Biomass Of Large Herbivores Research Articles

Trait‐based mechanistic approach highlights global patterns and losses of herbivore biomass functional diversity

Abstract Mammalian herbivores play a pivotal role in Earth System processes by affecting biogeochemical cycles and ecosystem functioning, potentially leading to significant repercussions on atmosphere–biosphere feedbacks. Global dynamic models of mammalian populations can improve our understanding of their ecological role at large scales and the consequences of their extinctions. However, such models are still lacking and mammals are poorly integrated in Earth System Science. We developed a mechanistic global model of terrestrial herbivore populations simulated with 37 functional groups defined through the analysis of eco‐physiological traits across all extant herbivores (2599 species). We coupled this model with a global vegetation model to predict herbivores' maximum potential biomass in pre‐industrial and at present‐day and to study the environmental drivers explaining the distribution of herbivore biomass. Present‐day biomass was estimated by accounting for anthropogenic activity causing habitat and range losses. We show that natural ecosystems could have sustained a potential wild herbivore wet biomass of 330 Mt (95% CI: 245–417), comprised of 193 Mt (95% CI: 177–208) by large species (body mass >1–10 kg, depending on functional group) and 138 Mt (95% CI: 68–209) by small species. We estimate that the remaining present‐day large herbivores biomass is 82 Mt (95% CI: 32–133), reduced by 57% due to anthropogenic activity; consequently, small herbivores currently dominate global herbivore biomass with 98 Mt (95% CI: 91–106, −29%). Losses vary greatly across climatic zones and functional groups, suggesting that size is not the only discriminant feature of biomass decline. Actual evapotranspiration is the most important driver of total, large and small herbivore biomass and explains 64%, 59% and 49% of its variation, respectively. Distribution of modelled and observed large herbivores' biomass suggested a high dependency on energy and water with more biomass in hot and wet areas. These results challenge the notion that large herbivore biomass peaks primarily in ecosystems with intermediate precipitation levels such as savannas. Outside Africa and the Tropics, pre‐industrial biomass hotspots occur in areas today dominated by humans; this could undermine the recovery of larger species biomass in certain areas. Our herbivore biomass estimates provide a quantitative benchmark for setting conservation and rewilding goals at large spatial scales. The herbivore model and functional classification create new opportunities to integrate mammals into Earth System Science and models. Read the free Plain Language Summary for this article on the Journal blog.

Tree cover and its heterogeneity in natural ecosystems is linked to large herbivore biomass globally

Tree cover and its heterogeneity in natural ecosystems is linked to large herbivore biomass globally

Exploring a natural baseline for large‐herbivore biomass in ecological restoration

Abstract Large herbivores provide key ecosystem processes, but have experienced massive historical losses and are under intense pressure, leaving current ecosystems with dramatically simplified faunas relative to the long‐term evolutionary norm. Hampered by a shifting baseline, natural levels of large‐herbivore biomass are poorly understood and seldom targeted. This ‘Decade of ecosystem restoration’ calls for evidence‐based targets for restoring the natural diversity and biomass of large herbivores. We apply the scaling of the consumer–producer relationship to a global dataset of large‐herbivore density in natural areas. The analyses reveal that African ecosystems generally have much higher large‐herbivore biomass and also the strongest consumer–producer relationship. For Europe, Asia and South America, there are no significant relationships with primary productivity indicative of impoverished faunas. Compared to expectations from the African scaling relation, large‐herbivore biomass in ecosystems outside Africa is considerably lower than expected. Synthesis and applications. Ecological restoration and rewilding entail restoration of a natural grazing process. Our findings indicate that many nature reserves are depleted in large‐herbivore biomass, judged from their primary productivity. Meanwhile, overexploitation by seasonal livestock grazing takes place in other areas. It is thus difficult, but urgent, to reach scientific consensus regarding a natural baseline for large‐herbivore biomass. Until such agreement has been reached, we recommend to manage, or rewild, large herbivores in year‐round near‐natural grazing and without predefined density targets, but following natural and fluctuating resource availability with minimal management intervention. The establishment of experimental rewilding sites with reactive herbivore management is needed to further advance our understanding of natural grazing density.

Retrodicting large herbivore biomass for the last glacial maximum on the Palaeo-Agulhas Plain (South Africa) using modern ecological knowledge of African herbivore assemblages and rainfall

AbstractHerbivore distribution throughout Africa is strongly linked to mean annual precipitation. We use that relationship to predict functional group composition of herbivore communities during the last glacial maximum (ca. 21 ka) on the now submerged Palaeo-Agulhas Plain (PAP), South Africa. We used metabolic large herbivore biomass (MLHB) from 39 South African protected areas, in five functional groups (characterized by behavior and physiology). We examined how modern factors influenced MLHB and considered the effects of biome, annual rainfall, percentage winter rainfall, and protected area size. Overall, biome was the most important factor influencing the relationship between MLHB and rainfall. In general, MLHB increased with rainfall, but not for the grassland biome. Outside grasslands, most functional groups’ metabolic biomass increased with increasing rainfall, irrespective of biome, except for medium-sized social mixed feeder species in savanna and thicket. Protected area size was influential for medium-sized social mixed feeders and large browsers and rainfall influenced medium-sized social mixed feeders, offering some perspectives on spatial constraints on past large herbivore biomass densities. These results improve our understanding of the likely herbivore community composition and relative biomass structure on the PAP, an essential driver of how early humans utilized large mammals as a food resource.

Evidence of a high-density brown hyena population within an enclosed reserve: the role of fenced systems in conservation

Small, enclosed reserves are now common across Africa, and their conservation importance as wildlife refuges is increasingly acknowledged. Whilst such reserves represent areas safe from human persecution, they can also become threats themselves when the natural processes of emigration and immigration are prohibited. As a result, wildlife populations residing in enclosed reserves require careful management to safeguard their long-term persistence. As successful conservation management relies on precise population estimates, we estimated brown hyena density within a 180-km2 enclosed reserve in north-central Namibia. Using camera trapping methods in combination with spatially explicit capture-recapture (SECR) models, brown hyena density was estimated at 24.01 brown hyenas/100 km2 (± 3.47, 95% CI’s 18.12–31.81), the highest recorded to date for the species. The high density is attributed to the relatively high density of leopard within the reserve, which may facilitate brown hyenas by providing access to the large herbivore biomass through kleptoparasitism, coupled with protection from human persecution. Results highlight the potential for enclosed reserves to host high-density populations of a persecuted large carnivore and show that, despite their often small size, such systems can aid conservation efforts. However, such results suggest reserve managers will be increasingly faced with the dilemma of dealing with surplus individuals when populations exceed carrying capacity. Therefore, the development of methods estimating carrying capacity for scavenging species, along with creating meta-population management schemes for all large carnivore species are essential next steps for conservation in Africa.

Top–down limits on prey populations may be more severe in larger prey species, despite having fewer predators

Variation in the vulnerability of herbivore prey to predation is linked to body size, yet whether this relationship is size‐nested or size‐partitioned remains debated. If size‐partitioned, predators would be focused on prey within their preferred prey size range. If size‐nested, smaller prey species should become increasingly more vulnerable because increasingly more predators are capable of catching them. Yet, whether either of these strategies manifests in top–down prey population limitation would depend both on the number of potential predator species as well as the total mortality imposed. Here we use a rare ecosystem scale ‘natural experiment’ comparing prey population dynamics between a period of intense predator persecution and hence low predator densities and a period of active predator protection and population recovery. We use three decades of data on herbivore abundance and distribution to test the role of predation as a mechanism of population limitation among prey species that vary widely in body size. Notably, we test this within one of the few remaining systems where a near‐full suite of megaherbivores occur in high density and are thus able to include a thirtyfold range in herbivore body size gradient. We test whether top–down limitation on prey species of particular body size leads to compositional shifts in the mammalian herbivore community. Our results support both size‐nested and size‐partitioning predation but suggest that the relative top–down limiting impact on prey populations may be more severe for intermediate sized species, despite having fewer predators than small species. In addition we show that the gradual recovery of predator populations shifted the herbivore community assemblage towards large‐bodied species and has led to a community that is strongly dominated by large herbivore biomass.

Determinants of patchiness of woody vegetation in an African savanna

AbstractQuestionsHow is woody vegetation patchiness affected by rainfall, fire and large herbivore biomass? Can we predict woody patchiness and cover over large‐scale environmental gradients?LocationHluhluwe‐iMfolozi Park, South Africa.MethodsWe quantified variation in local patchiness as the lacunarity of woody cover on satellite‐derived images. Using Random Forest regression we analysed how both average woody cover and its patchiness depend on annual rainfall, fire frequency and grazer and browser metabolic biomass densities.ResultsFire frequency and rainfall were the clearest predictors, whereas effects of large herbivores on woody vegetation were smaller and more complex. Under low rainfall conditions (500 mm·yr−1) trees had less total cover and were more regularly spaced across the landscape (lower patchiness). Woody cover and vegetation patchiness increased with rainfall whereas fire frequency decreased woody cover and further increased patchiness.ConclusionThese results suggest a switch from competition between neighbouring trees under low rainfall conditions towards benefits among neighbours with increasing fire frequencies. Whereas overall woody cover and its patchiness are two independent aspects of savanna woody vegetation patterns, both need to be investigated to obtain a good understanding of the functioning and diversity of savanna ecosystems.

Using dung fungi to interpret decline and extinction of megaherbivores: problems and solutions

Fungi which produce their spores on the dung of large herbivores show promise as indicators of the distribution and relative abundance of large herbivores in past environments. Recently, several studies have used counts of spores of such fungi, Sporormiella in particular, to resolve the timing and reveal the ecological consequences of extinction of Pleistocene megafauna. However, there are several problems in the interpretation of the dung-fungus proxy, relating mostly to taphonomic effects on spore accumulation. Here, we describe these problems and show how they can be solved, using new data from the Lynch's Crater site in northeastern Australia. Effects of variation in spore accumulation in relation to position in the sedimentary basin can be controlled by comparing cores from different locations; temporal variation in spore accumulation rates can be attributed to changes in herbivore populations, as distinct from time-varying taphonomic effects, by comparing trends in fungi exclusively associated with herbivore dung to trends for fungi that also sporulate on other substrates; effects of changing vegetation composition can be removed by measuring spore influx rates rather than expressing counts relative to the pollen sum. At Lynch's Crater, these approaches increase our confidence that a decline in dung fungi at ∼40ka indicates an unprecedented drop in biomass of large herbivores. We also show that before this decline, the biomass of large herbivores at this site was evidently similar to that in North America and western Europe.

Biomass of large herbivores in South African subtropical thicket

Plate S1 African elephants (Loxodonta africana) browsing in succulent thicket in the Addo Elephant National Park. Photo credit: R.M. Cowling. Data S1 Additional information on study context, study sites and methods. Figure S1 Biomass in Addo Elephant National Park (AENP), as recorded in annual game counts. Table S1 Mean annual rainfall, soil fertility status and large herbivore biomass densities for 51 African savanna protected areas, and Addo Elephant National Park (AENP) and Great Fish River Nature Reserve (GFRNR) (italicised), in ascending order of biomass density. Table S2 Biomass data and presence of species for Addo Elephant National Park (AENP) and Great Fish River Nature Reserve (GFRNR). Unit weight data from Coe, Cumming & Phillipson (1976). Table S3 Coefficients for biomass estimation regression equations calculated for 51 savanna protected areas throughout Africa (listed in Table S1, Supporting Information), based on their mean annual rainfall and soil fertility status (low, medium or high). Table S4 Actual and modelled biomass estimates for Addo Elephant National Park (AENP) and Great Fish River Nature Reserve (GFRNR). Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Herbivore Dynamics and Range Contraction in Kajiado County Kenya: Climate and Land Use Changes, Population Pressures, Governance, Policy and Human-wildlife Conflicts

Wildlife populations are declining severely in many protected areas and unprotected pastoral areas of Africa. Rapid large-scale land use changes, poaching, climate change, rising population pressures, governance, policy, economic and socio-cultural transformations and competition with livestock all contribute to the declines in abundance. Here we analyze the population dynamics of 15 wildlife and four livestock species monitored using aerial surveys from 1977 to 2011 within Kajiado County of Kenya, with a rapidly expanding human population, settlements, cultivation and other developments. The abundance of the 14 most common wildlife species declined by 67% on average (2% / yr) between 1977 and 2011 in both Eastern (Amboseli Ecosystem) and Western Kajiado. The species that declined the most were buffalo, impala, wildebeest, waterbuck, oryx, hartebeest, Thomson's gazelle and gerenuk in Eastern Kajiado (70% to 88%) and oryx, hartebeest, impala, buffalo, waterbuck, giraffe, eland and gerenuk in Western Kajiado (77% to 99%). Only elephant (115%) and ostrich (216%) numbers increased contemporaneously in Eastern and Western Kajiado, respectively. Cattle and donkey numbers also decreased on average by 78% in Eastern Kajiado and by 37% in Western Kajiado. Sheep and goats decreased the least in Eastern (28%) but increased in Western (96%) Kajiadio. Livestock dominated (70-80%) the total large herbivore biomass throughout the 1977-2011 monitoring period. The distribution of wildlife contracted dramatically during 1977-2011, most especially for wildebeest, giraffe and impala. Only zebra and ostrich distributions expanded in the county. However, livestock distribution expanded to densely cover most of the county. Our findings point to recurrent droughts, intensifying human population pressures, land use changes and other anthropogenic impacts, decades of ineffective or failed government policies, legislations, law enforcement, management institutions and strategies as the salient causes of the declines and range compressions. We recommend several urgent measures to rehabilitate the depleted wildlife populations and habitat richness, restore their ecological resilience to droughts and secure pastoral livelihoods.

Ungulate carrying capacity in Pleistocene Mediterranean ecosystems: Evidence from the Atapuerca sites

Large herbivore carrying capacity, that is, the maximum biomass of large herbivorous mammals that an ecosystem is able to sustain for the long term, is a key factor in ecosystems trophic dynamics. The carrying capacity of Pleistocene ecosystems conditioned the survival opportunities and colonization capabilities of hominin populations in Europe. In this study, we use the amphibian and squamate record of two Early and Middle Pleistocene sites from Sierra de Atapuerca (Spain) to obtain estimates of past temperature and rainfall values. A function derived from the analysis of a wide set of recent mammalian communities is used to infer the large herbivore carrying capacity of the Atapuerca ecosystems during the Pleistocene from those climatic variables. This function provides reliable estimates of large herbivore carrying capacity in open environments but not in forest communities. The results presented in this study indicate that carrying capacity was higher at Atapuerca during most of the sequence than in the present. Our data also suggest that in most Mediterranean ecosystems, large herbivore biomass is currently below the carrying capacity of the environment due to the relatively low diversity of the large herbivore guild in most recent communities. Although the carrying capacity was high at Atapuerca in the periods the area was occupied by humans, it was also high in other periods for which no evidence of human presence has been recorded. Thus, the relationship between human occupation of the territory and carrying capacity does not appear to be simple.

Termite activity, not grazing, is the main determinant of spatial variation in savanna herbaceous vegetation

Summary1. Termites and large herbivores represent important functional groups in savanna ecosystems. Termites affect vegetation far beyond their mounds. In addition, large herbivores feed selectively on termite mound vegetation or in the vicinity of mounds. Previous studies of savanna vegetation communities have focused on termites and large herbivores separately, although interaction effects may be predicted.2. We studied the effects of large herbivores and large vegetated Macrotermes mounds on the herbaceous vegetation in Lake Mburo National Park in Uganda. We recorded herbaceous vegetation change over 3 years on savanna areas (with and without large herbivores) and on corresponding termite mounds (with and without large herbivores) in a randomized block design.3. Termite mounds and savannas had significantly different plant communities, but large herbivore grazing exclusions did not result in significant shifts in plant communities during this study period. A canonical correspondence analysis separated species mainly along an axis from termitaria to savanna. Only a few species responded to grazing exclusion. Some erect species, such as Hyparrhenia filipendula and Themeda triandra, increased in cover, and creeping species, such as Cynodon dactylon, decreased, following the exclusion of grazers. Forbs dominated mound areas, while graminoids dominated the savanna areas. Fencing increased the cover of graminoids over time and led to gradual increase in the relative cover of graminoids compared with forbs.4. Mound soil was higher in pH, calcium and magnesium and lower in sodium compared with adjacent savanna areas. Nitrogen and carbon soil content did not differ between the two habitats. Soil phosphorus increased following grazing exclusion.5. Synthesis. This study shows that termites may exert a far more important effect on the herbaceous community than large herbivores in savanna areas, even if the biomass of large herbivores is relatively high. Thus, future studies on savanna vegetation ecology should focus increasingly on important insect groups in addition to the more conspicuous large mammal guild.

Spatio‐temporal variation in large herbivore pressure in Norway during 1949‐1999: has decreased grazing by livestock been countered by increased browsing by cervids?

AbstractDuring recent decades, rough livestock grazing has decreased markedly on unimproved land (i.e. natural and semi‐natural habitats) across most of Europe, whilst the number of wild cervids has increased. However, we still know little about the overall changes in the herbivore pressure and how herbivore regimes vary between biogeographic regions. We have quantified the spatio‐temporal variation in herbivore pressure indirectly by estimating the metabolic biomass of large herbivores in mountain, coastal and inland municipalities of Norway every 10th year during 1949‐1999. We quantified how much livestock biomass has decreased, whether this corresponded to increasing cervid biomass, and whether the proportion of grazing relative to browsing has changed within the herbivore community. Total metabolic biomass of livestock and cervids (MBAtotal) decreased from 126 kg/km2 in 1949 to 107 kg/km2 in 1999 (∼85% of MBAtotal in 1949). Changes differed markedly between regions. Herbivore pressure in the coastal region nearly halved from 1949 to 1999, while the decrease was minor in the inland and mountain regions. Livestock grazing more than halved, whereas the metabolic biomass of cervids increased by 276% from 1949 to 1999. Cervids dominated the community of large herbivores on unimproved land in Norway in 1999 (54% of MBAtotal). Livestock dominated in the mountain (52% of MBAtotal) and in the coastal region (54% of MBAtotal) in 1999, while cervids dominated in the inland region (67% of MBAtotal). Most herbivore foraging consisted of grazing in 1949 (89% at a national scale). This proportion was reduced to 54% by 1999. Percent browsing was especially high (> 90%) in several municipalities in southeastern Norway in 1999. The increase of wild cervids is exceptional in a historical perspective, and managers have to adapt to wild cervids being the major ecosystem engineers in many landscapes.

Estimating the Biomass of Large Mammalian Herbivores in a Tropical Montane Forest: A Method of Faecal Counting That Avoids Assuming a 'Steady State' System

1. Faecal counting techniques were used to census five large mammalian herbivores during 1988 and 1989 in the Parc National des Volcans in Rwanda. These five herbivores were the black-fronted duiker (Cephalophus nigrifrons), the bushbuck (Tragelaphus scriptus), the Cape buffalo (Syncerus caffer), the mountain gorilla (Gorilla gorilla beringei) and the African elephant (Loxodonta africana). 2. Population density estimations from standing crop counts of faeces usually correct the counts for the defecation rate of the animal and the decomposition rate of the dung, assuming that the decay of the dung is constant. However, this study found that the dung decay was not constant. For bushbucks, exponential decay curves were found in the wet seasons and sigmoidal decay curves in the dry seasons. Only sigmoidal curves were found for buffalos and elephants. Therefore, measures of dung decomposition throughout the year were used in a computer model which estimated iteratively the population density. 3. Ecological density estimates were obtained for eight habitat types found in the Park. Habitats at the summit of volcanos sustain the lowest biomass of large herbivores at 10-15 kg ha −1 whilst meadows sustain the highest biomass at 45-50 kg ha −1 . The biomass for the whole study area was calculated as 31 kg ha −1 , one of the highest biomasses for any forest yet studied. The bushbuck and the buffalo dominated this biomass. The implications of this for the conservation of the mountain gorilla are discussed and it is concluded that currently these animals have little impact on the gorilla's food supply

Density and biomass of large herbivores and other mammals in a dry tropical forest, western Thailand

ABSTRACTDensity and biomass of four ungulate species, elephant (Elephas maximus) and seven other mammal species were estimated in an area of about 50 km2in a dry tropical forest in Huai Kha Khaeng Wildlife Sanctuary, western Thailand. Density estimations employed line transects, using either direct sightings or indirect signs. Total biomass of these ungulates and elephant was 1450 kg km–2which was lower than that found in a well protected and managed area of similar forest, Nagarahole National Park, in India. This is due to the intensive poaching activity and the lack of wildlife management in this study site. Three species of ungulate, banteng (Bos javanicus), gaur (Bos gaurus) and sambar deer (Cervus unicolor), contributed over 70% of the estimated herbivore biomass. This situation is similar to that found in other parts of Asia. The high biomass of a subterranean mammal,Cannomys badius, has not been documented elsewhere in Asia; this species probably influences the forest dynamics and ecology of small carnivores in this area.

Population structure, density and biomass of large herbivores in the tropical forests of Nagarahole, India

ABSTRACTWe studied the population structure, density and biomass of seven ungulate and two primate species in the tropical forests of Nagarahole, southern India, using line transect sampling and roadside/platform counts, during 1986–87. The estimated ecological densities of large herbivore species in the study area are: 4.2 muntjac km−2, 50.6 chital km−2, 5.5 sambar km−2, 0.8 four-horned antelope km−2, 9.6 gaur km−2, 4.2 wild pig km−2, 3.3 elephant km−2, 23.8 hanuman langur km−2and 0.6 bonnet macaque km−2. Most ungulates have female-biased adult sex ratios. Among common ungulate species, yearlings and young of the year comprise about a third of the population, suggesting relatively high turn-over rates. Three species (muntjac, sambar and four-horned antelope) are solitary, while others form groups. The study area supports a wild herbivore biomass density of 14,744 kg km−2. Among the three habitat types within the study area, biomass is lower in dry deciduous forests when compared with moist deciduous or teak plantation dominant forests. Using our results, we have examined the factors that may contribute towards maintenance of high ungulate biomass in tropical forests.

Population estimates, densities and biomass of large herbivores in Simanjiro Plains, Northern Tanzania

SummaryA total of twenty‐four aerial censuses were carried out in the Simanjiro Plains, northern Tanzania, from 1970 to 1972 in order to estimate the populations, densities and biomass of eleven common large herbivores. Results show that amongst wild herbivores zebra and wildebeest have the highest populations which reach a peak during the wet season between March and May. They were estimated to be about 6000 and 5000, respectively. The corresponding densities were 10.96/km2 and 7.44/km2, respectively. There were practically none of these species in the area during the dry season. Figures for the other species are given. Cattle have the highest population which reaches a peak during the dry season. It was estimated to be about 26,000 with a corresponding density of 44.83/km2. The average total biomass density for all herbivores was 8500 kg/km2.RÉSUMEÉUn total de 24 recencements atriens furent menés dans les Plaines du Simanjiro, en Tanzanie du Nord entre 1970 et 1972, en vue d'estimer les densités et biomasses des populations de 11 grands herbivores communs. Les résultats montrent que, parmi les herbivores, le zèbre et le gnou ont les populations les plus élvées, qui atteignent un maximum durant la saison des pluies entre mars et mai. On a estimé ces populations à 6000 et 5000 respectivement. Les densités correspondantes sont de 10,96/km2 et de 7,44/km2 respectivement. 11 n' y a pratiquement aucune de ces espéces dans la région durant la saison sèche. Les résultats concernant les autres espèces sont donnés. C'est le bétail qui a la plus haute densité de population, atteignant un maximum pendant la saison séche. II a été estiméà environ 26.000, correspondant à une densité de 44,83/km2. La biomasse moyenne totale pour tous les herbivores est de 8500 kg/km2.

The Depression of Reptile Biomass by Large Herbivores

I hypothesize that an apparent very low density of reptiles in a wide variety of African habitats is due to exceptional predation pressure on reptiles by a large array of carnivores that are maintained in two ways by the exceptionally large biomass of large herbivores in these habitats. First, there is anecdotal and circumstantial evidence suggesting that some of the regular predators on reptiles may take carrion or other products from big game in times of short supply of regular prey, thereby maintaining higher population densities than would otherwise be the case. Second, there is anecdotal evidence suggesting that regular consumers of large game may take reptiles as the occasion permits. A brief examination of the reptile fauna of eastern and southern Africa, in search of traits expected of a reptile fauna under exceptional predator pressure, reveals little to support or deny this hypothesis. Additionally, but not developed in depth, it is postulated that African large herbivores may substantially reduce reptile biomass through habitat destruction, especially in more seasonal areas where local water sources and riparian vegetation are important to reptiles, their prey, and large herbivores.