Unexpected overlapping use of tree hollows by birds, reptiles and declining mammals in an Australian tropical savanna

Penton, Cara E.; Radford, Ian J.; Woolley, Leigh‐Ann; Takach, Brenton von; Murphy, Brett P.

doi:10.1007/s10531-021-02231-6

Cited by 11 publications

(10 citation statements)

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“…40% in the long term) would have negative consequences for northern Australian savanna biodiversity. In contrast, some of the groups of highest conservation concern, such as arboreal mammals, are likely to benefit from increases in the abundance of trees, and especially the retention of large, old trees under relatively low‐severity fire regimes (Penton et al, 2021; Woinarski et al, 2011). There is strong evidence that the reduced frequency of high‐severity fires benefits many declining plant communities (e.g., sandstone heathlands; Russell‐Smith et al, 2002) and taxa (e.g., northern cypress‐pine [ Callitris intratropica ] and other noneucalypts; Lawes, Murphy, et al, 2011; Trauernicht et al, 2016) within the northern Australian savanna matrix.…”

Section: Discussionmentioning

confidence: 99%

Using a demographic model to project the long‐term effects of fire management on tree biomass in Australian savannas

Murphy

Whitehead

Evans

et al. 2023

Ecological Monographs

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Tropical savannas are characterized by high primary productivity and high fire frequency, such that much of the carbon captured by vegetation is rapidly returned to the atmosphere. Hence, there have been suggestions that management‐driven reductions in savanna fire frequency and/or severity could significantly reduce greenhouse gas emissions and sequester carbon in tree biomass. However, a key knowledge gap is the extent to which savanna tree biomass will respond to modest shifts in fire regimes due to plausible, large‐scale management interventions. Here, we: (1) characterize relationships between the frequency and severity of fires and key demographic rates of savanna trees, based on long‐term observations in vegetation monitoring plots across northern Australia; (2) use these relationships to develop a process‐explicit demographic model describing the effects of fire on savanna tree populations; and (3) use the demographic model to address the question: to what extent is it feasible, through the strategic application of prescribed burning, to increase tree biomass in Australian tropical savannas? Our long‐term tree monitoring dataset included observations of 12,344 tagged trees in 236 plots, monitored for between 3 and 24 years. Analysis of this dataset showed that frequent high‐severity fires significantly reduced savanna tree recruitment, survival, and growth. Our demographic model suggested that: (1) despite the negative effects of frequent high‐severity fires on demographic rates, savanna tree biomass appears to be suppressed by only a relatively small amount by contemporary fire regimes, characterized by a mix of low‐ to high‐severity fires; and (2) plausible, management‐driven reductions in the frequency of high‐severity fires are likely to lead to increases in tree biomass of about 11.0 t DM ha−1 (95% CI: −1.2–20.8) over a century. Accounting for this increase in carbon storage could generate significant carbon credits, worth, on average, three times those generated annually by current greenhouse gas (methane and nitrous oxide) abatement projects, and has the potential to significantly increase the economic viability of fire/carbon projects, thereby promoting ecologically sustainable management of tropical savannas in Australia and elsewhere. This growing industry has the potential to bring much‐needed economic activity to savanna landscapes, without compromising important natural and cultural values.

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Section: Discussionmentioning

confidence: 99%

Using a demographic model to project the long‐term effects of fire management on tree biomass in Australian savannas

Murphy

Whitehead

Evans

et al. 2023

Ecological Monographs

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“…hollows in mesic savannas on Melville Island. The hollowdependent mammals we studied have been shown to use 2-6 dens in a fortnightly period, overlap in home range, and often use hollows of similar attributes (Penton et al, 2020b(Penton et al, , 2021. Northern Australian arboreal mammals may also be more socially tolerant (Kerle, 1998), allowing them to adapt their denning behavior (e.g., increase their propensity to share dens) in areas where hollows are limiting (Banks et al, 2011).…”

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confidence: 98%

“…The brush-tailed rabbitrat dens close to the ground or in hollow logs on the ground and spends much of its time foraging for grass seeds (Firth et al, 2005(Firth et al, , 2006bPenton et al, 2020b). Though the blackfooted tree-rat dens higher in the canopy (Penton et al, 2021), its reliance on fruiting shrubs, and its large home range (Friend, 1987;Pittman, 2003;Rankmore, 2006) suggests that this species frequently moves across the savanna floor. In comparison, the northern brushtail possum likely spends less time on the savanna floor as it has a smaller home range and does not exhibit large movements across the savanna (Kerle, 1998;Woinarski, 2004;Rankmore, 2006).…”

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confidence: 99%

A Hollow Argument: Understory Vegetation and Disturbance Determine Abundance of Hollow-Dependent Mammals in an Australian Tropical Savanna

Penton

Davies

Radford³

et al. 2021

Front. Ecol. Evol.

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Native mammals are suffering widespread and ongoing population declines across northern Australia. These declines are likely driven by multiple, interacting factors including altered fire regimes, predation by feral cats, and grazing by feral herbivores. In addition, the loss of tree hollows due to frequent, intense fires may also be contributing to the decline of hollow-dependent mammals. We currently have little understanding of how the availability of tree hollows influences populations of hollow-dependent mammals in northern Australian savannas. Here, we test the hypothesis that the abundance of hollow-dependent mammals is higher in areas with a greater availability of tree hollows. We used camera-trap data from 82 sites across the savannas of Melville Island, the largest island in monsoonal northern Australia. Royle–Nichols abundance-induced heterogeneity models were used to investigate the biophysical correlates of the abundance of three threatened mammals: northern brushtail possum (Trichosurus vulpecula arnhemensis), black-footed tree-rat (Mesembriomys gouldii), and brush-tailed rabbit-rat (Conilurus penicillatus). Our analyses included two variables that reflect the availability of tree hollows: the density of tree hollows, estimated from the ground, and the density of large eucalypt trees (Eucalyptus and Corymbia spp.). We found no evidence that the abundance of the three hollow-dependent mammals is positively associated with the availability of tree hollows on Melville Island. Despite their reliance on hollow-bearing trees for denning, the abundance of these mammals appears to be more strongly associated with other factors, such as the characteristics of the understory (i.e., shrub density), which affords protection from predators (including feral cats) and access to food resources. Future conservation management should aim to maintain a dense, diverse understory by managing fire and feral herbivores to facilitate the persistence of hollow-dependent mammals across northern Australia.

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“…While many areas are lacking quantitative historical data on population sizes, our results agree with a small number of studies and anecdotal data suggesting that northern quoll populations were indeed declining prior to the introduction and spread of cane toads (Braithwaite & Griffiths, 1994;Woinarski et al, 2008). Such declines have also been occurring in a range of other native mammal species across northern Australia (Fisher et al, 2014;Penton et al, 2021;von Takach et al, 2020;Woinarski et al, 2010). This massive conservation problem appears to be driven by a suite of interacting factors, including habitat degradation due to feral herbivores and pastoralism (Legge et al, 2011), increased predation due to feral cats (Felis catus) (Frank et al, 2014), frequent or high-intensity fires (von Takach et al, 2020(von Takach et al, , 2022, and possibly climate change (Kutt et al, 2009;Traill et al, 2011).…”

Section: Discussionmentioning

confidence: 99%

Population genomics of a predatory mammal reveals patterns of decline and impacts of exposure to toxic toads

et al. 2022

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Mammal declines across northern Australia are one of the major biodiversity loss events occurring globally. There has been no regional assessment of the implications of these species declines for genomic diversity. To address this, we conducted a species‐wide assessment of genomic diversity in the northern quoll (Dasyurus hallucatus), an Endangered marsupial carnivore. We used next generation sequencing methods to genotype 10,191 single nucleotide polymorphisms (SNPs) in 352 individuals from across a 3220‐km length of the continent, investigating patterns of population genomic structure and diversity, and identifying loci showing signals of putative selection. We found strong heterogeneity in the distribution of genomic diversity across the continent, characterized by (i) biogeographical barriers driving hierarchical population structure through long‐term isolation, and (ii) severe reductions in diversity resulting from population declines, exacerbated by the spread of introduced toxic cane toads (Rhinella marina). These results warn of a large ongoing loss of genomic diversity and associated adaptive capacity as mammals decline across northern Australia. Encouragingly, populations of the northern quoll established on toad‐free islands by translocations appear to have maintained most of the initial genomic diversity after 16 years. By mapping patterns of genomic diversity within and among populations, and investigating these patterns in the context of population declines, we can provide conservation managers with data critical to informed decision‐making. This includes the identification of populations that are candidates for genetic management, the importance of remnant island and insurance/translocated populations for the conservation of genetic diversity, and the characterization of putative evolutionarily significant units.

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Unexpected overlapping use of tree hollows by birds, reptiles and declining mammals in an Australian tropical savanna

Cited by 11 publications

References 100 publications

Using a demographic model to project the long‐term effects of fire management on tree biomass in Australian savannas

Using a demographic model to project the long‐term effects of fire management on tree biomass in Australian savannas

A Hollow Argument: Understory Vegetation and Disturbance Determine Abundance of Hollow-Dependent Mammals in an Australian Tropical Savanna

Population genomics of a predatory mammal reveals patterns of decline and impacts of exposure to toxic toads

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