing a new or extirpated species to an ecosystem is risky, and managers need quantitative methods that can predict the consequences for the recipient ecosystem. Proponents of keystone predator reintroductions commonly argue that the presence of the predator will restore ecosystem function, but this has not always been the case, and mathematical modeling has an important role to play in predicting how reintroductions will likely play out. We devised an ensemble modeling method that integrates species interaction networks and dynamic community simulations and used it to describe the range of plausible consequences of 2 keystone‐predator reintroductions: wolves (Canis lupus) to Yellowstone National Park and dingoes (Canis dingo) to a national park in Australia. Although previous methods for predicting ecosystem responses to such interventions focused on predicting changes around a given equilibrium, we used Lotka–Volterra equations to predict changing abundances through time. We applied our method to interaction networks for wolves in Yellowstone National Park and for dingoes in Australia. Our model replicated the observed dynamics in Yellowstone National Park and produced a larger range of potential outcomes for the dingo network. However, we also found that changes in small vertebrates or invertebrates gave a good indication about the potential future state of the system. Our method allowed us to predict when the systems were far from equilibrium. Our results showed that the method can also be used to predict which species may increase or decrease following a reintroduction and can identify species that are important to monitor (i.e., species whose changes in abundance give extra insight into broad changes in the system). Ensemble ecosystem modeling can also be applied to assess the ecosystem‐wide implications of other types of interventions including assisted migration, biocontrol, and invasive species eradication.
Refaunation and the reinstatement of the seed‐dispersal function in Gorongosa National Park
Abstract: Large animals are important seed dispersers; however, they tend to be under a high extinction risk worldwide. There is compelling evidence that the global biodiversity crisis is leading to the deterioration of several ecosystem functions, but there is virtually no information on how large‐scale refaunation efforts can reinstate seed dispersal. We evaluated the effectiveness of a 62‐km2 wildlife sanctuary, which was established to recover populations of large mammals in Gorongosa National Park (Mozambique), in restoring seed dispersal. We collected animal scats during the dry season of 2014 (June–August) along 5 transects inside and 5 transects outside the sanctuary fence (50 km total) with the same type of plant community, identified animal and plant species in the transects, and quantified the number of seeds in each scat. Based on these data, we built bipartite networks and calculated network and species‐level descriptor values, and we compared data collected inside and outside the sanctuary. There were more scats (268 vs. 207) and more scats containing seeds (132 vs. 94) inside than outside the sanctuary. The number of mammal dispersers was also higher inside (17) than outside the sanctuary (11). Similarly, more seeds (2413 vs. 2124) and plant species (33 vs. 26) were dispersed inside than outside the sanctuary. Overall, the seed‐dispersal network was less specialized (0.38 vs. 0.44) and there was a greater overlap (0.16 vs. 0.07) inside than outside the sanctuary. Both networks were significantly modular and antinested. The high number and richness of seeds dispersed inside the sanctuary was explained mostly by a higher abundance of dispersers rather than by disperser identity. Our results suggest conservation efforts aimed at recovering populations of large mammals are helping to reestablish not only target mammal species but also their functional roles as seed dispersers in the ecosystem.
WHEN THE WORLD BURNS, HOW DO PREDATORS RESPOND?
Over the past year, many regions of the world have experienced extensive and severe fires. More than ten million hectares across eastern and southern Australia were incinerated over the 2019/2020 bushfire season alone, an area larger than South Korea. Fires in the Amazon, the Arctic, and California have also captured global media headlines. In Australia, we now know that the fires have impacted the ranges and habitats of hundreds of plant and animal species, many of which were already threatened with extinction. As climate change continues, large, intense, and severe fires are predicted to occur more frequently. So what does this mean for the animals living in fire-prone environments? Our research, published recently in the Journal of Animal Ecology, looked at studies from around the world to identify how predators, which themselves have a strong influence on ecosystems and their dynamics, respond to fire. We found that some predators seem to benefit from fires, others appear to be adversely affected, and the remainder seem largely indifferent. In a changing climate, we need to understand how fires affect predators—and potentially their prey in turn—in order to keep ecosystems healthy and manage species appropriately, including exotic and invasive species. Predators: the good and the bad Large predators, like wolves and lions, often play important roles in ecosystems, regulating food webs by reducing the abundance or changing the behaviour of herbivores and smaller, subordinate predators. Many large predators are at risk of extinction within their native ranges due to loss of habitat, lethal control associated with livestock protection, and human exploitation. In contrast, introduced predators, such as feral cats, red foxes, and mustelid species, have spread to new regions, where they have devastated native wildlife. Fires can offer new opportunities as well as pose problems for predators. Some predators take advantage of charred, more open landscapes to hunt exposed prey. Others need thick vegetation to ambush their prey, and their hunting success is diminished in burnt landscapes where there are fewer places to hide and launch attacks from. But until now, we have not had a good global perspective on which predators are typically drawn to fire, which are repelled by it, and which don’t care either way. Synthesising information on how different kinds of predators (for example, large or small, pursuit or ambush) respond to fire is vital for both the conservation of native top predators and to help protect native prey from introduced predators . Some like it hot We reviewed studies from around the world to identify how different vertebrate predators (birds, mammals, and reptiles) respond to fire in different ecosystems. We found 160 studies on the response of 188 predator species to fire, including wolves, coyotes, foxes, cats, hawks, owls, monitor lizards, and snakes, amongst others. The studies came from 20 different countries, although most were from North America or Australia, and focused on canid and felid species. There were 36 studies for which we could conduct a meta-analysis. This revealed that some predators seem to like fire: they were more abundant, or spent more time in, recently burnt areas than unburnt areas. We found that red foxes (Vulpes vulpes) mostly respond positively to fire and become more active in burned areas. Some species benefit from fire to such an extent they have even been observed helping to spread it. In northern Australia, raptors have been observed carrying burning sticks and dropping them in unburnt areas beyond the fire front, helping to spread fire and targeting prey as they flee the fire. For other predators, fire appears to be bad news. Following wildfires in California, numbers of eastern racer snakes decreased in burnt areas. Likewise, lions in Serengeti National Park, Tanzania, avoided recently burned areas, because the dense vegetation from which they ambush prey is destroyed by fire.  *This image is copyright of its original author Figure 1: A global summary of studies examining predators and fire.The papers we reviewed highlighted food availability, vegetation cover, and competition with other predators as the most likely factors mediating how different species responded to fire. On the other hand, some species, including bobcats and the striped skunk, appeared largely unaffected by fire. Of the affected species, some (such as spotted owls and garter snakes) responded differently to fire in different places. This could be put down to differences in the fires being studied (e.g. high-severity fire vs. low-severity fire) or it could be due to the species behaving differently in different locations. Overall, we found it is difficult to reliably predict how a predator species will respond to fire. We still have a lot to learn Our results show that while many predators appear to adapt to the changes that fires bring about, some are impacted by fire, both negatively and positively. The problem is that, with a few exceptions, we will struggle to know how a given fire will affect a predator species without local knowledge, especially given that individual species, such as spotted owls, appear to respond differently across their geographic range. This means environmental managers need to monitor the local outcomes of fire management, such as prescribed burns. There may be situations in which predator management needs to be coupled with fire management to help prevent native wildlife becoming fox food after fire. There have even been trials to see if artificial shelters can help protect native wildlife from introduced predators after fire. Getting our knowledge base right Critically, inference and our ability to apply knowledge, have been hampered by inconsistency in reporting or a total lack of contextual information in many studies. No two fires are the same—they differ in size, intensity, severity, and season—but these details are often not recorded or reported. The literature is also strongly biased towards felid and canid species (24% and 25%, respectively), and there are relatively few studies from Africa, Asia, and South America on predator responses to fire. It is important to note that the effects of fire on predators may sometimes be overlooked due to the way experiments are carried out, or because monitoring happens too long after fires, potentially missing the critical window to detect predator and prey responses. Standardising how fire, predator numbers, and environmental features are recorded would help future studies predict how predators might react to different types of fires in various situations. To assist future synthesis, we developed a list of key variables that ecologists and practitioners studying predator responses to fire should aim to record and report (Figure 2).  *This image is copyright of its original author Figure 2: Summary of the key variables that should be recorded and reported in predator fire studiesAs wildfires become more frequent and severe under climate change, understanding how fire intensity and frequency shapes predator and populations will be critical for effective and informed ecosystem management and conservation. Read the paper Geary, WL, Doherty, TS, Nimmo, DG, Tulloch, AIT, Ritchie, EG. (2020) Predator responses to fire: A global systematic review and meta‐analysis. Journal of Animal Ecology, 89, 995-971, https://doi.org/10.1111/1365-2656.13153
Hotter climate = more bark beetles + more severe fires = weakened trees more susceptible to fire = less trees + inability to recover
"The found that for forests that suffer from a severe bark beetle outbreak followed by wildfire within about five years, Engelmann spruce and subalpine fir trees failed to recover in 74% of the 45 sites sampled" Aspen stop these forests transitioning into grasslands as their roots survive underground and this is how they recover, where spruce and fir rely on seed regeneration, of which there isn't enough to recover. Read about it here: Combined bark beetle outbreaks and wildfire spell uncertain future for forests (phys.org)
Large mammals make soil more fertile in tropical forests
21 January 2021 By BES Press Office Agência FAPESP press release. Research published in Functional Ecology reveals the importance of large frugivores like peccaries and tapirs to the nitrogen cycle in Brazil’s Atlantic Rainforest.  *This image is copyright of its original author Peccary herd. Credit: João João Paulo KrajewskiThe White-lipped peccary Tayassu pecari is a boar-like hoofed mammal found throughout Central and South America. These animals roam the forest in bands of 50 to 100 individuals, eating a wide variety of foods. In Brazil’s Atlantic Rainforest, they prefer the fruit of the jussara palm Euterpe edulis. The jussara is very abundant in this biome, probably thanks to vast amounts of dung, urine, and soil trampling by peccaries as well as tapirs (Tapirus terrestris) and other fruit-eating animals, or frugivores. This behavior releases forms of nitrogen, a key element in plant growth. A study supported by FAPESP and published in the journal Functional Ecology showed that in areas free of these frugivores the level of ammonium, a form of nitrogen in soil, was up to 95% lower. The findings evidence for the first time the importance of these animals to the nitrogen cycle and serve as yet another warning of the ecosystem losses caused when large mammals disappear from tropical forests. “Any farmer knows how crucial the nitrogen cycle is to achieve high crop yields. Studies in other environments have already shown that the presence of ruminants stimulates the growth of grasses thanks to the effect of their excretions on the nitrogen cycle, including optimization of microorganism activity. Our latest study has now shown that large fruit-eating mammals provide the same service in tropical forests,” said Nacho Villar, first author of the article. Villar is a researcher affiliated with São Paulo State University’s Institute of Biosciences (IB-UNESP) in Rio Claro, Brazil. Currently he is a postdoctoral fellow at the Netherlands Institute of Ecology (NIOO-KNAW).  *This image is copyright of its original author Infographic provided by study authors.The study also shows that these animals redistribute nitrogen, fertilizing areas that would otherwise be nutrient-poor, and hence sustain plant growth. According to the researchers’ estimates, such areas receive four times more ammonium and 50 times more nitrate than areas without frugivores. The study was part of the Thematic Project “Ecological consequences of defaunation in the Atlantic Rainforest”, for which the principal investigator was Mauro Galetti, a professor at IB-UNESP, and was conducted under the auspices of FAPESP’s Research Program on Biodiversity Characterization, Conservation, Restoration and Sustainable Use (BIOTA-FAPESP). The researchers used South America’s leading herbivore exclosure experiment, comprising 86 forest plots measuring 15 square meters in Serra do Mar State Park (São Paulo State), Brazil’s largest continuous Atlantic Rainforest reserve. Half the plots have been fenced since 2010 to prevent the entry of large mammals. All animals can roam freely into and out of the other plots. Camera traps on fenced and open plots demonstrated the presence or absence of White-lipped peccaries, Collared peccaries (Pecari tajacu) and tapirs, among other frugivores. Microorganisms, ammonium and nitrate In this study, the researchers analyzed soil samples from eight exclusion plots and their paired open controls, collected in the wet and dry seasons. Jussara palm abundance varied across the different plots. In soil from open plots, ammonium levels were 95% higher, and rates of nitrification (conversion of ammonium to nitrate) were also higher owing to the frugivore-driven abundance of microorganisms in the soil. Although plants absorb ammonium, their metabolism can immediately use nitrate, which is therefore considered more valuable in terms of plant growth. “Peccaries account for 80% to 90% of the total mammal biomass in the Atlantic Rainforest. Large groups of these animals roam extensive territories, fertilizing the forest,” Villar said. “Tapir density is lower, so their contribution to the nitrogen cycle isn’t as great, but the amount excreted by each individual is considerable, as is each animal’s range as it disperses seeds.” Another study by the same group had already shown how peccaries and tapirs contribute to plant species diversity and abundance (read more at: https://agencia.fapesp.br/31840). This large frugivore biomass is attracted by the vast amount of fruit from jussara palms, whose abundance is due to fertilization of the soil by the animals’ excretions (which also probably increase the palms’ fruit-bearing capacity). The outcome is a virtuous cycle for animals, plants and soil microorganisms (also stimulated by the excretions), leading the researchers to propose the term “fruiting lawns” as a description of such areas. The term is considered analogous to the concept of grazing lawns, which refers to the positive feedback between ruminant food consumption and food availability in African savannas and other grassland landscapes. The next steps in the group’s research will include investigating whether the increase in nitrogen due to plants’ interaction with large mammals boosts their carbon absorption and reduces the release of greenhouse gases from the soil. If so, plant-animal interaction should play a major role in regulating global climate change. The article “Frugivory underpins the nitrogen cycle” by Nacho Villar, Claudia Paz, Valesca Zipparro, Sergio Nazareth, Leticia Bulascoschi, Elisabeth S. Bakker and Mauro Galetti can be read at: https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2435.13707.
An introductory paper to the exploration of consumer controlled "brown" (herbivore controlled) and "black" (fire controlled) ecosystems, as opposed to "green" (resource controlled) ecosystems considered the baseline for biome potential. This is a concept briefly explored in a paper I've posted in the paleoecology thread about megafauna function from the pleistocene to the holocene.
These are explored looking at Whittaker's ecosystem uncertain areas. These are where resources (characterised as temperature + rainfall) are of less importance in predicting a biome, where grassland or woody biomes can occur, suggesting these can be black or brown controlled.  *This image is copyright of its original author An example of an ecosystem uncertain zone is in south africa, where the consumer effects of megaherbivores and fire supress woody growth. The incongruence between what climate suggests and what consumers actualise can be seen below.  *This image is copyright of its original author More information is available in the full paper: Sci-Hub | Large parts of the world are brown or black: A different view on the “Green World”hypothesis. Journal of Vegetation Science, 16(3), 261–266 | 10.1111/j.1654-1103.2005.tb02364.x (sci-hub.st)
Very fascinating perspective on the predator/prey relationship
Populations of high-value predators reflect the traits of their prey Abstract The extent to which prey traits combine to influence the abundance of predators is still poorly understood, particularly for mixed predators in sympatry and in aquatic ecosystems. In this study, we characterise prey use and distribution in iconic bird (grey wagtails and Eurasian dippers) and fish species (brown trout and Atlantic salmon) to assess whether prey traits could predict populations of these four riverine predators. Specifically, we hypothesised that: 1) prey key traits would predict predator populations more effectively than 2) diversity of prey traits, 3) the taxonomic abundance or richness of prey (known as traditional or mass-effect types of biodiversity) or 4) the prevailing environmental conditions. Combined predator population sizes were predicted better by a few key traits – specifically those revealing prey habitat use, size and drifting behaviour – than by prey diversity or prey trait diversity or environmental conditions. Our findings demonstrate that the complex relationships between prey assemblages and multiple predator species can be represented mechanistically when the key prey traits that govern encounter and consumption rates are identified. Given their apparent potential to reveal trophic relationships, and to complement more traditional measures of prey abundance, we advocate further development of trait-based approaches in predator–prey research.
Do large herbivores maintain open habitats in temperate forests?
Abstract In recent decades, grazing by wild and domestic ungulates has become a strategy for conservation management to restore or maintain open landscapes. One of the species playing an increasing role in ecological restoration is the European bison – the largest terrestrial mammal in Europe. We studied the impact of this large herbivore and other ungulates (moose, red deer, and roe deer) on tree encroachment in open habitats in the Białowieża Primeval Forest (Poland). On 30 study plots located in meadows, we measured crown volume and the density of woody vegetation and monitored visitation and behavior of ungulates with the use of camera traps. The mean visitation rate to meadows by European bison was 0.11 ind./day/plot, and 0.22 ind./day/plot by other ungulates. The duration of foraging was significantly higher in European bison (55.8 s) than in other ungulates (16.3 s). The density of woody vegetation on meadows varied from 13 to 6213 ind./ha and the crown volume from 0.6 to 1145 m3/ha. We found that increased visitation by European bison resulted in a significant reduction in the density and volume of woody vegetation in meadows. The reducing effect on woody vegetation was over eight times higher in frequently visited plots when compared to unvisited plots – the density of woody vegetation decreased from 879 to 101 saplings/ha, while the crown volume declined from 295 to 35 m3/ha. In addition, the density of woody vegetation was related to the level of meadow openness. Less open (smaller) meadows had a significantly higher density of woody vegetation than meadows characterized by high openness. Combined visitation by other ungulates did not affect either the volume or density of woody vegetation. The most plausible mechanism of observed patterns can be a remarkably higher foraging activity in meadows by bison in comparison to other ungulates. As a consequence, European bison, being adapted to open habitats, can effectively reduce the growth of tree seedlings and limit tree encroachment at the initial stages of forest succession. Thus, populations of this wild herbivore can play a role in the restoration or maintenance of open habitats and woody pastures that serve as an important foraging ground for bison in suboptimal forests, where populations of these herbivores were restored.
Equids engineer desert water availability
Abstract Megafauna play important roles in the biosphere, yet little is known about how they shape dryland ecosystems. We report on an overlooked form of ecosystem engineering by donkeys and horses. In the deserts of North America, digging of ≤2-meter wells to groundwater by feral equids increased the density of water features, reduced distances between waters, and, at times, provided the only water present. Vertebrate richness and activity were higher at equid wells than at adjacent dry sites, and, by mimicking flood disturbance, equid wells became nurseries for riparian trees. Our results suggest that equids, even those that are introduced or feral, are able to buffer water availability, which may increase resilience to ongoing human-caused aridification. |
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