Keystone effects of an alien top-predator stem extinctions of native mammals

Letnic, Mike; Koch, Freya; Gordon, Chloe S.; Crowther, Mathew S.; Dickman, Chris R.

doi:10.1098/rspb.2009.0574

Cited by 189 publications

(228 citation statements)

References 37 publications

(63 reference statements)

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“…Further, almost all of our studies of the effects of sheep grazing occurred in areas where dingo (Canis dingo) populations are suppressed through fencing, poisoning, or shooting (Letnic and Crowther 2013). Kangaroo populations typically irrupt in areas where dingoes are suppressed resulting in dramatic increases in total grazing pressure and the depletion of their preferred forage, grasses (Norbury et al 1993, Letnic et al 2009). The paucity of sheep grazing studies in the presence of dingoes precluded us from using the presence of dingoes as a control for this residual grazing, which would have dampened the grazing effect we encountered.…”

Section: Methodological Consideration: Limitations To Our Studymentioning

confidence: 99%

“…Australia has a very short history of grazing by European domestic livestock (<200 yr) and therefore livestock have not co-evolved with the existing vegetation. Prior to the introduction of livestock, Australia supported extensive but low densities of mammalian herbivores, such as kangaroos, whose densities were low because of sparse and unreliable water supplies and predation by dingoes (Letnic et al 2009). …”

Section: Introductionmentioning

confidence: 99%

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Ecosystem structure, function and composition in rangelands are negatively affected by livestock grazing

Eldridge¹,

Poore²,

Ruíz-Colmenero³

et al. 2015

Ecological Applications

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116

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Abstract.Reports of positive or neutral effects of grazing on plant species richness have prompted calls for livestock grazing to be used as a tool for managing land for conservation. Grazing effects, however, are likely to vary among different response variables, types, and intensity of grazing, and across abiotic conditions. We aimed to examine how grazing affects ecosystem structure, function, and composition. We compiled a database of 7615 records reporting an effect of grazing by sheep and cattle on 278 biotic and abiotic response variables for published studies across Australia. Using these data, we derived three ecosystem measures based on structure, function, and composition, which were compared against six contrasts of grazing pressure, ranging from low to heavy, two different herbivores (sheep, cattle), and across three different climatic zones. Grazing reduced structure (by 35%), function (24%), and composition (10%). Structure and function (but not composition) declined more when grazed by sheep and cattle together than sheep alone. Grazing reduced plant biomass (40%), animal richness (15%), and plant and animal abundance, and plant and litter cover (25%), but had no effect on plant richness nor soil function. The negative effects of grazing on plant biomass, plant cover, and soil function were more pronounced in drier environments. Grazing effects on plant and animal richness and composition were constant, or even declined, with increasing aridity. Our study represents a comprehensive continental assessment of the implications of grazing for managing Australian rangelands. Grazing effects were largely negative, even at very low levels of grazing. Overall, our results suggest that livestock grazing in Australia is unlikely to produce positive outcomes for ecosystem structure, function, and composition or even as a blanket conservation tool unless reduction in specific response variables is an explicit management objective.

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Section: Methodological Consideration: Limitations To Our Studymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ecosystem structure, function and composition in rangelands are negatively affected by livestock grazing

Eldridge¹,

Poore²,

Ruíz-Colmenero³

et al. 2015

Ecological Applications

Self Cite

116

View full text Add to dashboard Cite

show abstract

“…The same principles apply as on islands but the effects of the introduced predators' interactions with pre-existing indigenous predators, and the existing potential for non-lethal responses that are present because of the indigenous predators, makes predictions about the relative strength of lethal and non-lethal effects more difficult (Letnic et al 2009). It seems likely that introduced predators that have a functionally indigenous equivalent will exert lower lethal effects on their prey, though prey populations may decline because they have to make a greater level of non-lethal response to the increased predator density.…”

Section: Evolutionary or Cultural Lag And Constraints On Non-lethal Cmentioning

confidence: 99%

Predation in bird populations

Cresswell

2010

J Ornithol

237

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One of the classic ecological questions is how predators affect population size. This is often assessed by measuring how many individuals are killed by a predator, yet such direct effects may only be a relatively minor part of population dynamics. Predators frequently affect prey populations indirectly, with the fear of predation resulting in costly behavioural compensation leading to potentially large population and community effects. Large observable lethal effects may then just represent the most easily observed "special" cases of the effects of predation on populations, with the costs of non-lethal effects being ubiquitous and usually dominant. This review explores these two ideas: that cases where there are no population effects due to predation, and cases where lethal effects dominate, are unusual and involve special circumstances. First, systems where predation effects appear not to arise include complete avoidance of predators by prey; when other environmental factors limit populations so that predation is not additive to mortality; when there are other more vulnerable prey for a predator; when predators interact; because the relationship of perceived predation risk with predator abundance is usually a non-linear function, and simply because non-lethal effects have not been considered. Second, lethal effects tend to dominate over non-lethal effects when there is a high cost of compensating for predation risk associated with either resource constraint or a particularly vulnerable niche or life history stage (e.g. the nest stage generally for birds); when prey are the most popular prey of a predator or linear trophic chains operate; when there is evolutionary lag such as introduced predators and naïve prey populations; and when there are several predator species hunting the same prey in diverse ways. The presence of predators may or may not affect the size of a bird population at any particular life history stage, although in most cases it will through non-lethal effects and occasionally through lethal effects.But the presence of predators will always affect intra-and interspecific competition and so will always affect population dynamics. Studies that wish to fully demonstrate that predation has no effect on bird populations must show that lethal effects and the costs of non-lethal compensation by the prey do not significantly change its density and so the level of competition.3

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“…They do so by killing or instilling fear in competitors and prey [3,4], thereby inducing trophic cascades that flow through entire ecosystems [5]. Despite 40% of the Earth's terrestrial surface being dominated by agriculture [6] and human effects permeating into more natural areas [7], much research on trophic cascades has focused on relatively intact conservation reserves.…”

Section: Introductionmentioning

confidence: 99%

Incorporating anthropogenic effects into trophic ecology: predator–prey interactions in a human-dominated landscape

et al. 2015

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Apex predators perform important functions that regulate ecosystems worldwide. However, little is known about how ecosystem regulation by predators is influenced by human activities. In particular, how important are top-down effects of predators relative to direct and indirect human-mediated bottom-up and top-down processes? Combining data on species' occurrence from camera traps and hunting records, we aimed to quantify the relative effects of topdown and bottom-up processes in shaping predator and prey distributions in a human-dominated landscape in Transylvania, Romania. By global standards this system is diverse, including apex predators (brown bear and wolf), mesopredators (red fox) and large herbivores (roe and red deer). Humans and free-ranging dogs represent additional predators in the system. Using structural equation modelling, we found that apex predators suppress lower trophic levels, especially herbivores. However, direct and indirect topdown effects of humans affected the ecosystem more strongly, influencing species at all trophic levels. Our study highlights the need to explicitly embed humans and their influences within trophic cascade theory. This will greatly expand our understanding of species interactions in human-modified landscapes, which compose the majority of the Earth's terrestrial surface.

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Keystone effects of an alien top-predator stem extinctions of native mammals

Cited by 189 publications

References 37 publications

Ecosystem structure, function and composition in rangelands are negatively affected by livestock grazing

Ecosystem structure, function and composition in rangelands are negatively affected by livestock grazing

Predation in bird populations

Incorporating anthropogenic effects into trophic ecology: predator–prey interactions in a human-dominated landscape

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