75 years of dryland science: Trends and gaps in arid ecology literature

© 2017 Greenville et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Growth in the publication of scientific articles is occurring at an exponential rate, prompting a growing need to synthesise information in a timely manner to combat urgent environmental problems and guide future research. Here, we undertake a topic analysis of dryland literature over the last 75 years (8218 articles) to identify areas in arid ecology that are well studied and topics that are emerging. Four topics - wetlands, mammal ecology, litter decomposition and spatial modelling, were identified as 'hot topics' that showed higher than average growth in publications from 1940 to 2015. Five topics-remote sensing, climate, habitat and spatial, agriculture and soils-microbes, were identified as 'cold topics', with lower than average growth over the survey period, but higher than average numbers of publications. Topics in arid ecology clustered into seven broad groups on word-based similarity. These groups ranged from mammal ecology and population genetics, broad-scale management and ecosystem modelling, plant ecology, agriculture and ecophysiology, to populations and paleoclimate. These patterns may reflect trends in the field of ecology more broadly. We also identified two broad research gaps in arid ecology: population genetics, and habitat and spatial research. Collaborations between population genetics and ecologists and investigations of ecological processes across spatial scales would contribute profitably to the advancement of arid ecology and to ecology more broadly

Population dynamics of desert mammals: Similarities and contrasts within a multispecies assemblage

© 2016 Greenville et al. Understanding the temporal and spatial dynamics of species populations remains a key focus of population biology, providing vital insight into the drivers that influence demography and into sub-populations that are vulnerable to extinction. Across regional landscapes, spatially separated sub-populations may fluctuate in synchrony, or exhibit sub-structuring due to subtle differences in local intrinsic and extrinsic factors. Using a long-term data set (17-22 yr) obtained from a large (8000 km2) study region in arid central Australia, we tested firstly for regional synchrony in annual rainfall and the dynamics of five small mammal species across nine widely separated sites. Using Moran's theorem, we predicted that the spatial correlation between the regional sub-populations of these species would equal that between local density-independent conditions (annual rainfall). For species that showed synchronous spatial dynamics, we then used multivariate state-space (MARSS) models to predict that regional rainfall would be positively associated with their populations, whereas species with asynchronous sub-populations would be influenced largely by other factors. For these latter species, we used MARSS models to test four hypotheses. These were that sub-population structures: (1) were asynchronous and governed by local site-specific factors, (2) differed between oasis and non-oasis sites, (3) differed between burnt and unburnt sites, and (4) differed between three sub-regions with different rainfall gradients. We found that the spatial population dynamics of our study small mammals differed between and within families. Two species of insectivorous dasyurid marsupials showed asynchronous dynamics, which most likely tracked local conditions, whereas a larger carnivorous marsupial and two species of rodents had strongly synchronous dynamics. These latter species exhibited similar spatial correlations to local and regional rainfall events, providing evidence that the Moran effect operates for some, but not all, species in this arid system. Our results suggest that small mammal populations do not respond in similar ways to shared environmental drivers in arid regions, and hence will vary in their responses to climate change. As arid lands globally are predicted to face climatic shifts that will exacerbate rainfall-drought cycles, we suggest that future work focuses on exploring these responses at different spatial scales across multiple dryland taxa

Experiments in no-impact control of dingoes: Comment on Allen et al. 2013

There has been much recent debate in Australia over whether lethal control of dingoes incurs environmental costs, particularly by allowing increase of populations of mesopredators such as red foxes and feral cats. Allen et al. (2013) claim to show in their recent study that suppression of dingo activity by poison baiting does not lead to mesopredator release, because mesopredators are also suppressed by poisoning. We show that this claim is not supported by the data and analysis reported in Allen et al.'s paper. © 2014 Johnson et al.; licensee BioMed Central Ltd

Predator manipulation experiments: impacts on populations of terrestrial vertebrate prey

Quantifying the relative impacts of top-down vs. bottom-up control of ecosystems remains a controversial issue, with debate often focusing on the perennial question of how predators affect prey densities. To assess predator impacts, we performed a worldwide meta-analysis of field experiments in which the densities of terrestrial vertebrate predators were manipulated and the responses of their terrestrial vertebrate prey were measured. Our results show that predation indeed limits prey populations, as prey densities change substantially after predator manipulations. The main determinant of the result of an experiment was the efficiency of predator manipulation. Positive impacts of predator manipulation appeared to increase with duration of the experiment for non-cyclic prey, while the opposite was true for cyclic prey. In addition, predator manipulation showed a large positive impact on cyclic prey at low prey densities, but had no obvious impact at peak prey densities. As prey population densities generally respond predictably to predator manipulations, we suggest that control of introduced vertebrate predators can be used to effectively conserve and manage native wildlife. However, care should be taken when controlling native predators, especially apex species, owing to their importance as strong interactors and the biodiversity value of their habitats. We discuss gaps in our knowledge of predator-prey relationships and methodological issues related to manipulation experiments. An important guideline for future studies is that adequate monitoring of predator numbers before and during the experiment is the only way to ensure that observed responses in prey populations are actually caused by changes in predation impacts

Top predators constrain mesopredator distributions

© The Author(s) 2017. Top predators can suppress mesopredators by killing them, competing for resources and instilling fear, but it is unclear how suppression of mesopredators varies with the distribution and abundance of top predators at large spatial scales and among different ecological contexts. We suggest that suppression of mesopredators will be strongest where top predators occur at high densities over large areas. These conditions are more likely to occur in the core than on the margins of top predator ranges. We propose the Enemy Constraint Hypothesis, which predicts weakened top-down effects on mesopredators towards the edge of top predators' ranges. Using bounty data from North America, Europe and Australia we show that the effects of top predators on mesopredators increase from the margin towards the core of their ranges, as predicted. Continuing global contraction of top predator ranges could promote further release of mesopredator populations, altering ecosystem structure and contributing to biodiversity loss

Structural basis for CRISPR RNA-guided DNA recognition by Cascade

The CRISPR (clustered regularly interspaced short palindromic repeats) immune system in prokaryotes uses small guide RNAs to neutralize invading viruses and plasmids. In Escherichia coli, immunity depends on a ribonucleoprotein complex called Cascade. Here we present the composition and low-resolution structure of Cascade and show how it recognizes double-stranded DNA (dsDNA) targets in a sequence-specific manner. Cascade is a 405-kDa complex comprising five functionally essential CRISPR-associated (Cas) proteins (CasA1B2C6D1E1) and a 61-nucleotide CRISPR RNA (crRNA) with 5′-hydroxyl and 2′,3′-cyclic phosphate termini. The crRNA guides Cascade to dsDNA target sequences by forming base pairs with the complementary DNA strand while displacing the noncomplementary strand to form an R-loop. Cascade recognizes target DNA without consuming ATP, which suggests that continuous invader DNA surveillance takes place without energy investment. The structure of Cascade shows an unusual seahorse shape that undergoes conformational changes when it binds target DNA.

When Does an Alien Become a Native Species? A Vulnerable Native Mammal Recognizes and Responds to Its Long-Term Alien Predator

The impact of alien predators on native prey populations is often attributed to prey naiveté towards a novel threat. Yet evolutionary theory predicts that alien predators cannot remain eternally novel; prey species must either become extinct or learn and adapt to the new threat. As local enemies lose their naiveté and coexistence becomes possible, an introduced species must eventually become ‘native’. But when exactly does an alien become a native species? The dingo (Canis lupus dingo) was introduced to Australia about 4000 years ago, yet its native status remains disputed. To determine whether a vulnerable native mammal (Perameles nasuta) recognizes the close relative of the dingo, the domestic dog (Canis lupus familiaris), we surveyed local residents to determine levels of bandicoot visitation to yards with and without resident dogs. Bandicoots in this area regularly emerge from bushland to forage in residential yards at night, leaving behind tell-tale deep, conical diggings in lawns and garden beds. These diggings were less likely to appear at all, and appeared less frequently and in smaller quantities in yards with dogs than in yards with either resident cats (Felis catus) or no pets. Most dogs were kept indoors at night, meaning that bandicoots were not simply chased out of the yards or killed before they could leave diggings, but rather they recognized the threat posed by dogs and avoided those yards. Native Australian mammals have had thousands of years experience with wild dingoes, which are very closely related to domestic dogs. Our study suggests that these bandicoots may no longer be naïve towards dogs. We argue that the logical criterion for determining native status of a long-term alien species must be once its native enemies are no longer naïve