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

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

Assessing the potential for intraguild predation among taxonomically disparate micro-carnivores: Marsupials and arthropods

© 2018 The Author(s). Interspecific competition may occur when resources are limited, and is often most intense between animals in the same ecological guild. Intraguild predation (IGP) is a distinctive form of interference competition, where a dominant predator selectively kills subordinate rivals to gain increased access to resources. However, before IGP can be identified, organisms must be confirmed as members of the same guild and occur together in space and time. The lesser hairy-footed dunnart (Sminthopsis youngsoni, Dasyuridae) is a generalist marsupial insectivore in arid Australia, but consumes wolf spiders (Lycosa spp., Lycosidae) disproportionately often relative to their availability. Here, we test the hypothesis that this disproportionate predation is a product of frequent encounter rates between the interactants due to high overlap in their diets and use of space and time. Diet and prey availability were determined using direct observations and invertebrate pitfall trapping, microhabitat use by tracking individuals of both species-groups, and temporal activity using spotlighting and camera traps. Major overlap (greater than 75% similarity) was found in diet and temporal activity, and weaker overlap in microhabitat use. Taken together, these findings suggest reasonable potential, for the first time, for competition and intraguild predation to occur between taxa as disparate as marsupials and spiders

Carte réduite du Golphe de Gascogne / N. Bellin

© 2017 The Authors. Climate change is predicted to place up to one in six species at risk of extinction in coming decades, but extinction probability is likely to be influenced further by biotic interactions such as predation. We use structural equation modelling to integrate results from remote camera trapping and long-term (17-22 years) regional-scale (8000 km2) datasets on vegetation and small vertebrates (greater than 38 880 captures) to explore how biotic processes and two key abiotic drivers influence the structure of a diverse assemblage of desert biota in central Australia. We use our models to predict how changes in rainfall and wildfire are likely to influence the cover and productivity of the dominant vegetation and the impacts of predators on their primary rodent prey over a 100-year timeframe. Our results show that, while vegetation cover may decline due to climate change, the strongest negative effect on prey populations in this desert system is top-down suppression from introduced predators

Dynamics, habitat use and extinction risk of a carnivorous desert marsupial

Animals in hot desert environments often show marked fluctuations in population size, persisting in low numbers in refuge habitats during dry periods and expanding after rain when resources increase. Understanding drought-wet cycle dynamics is important for managing arid ecosystems, particularly if populations of threatened species are present. Such species may face increased risks of extinction if all populations decrease synchronously toward zero during low-resource periods, and if key refuge habitats needed during these periods are disturbed or unavailable. Here, we describe the dynamics and habitat requirements of two sub-populations of the kowari, Dasyuroides byrnei (Marsupialia: Dasyuridae), during long-term sampling (2000–2015) that encompassed multiple drought-wet cycles. This species is listed currently as Vulnerable on the IUCN Red List. We found that the study region contains favourable habitat, with kowari occurring on hard stony (gibber) pavements in association with coverage of sand that may facilitate construction of burrows. Both sub-populations of kowari declined over the study period irrespective of climatic conditions, despite some evidence that both body condition and reproductive output increased after rain. We suggest that the studied sub-populations are under stress from extrinsic rather than intrinsic factors, with livestock grazing and introduced predators perhaps having the most negative effects. If similar demographic trends are apparent elsewhere in the species’ small geographical range, the species would be eligible for listing on the IUCN Red List as Endangered, with a 20% chance of extinction within the next 20 years. Urgent research is required to quantify and mitigate the extrinsic threats to kowari populations. Proactive measures such as captive breeding to act as insurance populations would be prudent

Spatial and temporal synchrony in reptile population dynamics in variable environments.

Resources are seldom distributed equally across space, but many species exhibit spatially synchronous population dynamics. Such synchrony suggests the operation of large-scale external drivers, such as rainfall or wildfire, or the influence of oasis sites that provide water, shelter, or other resources. However, testing the generality of these factors is not easy, especially in variable environments. Using a long-term dataset (13-22 years) from a large (8000 km(2)) study region in arid Central Australia, we tested firstly for regional synchrony in annual rainfall and the dynamics of six reptile species across nine widely separated sites. For species that showed synchronous spatial dynamics, we then used multivariate follow a multivariate auto-regressive state-space (MARSS) models to predict that regional rainfall would be positively associated with their populations. For asynchronous species, we used MARSS models to explore four other possible population structures: (1) populations were asynchronous, (2) differed between oasis and non-oasis sites, (3) differed between burnt and unburnt sites, or (4) differed between three sub-regions with different rainfall gradients. Only one species showed evidence of spatial population synchrony and our results provide little evidence that rainfall synchronizes reptile populations. The oasis or the wildfire hypotheses were the best-fitting models for the other five species. Thus, our six study species appear generally to be structured in space into one or two populations across the study region. Our findings suggest that for arid-dwelling reptile populations, spatial and temporal dynamics are structured by abiotic events, but individual responses to covariates at smaller spatial scales are complex and poorly understood