Remotely sensed primary productivity shows that domestic and native herbivores combined are overgrazing Patagonia

Oliva, Gabriel; Paredes, Paula Natalia; Ferrante, Daniela; Cepeda, Carla; Rabinovich, Jorge E.

doi:10.1111/1365-2664.13408

Cited by 27 publications

(46 citation statements)

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“…The main argument of Marino et al (2020) is that grazing is not at equilibrium because domestic stocks have been withdrawn or lost in large areas of Patagonia, with the remaining animals concentrated and overgrazing still-productive land. We agree with this view, but we consider that it does not contradict our previous conclusions because the historic trend of domestic stocks to adjust to carrying capacity at a regional (and even provincial) scale in the last century shown by hard data in Oliva et al (2019) does not preclude the existence of overgrazing and under-grazing at smaller (local) scales. Marino et al (2020) estimated that land that remains dedicated to sheep production would have 73% and 28% overgrazing in Santa Cruz and Chubut Provinces, respectively.…”

Section: Are Dome S Ti C S To Ck N Umb Er S At Equ Ilib Ri Um With supporting

confidence: 84%

“…Marino et al (2020) also mention 'ecological release (Begon, Townsend, & Harper, 2006) of guanacos after sheep removal has been documented, confirming competitive exclusion by a process-oriented approach (Burgi, Marino, Rodríguez, Pazos, & Baldi, 2012) (Table 3). Sheep and guanaco numbers were compared to the MOD17/A3 herbivore carrying capacity as presented in Oliva et al (2019;Table 3). These active farms show high densities of guanaco in interaction with sheep, and in all but one of the farms, guanaco grazing pressure in Animal Units (that compensate for mass differences between the herbivore species)…”

Section: Are Dome S Ti C S To Ck N Umb Er S At Equ Ilib Ri Um With mentioning

confidence: 99%

“…Since 2000, guanaco populations have increased and, in some areas, as a result, the combined grazing pressure is once again above carrying capacity. Marino, Rodriguez, and Schroeder (2020) have disputed some of the conclusions of Oliva et al (2019), arguing that grazing is not at equilibrium because domestic stock has been withdrawn from some less-productive or degraded areas and concentrated in others. They claim that guanaco populations are self-regulated by behavioural mechanisms, that they are competitively inferior to sheep and consume low-quality forage when in mixed systems.…”

Section: Introductionmentioning

confidence: 99%

“…Marino et al (2020) claim that regional carrying capacity estimations of theOliva et al (2019) analysis are unrealistic because they provide estimates for different species based on the assumption of 'each herbivore having exclusive use of the land'. We suggest that this is based on a misinterpretation of our approach, as it is clear that different domestic and native herbivore species share the land.…”

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confidence: 99%

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Are Patagonia grasslands being overgrazed? A response to Marino et al. (2020)

Oliva

Paredes

Ferrante

et al. 2020

Journal of Applied Ecology

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1. Based upon primary productivity estimates, Oliva et al. (2019) concluded that, at the end of last century and after long periods of overgrazing, Patagonia's domestic stocks adjusted to regional-scale herbivore carrying capacity. Populations of guanaco, a native camelid, increased thereafter, driving combined grazing pressures once again over carrying capacity in some areas. 2. Marino et al. (2020) argued that grazing is not really at equilibrium because domestic stocks are concentrated in areas that remain overgrazed. They support the ideas that guanaco density is auto-regulated by resource-defence territoriality, and that guanacos are weak competitors with domestic stock, occupying only marginal areas. In their view, Oliva et al. (2019) put guanacos in the role of scapegoats, leaving domestic stocks unchecked. 3. Equilibrium at regional scale does not preclude overgrazing and under-grazing at local scales. By separating areas with and without domestic stocks, Marino et al. (2020) estimated overgrazing at 28% in Chubut Province and 73% in Santa Cruz Province. Our recalculations show 28% and 47% domestic overgrazing, respectively. However, when combined with guanaco densities, these increase to 48% for Chubut and 108% for Santa Cruz. 4. We question the hypothesised lack of competitive value and efficient selfregulating mechanisms that would prevent guanaco populations from overshooting carrying capacity. A dataset of 13 sheep farms showed mean density of 26 ± 3.8 guanacos/km 2 and high combined grazing pressures. This was also observed in a protected area of Chubut that reached 42 guanacos/km 2 and crashed during drought, with 60% mortality. Thereafter, guanacos increased to 70 guanacos/km 2 , with recruitment rates that showed a complex response of density dependence but remained relatively elevated at densities above the estimated carrying capacity. 5. Synthesis and applications. Marino et al. (2020) are right to question the apparent equilibrium of domestic stocks that are concentrated in areas that may be still overgrazed. But ground data show that guanaco populations have inefficient density population regulation and can reach densities well over carrying capacity, even in the presence of sheep. This does not mean that the main control should be on growing guanaco populations but it stresses our conclusion that of the Provinces of Chubut and Santa Cruz a guanaco population value as estimated by Bay Gavuzzo et al. (2015; Table 2); as these authors did not provide estimates for the Dry and Humid joint management of the native-domestic herbivore system is urgently needed. Joint management can be effected through local plans, as current guanaco management permits can only be issued in areas that are not overgrazed by sheep. Farm management plans may in this way transform an apparent competitor into a valuable resource, complementary to sheep raising.

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Section: Are Dome S Ti C S To Ck N Umb Er S At Equ Ilib Ri Um With supporting

confidence: 84%

Section: Are Dome S Ti C S To Ck N Umb Er S At Equ Ilib Ri Um With mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Are Patagonia grasslands being overgrazed? A response to Marino et al. (2020)

Oliva

Paredes

Ferrante

et al. 2020

Journal of Applied Ecology

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“…Recently, an article titled 'Remotely-sensed primary productivity shows that domestic and native herbivores combined are overgrazing Patagonia' was published in the Journal of Applied Ecology. In this article, Oliva, Paredes, Ferrante, Cepeda, and Rabinovich (2019) compared their carrying capacity (CC) estimates with wild and domestic herbivore numbers. The authors concluded that after decades of stock adjustment, total domestic grazing pressure came close to CC, but in the Chubut and Santa Cruz Provinces, guanaco Lama guanicoe populations may have altered the balance in the last two decades.…”

Section: Introductionmentioning

confidence: 99%

Wild guanacos as scapegoat for continued overgrazing by livestock across southern Patagonia

Marino

Rodríguez

Schroeder

2020

Journal of Applied Ecology

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1. In a recently published paper, Oliva et al. concluded that domestic grazing pressure across Patagonian rangelands approached carrying capacity due to decades of stock adjustment, but that guanaco overpopulation may have altered that balance. The authors argued that unless guanaco numbers are controlled, they will reduce forage available for domestic stock and will negatively affect rangelands. We consider that the herbivore-stock analysis presented is inaccurate and deserves revision, and that the stated conclusions lack empirical support. 2. When the spatial distribution of herbivores is accounted for in the Oliva et al. analysis, domestic stock is far above carrying capacity, indicating that domestic overgrazing continues. 3. Theoretical and empirical evidence on bottom-up regulation and competitive exclusion challenges the supposed guanaco overpopulation and the hypothetical reduction of forage available for livestock. 4. Even if guanaco numbers are reduced, grassland degradation and production losses will continue because their main drivers, domestic overstock and heterogeneous grazing, are still operating. 5. Synthesis and applications. Oversimplified models with poor ecological insight can lead to erroneous conclusions and misguide management decisions. The incorrect inference that Patagonian domestic stock is adjusted to carrying capacity could help to consolidate current domestic overgrazing by reducing incentives to improve livestock management practices. Regarding guanacos, a controversial species in an unfavourable context, control-oriented harvest without a clear justification threatens populations' viability and genuine attempts of productive diversification. Addressing relevant ecological processes, such as niche partitioning, competitive exclusion and population regulation, is essential to correctly assess joint carrying capacity in multi-herbivore systems, as well as to identify the true factors driving degradation processes and to optimize rangeland use on a sustainable basis.

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Herbivores disrupt the flow of food resources to termites in dryland ecosystems

Wijas

Cornwell

Letnic

2023

Ecology

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Irruption of herbivore populations due to the extirpation of predators has led to dramatic changes in ecosystem functioning worldwide. Herbivores compete with other species for their primary source of nutrition, plant biomass. Such competition is typically considered to occur between species in closely related clades and functional groups but could also occur with detritivores that consume senescent plant biomass. In this study, we tested predictions that in ecosystems where herbivores are not regulated by predators, their indirect impacts on dead vegetation increase with primary productivity and extend to termites that feed on senescent vegetation. We compared dead vegetation cover and termite activity in herbivore exclosures and associated grazed plots at three locations situated along a rainfall gradient in arid Australia where kangaroo populations have irrupted. Dead vegetation cover and termite activity increased with rainfall in ungrazed plots but showed a negligible response to rainfall in grazed plots. Our results suggest that grazing can disrupt the flow of energy to detritivores and decouple the relationship between termite activity and primary productivity. Such disruption could have far‐reaching impacts on arid ecosystems because many organisms sit within “brown food webs” that are sustained by energy derived from the decomposition of senescent plant tissues.

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Remotely sensed primary productivity shows that domestic and native herbivores combined are overgrazing Patagonia

Abstract: 1. Carrying capacity is the maximum animal density an area can sustain without deterioration of its resources. Overgrazing has degraded Patagonia, but sheep stocks decreased and gave way to mixed systems with cattle, goats and guanacos (native wild camelids).

Cited by 27 publications

References 46 publications

Are Patagonia grasslands being overgrazed? A response to Marino et al. (2020)

Are Patagonia grasslands being overgrazed? A response to Marino et al. (2020)

Wild guanacos as scapegoat for continued overgrazing by livestock across southern Patagonia

Herbivores disrupt the flow of food resources to termites in dryland ecosystems

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