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
Mills and Letnic 2018 Reversing functional extinction of mammals prompts a rethink of paradigms about seed fate in arid Australia

Abstract:

Functional extinction of once abundant species has frequently preceded understanding of their ecological roles. Consequently, our understanding of ecosystems is prone to shifting baselines because it often relies on observations made on depauperate species assemblages. In Australian deserts, current paradigms are that ants are the dominant granivores, mammals are unimportant seed predators and that myrmecochory in many Australian shrubs is an adaptation to increase dispersal distance and direct seeds to favourable germination sites. Here, we ask whether these paradigms could be artefacts of mammal extinction. We take advantage of a predator-proof reserve within which locally extinct native mammals have been reintroduced to compare seed removal by ants and mammals. Using foraging trays that selectively excluded mammals and ants we show that a reintroduced mammal, the woylie (Bettongia penicillata) was at least as important as ants in the removal of seeds of two shrub species (Dodonaea viscosa and Acacia ligulata). Our results provide evidence that the dominance of ants as granivores and current understanding of the adaptive benefit of myrmecochory in arid Australia may be artefacts of the functional extinction of mammals. Our study shows how reversing functional extinction can provide the opportunity to rethink contemporary understanding of ecological processes.

Access the paper here: https://doi.org/10.1098/rsos.171977

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Steindler et al 2018 Discrimination of introduced predators by ontogenetically naïve prey scales with duration of shared evolutionary history

Abstract: Hypotheses on the discrimination and recognition of predators by prey are divided as to whether the prey species' ability to recognize and avoid predators is proportionate to the duration of evolutionary exposure to specific predators or is a result of more generalized discrimination processes. Moreover, understanding of the timeframes necessary for prey species to maintain or acquire appropriate responses to introduced predators is poorly understood. We studied a population of wild, ontogenetically predator naïve greater bilbies, Macrotis lagotis, living within a large (60 km2) predator-free exclosure, to determine whether they modified their burrow-emergence behaviour in response to olfactory stimuli from introduced predators, dogs, Canis familiaris, and cats, Felis catus. Greater bilbies have shared over 3000 years of coevolutionary history with dogs but less than 200 years with cats. Bilbies spent more time only partially emerged (with at most head and shoulders out) as opposed to fully emerged (standing quadrupedally or bipedally) from their burrows when dog faeces were present, in comparison to faeces of cats, rabbits and an unscented control. Our results were consistent with the ‘ghosts of predator past’ hypothesis, which postulates that prey species' abilities to respond to the odours of predators scales with their period of coexistence. Our study supports the notion that introduced predators should be regarded as naturalized if prey possess an innate ability to detect their cues and respond accordingly.

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West et al. 2018 Predator exposure improves anti‐predator responses in a threatened mammal

Abstract

1. Incorporating an understanding of animal behaviour into conservation programmes can influence conservation outcomes. Exotic predators can have devastating impacts on native prey species and thwart reintroduction efforts, in part due to prey naïveté caused by an absence of co‐evolution between predators and prey. Attempts have been made to improve the anti‐predator behaviours of reintroduced native prey by conducting laboratory‐based predator recognition training but results have been varied and have rarely led to improved survival in reintroduction programmes.

2. We investigated whether in situ predator exposure could improve anti‐predator responses of a predator‐naïve mammal by exposing prey populations to low densities of introduced predators under controlled conditions. We reintroduced 352 burrowing bettongs to a 26‐km2 fenced exclosure at the Arid Recovery Reserve in South Australia and exposed them to feral cats (density 0.03–0.15 cats/km2) over an 18‐month period. At the same time, we translocated a different group of bettongs into an exclosure free of introduced predators, as a control. We compared three behaviours (flight initiation distances, trap docility and behaviour at feeding trays) of cat‐exposed and control bettongs before the translocations, then at 6, 12 and 18 months post‐translocation.

3. Cat‐exposed bettongs displayed changes in behaviour that suggested increased wariness, relative to control bettongs. At 18 months post‐reintroduction, cat‐exposed bettongs had greater flight initiation distances and approached feed trays more slowly than control bettongs. Cat‐exposed bettongs also increased their trap docility over time.

4. Synthesis and applications. Translocation is recommended as a conservation tool for many threatened species yet success rates are generally low. We demonstrate that controlled levels of in situ predator exposure can increase wariness in the behaviour of naïve prey. Our findings provide support for the hypothesis that in situ predator exposure could be used as a method to improve the anti‐predator responses of predator‐naïve threatened species populations.

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Letnic et al. 2018 Strength of a Trophic Cascade Between an Apex Predator, Mammalian Herbivore and Grasses in a Desert Ecosystem Does Not Vary with Temporal Fluctuations in Primary Productivity

Abstract: There has long been debate regarding the primacy of bottom-up and top-down effects as factors shaping ecosystems. The exploitation ecosystems hypothesis (EEH) predicts that predators indirectly benefit plants because their top-down effects limit herbivores’ consumption of plants, and that the strength of trophic cascade increases with increasing primary productivity. However, in arid environments, pulses of primary productivity produced by irregular rainfall events could decouple herbivore–plant and predator–prey dynamics if high conversion efficiency from seed biomass to consumers allows the rapid build-up of consumer populations. Here, we test predictions of the EEH in an arid environment. We measured activity/abundances of dingoes, red kangaroos and grasses, and diet of dingoes, in landscapes where dingoes were culled or not culled over 3 years. Dingo activity was correlated with rainfall, and their tracks were less frequent at culled sites. Kangaroo abundance was greater at sites where dingoes were culled and increased with rainfall in the previous 6 months. Grass cover was greater at sites where dingoes were not culled and increased with rainfall in the previous 3 months. During a period of average rainfall, dingoes primarily consumed rodents and increased their consumption of kangaroos during a period of drier conditions. Our results are consistent with the hypothesis that suppression of an apex predator triggers a trophic cascade, but are at odds with the EEH’s prediction that the magnitude of trophic cascades should increase with primary productivity. Our study demonstrates that temporal fluctuations in primary productivity can have effects on biomasses of plants and consumers which are in many ways analogous to those observed along spatial gradients of primary productivity.

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Moseby et al. 2018 Designer prey: Can controlled predation accelerate selection for anti-predator traits in naïve populations?

Abstract: Prey naïveté is thought to be a significant factor contributing to the failure of native prey to re-establish in the presence of introduced predators. We tested whether exposing naïve prey to low levels of in situ predation pressure from introduced predators could cause accelerated selection for certain physical or behaviour traits. Such selection could improve the chance of future co-existence between introduced predators and native prey. In 2014, we reintroduced 352 burrowing bettongs (Bettongia lesueur) into a 26 km2 fenced paddock where predation levels could be carefully controlled. Four feral cats (Felis catus) were introduced to the paddock several months after bettong reintroduction and predation events were subsequently recorded. We measured a suite of physical and behavioural traits on the bettongs prior to release and compared these between individuals that survived or were assumed to have died. Population level parameters were also compared between the reintroduced population and the predator-free source population. No a priori measured physical or behavioural traits were significant predictors of individual survival after release and the high survival rate of radio-collared bettongs and the positive population growth rate suggests that the predation pressure from the introduced feral cats may not have been sufficiently high to cause strong selection over a short time period. However, population level comparisons found cat-exposed male bettongs had significantly longer hind feet than the source population at 18–22 months after release. Hind foot length was consistently longer in both older released animals and younger recruits and thus may be an indicator of selection and/or phenotypic change in response to the presence of predators. Our study suggests that predation may cause phenotypic change over short time periods but that higher cat predation pressure may be required to enable the benefits of accelerated natural selection to be adequately assessed.

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Mills et al. 2018 Rewilded mammal assemblages reveal the missing ecological functions of granivores

Abstract:

1. 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 and 5,000 g inside of predator‐proof exclosures.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

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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/

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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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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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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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

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

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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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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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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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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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