Mike Letnic

Dr Mike Letnic

My research is focused on the conservation and management of ecosystems. I am particularly interested in improving understanding of landscape and continental-scale processes that influence the structure of terrestrial and aquatic ecosystems and threaten biodiversity. I am currently investigating the role that top predators play in sustaining biodiversity, improving the reintroduction success of endangered animals, the ecology and biology of crocodiles and landscape scale approaches to control the impacts of invasive species, particularly, cane toads and foxes.

Publications

Author Date Title Link PDF
Morris and Letnic 2017 Removal of an apex predator initiates a trophic cascade that extends from herbivores to vegetation and the soil nutrient pool

Abstract: It is widely assumed that organisms at low trophic levels, particularly microbes and plants, are essential to basic services in ecosystems, such as nutrient cycling. In theory, apex predators' effects on ecosystems could extend to nutrient cycling and the soil nutrient pool by influencing the intensity and spatial organization of herbivory. Here, we take advantage of a long-term manipulation of dingo abundance across Australia's dingo-proof fence in the Strzelecki Desert to investigate the effects that removal of an apex predator has on herbivore abundance, vegetation and the soil nutrient pool. Results showed that kangaroos were more abundant where dingoes were rare, and effects of kangaroo exclusion on vegetation, and total carbon, total nitrogen and available phosphorus in the soil were marked where dingoes were rare, but negligible where dingoes were common. By showing that a trophic cascade resulting from an apex predator's lethal effects on herbivores extends to the soil nutrient pool, we demonstrate a hitherto unappreciated pathway via which predators can influence nutrient dynamics. A key implication of our study is the vast spatial scale across which apex predators' effects on herbivore populations operate and, in turn, effects on the soil nutrient pool and ecosystem productivity could become manifest.

Rees et al. 2017 In the absence of an apex predator, irruptive herbivores suppress grass seed production: Implications for small granivores

Abstract

Many examples exist of species disappearing shortly after the extinction of a previously co-occurring apex predator, however processes connecting these events are often obscure. In Australian deserts, dingo Canis dingo eradication is associated with declines in abundances of small granivorous birds, even though dingoes and these flying birds rarely directly interact. We hypothesised that dingoes facilitate small granivores by reducing populations of large, grazing kangaroos Macropus spp., thereby increasing grass seed production and availability. To test this prediction, we monitored kangaroo abundances and surveyed grass seed production and biomass of native pastures in matched, desert habitats with dingoes and where dingoes were functionally extinct. Dingo absence was associated with 99.9% greater abundances of kangaroos, 88% - 98% lower pasture biomasses and 85% - 97% lower densities of grass seed heads. To test that these vegetation effects were related to kangaroo grazing, we constructed large herbivore exclosures in areas where dingoes where functionally extinct and there were no grazing livestock. After three years of kangaroo exclusion, pasture biomass and grass seed production were each 87% greater than in adjacent, grazed control plots. Regeneration of vegetation within the kangaroo exclosures demonstrated that kangaroo grazing was responsible for the differences in native pastures we had observed associated with the functional extinction of dingoes. Our results indicate that reduction of grass seed availability by kangaroo grazing is a likely explanation for the relative rarity of small granivorous birds in areas where dingoes are functionally extinct. In areas where apex predators have been eradicated, reintroducing and conserving apex predators or intensively controlling mammalian herbivores would be necessary to mitigate destructive herbivory.

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Mills et al. 2017 Rewilded mammal assemblages reveal the missing ecological functions of granivores

Rewilding is a strategy for ecological restoration that uses reintroductions of animals to re-establish the ecological functions of keystone species. Globally, rewilding efforts have focused primarily on reinstating the ecological functions of charismatic megafauna. In Australia, rewilding efforts have focused on restoring the ecological functions of herbivorous and omnivorous rodents and marsupials weighing between 30-5000g inside of predator-proof exclosures.
In many arid ecosystems, mammals are considered the dominant seed predators. In Australian deserts, ants are considered to be the primary removers and predators of seeds and mammals unimportant removers and predators of seeds. However, most research on granivory in Australian deserts has occurred in areas where native mammals were functionally extinct.
Here, we compare rates of seed removal by mammals and ants on shrub seeds and abundance of shrub seedlings in two rewilded desert ecosystems (Arid Recovery Reserve and Scotia Wildlife Sanctuary) with adjacent areas possessing depauperate mammal faunas. We used foraging trays containing seeds of common native shrubs (Acacia ligulata and Dodonaea viscosa) to examine rates of seed removal by ants and mammals. We quantified the abundance of A. ligulata and D. viscosa seedlings inside and outside of rewilded areas along belt transects.
By excluding ants and mammals from foraging trays, we show that ants removed more seeds than mammals where mammal assemblages were depauperate, but mammals removed far more seeds than ants in rewilded areas. Shrub seedlings were more abundant in areas with depauperate mammal faunas than in rewilded areas.
Our study provides evidence that rewilding of desert mammal assemblages has restored the hitherto unappreciated ecological function of omnivorous rodents and bettongs as seed predators. We hypothesize that the loss of omnivorous mammals may be a factor that has facilitated shrub encroachment in arid Australia.
We contend that rewilding programs aimed at restoring ecological processes should not ignore consumers with relatively lower per capita consumptive effects. This is because consumers with low per capita consumptive effects often occur at high population densities or perform critical ecological functions and thus may have significant population level impacts that can be harnessed for ecological restoration.

See the press release here: https://newsroom.unsw.edu.au/news/science-tech/re-introduction-native-ma...
Hear Mike Letnic discuss the paper on the radio: http://www.abc.net.au/radio/programs/pm/small-mammals-could-help-to-rest...

Access the paper here: http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12950/full

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Gordon et al. 2017 Shrub encroachment is linked to extirpation of an apex predator

Abstract The abundance of shrubs has increased throughout Earth's arid lands. This ‘shrub encroachment’ has been linked to livestock grazing, fire-suppression and elevated atmospheric CO2 concentrations facilitating shrub recruitment. Apex predators initiate trophic cascades which can influence the abundance of many species across multiple trophic levels within ecosystems. Extirpation of apex predators is linked inextricably to pastoralism, but has not been considered as a factor contributing to shrub encroachment. Here, we ask if trophic cascades triggered by the extirpation of Australia's largest terrestrial predator, the dingo (Canis dingo), could be a driver of shrub encroachment in the Strzelecki Desert, Australia. We use aerial photographs spanning a 51-year period to compare shrub cover between areas where dingoes are historically rare and common. We then quantify contemporary patterns of shrub, shrub seedling and mammal abundances, and use structural equation modelling to compare competing trophic cascade hypotheses to explain how dingoes could influence shrub recruitment. Finally, we track the fate of seedlings of an encroaching shrub, hopbush (Dodonaea viscosa angustissima), during a period optimal for seedling recruitment, and quantify removal rates of hopbush seeds by rodents from enriched seed patches. Shrub cover was 26–48% greater in areas where dingoes were rare than common. Our structural equation modelling supported the hypothesis that dingo removal facilitates shrub encroachment by triggering a four level trophic cascade. According to this model, increased mesopredator abundance in the absence of dingoes results in suppressed abundance of consumers of shrub seeds and seedlings, rodents and rabbits respectively. In turn, suppressed abundances of rodents and rabbits in the absence of dingoes relaxed a recruitment bottleneck for shrubs. The results of our SEM were supported by results showing that rates of hopbush seedling survival and seed removal were 1·7 times greater and 2·1 times lower in areas where dingoes were rare than common. Our study provides evidence linking the suppression of an apex predator to the historic encroachment of shrubs. We contend that trophic cascades induced by apex predator extirpation may be an overlooked driver of shrub encroachment.

Online: http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12607/full

Check out the cartoon! https://kapowecology.wordpress.com/2017/01/20/dingoes-run-the-show-right-down-to-the-shrubs/

Letnic et al. 2016 The crest-tailed mulgara (Dasycercus cristicauda) in the south-eastern Strzelecki Desert

Our survey trips always uncover something surprising. Recently we observed a range extension of the crest-tailed mulgara or ampurta, (Dasycercus cristicauda), which was very exciting! We discuss our observations in an article published in Australian Mammalogy. The article can be accessed here: http://www.publish.csiro.au/paper/AM15027.htm 

The abstract of this article is reproduced below.

We report observations of the crest-tailed mulgara (Dasycercus cristicauda) in the south-eastern Strzelecki Desert. Our observations, made during spotlight surveys and using infrared cameras, extend the contemporary range of D. cristicauda to the east by 180 km but subfossil records show that these observations are within the pre-European-settlement range of the species. Whether our observations represent a range expansion or localised population irruption of a previously unknown refuge population is not known. Future studies are recommended to establish the distribution of D. cristicauda in the region and the factors determining its distribution and abundance

Purwandana et al. 2016 Ecological allometries and niche use dynamics across Komodo dragon ontogeny

Ontogenetic allometries in ecological habits and niche use are key responses by which individuals maximize lifetime fitness. Moreover, such allometries have significant implications for how individuals influence population and community dynamics. Here, we examined howbody size var- iation in Komodo dragons (Varanus komodoensis)influenced ecological allometries in their: (1) prey size preference, (2) daily movement rates, (3) home range area, and (4) subse- quent niche use across ontogeny. With increased body mass, Komodo dragons increased prey size with a dramatic switch from small (≤10 kg) to large prey (≥50 kg) in lizards heavier than 20 kg. Rates of foraging movement were described by a non-linear concave down response with lizard increasing hourly movement rates up until ∼20 kg body mass before decreasing daily movement suggesting reduced foraging ef- fort in larger lizards. In contrast, home range area exhibited a sigmoid response with increased body mass. Intrapopulation ecological niche use and overlap were also strongly structured by body size. Thus, ontogenetic allometries suggest Komodo dragon’s transition from a highly active foraging mode exploiting small prey through to a less active sit and wait feeding strategy focused on killing large ungulates. Further, our results suggest that as body size increases across ontogeny, the Komodo dragon exhibited marked ontogenetic niche shifts that enabled it to function as an entire vertebrate predator guild by by exploiting prey across multiple trophic levels.

 

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Parr et al 2016 Cranial Shape and the Modularity of Hybridization in Dingoes and Dogs; Hybridization Does Not Spell the End for Native Morphology

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Rees et al. 2015 Ravens are a key threat to beach-nesting birds

Fish waste left on beaches by recreational fishers could harm shore-nesting birds by attracting native crows that eat the birds’ eggs. To read full publication, click here

Hunter et al. 2015 Reintroduction of Tasmanian devils to mainland Australia can restore top-down control in ecosystems where dingoes have been extirpated

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Leo et al 2015 Interference competition: odours of an apex predator and conspecifics influence resource acquisition by red foxes

Apex predators can impact smaller predators via lethal effects that occur through direct killing, and non-lethal effects that arise when fear-induced behavioural and physiological changes reduce the fitness of smaller predators. To read full publication, click here

Morris et al. 2015 Divergent foraging behaviour of a desert rodent, Notomys fuscus, in covered and open microhabitats revealed using GUDs and video analysis

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Feit et al. 2015 Invasive Cane Toads’ Predatory Impact on Dung Beetles is Mediated by Reservoir Type at Artificial Water Points

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Ripple et al. 2014 Status and ecological effects of the world’s largest carnivores

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Letnic et al. 2014 Artificial watering points are focal points for activity by an invasive herbivore but not native herbivores in conservation reserves in arid Australia
Ripple et al. 2013 Widespread mesopredator effects after wolf extirpation

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Somaweera et al. 2013 Why does vulnerability to toxic invasive cane toads vary among populations of Australian freshwater crocodiles?

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Tingley et al. 2013 Identifying optimal barriers to halt the invasion of cane toads Rhinella marina in arid Australia

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Letnic et al. 2013 Ecologically functional landscapes and the role of dingoes as trophic regulators in south-eastern Australia and other habitats

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Letnic and Crowther 2013 Patterns in the abundance of kangaroo populations in arid Australia are consistent with the exploitation ecosystems hypothesis

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Radford et al. 2012 An assessment of the taxonomic status of wild canids in south-eastern New South Wales: phenotypic variation in dingoes

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Ritchie et al. 2012 Ecosystem restoration with teeth: what role for predators?

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Fillios et al. 2012 The impact of the dingo on the thylacine in Holocene Australia

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Letnic 2012 Us and them: Correspondence

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Letnic et al. 2012 Could direct killing by larger dingoes have caused the extinction of the thylacine from mainland Australia?

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Letnic et al. 2012 Top predators as biodiversity regulators: the dingo Canis lupus dingo as a case study

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